PROCESSING AND PROPERTY EVALUATION OF POLY(LACTIC ACID)/CELLULOSE 

NANOCRYSTALS EXTRUDED CAST FILMS 

 

By 

Yuzhu Liu 

A THESIS 

Submitted to 

Michigan State University 

in partial fulfillment of the requirements 

for the degree of 

Packaging - Master of Science 

2018 

 

 

 

ABSTRACT 

PROCESSING AND PROPERTY EVALUATION OF POLY(LACTIC ACID)/CELLULOSE 

NANOCRYSTALS EXTRUDED CAST FILMS 

By 

Yuzhu Liu 

Poly(lactic acid) (PLA), a bio-based polymer with poor water and moderate oxygen barrier 

performance, has become a material of interest in the packaging industry due to its sustainability. 

Cellulose nanocrystals (CNCs) are added into PLA film to enhance its barrier performance without 

affecting its transparency. Beside these attributes, heat sealing and mechanical properties are also 

important features for films intended for packaging applications and need to be investigated. This 

study assessed the influence of CNC addition (0.5 to 2 wt%) on the surface texture, heat sealing, 

mechanical and barrier properties of PLA cast films manufactured through a continuous extrusion 

melt-process. Irrespective of CNC content, the addition of CNC increased the surface roughness 

of  PLA  due  to  the  presence  of  CNC  agglomerates  indicating  a  poor  dispersion.  The  sealing 

performance, i.e., the hot tack strength and seal strength of PLA films as well as the burst pressure 

of  PLA  pouches,  significantly  improved  by  adding  up  to  1%  CNC  into  PLA  matrix,  probably 

attributed to the increased stress transfer efficiency at the interface. Significant improvements in 

both the tensile strength and modulus were achieved by adding CNC into PLA matrix, insensitive 

to CNC content. Nevertheless, these occurred at the expense of ductility since both the elongation 

at break and the energy to break decreased, results supported by the dart impact strength showing 

that  PLA/CNC  composite  films  were  more  brittle  than  neat  PLA  films.  Both  water  vapor  and 

oxygen  permeabilities  decreased  significantly  with  the  increased  CNC  content  because  of  the 

tortuosity effect. The overall performance of the studied PLA/CNC films indicated that they had 

great potential to be used in packaging applications. 

 

 

Copyright by 
YUZHU LIU 
2018 
 

 

 

 

Dedicated to my parents 
Ziyong Sun and Wei Liu 

iv 

ACKNOWLEDGEMENTS 

Foremost, I would like to express my sincere gratitude to my advisor, Dr. Laurent Matuana 

(School of Packaging, Michigan State University) for his  continuous guidance and support. No 

matter what kinds of problems I had, he has always been an excellent teacher and mentor to guide 

me for solutions. It has been a pleasure to have his suggestions to survive the hard times and to 

improve myself in every aspect of my career including research methods, scientific writing, and 

communication skills. Moreover, my sincere thanks goes to my committee members: Dr. Donatien 

Pascal Kamdem (School of Packaging, Michigan State University) and Dr. Yan Liu (Biosystems 

and  Agricultural  Engineering,  Michigan  State  University)  for  their  insightful  suggestions, 

invaluable time commitment and expertise. 

I would like to acknowledge Mr. Aaron Walworth (School of Packaging, Michigan State 

University) for all the essential trainings on the equipment used in this study. I would also like to 

thank the undergraduate students, Haley Ferer and Hannah Brubaker for their help in this research. 

Additionally, I am grateful to my colleague, Sonal Karkhanis for being a terrific companion and a 

great friend. 

Last but not least, this journey would have never been possible without the support of my 

family and friends. I must express my very profound gratitude to my parents for providing me with 

unfailing support and never-ending encouragement in all of my pursuits and inspirations to follow 

my dreams. This thesis would not have been possible without them. I am so very thankful to all 

my friends, especially friends in School of Packaging, for constantly cheering me up during the 

travel down the rough roads. Thank you. 

 

v 

TABLE OF CONTENTS 

LIST OF TABLES ....................................................................................................................... viii 

LIST OF FIGURES ........................................................................................................................ x 

Chapter 1 ......................................................................................................................................... 1 
INTRODUCTION .......................................................................................................................... 1 
1.1 Introduction ................................................................................................................... 1 
1.2 Objectives ..................................................................................................................... 5 
1.3 Hypothesis..................................................................................................................... 6 
1.4 Structure of thesis ......................................................................................................... 6 
REFERENCES ............................................................................................................................... 7 

Chapter 2 ....................................................................................................................................... 12 
BACKGROUND AND LITERATURE REVIEW ...................................................................... 12 
2.1 Introduction ................................................................................................................. 12 
2.2 Poly(lactic acid) .......................................................................................................... 12 
2.2.1 Synthesis of PLA ......................................................................................... 12 
2.2.2 Properties of PLA ........................................................................................ 17 
2.2.2.1 Sealing properties.......................................................................... 18 
2.2.2.2 Mechanical properties ................................................................... 19 
2.2.2.3 Barrier properties .......................................................................... 20 
2.3 Processing technologies of PLA ................................................................................. 23 
2.3.1 Drying .......................................................................................................... 23 
2.3.2 Extrusion ...................................................................................................... 24 
2.3.2.1 Cast film extrusion ........................................................................ 25 
2.3.2.2 Blown film extrusion .................................................................... 27 
2.3.2.3 Extrusion blow molding ................................................................ 29 
2.3.3 Injection ....................................................................................................... 30 
2.3.3.1 Injection blow molding ................................................................. 31 
2.3.3.2 Injection stretch blow molding ..................................................... 32 
2.3.4 Thermoforming ............................................................................................ 32 
2.4 Improving PLA’s property .......................................................................................... 33 
2.5 Cellulose nanocrystals (CNCs) ................................................................................... 33 
2.5.1 Extraction of CNCs ...................................................................................... 33 
2.5.2 Properties of CNCs ...................................................................................... 35 
2.5.3 Use of CNCs in bio-based polymers ............................................................ 36 
2.6 Processing technologies of composite films ............................................................... 38 
2.6.1 Casting-evaporation process .................................................................................... 38 
2.6.2 Melt processing ........................................................................................................ 39 
2.6.3 Electrospinning ........................................................................................................ 40 
REFERENCES ............................................................................................................................. 42 

 

 

 

vi 

Chapter 3 ....................................................................................................................................... 49 
EXPERIMENTAL ........................................................................................................................ 49 
3.1 Materials ..................................................................................................................... 49 
3.2 Sample manufacturing ................................................................................................ 49 
3.3 Property evaluation ..................................................................................................... 51 
3.3.1 Light microscopy ..................................................................................................... 51 
3.3.2 Thickness measurement ........................................................................................... 51 
3.3.3 Profilometry ............................................................................................................. 52 
3.3.4 Hot tack performance ............................................................................................... 53 
3.3.5 Seal strength ............................................................................................................. 55 
3.3.6 Burst pressure........................................................................................................... 55 
3.3.7 Tensile properties ..................................................................................................... 56 
3.3.8 Falling dart impact strength ..................................................................................... 57 
3.3.9 Water Vapor Permeability (WVP) ........................................................................... 57 
3.3.10 Oxygen Permeability (OP) ..................................................................................... 58 
3.3.11 Statistics ................................................................................................................. 59 
REFERENCES ............................................................................................................................. 60 

Chapter 4 ....................................................................................................................................... 62 
RESULTS AND DISCUSSION ................................................................................................... 62 
4.1 Effect of CNC content on the surface texture of PLA cast films ................................ 62 
4.2 Effect of CNC content on the barrier properties of PLA cast films............................ 69 
4.3 Influence of CNC content on the sealing properties of PLA cast films...................... 71 
4.4 Effect of CNC content on the tensile and impact properties of PLA cast films ......... 75 
APPENDICES ...............................................................................................................................83 
APPENDIX A  Effect of CNC content on the thickness of PLA cast films ..................... 84 
APPENDIX B  Effect of CNC content on the surface texture of PLA cast films ............ 90 
APPENDIX C  Effect of CNC content on the water vapor and oxygen barrier 

properties of PLA cast films .................................................................... 93 

APPENDIX D  Effect of CNC content on the hot tack performance, seal strength 

and burst pressure of PLA cast films ....................................................... 97 
APPENDIX E  Effect of CNC content on the tensile properties of PLA cast films ...... 104 
APPENDIX F  Effect of CNC content on the dart impact strength of PLA cast 

films ....................................................................................................... 113 
REFERENCES ........................................................................................................................... 118 

Chapter 5 ..................................................................................................................................... 122 
CONCLUSIONS......................................................................................................................... 122 
5.1 Conclusions ............................................................................................................... 122 
5.2 Future works ............................................................................................................. 124 

 

 

 

vii 

LIST OF TABLES 

Table 2.1:  

Characteristics of various grades of PLA and petroleum-based polymers. .......... 17 

Table 2.2:  

Tensile  properties  of  various  grades  of  PLA  and  petroleum-based    
polymers. ............................................................................................................... 20 

Table 2.3:  

Permeability  of  different  grades  of  PLA  and  other  petroleum-based 
polymers. ............................................................................................................... 22 

Table 4.1:  

Thicknesses  of  neat  PLA  and  composite  films  measured  using  digital 
micrometer and density methods. ......................................................................... 68 

Table 4.2:  

The effect of CNC content on water vapor permeability (WVP) and oxygen 
permeability (OP) of PLA films. .......................................................................... 69 

Table 4.3:  

The effect of CNC content on the hot tack initiation temperature (HTIT), 
maximum  hot  tack  strength  (MHTS)  and  temperature  where  MHTS 
occurred of PLA films. ......................................................................................... 72 

Table 4.4:  

The effect of CNC content on the seal strength of PLA films. ............................. 73 

Table 4.5  

The effect of CNC content on the percentage of failure mode of neat PLA 
films in burst test. .................................................................................................. 75 

Table 4.6:  

The effect of CNC content on the tensile properties of PLA films in both 
machine and cross machine directions. ................................................................. 77 

Table 4.7:  

The effect of CNC content on the impact strength of PLA cast films. ................. 82 

Table A.1:   Thickness measurement of neat PLA films. ......................................................... 86 

Table A.2:   Thickness measurement of PLA with 0.5% CNC films. ...................................... 87 

Table A.3:   Thickness measurement of PLA with 1% CNC films. ......................................... 88 

Table A.4:   Thickness measurement of PLA with 2% CNC films. ......................................... 89 

Table B.1:  

Surface roughness (Ra) and peak-to-peak values across neat PLA and PLA 
with 1% CNC films. .............................................................................................. 91 

Table B.2:  

Effect of CNC content on the surface roughness of PLA cast films in both 
machine direction (MD) and cross machine direction (CMD). ............................ 92 

Table C.1:  

Effect of CNC content on the water vapor permeability (WVP) of PLA cast 
films at 38oC and 85%RH. .................................................................................... 94 

 

viii 

Table C.2:  

Effect of CNC content on the oxygen permeability (OP) of PLA cast films 
at 23oC and 0%RH. ............................................................................................... 95 

Table C.3:  

Effect  of  testing  relative  humidity  (RH)  on  the  OP  of  PLA  and 
PLA/2%CNC composite films. ............................................................................. 96 

Table D.1:   Effect  of  CNC  content  on  the  hot  tack  profiles  of  neat  PLA  films  as 

temperature increases from 60oC to 110oC. .......................................................... 98 

Table D.2:   Effect  of  CNC  content  on  the  hot  tack  initiation  temperature  (HTIT), 
temperature  where  maximum  hot  tack  strength  occurred  (TMHTS),  and 
maximum hot tack strength (MHTS) of neat PLA films at the temperature 
range of 60oC to 110oC. ........................................................................................ 99 

Table D.3:   Effect of CNC content on the seal strength of neat PLA cast films. .................. 100 

Table D.4:   Effect of CNC content on the burst pressure of neat PLA cast films. ................ 103 

Table E.1:  

Effect of CNC content on the tensile modulus of neat PLA cast films in both 
machine and cross machine directions. ............................................................... 105 

Table E.2:  

Effect of CNC content on the tensile strength of neat PLA cast films in both 
machine and cross machine directions. ............................................................... 107 

Table E.3:  

Effect of CNC content on the energy at break of neat PLA cast films in both 
machine and cross machine directions. ............................................................... 109 

Table E.4:  

Effect of CNC content on the elongation at break of neat PLA cast films in 
both machine and cross machine directions. ....................................................... 111 

 
 

 

 

ix 

LIST OF FIGURES 

Figure 2.1:   Chemical structure of L(+)- lactic acid and D(-)- lactic acid................................ 13 

Figure 2.2:   Chemical structures of lactide. .............................................................................. 14 

Figure 2.3:   Cationic polymerization mechanism of lactides. .................................................. 15 

Figure 2.4:   Anionic polymerization mechanism of lactides. ................................................... 15 

Figure 2.5:   Coordination-insertion mechanism of lactides using Sn(II) as a catalyst. ............ 16 

Figure 2.6:   Conventional extruder in extrusion processes. ..................................................... 24 

Figure 2.7:   Three types of dies used in extrusion processes. .................................................. 25 

Figure 2.8:   Cast film extrusion process. .................................................................................. 26 

Figure 2.9:   Blown film extrusion process. .............................................................................. 28 

Figure 2.10:   Schematic representation of extrusion blow molding. .......................................... 29 

Figure 2.11:   Schematic representation of injection molding..................................................... 30 

Figure 2.12:   Schematic representation of injection and injection stretch blow molding. ......... 31 

Figure 2.13:   Thermoformed containers of (a) PLA and (b) PLA/1%CNC. .............................. 32 

Figure 2.14:   Chemical structure of cellulose with repeating unit of cellobiose. ....................... 34 

Figure 2.15:   Schematic representation of casting-evaporation process. ................................... 39 

Figure 2.16:   Schematic representation of electrospinning. ....................................................... 41 

Figure 3.1:   Schematic representation of the cast film extrusion process. ............................... 50 

Figure 3.2:   Hot tack profile showing three important parameters: (i) hot tack initiation 
temperature  (HTIT),  (ii)  maximum  hot  tack  strength  (MHTS)  and  (iii) 
temperature where maximum hot tack strength occurred (TMHTS). ...................... 54 

Figure 3.3:   Two types of pouch configurations for the burst test. .......................................... 56 

Figure 4.1:   Light microscope images of (a) PLA, (b) PLA/0.5%CNC, (c) PLA/1%CNC 

and (d) PLA/2%CNC films. .................................................................................. 63 

 

x 

Figure 4.2:   Surface  texture  profiles  of  (a)  neat  PLA  and  (b)  PLA/1%CNC  films 
collected at 3 different locations across the film’s width: left (a1 and b1); 
center (a2 and b2); and right (a3 and b3) along the machine direction. ............... 65 

Figure 4.3:   Surface texture profiles of neat PLA (first row) and PLA with 0.5% CNC 
(second row), 1% CNC (third row), and 2% CNC (fourth row). Samples in 
the left column were tested in the machine direction whereas those in the 
right column in the cross machine direction. ........................................................ 66 

Figure 4.4:   Effect of CNC content on roughness (Ra) and peak-to-peak values of PLA 

cast films. .............................................................................................................. 67 

Figure 4.5:   Effect  of  testing  relative  humidity  (RH)  on  the  OP  of  PLA  and 

PLA/2%CNC composite films. ............................................................................. 70 

Figure 4.6:   Experimental hot tack profiles of neat PLA and PLA/CNC composite films.

............................................................................................................................... 71 

Figure 4.7:   The effects of CNC content and pouch configuration on the burst pressure 

of neat PLA films. ................................................................................................. 74 

Figure 4.8:   Stress-strain curves of neat PLA films in machine (a1) and cross machine 
(a2) directions as well as of PLA/CNC composite films in machine (b1) and 
cross machine (b2) directions. .............................................................................. 76 

Figure 4.9:   The effect of CNC content on the energy at break in machine (a1) and cross 
machine (a2) directions as well as on the elongation at break in machine (b1) 
and cross machine (b2) directions, of PLA cast films. ......................................... 79 

Figure 4.10:   Effect of CNC content on the (a) tensile strength at break and (b) modulus 
of PLA films along machine direction (MD) and cross machine direction 
(CMD). .................................................................................................................. 81 

Figure F.1:   The dart impact test results for neat PLA cast films. .......................................... 114 

Figure F.2:   The dart impact test results for PLA with 0.5% CNC cast films. ....................... 115 

Figure F.3:   The dart impact test results for PLA with 1% CNC cast films. .......................... 116 

Figure F.4:   The dart impact test results for neat PLA with 2% CNC cast films. .................. 117 

 

 

xi 

Chapter 1 

INTRODUCTION 

1.1 Introduction 

Petroleum-based  polymers  have  been  widely  used  in  many  fields  in  the  United  States. 

However,  there  are  rising  demand  for  bio-based  plastics  as  an  alternative  to  the  fossil-derived 

polymers to alleviate U.S. dependency on foreign oil and environmental concerns associated with 

production  and  disposal  of  petroleum-based  polymer  [1-4].  The  value  of  bioplastics  market  is 

predicted to reach $34.24 billion globally by 2024 [5]. Poly (lactic acid) (PLA), a polymer derived 

from sugar beets and corns, has attracted many research and industrial interests due to its bio-based 

and bio-degradable nature. It has great potentials to serve as a packaging material because of its 

high stiffness, excellent barrier to aroma and flavor, reasonable strength and bio-degradability [1-

4]. In fact, the global PLA market reached $304.9 million in 2014 and 54.6% of the market shares 

are garnered by the packaging industry [6,7]. In 2020, the global PLA market is projected to reach 

$5.32  billion  [8].  Although  the  increasing  demand  and  attractive  properties  have  shown  a 

promising market for PLA, several drawbacks such as brittleness, low impact resistance, as well 

as poor water and moderate oxygen barrier properties, have limited its application in the packaging 

industry [4]. 

The brittleness and low impact resistance pose challenges in the flexible packaging as the 

PLA  film  is  subjected  to  tears  and  cracks.  The  barrier  properties  are  important  for  packaging 

materials. Water barrier property is crucial to package water sensitive products as moisture uptake 

or loss by the product will change the texture, deteriorate the quality and shorten its shelf life [9]. 

Oxygen content within the package is important since excessive or lack of oxygen will impair the 

 

1 

quality of the products. Improving these drawbacks will broaden the PLA films in packaging of 

food and drugs as well as other engineering applications where toughness, flexibility, and excellent 

barrier properties are paramount. 

The brittleness and impact strength of PLA have been enhanced by modifying its physical 

properties  through  several  approaches  with  renewable  and  biodegradable  materials  in  order  to 

maintain its biodegradation nature [1,2,10-18]. These include copolymerization of lactides with 

other  monomers  such  as  ε-caprolactone  [10],  foaming  [1,11],  blending  of  PLA  with  a 

biodegradable second polymer [12-15], and plasticizing with modified vegetable oils [2,16-18]. 

The barrier properties could be improved by crystallization. Presence of crystallites in the 

polymer matrix increases the diffusion time of permeants due to a more tortuous diffusion path 

created. This phenomenon is referred as the tortuosity effect [9,19,20]. 

Increased  crystallinity  is  achieved  through  adjusting  the  processing  conditions  or 

modifying  the  material  formulations.  As  polymer  melt  exits  the  die,  any  stretching  in  either 

machine or cross machine direction aligns molecules to create the order, which further increases 

the degree of crystallinity [21-23]. The cooling rate of polymer melt also affects the crystallization. 

As the cooling rate decreases, the degree of crystallinity increases as more time is given to form 

crystallites [23,24]. 

Another method to increase the crystallinity is to modify the materials’ formulations by 

adding organic and inorganic additives into the polymer matrices. Although inorganic additives 

such as talc [25,26], calcium carbonate [27], etc. are employed as the nucleating agent to increase 

the  degree  of  crystallinity  of  polymers,  they  could  also  affect  the  biodegradable  nature  of  bio-

plastic like PLA [28] and increase its density. Thus, more attention is currently paid to light weight 

 

2 

organic additives from natural resources such as  plant fibers, cellulose nanomaterials [9,19,29], 

chitosan [30], etc. 

Over  the  past  few  years,  cellulose  nanocrystals  (CNCs)  have  attracted  many  research 

interests. They are the rod-shaped nanoparticles derived from lignocellulosic plants and are often 

used as a property enhancer in the bio-based polymer matrix because of its bio-degradability and 

high  surface  area  and  aspect  ratio  [31-33].  Recent  studies  have  shown  that  the  homogenous 

dispersion of CNCs in PLA matrix improves the mechanical performance of the composites and 

this is contributed to efficient stress transfer at the interface [34,35]. Furthermore, the addition of 

CNCs  enhances  the  water  and  oxygen  barrier  properties  of  PLA/CNC  films  due  to  increased 

crystallinity  [19]  because  CNCs  are  crystallites  and  act  as  the  nucleating  agent.  The  improved 

barrier and mechanical properties have been reported for PLA/CNC films manufactured through 

solvent casting techniques (a batch process) [32,33,36] and melt-processing (a continuous process) 

methods [9,19,31,37-39]. All these improvements are achieved without significantly affecting the 

film transparency [19], making such films ideal for food packing applications. 

Although transparency and barrier properties are amongst the important attributes for films 

intended for packaging applications, films that offer good sealing strength, high impact strength, 

and good puncture resistance are also important for food packaging. 

For example, packaging pouches, manufactured by heat sealing films, are used in many 

applications and can have multiple purposes such as to protect products during shipment, extend 

product shelf life, enhance product presentation, etc. Heat sealing in flexible packaging involves 

the fusion of one film to another or to a rigid container to create a hermetic seal. Sealing is crucial 

in packaging because it helps keep product in the package until the consumer or user opens it and 

 

3 

protect  the  product  from  the  outside  environment  [40].  Poor  seals  could  act  as  entrances  for 

contaminants, which can lead to the spoilage of packaged food products. In contrast, a good heat 

seal  helps  the  package  provide  one  of  its  primary  functions  of  protecting  the  product.  For  the 

packaging of food for example, the seal helps ensure product freshness. While the seal strength is 

crucial in maintaining the desired shelf life [40], the hot tack strength, i.e., the strength of a polymer 

in its semi-viscous state, is crucial during the form-fill-seal (FFS) process, to ensure that the seal 

is strong enough to hold the weight of the product immediately after the seal is made at production 

speeds [41]. The burst pressure measures the pressure resulting in the failure of a sealed package 

[2].  This  strength  is  crucial  in  maintaining  the  integrity  of  the  packaging  system  during 

transportation.  During  the  transportation  process,  the  package  may  expand  to  explode  when 

manufactured at sea level and transported to locations with high altitude.  Mechanical properties 

such as the tensile strength and the impact resistance are crucial to packaging industry to maintain 

the integrity of the packages during transportation and distribution [42]. Therefore, it is important 

to study the heat sealability and mechanical properties of the films. 

Lack of sealing strength, mechanical and barrier properties could lead to the failures of the 

packages  during  manufacturing,  distribution  and  transportation  process,  creating  waste  of  both 

packaging materials and products. This waste could increase the manufacturing costs, delay the 

production  efficiency,  further  impair  the  benefits  of  stakeholders  as  well  as  pose  deleterious 

impacts on the environment. Understanding how the addition of CNCs in PLA cast films affects 

the packaging performances is of paramount important to avoid such wastes. 

To  the  best  of  our  knowledge,  no  research  has  been  reported  on  the  influence  of  CNC 

addition on the seal strengths, mechanical, and barrier properties of PLA cast films manufactured 

through a continuous melt-process. 

 

4 

Therefore,  the  objectives  of  this  study  were  to  manufacture  and  evaluate  the  physico-

mechanical properties, including sealing, mechanical, and barrier properties, of PLA cast films and 

its  composites  with  various  CNC  contents  to  expand  the  packaging  applications  of  such 

nanocomposites films. 

1.2 Objectives 

The  goal  of  this  study  was  to  utilize  a  continuous  extrusion  process  that  efficiently 

incorporates  CNCs  into  a  PLA  matrix  in  order  to  manufacture  PLA/CNC  cast  films  for  the 

packaging application. To achieve this objective, the following specific objectives were proposed: 

1.  Manufacture  PLA/CNC  extruded  cast  films  with  various  CNC  content  in  the  films  and 

characterize their physico-mechanical properties; 

2.  Explore the effect of CNC content on the surface texture of PLA cast films and determine 

the thickness of neat PLA and composite films; 

3.  Study  the  effect  of  CNC  content  on  the  water  and  oxygen  barrier  properties  of  PLA 

extruded cast films to gain an in-depth understanding of the diffusion mechanism with the 

addition of CNC content; 

4.  Investigate the influence of CNC content on the sealing properties, including seal strength, 

hot tack performance and burst pressure of PLA cast films; 

5.  Evaluate  the  effect  CNC  content  on  the  impact  strength,  brittleness  and  other  tensile 

properties of PLA films. 

 

 

 

5 

1.3 Hypothesis 

This research was intended to test the hypothesis that the addition of a small amount of 

CNCs into PLA films will enhance its water and oxygen barrier performance without negatively 

affecting  the  tensile  strength,  impact  strength,  hot  tack  performance,  seal  strength  and  burst 

pressure of the composite films. 

1.4 Structure of thesis 

The first chapter of the thesis introduces the rationale of this research. A background on 

poly(lactic  acid),  cellulose  nanocrystals,  their  synthesis,  properties  and  blending  techniques  are 

reviewed  in  Chapter  2.  The  detailed  experimental  methods,  including  material  specifications, 

sample  manufacturing  and  property  evaluation  are  described  in  Chapter  3.  The  experimental 

results in evaluating the effect of CNC content on the surface texture, barrier, seal and mechanical 

properties  of  neat  PLA  cast  films  are  discussed  in  Chapter  4.  In  Chapter  5,  the  conclusions 

summarized from the experimental data and proposed future work are presented. 

 

 

6 

REFERENCES 

 

7 

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Biomaterials and Biomedical-TechConnect Briefs 2016, 3, 1-4. 

10. Harada,  M.,  Iida,  K.,  Okamoto,  K.,  Hayashi,  H.,  and  Hirano,  K.  (2008).  Reactive 
compatibilization of biodegradable poly(lactic acid)/poly(ɛ-caprolactone) blends with reactive 
processing agents. Polymer Engineering and Science, 48(7), 1359-1368. 

11. Matuana,  L.M.,  Faruk,  O.,  and  Diaz,  C.A.  (2009).  Cell  morphology  of  extrusion  foamed 
poly(lactic acid) using endothermic chemical foaming agent. Bioresource Technology, 100(23), 
5947-5954. 

8 

12. Afrifah,  K.A.  and  Matuana,  L.M.  (2010).  Impact  modification  of  polylactide  with  a 
biodegradable  ethylene/acrylate  copolymer.  Macromolecular  Materials  and  Engineering, 
295(9), 802-811. 

13. Schreck, K.M. and Hillmyer, M.A. (2007). Block copolymers and melt blends of polylactide 
with  NodaxTM  microbial  polyesters:  preparation  and  mechanical  properties.  Journal  of 
Biotechnology, 132(3), 287-295. 

14. Ishida, S., Nagasaki, R., Chino, K., Dong, T., and Inoue, Y. (2009). Toughening of poly(L-
lactide) by melt blending with rubbers. Journal of Applied Polymer Science, 113(1), 558-566. 

15. Semba, T., Kitagawa, K., Ishiaku, U.S., and Hamada, H. (2006). The effect of crosslinking on 
the  mechanical  properties  of  polylactic  acid/polycaprolactone  blends.  Journal  of  Applied 
Polymer Science, 101(3), 1816-1825. 

16. Al-Mulla,  E.A.J.,  Yunus,  W.M.Z.W.,  Ibrahim,  N.A.B.,  and  Rahman,  M.Z.A.  (2010). 
Properties of epoxidized palm oil plasticized polytlactic acid.  Journal of Materials Science, 
45(7), 1942-1946. 

17. Ali, F., Chang, Y., Kang, S.C., and Yoon, J.Y. (2009). Thermal, mechanical and rheological 
properties of poly (lactic acid)/epoxidized soybean oil blends. Polymer Bulletin, 62(1), 91-98. 

18. Xu, Y. and Qu, J. (2009). Mechanical  and  rheological  properties of epoxidized soybean oil 

plasticized poly(lactic acid). Journal of Applied Polymer Science, 112(6), 3185-3191. 

19. Karkhanis,  S.S.,  Stark,  N.M.,  Sabo,  R.C.,  and  Matuana,  L.M.  (2017).  Performance  of 
poly(lactic  acid)/  cellulose  nanocrystal  composite  blown  films  processed  by  two  different 
compounding approaches. Polymer Engineering and Science. DOI: 10.1002/pen.24806. 

20. Choudalakis,  G.  and  Gotsis,  A.D.  (2009).  Permeability  of  polymer/clay  nanocomposites:  a 

review. European Polymer Journal, 45(4), 967-984. 

21. Kokturk, G., Serhatkulu, T.F., Cakmak, M., and Piskin, E. (2002). Evolution of phase behavior 
and orientation in uniaxially deformed polylactic acid films. Polymer Engineering and Science, 
42(8), 1619-1628. 

22. Houichi,  H.,  Maazouz,  A.,  and  Elleuch,  B.  (2015).  Crystallization  behavior  and  spherulitic 
morphology of poly(lactic acid) films induced by casting process. Polymer Engineering and 
Science, 55(8), 1881-1888. 

23. Yu, L., Liu, H., Xie, F., Chen, L., and Li, X. (2008). Effect of annealing and orientation on 
microstructures  and  mechanical  properties  of  polylactic  acid.  Polymer  Engineering  and 
Science, 48(4), 634-641. 

24. Haudin, J.M. (2013). Chapter 15 Crystallization in processing conditions.  In E. Piorkowska 
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Jersey, USA: John Wiley & Sons, Inc. 

9 

25. Zbik, M. and Smart, R.S.C. (2002). Dispersion of kaolinite and talc in aqueous solution: nano-

morphology and nano-bubble entrapment. Minerals Engineering, 15(4), 277-286. 

26. Yu, F., Liu, T., Zhao, X., Yu, X., Lu, A., and Wang, J. (2012). Effects of talc on the mechanical 
and thermal properties of polylactide. Journal of Applied Polymer Science, 125(S2), E99-E109. 

27. Kasuga, T., Maeda, H., Kato, K., Nogami, M., Hata, K.I., and Ueda, M. (2003). Preparation of 
poly(lactic  acid)  composites  containing  calcium  carbonate  (vaterite).  Biomaterials,  24(19), 
3247-3253. 

28. Ghoshi, S.B., Bandyopadhyay-ghosh, S., and Sain, M. (2010). Chapter 18 Composites. In R. 
Auras, L.T. Lim, S.E.M. Selke, and H. Tsuji (Eds.), Poly(lactic acid): synthesis, structures, 
properties,  processing,  and  applications  (pp.  293-310).  Hoboken,  New  Jersey,  USA:  John 
Wiley & Sons, Inc. 

29. Mariano,  M.  and  Dufresne,  A.  (2017).  Chapter  11  Nanocellulose:  common  strategies  for 
processing  of  nanocomposites.  In  U.P.  Agarwal,  R.H.  Atalla,  and  A.  Isogai  (Eds.), 
Nanocelluloses: their  preparation, properties, and applications  (pp. 203-225). Washington, 
D.C., USA.: American Chemical Society. 

30. Suyatma,  N.E.,  Copinet,  A.,  Tighzert,  L.,  and  Coma,  V.  (2004).  Mechanical  and  barrier 
properties of biodegradable films made from chitosan and poly (lactic acid) blends. Journal of 
Polymers and the Environment, 12(1), 1-6. 

31. Hietala,  M.,  Mathew,  A.P.,  and  Oksman,  K.  (2013).  Bionanocomposites  of  thermoplastic 
starch and cellulose nanofibers manufactured using twin-crew extrusion. European Polymer 
Journal, 49(4), 950-956. 

32. Fortunati,  E.,  Peltzer,  M.,  Armentano,  I.,  Torre,  L.,  Jiménez,  A.,  and  Kenny,  J.M.  (2012). 
Effects of modified cellulose nanocrystals on the barrier and migration properties of PLA nano-
biocomposites. Carbohydrate Polymers, 90(2), 948-956. 

33. Fortunati, E., Armentano, I., Zhou, Q., Puglia, D., Terenzi, A., Berglund, L.A., and Kenny, 
J.M. (2012). Microstructure and nonisothermal cold crystallization of PLA composites based 
on  silver  nanoparticles  and  nanocrystalline  cellulose.  Polymer  Degradation  and  Stability, 
97(10), 2027-2036. 

34. Mathew,  A.P.,  Oksman,  K.,  and  Sain,  M.  (2005).  Mechanical  properties  of  biodegradable 
composites  from  poly  lactic  acid  (PLA)  and  microcrystalline  cellulose  (MCC).  Journal  of 
Applied Polymer Science, 97(5), 2014-2025. 

35. Shi, Q., Zhou, C., Yue, Y., Guo, W., Wu, Y., and Wu, Q. (2012). Mechanical properties and 
in  vitro  degradation  of  electrospun  bio-nanocomposite  mats  from  PLA  and  cellulose 
nanocrystals. Carbohydrate Polymers, 90(1), 301-308. 

36. Pei,  A.,  Zhou,  Q.,  and  Berglund,  L.A.  (2010).  Functionalized  cellulose  nanocrystals  as 
biobased nucleation agents in poly(L-lactide) (PLLA)-crystallization and mechanical property 
effects. Composites Science and Technology, 70(5), 815-821. 

10 

37. Jonoobi,  M.,  Harun,  J.,  Mathew,  A.P.,  and  Oksman,  K.  (2010).  Mechanical  properties  of 
cellulose nanofiber (CNF) reinforced polylactic acid (PLA) prepared by twin screw extrusion. 
Composites Science and Technology, 70(12), 1742-1747. 

38. Herrera,  N.,  Mathew,  A.P.,  and  Oksman,  K.  (2015).  Plasticized  polylactic  acid/cellulose 
nanocomposites  prepared  using  melt-extrusion  and  liquid  feeding:  mechanical,  thermal  and 
optical properties. Composites Science and Technology, 106(16), 149-155. 

39. Herrera, N., Roch, H., Salaberria, A.M., Pino-Orellana, M.A., Labidi, J., Fernandes, S.C.M., 
Radic,  D.,  Leiva,  A.,  and  Oksman,  K.  (2016).  Functionalized  blown  films  of  plasticized 
polylactic acid/chitin nanocomposite: preparation and characterization. Materials and Design, 
92, 846-852. 

40. Morris,  B.A.  (Ed.).  (2017).  Chapter  7  Heat  seal.  The  science  and  technology  of  flexible 
packaging: multilayer films from resin and process to end use (pp. 181-257). Oxford, United 
Kingdom: Elsevier Inc. 

41. Falla, D. and Li, M. (2014). Reliable hot tack testing of polyolefin films. SPE ANTEC 2014, 

1460-1475. 

42. Morris, B.A. (Ed.). (2017). Chapter 9 Strength, stiffness, and abuse resistance. The science and 
technology of flexible packaging: multilayer films from resin and process to end use (pp. 309-
350). Oxford, United Kingdom: Elsevier Inc. 

 

 

11 

Chapter 2 

BACKGROUND AND LITERATURE REVIEW 

2.1 Introduction 

Consistent with the scope of this study, a background and literature review on the current 

studies of processing poly(lactic acid) (PLA)/cellulose nanocrystals (CNCs) films are presented in 

this  chapter.  The  review  focuses  on  the  effects  of  CNC  addition  on  the  physico-mechanical 

properties  and  packaging  performances  of  PLA  cast-films;  including  surface  texture,  sealing, 

mechanical  and  barrier  properties,  as  well  as  the  manufacturing  approaches  for  PLA/CNC 

composite films. 

2.2 Poly(lactic acid) 

Poly(lactic  acid),  a  biodegradable  and  compostable  polymer  derived  from  renewable 

sources, such as sugar beets  and  corns, belongs to the family of  aliphatic polyesters [1].  It  is  a 

thermoplastic  with  reasonable  strength,  good  heat  sealability,  easy  fabrication  with  existing 

processing techniques, as well as excellent flavor and aroma barrier properties [2-4]. 

2.2.1 Synthesis of PLA 

Lactic acid (2-hydroxy propionic acid), the basic building block of PLA, has two optical 

isomers, due to the chirality: L-lactic acid (LLA) and its mirror image, D-lactic acid (DLA) (Figure 

2.1) [5]. 

12 

Figure 2.1: Chemical structure of L(+)- lactic acid and D(-)- lactic acid. 

 

Two ways to produce lactic acid is through fermentative and chemical synthesis [6,7]. The 

lactic acid with desired stereoisomer can be converted from various carbohydrates sources (corn 

syrup, cane, whey, etc.) by bacterial fermentation using homolactic organism, such as modified 

strains  of  the  genus  Lactobacilli  [7,  8-10].  Bacterial  fermentation  is  commercially  used  in  the 

industry and can produce both D(-)- and L(+)- enantiomers [10]. The chemical synthesis routes 

for lactic acid production, including oxidation of propylene glycol, base catalyzed degradation of 

sugars,  hydrolysis  of  chloropropionic  acid  as  well  as  reaction  of  the  mixture  of  acetaldehyde, 

carbon  monoxide  and  water  at  elevated  temperatures  and  pressures,  only  produce  the  racemic 

lactic acid [7]. 

Two most used production techniques to obtain PLA through the polymerization of lactic 

acid  are:  (1)  direct  condensation  polymerization;  (2)  ring-opening  polymerization  (ROP).  The 

direct condensation method uses solvent under high vacuum and temperatures to remove the water 

generated in the process, and produce polymer with low to intermediate molecular weight, which 

can be used or coupled with isocyantes, peroxide to further produce a range of molecular weight 

polymers [10]. 

13 

ROP technique, the most commonly used method patented by Cargill Inc., requires catalyst 

but generates PLA with controlled molecular weight [10,11]. In this method, the lactide is formed 

by the two lactic acid molecules and has three types of stereoisomers, due to the chirality of lactic 

acid monomer: L-lactide (two L-lactic acid isomers), meso-lactide (an L-lactic acid and a D-lactic 

acid isomers) and D-lactide (two D-lactic acid isomers), shown in Figure 2.2 [12,13]. 

Figure 2.2: Chemical structures of lactide. 

 

PLA  can  undergo  three  routes  of  ring-opening  polymerizations:  cationic,  anionic  and 

coordination-insertion  polymerizations.  The  cationic  ROP  uses  trifluoromethane  sulfonic  acid 

(triflic acid) or methyl trifluoromethane sulfonic acid (methyl triflate), as those are the only two 

cationic initiators to polymerize lactide [8]. The mechanism of the cationic ROP is shown in Figure 

2.3. 

14 

Figure 2.3: Cationic polymerization mechanism of lactides [1]. 

 

Anionic ROP is proceeded through the nucleophilic reaction of the anion with the carbonyl 

and the acyl-oxygen cleavage [8,14]. Figure 2.4 depicts the anionic initiation process of lactides. 

It is found that initiator with higher nucleophilicity can initiate the lactide, weaker bases, such as 

potassium phenoxide, serve as initiator only at high temperatures [8,15]. However, both anionic 

and cationic ROP, are often performed in the solvent system and susceptible to transesterification, 

racemization and impurity levels, which are not suitable for mass production for industrial usage.  

Figure 2.4: Anionic polymerization mechanism of lactides [1]. 

 

15 

Coordination-insertion  ROP,  on  the  other  hand,  utilizes  metal  catalysts  and  forms  high 

molecular  weight  PLA  easily,  which  is  preferred  for  large-scale  commercial  use  [8,16].  Tin 

compounds, such as Sn (II), are commonly used as a catalyst in PLA synthesis, because of its low 

toxicity (FDA approval) and high catalytic activity [8,14]. Figure 2.5 demonstrates the mechanism 

of coordination-insertion using tin, Sn(II), as a catalyst. 

(a) 

(b) 

(c) 

(f) 

(e) 

(d) 

 

Figure 2.5: Coordination-insertion mechanism of lactides using Sn(II) as a catalyst [17]. 

 

 

16 

2.2.2 Properties of PLA 

The properties of PLA such as thermal, barrier and mechanical are dependent on PLA’s 

degree of crystallinity and other parameters. The crystallinity of PLA is governed by the types of 

stereoisomers and its relative amount in the polymer. Poly(L-lactide), the resultant polymer from 

polymerization of greater than 93% L-lactide content, is semi-crystalline and has very high melting 

point,  high  crystallinity  and  poor  processing  properties  [12,18].  However,  when  the  L-lactide 

content is between 50 to 93%, the resultant polymer is amorphous [12]. The D,L-PLA, PLA with 

meso-lactide, is  an amorphous polymer with the glass transition temperature (Tg) of 60oC [18]. 

Due to higher degree of crystallinity, generally, semi-crystalline PLA has higher Tg and melting 

temperature than amorphous PLA. The thermal properties and melt flow index of different PLA 

grades are summarized in Table 2.1. 

Table 2.1: Characteristics of various grades of PLA and petroleum-based polymers. 

Materials 

D-lactide 

MFIa 

(%) 

(g/10min) 

Thermal propertiesb 

Tg (oC) 

Tm (oC) 

χc (%) 

PLA 2003D [19] 

4-4.5 

39.93 

61.69 

167.03 

11.92 

PLA 3052D [19] 

PLA 4043D [19] 

PLA 8302D [19] 

PET [20] 

PS [20] 

4 

4.8 

10 

- 

- 

28.80 

61.43 

165.93 

4.12 

47.07 

62.11 

167.68 

12.38 

18.47 

60.06 

- 

- 

- 

73-80 

245-265 

74-105 

- 

- 

- 

- 

aMFI is the melt flow index of different polymers. 
bTg,  Tm,  and  χc  are  the  glass  transition  temperature,  melting  temperature,  and 
percent crystallinity of different polymers. 

 

17 

In general, PLA is more heat sensitive compared to petroleum-based plastics. As shown in 

Table 2.1, PLA has lower Tg and Tm than that of polyethylene terephthalate (PET) and polystyrene 

(PS). PLA is susceptible to thermal degradation due to several factors: hydrolysis by slight amount 

of  water;  depolymerizaion;  oxidative  and  random  main-chain  scission;  and  formation  of  cyclic 

oligomers  of 

lactides  from 

intra-molecular 

transesterification  reactions; 

intermolecular 

transesterification to monomer and oligomeric esters [21-23]. 

2.2.2.1 Sealing properties 

Heating  sealing  refers  to  the  process  utilizing  heat  and  pressure  to  seal  two  structures, 

where at least one of the structures contains thermoplastic layer [24]. A good seal requires enough 

molecular entanglement within the polymer chains, between two thermoplastic sealing layers, so 

that the original interface is destroy to form a homogenous layer, which remains homogenous after 

cooling [24]. It is important to acquire a good seal to maintain the desired shelf life of the products. 

Factors  such  as  melting  point,  viscosity,  molecular  weight  and  polarity  of  the  plastics  have 

significant effects on the sealing performance [25]. 

The performance of a seal can be estimated by measuring the seal strength, the hot tack 

strength, burst strength, etc. Seal strength reflects the force needed to open a sealed film and can 

be measured using the peel test after the seal is made and cooled down to the room temperature. 

Hot tack strength, on the contrary, is a force measured in the polymers’ semi-molten state, while 

the seal remains hot [26]. Hot tack strength is crucial in the vertical form-fill-seal (FFS) process 

where the product is dropped on the sealed package immediately after it is made. It is essential to 

ensure the seal is strong enough to hold the weight of the product in this process [25]. The burst 

pressure measures the pressure resulting in the failure of a sealed package [27]. This strength is 

18 

crucial  in  maintaining  the  integrity  of  the  packaging  system  during  transportation,  and  can  be 

measured  through  the  internal  burst  test.  During  the  transportation  process,  the  package  may 

expand to explode when manufactured at sea level and transported to locations with high altitude. 

The sealing properties of PLA have not been extensively studied. Thumsorn and coworkers 

had investigated the seal characteristic of PLA films and reported that the seal strength of PLA 

films was from 5.87 to 26.51 N/15 mm for seals made with the heat bar temperature in the range 

of 90 to 100 oC, and seal time from 0.2 to 2 s with constant seal pressure of 0.2 MPa [28]. Tabasi 

and coworkers had studied the sealing and mechanical properties of PLA/polycaprolactone (PCL) 

blends. They found that the hot tack plateau strength of PLA was 800 g/25.4mm under constant 

pressure and sealing time as 0.5 N/mm2 and 1s, respectively. The addition of PCL decreased the 

sealing  and  hot  tack  initiation  temperature,  while  increasing  the  seal  and  hot  tack  strength. 

Furthermore, PCL act as a plasticizer to increase the elongation at break up to 150% [29]. 

2.2.2.2 Mechanical properties 

The mechanical properties, especially strength, ductility and impact resistance, are crucial 

in packaging industry to maintain the structural integrity of the package. The package will fail or 

deform  if  the  tensile  strength  is  not  sufficient  to  hold  the  weight  of  the  product  [30].  Impact 

resistance is important to maintain the integrity of the package during rough handling conditions. 

The mechanical properties of PLA vary in a large range from soft and elastic to stiff and 

high strength materials as they are dependent on the molecular weight [31,32]. Table 2.2 provides 

insights of mechanical properties of PLA. The tensile strength of semi-crystalline PLA is between 

50-70 MPa, elongation at  break of 2-10%, and the elastic modulus  is  between 3000-4000 MPa 

[32]. A summary of tensile properties of various PLA grades and that of petroleum-based polymers 

19 

is shown in Table 2.2. It is worth mentioning that different methods used in material processing 

affect the mechanical properties of PLA. 

Table 2.2: Tensile properties of various grades of PLA and petroleum-based polymers. 

Materials 

Tensile strength (MPa) 

Yield 

Break 

PLA 2002D [16] 

PLA 2100D [16] 

60 

62 

PLA 4030D [33] 

65-72 

53 

56 

- 

Tensile 
modulus 

(GPa) 

3.5 

3.5 

Elongation (%) 

Yield 

Break 

- 

- 

6.0 

3.0 

2.11-2.54 

4.5-4.7 

5.5-10.7 

PLA 4031D [34] 

- 

28.5 ± 3.8 

1.7 ± 0.2 

- 

>100 

PLA 4040D [33] 

74-84 

- 

2.31-2.87 

3.4-4.2 

78.2-96.9 

PET [20] 

PS [20] 

- 

- 

48.2-72.3 

2.76-4.14 

35.8-51.7 

2.27-3.27 

 

 

30-3000 

1.2-2.5 

2.2.2.3 Barrier properties 

Barrier properties, the ability of the materials to obstruct the penetration of permeants, are 

crucial in packaging industry. The barrier properties commonly studied in the packaging field are 

barrier against water vapor, oxygen (O2) and carbon dioxide (CO2). Those properties are extremely 

useful in determining the applications of polymers in food packaging as well as maintaining the 

desired shelf life. As most of food products are sensitive to water vapor, O2 and CO2, being exposed 

to those substances may cause off-flavors, loss of crunchiness, mold growth, further deteriorate 

the quality and shorten the shelf life of packaged products. 

20 

Permeability,  diffusivity  and  solubility  coefficients  are  parameters  often  used  to 

characterize the barrier properties of a plastic. For the materials with identical thickness, higher 

permeability  results  in  poor  barrier  properties.  Auras  and  co-workers  had  studied  the  barrier 

properties of films made with two grades of PLA, PLA 4030D with 98% L-lactide and 4040D with 

94% L-lactide, and found that the O2 and CO2 permeability coefficients of both grades were lower 

than that of PS, and in a comparable range with PET [33].  

Recently, the barrier properties of PLA blown films had also been assessed. Matuana and 

coworkers  had  investigated  the  effect  of  cellulose  nanocrystals  (CNCs)  on  the  water  vapor 

transmission  rate  (WVTR)  and  O2  transmission  rate  of  PLA  blown  films,  made  with  semi-

crystalline  PLA  4044D  pellets.  The  water  vapor  and  O2  barrier  properties  were  significantly 

increased with the addition of 1% CNC. They had further discovered that the relative humidity 

(RH) and temperature had more influence on the water vapor barrier property of neat PLA blown 

films than that of PLA/CNC films [37]. The effect of RH on O2 barrier property of neat PLA and 

modified PLA with hydrophilic additives blown films had been investigated by Kunanusont and 

coworkers.  The  O2  permeability  of  neat  PLA  blown  film  was  not  significantly  affected  by  the 

increasing  RH  due  to  the  polarity  of  the  films,  further  supported  by  the  contact  angle  results 

indicating that the surface of PLA films was slightly hydrophilic (contact angle was less than 90o). 

The O2 permeability of modified PLA, on the other hand, increased with increasing RH [35]. Table 

2.3  summarizes  barrier  properties  between  different  grades  of  PLA  and  those  of  common 

petroleum-based plastics. 

 

 

21 

Table 2.3: Permeability of different grades of PLA and other petroleum-based polymers. 

Permeability 

Materials 

PLA 2003D [35] 

PLA 3051D [36] 

PLA 4030D [33] 

PLA 4040D [33] 

O2 

CO2 

Water vapor 

(10-18 kg-m/m2-s-Pa) 

(10-17 kg-m/m2-s-Pa) 

(10-14 kg-m/m2-s-Pa) 

23oC, 0%RH 

2.49-3.32 

25 ± 1oC 

4.98 ± 0.16 

- 

- 

- 

20oC, 50 ± 2%RH 

1.04 ± 0.18 

25oC, 70%RH 

25oC, 0%RH 

37.8oC, 40-90%RH 

1.21 ± 0.07 

2.77 ± 0.05 

1.52 ± 0.05 

25oC, 70%RH 

25oC, 0%RH 

37.8oC, 40-90%RH 

1.39 ± 0.14 

1.99 ± 0.06 

1.48 ± 0.07 

PLA 4044D [37] 

23oC, 0%RH 

10.47 ± 2.13 

- 

23oC, 46%RH 

2.08-2.61 

25oC, 70%RH 

25oC, 0%RH 

25oC, 40-90%RH 

PET [33] 

PS [33] 

 

 

0.188 

25oC 

27 

 

0.173 

0.11 ± 0.01 

25oC, 0%RH 

15.5 

25oC 

0.67 

22 

2.3 Processing technologies of PLA 

The widely used technique to convert PLA resins to the end products is the melt processing. 

This process first uses heat to bring PLA resins above its melting point, transferring the resins from 

the solid to viscous state, in order to reshape into desired format, then cools the resins below its 

glass  transition  temperature  to  stabilize  the  desired  dimensions.  Melt  processed  PLA  can  be 

converted  into  extruded  blown  and  cast  films,  as  well  as  extruded  blow  molded  bottles. 

Additionally, the pre-formed parts can be obtained through melt processed PLA and are further 

processed  to  form  injection  stretch  molded  bottles,  and  thermoformed  containers  or  cups  for 

packaging applications. This section of the chapter discusses the common processing methods with 

the emphasis on the cast film extrusion process. 

2.3.1 Drying 

Prior to melt processing, it is essential to dry PLA sufficiently to avoid loss of physical 

properties due to the hydrolytic degradation. The drying temperature should be carefully chosen 

to be below the glass transition temperature (Tg) to prevent sticking of pellets.  In general, PLA 

resins  are  dried  in  a  chamber  with  less  than  250  ppm  moisture  presence  [38].  As  most  of  the 

commercial PLA grades  are crystalline pellets,  they can be dried in  a temperature range of 60-

90oC [38]. However, a lower temperature range (30-40oC) is needed to dry amorphous PLA pellets 

due to their low Tg (approximately 60oC) [38]. The drying time can vary, depending on the drying 

temperature [38]. 

 

 

23 

2.3.2 Extrusion 

A homogenous PLA melt can be converted into the end products through extrusion, one of 

the most common processing techniques. PLA bottles can be formed using blow molding, whereas 

PLA films and sheets can be obtained through cast or blown film extrusion processes. The key 

element  in  the  extrusion  process  is  the  extruder  with  three  sections:  feed,  compression  and 

metering. Figure 2.6 is a schematic representation of a conventional extruder. The feed section is 

where the polymer resins are received and conveyed into the screw. In the compression section, 

shown as melting region in Figure 2.6, the diameter of screw is increased in order to efficiently 

compress the polymer pellets. The metering section serves as a pump to meter the desired quantity 

of polymer to the die region [39]. 

Figure 2.6: Conventional extruder in extrusion processes [40]. 

 

 

 

24 

The die is another important component in the extrusion process as it shapes the polymer 

melt into the desired end products. In general, there are three types of dies (Figure 2.7): slit dies 

(or flat dies) in the cast film extrusion to product films and sheets, annular dies in the blown film 

extrusion to form tubular films or pipes, and capillary dies for filament and rods [41]. 

 

 

 

 

 

 

 

 

 

(a) Slit die [42] 

(b) Annular die [43] 

(c) Capillary die [44] 

Figure 2.7: Three types of dies used in extrusion processes. 

2.3.2.1 Cast film extrusion 

Cast film extrusion is one of the most commonly used techniques in the flexible packaging 

industry. In fact, nearly 12% of all polyethylene films are produced by cast film extrusion [45]. As 

shown in Figure 2.8, in cast film extrusion, the polymer is melted and extruded through a slit die, 

in  tangentially  contact  and  stretched  by  the  chill  rollers  to  form  the  film,  and  collected  by  the 

winder. The chill rollers are often water-cooled and have a highly polished smooth surface. 

 

 

25 

Side view of cast film extrusion 

 

 

Top view of the extruded cast film 

 

 

 

Figure 2.8: Cast film extrusion process. 

 

As illustrated in Figure 2.8, the direction which the extrudate exits the die is often defined 

as  machine  direction  (MD).  The  direction  perpendicular  to  the  machine  direction  is  referred  as 

cross  machine  direction  (CMD),  or  transverse  direction.  When  equipped with  chill  rollers,  cast 

film extrusion process produces the uni-axial oriented films where the polymer melt is stretched 

in MD resulting in the polymer molecular chain alignment only at that direction. The unbalanced 

films may have better mechanical properties when tested in MD compared to that tested along the 

CMD. However, with the addition of the tenter frame at the die exit to stretch the films in CMD, 

cast film extrusion can also manufacture bi-axially oriented films. 

26 

The  fabrication  of  film  and  sheet  through  cast  film  extrusion  is  practically  identical. 

Typically,  films  are  defined  as  the  thickness  of  end  products  is  below  0.076  mm  (0.003in.), 

whereas, the thickness of the sheets is greater than 0.25 mm (0.01in.) [39]. The thickness of the 

cast films can be easily controlled through the speed of rotational screw, chill rollers and winders. 

Due to the tangential contact between extrudate and chill rollers, the thickness of the cast films 

across the films is more uniform. In addition, compare to other films manufacturing techniques, 

cast films extrusion process produce films with better transparency as the extrudate is cooled down 

by  the  chill  rollers  allowing  less  crystallites  to  form  [46].  One  of  the  advantages  of  cast  film 

extrusion is that it provides ease of processing, thus, it is more suitable to polymers with low melt 

strength. 

PLA with L-lactide contents between 92-98% can be successfully manufactured through 

cast  film  extrusion  [39].  However,  necking  likely  occurs  due  to  the  low  melt  strength  of  PLA, 

which form films with thicker edges and narrower width. Necking can be mitigated by positioning 

the chill rollers as close as the die exit, or by edge pinning including electrostatic or low pressure 

air  [39].  Additionally,  PLA  can  also  be  co-extruded  with  other  polymers  into  multi-layered 

structures to obtain enhanced properties. 

2.3.2.2 Blown film extrusion 

In blown film extrusion, after exiting an annular die, the extruded polymer is drawn upward 

by the take-up rollers with air inside the polymer tube to inflate and form the film [19]. An air ring 

is used at a certain distance from the die exit to cool the formed polymer tube. The tube is further 

flattened by the take-up rollers and collected by the winder. Shown in Figure 2.9, the polymer melt 

is stretched in the machine direction by the take up rollers. As the polymer tube is inflated by the 

27 

air, which results in the films’ orientation in the transverse direction, the bi-axially oriented films 

with better balance of mechanical properties in both directions are formed. 

Figure 2.9: Blown film extrusion process [47]. 

 

One of major disadvantages of blown film extrusion is that it requires polymers to have 

moderate or high melt strength. PLA’s low melt strength hinders the blown film extrusion process. 

Melt sag, referring as the accumulation of the polymer near the die exit, likely occurs due to its 

low  melt  strength.  Other  instabilities,  such  as  bubble  dancing,  draw  resonance,  also  hinder  the 

blown film extrusion process for PLA films. Karkhanis and coworkers had examined the effects 

of  the  temperature  profile,  internal  air  pressure  and  processing  speed  ratio  (PSR),  which  was 

referred as the speed ratio of the take-up rollers to the rotational screw, on the blow-up ratio (BUR) 

of PLA blown films. BUR was defined as the ratio of the annular die’s diameter to the final film’s 

diameter, and it affected the film thickness. The film became thinner as higher BUR was achieved. 

A  stable  PLA  blown  films  was  successfully  manufactured  without  using  any  melt  strength 

28 

enhancers.  The  instabilities  mentioned  previously  were  solved  by  controlling  the  internal  air 

pressure and PSR [19]. 

2.3.2.3 Extrusion blow molding 

Hollow products, including bottles or jugs, can be manufactured through extrusion blow 

molding. In this process, polymer pellets are melted and continuously form a parison by an annular 

die. The parison is then pinched off from the continuous parison and placed in a mold. As shown 

in Figure 2.10, air is used to inflate the parison to fill the cavity of the closing mold. The cooling 

is performed by the direct contact of molten polymer and the mold. The formed part is ejected and 

trimmed  after  cooling.  Extrusion  blow  molding  process  utilizes  the  blowing  air  to  ensure  the 

stretching of the polymer in the radial direction [48]. This process requires thermoplastic with high 

melt strength to support its own weight while forming and maintaining a parison until the mold 

closes around it. Compared to other manufacturing processes for bottles, which will be discussed 

later in this chapter, extrusion blow molding produces more waste as the bottom of the parison, 

where the mold closes, needs to be trimmed off (Figure 2.10). 

Figure 2.10: Schematic representation of extrusion blow molding [49]. 

 

29 

2.3.3 Injection 

Injection molding is a suitable processing technique to manufacture parts requiring precise 

dimensions with low tolerances, such as closures. It can also be used to manufacture parts which 

can be converted into bottles later on through the injection blow molding or injection stretch blow 

molding process. 

Shown in Figure 2.11, the polymer is melted by the heat in the injection unit, which consists 

of a barrel, screw and nozzle. The screw in the barrel melts, compresses and conveys the polymer 

to a mold with desired shape through the nozzle. The mold is controlled by the clamping unit and 

equipped with an ejector pin, which ejects the formed plastic parts from the mold after the molten 

plastic  is  solidified.  Polymers  with  low  viscosity,  which  allows  ease  in  flowing  and  filling  the 

molds, are often used in the injection molding [50]. 

(a) 

(c) 

(b) 

(d) 

 

Figure 2.11: Schematic representation of injection molding [51]. 

 

 

30 

2.3.3.1 Injection blow molding 

Injection blow molding is an alternative to produce hollow shaped containers. This process 

starts with a pre-formed part from the injection molding process. Shown in Figure 2.12, the length 

of the preform is the same as the mold and the final product. The preform is re-heated to soften 

inside a mold cavity. The air is blown into the softened preform in the mold to stretch the preform 

in the radial direction until filling the mold cavity, thus resulting in an uniaxial orientation. The 

formed part is ejected after cooling [50]. Compared to the extrusion blow molding process, this 

process  produces  higher  quality  end  products  with  less  waste  as  no  parts  need  to  be  trimmed. 

Furthermore, this process is more suitable to manufacture polymer with low melt strength. 

Injection blow molding [52] 

 

Air in 

(a) 

(b) 

 

(c) 

 

Injection stretch blow molding [53] 

 

 

(a) 

(b) 

 

Figure 2.12: Schematic representation of injection and injection stretch blow molding. 

31 

2.3.3.2 Injection stretch blow molding 

The difference between injection stretch blow molding and injection blow molding is the 

addition of a stretching step. As illustrated in Figure 2.12, the preform with the length shorter than 

that of the final product, is blown by the air to stretch in the radial direction as well as pulled by a 

plug to stretch vertically, creating a biaxial orientation. Hence, unlike injection blow molding, this 

process produces end products oriented in both machine and transverse directions, which offers 

better balanced mechanical properties in both directions [50]. 

2.3.4 Thermoforming 

Thermoforming is a widely used process to produce rigid containers at low costs. In this 

process, a sheet is heated to re-shape into a three dimensional article into or around a mold. The 

molded  part  is  ejected  and  trimmed  after  sufficient  cooling.  PLA  can  be  thermoformed  into 

disposable  cups  and  trays  for  food  packaging  applications  [41].  Attempts  of  manufacturing 

thermoformed  containers  from  PLA  and  cellulose  nanocrystals  (CNCs)  have  also  been  made. 

Figure 2.13 shows examples of thermoformed PLA and PLA/1%CNC containers. 

(a) 

(b) 

Figure 2.13: Thermoformed containers of (a) PLA and (b) PLA/1%CNC. 

 

32 

2.4 Improving PLA’s property 

As  mentioned,  PLA’s  poor  water  vapor  and  moderate  oxygen  barrier  properties  have 

limited its application in the packaging industry. The barrier properties can often be improved by 

increased crystallinity through adjusting the processing conditions (stretching and cooling rates) 

or  modifying  the  material  formulations  (use  of  organic  and/or  inorganic  additives).  This  study 

selected cellulose nanocrystals, organic additives from wood, to improve the barrier properties of 

PLA. 

2.5 Cellulose nanocrystals (CNCs) 

Cellulose  nanocrystals  (CNCs),  a  derivative  from  lignocellulosic  biomass,  has  attracted 

many academic and industrial interests, due to their low weight, biodegradability, biocompatibility, 

low toxicity, high stiffness and tensile strength as well as high surface area [4,54-56]. It has a wide 

range of applications in a variety of fields including biomedical engineering, wastewater treatment, 

energy and electronics, packaging, etc. [54]. 

2.5.1 Extraction of CNCs 

CNCs, rod-like nanoparticles often referred as nanowhiskers, nanofibers, microcrystals and 

micro-crystallites, can be isolated from cellulose. Cellulose, the most abundant natural polymer, is 

a  fibrous,  tough  and  water-insoluble  polymer  presented  in  living  species,  such  as  algae,  fungi, 

various plants as well as sea animals such as tunicates [57]. The chemical structure of cellulose is 

shown  in  Figure  2.14,  it  is  a  high  molecular  weight  homopolymer  with  the  repeating  unit  of 

cellobiose, a dimer of glucose which consists two glucose residues linked via a β-1,4 glycosidic 

bond  [58,59].  The  degree  of  polymerization  varies  and  can  be  up  to  20,000  depending  on  the 

33 

sources that celluloses are derived. The cellulose molecule chains can form elementary fibrils and 

further pack into larger microfibrils through hydrogen bonds and van der Waals forces [59,60]. 

The highly ordered crystalline regions and disordered amorphous regions can both present in the 

microfibrils [58,59,61]. The characteristic properties, including degree of crystallinity, crystalline 

state and molecular weight, can be highly variable, depending on the derived sources [62,63]. 

Figure 2.14: Chemical structure of cellulose with repeating unit of cellobiose [57]. 

 

The highly crystalline regions from microfibrils can be extracted to form CNCs. The main 

process to isolate CNCs from cellulose fibers is based on acid hydrolysis. Since the disordered or 

paracrystalline regions of cellulose are susceptible to acid attack, whereas crystalline regions have 

a  higher  resistance  to  the  hydrolysis  and  more  likely  to  remain  intact,  cellulose  rod-like 

nanocrystals can be obtained by an acid treatment [57]. Typically, the production of CNCs need 

to  be  carried  out  under  strictly  controlled  conditions  of  temperature,  agitation,  and  time. 

Parameters,  including  the  nature  of  the  acid  and  the  acid-to-cellulosic  fibers  ratios,  are  also 

important to the preparation of CNCs. In general, the acid hydrolysis involves the starting material 

to mix into deionized water with a specific concentration of acid, such as sulfuric, hydrochloric 

and maleic acids [60]. The mixture is diluted with deionized water to quench the reaction after 

desired reaction time. This mixture is then treated with a series of separation process, including 

centrifugation or filtration. Removal of the remaining free acid molecules from the dispersion is 

34 

achieved  through  dialysis  against  distilled  water  [60].  Sulfuric  and  hydrochloric  acids  are 

extensively used to extract CNCs from the cellulose, however, phosphoric and hydrobromic acids 

are also reported to achieve such purpose [58]. It is worth mentioning that different acids used in 

the preparation process may affect the dispersion, thermostability, rheological behavior of CNCs 

[58]. 

Due  to  the  abundance  of  hydroxyl  groups  at  the  surface  of  CNCs,  approaches  such  as 

esterification, etherification, oxidation, silylation, polymer grafting, etc., have been attempted to 

chemically modify CNCs. Those chemical modification methods are used to achieve two goals: 

(1) to obtain a better dispersion by introducing stable electrostatic charges on the CNCs’ surfaces 

and  (2)  to  improve  compatibility  of  CNCs  when  used  in  nonpolar  or  hydrophobic  matrices  by 

tuning the surface energy [58]. 

2.5.2 Properties of CNCs 

The aspect ratio of CNCs, defined as the length to diameter ratio (L/D), often determines 

the  reinforcing  capability  as  it  is  crucial  in  the  formation  of  percolated  networks  to  control  the 

properties  of  CNC-based  materials  [64,65].  CNCs  have  high  aspect  ratio,  indicating  a  better 

reinforcing  ability, and the value highly varies depending on the sources [57].  The  geometrical 

dimensions of CNCs also vary widely with the derived sources. In general, the width of CNCs 

ranges from 10 to 20 nm and length varies to several hundred nanometers [64]. For instance, CNCs 

from wood are 3-5 nm in width and 100-200 nm in length. Those from cotton are reported to have 

width of 5-10 nm and length of 100-300 nm [57,58]. 

The  thermal  properties  of  CNCs  depend  on  the  particle  type  and  the  type  of  surface 

modification.  In  general,  the  onset  of  thermal  chemical  degradation  of  CNCs  can  be  measured 

35 

through  thermogravimetric  analysis  (TGA)  and  is  between  200-300oC  [60].  CNCs  do  not  have 

adsorption  in  the  optical  range  because  of  the  cellulose  structure.  Nevertheless,  the  optical 

properties of CNCs depend on their nanoscale in size, structures, concentration and aspect ratio 

[60]. Many research interests have been paid to the mechanical properties of CNCs. However, the 

quantitative  evaluation  of  the  tensile  modulus  and  strength  of  CNCs  is  challenging  due  to  the 

limitations in measurements of mechanical properties of nanomaterials along multiple axis [57]. 

CNCs have good mechanical properties as the elastic modulus ranges between 60-105 GPa in the 

axial direction and 20-50 GPa in the transverse direction [57,66]. 

2.5.3 Use of CNCs in bio-based polymers 

CNCs have a wide range of applications in the domain of nanomaterials. In general, the 

application of CNCs can be majorly divided into two broad types: utilizing the functionalized or 

non-functionalized  as-synthesized  CNCs,  or  incorporation  with  the  polymer  matrix  as  a 

reinforcing  agent.  As-synthesized  CNC  itself  has  great  potentials  for  applications  including 

nanopapers,  pH  sensors,  stabilizing  of  oil/water  interfaces,  etc.  [57].  Additionally,  CNCs  have 

been incorporated into a variety of polymer matrices to form polymer nanocomposite, a multiphase 

material where a nanomaterial is used to reinforce the polymer phase [57]. Research has reported 

application of CNCs in the synthetic polymers including poly(vinyl alcohol), poly(vinyl acetate), 

epoxides, polyethylene, poly(vinyl chloride), polypropylene, polyurethane, as well as biopolymers, 

such as starch-based polymers, chitosan, poly(lactic acid) [58]. 

The  application  of  CNCs  at  low  concentration  (<30  wt%)  as  a  reinforcing  agent  in  the 

polymer  matrix  has  been  extensively  studied  [60].  CNCs  can  be  used  as  the  load-bearing 

constituent  in  the  polymer  composite  materials  to  improve  the  mechanical  properties  with  low 

36 

volume fractions. The improvement is attributed to two factors: formation of percolated network-

type  architecture within  the polymer matrix and the aspect  ratio [57]. Higher aspect  ratio often 

gives the better reinforcing effect [65]. 

Furthermore,  the  addition  of  CNCs  into  the  polymer  matrix  can  improve  the  barrier 

properties of neat polymer films, as CNCs serve as crystallites in the polymer matrix to increase 

the diffusion time of permeants, resulting in a more tortuous diffusion path, which is referred as 

the  tortuosity  effect  [37,67,68].  It  had  reported  that  both  of  oxygen  and  water  vapor  barrier 

properties of neat PLA blown films improved significantly with the addition of 1% CNC, attributed 

to the increased crystallinity as well as the tortuosity effect [37]. 

It  is  worth  noting  that  the  improved  properties  can  be  achieved  with  good  matrix-filler 

interaction and homogeneous dispersion of nanocrystals within the polymer matrix. However, the 

good dispersibility of CNCs  in  the polymer matrix is  challenging due to its intrinsically strong 

interactions [58]. CNCs have a natural tendency to aggregate due to the hydroxyl groups on their 

surface forming new interparticle H bonds. Agglomeration of CNC is undesirable as it decreases 

the surface area and further reduces the filler-polymer interactions. It also induces voids and holes 

in the composite structure [69]. 

 

 

37 

2.6 Processing technologies of composite films 

Processing  techniques  play  an  important  role  on  the  final  properties  of  the  composite 

materials. The dispersion of CNCs is highly dependent on the processing techniques. Other factors 

related to the intrinsic properties of CNCs, the interfacial characteristics, nature of the polymer 

matrix, such as solubility and degradation, as well as the properties of the end products, should be 

taken into considerations when selecting the processing techniques [58]. Composite films can be 

formed  through  various  processing  methods,  including  casting  evaporation,  melt  processing  as 

well as electrospinning. 

2.6.1 Casting-evaporation process 

Casting-evaporation process, also known as solvent casting, is one of the most common 

methods to produce nanocomposite films. Due to the hydrophilic character of CNCs, the water-

soluble matrix is the simplest way to incorporate CNCs as a filler in the polymer matrix [58,65]. 

As illustrated in Figure 2.15, the polymer solution is prepared first by dissolving polymers in the 

solvent,  such  as  water,  alcohol  or  any  organic  solvent.  The  fillers,  including  natural  fibres  and 

CNCs,  are mixed with  the polymer matrix through mechanical  stirring.  Enhanced formation  or 

improved properties of the final films are achieved through adjusting the temperature or the pH. 

The mixture is then casted into a mold or onto a flat surface. The final composite films are obtained 

after the solvent is removed [70]. This process provides good dispersion of CNCs in the polymer 

matrix. However, it has various drawbacks as the solvent disposal arouses environmental concerns, 

and the residual solvent can serve as a plasticizer to reduce the mechanical and barrier properties 

[67]. In addition, this process is suitable to produce composite materials in the small scale not mass 

production, which poses difficulties in implementation by the industry [69]. 

38 

Figure 2.15: Schematic representation of casting-evaporation process [70]. 

 

2.6.2 Melt processing 

The  melt  processing  method  to  prepare  cellulose-based  composites  is  quite  new  with 

increasing number of publications during the last five to ten years. It has attracted many industrial 

interests as this approach offers less processing time, ease implementation and does not involve 

solvent, which is much greener than cast-evaporation method [67,69]. 

Melt processing requires an extruder. It utilizes the heat to soften the polymer and provides 

sufficient shear to maximize the dispersion of CNCs in the polymer matrix. It was used along with 

the solvent casting method to prepare composites in a two-step process. A master batch is prepared 

using  solvent  casting  technique  and  then  diluted  with  PLA  through  melt-compounding  by  an 

extruder [71]. Another method to disperse aqueous suspensions of CNCs into the polymer matrix 

is melt-compounding through liquid feeding in a vented extruder. Attempts in manufacturing PLA 

and 1% CNC as well as chitin nanocrystal nanocomposites through liquid feeding using a vented 

twin  screw  extruder  have  been  made  [72].  Although  a  good  dispersion  was  achieved  through 

39 

techniques mentioned previously, it has the similar drawbacks including environmental concerns 

with solvent disposal, as the solvent casting techniques. 

Alternatives  approaches  to  manufacture  CNCs  composites  are  proposed.  Karkhanis  and 

coworkers  had  investigated  two  solvent-free  approaches  to  incorporate  CNCs  into  PLA  matrix 

[67].  The  first  proposed  method  was  to  use  a  three-piece  internal  batch  mixer  to  achieve 

homogenous dispersion of CNCs. The second approach used a conventional direct dry-blending, 

which  was  more  time  and  energy  efficient.  Blown  films  were  obtained  followed  by  those  two 

approaches  to  compare  the  water  vapor  barrier  property.  It  was  found  that  both  compounding 

approaches provided good dispersion of CNCs and the water vapor barrier property were improved. 

However, the blown film from melt-blended process was subjected to more thermal degradation 

because  of  the  additional  heating  exposure  in  the  three-mixer  prior  to  the  film  manufacturing 

process. The extent of thermal degradation was further quantified by various analytical methods 

including  gel  permeation  chromatography,  Fourier  transformation  infrared  spectroscopy,  and 

differential scanning calorimetry [67]. 

2.6.3 Electrospinning 

Spinning is a process where the polymer melt or solution is pushed through a small orifice, 

then coagulated in a solution or drying environment. Electrospinning is commonly used to produce 

fibers for tissue engineering. As shown in Figure 2.16, an insulated syringe is employed to hold 

the solution mixture of cellulose/polymer. Under pressure and high voltage (10-30 kV), a jet of 

the solution is accelerated out of the metallic needle toward a collector plate [60]. The solvent is 

removed through the evaporation during the movement of the solution to form the composites [60]. 

40 

The  electrospinning  produces  fibers  with  diameter  ranging  from  less  than  100  nm  to  several 

micrometers [60]. 

Figure 2.16: Schematic representation of electrospinning [73]. 

 

One  of  the  advantages  of  the  electrospinning  is  that  CNCs  are  oriented  along  the  axis 

resulting 

in  an  uni-axially  oriented  composites  with 

improved  mechanical  properties. 

Electrospinning  has  been  used  to  incorporate  CNCs  into  polymers  including  silk  fibroin, 

polyethylene  oxide,  poly(acrylic  acid),  poly(lactic  acid),  poly(methyl  methacrylate),  poly(vinyl 

alcohol) and polycaprolactone [59,60,65]. Xiang and coworkers had investigated the mechanical 

properties of electrospun PLA/CNC fibers, and reported that with the addition of only 1% CNC, 

the tensile strength was improved significantly due to the increased crystallinity and decreased the 

diameter of the electrospun fibers [74]. 

 

41 

 

 

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42 

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147-155. 

 
 

 

48 

Chapter 3 

EXPERIMENTAL 

3.1 Materials 

PLA 4044D resin with less than 4% D-lactide content [1] received from NatureWorks LLC 

(Minnetonka,  MN,  USA)  and  Cellulose  Nanocrystals 

(CNCs) 

(2015-FPL-CNC-071) 

manufactured in  U.S.  Forest  Service  (Madison, WI, USA)  were used in this study.  CNCs  were 

placed into the blender model MX1050XTS (Conair Corporation, Stamford, CT, USA) to break 

the CNCs cake into powders for 1 min at the speed of 22,000 rpm. Both materials were dried in 

the oven at 50°C for at least 24 hours. Prior to film manufacturing, the direct dry blending method 

were adopted to pre-mix the CNCs into PLA matrix [2,3]. CNC contents at 0.5 wt%, 1 wt% and 2 

wt% were compounded with PLA pellets in the mixer at 22,00 rpm for 1 minute. The compounded 

materials and the control sample (neat PLA) were used in the following cast film extrusion process. 

3.2 Sample manufacturing 

A  conical  counter-rotating  twin  screw  extruder  (C.W.  Brabender  Instruments,  South 

Hackensack,  NJ,  USA)  with  a  length-to-diameter  ratio  of  13:1  and  screw  diameter  of  32  mm, 

powered  by  a  5.6  kilowatt  (7.5  hp)  Intelli-Torque  Plasti-Corder  Torque  Rheometer  (C.W. 

Brabender Instruments, South Hackensack, NJ, USA) was used to manufacture the neat PLA and 

its composites cast films. The schematic representation of the cast films extrusion process is shown 

in Figure 3.1. 

 

 

49 

Side view of cast film extrusion 

 

 

Top view of the extruded cast film 

 

 

 

 

Figure 3.1: Schematic representation of the cast film extrusion process. 

The extruder was equipped with a slit die of width and measured die gap of 203.2 mm and 

3.4 mm, respectively. The temperature profile was set as 180 - 180 - 175 - 155 oC starting from 

the  hopper  to  the  die.  Upon  exiting  the  slit  die,  the  extrudate  was  stretched  by  the  rollers 

(Randcastle  Extrusion  system,  Inc.,  Cedar  Grove,  NJ,  USA),  which  were  powered  by  a  speed 

control drive (Model KBMD-240D, KB Electronics, Inc., Coral Springs, FL, USA) with a 0.06 hp 

motor (ABB Motors and Mechanical In., Fort Smith, AR, USA) and collected by the winder. The 

temperature  of  the  rollers  was  set  at  50°C  using  “LE”  series  Sentra  temperature  controller 

(Advantage Engineering, Inc., Greenwood, IN, USA). The speeds of extruder’s rotational screws, 

chill rollers, and winder were 30 rpm, 20 rpm and 20 rpm, respectively, to achieve the targeted 

50 

film thickness of 50 µm. All film compositions were manufactured employing similar processing 

conditions to allow comparison between the neat and composites films. 

3.3 Property evaluation 

3.3.1 Light microscopy 

An optical microscope (Olympus BX41, Olympus, Center Valley, PA, USA) with a camera 

(Olympus Qcolor3) was used to evaluate the distribution and dispersion of CNCs into PLA matrix. 

3.3.2 Thickness measurement 

Once films were made, their sealing, mechanical and barrier properties were evaluated. In 

order to evaluate these properties, thickness must first be measured because barrier and mechanical 

properties are thickness dependent. Two methods were used to measure the thickness of the films, 

including the digital micrometer method and the density method. 

Neat PLA and composite films were cut into strips with dimension of 25.4 mm x 177.8 

mm. The thickness of the film strip was first determined by the digital micrometer, followed by 

the  density  method.  The  thickness  of  six  strips  per  film  formulation  was  assessed.  The  digital 

micrometer method was carried out using a digital micrometer (TMI 49-70 Series Micrometers, 

Testing Machines, Inc., New Castle, DE, USA). To avoid inaccuracy in the thickness of composite 

films  due  to  their  rough  surfaces  caused  by  CNC  agglomerations,  the  thickness  measurements 

through density method were performed following the approach described in the literature [4]: 

 

 

51 

(Equation 3.1) 

 

where 

 and 

 are the densities of the sample and water at room temperature, which was 

0.9956502 g/mL at 30oC, respectively; and Wair and Wwater are the sample’s weight in air and water, 

respectively. 

The densities of PLA and composite films calculated using the equation mentioned above 

were then used to calculate their thickness (l) as follows [4]: 

 

(Equation 3.2) 

where A is the area of the sample film, which was 4.5 x 103 mm2. 

3.3.3 Profilometry 

A  surface  profilometer  (NanoMap  500LS  3D  Stylus  Surface  Profilometer,  AEP 

Technology, Santa Barbara, CA, USA) was used to monitor the surface texture of the neat PLA 

and its composite films. The scan speed was set to 50 µm/s with contact force of 5.41 mg. The 

sample  frequency  and  data  resolution  were  100  pts/s  and  5  µm,  respectively.  NanoMap  50  LS 

software was used to collect and analyze the data. A surface texture profile with Y-axis indicating 

the amplitude of the surface and X-axis as horizontal scan distance was generated for each scan. 

Three locations of neat  PLA and PLA with  1% CNC films in  the machine direction, from  left, 

center and right edges along the width of the films, were scanned with the scan distance of 3 mm. 

52 

waterwaterairairsampleWWWsamplewatersampleairAWlTwo areas from neat PLA and composite films in both machine and cross machine direction were 

randomly selected for scanning distance of 2 mm. 

Two  values,  Ra  and  peak-to-peak,  were  extracted  from  each  surface  texture  profile 

generated  for  each  scan.  The  mean  roughness  or  the  roughness  average  Ra,  is  the  arithmetic 

average of amplitude in the surface texture profile [5]. Peak-to-peak values (P-t-P) refers to the 

distance between the highest peak and the lowest valley in the selected scanning range. 

3.3.4 Hot tack performance 

The  hot  tack  performance  was  assessed  by  Lako  Tool  SL-10  Hot  Tack  Tester  (Testing 

Machine Inc., New Castle, DE, USA) according to the procedures described in ASTM F1921-98. 

PLA and PLA/CNC composite films were cut into strips with 342.9 mm length x 25.4 mm width. 

The pressure and dwell time were maintained as 0.3 N/mm2 and 2 s, respectively. Seal was formed 

at temperature starting from 60oC to 110oC with 5oC increment with the seal area of 25.4 mm x 

25.4 mm. Five replicates from each film composition were tested at each sealing temperature to 

generate a hot tack profile. 

 

 

53 

An  example  of  a  hot  tack  profile  is  illustrated  in  Figure  3.2  where  three  important 

parameters could be extracted including (i) hot tack initiation temperature (HTIT), (ii) maximum 

hot tack strength (MHTS) and (iii) temperature where maximum hot tack strength occurs (TMHTS) 

[6-8]. 

Figure 3.2: Hot tack profile showing three important parameters: (i) hot tack initiation 

temperature (HTIT), (ii) maximum hot tack strength (MHTS) and (iii) temperature where 

maximum hot tack strength occurred (TMHTS). 

 

Hot tack initiation temperature (HTIT) is the onset temperature where the hot tack strength 

increases  rapidly  [6-8].  The  maximum  hot  tack  strength  (MHTS)  is  the  highest  force  obtained 

throughout  the  tested  temperature  range  whereas  the  temperature  where  maximum  hot  tack 

strength occurred (TMHTS) is its corresponding temperature. As shown in Figure 3.2, a tangent line 

54 

was drawn from the linear portion of the hot tack profile where the temperature increased rapidly 

and the X-intercept of this tangent line was the estimated HTIT. 

3.3.5 Seal strength 

The fin seal was made prior to the seal strength test at 130oC, 0.303 N/mm2 for 0.5s dwell 

time with the seal area of 25.4mm x 25.4mm using Lako Tool SL-10 Hot Tack Tester (Testing 

Machine Inc., New Castle, DE, USA). The sealed samples were placed at the room condition for 

at  least  24  hours  for  cooling.  Seal  strength  tests  of  PLA  and  PLA/CNC  composite  films  were 

carried out in accordance of the procedures in ASTM F88/F88M using Instron 3345 tensile test 

machine (Instron, Norwood, MA, USA). The rate of grip separation was set as 254 mm/min and 

the distance between grips was 25.4 mm. The seal strength was measured using technique A, where 

the  seal  area  remained  unsupported  during  the  tests.  Forty  samples  were  tested  and  the  data 

analyzed through Instron Bluehill 3, version 3.61 software. The load at break and mode of failure 

were recorded. 

3.3.6 Burst pressure 

The  burst  pressure  of  pouches  made  with  neat  PLA  and  composite  films  was  measured 

following the procedures described in ASTM F2054/F2054M. Prior to the burst test, the pouch 

with  inside  dimensions  of  100  mm  x  100  mm  was  formed  by  assembling  two  pieces  of  films, 

where three sides (two sides and one bottom) were sealed and the forth side remained open. The 

seals were made with intermittent sealing time of 3 s and cooling time of 3 s, using a table-style 

pedal  impulse  sealer  (Model  MFSA-450,  Technopack  Corporation,  Sunrise,  FL,  USA)  with 

voltage of 110 v (60Hz) and motor power of 1540 W. Two types of pouch configurations were 

formed for each formulation depending on the numbers of seals made in machine direction (MD) 

55 

and cross machine direction (CMD). As illustrated in Figure 3.3, the first type (type 1) sealed the 

two sides in MD and the bottom seal was made along CMD, whereas the second type (type 2) had 

two sides seals form along CMD and the bottom seal in MD. 

Type 1 (MD) 

Type 2 (CMD) 

 

 

 

 

 

 

Figure 3.3: Two types of pouch configurations for the burst test. 

After the pouches were made and cooled at the room temperature, the burst pressure was 

measured  using  a  burst  tester  (Test-A-Pack  Systems  2000,  Cobham  plc,  Dorset,  UK)  and  the 

pressure causing the failure of the pouch was documented. Eight pouches per type were tested for 

each formulation. 

3.3.7 Tensile properties 

The tensile test was performed using Instron 3345 tensile test machine (Instron, Norwood, 

MA, USA) in accordance of the procedures outlined in ASTM D882. The results were analyzed 

by the Instron Bluehill 3, version 3.61 software. The distance between grips was 101.6 mm (4 in). 

56 

The test was carried out at room condition with the rate of grips separation of 50 mm/min in both 

the machine and cross machine directions of PLA and its composite films. The films were cut into 

152.4  mm  long  and  25.4  mm  wide  strips.  Tensile  strength  at  yield,  tensile  strength  at  break, 

modulus,  energy  at  break,  and  percentage  of  elongation  at  break  were  obtained.  At  least  seven 

replicates of each composition were tested. 

3.3.8 Falling dart impact strength 

Impact strength of the films was determined using Labthink FDI-01 Falling Dart Impact 

Tester (Labthink International, Inc., Medford, MA, USA) in agreement with method A described 

in ASTM D1709 with slight modifications. Two layers of the film specimen were secured using 

clamps with inside diameter of 76.2 mm. A customized 10 g dart with diameter of 38.2 mm was 

dropped from a height of 0.33 m (13 in) and the film was assessed as failed or non-failed. “Failure” 

was defined as film rupture so that the dart penetrates through the film and “non-failure” indicated 

the situation where the film sustained its integrity to hold the dart. Testing followed a stair-step 

approach with the increment of dart weight of 5 g, meaning that the weight of the dart increased 

by 5 g if “non-fail” occurred or decreased by 5 g in case of film failure. At least ten fails and ten 

non-fails were required to complete a test. Each test generated failure weight as a measurement of 

impact strength and at least three tests were performed for each film composition. 

3.3.9 Water Vapor Permeability (WVP) 

Water vapor transmission rates of neat PLA and composite films were measured by the 

desiccant method described in ASTM E96 at 38oC and 85% RH. Each film specimen was mounted 

to a vapometer cup (Thwing-Albert Instrument Co., West Berlin, NJ, USA) with 3/4” (19.05 mm) 

depth. At least nine replicates were tested in the humidity chamber (Model  LH 1.5, Associated 

57 

Environmental  Systems,  Ayer,  MA,  USA)  for  24  hours.  The  cups  were  weighed  before  being 

placed in the chamber. The final weights were measured after 24 hours to obtain the weight gain 

to calculate WVTR using the following equation: 

 

(Equation 3.3) 

where W is the weight gain at time t (24 hours), and A is the effective area of exposed film as 

31.67 x 10-4 m2 [2,3]. 

The water vapor permeability can be calculated from WVTR as follows: 

 

(Equation 3.4) 

where 

 is  the  difference  in  the  partial  pressure  at  the  testing  condition,  which  is  85%  of  the 

saturated  water  vapor  pressure  (Ps)  at  38oC,  and  l  is  the  thickness  of  the  film  measured  by  the 

density method. Since Ps at 38oC was found to be 6,626.12 Pa, the 

 was 5,632.20 Pa. 

3.3.10 Oxygen Permeability (OP) 

Oxygen transmission rate (OTR) was determined through Mocon Ox-Tran 2/22 Model L 

(Mocon Inc., Minneapolis, MN, USA) according to the procedures described in ASTM D3985 as 

previously reported [2,3]. At least four replicates were tested at 23oC and 0% relative humidity 

(RH). The effect of RH on OTRs of neat PLA and PLA with 2% CNC films were tested at constant 

58 

AW/tWVTRplWVTRWVPpptemperature of 23oC but at various RH values of 25%, 50% and 75%. At least four replicates were 

tested at each condition. 

Oxygen  permeability  (OP)  can  be  calculated  by  normalizing  the  thickness  (l)  and 

difference in partial pressure (

) of permeants across the tested films: 

 

(Equation 3.5) 

where 

 was 1 atm, which was 101,325 Pa, and l is the thickness of the film measured by the 

density method. 

3.3.11 Statistics 

All test results were analyzed based on T Test at  5% significance level using Microsoft 

Excel 2016. 

 

 

59 

pΔplOTROPp 

 

REFERENCES 

60 

REFERENCES 

1.  Gendron, R. and Mihai, M. (2016). Chapter 5 Extrusion foaming of polylactide. In S.-T. Lee 
(Ed),  Polymeric  foams:  innovations  in  processes,  technologies,  and  products  (pp.107-157). 
Boca Raton, Florida, USA: Taylor & Francis Group, LLC. 

2.  Matuana, L.M., Karkhanis, S.S., Stark, N.M., and Sabo, R.C. (2016). Cellulose nanocrystals 
as barrier performance enhancer of extrusion-blown PLA film for food applications. Biotech, 
Biomaterials and Biomedical-TechConnect Briefs, 3, 1-4. 

3.  Karkhanis,  S.S.,  Stark,  N.M.,  Sabo,  R.C.,  and  Matuana,  L.M.  (2017).  Performance  of 
poly(lactic  acid)/  cellulose  nanocrystal  composite  blown  films  processed  by  two  different 
compounding approaches. Polymer Engineering and Science. DOI: 10.1002/pen.24806. 

4.  Kunanusont, N., Pongsa, U., Bunsiri, A., and Somwangthanaroj, A. (2014). Effect of relative 
humidity on oxygen permeability of modified poly(lactic acid) blown films. Pure and Applied 
Chemistry International Conference 2014, 630-633. 

5.  Maldas,  D.C.  and  Kamdem,  D.P.  (1998).  Surface  characterization  of  chromated  copper 
arsenate (CCA)-treated red maple. Journal of Adhesion Science and Technology, 12(7), 763-
772. 

6.  Falla, D. and Li, M. (2014). Reliable hot tack testing of polyolefin films. SPE ANTEC 2014, 

1460-1475. 

7.  Morris,  B.A.  (Ed.).  (2017).  Chapter  7  Heat  seal.  The  science  and  technology  of  flexible 
packaging: multilayer films from resin and process to end use (pp. 181-257). Oxford, United 
Kingdom: Elsevier Inc. 

8.  Tabasi, R.Y., Najarzadeh, Z., and Ajji, A. (2014). Development of high performance sealable 
films  based  on  biodegradable/compostable  blends.  Industrial  Crops  and Products,  72,  206-
213. 

 

 

61 

Chapter 4 

RESULTS AND DISCUSSION 

4.1 Effect of CNC content on the surface texture of PLA cast films 

Once  films  were  made,  their  physico-mechanical  properties  were  evaluated,  including 

barrier, tensile, impact strength, hot tack performance, seal strength and burst pressure. In order to 

evaluate  these  properties,  thickness  measurement  must  first  be  completed  because  barrier  and 

mechanical  properties  are  thickness  dependent.  However,  previous  studies  showed  that 

homogeneous distribution of CNCs in the PLA matrix was successfully achieved but the dispersion 

of CNCs into blown PLA matrix film was not good since some agglomerates were present in the 

film.  The  distribution  was  measured  as  the  uniformity  of  CNCs  in  the  PLA  matrix,  whereas 

dispersion was defined as the degree of large CNC agglomerates breaking into small particles [1,2]. 

The  neat  PLA  and  PLA/CNC  composite  films  were  examined  using  the  light  microscopy  for 

distribution and dispersion of CNCs in PLA matrix (Figure 4.1). Shown in Figure 4.1, CNCs were 

present  throughout  the  PLA  matrix  for  all  three  PLA/CNC  composite  films  indicating  a  good 

distribution  of  CNCs.  However,  agglomerations  of  CNC  were  observed  indicating  a  poor 

dispersion. 

 

 

62 

a 

c 

b 

d 

 

 

 

 

200 µm 

 

200 µm 

 

 

 
 

 

200 µm 

 

200 µm 

 

Figure 4.1: Light microscope images of (a) PLA, (b) PLA/0.5%CNC, (c) PLA/1%CNC and (d) 

PLA/2%CNC films. 

Those  agglomerates  introduced  the  surface  roughness  of  PLA/CNC  composite  films 

preventing accurate thickness measurement. The profilometer was used to characterize the surface 

roughness.  Shown  in  Figure  4.2  and  Figure  4.3,  the  amplitude  of  surface  texture  (Z-axis)  was 

recorded as a function of scan distance (X-axis). Figure 4.2 shows the surface texture profiles of 

neat PLA and PLA/1%CNC films with the scan distance of 3 mm at three different locations across 

the  film’s  width  in  the  machine  direction.  Large  peaks  were  observed  in  all  three  locations  of 

PLA/1%CNC films whereas neat PLA films had a relatively smooth surface within the same scan 

distance. Irrespective of the sample locations, PLA with 1% CNC films were rougher than neat 

63 

PLA  films.  To  further  verify  the  presence  of  the  surface  roughness  in  all  composite  films,  the 

surface  texture  profiles  of  all  neat  PLA  and  PLA/CNC  composite  films  were  obtained  in  both 

machine and cross machine directions (Figure 4.3). As seen in Figure 4.3, large peaks and valleys 

were present in all PLA/CNC composite films in both machine and cross machine directions at the 

scan distance of 2 mm. The surface texture profiles indicated that regardless of the film location 

and direction, the surface of all composite films  were  rougher than that of PLA  films, as more 

peaks and valleys were observed on the surface of the composite films, attributed to the formation 

of CNC agglomerates observed in light microscope images (Figure 4.1). 

 

 

64 

 

 

a1 

a2 

a3 

Ra: 0.3581 µm 

P-t-P: 2.3719 µm 

 
 

Ra: 0.3249 µm 

P-t-P: 1.9785 µm 

 
 

Ra: 0.3441 µm 

P-t-P: 2.2905 µm 

b1 

b2 

b3 

 

 

 

Ra: 1.1177 µm 

P-t-P: 14.9756 µm 

 
 

Ra: 1.8598 µm 

P-t-P: 13.0534 µm 

 
 

Ra: 1.3102 µm 

P-t-P: 11.8594 µm 

 

 

 

 

 

Figure 4.2: Surface texture profiles of (a) neat PLA and (b) PLA/1%CNC films collected at 3 

different locations across the film’s width: left (a1 and b1); center (a2 and b2); and right (a3 and 

b3) along the machine direction. 

 

65 

-6061218-1500-75007501500Z (micrometer)X (micrometer)-6061218-1500-75007501500Z (micrometer)X (micrometer)-6061218-1500-75007501500Z (micrometer)X (micrometer)-6061218-1500-75007501500Z (micrometer)X (micrometer)-6061218-1500-75007501500Z (micrometer)X (micrometer)-6061218-1500-75007501500Z (micrometer)X (micrometer)MD 

 

Ra: 0.2868 µm 

P-t-P: 1.6950 µm 

 

 

Ra: 1.1302 µm 

P-t-P: 7.5198 µm 

 

 

Ra: 1.0111 µm 

P-t-P: 8.8358 µm 

 

 

Ra: 1.2174 µm 

P-t-P: 12.1893 µm 

0% 
CNC 

0.5% 
CNC 

1% 
CNC 

2% 
CNC 

 

 

 

 

CMD 

 

Ra: 0.2088 µm 

P-t-P: 1.8543 µm 

 

 

Ra: 0.9051 µm 

P-t-P: 9.7599 µm 

 

 

Ra: 0.9781 µm 

P-t-P: 6.7811 µm 

 

 

Ra: 1.4491µm 

P-t-P: 6.8791 µm 

 

 

 

 

 

 

Figure 4.3: Surface texture profiles of neat PLA (first row) and PLA with 0.5% CNC (second 

row), 1% CNC (third row), and 2% CNC (fourth row). Samples in the left column were tested in 

the machine direction whereas those in the right column in the cross machine direction. 

66 

Surface roughness was further quantified into two parameters: i) roughness (Ra) value, the 

arithmetic  mean  of  the  amplitude  [3]  and  ii)  peak-to-peak  value  (P-t-P),  which  indicates  the 

distance between the highest and lowest points on the scanned surface. The addition of CNC into 

the  PLA  matrix  increased  both  the  peak-to-peak  and  Ra  values  indicating  a  rougher  surface 

compared to the surface of neat PLA films (Figure 4.4). Results from profilometry showed that 

irrespective of the film direction and location, incorporation of CNCs into PLA matrix introduced 

surface roughness, attributed to the agglomeration of CNC in the PLA matrix. The fact that this 

roughness existed in different locations throughout PLA/CNC films supported the finding that a 

good distribution of CNCs in PLA matrix was achieved. 

Ra

P-t-P

)
r
e
t
e
m
n
o
r
c
m

i

(
Z

15

12

9

6

3

0

0

0.5

1

2

CNC content (%)

 

Figure 4.4: Effect of CNC content on roughness (Ra) and peak-to-peak values of PLA cast films. 

 

 

67 

Since the surfaces of PLA/CNC composite films were found to be rougher than that of neat 

PLA film, it was more accurate to consider the thickness of PLA/CNC films to be the same as that 

of neat and smooth PLA films, as films from all formulations were manufactured using identical 

processing conditions.  The results from two thickness  measurement methods further confirmed 

this hypothesis. Shown in Table 4.1, the density method resulted in similar thicknesses for PLA 

and composite films (~0.042 mm) as expected since all films were manufactured using identical 

processing conditions. It was worth mentioning that the thickness of neat PLA films measured by 

the density method was slightly lower than that measured by digital micrometer, attributed to the 

small peaks observed in the surface texture profiles of neat PLA films in Figure 4.2. Since density 

method provided more accurate measurements, the thickness obtained from this method was used 

to calculate the water vapor and oxygen permeability using equations 3.4 and 3.5, respectively. 

Table 4.1: Thicknesses of neat PLA and composite films measured using digital micrometer and 

density methods. 

Thickness* (mm) 

Materials 

Digital micrometer method 

Density method 

PLA 

0.052 ± 0.006A 

0.042 ± 0.004A 

PLA + 0.5%CNC 

0.078 ± 0.010B 

0.042 ± 0.005A 

PLA + 1%CNC 

0.079 ± 0.008B 

0.043 ± 0.004A 

PLA + 2%CNC 

0.091 ± 0.018C 

0.043 ± 0.002A 

*Different  superscript  letters  within  the  same  column  are  significantly  different 
based on the T Test results at 5% significance level. 

 

 

68 

4.2 Effect of CNC content on the barrier properties of PLA cast films 

Table 4.2 summarizes the effect of CNC content on water vapor permeability (WVP) and 

oxygen permeability (OP) of PLA films. The addition of CNCs into PLA matrix reduced the WVP 

and OP significantly. A decrease of approximately 45% in WVP and 49% in OP was observed by 

adding 2% CNC. 

Table 4.2: The effect of CNC content on water vapor permeability (WVP) and oxygen 

permeability (OP) of PLA films. 

WVP at 38oC 85% RH* 

OP at 23oC 0% RH* 

Materials 

(10-16 kg-m/m2-s-Pa) 

(10-20 kg-m/m2-s-Pa) 

Average 

% Decrease 

Average 

% Decrease 

PLA 

159.4 ± 9.7A 

PLA+0.5%CNC 

117.0 ± 4.2 B 

PLA+1%CNC 

110.4 ± 6.6C 

PLA+2%CNC 

87.0 ± 8.0D 

- 

26.6 

30.8 

45.4 

353.6 ± 54.4A 

267.4 ± 48.4B 

212.1 ± 25.9B,C 

178.8 ± 26.4C 

- 

24.4 

40.0 

49.4 

*Different  superscript  letters  within  the  same  column  are  significantly  different 
based on the T Test results at 5% significance level. 

This improvement could be attributed to the increased crystallinity. Crystallites distributed 

in  PLA  matrix  form  impermeable  regions.  Those  impermeable  regions  create  a  more  tortuous 

diffusion path for permeants, leading to a slower diffusion process [1,4-8]. Additionally, several 

studies  have  shown  that  CNCs  also  act  as  a  nucleating  agent  to  induce  crystallization  which 

resulted in higher degree of crystallinity [1,9-11]. Karkhanis and coworkers had reported that the 

addition of 1% CNC in PLA blown films increased the degree of crystallinity based on the results 

obtained from differential scanning calorimetry [1]. 

69 

The oxygen permeability (OP) of PLA and PLA with 2% CNC films remained constant as 

the RH increased from 0% RH to 75% RH at 23oC (Figure 4.5). Similar results were reported by 

Kunanusont and coworkers [12]. They found that both oxygen permeability and transmission rates 

of PLA blown films were not affected by the elevating relative humidity. This was due to polarity 

of films. The contact angle results demonstrated that the surface of PLA films was hydrophilic as 

the contact angle was less than 90o, thus, more unlikely to be affected by RH [12]. 

)
a
P

-
s
-
2

/

m
m
-
g
k
0
2
-
0
1
(
 

P
O

PLA

PLA + 2%CNC

480

360

240

120

0

0

25

50

75

RH (%)

 

Figure 4.5: Effect of testing relative humidity (RH) on the OP of PLA and PLA/2%CNC 

composite films. 

 

 

70 

4.3 Influence of CNC content on the sealing properties of PLA cast films 

The  effect  of  CNC  content  on  the  sealing  properties  was  evaluated  based  on  the  data 

obtained from seal, hot tack and burst tests. Figure 4.6 illustrates the experimental hot tack profiles 

of neat PLA and PLA/CNC composite films where the hot tack strength (force) was graphed as a 

function of temperature. 

PLA

PLA+0.5%CNC

PLA+1%CNC

PLA+2%CNC

2000

1500

1000

500

)
g
(
 
e
c
r
o
F

0

60

70

80

90

100

110

Temperature (°C)

 

Figure 4.6: Experimental hot tack profiles of neat PLA and PLA/CNC composite films. 

For all formulations, the hot tack strength increased rapidly starting from 75oC and reached 

the peak at 85oC. The hot tack parameters estimated from the profiles are listed in Table 4.3. The 

addition of CNCs into PLA matrix did not affect the HTIT nor temperature where MHTS occurred, 

which indicated that same sealing conditions could be applied to seal both neat PLA and PLA/CNC 

71 

composite films. However, the average of maximum hot tack strength (MHTS) increased as the 

CNC content increased up to 1%. 

Table 4.3: The effect of CNC content on the hot tack initiation temperature (HTIT), maximum 

hot tack strength (MHTS) and temperature where MHTS occurred of PLA films. 

Materials 

Hot tack initiation 
temperature* (oC) 

Temperature where 
MHTS occurred* (oC) 

Maximum hot tack 

strength* (g) 

PLA 

74.6 ± 0.8A 

88.0 ± 4.5A 

1,076.8 ± 244.7A 

PLA+0.5%CNC 

73.6 ± 0.8A 

86.0 ± 2.2A 

1,302.0 ± 202.3A 

PLA+1%CNC 

74.5 ± 0.7A 

85.0 ± 0.0A 

1,641.6 ± 215.9B 

PLA+2%CNC 

73.7 ± 0.5A 

90.0 ± 11.2A 

1,197.2 ± 121.6A 

*Different  superscript  letters  within  the  same  column  are  significantly  different 
based on the T Test results at 5% significance level. 

Incorporating  1%  CNC  into  PLA  matrix  significantly  improved  the  hot  tack  strength, 

which indicated the formation of a stronger seal, probably attributed to the increased stress transfer 

efficiency at the interface [13]. However, MHTS began to decrease when the CNC content reached 

2%,  attributed  to  poor  adhesion  between  interface  due  to  rougher  surfaces  created  by  the 

agglomerations of CNC. As the volume fraction of CNCs increased, the surface became rougher. 

The  surface  roughness  between  sealing  interfaces  created  surface  irregularities  preventing  the 

intimate direct contact at seal area, further hindering the heat diffusion at the interface and forming 

a weaker seal [14]. 

Nevertheless, it is worth mentioning that the average of MHTS for all PLA/CNC composite 

films was higher than that of neat PLA films. Additionally, once the TMHTS was reached (Figure 

4.6), the hot tack strength of PLA and composite films with 0.5 and 1% CNC decreased as the 

72 

sealing temperature increased. In contrast, the hot tack strength of composite films with 2% CNC 

appeared to be not affected by the increasing sealing temperature. As a result, the hot tack force of 

PLA/2%CNC at 110oC was higher than that of neat PLA and other composite films, implying a 

broader processing window with the addition of 2% CNC into PLA matrix [14]. 

The seal strength of neat PLA and PLA/CNC composite films are summarized in Table 4.4. 

The  adhesive  failure  is  defined  as  the  separation  of  the  seal  at  the  interface,  whereas  cohesive 

failure occurs when the material breaks before the seal [15]. The addition of CNCs into PLA matrix 

increased  the  seal  strength  significantly,  irrespective  of  CNC  content  (Table  4.4).  As  the  CNC 

content increased up to 1%, the cohesive failure was more likely to occur indicating stronger seals 

formed. This was attributed to the efficient stress transfer in the matrix [13]. However, with the 

addition of 2% CNC, the mode of failure was less likely to be cohesive. This could be explained 

as the rough surface preventing the heat diffusion further forming weaker seals. 

Table 4.4: The effect of CNC content on the seal strength of PLA films. 

Materials 

Seal strength* (N) 

% Failure mode 

PLA 

PLA+0.5%CNC 

PLA+1%CNC 

PLA+2%CNC 

8.2 ± 5.6A 

14.4 ± 9.9B 

11.8 ± 8.7B 

11.9 ± 5.1B 

85% Adhesive 

100% Cohesive 

100% Cohesive 

85% Cohesive 

*Different  superscript  letters  within  the  same  column  are  significantly  different 
based on the T Test results at 5% significance level. 

 

 

73 

The  burst  pressures  of  neat  PLA  and  composite  films  are  shown  in  Figure  4.7.  Type  1 

referred to pouches made with two sides sealed along the machine direction (MD) and bottom seal 

in cross machine direction (CMD). Type 2 defined as pouches with two sides in CMD and bottom 

seal  in  MD.  As  shown  in  Figure  4.7,  regardless  of  the  types  of  pouches,  the  addition  of  CNC 

content increased the burst pressure, when compared with that of pouches made with neat PLA 

films, owing to the effective stress transfer between CNCs and PLA matrix [13]. However, as the 

CNC  content  increased  to  2%,  the  burst  pressure  decreased  due  to  the  disruption  of  interfacial 

adhesion.  Incorporating  more  CNCs  may  induce  microvoids  and  preventing  the  efficient  stress 

transfer [14]. 

Type 1 (MD)

Type 2 (CMD)

)

O
2
H

 
.

n
i
(
 
e
r
u
s
s
e
r
P

300

250

200

150

100

50

0

0

0.5

1

2

CNC content (%)

 

Figure 4.7: The effects of CNC content and pouch configuration on the burst pressure of neat 

 

 

PLA films. 

74 

Two modes of failures, adhesive and cohesive, occurred during the burst test. As defined 

previously, the cohesive failure refers to the breakage of the material before the seal, and adhesive 

failure is defined as the separation of the seal interfaces [15]. The effect of CNCs on the percentage 

of  failure  mode  of  neat  PLA  films  is  summarized  in  Table  4.5.  Irrespective  of  the  pouch 

configurations, majority of failures was cohesive failure, indicating the formation of stronger seals. 

Table 4.5 The effect of CNC content on the percentage of failure mode of neat PLA films in 

burst test. 

 

PLA 

PLA + 0.5%CNC  PLA + 1%CNC  PLA + 2%CNC 

Type 1 (MD) 

80% Cohesive 

100% Cohesive 

90% Cohesive 

90% Cohesive 

Type 2 (CMD)  100% Cohesive 

100% Cohesive 

100% Cohesive 

100% Cohesive 

 

4.4 Effect of CNC content on the tensile and impact properties of PLA cast films 

Figure 4.8 illustrates the stress-strain of neat PLA and its composite films when the test 

was  performed  along  films’  machine  direction  (MD)  and  cross  machine  direction  (CMD).  The 

tensile  property  data  of  each  replicate  was  extracted  from  those  stress-strain  curves  and 

summarized in Table 4.6 with averages and standard deviations of tensile strength at yield, tensile 

strength at break, modulus, energy at break and elongation at break. 

The results indicated that increasing CNC content into PLA matrix increased the brittleness 

of PLA film (Figure 4.8). Shown in Figure 4.8a1, when tested in the machine direction, neat PLA 

films  demonstrated  a  well-defined  yield  point  and  elongation  at  break  reached  91.5%  with  the 

tensile  strength  at  break  of  41  MPa  (Table  4.6).  On  the  other  hand,  all  of  the  composite  films 

75 

showed no yielding behaviors and failed at a much lower range of strain (below 4%) with a higher 

tensile  strength  at  break,  when  compared  with  that  of  neat  PLA  films.  The  brittleness  of  the 

composite films was attributed to the high degree of brittleness inhered in the cellulose [17]. 

MD 

CMD 

130

a1 

104

)
a
P
M

(
 
s
s
e
r
t
S

78

52

26

0

 

 

130

b1 

104

)
a
P
M

(
 
s
s
e
r
t
S

78

52

26

0

20

40
60
Strain (%)

 

PLA + 0.5% CNC

PLA + 1% CNC

PLA + 2% CNC

PLA

1

2

Strain (%)

 

3

4

PLA + 0.5% CNC

PLA + 1% CNC

PLA + 2% CNC

1

2

3

4

Strain (%)

 

 

 

PLA

 

a2 

)
a
P
M

(
 
s
s
e
r
t
S

75

60

45

30

15

80

100

0

0

 

 

b2 

)
a
P
M

(
 
s
s
e
r
t
S

75

60

45

30

15

0

0

0

0

1

2

3

Strain (%)

 

4

 

Figure 4.8: Stress-strain curves of neat PLA films in machine (a1) and cross machine (a2) 

directions as well as of PLA/CNC composite films in machine (b1) and cross machine (b2) 

directions. 

76 

Table 4.6: The effect of CNC content on the tensile properties of PLA films in both machine and cross machine directions. 

Materials 

Tensile strength 
at yield (MPa) 

Tensile strength 
at break* (MPa) 

Modulus* 

Energy at break* 

(GPa) 

(10-3 J) 

Elongation at 

break* (%) 

PLA 

59.9 ± 6.3 

41.0 ± 22.7A 

2.8 ± 0.3A 

4439.7 ± 1356.3A 

91.5 ± 25.4A 

Machine Direction 

PLA + 0.5%CNC 

PLA + 1%CNC 

PLA + 2%CNC 

PLA 

PLA + 0.5%CNC 

PLA + 1%CNC 

PLA + 2%CNC 

- 

- 

- 

- 

- 

- 

- 

115.6 ± 12.7B 

5.7 ± 0.2B 

209.6 ± 37.2B 

3.1 ± 0.4B 

82.7 ± 25.1C 

5.2 ± 0.7C 

199.4 ± 131.6B,C 

3.4 ± 1.8B 

61.8 ± 28.2A 

4.4 ± 0.7D 

151.8 ± 70.0C 

3.2 ± 1.3B 

Cross Machine Direction 

23.4 ± 9.6A 

2.8 ± 0.1A 

16.4 ± 5.8A 

1.1 ± 0.2A 

61.6 ± 12.8B 

5.6 ± 0.1B 

52.7 ± 11.8B 

1.5 ± 0.2B 

42.6 ± 19.0C 

5.9 ± 1.0B 

23.2 ± 11.6A 

1.0 ± 0.2C 

23.3 ± 6.6A 

3.7 ± 0.1C 

11.8 ± 3.2C 

0.9 ± 0.1C 

*Different  superscript  letters  within  the  same  column  are  significantly  different  based  on  the  T  Test  results  at  5% 
significance level when tested in the same direction. 

77 

Additionally, the high elongation at break of neat PLA films was not uncommon, as other 

investigators  reported  similar  values.  Petersson  and  coworkers  reported  the  elongation  at  break 

greater than 100% for PLA films prepared by solution casting [18]. Garlotta also concluded that 

the  elongation  at  break  for  high-molecular  weight  oriented  PLA  ranged  from  15-160%  [19]. 

However,  it  is  worth  mentioning  that  neat  PLA  films  failed  at  strain  of  1.2%  with  the  tensile 

strength at break of 23.4 MPa in the cross machine direction, which were much lower than that of 

machine direction, attributed to the uniaxial oriented morphology induced by the stretching in the 

film manufacturing process [20]. The drawing in the melt state of the polymer may induce a “shish-

kebab” structure of PLA chains  along the drawing direction, which was the machine direction, 

further resulting a higher elongation at break and tensile strength in that direction compared to that 

of the cross machine direction [21-23]. 

Figure 4.9 illustrates the effect of CNC content on the energy and elongation at break of 

PLA  cast  films.  In  machine  direction,  the  general  decrease  of  both  energy  (Figure  4.9a1)  and 

elongation  (Figure  4.9b1)  at  break  with  the  addition  of  CNCs  confirmed  the  brittleness  of  the 

composite films, irrespective of CNC content. These properties decreased by adding only 0.5% 

CNC into PLA and a further increase in CNC content did not change the energy and elongation at 

break. Interestingly, different trend was observed in the cross machine direction where the addition 

of up to 0.5% CNC into PLA matrix increased both energy (4.9a2) and elongation (4.9b2) at break 

of  the  samples.  However,  both  the  energy  and  elongation  at  break  decreased  when  the  CNC 

concentration increased above 0.5%. 

 

 

78 

MD 

MD 

a1 

b1 

 

CMD 

a2 

 

CMD 

b2 

 

 

 

 

 

 

Figure 4.9: The effect of CNC content on the energy at break in machine (a1) and cross machine 

(a2) directions as well as on the elongation at break in machine (b1) and cross machine (b2) 

directions, of PLA cast films. 

 

 

79 

In contrast, the tensile strength at break and modulus for all of the composite films were 

higher than that of neat PLA films, indicating the composite films were stronger and stiffer than 

neat PLA films. Shown in Figure 4.10a and 4.10b, in the machine direction, both of the tensile 

strength and modulus increased with the addition of 0.5% CNC with a slight drop when the CNC 

concentration reached 2%. Similar trend was observed in cross machine direction. Irrespective of 

CNC concentration and testing direction, incorporating CNCs into PLA matrix improved tensile 

strength as well as the modulus, attributed to the effective stress transfer and the rule of mixtures, 

respectively [17,24,25]. The slight drop of tensile strength and modulus could be explained as the 

reduced interfacial adhesion between PLA matrix and CNCs. As CNC content increased from 0.5% 

to 2%, the intimate interfacial adhesion may be disrupted. The poor dispersion of CNCs facilitated 

the formation of numerous irregularly shaped microvoids, and further impacted the efficient stress 

transfer between matrix and CNCs [25]. 

 

 

80 

a 

140

)
a
P
M

(
 
h
t
g
n
e
r
t
s
e

 

l
i

s
n
e
T

120

100

80

60

40

20

0

b 

8

)
a
P
G

(
 

l

s
u
u
d
o
M

6

4

2

0

 

 

 

MD CMD

0

0.5

1

2

CNC content (%)

 

MD

CMD

0

0.5

1

2

CNC content (%)

 

 

Figure 4.10: Effect of CNC content on the (a) tensile strength at break and (b) modulus of PLA 

films along machine direction (MD) and cross machine direction (CMD). 

 

 

81 

The  results  from  tensile  test  illustrated  that  irrespective  of  CNC  concentration, 

incorporating CNCs into PLA matrix improved the modulus and tensile strength of neat PLA cast 

films, at the expense of ductility. The brittleness of the composite films was further supported by 

the  results  from  dart  impact  test.  The  impact  strength  of  neat  PLA  and  composite  films  is 

summarized in Table 4.7. The failure mass of all composite films was significantly lower than that 

of neat PLA films, indicative of brittleness in the PLA/CNC composite films. 

Table 4.7: The effect of CNC content on the impact strength of PLA cast films. 

Materials 

PLA 

PLA + 0.5% CNC 

PLA + 1% CNC 

PLA + 2% CNC 

Failure mass* (g) 

% Decrease 

38.8 ± 3.5A 

33.0 ± 2.2B 

33.2 ± 2.4B 

32.1 ± 4.7B 

- 

14.9 

14.4 

17.3 

*Different  superscript  letters  within  the  same  column  are  significantly  different 
based on the T Test results at 5% significance level. 

 

 

82 

APPENDICES 

 

 

83 

APPENDIX A 

Effect of CNC content on the thickness of PLA cast films 

 

 

84 

Thickness (l) was calculated using the density method as follows: 

 

 

(Equation 3.1) 

(Equation 3.2) 

 

 

where Wair and Wwater are the sample’s weight in air and in water, respectively, 

 and 

 

are  the  densities  of  the  sample  and  water  at  room  temperature,  which 

 at  30oC  was 

0.9956502 g/mL, area (A) was 4.5 x 103 mm2. 

 

85 

waterwaterairairsampleWWWsampleairAWlsamplewaterwaterTable A.1: Thickness measurement of neat PLA films. 

Water density method 

Digital micrometer 

method 

Wair (g)  Wwater (g) 

Density 
(g/cm3) 

Thickness 

(mm) 

Thickness (mm) 

0.057 

0.056 

0.049 

0.052 

0.051 

0.049 

0.052 

0.006 

Materials 

PLA 

0.2526 

0.0670 

1.36 

0.041 

0.2592 

0.0601 

1.30 

0.044 

0.2386 

0.0448 

1.23 

0.043 

0.2261 

0.0707 

1.45 

0.035 

0.2225 

0.0102 

1.04 

0.047 

0.2373 

0.0438 

1.22 

0.043 

Average 

0.2394 

0.0494 

1.27 

0.042 

Std Dev 

0.0144 

0.0222 

0.14 

0.004 

 

 

 

86 

Table A.2: Thickness measurement of PLA with 0.5% CNC films. 

Water density method 

Digital micrometer 

method 

Wair (g)  Wwater (g) 

Density 
(g/cm3) 

Thickness 

(mm) 

Thickness (mm) 

0.071 

0.081 

0.081 

0.082 

0.083 

0.067 

0.078 

0.010 

Materials 

PLA + 

0.5%CNC 

0.2721 

0.1267 

1.86 

0.032 

0.2936 

0.0914 

1.45 

0.045 

0.2932 

0.0864 

1.41 

0.046 

0.2992 

0.0904 

1.43 

0.046 

0.3187 

0.1374 

1.75 

0.040 

0.2791 

0.0901 

1.47 

0.042 

Average 

0.2927 

0.1037 

1.56 

0.042 

Std Dev 

0.0163 

0.0223 

0.19 

0.005 

 
 

 

87 

Table A.3: Thickness measurement of PLA with 1% CNC films. 

Water density method 

Digital micrometer 

method 

Wair (g)  Wwater (g) 

Density 
(g/cm3) 

Thickness 

(mm) 

Thickness (mm) 

0.071 

0.083 

0.087 

0.079 

0.078 

0.074 

0.079 

0.008 

Materials 

PLA + 
1%CNC 

0.2857 

0.0785 

1.37 

0.046 

0.2697 

0.1055 

1.64 

0.037 

0.3186 

0.1222 

1.62 

0.044 

0.2858 

0.1040 

1.57 

0.040 

0.2948 

0.0984 

1.49 

0.044 

0.2683 

0.0535 

1.24 

0.048 

Average 

0.287 

0.094 

Std Dev 

0.019 

0.024 

1.49 

0.15 

0.043 

0.004 

 

 

 

88 

Table A.4: Thickness measurement of PLA with 2% CNC films. 

Water density method 

Digital micrometer 

method 

Wair (g)  Wwater (g) 

Density 
(g/cm3) 

Thickness 

(mm) 

Thickness (mm) 

0.108 

0.089 

0.079 

0.089 

0.086 

0.095 

0.091 

0.018 

Materials 

PLA + 
2%CNC 

0.3955 

0.1950 

1.96 

0.045 

0.3495 

0.1680 

1.92 

0.040 

0.3989 

0.2113 

2.12 

0.042 

0.3433 

0.1625 

1.89 

0.040 

0.3497 

0.1498 

1.74 

0.044 

0.4126 

0.2063 

1.99 

0.046 

Average 

0.3749 

0.1822 

1.94 

0.043 

Std Dev 

0.0307 

0.0254 

0.12 

0.002 

 

 

89 

APPENDIX B 

Effect of CNC content on the surface texture of PLA cast films 

 

 

 

90 

Table B.1: Surface roughness (Ra) and peak-to-peak values across neat PLA and PLA with 1% 

CNC films. 

Materials 

Location 

Ra (μm) 

Peak-to-peak (μm) 

PLA 

Left 

Center 

Right 

Left 

PLA+1%CNC 

Center 

Right 

0.3581 

0.3249 

0.3441 

1.1177 

1.8598 

1.3102 

2.3719 

1.9785 

2.2905 

14.9756 

13.0534 

11.8594 

 

 

91 

Table B.2: Effect of CNC content on the surface roughness of PLA cast films in both machine direction (MD) and cross machine 

direction (CMD). 

CNC content 

0% 

0.5% 

1% 

2% 

Direction 

Ra (μm) 

Peak-to-
peak (μm) 

Ra (μm) 

Peak-to-
peak (μm) 

Ra (μm) 

Peak-to-
peak (μm) 

Ra (μm) 

Peak-to-
peak (μm) 

CMD 

0.2088 

1.8543 

0.9051 

9.7599 

0.9781 

6.7811 

1.4491 

6.8791 

MD 

0.2868 

1.6950 

1.1302 

7.5198 

1.0111 

8.8358 

1.2174 

12.1893 

CMD 

0.3197 

2.0554 

1.6460 

6.8726 

0.9336 

7.8103 

2.2842 

10.6988 

MD 

0.2269 

2.9652 

1.3288 

7.0541 

0.6224 

4.4043 

0.8189 

7.4929 

Average 

0.2606 

2.1425 

1.2525 

7.8016 

0.8863 

6.9579 

1.4424 

9.3150 

Std Dev 

0.0516 

0.5680 

0.3143 

1.3337 

0.1788 

1.8978 

0.6186 

2.5449 

 
 

 

92 

APPENDIX C 

Effect of CNC content on the water vapor and oxygen barrier properties of PLA cast films 

 

 

 

93 

Table C.1: Effect of CNC content on the water vapor permeability (WVP) of PLA cast films at 

38oC and 85%RH. 

WVP (10-16 kg-m/m2-s-Pa) at 38oC and 85%RH 

CNC content 

0% 

0.5% 

1% 

2% 

153.69 

117.72 

111.15 

101.11 

 

 

 

 

 

 

 

 

 

 

162.19 

119.68 

121.86 

163.50 

120.99 

115.17 

168.08 

113.80 

111.82 

169.39 

108.56 

101.77 

168.08 

118.37 

110.48 

159.58 

116.41 

106.46 

149.77 

121.64 

113.83 

140.61 

120.34 

101.11 

- 

112.49 

- 

91.06 

92.40 

92.40 

73.65 

87.04 

85.71 

85.04 

76.33 

85.04 

86.98 

7.99 

Average 

159.43 

117.00 

110.40 

Std Dev 

9.70 

 

4.22 

6.56 

94 

 

 

Table C.2: Effect of CNC content on the oxygen permeability (OP) of PLA cast films at 23oC 

and 0%RH. 

OP (10-20 kg-m/m2-s-Pa) at 23oC and 0%RH 

CNC content 

0% 

0.5% 

1% 

2% 

 

 

 

 

 

308.18 

246.20 

216.48 

180.32 

418.50 

228.32 

222.60 

182.71 

309.07 

319.77 

245.03 

144.13 

378.62 

319.39 

175.58 

208.22 

- 

223.33 

200.63 

- 

Average 

353.59 

267.40 

212.06 

178.84 

Std Dev 

54.42 

 

48.38 

25.88 

26.36 

95 

 

 

Table C.3: Effect of testing relative humidity (RH) on the OP of PLA and PLA/2%CNC composite films. 

OP (10-20 kg-m/m2-s-Pa) at 23oC 

RH 

0% 

25% 

50% 

75% 

CNC content 

0% 

2% 

0% 

2% 

0% 

2% 

0% 

2% 

 

 

 

 

 

 

 

 

 

 

308.18 

180.32 

376.72 

279.85 

232.61 

121.00 

257.87 

147.56 

418.50 

182.71 

324.81 

141.34 

260.49 

111.06 

214.77 

148.38 

309.07 

144.13 

277.73 

157.16 

453.38 

133.14 

250.81 

132.00 

378.62 

208.22 

279.04 

165.23 

359.92 

123.02 

221.33 

121.59 

248.83 

140.97 

302.46 

132.55 

293.64 

294.80 

289.05 

238.91 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

150.50 

258.93 

162.72 

259.67 

- 

- 

- 

- 

250.25 

367.25 

- 

- 

- 

- 

- 

- 

- 

- 

Average 

308.21 

164.82 

314.58 

185.90 

326.60 

135.24 

260.11 

137.38 

Std Dev 

54.00 

29.94 

46.86 

63.42 

100.65 

21.61 

46.64 

12.94 

 

96 

APPENDIX D 

Effect of CNC content on the hot tack performance, seal strength and burst pressure of 

PLA cast films 

 

 

97 

Table D.1: Effect of CNC content on the hot tack profiles of neat PLA films as temperature increases from 60oC to 110oC. 

Peak force (g) 

CNC 

content 

Temper
ature 
(oC) 

1 

2 

60 

49 

13 

0% 

0.5% 

1% 

2% 

Number of replicates 

3 

0 

4 

5 

1 

2 

3 

4 

5 

1 

2 

3 

4 

5 

1 

2 

3 

4 

5 

16 

21 

28 

18 

17 

16 

17 

67 

18 

16 

14 

14 

94 

20 

19 

17 

21 

65 

18 

21 

21 

17 

16 

12 

19 

13 

21 

12 

14 

16 

13 

17 

9 

14 

18 

17 

0 

0 

70 

34 

24 

26 

37 

30 

20 

23 

18 

21 

30 

18 

15 

15 

16 

24 

0 

0 

18 

28 

39 

75 

105 

48 

40 

54 

133 

65 

50 

42 

64 

105 

57 

51 

31 

35 

60  118 

80 

81 

55 

109 

80 

642  210  174  146  916  632  770  931  1,248 1,085  812  879  447  1,242 1,584  563  544  885  1,121 1,018 

85 

1,146  859  819  461  1,461 1,290 1,170 1,069 1,544 1,143 1,781 1,638 1,317 1,588 1,884 1,043 1,123 1,188 1,243 1,378 

90 

1,119  856  882  587  1,202  884  976  1,463 1,218 1,070 1,129 1,390 1,257 1,360 1,557  972  786  992  1144  1,209 

95 

934  694  642  1,034  850  661  1,037 1,274  783  1,089 1,429 1,037  988  1,178 1,396  981  649  788  892  1,006 

100 

781  543  359  800  953  897  991  931  766  785  1,099  884  887  962  989  812  749  688  806  908 

105 

273  209  331  772  523  679  856  1,026  585  598  656  621  536  256  594  817  647  659  797  1,001 

110 

364  233  244  393  636  492  542  583  313  364  443  297 

59 

352  160  1,061  546  704  936  929 

 

98 

Table D.2: Effect of CNC content on the hot tack initiation temperature (HTIT), temperature where maximum hot tack strength 

occurred (TMHTS), and maximum hot tack strength (MHTS) of neat PLA films at the temperature range of 60oC to 110oC. 

 

HTIT (oC) 

TMHTS (oC) 

MHTS (g) 

CNC content 

0% 

0.5% 

1% 

2% 

0% 

0.5% 

1% 

2% 

0% 

0.5% 

1% 

2% 

 

 

 

 

 

73.94 

74.59 

74.88 

73.79 

85 

75.40 

74.08 

74.61 

74.42 

75.58 

73.37 

76.54 

73.58 

74.59 

73.57 

73.85 

73.21 

73.70 

72.50 

73.55 

73.42 

85 

90 

95 

85 

Average 

74.64 

73.62 

74.69 

73.68 

88.00 

85 

85 

90 

85 

85 

86 

85 

85 

85 

85 

85 

85 

110 

1,146 

1,290 

1,781 

1,061 

85 

85 

85 

85 

859 

1170 

1638 

1123 

882 

1463 

1317 

1181 

1,034 

1,544 

1,588 

1,243 

1,461 

1,143 

1,884 

1,378 

90.00  1,076.40  1,322.00  1,641.60  1,197.20 

Std Dev 

0.84 

0.79 

1.17 

0.46 

4.47 

2.24 

0 

11.18 

244.75  177.01 

215.89 

121.56 

 

 

99 

Table D.3: Effect of CNC content on the seal strength of neat PLA cast films. 

CNC content 

0% 

0.5% 

1% 

2% 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Force (N) 

Mode of 
failure 

Force (N) 

Mode of 
failure 

Force (N) 

Mode of 
failure 

Force (N) 

Mode of 
failure 

3.474 

Adhesive 

10.401 

Cohesive 

7.315 

Cohesive 

13.163 

Cohesive 

6.439 

Adhesive 

40.015 

Cohesive 

5.773 

Cohesive 

11.482 

Cohesive 

4.092 

Adhesive 

16.090 

Cohesive 

5.201 

Cohesive 

10.255 

Cohesive 

11.685 

Adhesive 

7.507 

Cohesive 

14.641 

Cohesive 

15.268 

Cohesive 

4.615 

Adhesive 

24.396 

Cohesive 

38.548 

Cohesive 

14.955 

Adhesive 

7.822 

Cohesive 

9.390 

Cohesive 

14.492 

Cohesive 

3.910 

Adhesive 

3.992 

Adhesive 

13.179 

Cohesive 

9.907 

Cohesive 

5.450 

Adhesive 

3.869 

Adhesive 

3.430 

Cohesive 

3.323 

Cohesive 

5.123 

Adhesive 

6.759 

Adhesive 

27.042 

Cohesive 

8.570 

Cohesive 

11.919 

Cohesive 

6.199 

Adhesive 

10.332 

Cohesive 

37.524 

Cohesive 

15.563 

Cohesive 

4.494 

Adhesive 

10.471 

Cohesive 

3.099 

Cohesive 

7.289 

Adhesive 

6.789 

Adhesive 

9.159 

Cohesive 

2.799 

Cohesive 

9.350 

Cohesive 

7.388 

Adhesive 

9.298 

Cohesive 

3.599 

Cohesive 

16.352 

Cohesive 

 

100 

Table D.3 (cont’d) 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6.085 

Adhesive 

11.144 

Cohesive 

4.847 

Cohesive 

26.980 

Cohesive 

2.681 

Adhesive 

15.684 

Cohesive 

8.439 

Cohesive 

10.731 

Adhesive 

3.846 

Adhesive 

8.428 

Cohesive 

15.700 

Cohesive 

13.001 

Cohesive 

4.434 

Adhesive 

5.374 

Cohesive 

8.746 

Cohesive 

14.125 

Cohesive 

6.041 

Adhesive 

33.629 

Cohesive 

9.347 

Cohesive 

13.227 

Cohesive 

5.615 

Adhesive 

5.131 

Cohesive 

2.605 

Cohesive 

26.690 

Cohesive 

7.083 

Adhesive 

13.499 

Cohesive 

16.144 

Cohesive 

14.071 

Cohesive 

3.463 

Adhesive 

11.219 

Cohesive 

15.637 

Cohesive 

10.561 

Cohesive 

8.619 

Adhesive 

7.999 

Cohesive 

25.542 

Cohesive 

20.720 

Cohesive 

11.270 

Adhesive 

9.921 

Cohesive 

21.640 

Cohesive 

9.388 

Cohesive 

24.412 

Adhesive 

34.102 

Cohesive 

5.983 

Cohesive 

7.267 

Cohesive 

11.391 

Cohesive 

14.520 

Cohesive 

14.611 

Cohesive 

5.915 

Cohesive 

12.020 

Cohesive 

6.727 

Cohesive 

12.700 

Cohesive 

10.279 

Cohesive 

23.675 

Adhesive 

3.532 

Cohesive 

3.437 

Cohesive 

11.673 

Cohesive 

7.921 

Adhesive 

7.948 

Cohesive 

5.619 

Cohesive 

11.427 

Cohesive 

3.400 

Adhesive 

28.051 

Cohesive 

3.095 

Cohesive 

5.414 

Cohesive 

 

101 

Table D.3 (cont’d) 

 

 

 

 

 

 

 

 

 

 

 

7.129 

Adhesive 

32.975 

Cohesive 

21.842 

Cohesive 

9.702 

Cohesive 

9.243 

Adhesive 

27.489 

Cohesive 

10.658 

Cohesive 

16.855 

Cohesive 

13.046 

Adhesive 

9.406 

Cohesive 

8.008 

Cohesive 

13.677 

Cohesive 

8.043 

Cohesive 

33.157 

Cohesive 

4.873 

Cohesive 

12.238 

Cohesive 

2.748 

Adhesive 

8.262 

Cohesive 

15.901 

Cohesive 

6.815 

Cohesive 

26.894 

Adhesive 

16.362 

Cohesive 

14.832 

Cohesive 

6.015 

Cohesive 

9.029 

Adhesive 

9.353 

Cohesive 

7.970 

Cohesive 

13.323 

Cohesive 

5.373 

Cohesive 

5.285 

Cohesive 

15.358 

Cohesive 

15.399 

Cohesive 

7.110 

Adhesive 

8.659 

Cohesive 

11.501 

Cohesive 

11.937 

Cohesive 

7.947 

Adhesive 

4.883 

Cohesive 

4.598 

Cohesive 

8.359 

Cohesive 

10.957 

Adhesive 

13.410 

Cohesive 

25.443 

Cohesive 

11.060 

Cohesive 

Average 

8.177 

Std Dev 

5.574 

- 

- 

% Mode of 

failure 

- 

85% 

Adhesive 

14.421 

9.913 

- 

- 

- 

100% 

Cohesive 

11.747 

8.739 

- 

- 

- 

100% 

Cohesive 

11.923 

5.080 

- 

- 

- 

85% 

Cohesive 

 

102 

Table D.4: Effect of CNC content on the burst pressure of neat PLA cast films. 

 

 

Burst pressure (in. H2O) 

Type 1 (MD) 

Type 2 (CMD) 

CNC content 

0% 

0.5% 

1% 

206.7 

123.8 

114.1 

202.8 

93.2 

76.0 

212.4 

237.1 

183.3 

222.6 

2% 

54.0 

34.7 

87.8 

26.9 

95.9 

164.1 

234.5 

160.1 

197.8 

207.5 

27.9 

0% 

73.7 

61.2 

67.0 

0.5% 

164.6 

141.9 

1% 

37.4 

91.7 

2% 

117.6 

148.4 

183.2 

227.0 

128.2 

123.9 

188.6 

197.5 

40.5 

113 

94.4 

77.7 

200.2 

228.5 

220.2 

141.0 

196.8 

245.6 

176.0 

159.7 

65.0 

70.5 

 

 

 

 

 

 

 

 

Average 

Std Dev 

51.4 

24.8 

61.9 

48.4 

21.9 

36.4 

33.8 

21.8 

37.6 

15.0 

148.4 

92.8 

220.6 

133.5 

219.3 

54.5 

165.0 

174.6 

43.8 

66.2 

90% 

88.5 

69.9 

90% 

93.1 

27.5 

176.9 

149.1 

129.5 

27.2 

77.3 

73.5 

100% 

100% 

100% 

100% 

% Mode of 

80% 

100% 

failure 

Cohesive 

Cohesive 

Cohesive 

Cohesive 

Cohesive 

Cohesive 

Cohesive 

Cohesive 

 

 

103 

APPENDIX E 

Effect of CNC content on the tensile properties of PLA cast films 

 

 

104 

Table E.1: Effect of CNC content on the tensile modulus of neat PLA cast films in both machine and cross machine directions. 

 

 

CNC 

Content 

Tensile modulus (MPa) 

Machine direction 

Cross machine direction 

0% 

0.5% 

1% 

2% 

0% 

0.5% 

1% 

2% 

 

 

 

 

 

 

 

 

 

 

 

 

2,727.977 

5,439.484 

4,976.195 

5,604.761 

2,883.113 

5,645.779 

3,872.461 

3,628.285 

2,848.442 

5,460.088 

4,648.636 

3,989.295 

2,797.365 

5,765.433 

4,124.440 

3,526.297 

2,811.679 

5,497.720 

4,997.701 

3,839.115 

2,770.386 

5,228.406 

4,673.136 

3,546.088 

3,038.820 

5,814.096 

5,076.374 

4,155.284 

2,824.040 

5,692.100 

5,630.776 

3,600.143 

2,477.109 

5,813.165 

6,188.784 

4,206.754 

2,715.320 

5,674.032 

6,390.407 

3,449.277 

3,356.111 

5,771.622 

4,375.433 

5,540.027 

2,872.735 

5,700.582 

6,790.661 

3,679.156 

2,497.236 

5,397.827 

4,158.570 

4,186.421 

2,843.386 

5,556.249 

5,922.063 

3,688.294 

- 

- 

- 

- 

- 

5,930.891 

5,188.200 

4,137.694 

2,836.766 

5,611.405 

5,821.641 

3,654.274 

5,655.476 

5,412.282 

4,066.708 

2,626.055 

5,561.038 

- 

3,788.153 

5,561.696 

5,464.273 

5,011.173 

2,562.660 

5,534.997 

6,213.452 

3,825.936 

6,183.621 

6,094.474 

5,179.569 

- 

5,297.119 

3,830.017 

- 

- 

5,588.850 

6,864.387 

3,696.433 

5,624.395 

7,681.995 

3,671.949 

 

105 

Table E.1 (cont’d) 

 

 

 

 

 

 

 

 

 

 

 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

4,738.920 

3,852.644 

5,138.348 

6,539.004 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

5,489.546 

6,791.042 

5,335.381 

6,008.000 

5,356.586 

5,822.125 

5,334.963 

6,131.853 

5,642.988 

5,616.373 

5,474.566 

5,632.892 

5,568.045 

5,714.137 

5,509.058 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

Average  2,822.482 

5,684.153 

5,219.621 

4,430.728 

2,773.183 

5,559.035 

5,915.896 

3,646.191 

Std Dev 

307.233 

243.753 

659.036 

655.145 

107.218 

137.263 

1033.270 

106.252 

 

 

106 

Table E.2: Effect of CNC content on the tensile strength of neat PLA cast films in both machine and cross machine directions. 

 

 

CNC 

content 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tensile strength (MPa) 

Machine direction 

Cross machine direction 

0% 

0.5% 

1% 

2% 

0% 

0.5% 

1% 

2% 

Yield  Break  Yield  Break  Yield  Break  Yield  Break  Yield  Break  Yield  Break  Yield  Break  Yield  Break 

55.546  17.353 

- 

122.105 

- 

85.552 

- 

113.168 

- 

17.394 

- 

61.385 

- 

21.281 

- 

21.197 

56.242  28.782 

61.753  67.324 

63.495  52.314 

54.344  27.773 

71.823  72.578 

56.289  21.025 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

82.713 

110.308 

123.557 

- 

- 

- 

80.134 

75.358 

92.525 

116.718 

-  122.196 

111.219 

119.529 

125.033 

111.046 

117.452 

- 

- 

- 

- 

- 

76.730 

56.975 

84.480 

23.650 

99.064 

131.581 

-  124.825 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

70.409 

50.556 

27.777 

64.794 

111.322 

69.245 

50.148 

72.872 

30.711 

61.563 

107 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

20.650 

29.965 

23.152 

11.026 

34.541 

22.291 

33.974 

33.297 

7.336 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

64.305 

63.300 

60.263 

79.880 

72.005 

28.534 

60.882 

74.437 

71.086 

64.757 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

26.688 

22.544 

37.023 

65.495 

67.963 

32.484 

25.550 

17.425 

58.703 

29.663 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

30.439 

28.958 

15.159 

15.125 

10.268 

27.029 

23.068 

30.386 

27.859 

23.780 

Table E.2 (cont’d) 

 

 

 

 

 

 

 

 

 

 

 

 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

Avg  59.927  41.021 

Std Dev  6.255  22.732 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

115.569 

12.726 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

99.584 

62.009 

70.424 

87.538 

- 

- 

- 

- 

- 

- 

- 

- 

82.736 

25.131 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

 

 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

19.745 

60.906 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

61.786 

28.148 

108 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

23.363 

9.621 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

74.963 

68.870 

63.258 

62.719 

69.157 

55.714 

44.855 

37.664 

74.186 

64.152 

59.436 

40.049 

61.559 

12.841 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

77.564 

45.453 

40.677 

53.627 

59.106 

- 

- 

- 

- 

- 

- 

- 

42.578 

18.957 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

26.305 

 

 

 

 

 

 

 

 

 

 

 

23.298 

6.637 

Table E.3: Effect of CNC content on the energy at break of neat PLA cast films in both machine 

and cross machine directions. 

Energy at break (J) 

Machine direction 

Cross machine direction 

 

 

CNC content 

0% 

0.5% 

1% 

2% 

0% 

0.5% 

1% 

2% 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.083 

0.230 

0.157 

0.208 

0.009 

0.037 

0.018 

0.017 

4.800 

0.304 

0.107 

0.093 

0.023 

0.043 

0.010 

0.015 

4.932 

0.174 

0.456 

0.218 

0.019 

0.044 

0.011 

0.013 

3.542 

0.193 

0.170 

0.275 

0.010 

0.041 

0.016 

0.010 

5.330 

0.182 

0.238 

0.103 

0.013 

0.082 

0.037 

0.004 

6.284 

0.234 

0.101 

0.157 

0.021 

0.058 

0.042 

0.012 

4.107 

0.215 

0.414 

0.107 

0.010 

0.060 

0.011 

0.011 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

0.204 

0.103 

0.280 

0.021 

0.057 

0.016 

0.013 

0.186 

0.092 

0.106 

0.024 

0.069 

0.013 

0.013 

0.178 

0.130 

0.108 

0.014 

0.057 

0.031 

0.011 

- 

- 

- 

- 

- 

- 

- 

- 

0.069 

0.027 

0.010 

0.063 

0.044 

0.012 

0.050 

0.015 

0.039 

0.017 

0.046 

0.029 

0.051 

0.034 

0.053 

0.036 

- 

- 

- 

- 

- 

- 

- 

- 

0.206 

0.198 

0.135 

- 

- 

- 

- 

- 

- 

- 

0.139 

0.090 

0.077 

0.094 

0.160 

0.449 

- 

- 

- 

- 

- 

- 

- 

- 

109 

Table E.3 (cont’d) 

 

 

 

 

 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

0.040 

0.060 

0.042 

0.059 

0.056 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

Average 

4.4397 

0.2096 

0.1990 

0.1518 

0.0164 

0.0527 

0.0232 

0.0118 

Std Dev 

1.3563 

0.0372 

0.1310 

0.0698 

0.0058 

0.0118 

0.0116 

0.0032 

 

110 

 

 

Table E.4: Effect of CNC content on the elongation at break of neat PLA cast films in both 

machine and cross machine directions. 

 

 

Elongation at break (%) 

Machine direction 

Cross machine direction 

CNC content 

0% 

0.5% 

1% 

2% 

0% 

0.5% 

1% 

2% 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

43.629 

3.365 

2.872 

3.119 

0.903 

1.232 

1.231 

1.067 

106.202 

4.182 

2.380 

2.380 

1.395 

1.312 

0.737 

0.984 

96.198 

2.871 

6.644 

4.922 

1.231 

1.394 

0.820 

0.903 

77.828 

2.873 

2.954 

5.906 

0.902 

1.312 

0.820 

0.821 

111.945 

2.789 

3.200 

2.462 

1.067 

1.886 

1.149 

0.574 

118.258 

3.364 

2.379 

2.625 

1.313 

1.558 

1.229 

0.904 

86.192 

3.199 

7.464 

2.543 

0.903 

1.640 

0.656 

0.821 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

2.953 

2.215 

5.824 

1.313 

1.559 

0.821 

0.903 

2.871 

2.052 

2.543 

1.395 

1.722 

0.821 

0.903 

2.789 

2.462 

2.298 

1.067 

1.559 

1.067 

0.821 

- 

- 

- 

- 

- 

- 

- 

- 

1.722 

0.985 

0.820 

1.640 

1.149 

0.903 

1.476 

0.738 

1.315 

0.821 

1.394 

1.067 

1.476 

1.149 

1.476 

1.230 

- 

- 

- 

- 

- 

- 

- 

- 

2.871 

2.873 

2.543 

- 

- 

- 

- 

- 

- 

- 

2.543 

2.544 

1.970 

2.461 

3.036 

6.070 

- 

- 

- 

- 

- 

- 

- 

- 

111 

Table E.4 (cont’d) 

 

 

 

 

 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

1.312 

1.559 

1.312 

1.559 

1.560 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

Average 

91.465 

3.102 

3.408 

3.244 

1.149 

1.487 

0.954 

0.869 

Std Dev 

25.426 

0.418 

1.774 

1.347 

0.204 

0.172 

0.194 

0.119 

 

112 

 

 

APPENDIX F 

Effect of CNC content on the dart impact strength of PLA cast films 

 

113 

 
 

 

 

 

 

 

 

Figure F.1: The dart impact test results for neat PLA cast films. 

114 

 

 

 

 

Figure F.2: The dart impact test results for PLA with 0.5% CNC cast films. 

 

 

 

 

115 

Figure F.3: The dart impact test results for PLA with 1% CNC cast films. 

 

 

116 

 

 

 

 

 

 

 
 

 
 

Figure F.4: The dart impact test results for neat PLA with 2% CNC cast films. 

 

117 

 

 

REFERENCES 

118 

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12. Kunanusont, N., Pongsa, U., Bunsiri, A., and Somwangthanaroj, A. (2014). Effect of relative 
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24. Afrifah,  K.A.  and  Matuana,  L.M.  (2010).  Impact  modification  of  polylactide  with  a 
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121 

Chapter 5 

CONCLUSIONS 

5.1 Conclusions 

The  aim  of  this  study  was  to  utilize  a  continuous  extrusion  process,  which  efficiently 

incorporates CNCs into a PLA matrix, in order to manufacture PLA/CNC cast films and further 

investigate its properties  for the packaging  application.  To achieve this goal,  a counter rotating 

twin-screw extruder was used to manufacture the PLA/CNC cast films. Once the films were made, 

the distribution and dispersion of CNCs in PLA matrix were examined. As the physico-mechanical 

properties of neat  PLA and its composite films are thickness  dependent.  The surface texture of 

PLA  and  its  composite  films  were  determined  to  assure  proper  comparison.  Two  methods,  the 

density  and  digital  micrometer  methods,  were  used  to  measure  the  thickness  of  both  neat  and 

composite films to assure the accuracy of the thickness. To expand the packaging application, the 

effect of CNC content on the hot tack performance, seal strength, and burst strength of PLA cast 

films  was  studied.  Additionally,  this  study  examined  the  effect  of  CNC  content  on  the  tensile 

property and impact strength of PLA cast films. The water and oxygen barrier properties of neat 

PLA  and  its  composite  films  were  further  investigated.  The  following  conclusions  were  drawn 

from this study. 

1.  The addition of CNCs into PLA matrix increased the surface roughness of PLA cast films. 

a.  From the images of light microscopy, a homogenous distribution of CNCs into PLA 

matrix  was  achieved,  however,  there  were  CNC  agglomerates  indicating  a  poor 

dispersion. 

 
 

122 

b.  The agglomeration of CNCs led to the surface roughness which further verified by 

profilometry.  Results  from  profilometry  showed  that  irrespective  of  the  film 

direction and location, incorporating of CNCs into PLA matrix introduced surface 

roughness, attributed to the agglomeration of CNC in the PLA matrix. The presence 

of  roughness  throughout  the  PLA/CNC  films  supported  the  finding  that  a  good 

distribution was achieved. 

2.  The thickness measurements obtained from the density method showed that there were no 

significant differences in the thickness between neat PLA and composite films. 

a.  The thickness of neat PLA films obtained from the density method were slightly 

lower  than  that  measured  by  the  digital  micrometer,  due  to  the  slight  surface 

roughness supported by the surface profiles from profilometry. 

3.  The addition of CNCs into PLA matrix did not negatively affect the hot tack performance 

and seal strength. 

a.  Both the hot tack initiation temperature and temperature where the maximum hot 

tack strength occurred were not affected by the addition of CNC content. In contrast, 

the maximum hot tack strength appeared to increase with CNC content up to 1% 

and slightly decreased with further CNC content increase. The optimum maximum 

hot tack strength occurred with the addition of 1% CNC. 

b.  Incorporating CNCs into the PLA matrix significantly increased the seal strength 

of PLA cast films, regardless of CNC content. 

 
 

123 

c.  Regardless  of the  pouch configuration (sealing directions) and CNC content, the 

addition of CNCs into PLA matrix increased the burst pressure of the pouches. 

4.  Irrespective  of  CNC  concentration,  the  addition  of  CNC  content  in  the  PLA  matrix 

improved the tensile strength and modulus of neat PLA cast films, resulting stronger and 

stiffer  composite  films.  These  improvements  were  achieved  at  the  expense  of  ductility 

since both the elongation at break and the energy to break decreased, results supported by 

the dart impact strength showing that PLA/CNC composite films were more brittle than 

neat PLA films. 

5.  The addition of CNCs into PLA matrix significantly improved the water and oxygen barrier 

properties of the films. 

a.  By adding 2% CNC into the PLA matrix, improvements of approximately 45% and 

49%  in  water  vapor  and  oxygen  permeabilities  of  PLA  films,  were  respectively 

observed.  These  improvements  were  attributed  to  the  tortuous  diffusion  path 

created by crystallites, as CNCs can serve as both crystallites and a nucleating agent. 

b.  The oxygen permeability of PLA and PLA with 2% CNC films remained constant 

as the relative humidity increased from 0% to 75% at 23oC. 

5.2 Future works 

While this study focused on the processing and the physico-mechanical property evaluation 

of PLA/CNC extruded cast films for the food  packaging application, other properties including 

optical  (haze,  color,  clarity)  and  thermal  (glass  transition  and  melting  temperatures,  thermal 

stability)  must  also  be  studied.  In  addition,  to  ensure  the  packaging  integrity  throughout  the 

 
 

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distribution  environment,  properties  related  to  vibration  and  shock  absorption,  must  also  be 

evaluated. As this study showed that stretching in the machine direction at the melt state of PLA 

had significant effect on the elongation at break of neat PLA films due to the oriented polymer 

chains  alignment,  it  would  be  appropriate  to  further  investigate  and  develop  an  in-depth 

understanding of the relationship between tensile properties, melt state drawing and polymer chain 

alignment.  In addition, the effect of melt state stretching on the CNC alignment should also be 

studied. Furthermore,  in  order to  expand the use  of CNCs  in  PLA extruded cast  films for  food 

packaging application, a thorough migration study and shelf life study for PLA/CNC films would 

be beneficial to carry out using real food products to assure the safety of consuming the products. 

 

 
 

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