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MICHIGAN T

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This is to certify that the

thesis entitled

PERMEATION OF ETHYL ACETATE VAPOR
THROUGH SILICA DEPOSITED
POLYETHYLENE TEREPHTHALATE FILM
AND COMPOSITE STRUCTURES

presented by

Takashi Sajiki

has been accepted towards fulfillment
of the requirements for

Master's egree in Science

aLK-W

D . ack R. Giacin

Major professor

Date July 1, 1991

 

0-7 539 MS U is an Affirmative Action/Equal Opportunity Institution

 

LIBRARY
Michigan State
University

 

 

 

PLACE IN RETURN BOX to remove We checkout from your record.
TO AVOID FINES return on or before due due.

DATE DUE DATE DUE DATE DUE

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU is An Affinnetive ActionlEquel Oppomnity Institution

ammo-m

 

 

PERMEATION OF ETHYL ACETATE VAPOR
THROUGH SILICA DEPOSITED POLYETHYLENE TEREPHTHALATE FILM
AND COMPCEITE STRUCTURES

By
Takashi Sajiki

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

School of Packaging
1991

,J, ’
(O

7

ABSTRACT

PERMEATION OF ETHYL ACETATE VAPOR
THROUGH SILICA DEPOSITED POLYETHYLENE TEREPHTHALATE FILM
AND COMPOSITE STRUCTURES

By
Takashi Sajiki

The effect of temperature, relative humidity and retort sterilization
conditions on the permeation of ethyl acetate vapor through silica
deposited polyethylene terephthalate (SiOx PET) films and laminate
structures was studied. The permeability of an ethylene! vinyl alcohol
copolymer (EVOH) and a EVOH laminate structure was also determined.

At 22°C, the SiOx PET film showed excellent barrier properties. It

also exhibited relatively high temperature dependence (Ea - 23 kcal/ mol),

but was unaffected by sorbed water. For the SiOx PET based retort pouch,

an average increase of 260% in the permeation rate was observed

following retorting, when the retort temperature was increased from 125

to 130°C. The transmission rate increase was on the order of 30%, in

going from 120° to 125°C, retorting temperature. At each temperature,

heating times of 20, 40, and 60 minutes were evaluated, and a direct

correlation was found between processing time and permeation rate.
Analysis by optical microscopy on the SiOx surface showed a direct

relationship between permeability and fracture of the SiOx coating.

Further, a direct correlation between retorting conditions and surface

damage was found.

To my parents and my lovely wife.

iii

ACKNOWLEDGEMENTS

I would like to express my appreciation to Dr. Jack R. Giacin for his
guidance and professional advice throughout my research.

I would like to thank members of the graduate committee, Dr. Bruce
Harte, Dr. Ruben J. Hernandez and Dr. Ian Gray, for their advice and review
of the manuscript.

I also want to thank Dr. Parvin (Heidi) Hoojjat for her advice on the use
of laboratory facilities.

Finally I am indebted to Toppan Printing Co., Ltd. for sponsoring the
necessary expenditures during my studies in the school of Packaging at

Michigan State University.

iv

TABLE OF CONTENTS

Page

LIST OF TABLES ----------------------------------------- viii
LIST OF FIGURES ----------------------------------------- x
INTRODUCTION ----------------------------------------- 1
LITERATURE REVIEW -------------------------------------- 3
Silica Deposited Film ------------------------------ 3
Evolution of Silica Deposited Film -------------- 3

Properties of Silica Deposited Film ------------ 4

Oxygen Barrier ------------------------------- 8

Moisture Barrier ----------------------------- 9

Retortability -------------------------------- 1 2

An Alternative Approach ----------------7 ----- 12

Permeation of Organic Vapors through Polymer Films - - 15
Permeation Theory -------------------------------- 17
Permeability Measurements ------------------------ 20

. MATERIALS AND METHODS --------------------------------- 23
Materials ----------------------------------------- 23

Film Samples -------------------------------- 23

Retort Pouch --------------------------------- 24

Permeant ---------------------------------------- 24

Carrier Gas ---------------------------------- 25

Procedure ---------------------------------------- 25
Permeability Measurements ------------------- 25

Operation ----------------------------------- 29

Retorting Process ---------------------------- 30

Analytical ---------------------------------------- 31

Page

Gas Chromatographic Analysis ----------------- 31
Analysis of SiOx Surface by Optical Microscopy - - 33
RESULTS AND DISCUSSION --------------------------------- 3 4

Determination of the Appropriate Conditions for
the Permeation of Ethyl Acetate Vapor through

SiOx PET Film and Other Test Films ------------------ 34
Preliminary studies -------------------------- 34

The Effect of Temperature of the Permeation of

Ethyl Acetate Vapor through SiOx PET Film ----------- 41
Experiments at 65°C -------------------------- 41
Experiments at 76°C -------------------------- 47
Transmission rate and Permeance -------------- 53

The Effect of Relative Humidity on the Permeation of
Ethyl Acetate Vapor through SiOx PET and EVOH ------- 59

Experiments at 87% RH. and 56% RH. ----------- 59
The Effect of Retort Pasteurization on the Permeation of
Ethyl Acetate through the PET/SiOx PET/CPP
Retort Pouch Structure ----------------------------- 62

Dependency of Retorting Time on Vapor Barrier
Characteristics ------------------------------ 6 2

Dependency of Retorting Temperature on

Vapor Barrier Characteristics ----------------- 66
Transmission rate and Permeance -------------- 66
Analysis of SiOx Layer Surface ---------------- 76

vi

CONCLUSION ............................................. 3 3

FUTURE RESEARCH --------------------------------------- 8 6
APPENDICES ----------------------------------------- 87
Appendix A. Standard Calibration for Ethyl Acetate - - - 87

Appendix B. Oxygen Permeance of SiOx PET and Other
Films Used in This study --------------- 91

Appendix C. Estimation of the Upper Limit of
the Transmission Rates of
Ethyl Acetate Vapor
through SiOx PET Film ----------------- 92

BIBLIOGRAPHY ------------------------------------------- 93

v11

Table Page
1 Oxygen permeance of PET, SiOx PET and SiOx PET

laminated structure --------------------------------- 10
2 Oxygen permeance of SiOx laminated film and

other laminated films ------------------------------- 10
3 Water vapor transmission rate of PET, SiOx PET

and SiOx PET laminated structure --------------------- 1 1
4 Water vapor transmission rate of SiOx laminated film

and other laminated films --------------------------- 11
5 Oxygen permeance of SiOx laminated film and

other films before and after retort process ------------ 13
6 Comparison of characteristics among SiOx PET

and other barrier materials -------------------------- 14
7 Gas chromatographic conditions for 5890 and 5830 A ~ - - 32
8 Effect of temperature on transmission rate

of ethyl acetate vapor through SiOx PET and other films - 54
9 Effect of temperature on Permeance of

ethyl acetate vapor through SiOx PET and other films - - - 55
10 Activation energy of permeation of ethyl acetate

vapor through SiOx PET, PET and EVOH ----------------- 57
11 Effect of relative humidity on transmission rate and

LIST OF TABLES

permeance of ethyl acetate vapor through
SIOX PET and EVOH .................................. 61

viii

12

13

14

15

A1

A2

A3

Page

Effect of retort conditions on transmission rate

of ethyl acetate vapor through PET/SiOx PET/CPP ------ 71
The Effect of retort conditions on permeance of

ethyl acetate vapor through PET/SiOx PET/CPP --------- 72
The Effect of retort conditions on permeance of

ethyl acetate vapor through PET/SiOx PET/CPP --------- 73
Observation of SiOx layer of retort pouches ------------ 77
Ethyl acetate calibration curve data for gas

chromatograph 5890 -------------------------------- 8 8

Ethyl acetate calibration curve data for gas
chromatograph 5830 A ------------------------------ 88

Oxygen permeance of SiOx PET and other films
used in this study ................................... 91

ix

LIST OF FIGURES

Figure Page
1 Cross-sectional view of the silica deposited PET film - - 5
2 Cross-sectional view of a typical retort pouch

structure with silica deposited film ------------------ 5
3 Oxygen permeation through SiOx deposited PET as a

function of coating thickness ------------------------ 7
4 Effect of chemical composition on the oxygen

permeation through SiOx deposited PET ---------------- 7
5 Generalized transmission profile curve for the quasi-

isostatic method ----------------------------------- 21
6 Schematic of permeation test apparatus at

non-humidified condition ---------------------------- 26
7 Schematic of permeation test apparatus for

evaluating the effect of relative humidity ------------- 28
8 Transmission rate profile curves of ethyl acetate vapor

through SiOx PET and other films in the determination of

the appropriate conditions --------------------------- 37
9 Transmission rate profile curves of ethyl acetate vapor

through PET and SiOx PET in the determination of

the appropriate conditions --------------------------- 38
10 Transmission rate profile curves of ethyl acetate vapor

through SiOx PET and EVOH in the determination of
the appropriate conditions --------------------------- 39

11

12

13

14

15

16

17

18

19

20

Stability of the center cell concentration of

Page

ethyl acetate vapor --------------------------------- 40

Transmission rate profile curves of ethyl acetate
through SiOx PET and other films

vapor

at 65°C -300ppm - non-humidified condition ----------- 42

Transmission rate profile curves of ethyl acetate
through SiOx PET and other high barrier films

vapor

at 65°C -300ppm - non-humidified condition ----------- 43

Transmission rate profile curves of ethyl acetate
through PET and PET/PET/CPP

vapor

at 65°C -300ppm - non-humidified condition ........... 44

Transmission rate profile curves of ethyl acetate
through SiOx PET and EVOH

vapor

at 65°C -300ppm - non-humidified condition ----------- 45

Transmission rate profile curves of ethyl acetate
through PET/SiOx PET/CPP and PET/EVOH/CPP

vapor

at 65°C -300ppm - non-humidified condition ----------- 46

Transmission rate profile curves of ethyl acetate

' through SiOx PET and other films at

vapor

76°C - 300ppm - non-humidified condition ------------- 48

Transmission rate profile curves of ethyl acetate
through SiOx PET and other high barrier films

vapor

at 76°C -300ppm - non-humidified condition ----------- 49

Transmission rate profile curves of ethyl acetate
through PET and PET/PET/CPP

vapor

at 76°C - 300ppm - non-humidified condition ---------- 50

Transmission rate profile curves of ethyl acetate
through SiOx PET and EVOH

vapor

at 76°C ~300ppm - non-humidified condition ----------- 51

xi

21

22

23

24

25

26

27

28

29

30

Transmission rate profile curves of ethyl acetate vapor
through PET/SiOx PET/CPP and PET/EVOH/CPP

at 76°C -300ppm - non-humidified condition ----------

Temperature dependence of transmission rate for

Page

-52

ethyl acetate vapor through PET, SiOx PET and EVOH - - - - 56

Transmission rate profile curves of ethyl acetate vapor
through SiOx PET and EVOH

at 22°C -190ppm - 87% and 56% RH. .................

Effect of retorting time on the transmission rate
of Ethyl acetate vapor through PET/SiOx PET/CPP

(Retort temperature 120°C) .........................

Effect of retorting time on the transmission rate
of Ethyl acetate vapor through PET/SiOx PET/CPP

(Retort temperature 125°C) .........................

Effect of retorting time on the transmission rate
of Ethyl acetate vapor through PET/SiOx PET/CPP

(Retort temperature 130°C) .........................

Transmission rate profile curves of ethyl acetate vapor

through PET/SiOx PET/CPP (Not Retorted Pouches) -----

Effect of retorting temperature on the transmission
rate of ethyl acetate vapor through PET/SiOx PET/CPP

(Retort time 20min.) ...............................

Effect of retorting temperature on the transmission
rate of ethyl acetate vapor through PET/SiOx PET/CPP

(Retort time 40min.) ...............................

Effect of retorting temperature on the transmission
rate of ethyl acetate vapor through PET/SiOx PET/CPP

(Retort time 60min.) ...............................

xii

-60

-63

-64

-65

-67

-68

-69

-7O

31

32

33

34

35

36

A1

A2

Dependency of transmission rate of ethyl acetate vapor
through PET/SiOx PET/CPP on retorting temperature -- -- 74
Dependency of transmission rate of ethyl acetate vapor
through PET/SiOx PET/CPP on retorting time ----------- 75
Micrographs of SiOx surface - retorted at 120°C -------- 78
Micrographs of SiOx surface - retorted at 125°C -------- 79
Micrographs of SiOx surface - retorted at 130°C -------- 80
Micrographs of SiOx surface - retorted at 120, 125

and 130°C ----------------------------------------- 81
Ethyl acetate calibration curve for

gas chromatograph 5890 ---------------------------- 89
Ethyl acetate calibration curve for

gas chromatograph 5830 A --------------------------- 90

xiii

INTRODUCTION

Ethylene vinyl alcohol copolymer (EVOH), polyvinylidene chloride
(PVDC) and meta xylene diamine nylon (MXD-6) are well known plastic
high barrier polymeric materials. Recently, development of a new high
barrier silica deposited film has been the subject of major interest for
various packaging material related manufacturers (Brody, 1988;
Sakamaki and Kano, 1989). This film, which is based on silicon oxide
deposition onto polyethylene terephthalate (PET), exhibits a number of
important characteristics such as:

1) Excellent and stable barrier properties: It has very high barrier
properties for water vapor and oxygen. Furthermore, the barrier
properties are influenced little by variation of temperature or
relative humidity.

2) Transparency: Inside contents are visible through this film.

3) Retortability: It can sustain the retort sterilization process.

4) Microwaveability: Unlike aluminum foil and aluminum metallized

film, this film can be safely used in the microwave oven.

This silica deposited film was commercialized as a retort pouch
material in lamination with PET and polypropylene in Japan, in 1988
(Sasaki, 1988). This material allows microwave reheating of the pouch
contents (e.g. pasta sauces), prior to serving.

Since its introduction in 1988, several reports have been published

on the water vapor and oxygen barrier properties of the silica deposited
film, and the barrier data compared to other high barrier films (Toppan,
1988; Brody, 1988; Kaiho, 1990). The articles published indicated

that this film also has good aroma and flavor barrier characteristics.
However, data on the permeation of organic molecules through this film
have not been presented. Since this material shows both excellent

water vapor and oxygen barrier properties, packaging designers assumed
that this film would also have good organic vapor barrier

characteristics. Although this assumption is intuitive, no researcher

has engaged in a systematic investigation of this subject.

This study, therefore, focuses specifically on determining the
transmission rate of organic vapors through a silica (inorganic)
deposited polyethylene terephthalate film (SiOx PET), as compared to
other high barrier film structures, under similar conditions of test.

Objectives of the proposed study include:

1) Determination of the vapor transmission rate of ethyl acetate
through silica deposited film, as well as through other high

barrier films and laminate structures, under varying temperature

and relative humidity regimes.

2) Evaluation of the permeation of organic vapor through retort

pouch structures which contain a silica deposited film barrier

layer, before and after the retort sterilization process.

3) Characterization of processing-induced damage of the SiOx
coating layer and its relationship to mass transport property

changes.

LITERATURE REVIEW

Silica Deposited Film

l i f 'i
The vacuum coating of polymer films with transparent metal oxides

has been known since 1964 (Krug and Rt'ibsam, 1990a), and was
developed to improve the barrier properties of polymeric films to
oxygen and water vapor. Processes for the continuous coating of silica
oxide (SiOx) onto a polymer web by vacuum deposition had been
developed by DuPont de Nemours and Company (DuPont,1964), and also by
Unitica Co., Ltd. (Unitica, 1972). However, the lack of a low cost
production technology and a low demand from the end user-market's
made these products unsuccessful (Sakamaki and Kano, 1988).

Recently, however, the increasing number of microwave ovens in
households in both the United States and Japan has resulted in a
corresponding increase in the demand for microwaveable food packaging.
For example, in United States households, the penetration of microwave
ovens reached approximately 80% (Martin, 1988). In 1988, silica oxide
deposited film was, for the first time, commercialized as a retort
pouch material in lamination with polyethylene terephthalate (PET) and
polypropylene by the cooperative work of the following Japanese firms;
Toppan Printing Co., Ltd., Ajinomoto Co., Ltd. and Toyo Ink Manufacturing

Co., Ltd. (Sasaki, 1988). This material allowed microwave reheating of

the pouch contents (e.g. pasta sauces) prior to serving, with the silica
deposited PET layer exhibiting similar functional properties as
metallized films, in terms of laminate structure and barrier properties
to oxygen and water vapor. The structure of the silica deposited film

and its typical pouch structure are shown below (Figure 1 and 2).

E |' [ST E 'l IE'I

The efficient coating of metal oxides, such as silica oxide to
polymer films required development of new processing techniques,
since the physical properties such as vapor pressure and evaporation -
not from the liquid but from the solid state - are completely different.

To be effective, silicon monoxide (SiO) has to be reactively evaporated
to get a SiOx coating with barrier properties. The oxygen content (x)
varies from 1.5 to 2, in accordance with the evaporation conditions
(SiOx, where 1.5 < x < 2).

SiOx coatings are generally produced by evaporation of silicon-
monoxide (x=1) either by thermal or by electron beam gun evaporation
(Krug and Riibsam, 1990a). The thermal process involves vacuum web
coaters, using intermetallic boats as point sources across the web
width. The web speed is limited, however, by the SiO evaporation rate
from the boats, and nonuniformity at the highest evaporation rates
(Krug and Rubsam, 1990b).

Electron beam vacuum coating indicates that the power required to
enable thermal evaporation of a coating material is supplied by means
of an electron beam (Krug and Ludwig, 1990). The power conversion

efficiency of an electron beam is better than with conventional sources

 

Silica oxide coating
(SiOx)

PETIZu

 

   

W

Figure 1. Cross-sectional view of the silica deposited PET
film.

 

PET 1211

W Adhesive

Silica deposited PET 1211

W Adhesive

Cast polypropylene (CPP)
601.1

 

 

 

Figure 2. Cross-sectional view of a typical retort pouch
structure with silica deposited film.

for thermal evaporation. Furthermore, electron beam guns are
applicable to several metals and metal oxides (Krug and Rilbsam,
1990b)

Since SiO is sublimed from the solid state and is not simply
evaporating from a liquid surface, a special crucible is necessary (Krug
and Rt'ibsam, 1990a). For commercial production, a relative web speed
of approximately 4 m/s, with an evaporation temperature of
approximately 1350°C is observed. The vapor of SiO is oxidized in a
controlled reactive atmosphere to achieve a degree of oxidation

between x a 1.5 and 1.8 (SiO1 .5 - SiO1 .8), with a thickness of 800A.

Generally SiOx-layers are relatively fragile when the coating thickness
is less than 1500 A, and its chemical inertness makes it corrosion
resistant. Further, the barrier and mechanical properties of the silica
oxide deposited PET based retort pouch are not adversely affected by
moisture during retorting (Sakamaki and Kano, 1989). In addition, the
surface is printable, and not affected by the inks (Chahroudi, 1989).
Typically the SiOx coating consists of a mixture of SiO (silicon
monoxide), Si203 (disilicon trioxide) and Si02 (silicon dioxide), and it,
therefore, has a slightly yellowish appearance (Krug and Riibsam,
1990a). In contrast to evaporated aluminum, which has a
microcrystalline structure, SiOx is deposited as a glassy network and is
therefore totally amorphous. The transparency and the barrier
properties are mainly influenced by the coating thickness and chemical
composition. The effect of coating thickness, at a fixed chemical
composition (i.e. fixed oxygen content), is shown in Figure 3, where

oxygen transmission rates are plotted as a function of coating

 

 

 

 

 

100
O
'6'
"E o
a?
ES. 10 . 17 PE'I'19 pm.
X. .
o. 4 \g“ 0
g 2 ‘~~~‘W
(é x-1.5 I’m
1

3
6

 

 

 

'—

20050 6006001000

coating thickness IA]

Figure 3. Oxygen permeation through SiOx deposited PET as a

function of coating thickness (Krug and Riibsam,
1990b).

18

 

16-4
14%|
121
104

6-i
4-1

02-permealion [cmal r112 d]

 

qufi

1,5

PE‘I’19 pm

 

I I T I

1.6 1,7 1,8 1,9 2
X -)

Figure 4. The effect of chemical composition on the oxygen

permeation through SiOx deposited PET (Krug and
Rinsam, 1990b).

thickness. The general behavior of oxygen permeation as the function of
coating thickness is similar to that of metallized films, where with
increasing coating thickness the oxygen permeation rate decreases
drastically (Krug and Riibsam, 1990a).

However, the mechanism for permeation is different. While
aluminum coatings are a microcrystalline structure, the silica coatings

are comprised of an amorphous glassy network of SiO, Si203 and SiOz.

These coatings are nearly free of pin-holes and oxygen permeation takes
place through the glassy network itself, as compared to transmission
through pinholes, which is the case for aluminum metallized film (Krug
and Rubsam, 1990b).

The mechanism of nucleation and growth of the layer is also similar
to aluminum metallization. Therefore the general barrier behavior is

similar; with increasing coating thickness the O2 permeation rate

decreases until a layer thickness of approximately 600 A, beyond which
no further reductions in oxygen transmission rates observed (Figure 3).
As SiO is a two-element-system, the properties of the coating are
generally influenced by the layer thickness and the chemical
composition, or degree of oxidation (oxygen content). The effect of
chemical composition on the barrier properties of SiOx deposited PET

film is shown in Figure 4 (Krug and Riibsam, 1990b).

W
The structure of silica deposited film (GL film) consists of a base
film and the SiOx coating. GL film is a trademark of the silica
deposited PET film produced by the Toppan Printing Co., Ltd. The amount

of oxygen permeating through the SiOx coated structure decreases to
1/100 that of the uncoated base film (biaxially oriented polyethylene
terephthalate BOPET 12p). Further, when silica deposited film is
laminated with the other films to provide a multi-layer retortable
material, the level of oxygen permeation decreases to 1/300, the rate
of the uncoated base film (See Table 1). The oxygen barrier properties
of this laminated silica deposited film are better than that of
polyvinylidene chloride (PVDC) or polyamide, and slightly higher than
that of EVOH, at dry conditions (Table 2). As a transparent, high barrier
packaging material, this barrier level, 0.50c/ m2 day atm allows a long
shelf life for most processed foods. Another important property of the
silica deposited film is the limited effect of temperature and humidity

on the films barrier properties. Kaiho (1987) stated that high humidity
conditions have little effect on SiOx film's oxygen permeation rates,

and its temperature dependency is also relatively low.

WEIR!

The moisture barrier properties of silica deposited film (GL film) is
also excellent. Silica deposited film shows only 1/40 the moisture
transmission rate (Water Vapor Transmission Rate, WVTR) of the
uncoated base film (PET,12 u). Lamination with cast polypropylene
(CPP) film reduces the WVTR to less than 1/100 (Table 3) of the base
film. In comparison to other commonly used barrier films, the silica
deposited film's WVTR (0.5 g/ m2 day) is equivalent to that of a
laminated aluminum metallized film, and that of 500p CPP (Table 4). In
production, the 1.0 g/m2 day WVTR is a difficult target for transparent

10

Table 1- Oxygen Permeance of PET. SiOx PET and SiOx PET
laminated structure. (a)

 

Structure 0W
PET 1211 155
GL film: PET 12p lSiOx coating 1.5
PET 12p / GL film ICPP 60p 0.5

 

Units of 02 permeance - cc/m2 day atm at 25 °C, 70% RH
(a) from Sakamaki and Kano, 1989

Table 2. Oxygen permeance of SiOx laminated film and other
laminated films. (a)

 

Structure Oxyggnmtmeange—
PET 12w GL film/ CPP 60p 0.5
ONy 25p! onclbhsu/ CPP sou 10.5
PET 12w oncl°l15w ONy 15w CPP 6011 1.6
PET 12w onclclzsw ONy 15w CPP 60)). 1.0
1 PET 12w EVOH(d)15u/ CPP 601.1 0.3
osulehstuONy 15w CPP 6011 3.8
ONy 25w CPP sou 15.6

 

Units of O2 permeance - cc/rn2 day atm at 25 °C, 70% RH
(a) from Sakamaki and Kano, 1989

(b) KUREHACO. "K-Flex"

(c) ASAHI KASEI CO. "SARAN U8"

((1) KURARE CO. ”EVAL"

(e) 10m "OSM: metaxylen diamine-adipic

acid copolymer

11

Table 3. Water vapor transmission rate of PET, SiOx PET and
SiOx laminated structure. (a)

 

Structure WVTR
PET 12p 47
GL film: PET 12p. ISiOx coating 1.2
PET 121.1 / GL film ICPP 60p 0.5

 

Unit of WVTR - g/m2 day at 40°C, 100 RH.
(a) from Sakamaki and Kano, 1989

Table 4. Water vapor transmission rate of SiOx laminated film
and other laminated films. (a)

 

Structure WVTR

PET 1211/ GL film/ CPP 6011 0.5
KOP 25p! CPP 25p 4.0

. OPP 25w EVOH 15w CPP 251.1 2.5
ONy 25w CPP 6011 7.8
PET 12w AL metallizing/ CPP 251.1 0.6
CPP 5001.1 0.5

 

Unit of WVTR - g/m2 day at 40°C, 100 RH.
(a) from Sakamaki and Kano, 1989

12

flexible films of less than 100p thickness, even though PVDC coated
oriented polypropylene (OPP) or high density polyethylene (HDPE) are
_ used (Sakamaki and Kano, 1988).

Mobility

Table 5 lists the oxygen permeance of several laminated barrier
films, before and after retort processing (125°C-20 min). As shown,
laminated GL film experienced minimum change in oxygen permeance
following retort processing, maintaining a permeance of less than
1cc/m2 day atm.

A comparison between silica deposited film and other barrier
materials used in food packaging in terms of oxygen barrier, water
vapor barrier, retortability, microwaveability and transparency is

presented in Table6 (Toppan, 1989).

AnAItematileAmmaQtl

An alternative method to manufacture silica deposited films was
developed by The EASTPAC Company, a joint venture between Airco
Coating Technology and Eastman Chemical Company (Eastman News,
1990). The commercialization of a chemical plasma deposition system
for the application of a high gas barrier transparent coating was
announced by the company under the QLF® (Quartz-Like Film) coating
trademark.

The plasma enhanced chemical vapor deposition (PECVD) process is

13

Table 5. Oxygen permeability of SiOx laminated film and other
ilms before and after retort process. (a)

 

Structure 02 permeability Ozpermeability
before reto rting W
PET 1211/ GL film/ CPP 6011 0.5 0.7
ONy 2511/ oncibhsu/ CPP 6011 10.5 8.2
PET 12u/PVDC(°)15u/0Ny 15u/CPP 601.1 1.6 2.6
PET 12vaoclcizsu/0Ny 15u/CPP 60):. 1.0 1.6
PET 1211/ EVOH(d)15u/ CPP 60p 0.3 16.6
CHM(°)15u/ONy 15w CPP 60); 3.6 6.0
ONy 25p! CPP 6011 15.8 21.5

 

(a) from Sakamaki and Kano, 1989

(b) KUREHA CO. 'K-Flex"
(c) ASAHI KASEI CO. ”SARAN UB"
' (d) KURARE CO. 'EVAL"
(e) TOYOBO "OSM: metaxylen diamine-adipic

acid copolymer

Retort condition: 125 °C - 20 min.

Unit of O2 permeability a cc/m2 day atm at 25 °C, 70% RH
Pouched material: water/oil - 1/1 mixed material

14

Table 6. Comparison among silica deposited film and other

barrier materials.‘ 5‘)

Silica Aluminum Aluminum EVOH PVDC
deposited foil metallized
fi l m fi l m

 

Oxygen barrier
25°C - Dry Good Good Good Good Good

HiTemp-Hi RH Good Good Good Low-Med Medium

W.V. barrier Good Good Good Poor Medium

Retortability Good Good Poor(b) Poor-Good Medium

Microwave-
ability Good Poor“) PoorId) Good Good
Transparency Goodie) No hb Good Good

 

. (a) from Toppan, 1989
(b) Delamination

(0) Reflection

(d) Spark

(6) Slightly yellowish

15

a modification of the semiconductor technique. It is a cold temperature
process that is non-destructive to plastic, and employs organosillicons
as a non-toxic liquid process monomer, rather than silane gas, which is
pyrophoric. Plasma-based processing (including QLF) also offers the
advantage of being multi-directional, since a coating is deposited on all
areas where the plasma contacts a surface. PECVD enables one to
obtain uniform coatings on all types of rigid packaging, especially
packages of complex shapes, such as bottles, or coating both sides of a
surface simultaneously (Felts, 1990).

The gas barrier properties of the PECVD processed film is claimed
to be superior to the evaporated films (Felts, 1990). The EASTPAC
process also claims recyclability and cost competitiveness (Eastman
News, 1990). However, the material has not been used commercially.

Therefore its advantageous attributes are yet to be confirmed.

Permeation of Organic Vapors through Polymer Films

Since the transport of organic vapors through packaging materials
has been the subject of a number of investigations, various procedures
have been developed for quantifying the rate of diffusion of organic
vapors through barrier membranes. Pye et al. (1976) described a
continuous or isostatic procedure for measuring the diffusivity
properties of polymer membranes that used two gas chromatographs

connected to a cell. The apparatus developed by Pye et al. and Niebergall

16

(1978) was designed to allow measurement of transmission rates for
mixtures of organic vapors through barrier structures as a function of
permeant concentration, temperature, and relative humidity.

lsostatic methods were also reported by Zobel (1982) and DeLassus
(1985). Hernandez (1984) and Baner et al. (1986) also employed an
isostatic procedure for determining the permeability of organic
penetrants through polymer membranes. Analysis of permeated vapor
was based on a gas chromatographic technique with flame ionization

detection.
I 1 Hilton and N66 (1978) developed an accumulation or quasi-isostatic
test method for determining the permeability of organic vapors through
barrier films. In his 1985 publication, Murray expanded his
quasi-isostatic procedure and reported a number of examples for which
the test apparatus was employed to determine the relative permeation
rates of organic vapors through barrier structures. However these
methods (are limited to determining the transmission rates and
permeability constant values for only saturation vapor pressure of the
liquid penetrant, at a given temperature.)

Gilbert et al. (1983) evaluated the barrier properties of polymeric
films to various organic penetrants by a quasi-isostatic procedure. To
provide a constant concentration or partial pressure gradient, the
authors continually flowed a penetrant vapor stream through the high
concentration chamber of the permeability test cell. In determining the
diffusion of organic penetrants through polymer films Baner et al.
(1986) also employed the continuous flow of organic vapor through the

high concentration cell chamber to assure a constant vapor gradient. A

17

gas chromatographic method was developed for the permeation rate
measurements.

Shirakura (1987) studied the effect of temperature on the diffusion
of ethyl acetate through oriented polyethylene terephthalate films of
varying thermomechanical history. The effect of relative humidity on
the permeability of toluene vapor through a multi-layer coextruded film
containing hydrophilic layers was evaluated by Liu et al. (1988)

The transport of small molecules in polymers can also be evaluated
by sorption-desorption methods. Fujita (1961) has described the
general behavior of sorption and permeability of organic vapors. Other
authors employing sorption-desorption methods include Bischoff, et al.
(1984) and Choy et al. (1984).

Permeation Theory

Permeability is often referred to as the ease of transmission of
gases or vapors through a resisting material which has no macroscopic
pores (Paine, 1983). The transport of a gas or vapor through polymeric
films commonly used in packaging typically involves the activated
diffusion process. Such a process involved three steps; (1) absorption
of the permeating species, in which gas or vapor dissolves into the
polymer matrix at the high penetrant concentration surface; (2)
diffusion through the polymer wall along a concentration gradient; and
(3) desorption from the surface at the lower concentration (Stannett
and Yasuda, 1965).

18

The diffusion flux (F) of a permeant in a polymer can be defined as
the amount passing through a surface of unit area normal to the
direction of flow during unit time, independent of the aggregation of

polymer. That is:

F=Q/At (1)

where Q is the total amount of permeant which has passed through area
A during time t. The transfer of a diffusant through a unit area can be
expressed as being proportional to the negative gradient of
concentration at any point in the polymer. This can be described by
Fick's first law of diffusion (Crank and Park, 1968).

F = - o (dC/Dx) (2)

where D is the diffusion coefficient with units of (length)2 time ’1 (e.g.
cmzs"), x is the length in the direction in which transport of the
permeant occurs, and C is the concentration of the permeant in the
polymer. As diffusion proceeds, Fick's second law of diffusion
describes the non-steady state (Crank, 1975).

Equation (1) can be integrated, where D is independent of

concentration, to give:

F=D (c1 - 02) / L (3)

19

where C1 and 02 are the steady state concentration of the permeant at

the two surfaces of the film and L is the film thickness.

For experimental and predictive purposes it is convenient to relate
the concentration of the permeant at the polymer surface to the
concentration of permeant in the surrounding gas phase. For gases and
vapors, the permeant concentration is proportional to the partial
pressure of the permeant, through the ideal gas law equation (Henry's
Law). The concentration of the permeant in the polymer, C, can thus be

expressed by:

C = ($0) (AP) (4)

where the solubility (Sp) is a function of temperature and may be a

function of the partial pressure (Ap) or C. When Henry's law is assumed:

C = S (Ap) (5)

where S is the Henry's law solubility coefficient, which is independent
of Ap and C (Crank, 1975). Substitution in equation (3) yields:

F=DS (p1 - p2) / L (6)

where p1 and p2 are the permeant partial pressures at the two surfaces
of the film, and the product D‘S defines the permeability coefficient
(P), by the relationship D‘S = P (Barrer, 1939).

When both D and S are independent of penetrant concentration, P is

20

a constant at any given temperature. However, where considerable
Interaction between the polymer and the permeant takes place, P is no
longer constant but will vary with C and Ap (Zobel, 1982; Hernandez et
al., 1986 and references cited therein ). For the specific case, where
the diffusion coefficient is time-dependent, the transmission process
will be anomalous and it is said to be non-Fickian (Fujita, 1961; Meares,
1965; Crank and Park, 1968).

Permeability Measurements

Experimental methods and test apparatus for performing
permeability measurements have been described by a number at
investigators (Rogers, 1956; Zobel, 1982; Hernandez et al., 1986). One
common method for determining permeability is the quasi-isostatic
method, or the accumulation method. In this method, the permeated gas
or vapor is accumulated and monitored as a function of time. A
generalized transmission rate profile curve describing the transport of
a permeant through a polymer film by the quasi-isostatic method is
illustrated in Figure 5.

The permeability coefficient, P is calculated as:

13: _L
AtAb (7)

where Q is the quantity of gas or vapor which has permeated in the

21

 

Total Quantity Permeated (Q)

 

 

I
l—- 0 -—1 Time (t)

Figure 5. Generalized transmission profile curve for the quasi-
isostatic method.

22

time interval At in the steady state of flow. A is the area of the film
exposed to the permeant. L is the average film thickness, and b is the
driving force given by the concentration or partial pressure gradient.
For the specific set of experimental conditions, where the film is
initially free of permeant and the receiving volume is maintained at
essentially zero concentration of penetrant, Barrer (1939) has shown

that the diffusion coefficient can be calculated by:

[)= _L?_
6 6 (8)

where 6 is the intercept of the time axis of the extrapolated linear
steady state portion of the curve (Figure 5) and is called the lag time.
Therefore, in theory, all three parameters can be calculated from the
quasi-isostatic method; P from the steady state flux; D from the lag
time; and S from P/D.

MATERIALS AND METHODS

Materials
Eilmfiamoles
In this study, three different films and three different laminate film
structures were investigated. These films were obtained from Toppan

Printing Co., Ltd.(Tokyo, Japan).

1) Films
3. PET,1 211m (0.5 mil) Polyethylene Terephthalate (as a base film]
b. SiOx PET, 12pm (0.5 mil) Silica deposited PET.
Thickness of SiOx : 1200 A, fixed oxygen content x: 1.7
c. EVOH,15 um (0.6 mil) Ethylene Vinyl Alcohol Copolymer
(EVAL-F)
‘ A cross-sectional view of the silica deposited PET film is depicted in

Figure 1.

2) Composite Films

a. PET 12pm / PET 12pm / CPP 60pm [as a base pouch]

0. PET 12pm / SiOx PET 12pm / CPP 60pm

0. PET 12pm / EVOH 15pm / CPP 60pm

A cross-sectional view of the laminated silica deposited PET film is
depicted in Figure 2.

23

24

PET 12pm: Degree of Orientation -- 350% based on initial
dimensions (biaxially)

% Crystallinity - 56%

EVOH 15pm: EVAL - F (Ea-32%)

SiOx PET 12pm: PET 12pm described above was coated with silica
oxide layer by Toppan Printing Co., Ltd.(Tokyo,
Japan)
Thickness of SiOx : 1200 A, fixed oxygen content
x= 1.7

CPP 60pm: Retort grade as a heat seal layer

Adhesive: Urethane type (Retort resistant)

861063111100

Retort pouches were analyzed to evaluate the effect of retort
sterilization process on the composite film. The retort pouch

structure was identical to the composite film (b).

Structure PET 12pm/SiOx PET 12pm/CPP 60pm
Size 130mm x 170mm, three sides sealed
Eenmeam

Ethyl acetate was used as the organic vapor permeant. The
selection is based on the ease of analysis and the known contribution
of this compound to the aroma profile of food products.

Research grade ethyl acetate was obtained from Aldrich Chemical
Co. Inc. (Milwaukee, WI) and was employed throughout, as the

permeant vapor.

25

CartieLGas
High purity dry grade nitrogen gas produced by AGA Inc. (Cleveland,
OH) was employed throughout the experiment as the carrier of the

permeant.

Procedure

E | TI I l |

The permeation test system, based on the quasi-isostatic method,
was designed, assembled and tested as part of this study. Figure 6
presents a schematic diagram of the permeation test apparatus. It
allows the collection of permeation data as a function of temperature
and vapor concentration.

The permeability cell, constructed of aluminum, is composed of
two cell chambers and a hollow center ring. The right and left cell
chambers each have a volume of 50 cm3; the volume of the center
cavity is approximately 50 cm3. In operation, the test films are
placed in the cell so that the center ring effectively isolates the right
and left cell chambers. Hermetic isolation of the chambers from each
other and from the atmosphere is achieved by the compression of
overlapping Viton O-rings on the film specimen. Viton is a
fluorocarbon elastomer that is resistant to attack and swelling
by most organic vapors. The cell chambers and the center ring are
equipped with an inlet and outlet valve and sampling port. The films

to be tested are mounted in the permeability cell and the cell

26

  

  
 

 

——- -——d

  

B - Water bath, generation of permeant Pc - Permeability cell
vapor phase diluted In Nitrogen R - Rotameter
H - Oven T - Nitrogen tank
V,I - Organic vapor generator

N - Needle valve

Figure 6. Schematic of permeation test apparatus for non-
humidified condition.

27

assembled. A constant, low partial pressure of permeant vapor is
then flowed through the center cell chamber at a flow rate in the
range of 5 to 10 ml/min. This allows the permeability of two film
specimens to be determined concurrently, under identical conditions
as reported by Baner et al. (1986).

A constant concentration of permeant vapor is produced by
bubbling nitrogen gas through the liquid permeant. This is carried out
by assembling a vapor generator consisting of a gas washing bottle,
with a fritted dispersion tube, containing the organic liquid. To
obtain a lower vapor concentration, the permeant vapor stream is
mixed with another stream of pure carrier gas (nitrogen). As shown
in Figure 6 flow meters were used to provide a continuous indication
that a constant rate of flow was maintained. Gas flow was regulated
with NU PRO needle valves, Type B-25G. The vapor generator system
was kept at a constant temperature of 21 :l: 1°C. The penetrant vapor
concentrations are expressed throughout in ppm (mass/volume) vapor
in nitrogen, where 1 ppm equals 1ug ethyl acetate per cm3 of gas
mixture al 1 atm and 21°C.

To determine the effect of relative humidity on the permeation of
ethyl acetate vapor through barrier films, another test apparatus was
assembled. The major difference between the two test apparatus is
found in the vapor generator. The vapor generator system of the
second apparatus consists of three gas washing bottles with fritted
dispersion tubes, connected as shown in Figure 7. One gas washing
bottle (81) contained the liquid penetrant, a second gas washing
bottle (82) was filled with a mixture of distilled water and the

28

 

 

lat-516.3%-

-—--——— —_._..JW

 

 

.
... TV

it

[Penneation Cells

1

Ho

 

 

8r Organic vapor bubbler
82-Organic/water vapor bubbler
BJ-Water bubbler

(If-Four way valve

l-I - Hygrometer

Flo-Hood

Figure 7. Schematic of permeation test apparatus for
evaluating the effect of relative humidity.

29

organic liquid penetrant. The third gas washing bottle (B3) contained
pure distilled water. Needlevalves and flow meters were used to
obtain the desired penetrant concentration and relative humidity. The
humidified organic vapor stream was mixed with another stream of
nitrogen in order to obtain a lower than saturation concentration of

penetrant vapor.

Operation

In the Quasi-lsostatic procedure, the increase in penetrant
concentration in the lower concentration cell chambers was
determined by gas chromatography with flame ionization detection.
At predetermined time intervals, 0.5 ml of headspace gas was
removed from the right and left cell chambers with a gas-tight
syringe and injected directly into the gas chromatograph. A constant
total pressure of 1 atm was maintained throughout the run in both the
high and low permeant concentration cell chambers. A constant
pressure in the high concentration cell chamber was maintained by
continually flowing the vapor stream through the high concentration
cell chamber and discharging it at atmospheric pressure. To maintain
a constant, total pressure in the low concentration cell chamber, the
volume of headspace gas removed for analysis was replaced with an
equal volume of nitrogen.

The quantity of vapor permeated with time was monitored until a
steady-state rate of diffusion was maintained. In analyzing the
resultant data, the total quantity of organic vapor permeated as a

function of time was included, up to a level at which the vapor

30

concentration in the low concentration cell chambers did not exceed
3% of the penetrant concentration in the high concentration cell
chamber, that is, the center chamber. The low concentration cell
chambers should be purged of residual organic moieties using nitrogen

gas (N2) before the test run was initiated.

The film specimens in non-humidified condition measurements

were stored in a desiccator over calcium sulfate (CaSO4) desiccant

for two weeks at ambient temperature (23°C) prior to being tested.

As for the film specimens in humidified condition, humidity
conditioning was achieved by storing samples at ambient temperature
in relative humidity chambers of 57% and 87% RH, respectively.
These humidity conditions were maintained using various standard

salt solutions.

B | I' E .
Retort pouches used in this study were provided by Toppan
Printing Co., Ltd. (Tokyo, Japan). The specification of the pouches and
the conditions of retorting are described below. Retorting was
performed at three retorting temperatures, and with three retorting

times per temperature, to obtain 9 different samples.

Structure PET 12urn/SiOx/PET 12urn/CPP 60 um
Size 130mm x 170mm, three sides sealed
Content Distilled water (cold fill)

Volume 180 ml

Head Space Approximately 5cc

31

Retort Equipment RCS - 40RTG. N, Hisaka Works, Ltd. (Osaka, Japan)
Retort Conditions Temperature 120°C, 125°C, 130°C
Retorting Tlme 20min, 40min, 60min
Retorting Pressure 2.0 kg/cm2 at 120°C
2.1 kg/cm2 at 125°C
2.2 kg/cm2 at 130°C

Analytical

6 III | I . E I .

Analysis of permeant concentration was carried out by a gas
chromatographic procedure. A Hewlett-Packard Model 5890 gas
chromatograph equipped with flame ionization detection interfaced to
a Hewlett-Packard Model 3392A integrator was employed for
quantification for non-humidified test conditions. A Hewlett-Packard
Model 5830A gas chromatograph equipped with dual flame ionization
detection, interfaced to a 18850 A GC Hewlett-Packard terminal was
used for permeant detection at high relative humidity. The gas
chromatographic conditions are presented in Table 7.

The stationary phase of the capillary column (Supelcowax 10)
employed with the HP 5890 gas chromatograph was found to degrade
upon exposure to water vapor. Therefore, in the studies designed to
evaluate the effect of sorbed water on the films barrier
characteristics, analyses were carried out on the HP 5830A gas

chromatograph where the stationary phase was known to be

32

Table 7. Gas chromatographic conditions for 5890 and 5830 A.

ModeL5890

Column:

Carrier gas:

Temperature:

60 meter;

025mmLD"

Fused silica capillary;

Polar bonded stationary phase;

Supelcowax 10 (Supelco. lnc., Bellefonte, PA)
Helium at 32.6 mein.;

Injection temperature -- 180°C;

Detector temperature -- 250°C;

Oven temperature -- 150°C;

Temperature program rate -- 0°C/min.;

Retention time of ethyl acetate: 5.14 min.;

ModeliBflQA

Column:

Carrier gas:

Temperature:

10% Cabowax, 20M on 80/100 Supelcoport
(Supelco. lnc., Bellefonte, PA)

1/8" 00. x 6 ft. Stainless steel packed column
Helium at 33 ml/min.;

Injection temperature -- 175°C;

FID temperature -- 350°C;

Oven max temperature -- 225°C;

Column temperature -- 165°C;

Retention time of ethyl acetate: 0.98 min.;

33

unaffected by moisture.

A standard curve of detector response versus absolute quantity
was constructed from standard solutions of known concentration for
each gas chromatograph (Appendix A).

Standard solutions were prepared by dissolution of known

quantities of ethyl acetate in dichlorobenzene.

El' [S'QSI IDl'lll'

Analysis of the SiOx barrier coating on the composite retort pouch
structures was carried out with an optical microscope Olympus BH-2,
with an exposure control unit. The SiOx surface layer was examined
following retort processing, and also following completion of the
permeability studies. Approximately 1 cm2 specimens were cut from
the center of the retort pouches, the samples were then mounted on a
glass microscope slide and examined at 150 x magnification. The
samples were mounted with the cast polypropylene surface in contact
with the glass slide, with light transmission from the underside.
Photographs of the surface were taken with Polaroid 52 PolaPan 4x5

instant sheet film.

RESULTS AND DISCUSSION

Determination of the Appropriate Conditions
for the Permeation of Ethyl Acetate Vapor
through SiOx PET Film and Other Test Films

El" Sll'

Due to the paucity of data available on the permeation of organic
vapor through SiOx PET film, the appropriate conditions of temperature
and concentration of the ethyl acetate vapor were determined in a series
of preliminary studies prior to performing the proposed permeability
tests. As for the base PET film, it is known to have good organic vapor
barrier properties, compared to other plastic films. For example,
Shirakura (1987) reported that at 37°C, 0% RH and 300 ppm (wt/v) of
ethyl acetate vapor, no measurable permeation was observed through PET
. film (31% crystallinity) after 550 hours. The upper level of the
transmission rate was estimated to be less than 4 x 10'7 g/m2 hr.

In accordance with the above data, preliminary studies were carried
out at four test conditions, in order to determine the appropriate
conditions of temperature and vapor concentration for the analysis of the
permeation of ethyl acetate vapor through SiOx PET film. The first
condition was 22 :l: 1°C, 91 ppm vapor concentration, the second condition
was set at 50 :l: 1°C, 91 ppm. The third condition was also set at 50 :t 1°C,

but with 237ppm vapor concentration, and the last condition was 65 1:1 °C,

34

35

288ppm. The relative humidity was set at non-humidified level for all
the conditions of test.

The transmission rate profile curves for SiOx PET, PET, EVOH and
PET/PET/CPP are presented in Figure 8, where the total quantity of ethyl
acetate permeated in micrograms is plotted as a function of time for the
respective test regimes. Since good agreement was observed between
replicate samples, the reported data are the average of replicate runs,
with a confidence limit of 118% (maximum). Figure 9 presents the
permeation data for ethyl acetate vapor through PET film (as a
non-coated base film) and SiOx PET to illustrate the effect of the silica
oxide deposited layer on the barrier properties of the composite
structure.

Figure 10 presents the permeation data for ethyl acetate vapor
through SiOx PET and EVOH, to provide a comparison of these two high
barrier films. Figure 11 illustrates the stability of the center cell
concentration of ethyl acetate vapor. The fluctuation was :l:7%

. throughout all experiments. Scatter band of oven temperature was 11°C
throughout all experiments.

The results from the preliminary studies showed no measurable rate
of permeation for SiOx PET film at 50°C - 91 ppm and minimal
transmission levels at 50°C - 237ppm, although the driving force was
increased 2.5 times. As for EVOH, the increase in transmission rate over
the same concentration range was also small. However, at 65°C -
288ppm, a significant rate of permeation was observed for both of the
high barrier films. Based on the result of these studies, test condition of

65 and 76°C and a vapor concentration at 300 ppm (wt/v) were selected

36

to evaluate the effect of temperature on the permeation of ethyl acetate
vapor through SiOx PET film. These findings further indicate that
permeation rate values of SiOx PET and EVOH are more dependent on

temperature than on ethyl acetate vapor concentration.

37

 

 

 

200
a O
E 122 0| 50°C-91PPm 50°C-237ppm
g 91ppm
“CE; 150' 0 PET
g o ' SiOx PET
‘6 1: m4
“8’ 100-
E 9* PET/PET/CPP
2: ' *
=1 i
(St 50 " ' , 65°C-288ppm
O
E
‘6
I'-

 

 

 

 

 

Time (hours)

Figure 8. Transmission rate profile curves of ethyl acetate
vapor through SiOx PET and other films in
the determination of appropriate conditions.

38

 

 

50
1 o o PET
22°C '
4o 1 e Sle PET
91 ppm
50°C-919W" 65°C-288ppm
3° _ 50°C-237ppm

 

 

 

Total Quantity Permeated (micrograms)

 

     

 

 

2°-
10- a)”,
0 I I 1 '
0 200 400 600 800

Time (hours)

Figure 9. Transmission rate profile curves of ethyl acetate
vapor through PET and SiOx PET in the determination
of appropriate conditions.

39

 

 

 

 

 

 

 

 

75

E 22°C|| 65°C-288ppm
3 15 2‘ 99'“ 50°C-237ppm
'55" 50°C-91 ppm
'0

9' ' PET

.

g 10 - Sle

E n EVOH

O. a

E

E

w

a

o

_ U

E

O

I- I t

0 2 0 o 4 o o 6 0 0 8 0 0

Time (hours)

Figure 10. Transmission rate profile curves of ethyl acetate
vapor through SiOx PET and EVOH in the
determination of appropriate conditions.

 

4O

 

 

 

 

I Conc. Cell PET
0 Cone. Cell SiOx PET
400 0 Cone. Cell PET/PET/CPP
6 Cone. Cell EVOH
+ Conc. Cell (NEW)
0
30° " — 288ppm H—é-Q
3 t
i 86 1‘
237ppm W
200 -

Concentration in Center Call (ppm)

 

100 M91 ppm

 

 

 

 

 

 

I I
400 600 800

Time (hours)

Figure 11. Stability of the center cell concentration of ethyl

acetate vapor.

41

The Effect of Temperature on the Permeation of
Ethyl Acetate Vapor through SiOx PET Film

W

The transmission rate profile curves for SiOx PET, PET, EVOH,
PET/SiOx PET/CPP, PET/PET/CPP and PET/EVOH/CPP are presented in
Figure 12, where the total quantity of ethyl acetate permeated in
micrograms is plotted as a function of time. The test conditions for all
experiments were 65°C - 300ppm - non-humidified condition. Since good
agreement was observed between replicate samples tested in the same
run, the reported data are the average with a confidence limit of 13%
(maximum). For ease of comparison, Figure 13 presented permeation data
for ethyl acetate vapor through films which permeated at a rate less than
0.05 x 10‘6 g/hr, that is, films other than PET and PET/PET/CPP.

Figure 14 showsthe transmission rate profile of ethyl acetate vapor
through PET and PET/PET/CPP, to compare a base film and its composite
structure. As shown, the general shape of the transmission profile curve
' indicated typical Fickian behavior, where an initial induction time, a
non-steady state and a steady state rate of transmission were observed
(Crank, 1975). The permeation rate of ethyl acetate vapor through PET
was approximately twice that of PET/PET/CPP.

Figure 15 depicts the transmission rate profile curves of ethyl
acetate vapor through SiOx PET and EVOH, to compare the two high barrier
films. EVOl-l showed typical Fickian behavior, while the SiOx PET
appeared to show atypical behavior during the initial transport period.

For the first 24 hours, permeation through the SiOx PET film was not

42

(65°C-300ppm- Non-humidified condition)

 

 

 

 

300
’g o 0 PET
to 1 '
g» 0 SiOxPET
g 200.. . n M1
E 1» PET/PET/CPP
E? a PET/EVOl-l/CPP
E
6 s PET/SiOx PET/CPP
°- 100-
.E‘
E
(B
3
o
E ___.,, _______ ...-5-7
'2 0 24-. - .3;- 1- g.;§r§-gggf!’ 1 j I

0 100 200 300 400 500

Time (hours)

Figure 12. Transmission rate profile curves of ethyl acetate
vapor through SiOx PET and other films
at 65°C -300ppm - non-humidified condition.

43

(65°C-300ppm- Non-humidified condition)

 

 

 

 

 

so
’13 .
g 0 Sle PET
‘5': 1: am
E 20 . 1: PET/EVOI-l/CPP
'3 e PET/SiOx PET/CPP
if
m l
E
d)
O.
.E‘ 10-1
‘5
(U
3
0 1
a _ .
‘5
'—
o I V l ' I 1 I ‘
o 100 200 300 400 500

Time (hours)

Figure 13. Transmission rate profile curves of ethyl acetate
vapor through SiOx PET and other high barrier films
at 65°C -300ppm - non-humidified condition.

 

44

(65°C-300ppm- Non-humidified condition)

 

 

 

 

 

 

300
E 0 PET
g o
g ‘ o PET/PET/CPP
is
E. 200..
13
2
(U
0
E
0
0.
g 100-
E
w
:I
0
T9
0
i' 0 . , .
0 100 200 .300

TIME (hours)

Figure 14. Transmission rate profile curves of ethyl acetate
vapor through PET and PET/PET/CPP
at 65°C - 300ppm - non-humidified condition.

45

(65°C-300ppm- Non-humidified condition)

 

 

30
a

g 0 SiOxPET
6

.§ In EVO-l
E 20-

1!

<0

‘6 .

0

E

0

°' 10-

E:

E

as

3

o

.7!

O

'- 0". T '

 

 

     

 

- U I I I l U
0 100 200 300 400 500

TIME (hours)

Figure 15. Transmission rate profile curves of ethyl acetate
vapor through SiOx PET and EVOH
at 65°C ~300ppm - non-humidified condition.

46

(65°C-300ppm- Non-humidified condition)

 

    
     

A FEWfiOHHKWP

I FEWEWNMNW

 

Total Quantity Permeated (micrograms)

 

 

1 1 '
0 100 200 300

TIME (hours)

Figure 16. Transmission rate profile curves of ethyl acetate
vapor through PET/SiOx PET/CPP and PET/EVOH/CPP
at 65°C ~300ppm - non-humidified condition.

47

detectable. Following this initial induction period, a significant increase
in the transmission rate was observed, and after 96 hours a steady state
rate of transmission was recorded. As shown in Figure 15, at steady
state, the rate of permeation through the SiOx PET was lower than that of
EVO-l.

Figure 16 presents permeation data for ethyl acetate vapor through
PET/SiOx PET/CPP and PET/EVOH/CPP, which are high barrier composite
structures. PET/SiOx PET/CPP shows the same tendency as the SiOx PET

film.

Exoerimentsatlfiffi

The transmission rate profile curves for SiOx PET, PET, EVOH,
PET/SiOx PET/CPP, PET/PET/CPP and PET/EVOH/CPP at 76°C - 300ppm -
non-humidified condition are presented in Figure 17, where the total
quantity of ethyl acetate permeated in micrograms is plotted as a
function of time. Figure 18 presents the transport data for ethyl acetate
. vapor through SiOx PET, EVOH, PET/SiOx PET/CPP and PET/EVOH/CPP.
These films permeated at a rate less than 0.6 x 10'5g/hr. Because of the
high temperature (76°C), the lag time was short and non-steady state
was not clearly observed for any of the films.

Figure 19 shows the permeation data for ethyl acetate vapor through
PET and its composite structure, PET/PET/CPP. Figure 20 presents the
permeation data for ethyl acetate vapor through SiOx PET and EVOH, to
allow comparison of the two high barrier films. The transmission rate of
ethyl acetate vapor through EVOH at 76°C was approximately 10 times

greater than its transmission rate at 65°C. However, the SiOx PET film

Total Quantity Permeated (micrograms)

48

(76°C-300ppm- Non-humidified condition)

 

 

PET

PET/PET/CPP

EVOH °
PET/EVOI-I/CPP '

SiOx PET

PET/SiOx PET/CPP

DORDOO

 

50 100 150 200 250

Figure 17. Transmission rate profile curves of ethyl acetate

vapor through SiOx PET and other films at
76°C - 300ppm - non-humidified condition.

49

(76°C-300ppm- Non-humidified condition)

 

um
. I: am

100- 1- PET/EVOl-I/CPP
. 0 SiOx PET

,0. A PET/SiOx PET/CPP

 

Total Quantity Permeated (micrograms)
8

 

 

40-
20-1
0 ‘ ‘__-' fl ' T ' I '
0 50 100 150 200 250

TIME (hours)

Figure 18. Transmission rate profile curves of ethyl acetate
vapor through SiOx PET and other high barrier films
at 76°C -300ppm - non-humidified condition.

50

(76°C-300ppm- Non-humidified condition)
1mm

 

0 PET
80° - o PET/PET/CPP

um-

um-

Total Quantity Permeated (micrograms)

   
  

 

 

 

' ‘U

' I ' l
0 50 100 150 200 250

Time (hours)

Figure 19. Transmission rate profile curves of ethyl acetate
vapor through PET and PET/PET/CPP

at 76°C - 300ppm - non-humidified condition.

51

(76°C-300ppm- Non-humidified condition)

 

PEVU-I

 

Total Quantity Permeated (micrograms)

 

 

 

Time (hours)

Figure 20. Transmission rate profile curves of ethyl acetate
vapor through SiOx PET and EVOH
at 76°C -300ppm - non-humidified condition.

52

(76°C-300ppm- Non-humidified condition)

 

E PET/EVOH/CPP

1 A PET/SiOx PET/CPP

 

Total Quantity Permeated (micrograms)

 

 

 

Time (hours)

Figure 21. Transmission rate profile curves of ethyl acetate
vapor through PET/SiOx PET/CPP and PET/EVOH/CPP
at 76°C -300ppm - non-humidified condition.

53

showed a more modest increase in permeation, which was 4 times greater
than its transmission rate at 65°C.

Figure 21 presents permeation data for ethyl acetate vapor through
the high barrier pouches; PET/SiOx PET/CPP and PET/EVOH/CPP. As
observed for the EVOH film(Figure 20), the EVOH composite structure also
exhibited a significant increase in the permeation rate. With respect to
the SiOx PET composite structure, the increase in permeation was not as

pronounced.

I . . B I I E

The transmission rate and permeance were determined from the data
obtained in the above experiments. Tables 8 and 9 summarize the results
for the three test films, and the three composite structures at 50°C,
65°C and 76°C. The 50°C data was obtained from the results of the
pretest. The units for the transmission rate are g/m2 hr. The permeance
units are g/m2 day 100ppm for MKS units and kg/m2 sec Pascal for SI

units.
1 In Appendix B, oxygen permeance of test films and the respective
composite structures evaluated in this studies are presented. Oxygen
permeance was measured under 30°C - 0% RH. with OX-TRAN 10/50A
(Modern Controls, Inc.), with the assistance of Toppan Printing Co., Ltd.

An Arrhenius plot of the transmission rate of ethyl acetate vapor
through SiOx PET, PET and EVOH versus W is shown in Figure 22. SiOx
PET shows relatively high temperature dependence and a low
transmission rate. PET also shows relatively high temperature

dependence, but the transmission rate was greater than for SiOx PET and

 

54

Table 8. The effect of temperature on transmission rate of
ethyl acetate vapor through SiOx PET and other films.

 

 

 

TRANSMISSIQNBATE(3)
Sample Temperature (°C)
50 65 76
PEI’ 5.78 x 10510.51 4.38 x 10’4i0.16 8.20 x 10410.22

PET/PET/CPP 2.01 x 10510.36 1.97 x 10'4i0.13 2.38 x 10410.40

SiOx/PET 2.05 x 10'6i0.62 6.37 x 10' 6:0.85 2.86 x 10' 510.30
PET/SiOx PET/CPP ---------- 5.35 x 10610.22 1.57 x 10510.16
EVOH < 3.19 x 10:7 1.12 x 10510.13 1.14 x 10410.15
PET/EVOH/CPP ---------- 2.39 x 10610.23 9.33 x 10520.11

 

(a) Transmission rate values expressed as g/m2 hr

55

Table 9. The effect of temperature on permeance of ethyl acetate
vapor through SiOx PET and other films g/m2 hr.

 

 

PERMFANCE‘aI
Sample Temperature (°C)
50 65 76
PET 4.66 x 10410.41 3.53 x 10310.13 6.60 x 10’3i0.18
PET/PET/CPP 1.62 x 10410.29 1.59 x 10310.10 1.92 x 10310.09
SiOx/PET 1.65 x 10510.50 5.13 x 10'5i0.68 2.30 x 10410.24
PET/SiOx PET/CPP ---------- 4.31 x 10'5:l:0.18 1.26 x 10:41013
EVOH < 2.57 x 10'“: 9.02 x 10511.05 9.18 x 10411.21
PET/EVOH/CPP ---------- 1.92 x 10'5i0.18 7.51 x 10410.09

 

(a) Permeance values expressed as g/m2 day 100ppm

 

 

PERMEANCE (b)
Sample Temperature (°C)
SQ 65 76
PEI 1.77 x 10'15i0.16 1.28 x 104410.05 2.40 x 104420.06

PET/PET/CPP 6.16 x 104611.10 5.76 x 104510.36
SiOx/PET 6.26 x 104712.76 1.86 x 104510.25
PET/SiOx PET/CPP --------- 1.56 x 104610.06
EVOH < 9.76 x 10'18 3.27 x 104610.38
PET/EVOH/CPP -------- 6.98 x 104710.67

6.95 x 104511.17
8.09 x 104610.66
4.44 x 104610.45
3.22 x 104510.42
2.64 x 104510.03

 

(b) Permeance values expressed as g/m2 sec Pascal

56

 

 

 

10'2
0 PET
g 10-3 1:1 EVO-l
cg O SiOXPET
9 10"
2
E
10'5
C
.2
3
E 10'6
(D
C
E
*- 10.7
10.8: 1 T ‘ T a T '
2.6 2.9 3.0 3.1 3

HT (K-1x103)

Figure 22. Temperature dependence of permeability rate for

ethyl acetate vapor through PET, SiOx PET and EVOH.

57

EVOH. Based on the activation energy, the EVOH film exhibited very
significant temperature dependency (see Table 10).

As can be seen, the temperature dependency of the transmission rate,
over the temperature range studied (50 - 76°C), can be represented by the
expression:

P - DS - P0 exp (Ep/RT) (1)

From the slope of the Arrhenius plots, the activation energy for the

permeation process (Ep) was determined for the respective film samples,

and the values summarized in Table 10.

Table 10. Activation energy of permeation of ethyl acetate vapor
through SiOx PET, EVOH and PET.

 

_Sample WW
SiOx PET 22.1 kcal / mol
EVOH 48.8 kcal / mol
PET 23.2 kcal / mol

 

Shirakura (1987) reported a value for the activation energy of 23.3
kcal / mol for an ethyl acetate /PET system, which is quite similar to
the above PET value. The activation energy seemed to be high when
compared with the activation energy of oxygen gas through PET below Tg
(Ep - 8 kcal/mole) (Michaels at al., 1963). A possible explanation for
this is that the molecular size of ethyl acetate is larger than oxygen and

requires a higher activation energy for diffusion (Meares, 1953) through

58

the PET film sample.

The fact that the activation energy values for both the SiOx PET and
the PET base film were identical suggests that for the silica coated
structures, the temperature dependent process involves the diffusion of
ethyl acetate vapor through the PET layer, and nondiffusive transport
through the SiOx coating. The latter process appears to be independent
of temperature, within the temperature range studied. The permeation
process is controlled by diffusion through the PET layer and not by the
silica coating on the polyester, although silica coating controlled the
overall transmission rate that resulted in an improvement in ethyl
acetate barrier properties on 12pm polyester by a factor of 10 times. It
is assumed that a perfectly homogeneous SiOx surface layer would
exhibit a measurable diffusion rate (Norton, 1953) which would be
reflected in the activation energy values obtained.

While the functional role of the silica coating is not fully
understood, the following mechanism is proposed. For the silica
deposited PET film, the barrier properties of the structure are governed
by defects, nonohomogeneity of both the surface coating thickness and
composition, or preferential diffusion paths. All of which can contribute
to the observed permeability. The diffusion coefficients of the polymer
layers immediately adjacent to the silica coating are thus critical in
determining the effect of such defects.

59

The Effect of Relative Humidity on the Permeation of
Ethyl Acetate Vapor through SiOx PET and EVOH

W

The transmission rate profile curves for SiOx PET and EVOH are
presented in Figure 23, where the total quantity of ethyl acetate
permeated in micrograms is plotted as a function of time. The test
conditions were 22°C, 190ppm concentration of ethyl acetate vapor, at
87% and 56% RH. respectively. Fluctuation of relative humidity was 32%
and fluctuation of concentration was :l:5%.

In over 500 hours of continuous testing, there was no measurable
permeation at 56% RH The results indicate that both test films were
excellent ethyl acetate vapor barriers at 56% RH, and ambient
temperature. However, as shown, at 87% RH. the EVOH film had quite a
high transmission rate of ethyl acetate vapor, while the SiOx PET still
did not have any permeation.

. Table 11 shows transmission rate and permeance data. Also
presented in Table 11 are upper limit value estimations for the
transmission rates and permeance. The procedure for upper limit
estimation is described in Appendix C. As shown, permeation of ethyl
acetate vapor through SiOx PET was not influenced by relative humidity.
On the other hand, the permeation of ethyl acetate vapor through EVOH
was strongly affected by relative humidity. When EVOH is in a dry
condition, there is little permeation through the amorphous regions since
hydrogen bonding reduces polymer chain segmental mobility, and thus

restricts the diffusion of ethyl acetate vapor. When moisture is present,

60

(22°C-190 ppm)
150

 

I EVOH 87%R.H.
'3 EVOH 56%R.H.

100-

0 SiOx PET 87%R.H.
o SiOx PET 56%R.H.

 

 

Total Quantity Permeated (micrograms)

 

0 100 200 300 400 500

Time (hours)

Figure 23. Transmission rate profile curves of ethyl acetate
vapor through SiOx PET and EVOH
at 22°C ~190ppm - 87% and 56% RH.

61

sorbed water acts to plasticize the hydrophilic barrier polymer, which
decreases the cohesive forces between the polymer chain and increases
segmental mobility (Barrie, 1968). The plasticization of the barrier

layers will result in a significant increase in ethyl acetate vapor

diffusively and accounts for the accelerating effect of relative humidity
(Liu et al., 1988).

Table 11. The effect of relative humidity on the permeation of ethyl
acetate vapor through SiOx PET and EVOH.

 

Sample Transmission rate Permeance Permeance
(swimw—
(56% RH.)
SiOx PET < 2.1 x10'7 < 2.7 x106 <1.1 x10'17
EVOH < 4.2 x 10'7 < 5.4 x 10'6 < 2.2 x 10'17
. (87% RH.)
SiOx PET < 4.2 x 10'7 < 5.4 x 10'6 < 2.2 x 10'17

EVOH 1.13 x 1043016 1.45 x 10’3:t:0.21 8.39 x 104510.84

 

62

The Effect of Retort Sterilization on the Permeation of Ethyl
Acetate through the PET/SiOx PET/CPP
Retort Pouch Structure

I: | [BII' I' I! E'Dl |.|.

The permeability studies were carried out at the following
conditions; concentration of ethyl acetate vapor 300ppm, non-humidified
condition at 67°C. Fluctuation of concentration was 17%, and fluctuation
of temperature was i1°C. Since good agreement was obtained between
replicate samples tested, the reported data are the average of the two.
However, one set of the data obtained at 125°C, 20 min. was eliminated
because of extremely small values. The reason for the irregular value
was likely caused by the leakage of accumulated ethyl acetate vapor at
the cell sampling port.

Figures 24, 25 and 26 show the effect of retorting time under
specific retorting temperatures of, 120°C, 125°C and 130°C,

respectively. The three sets of retorting time/temperature studies were

- compared to non-retort control samples. Figure 24 shows the
permeation of ethyl acetate vapor through SiOx pouches after 120°C
retorting process. Figure 25 plots the permeation profile of ethyl
acetate vapor through the samples at 125°C retorting temperature, while
Figure 26 deals with the SiOx pouches which went through the 130°C
retorting process. As shown, a longer retorting time is likely to result

in an increase in permeation at each temperature.

Total Quantity Permeated (micrograms)

63

(67°C-300ppm-

Non-humldfled condition)

 

100

 

' 120°C-60 min
B 120°C-40 min
0 120°C-20 min

0 Control

 

 

l
100

Time

j .
200 300

(hours)

Figure 24. Effect of retorting time on the transmission rate
of ethyl acetate vapor through PET/SiOx PET/CPP
(Retort temperature 120°C).

64

(67°C-300ppm- Non-humidifed condition)

 

 

 

 

150 T.
’3‘ ' 125°C- 60 min
g ‘ a 125°C- 40 min a
i5 o , -
g, 10% o 125 c 20 min ‘
g 0 Control ' a
‘6
o . . a
E . °
8 a
a 50 "' n a .
E o
g o
O ‘ .
E A O
0 V
’- 0" " 4’ i ' l '

0 1 0 0 2 0 0 3 0 0

Time (hours)

Figure 25. Effect of retorting time on the transmission rate
of ethyl acetate vapor through PET/SiOx PET/CPP
(Retort temperature 125°C).

65

(67°C-300ppm- Non-humidified condition)

 

 

an
’a?
E
S
3’
$3 mm-
.5,
U
0
7:?
E M“
Q)
a 1
s?
5 100 -
3
0
I":
.2
0
Figure 26.

 

 

I 130°C-60 min
513 130°C-40 min
¢ 130°C-2O min
0 Control
' c
I I .....z 0
s
M» __‘,___‘—.'. ] '
100 200 300

Time (hours)

Effect of retorting time on the transmission rate
of ethyl acetate vapor through PET/SiOx PET/CPP
(Retort temperature 130°C).

66

I:o:|o:| . :; .... :“o:¢:( ; .. ... :. ' .. ..1; ‘ '
Figures 27, 28, 29 and 30 show the effect of retorting temperature
at constant retorting time, 0 (no retort), 20, 40, and 60 min.
respectively. Figure 27 represents permeation data for ethyl acetate
vapor through the control, non-retorted SiOx pouches, used as a standard
film in each experimental cycles. As shown, identical values were
obtained for the non-retort samples. in Figure 28 the transmission rate
profile curves for ethyl acetate vapor through SiOx pouches after 20 min.
retorting time are presented as a function of retort temperatures of
120°C, 125°C and 130°C. Figure 29 shows the permeation data through
samples after 40 min. retorting as a function of temperature.
Permeation data for the samples which were retorted for 60 min. at
120°C, 125°C and 130°C are shown in Figure 30. As shown, the higher

retort temperature resulted in an increase in the transmission rate.

WW

Tables 12,13 and 14 show the transmission rate and permeance,
. summarizing the results of the experiments described above. Figures 31
and 32 provide for an overview of permeation characteristics of the
pouch following the retorting process. Figure 31 illustrates the
dependency of the transmission rate on the retorting temperature. As
can be seen, an average 260% increase in the transmission rate occurred
when the retort temperature was increased from 125 to 130°C. At
125°C, only an average 30% increase in permeation was observed, as
compared to results obtained following retort processing at 120°C for

all hold times. Figure 32 describes the dependency of the transmission

67

(67°C-300ppm- non-humidified condition)

 

 

 

 

30
g l Control (130°C)
(5 a
3 0 Control (125°C)
0
.E 20 - o
v 0 Control (120°C)
.3: .
8 . o '
o
E . .I
0- 10 o 0 u
o
8 .° "
0 6’ I '
a P a- '
O
'- 0 L‘. i g I 1 v
o 100 200 .300

Time (hours)

Figure 27. Transmission rate profile curves of ethyl acetate
vapor through PET/SiOx PET/CPP
(Non retorted pouches).

68

(67°C-300ppm- Non-humidified condition)

 

 

 

 

200
E . I 130°C-20min
(U
:9? 150. o 125°C-20 min
— I
5 , - 120°C-20min
E
8 100-
E
Q. I
.‘2‘ u
.. °
0 ‘ o o o
a .
13 «4’

o 1 V 1 v

0 100 200 300

Time (hours)

Figure 28. Effect of retorting temperature on the transmission
rate of ethyl acetate vapor through
PET/SiOx PET/CPP (Retort time 20min).

69

(67°C-300ppm- Non-humidified condition)

 

I 130°C-4O min

0 125°C-40 min
2m . . 120°C-40 min

 

Total Quantity Permeated (micrograms)
ii"

 

 

100- I 0
II o o
m. o O o
o " . 1 . -
0 100 200 300

Time (hours)

Figure 29. Effect of retorting temperature on the transmission
rate of ethyl acetate vapor through
PET/SiOx PET/CPP (Retort time 40min).

70

(67°C-300ppm- Non-humidified condition)

 

I 130°C-60 min
300. o 125°C-60 min

. 120°060 min

100- o

 

Total Quantity Permeated (micrograms)

 

 

. .
0 100 200 300

Time (hours)

Figure 30. Effect of retorting temperature on the transmission
rate of ethyl acetate vapor through
PET/SiOx PET/CPP (Retort time 60min).

71

Table 12. The effect of retort conditions on transmission rate
of ethyl acetate vapor through PET/SiOx PET/CPP.

 

Sample Transmission rate(a)
Upper cell Lowegzell Average
Controlibl 1.61 x 10-5 1.22 x 10-5 1.22 x 10530.20

120°C-20min 2.76 x 10'5 3.30 x 10'5 3.03 x 10510.27
120°C-40min 6.04 x 10'5 5.45 x 10'5 5.75 x 10520.30
120°C-60min 6.55 x 10'5 9.31 x 10'5 7.93 x 10' 51:1.38

Control‘b) 1.76 x 10-5 1.37 x 10-5 1.57 x 10510.20
125°C-20min ------- 4.30 x 10'5 4.03 x 10'5- - - -
125°C-40min 6.03 x 10-5 7.77 x 10-5 6.90 x 10- 51:0.87
125°C-60min 9.68 x 10-5 1.23 x 10-4 1.10 x 10420.13

Controllb) 1.42 x 10-5 1.37 x 10'5 1.40 x 10'5i0.03
130°C-20min 1.53 x 10" 1.65 x 10'4 1.59 x 10410.06
130°C-40min 2.30 x 10-4 2.46 x 10-4 2.39 x 10410.09
130°C-60min 3.66 x 10-4 4.00 x 10-4 3.33 x 10410.17

 

(a) Transmission rate values expressed as g/m2 hr
(b) Not retorted.

72

Table 13. The effect of retort conditions on permeance of
ethyl acetate vapor through PET/SiOx PET/CPP.

 

 

Sample Permeance (a)
DWI! AveraoL_
Controllbi 1.29 x 10-4 9.76 x 10-5 1.14 x 10410.16

120°C-20min 2.21 x 10'4 2.64 x 10'4 2.42 x 10410.22
120°C-40min 4.83 x 10'4 4.36 x 10’4 4.60 x 10410.24
120°C-60min 5.24 x 10'4 7.45 x 10'4 6.34 x 10411.11

Controllb) 1.41 x 10-4 1.10 x 104 1.26 x 10‘4i0.16
125°C-20min ------- 3.44 x 104 3.44 x 10-4 - - - -
125°C-40min 4.62 x 10-4 6.22 x 104 5.52 x 10430.70
125°C-60min 7.74 x 10-4 9.84 x 10-4 6.79 x 10431.05

Control(b) 1.14 x 10'4 1.10 x 10" 1.12 x 10420.02
130°C-20min 1.22 x 10'3 1.32 x 10’3 1.27 x 10'3:i:0.05
130°C-40min 1.84 x 10'3 1.98 x 10'3 1.91 x 10'3i0.07
130°C-60min 2.93 x 10'3 3.20 x 10'3 3.06 x 10'3i0.14

 

(a) Permeance values expressed as g/m2 day 100ppm
(b) Not retorted.

73

Table 14. The effect of retort conditions on permeance of
ethyl acetate vapor through PET/SiOx PET/CPP.

 

Sample Permeance (o)

W Average——
Controlid) 4.46 x 10-16 3.52 x 10-16 4.06 x 1016 10.56
120°C-20min 7.96 x 10'16 9.52 x 10'16 8.74 x 10'15 10.78
120°C-40min 1.74 x 10-15 1.57 x 10-15 1.66 x 10-15 10.09
120°C-60min 1.69 x 10-15 2.66 x 10-15 2.29 x 10-15 10.30
Controlld) 5.06 x 10-16 3.95 x 10-16 4.52 x 10-16 10.57
125°C-20min 1.24 x 10-15 1.24 x 1015 - - - -
125°C-40min 1.74 x 10-15 2.24 x 10-‘5 1.99 x 10-15 10.25
125°C-60min 2.79 x 10'15 3.55 x 10'15 3.17 x 10'15 10.38
Control“) 4.09 x 10-16 3.95 x 10-16 4.02 x 10-16 10.07
130°C-20min 4.41 x 10-15 4.76 x 10-15 4.59 x 10-15 10.17
130°C-40min 6.63 x 10'15 7.15 x 10'15 6.89 x 10'15 10.26
130°C-60min 1.06 x 10-14 1.15 x 1014 1.10 x 10-14 10.05

 

 

(c) Permeance values expressed as g/m2 sec Pascal

(d) Not retorted.

74

(67°C-300ppm- Non-humidified condition)

 

 

 

 

 

tubA
, I 60 min
5 D 40 min
% 3mb4-
F]; 0 20 min
:3 0 Control
‘1 2.0004 .
C
.9
m
E
S
g LMhJ-
.-
..———f
o o 0
0.00040 . . . . . , .
115 120 125 130 135

Retort Temperature (°C)

Figure 31. Dependency of transmission rate of ethyl acetate
vapor through PET/SiOx PET/CPP on retorting
temperature.

75

(67°C-300ppm- Non-humidified condition)

 

 

 

 

4.0004
I 130°C
3:: 0 125°C
N 3.0004 -
E 0 120°C
3 d
2 I
(B
0: 2.0004 -
8
ca -
.9
S
5 1.00.4 -
...
0.000+o T 1 . . . . , .
o 2 0 4 o s 0 6 o

Retort Time (min)

Figure 32. Dependency of transmission rate of ethyl acetate
vapor through PET/SiOx PET/CPP on retorting time.

76

rate on retorting time. As shown, an increase in retorting time resulted
in an increased transmission rate for each sample. The increases in the
transmission rate at 120°C and 125°C are low. The increase rates per
retorting time are 1.12 x 10"sg/m2 hr/min and 1.60 x 10"5g/m2 hr/min,
respectively. However, at 130°C, the rate increase per minute retorting
time increased drastically to 6.15 x 10"5g/m2 hr/min.

The effect of temperature and hold time on the barrier
characteristics of the SiOx PET based retort pouch structure can be
attributed to process induced damage to the SiOx barrier coating during
the retorting step. This was confirmed by optical microscopy studies

which are described below.

9 l . t 5.0 | S E
To evaluate the effect of retort processing conditions on the

integrity of the SiOx barrier coating, optical microscopy analyses were

carried out, where the SiOx surface layer was examined following retort

_ processing and again following completion of the permeability studies.

The results are summarized in Table 15 and presented graphically in

Figures 33 - 36 for better illustration. In Figures 33-35, the

micrographs of the SiOx surface are shown for pouches retorted at 120,

125 and 130°C, and for hold times of 20, 40 and 60 minutes, respectively

at each temperature. As shown, within one temperature regime, as the

hold time was increased, there was an increase in the observed cracking

and crazing of the SiOx barrier layer. Further, as the retort temperature

was increased, and increase in the SiOx surface fracture was observed.

These results agreed well with the observed transmission data.

77

Table 15. Observation of SiOx layer of retort pouches.

 

 

_§ample Description

No Retort No crack

120°C - 20 min. No crack

120°C - 40 min. Tiny, non-continuous crack, one direction

120°C - 60 min. Non-continuous and continuous crack, one
direction

125°C - 20 min. Tiny non-continuous cracks in some parts

125°C - 40 min. Crack, one direction

125°C - 60 min. continuous crack, one direction

130°C - 20 min. continuous crack, one direction

130°C - 40 min. Wider, continuous crack, one direction

130°C - 60 min. Wider, webbed cracks

Temperature only

125°C - 48 hr. No crack

135°C - 48 hr. No crack

 

78

Figure 33. Micrographs of SiOx surface - retorted at 120°C.

o .. ..

.‘

c .. a .. .

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e..t...... ..1. 9.1.14.1; .. ... v r a
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79

Figure 34. Micrographs of SiOx surface - retorted at 125°C.

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125° — 20 min.

 

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80

Figure 35. Micrographs of SiOx surface - retorted at 130°C.

 

130°C — 40 min.

130°C — 20 min.

 

 

 

 

 

     

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81

Figure 36. Micrographs of SiOx surface
- retorted at 120, 125 and 130°C

   

     

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82

No significant differences were observed for the SiOx surface
following ethyl acetate vapor permeation.

To evaluate the effect of temperature on the integrity of the SiOx
coating, retort pouches were exposed to the following conditions, 135°C
for 48 hours with 0% RH. and 125°C for 48 hours with 0% RH. No
damage to the SiOx surface was observed by optical microscope. It was
therefore concluded that the observed cracking and crazing of the SiOx
layer during retort processing was not caused solely by temperature
change. The damage on the surface was likely to be caused by the
retorting process, that is, the combination of high temperature, physical
stress and water.

SiOx pouches sorb water from both sides of the structure. The inside
layer (CPP) is in contact with an aqueous phase, and the outside layer
(PET) is exposed to water vapor during steam retorting. Both the inner
and outer web of the laminate structure are capable of sorbing larger
amounts of water under the conditions of the retort process. The SiOx

layer may also sorb water. Kaiho (1987) reports the cast polypropylene
' layer of the retort pouches should have a small shrinkage rate, as stress
will result from such shrinkage.

lt is assumed, therefore that the stress and pressure to which the
SiOx layer is exposed during the retort process, coupled with the
sorption of water, is responsible for the observed damage to the barrier

coating.

CONCLUSION

The effect of temperature, relative humidity and retort processing
conditions on the permeation of ethyl acetate vapor through silica
deposited polyethylene terephthalate film and composite structures
were studied by a quasi-isostatic procedure. For comparison, the
permeation of ethyl acetate vapor through an ethylene/vinyl alcohol
copolymer (EVOH) and a EVOH laminate structure was also determined.

Based on the results of a series of preliminary studies, test
conditions of 65 and 76°C, and a vapor concentration at 300 ppm (wt/v)
were selected to evaluate the effect of temperature on the permeation
of ethyl acetate vapor through SiOx PET film. Lower temperature and
lower ethyl acetate vapor concentration levels did not yield measurable
permeation rates. The results also suggested that the permeability of
. SiOx PET is more dependent on temperature than on ethyl acetate vapor
concentration.

While the functional role of the silica coating is not fully understood,
the following mechanism is proposed. For the silica deposited PET film,
the barrier properties of the structure are governed by defects,
nonohomogeneity of both the surface coating thickness and composition,
or preferential diffusion paths. All of which can contribute to the
observed permeability. The diffusion coefficients of the polymer layers
immediately adjacent to the silica coating are thus critical in
determining the effect of such defects.

83

84

During the initial transport period at 65°C, EVOH showed typical
Fickian behavior, while the SiOx PET appeared to show atypical behavior.
For the first 24 hours, permeation through SiOx PET was not detectable.
Following this initial induction period, a significant increase in the
transmission rate was observed, and after 96 hours, a steady state rate
of transmission was recorded. At steady state, the rate of permeation
through the SiOx PET was lower than that of EVOH.

SiOx PET film showed relatively high temperature dependence, and
low transmission rates. PET also showed relatively high temperature
dependence. However, the transmission rate was much higher than for
SiOx PET and EVOH. EVOH showed a very high temperature dependence,
based on the activation energy of the process.

In over 500 hours of continuous testing, there was no measurable
permeation at 22°C, 56% RH. The result showed that both SiOx PET and
EVOH films were excellent ethyl acetate vapor barrier structures.
However, at 22°C, 87% RH, the EVOH film exhibited a permeation rate of
. 5.5 x 10'7g/hr for ethyl acetate vapor, while the SiOx PET film showed
no measurable permeation of the organic penetrant. Permeation of ethyl
acetate vapor through SiOx PET was not influenced by relative humidity
at ambient conditions, and the SiOx PET film showed excellent barrier
for ethyl acetate vapor.

With respect to the effect of retort processing variables on the
barrier properties of an SiOx PET based retort pouch, an average 260%
increase in the transmission rate occurred when the retort
temperature was increased from 125 to 130°C, while the transmission

rate increase was on the order of 30% in going from 120°C to 125°C for

85

all hold times. An increase in retorting time was also directly related
to higher transmission rates for each temperature.

When the permeation data and SiOx surface analysis by optical
microscopy were compared, a direct relationship was obtained between
an increase in permeation and wider, more continuous cracks of the SiOx
layer.

The effect of temperature on the structural integrity of the SiOx
coating of the retort pouch composite was evaluated, and no evidence of
cracks or crazing was observed. It was therefore concluded that cracks
were not induced solely as a result of temperature change. The damage
on the SiOx surface was likely caused by the retorting process, that is,
the combination of high temperature, physical stress and moisture
sorption. Stress was caused by shrinkage of the CPP film and pressure

during retorting process.

FUTURE RESEARCH

The results of this study showed that permeation of ethyl acetate
vapor through SiOx PET film had relatively low temperature dependence
at 50°C, 65°C and 76°C. No relative humidity dependence was observed
in the experiments performed at an ambient condition (22°C). With
respect to the effect of relative humidity, however, the examination of
SiOx PET film in high temperature and high humidity will be necessary.

Similar studies should be carried out with other organic vapor
penetrants, representing a range of polarities and molecular size, to
compare their relative behavior. This will contribute for further
developments in commercial use of SiOx PET film.

Detailed studies are needed to examine quantitatively the
relationship between the cracking of the SiOx layer and the transmission
, rate. ln addition, this study suggests that the combination of
temperature, physical stress and water induced cracking of the SiOx
layer. Further experiments in this area are of practical interest to
determine causes of cracking accurately, and to analyze its mechanism

to the full extent.

86

APPENDICES

Appendix A

Standard Calibration

Two standard calibration factors for ethyl acetate were employed,
depending on the gas chromatograph models (5890, 5830A).
Concentrations of 5, 8, 16, 20, 50, 100, 1000 and 10000 ppm (v/v) of
ethyl acetate in solvent were utilized to create the calibration curves.

A 0.5 pl sample was injected directly into the gas chromatograph and
the area response was recorded. Area unit response was plotted versus
the quantity injected per sample. The reciprocal of the slope equals the
calibration factor. Table A1 and Figure Al show the calibration data and
the standard curve of ethyl acetate for the 5890 G.C., respectively. The
calibration data and the standard curve of ethyl acetate for the 5830A

_ G.C. is presented in Table A2 and Figure A2.

Ethyl acetate standard calibration factor for 5890 G.C.
= 1.678 x 10'12 (gm/AU.)

Ethyl acetate standard calibration factor for 5830A G.C.
= 5.352 x 10'12 (gm/A.U.)

87

88

Table A1. Ethyl Acetate Calibration Curve Data for 5890 G.C.

PPM(v/v) Quantity of Area Unit Area Unit Area Unit

Ethyl WW

 

 

 

5 2.240 x10'9 1134 1086 1110
8 3.584 x 10'9 1899 1802 1851
16 7.168 x 10'9 3465 3461 3463
20 8.960 x 10‘9 4333 4677 4505
50 2.240x10‘8 11309 11123 11216
1 00 4.480 x 1 0‘8 24214 25452 24833
1000 4.480 x 10'7 269530 269190 269360
10000 4.480 x 105 2648100 2685600 2668500
Table A2. Ethyl Acetate Calibration Curve Data for 5830A G.C.
PPM(v/v) Quantity of Area Unit Area Unit Area Unit
Ethvl WW9
8 7.168 x 10'9 1328 1339 1334
20 1 .792 x 10‘8 3383 3051 3217
50 4.480 x 10'8 7984 7504 7744
100 8.960 x 10’8 16280 17120 16700
1 000 4.480 x 1 0'7 177400 171 900 1 74650
10000 8.960 x 1 0'5 1689000 1687000 1 688000

 

Area Response

89

 

I Ave. of Replicates

 

 

103 N y . - 570.76 + 5.9584e+11x R42 . 1.000

t'UU'VI'l

10‘5

V ‘ UIUVVV I V V“" V ' rtv'
I I 'I

... -
10'9 10” 10'7 10"

Quantity of Ethyl Acetate Injected (a)

Figure A-1. Ethyl acetate calibration curve for
gas chromatograph 5890.

Area Response

90

 

107

106

105

 

 

   

 

Ave. of Replicates

103 y - 1.73569+4 + 1.86839‘I’11X RAZ I 0,997
2

10 I ' ‘ "I ‘ '11t'" ' V V Vi... ' i 'U 'I"
10” 10'8 10'7 1o-6 10-5

Quantity of Ethyl Acetate injected (a)

Figure A-2. Ethyl acetate calibration curve for
gas chromatograph 5830A.

Appendix B

Table A3. Oxygen Permeance of SiOx PET and Other Films Used

 

in This Study
Structure OW
SiOx PET 2.0
PET/ SiOx PET/CPP 0.7
EVO-l 0.5
PET/EVOH/CPP 0.4
PET 159.7
PET/PET/CPP 74.9

 

Units of Oxygen permeance : oc/m2 day atm
at 30°C-0% RH. -

The values are averages of replicate runs.

91

Appendix C

Estimation of the Upper Limit of the Transmission Rates of
Ethyl Acetate Vapor through SiOx PET Film

Outlined below is the method used to estimate lower limit of
permeability rate by the gas chromatograph. The lowest area response
selected with 5830A G.C. for detecting ethyl acetate with good precision
and accuracy was assumed to be 1000 area unit.

In over 500 hours of continuous testing, the following data were
obtained; SiOx PET had less than 1000 AU at 56% R.H., 22°C, and less than
2000 AU at 87% R.H., 22°C. EVOH had less than 2000 AU at 56% R.H.,
22°C. These three data was fluctuating and did not show steady state.
The calibration factor for 5830A G.C. is 5.352 x 10'12 g/AU for ethyl
acetate. The total quantity of ethyl acetate vapor permeated through
. SiOx PET at 56% RH. 22°C after 500 hours was calculated as follows:

(Sample Calculation)
gm = 1000AU x (5. 352 x10'12)g x 500C / 0.50c =- 5.35 x10'7
50cc : Total cell volume
0.50c : Injection volume
Permeability Rate for SiOx Film at 56% FI.H., 22°C
5.35 x 10'7 g/500hrs / 0.005m2 = 2.14 x 10‘7 g/m2 hr
This represents an average transmission rate which does not

consider lag time.

92

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