37..) I'l‘l..1»’ol . 2:... . .i. :i It...) ‘ YHESIS RSI TY LIBRARI iii8 ”Hill MilliiiillllllliWilli 31293_ This is to certify that the thesis entitled The Effects of Dual Additive Systems on the Mechanical Properties of Aspen Fiber/Recycled High Density Polyethylene Composites presented by Maria D. Keal has been accepted towards fulfillment of the requirements for M. S. . Packa in degree 1n 9 g ., ‘QJMQ’A M Major professor Date ‘7/3C7I/90 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution LIBRARY Mlchlgan State PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE W3 ' : .9. ~ l: ‘ D n ,3 t MSU Is An Affirmative Action/Equal Opportunity Institution encircmnmii-D: THE EFFECTS OF DUAL ADDITIVE SYSTEMS ON THE MECHANICAL PROPERTIES OF ASPEN FIBER/RECYCLED HIGH DENSITY POLYETHYLENE COMPOSITES BY Maria D. Keal NQMQ anilm'fi'. ._ , ' ' g . Mei. u’i r abemte Submitted to Michigan State University In partial fulfillment of the requirements for the degree of MASTER OF SCIENCE School of Packaging 1990 G; 99' l t; i :5 é¢é~ ABSTRACT THE EFFECTS OF DUAL ADDITIVE SYSTEMS ON THE MECHANICAL PROPERTIES OF ASPEN FIBER/RECYCLED HIGH DENSITY POLYETHYLENE COMPOSITES BY Maria D. Keal Composites using a recycled polyethylene matrix and ‘wood fiber filler offer a low-cost, alternative use for recycled plastics. Using additives in the composite to promote interfacial bonding or dispersion of these two incompatible materials has been shown to offer some improvement of mechanical properties. This project studied the effects of combining two additives. The additives studied were stearic acid, a dispersing agent; maleic anhydride modified poly- propylene; and ionomer modified polyethylene, both used to improve interfacial bonding. Testing included impact strength, tensile properties, and creep. In all areas except impact strength, the use of additives improved properties. The MAPP/stearic acid additive system exhibited the best overall creep and tensile properties, but decreased impact strength. The stearic acid/ionomer combination was the only one that did not reduce impact strength. None of the dual additive systems offered significant improvement over using single additives. \3 (94%r-15 ABSTRACT THE EFFECTS OF DUAL ADDITIVE SYSTEMS ON THE MECHANICAL PROPERTIES OF ASPEN FIBER/RECYCLED HIGH DENSITY POLYETHYLENE COMPOSITES BY Maria D. Keal Composites using a recycled polyethylene matrix and wood fiber filler offer a low-cost, alternative use for recycled plastics. ‘Using additives in the composite to promote interfacial bonding or dispersion of these two incompatible materials has been shown to offer some improvement of mechanical properties. This project studied the effects of combining two additives. The additives studied were stearic acid, a dispersing agent; maleic anhydride modified poly- propylene; and ionomer modified polyethylene, both used to improve interfacial bonding. Testing included impact strength, tensile properties, and creep. In all areas except impact strength, the use of additives improved properties. The MAPP/stearic acid additive system exhibited the best overall creep and tensile properties, but decreased impact strength. 'The stearic acid/ionomer combination was the only one that did not reduce impact strength. None of the dual additive systems offered significant improvement over using single additives. DDT? é¢é~ ABSTRACT THE EFFECTS OF DUAL ADDITIVE SYSTEMS ON THE MECHANICAL PROPERTIES OF ASPEN FIBER/RECYCLED HIGH DENSITY POLYETHYLENE COMPOSITES BY Maria D. Keal Composites using a recycled polyethylene matrix and wood fiber filler offer a low-cost, alternative use for recycled plastics. Using additives in the composite to promote interfacial bonding or dispersion of these two incompatible materials has been shown to offer some improvement of mechanical properties. This project studied the effects of combining two additives. The additives studied were stearic acid, a dispersing agent; maleic anhydride modified poly- propylene; and ionomer modified polyethylene, both used to improve interfacial bonding. Testing included impact strength, tensile properties, and creep. In all areas except impact strength, the use of additives improved properties. The MAPP/stearic acid additive system exhibited the best overall creep and tensile properties, but decreased impact strength, The stearic acid/ionomer combination was the only one that did not reduce impact strength. None of the dual additive systems offered significant improvement over using single additives. ACKNOWLEDGMENTS I would like to thank my major professor Dr. Susan Selke (School of Packaging, Michigan State University), and ‘committee ‘members Dr; Jack, Giacin (School of Packaging, Michigan State University) and Dr. Otto Suchsland (Depart- ment of Forestry, Michigan State University) for all their guidance and support. I would also like to thank Mike Rich at the Composite Materials and Structures Center, Michigan State University, for his assistance and the use of the extruder. A special thanks to JoAnna Childress and Rodney Simpson for their help with extrusion and testing. I am also grateful to all the companies that donated material for use in this study, and the Plastics Institute of America for their generous support of my research. iii TABLE OF CONTENTS List of Tables ....................... . ............... v List of Figures ...................................... vii Introduction ................................... . ..... 1 Literature Review ............... . .................... 8 Composites ...................................... 8 Properties of Composites ........................ 10 Prior Research .................................. 19 Experimental Design .................................. 25 Materials ....................................... 25 Methods ......................................... 28 Results .............................................. 34 Impact Test ..................................... 34 Tensile Test .................................... 36 Creep Test ...................................... 39 Summary ........... . ......... . ..... . ..... . ....... 41 Discussion ........................................... 42 Impact Strength ................................. 42 Tensile Strength . ............... . ............... 44 Elongation at Break ............................. 47 Modulus of Elasticity ........................... 49 Creep ........................................... 53 Conclusions .......................................... 55 Recommendations ...................................... 56 Appendix ............................ ......... ........ 57 List of References ................................... 83 iv Table Table Table Table Table Table Table Table Table Table Table 7: 8: LIST OF TABLES Sample Composition ........................ 29 Impact Test Results ....................... 34 Tensile Strength .......................... 36 Percent Elongation at Break ............... 38 Young's Modulus of Elasticity ............. 39 Summary of Statistical Analysis ........... 41 Tensile Strength: Single Additives versus Dual Additives ..................... 46 Percent Elongation at Break: Single vs. Dual Additives ... ......................... 47 Modulus of Elasticity: Single vs. Dual Additives ................................. 51 Volume Fractions .......................... 52 Reinforcement Factors ..................... 53 Tables in Appendix: Table Table Table Table Table Table A1: A2: A3: A4: A5: Individual Results, Impact Strength ....... 57 Two-Way Analysis of Variance, Impact Strength .................. . ........ 58 Tukey's Test, Impact Strength ............. 59 Orthogonal Contrast, Impact Strength ...... 60 Class Comparison, Impact Strength ......... 62 Individual Results, Tensile Strength ...... 64 Table Table Table Table Table Table Table Table Table Table Table Table Table Table A7: A8: A9: A10: A11: A12: A13: A14: A15: A16: A17: A18: A19: A20: Two—Way Analysis of Variance, Tensile Strength .......................... 65 Tukey's Test, Tensile Strength ............ 66 Orthogonal Contrast, Tensile Strength ..... 67 Class Comparison, Tensile Strength ........ 69 Individual Results, Elongation at Break ...71 Two-Way Analysis of Variance, Elongation at Break ...................... .72 Class Comparison, Elongation at Break ..... 73 Tukey's Test, Elongation at Break ......... 75 Orthogonal Contrast, Elongation at Break ..76 Individual Results, Modulus of Elasticity .77 Two—Way Analysis of Variance, Modulus of Elasticity ..................... 78 Tukey's Test, Modulus of Elasticity ....... 79 Orthogonal Contrast, Modulus of Elasticity 80 Class Comparison, Modulus of Elasticity ...81 vi Figure Figure Figure Figure Figure 01 LIST OF FIGURES Results of Creep Test ...................... 40 Izod Impact Strength ....................... 43 Tensile Strength ... ........................ 45 Percent Elongation at Break ................ 48 Modulus of Elasticity . ..................... 50 Figure Figure Figure Figure Figure LIST OF FIGURES Results of Creep Test ... ........... . ....... 4O Izod Impact Strength ....................... 43 Tensile Strength .......... ................. 45 Percent Elongation at Break ... ........... ..48 Modulus of Elasticity ...................... 50 vii INTRODUCTION Much attention has recently been devoted to the escala- ting solid waste problem in this country. More municipal solid waste is being created every year, while the number of disposal facilities is declining. The volume of waste being created every year in the United States is up 80% since 1960 to about 160 million tons in'1989. (Beck et al., 1989) Landfills are being closed at a faster rate than new ones are being created, and at least seven states have less than five years of landfill capacity left (Beck et al., 1989). New landfills are not being created primarily because of citizen protests against landfills in their own communities. This is especially true in more densely populated areas, where the need for landfill space is greatest. Incineration is an] alternative to landfilling that has the advantage of recovering energy while reducing waste volume 90% (Beck et al., 1989). However, incineration has also been under fire recently. This is mainly because of public concern over its high cost and perceived lack of adequate control over hazardous emissions such as carcino— genic dioxins. Since it is desirable that the number of landfills and incinerators do not increase, alternatives that satisfy both industry and the general public must be investi- gated. The Michigan Department of Natural Resources (DNR) has suggested a waste management hierarchy approach to dealing with the problem (Resource Integration Systems Ltd., 1987). Of primary importance is source reduction. While this may seem obvious, it is important for the packaging industry to join forces to decrease the amount of packaging used without making it disadvantageous to do so. Much of the competitive advantage for consumer products lies in shelf visibility, which often means excess packaging. Unnecessary packaging is also generated when "convenience" features such as single- serving sizes are added in response to consumers' desires. These can also make a large contribution to products' competitive advantages, but add to sources of waste. Although environmental concern is growing, increased consumer education and awareness could reverse this trend as more and more consumers demand "environmentally friendly" packaging. Following source reduction, the DNR sees recycling as the next priority for dealing with solid waste, followed by incineration and, as a last resort, landfilling. Only 11% of municipal solid waste is currently being recycled. Newspapers, aluminum and glass make up most of the recycled materials. Plastics account for about 6.5% of waste, but only about one percent of plastics are recycled (Beck et al., 1989). Many difficulties are encountered when attempting to recycle post-consumer waste plastics. Plastics encompass a wide variety of resins, each with unique processing require— ments. The market for commingled plastic is extremely limited by the lack of existing facilities to process it. Sorted plastics have more value, but separation is time— consuming. Also, it is often difficult for consumers to distinguish among various resin types. Even when separated, high transportation costs due to the high volume to weight ratio make it difficult for recycled plastics to compete with virgin resin on a cost basis. Films and multi-layer plastics can not usually be recovered economically. The biggest barrier to recycling plastics is the lack of stable end markets (Resource Integration Systems, 1987). The volume of plastics in the waste stream is expected to grow to 9.8% of solid waste by 2000, mostly due to the predicted doubling in use of plastics for packaging (Resource Integration Systems, 1987). In order for plastics recycling to make an impact on the solid waste problem, it must be further investigated from two angles - designing plastic packaging and other disposable products out of materials that can easily be recycled, and finding uses for recycled resins. This research project focuses on the latter. Many difficulties are encountered when attempting to recycle post-consumer waste plastics. Plastics encompass a wide variety of resins, each with unique processing require- ments. The market for commingled plastic is extremely limited by the lack of existing facilities to process it. Sorted plastics have more value, but separation is time- consuming. Also, it is often difficult for consumers to distinguish among various resin types. Even when separated, high transportation costs due to the high volume to weight ratio make it difficult for recycled plastics to compete with virgin resin on a cost basis. Films and multi-layer plastics can not usually be recovered economically. The biggest barrier to recycling plastics is the lack of stable end markets (Resource Integration Systems, 1987). The volume of plastics in the waste stream is expected to grow to 9.8% of solid waste by 2000, mostly due to the predicted doubling in use of plastics for packaging (Resource Integration Systems, 1987). In order for plastics recycling to make an impact on the solid waste problem, it must be further investigated from two angles - designing plastic packaging and other disposable products out of materials that can easily be recycled, and finding uses for recycled resins. This research project focuses on the latter. 4 High density' polyethylene (HDPE) is readily available as a recyclable material in the form of discarded beverage bottles. The majority of these are used for milk; in fact, an estimated 12% of all plastic containers are HDPE Inilk jugs (Resource Integration Systems, 1987). Like polyethylene terephthalate (PET) soft drink bottles, these are easy for consumers to distinguish from other types of plastic con— tainers. Although several states have bottle deposit laws, HDPE containers usually do not carry a deposit. They are voluntarily recycled at a rate of about 1% and are used for such applications as agricultural drainage pipes, plastic lumber, flower pots, and even as the inner layer in co- extruded detergent bottles (Selke, 1990). The recycling rate would undoubtedly increase, reducing some solid waste, if more economically feasible markets could be developed for recycled HDPE. It has been shown (Pattan— akul, 1987) that re-processing HDPE does not significantly affect most of its mechanical properties, making this material ideal for recycling purposes. However, plastic post-consumer food and beverage containers are not reused for food contact applications because of contamination concerns. This negates the possibility of closed-loop recycling (as is the case with aluminum beverage containers), so other markets for recycled HDPE need to be investigated. 5 Since the properties of recycled HDPE are well-known, this research project focuses on HDPE/wood fiber composite, an alternative, low-cost material that can be made from recycled HDPE. Composites are defined as containing two or more separate materials, one dispersed in ‘the other, that give properties superior to the individual components (Hull, 1981). Creating a HDPE/wood fiber composite material provides one way to use recycled plastic, while obtaining increased stiffness from the fibers, to expand its range of potential applications in end use products. Wood fibers, in this case aspen hardwood fibers, were chosen as a filler because they are a plentiful, renewable resource. Wood fibers are also inexpensive, strong, and lightweight when compared with other types of fibers commonly used as rein— forcement in composite materials. The composite investigated here uses discontinuous, randomly dispersed wood fibers in a recycled HDPE matrix of reground post-consumer milk bottles. The major problem with using an HDPE 'matrix and. wood fillers is incompatibility: HDPE is hydrophobic and nonpolar, and wood is hydrophilic and polar. This reduces the fibers' potential for improving mechanical properties, but it may be increased somewhat with the inclusion of small amounts of additives that increase dispersion and/or improve adhesion. 5 Since the properties of recycled HDPE are well-known, this research project focuses on HDPE/wood fiber composite, an alternative, low-cost, material that can be made from recycled HDPE. Composites are defined as containing two or more separate materials, one dispersed in the other, that give properties superior to the individual components (Hull, 1981). Creating a HDPE/wood fiber composite material provides one way to use recycled plastic, while obtaining increased stiffness from the fibers, to expand its range of potential applications in end use products. Wood fibers, in this case aspen hardwood fibers, were chosen as a filler because they are a plentiful, renewable resource. Wood fibers are also inexpensive, strong, and lightweight when compared with other types of fibers commonly used as rein- forcement in composite materials. The composite investigated here uses discontinuous, randomly dispersed wood fibers in a recycled HDPE matrix of reground post-consumer milk bottles. The major problem with using an HDPE matrix and wood fillers is incompatibility: HDPE is hydrophobic and nonpolar, and wood is hydrophilic and polar. This reduces the fibers' potential for improving mechanical properties, but it may be increased somewhat with the inclusion of small amounts of additives that increase dispersion and/or improve adhesion. 6 The composite can be molded into almost any shape, is denser than HDPE alone, and is not abrasive. It could be used for applications where greater stiffness and creep resistance is required than offered by HDPE. The composite also has potential as a replacement for lumber, especially in developing countries and other areas where wood is scarce. Improving the mechanical properties over wood will expand the potential uses, which include furniture, pallets, storage bins, panelling, etc. A twin-screw extruder was used to process these compo- sites. Fibers were fed by hand into partially melted polymer in order to lessen fiber damage. Obviously, if there is any interest in this material on a larger, commercial basis, less labor-intensive techniques must be developed for it to be economically feasible. However, these samples will give an idea of how much the properties are enhanced by using combinations of additives shown to have some success. The objectives of this study are: 0 To determine if using two additives will show signi- ficant overall improvement beyond using only one additive already shown to improve some properties. 7 To identify any synergistic or antagonistic effects of combinations of these additives. To assess the potential for further study in the area of using additives to improve this composite material. LITERATURE REVIEW COMPOS ITES The field of reinforced polymer composites is still relatively new and practical usage has usually been limited to structural applications such as the automotive and construction industries. This is because of the high cost of production and of certain reinforcing materials. However, the consumption of reinforced plastics is expected to continue growing every year at a rate of 8 to 12%, which compares to an annual growth rate of only 4% in the consump- tion of all plastics (Vu-Khanh, 1987). The advantages to using polymer composites are many. When comparing density’ to performance, they' can. exhibit superior properties to metals (Vu-Khanh, 1987 and Jindal, 1986). By utilizing a variety of matrices and fillers, composites can be fabricated to meet specific property requirements. The cost of the individual materials can be relatively low. The most common resin type used is unsatur- ated reinforced polyester, a low cost, adaptable material representing about 70% of total usage. The remaining usage is evenly divided between other reinforced thermosets and reinforced thermoplastics (vu-Khanh, 1987). Glass fibers are, by far, the most common reinforcing material. Polymer composites can be classified into either advanced composites or high volume composites. High performance advanced composites contain continuous fibers and are the most costly in terms of processing (Phillips and Harris, 1977). Filament winding is one common method. The most common applications of advanced composites are as a metal replacement in the expanding aerospace and recrea- tional markets. Fer these types of applications, cost is usually not a factor. Many potential applications exist in the automotive area as well, but existing technology for mass production is limited and therefore extensive usage in the automotive industry is currently not cost effective (Vu- Khanh, 1987). The field of high volume composites is not predicted to grow as fast as high performance composites (Vu-Khanh, 1987). .Although their performance is diminished consider- ably as a result of using short fibers or particulates rather than continuous fibers, these composites have several advantages and are not really in competition with advanced composites. The manufacture of high volume composites can use cheaper, faster, and more versatile methods such as extrusion and injection molding (Phillips and Harris, 1977). This is especially true when the fibers are randomly dispersed throughout the matrix as opposed to being aligned. Random fibers also give the composites isotropic character- istics, which can be desirable in many applications. 10 However, improvement of properties while maintaining relatively simple processing methods is necessary in order to find more applications for high volume composites. The most common market for high volume composites is transpor— tation, where they offer light weight and corrosion resist- ance (Vu-Khanh, 1987). PROPERTIES OF COMPOSITES Many factors may affect the properties of composites. Individual properties of the matrix and reinforcing filler; size, shape, and orientation of the filler; and the degree of adhesion and dispersion of the phases can all contribute to performance. Models exist to predict some properties of composites, but caution must be used because of the high levels of variation possible, especially when using natural fibers. When a load is applied to a composite, the stress is first absorbed by the matrix material and then transferred to the filler (Agarwal and Broutman, 1980). The method of stress transfer depends on the length and orientation of the fibers, and affects tensile strength and modulus (McNally et al, 1978). A rule of ndxtures model for predicting the modulus of a composite, based on the stress transfer interface (STI) and moduli of the matrix and filler, has been used by McNally et a1. (1978): 11 EC = Eme + R Efvf (1) where: E = modulus of composite, matrix, and filler V = volume fraction R = reinforcement factor, representing both orientation and STI efficiency, with a value less than or equal to 1.0. The stress transfer interface is greatly affected by the type of filler used. Reinforcing fillers exist in 'three forms: particulates, continuous fibers, and discontinuous fibers. In particulate composites, most of the applied load is absorbed by the matrix, and failure is usually in the matrix or at the interface (Phillips and Harris, 1977). Particles are therefore used more to inhibit contraction of the matrix rather than as stress bearing elements. Fibers with a length to diameter (aspect) ratio of over 1000 are considered continuous fibers. In these composites, the load is shared by the matrix and the fiber in proportion to their cross-sectional areas and moduli (Phillips and Harris, 1977). Continuous fibers bear stress equally at all points along their length, because they are longer than the maximum length of stress transfer. Given a high volume 12 fraction and degree of orientation, these could exhibit the maximum reinforcement factor, with strength and stiffness limited only by the properties of the fiber. Short or discontinuous fibers are classified as having an aspect ratio between 10 and 1000 (Phillips and Harris, 1977). Composites using such fibers are unique because stress. is not absorbed. equally' along' the length. of 'the fiber. The load is transferred to the fiber ends and to the surface of the fiber near the ends and maximum stress occurs at the midpoint of the fiber length (Agarwal and Broutman, 1980). The stress distribution in a short fiber can be understood by examining the equilibrium of an infinitesimal length, dz, of a discontinuous fiber: (nr2)5f + (27cr dz)t = (1tr2) (5,; + de) or dOf = 2T (2) dz r (Agarwal and Broutman, 1980) where: 1 5f = fiber stress in the axial direction I = shear stress on the cylindrical fiber- matrix interface r = fiber radius The rate of increase of fiber stress is therefore propor- tional to the shear stress at the interface, for a fiber of 13 uniform radius. Equation (2) can be integrated to give the fiber stress at a cross-sectional distance 2 away from the fiber end: 2 Z Of = Ofo + - 1 dz (3) r o where: Bfo = stress on the fiber end Since short fiber composites have a larger stress concentra- tion in the matrix due to the fiber ends, interfacial bond and the strength of the matrix are far more crucial in obtaining good composite properties than for continuous fibers (Phillips and Harris, 1977). Bonding mechanisms between the matrix and the fiber are unique to each matrix-fiber system, depending greatly on the chemical and molecular properties of each component. Hull (1981) has outlined five :main ‘mechanisms by ‘which adhesion at the interface can occur: adsorption and wetting, interdiffusion, electrostatic attraction, chemical bonding and mechanical adhesion. These can take place either alone or in combination to promote bonding. The adsorption and wetting mechanism overcomes the inherent problems of two solids coming into contact with each other and bonding. At an atomic level, the surfaces of the solids are rough and contact is made only at isolated 14 points. For a polymer matrix to effectively wet a fiber surface, the liquid resin must be able to cover the entire surface of the fiber at a micro level, displacing all the air. The ability of the resin to wet the fiber depends on their surface energies, viscosity of the resin, and the degree of fiber contamination. Interdiffusion promotes bonding between two polymer surfaces by molecular entanglement. The strength of the bond depends on the degree of entanglement and the number of molecules involved. This can be enhanced by the use of plasticizers and solvents that increase molecular motion. Interdiffusion may occur when fibers are coated with polymer before they are introduced into the polymer matrix. Electrostatic attraction occurs between surfaces having opposite charges. The charge density affects the strength of this bond. Although electrostatic attraction is not a major factor in ultimate bond strength of the composites, the use of coupling' agents containing ionic bonds will orient the polymer at the surface to aid in chemical bonding. Chemical bonds are formed when compatible chemical groups exist in the fiber and the matrix. In order for interface failure to occur, the chemical bonds must be 15 broken. Strength of the fiber—matrix bond therefore depends on the number and type of chemical bonds. Mechanical adhesion is simply the interlocking of two surfaces, as when a liquid polymer is able to completely wet a rough solid surface. The degree of surface roughness affects its total area and thus the shear strength of the bond. The surface area of the fiber may also affect the potential for chemical bonds to form. It is generally accepted that for short fiber rein- forced polymers, the interfacial bond strength directly affects the stress transfer interface. The more effective the STI, the better the tensile properties of the composite (Bigg, 1987 and Crosby & Drye, 1986). The effects of good interfacial bond strength on the impact strength (stiffness) of the composite, however, is the subject of some debate. The question hinges on where the principal source of fracture energy lies - in work required to cause elastic debonding or in the work against friction necessary to pull fibers out of the matrix (Phillips and Harris, 1977). One theory is that a high level of adhesion promotes brittleness in the composite, which reduces resistance to crack initiation and thus lowers impact strength. This theory holds that other factors, including the degree of fiber orientation and the matrix stiffness, are the major 15 broken. Strength of the fiber—matrix bond therefore depends on the number and type of chemical bonds. Mechanical adhesion is simply the interlocking of two surfaces, as when a liquid polymer is able to completely wet a rough solid surface. The degree of surface roughness affects its total area and thus the shear strength of the bond. The surface area of the fiber may also affect the potential for chemical bonds to form. It is generally accepted that for short fiber rein- forced polymers, the interfacial bond strength directly affects the stress transfer interface. The more effective the STI, the better the tensile properties of the composite (Bigg, 1987 and Crosby & Drye, 1986). The effects of good interfacial bond strength on the impact strength (stiffness) of the composite, however, is the subject of some debate. The question hinges on where the principal source of fracture energy lies - in work required to cause elastic debonding or in the work against friction necessary to pull fibers out of the matrix (Phillips and Harris, 1977). One theory is that a high level of adhesion promotes brittleness in the composite, which reduces resistance to crack initiation and thus lowers impact strength. This theory holds that other factors, including the degree of fiber orientation and the matrix stiffness, are the major 16 determinants of impact strength (Crosby and Drye, 1986). The opposing theory states that, for short fiber composites, a large part of the energy required to fracture the compo- site is used in pulling the fiber ends from the matrix. In this theory, with good adhesion between the fiber and matrix, the greater the stress load absorbed by the fibers. This means fracture energy is reduced (Phillips and Harris, 1977). Properties of discontinuous fiber composites are also dependent on fiber length. The critical fiber length, 10, is defined as the ndnimum fiber length necessary to reach the breaking stress under load to the composite (Phillips and Harris, 1977). To determine 1C, the force required to pull a length of fiber of diameter d from a block of matrix can be considered: lC/d = Sf/zti (4) where: 8f = fiber tensile strength Ti = shear strength of interface or matrix, which- ever is weaker (Phillips and Harris, 1977) The reinforcing capacity of fibers decreases as they become shorter because a greater proportion of the total fiber length does not carry the full load (Hull, 1981). At 17 or beyond critical length, however, the full stress bearing capacity of the fiber is able to be employed. As mentioned earlier, the orientation of the fibers in short-fiber composites has significant effects on stress transfer and thus affects composite properties. Fibers that are not oriented in the direction of applied load show diminished reinforcement efficiency. 'Fhis is especially true for natural fibers, because they exhibit their maximum stiffness along the fibers and minimum stiffness in the transverse direction (Jindal, 1986). Aligned short fibers may approach up to 95% of the strength of continuous fibers in a composite, if the ratio of fiber length to critical length is greater than 10 (Phillips and Harris, 1977). It is very difficult in practice to align short fibers to the degree necessary to achieve these properties. Fibers randomly oriented in a plane offer up to three- eighths the reinforcement efficiency of aligned fibers. Random fibers in three dimensions, on the other hand, can only approach about one-sixth the reinforcement efficiency (Phillips and Harris, 1977). They do, however, offer the advantages of equal stress-bearing capacity in all direc- tions and ease of processing under conventional methods such as extrusion. One equation. to predict the ‘modulus of composites randomly oriented in a plane is: 18 Erandom = (3/8)EL + (5/8)ET (5) where: EL, ET = longitudinal and transverse :moduli of aligned composites having the same aspect ratio and volume fraction as the random composite (Agarwal and Broutman, 1980) Predicting the performance of composites with three- dimensional random fibers is more difficult because the processing methods used usually do not create a composite with completely random fibers. Fiber orientation changes during flow, and fibers tend to align with the extensional flow direction. The degree of orientation depends on the viscosity of the matrix, extensional and shear flow fields, the shape of the material being produced, and fiber charac- teristics (Hull, 1981). 19 PRIOR RESEARCH Properties of polymer composites using natural fibers as reinforcement usually have to be determined experi- mentally rather than by using mathematical models. The fibers themselves can be considered to be oriented short— fiber composites with cellulosic microfibers of varying lengths and volume fractions (Pavithran et al., 1987). These unique properties make it difficult to compare them to synthetic fibers. Natural fibers tend to vary consider- ably in length and diameter, and inherent surface roughness may present problems with interfacial bonding. The hydro— philic nature of natural fibers make wettability and interfacial bonding with hydrophobic polymers a problem. They can, however, exhibit strength and stiffness superior to glass fibers and many polymers, and are generally inexpensive and abundant. Several types of natural fibers used as fillers in composites have been studied. Ramirez and Solis (1984) used henequen fibers in a recycled polyethylene matrix. They found that the addition of mineral fillers, i.e. river sand, greatly improved environmental resistance at a low cost. Good mechanical properties were observed, and the surface of henequen fiber allowed for good wettability without the use of any coupling agents. 20 The use of coconut fibers (coir) as a potential replacement for glass fibers in thermosetting plastics was studied by Owolabi et al. (1985). Two treatments for improving coupling were employed. They treated fibers with NaOH solution and/or gamma-irradiation prior to manufac- turing the composite. NaOH was used to improve wettability, and gamma-irradiation to initiate graft copolymerization. Both methods showed comparable benefits over using no pre- treatment, but no synergistic effect of using both treat- ments was observed. The composites had very good mechanical properties, but did not achieve properties comparable to glass fiber reinforced plastics. Giridhar' et al. (1986) compared :moisture absorption characteristics of sisal and jute fiber composites with an epoxy matrix. Since moisture absorption is not a problem with glass fibers, this factor must be taken into account when using natural fibers in a composite. Although sisal fibers themselves are more compact and thus absorb less moisture than jute fibers, when used in the composite material the opposite effect was observed. This was attributed to the high cellulose content of sisal and to poor interfacial bonding. Sisal fiber used in a polyester composite has also been studied (Chand and Rohatgi, 1986). In this study, the sisal fibers were first treated with alkali solution to 21 possibly improve adhesion. The alkali treatment was found to improve tensile strength of the fiber" by about 100%, probably due to the thickening of the cell walls. Adhesion was improved as a result of the treatment. This may be due to removal of an incompatible cuticle layer, exposing cellulose and lignin, which is chemically compatible to the polyester resin. Surface roughness was also increased, leading to mechanical interlocking between the fiber and the resin. Bamboo fibers were also explored as reinforcement in polymer composites (Jindal, 1986). The matrix used was Araldite resin (CIBA-CY 230). It was found that bamboo fiber reinforced plastic composites have a similar ultimate tensile strength to mild steel, while their density is only one eighth the density of steel. The impact strength of these composites, however, was poor. Mechanical behavior of bamboo composites with different fiber orientations was found to be similar to behavior of other composites using traditional reinforcing fibers. Impact properties of natural fiber composites were studied by Pavithran et al. (1987). Properties of the composites were compared to properties of the fibers, which included sisal, banana, pineapple and coir. Fibers with higher toughness were found to also exhibit higher impact strength. In composites made with fibers having low 22 toughness, the matrix failed first, followed by fiber fracture, which reduced the work contribution of fiber pullout. The angle of microfibrils in natural fibers was also found to affect the impact behavior of the composites, and should be taken into account when predicting impact properties. The use of wood as a filler has been the subject of many studies. Lightsey et al. (1977) compared wood flour and pulp mill wood residue as fillers in composites of poly- ethylene and polystyrene. The wood residue, with an aspect ratio of 3 to 19, was found to give slightly better tensile properties in the composite than wood flour, with an aspect ratio of 2.5. Tensile modulus increased with increasing filler content for both matrices. Impact strength of the polystyrene matrix decreased with increasing filler content, and poor bonding between the phases was observed, No impact data was obtained for the polyethylene matrix. Klason et al. (1984) studied the effect of various cellulosic fillers on nmtrices of HDPE, polypropylene, and polystyrene, without using coupling agents. A substantial increase in modulus was observed by addition of fibers to the polymers. The increase tended to be higher for the matrices with lower moduli. Critical volume fractions of fillers were determined to be approximately 40% for poly- propylene and polystyrene, and about 30% for HDPE. Above 23 these levels, significant reductions in impact strength and tensile strength at break were observed. Studies comparing mechanical properties achieved by polyethylene/aspen fiber composites containing varying filler/matrix ratios were carried out by Gogoi (1989) and Yam (1987). Adding fibers to HDPE decreased its tensile strength by about ten percent. For fiber contents of 15-40%, tensile strength was fairly constant. At fiber contents above 45%, tensile strength decreased sharply. Modulus of elasticity increased linearly" with increasing amounts of fibers. At 40% fiber content, the modulus of the composite was nearly double the modulus of HDPE. Polyethylene/aspen fiber composites using a bonding agent to promote adhesion were studied by Raj et al. (1988). In this study, various isocyanates were used successfully to improve the tensile properties of the composites. The isocyanate groups are able to form covalent bonds with the hydroxyl groups in cellulose, and the other part of the isocyanate can bond by Van der Waals forces with the polymer. Various amounts of maleic anhydride were also included to coat the fibers. Slight increases in tensile stress and modulus were observed with the higher amount of maleic anhydride. Tensile properties of these composites were found to be comparable with mica and glass fiber reinforced composites. 24 The use of aspen fibers in a Ixflystyrene matrix was studied by Maldas and Kokta (1989). The focus of this study was the resistance of composites to various aging conditions. Fibers were treated with coupling agents, i.e. isocyanates, coated with hydrophobic thermoplastic, or grafted to the polystyrene matrix by covalent bonds. Treated composites were found to have superior mechanical properties and dimensional stability under various temper— ature and moisture conditions, suggesting good interfacial bonding. An attempt to improve properties of aspen fiber/HDPE composites was made by the use of various additives (Nieman, 1989). These included ionomer modified polyethylene and chlorinated polyethylene to aid interfacial bonding, low density polyethylene to decrease viscosity and crystallin— ity, stearic acid as a dispersant, and maleic anhydride modified polypropylene (MAPP) as a coupling agent. Ionomer and MAPP were shown to improve tensile strength and modulus, which may indicate good adhesion. All additives except stearic acid decreased impact strength. EXPERIMENTAL DESIGN MATERIALS The matrix material used in this study was high density polyethylene (HDPE) from post—consumer milk containers. HDPE is a highly crystalline polymer containing long, mostly unbranched hydrocarbon chains. The linear nature of these chains allows them to pack closely together, which gives the polymer its high density characteristics. The density of HDPE is approximately 0.96 g/cm3 (Briston, 1989). The structure of these chains is as follows: -CH2-CH2—CH2-CH2-CH2-CH2-CH2- / CH2 A few branches occur along the chains, but they are short and do not prevent the polymer from obtaining crystalline properties. Fibers were commercially available thermomechanical pulp aspen (Populus tremula) fibers. The composition of wood is approximately 40-50% cellulose, 20-35% hemicellu- lose, and 15-35% lignin (Wagenfuehr, 1984). The primary (outer) cell wall contains cellulose microfibrils in various orientations, and is incrusted with hemicellulose and lignin. The secondary (inner) cell‘ wall contains three 25 26 layers, each with different microfibril orientations, and is also incrusted with hemicellulose and deposits of lignin. The center of the cell is called the lumen, and the middle lamella is the intercellular material. The middle lamella is amorphous, readily dissolved, and has a high lignin and low cellulose content (Meylan and Butterfield, 1972). Hemicellulose tends to be amorphous and soluble. Cellulose, where most of the strength of wood is obtained, has a crystallinity of 50-83%. Early wood is more crystal— line than late wood. ("Early" and "late" refers to the time of year in which the wood has grown.) Cellulose is made of over 3000 glucose units held together by beta— glucosidic linkages (Wagenfuehr, 1984). The structure of cellulose is: (C H O ; n > 3000 6 10 5 n The three additives used were stearic acid (Sigma, St. Louis, MO), ionomer modified polyethylene (trade name Surlyn 1605; duPont, Wilmington, DE), and maleic anhydride modified polypropylene (trade name Hercoprime; Himont, Wilmington, DE). stearic acid was chosen to act as a dispersant. It has been previously used in polymer composites to decrease fiber 27 agglomeration in the polymer matrix (Klason et al, 1984), which can result in weak spots where fibers are not sufficiently wetted out by the matrix. This causes fiber pullout, decreasing the strength of the composite material. Although it has not been shown to significantly enhance mechanical properties when added to a wood fiber/HDPE composite (Nieman, 1989), it has not adversely affected them and may be beneficial in combination with a coupling agent. The structure of stearic acid is: C17H350=0 \ OH The carboxyl (-COOH) groups in stearic acid have the potential to react with hydroxyl (-OH) groups, which are found in cellulose, to lessen the polar nature of the wood. Ionomer modified polyethylene contains both ionic and covalent bonds, and was chosen for its potential to improve adhesion between HDPE and wood fibers. Improvement of tensile strength and modulus of composites containing ionomer indicate some degree of adhesion (Nieman, 1989) Since HDPE is hydrophobic and wood is hydrophilic, they are not chemically compatible. Addition of a component that could introduce ionic bonds between cellulose and HDPE may aid interfacial bonding. The structure of ionomer is similar to high density polyethylene and exhibits many of 28 the same characteristics (Briston, 1989). The difference lies in ionic cross-links located along the polymer chain. The anionic portion is created by carboxyl groups, and the cationic portion by metal ions, e.g. sodium. The structure of the ionomer is as follows (Briston, 1989): —c-c-c—c-c-c-c-c-c-c-c-c— / 0‘-c=o \M+ \ o*-c=o / -c-c-c-c-c-c-c-c-c-c-c-c- Maleic anhydride modified polypropylene (MAPP) has also been used as a coupling agent by providing a linkage between the wood fibers and the polymer matrix (Dalvag et al., 1985). MAPP has the potential to form covalent bonds with both wood and HDPE. Significant improvement of tensile strength and modulus has been reported, but MAPP was also shown to decrease impact strength (Nieman, 1989). This loss of impact strength could possibly be negated if ionomer or stearic acid were included in the composite. METHODS All four samples were composed of approximately 30% by weight wood fiber. For the control, the remaining 70% was recycled HDPE. The other three samples contained 29 approximately 60% recycled HDPE and 5% of each of two additives. Exact composition is shown in Table 1: Table 1 Sample Composition by weight Sample wood HDPE ionomer MAPP stearic no. acid 1 102 g 280 g 2 120 g 232 g 20 g 20 g 3 120 g 237 g 20 g 20 g 4 120 g 232 g 20 g 20 g Sample Composition bV percent 1) 26.8% wood/ 73.2% recycled HDPE 2) 30.6% wood/ 59.4% HDPE/ 5% ionomer/ 5% stearic acid 3) 30.2% wood/ 59.8% HDPE/ 5% stearic acid/ 5% MAPP 4) 30.6% wood 59.4% HDPE/ 5% MAPP/ 5% ionomer The fibers were air—dried at 23° C, 50% RH, and a sample weighed at regular intervals until reaching moisture equilibrium. The HDPE milk containers were rinsed, caps and labels removed, cut into fourths, and granulated with a BTP Granulator Model 68 SPL (Polymer Machinery, Berlin, CT). After weighing out the proper amount of each, the additives 30 were placed in a closed bag with the HDPE and mixed thor— oughly by shaking. This mixture was put in the hopper of the extruder. The extruder used was a 38mm, 11.1 L/D, MPC/V-3ODE Baker-Perkins corotating intermeshing twin-screw extruder (Baker-Perkins, Saginaw, MI). All four zones of the extruder and the die were heated to a temperature of 150 degrees C, with a compounder speed of 150 RPM, feed rate 5%, and average 80% load. Fibers were fed by hand into the partially melted resin in Zone 2 to minimize damage. Extruded material was cut into approximately 4" lengths before hardening. The extruded material was formed into testing specimens by first compression molding into plates approximately .125" thick. For this a Carver Model M 25 Ton laboratory press was used (Fred S. Carver, Inc.; Menomonee Falls, WI). Three lengths of material were used to make one plate. Platens were heated to 1500 C; the material was heated to this temperature for ten minutes, held for another ten minutes at 30,000 psi, and then allowed to cool down for fifteen minutes to 50° C while still under pressure. Four plates were made from each sample and the tensile, impact, and creep specimens were cut according to ASTM standards (ASTM, 1988). 31 Tensile and creep specimens were cut, using a Tensil- kut Model 10—13 specimen cutter (Tensilkut Engineering, Danbury, CT), into Type I dumbbell shapes with a 2" gauge length. These specimens were all cut parallel to the direction of the extrudate. Impact specimens were cut on a band saw into 2.5" x 0.5" x .125" bars and notched using a TMI Notching Cutter Model TMI 2205 (Testing Machines, Inc., Amityville, NY). Specimens were cut both lengthwise and crosswise to the direction of the extrudate to determine if this affects impact strength. All composite samples tested contained specimens cut from at least two different plates. Exact dimensions of all specimens used in testing were measured with vernier calipers and recorded. The samples were conditioned at 23° C, 50% RH for at least 40 hours prior to testing. Tensile testing followed ASTM D 638-77a: Tensile Properties of Plastics (ASTM, 1988). Tensile strength, percent elongation at break, and modulus of elasticity were determined by using an Instron Tester Model 4201 (Instron, Canton, MA). Crosshead speed was set at 2.0 in/min., at 400 lbs. full scale load. Abrasive paper was used to prevent slippage of specimens from the grips. Testing was replicated at least five times for each additive combination and the control. For impact testing, ASTM C 256-87: Impact Resistance of Plastics and Electrical Insulating Materials, was used 32 (ASTM, 1988). Impact strength was determined using a TMI 43-1 Izod Impact Tester (Testing Machines, Inc., Amityville, NY) with a 5 ft-lb. pendulum load. Sixteen impact tests were performed on each sample, with eight impacts parallel to the direction of the extrudate and eight perpendicular to the extrudate. Creep testing followed ASTM D 2990-77: Tensile, Compression and Flexural Creep and Creep Resistance of Plastics (ASTM, 1988). Both ends of the specimens were held firmly in metal clamps by using abrasive paper, and one end was hung from a sturdy metal rack. Fifty pounds of weights were attached to the other end of the specimens. Distances between the clamps were measured with vernier calipers and recorded regularly until no further creep was observed for at least one week. Three replications of each creep test were performed in a 23° C, 50% RH environment. Once testing results for impact strength, tensile strength, percent elongation at break, and modulus of elasticity were obtained, the following analyses were performed using the MSTAT statistical program (Version 5.0, Michigan State University, 1988): o A two-way analysis of variance to determine any statistically signifiCant treatment effects. 33 o A Tukey's Honestly Significant Difference Test to detect any significant differences among the treatment means. 0 Orthogonal contrasts to determine if the treat- ments showing the greatest improvement of proper- ties are statistically significant. o A class comparison to compare treatment effects and confirm results from other analyses. Results of the creep testing were averaged for all three replications and charted on a graph of time vs. creep distance for a comparative analysis. RESULTS“ IMPACT TEST The results of the impact testing are shown in Table 2. Each sample was tested with an impact both parallel and perpendicular to the direction of the extruded material, for a total of eight treatments. For' parallel impact, the specimens were cut with a crosswise orientation to the extrudate direction. Perpendicular impact was on specimens cut with a lengthwise orientation. There were eight replica- tions of each treatment for a total of 64 cases. Individual results are shown in Table A1 of the Appendix. Table 2 Impact Test Results (5 lb. izod test) # sample orientation mean s.d. 17233581 """"" IQSQEQQE;"'TEIS'EEIQZEBT""TSSE 2. control crosswise .717 .098 3. stearic/ion. lengthwise .835 .129 4. stearic/ion. crosswise .697 .149 5. MAPP/stearic lengthwise .573 .073 6. MAPP/stearic crosswise .551 .086 7. MAPP/ionomer lengthwise .630 .087 8. MAPP/ionomer crosswise .622 .063 * All raw data and statistical tables can be found in the Appendix. 34 35 Sample numbers correspond with treatment numbers used in the statistical analysis. For all treatments tested, impact perpendicular to the direction of the extrudate showed slightly higher impact strength than parallel impact. The treatments containing MAPP appeared to lower impact strength. To determine the statistical significance of these observations, several analyses of data using MSTAT were performed. Results of the two-way analysis of variance (Table A2) show that there was a highly significant treatment effect. In order to determine where the significant differences were between pairs of treatment means, a Tukey's Honestly Significant Difference Test was performed. The test ranked the means in order of size and then compared adjacent pairs, noting significant differences between the pairs at a confidence level of 95%. This is shown in Table A3. The test shows significant differences between at least one of the control samples and the additive systems containing MAPP. Since the test shows no significant differences between adjacent pairs of ranked means, it can be asserted that the direction of impact in relation to the direction of the extrudate does not have a significant effect on the impact strength. 36 To determine if the significant treatment effect was related.tx> the inclusion of additives, orthogonal contrast #1 was performed, comparing the means of the control samples with the means of the samples containing additives (Table A4). The resultant F-value shows a highly significant treatment effect as a result of including additives. Contrast #2, comparing means of samples containing MAPP to the rest of the means, shows an even higher F-value. The class comparison confirmed that the treatment effect was highly significant. TENSILE TEST Five replications of the tensile testing were used to obtain each treatment mean for a total of 20 cases. Tensile strength results are shown in Table 3. Table 3 Tensile Strength # sample mean s.d. 1. control 3247 psi 56 2. stearic/ion. 3279 320 3. MAPP/stearic 3912 540 4. MAPP/ionomer 3809 405 37 Individual results are shown in Table A6 of the Appendixn The samples containing’ MAPP appear to offer improved tensile strength over the other two samples. The two-way analysis of variance (Table A7) shows a significant treatment effect. The Tukey's test did not show any significant differences between pairs of ranked means at a 95% confidence level (Table .A8). To determine if the significant treatment effect was due to the inclusion of additives, orthogonal contrast #1 was performed. A signifi- cant effect was observed in samples containing additives (Table A9). Orthogonal contrast #2 was performed to compare the samples containing MAPP to the other samples. This showed a highly significant treatment effect due to MAPP (Table A9). The class comparison also showed a significant treatment effect (Table A10), confirming results obtained from the other tests. Mean values for percent elongation at break are shown in Table 4. Individual results can be found in Table All of the Appendix. 38 Table 4 Percent elongation at break percent elongation # sample mean s.d. 1. control 2.75% .41 2. stearic/ion. 2.47 .22 3. MAPP/stearic 3.12 .41 4. MAPP/ionomer 2.85 .31 The two-way analysis of variance (Table A12) and the class comparison (Table A13) showed no significant treatment effect. The Tukey's test also indicated no significant differences between means, as shown in Table A14. Since the MAPP/stearic acid additive combination showed the highest elongation at break, an orthogonal contrast was performed to determine if it was statistically significant (Table A15). The results show a significant treatment effect, compared to the other samples, when MAPP and stearic acid ‘were used together as additives. The modulus of elasticity for each sample is shown in Table 5. Individual results are in Table A16 of the Appendix. 39 Table 5 Young's modulus of elasticitv modulus # sample mean s.d. 1. control 201842 20347 2. stearic/ion. 237358 8329 3. MAPP/stearic 236326 6838 4. MAPP/ionomer 234557 3853 All three samples containing additives showed an increase in modulus of elasticity as compared to the control. Two-way analysis of variance for the modulus (Table A17) shows a highly significant treatment effect of at least one of the treatments. The Tukey's test (Table A18) shows a significant difference between the control and the adjacent treatment containing additives, and no signifi- cant differences between the three treatments using addi- tives. This is reinforced. by the orthogonal comparison, indicating a highly significant treatment effect when additives are included in the composite (Table A19). This is confirmed by the class comparison in Table A20. CREEP TEST A graph of the creep test results is shown in Figure l. Creep data for three replications was averaged for each sample, for a total of twelve tests. All samples exhibited 40 vmoB moouo mo muasmom ”a .ousmflm mass: as as a: as as s s s e as .. E emgs=s1\mm¢= . s_amscm\mm¢= . .mfia. aa2s=s_\usamafim a _aaL=ss a Na. 41 similar behavior, with most of the creep activity taking place within the first 24 hours or so. With the exception of the MAPP/ionomer additive system, extension tended to level off after 2 or 3 days. The three test replications for all samples except the MAPP/ionomer system gave very similar results. Since the data for the MAPP/ionomer specimens varied widely, the accuracy of its graph is questionable. SUMMARY A summary of the significant treatment effects found for each property is listed in Table 6. Table 6 Summary of statistical analysis property treatment(s) having significant effect impact strength MAPP/stearic acid (negative) MAPP/ionomer (negative) tensile strength MAPP/stearic acid MAPP/ionomer elongation at break MAPP/stearic acid modulus of elasticity stearic acid/ionomer MAPP/stearic acid MAPP/ionomer DISCUSSION IMPACT STRENGTH A graph comparing impact strength of the control with the three composites containing additives is shown in Figure 2. The impact strength of wood fiber/HDPE compo— sites did not improve as a result of using additives. The slightly lower fiber content of the control should not be a factor, since it has been shown that impact strength is not affected by fiber content in that range (Gogoi, 1989). It is not certain whether the lower impact strength is caused by good adhesion or' not, as the use of impact strength to predict the degree of adhesion is debatable (Phillips and Harris, 1977). Using stearic acid and ionomer, however, did not decrease impact strength compared to the control sample. This may be due to the inclusion of stearic acid, which has been reported earlier to have no effect on impact strength (Nieman, 1989). Slightly better results were obtained when the sample was cut along the direction of the extrudate. The slight improvement may be due to the tendency of more fibers to be oriented along the direction of flow (Hull, 1981). This means that more fibers would be perpendicular to the impact and would. be able to absorb 'more energy than the fibers oriented parallel to the impact. Since the difference is 42 43 wd NC 56:25 Loans: v05 ”N 3:2". .532. 6.6 m6 to 6.6 No to 06 E152 o 32» \ o<_2 .oEocB 3.33m 33:00 I _ _ mmzzuum 06.3505. 033320 44 not statistically significant, however, it indicates a high level of fiber randomization was achieved in extrusion. TENSILE STRENGTH As with impact strength, the use of stearic acid and ionomer as additives showed no effect on tensile strength of the composite (Figure 3). The use of MAPP with both ionomer and stearic acid showed approximately 19% improve— ment in tensile strength, which measures the maximum tensile stress a material can sustain (Briston, 1989). This indicates that good adhesion between the fiber and matrix was obtained when using MAPP. However, a tensile strength of approximately 4800 psi has been reported when using 5% MAPP alone as an additive (Nieman, 1989), an improvement of 24% over using no additive. This suggests some loss of potential bonding by combining MAPP with other additives. Prior research by Gogoi (1989) has shown that, at fiber contents of 18% and 35%, tensile strength remains the same. It can be assumed, therefore, that the slight difference in fiber content between the control and the composites containing additives had little effect on tensile strength characteristics. To determine if combining additives had a synergistic or antagonistic effect on tensile strength, a comparison of 45 Goo... comm. Goo m _ oomN H.222 59.2% 0:28... no 2 32.... 5o ooou ooms coo. com o — .oEocS \oo(5_ o 82w \ n22 3:62..” I I E s 32.63 46 the tensile strength of two single additives (Nieman, 1989) versus tensile strength of dual additives was used. This is illustrated in Table 7. Table 7 Tensile strength: single additives vs. dual additives tensile strength additive single additive dual additives stearic acid 3134 psi 3279 psi ionomer 4121 stearic acid 3134 3912 MAPP 4839 ionomer 4121 3809 MAPP 4839 Since the tensile strength of the dual additive systems showed no improvement over tensile strength of at least one of their component single additive systems, it is apparent that there is no advantage to combining additives. The ionomer/MAPP system had a lower tensile strength than either of its two components used alone in a composite, suggesting an antagonistic effect on the bonding capacity of both these additives. 47 ELONGATION AT BREAK Elongation at break is shown graphically in Figure 4. This indicates the material's ability to stretch while under load (Briston, 1989), and may be improved with good dispersion of fibers. The stearic acid/ionomer system decreased elongation at break, while the MAPP systems improved this property. Only the combination of MAPP and stearic acid showed a significant effect, indicating that good adhesion and/or dispersion was achieved. Ionomer may have had no effect on adhesion, since it did not improve elongation properties when in combination with the other additives. A comparison with percent elongation of compo- sites containing single additives (Nieman, 1989) is shown in Table 8. Table 8 Percent elongation at break: 4§ingle vs. dual additives percent elongation additive single additive dual additives stearic acid 4.08% 2.47% ionomer 3.10 stearic acid 4 08 3.12 MAPP 3.75 ionomer 3.10 2.85 48 xwotm “a 5:355 2529... a. 232.... :80qu m6 0.6 md 9N ms _ d H 0.? m6 0.0 _ _ _ 380:2 Eo<2 o :35 \ n22 .0285. 3.303. $2.62 49 None of the dual additive systems were able to achieve elongation properties comparable to properties obtained by either additive used alone. Again, these results show no advantage to combining additives. MODULUS Q_F_ ELASTICITY All additive systems improved the modulus of elasticity (Figure EU. Modulus is a measure of the stiffness of the material, defined by the stress/strain ratio over the range where this ratio is constant (Briston, 1989). Since all three additive systems performed equally well in improving the modulus, it is unclear whether this was a result of adhesion, dispersion, or both. A linear relationship between fiber content and modulus has been demonstrated (Gogoi, 1989), so part of the increase may be due to the 3-4% higher fiber content in the composites containing additives. Based on the results obtained when comparing moduli of composites with different fiber contents, this would account for an improvement of approximately 10000 psi over the control sample. Still, combining additives appears to show significant improvement over' the use of single additives (Nieman, 1989), suggesting possible interaction between additives. A comparison is shown in Table 9. 50 3.0335 co 2:352 ”m 0.52". 0000mm OOOOON oooomp _ ooooow oooom o 880:2 \on.<5_ 0 EB.» \ n22 BEES. $2.62 51 Table 9 Modulus of elasticitv: single vs. dual additives modulus of elasticity additive single additive dual additives stearic acid 146164 psi 237358 psi ionomer 212579 stearic acid 146164 236326 MAPP 166571 ionomer 212579 234557 MAPP 166571 One factor that should not be overlooked is the different proportion of HDPE in the control compared to composites containing additives. volume fractions of each component 'were determined. based. on.‘weight fractions. and density as shown in equation (6): vf = 1 - (1-wf)_fC (6) m (Kalyankar, 1989) where: Vf = volume fraction of filler Wf = weight fraction of filler Pb = density of composite Pm = density of matrix By solving for R, a reinforcement factor, equation (1) can be used to determine if the higher moduli achieved in composites containing additives was the result of a smaller 52 volume fraction of HDPE. EC = Eme + R Efo (1) (McNally et al, 1978) Moduli of 87000 psi for recycled HDPE (Yam, 1987), 800000 psi for aspen fibers (Bolz and Tuve, 1970), 59000 psi for ionomer, and 200000 psi for MAPP were used along with the volume fractions shown in Table 10. Since stearic acid is not a polymer and has no modulus, its value was assumed to be zero. The resulting R values are shown in Table 11. Table 10 Volume fractions ffiiEEYf _____________ Es ....... Y§93§-__-Y£_---Yees;3_-_Y299;2 none 201842 .79 .21 ionomer/stearic 237358 .64 .24 .06 .06 stearic/MAPP 236326 .65 .23 .06 .06 MAPP/ionomer 234557 .64 .24 .06 .06 53 Table 11 Bginforcement factors additive R 3332"”-"""""""""'T§; """" ionomer/stearic .93 stearic/MAPP .91 MAPP/ionomer .85 The reinforcement factors for the additive systems are somewhat higher than the control's. Since orientation should be similar for all treatments, the higher R value suggests a more efficient stress transfer interface. This is indicative of good adhesion between the fibers and the matrix. This may have been aided by fiber dispersion, since the composites containing stearic acid show the highest reinforcement factors. Modulus is the only property where combining additives has an advantage over single additives. CREEP The MAPP/stearic acid additive combination showed the best overall creep properties (Figure JJ. All composites using additives exhibited better initial creep resistance than the control, suggesting good adhesion was achieved. Fiber content may have contributed to this difference, 54 also, since composites containing more polymer are expected to show less creep resistance. After a period of about one week, however, all four samples exhibited similar behavior so it is difficult to draw any conclusions about the long term effects of dual additives on creep properties. Composites containing only one additive exhibited similar creep rates except the 5% MAPP composite, which showed very little increase for the first three days. After one week the extension was less than .01" (Nieman, 1989). In contrast, the composite containing 5% ionomer alone had an extension of nearly .02" after one week (Nieman, 1989). Since the effects of combined additives fell between the effects of single additives, the advan- tages of using more than one additive are questionable. CONCLUSIONS With the exception of impact strength, the use of dual additives in wood fiber/HDPE composites either improved or maintained the mechanical properties of a composite con- taining no additives. Combining additives to enhance properties offered no significant improvement over the use of only one additive, except for modulus of elasticity. The composite containing MAPP and stearic acid exhibited the best overall creep resistance, tensile strength, and elongation at break, but was shown to significantly decrease impact strength. The stearic acid/ionomer additive system had no effect on impact or tensile strength and decreased elongation at break. The use of MAPP and ionomer decreased impact strength, increased tensile strength, and had little effect on elongation at break. All additive systems performed equally well in improving initial creep resistance and modulus of elasticity. 55 RECOMMENDATION S Since these additive combinations appeared to offer no significant overall advantage over using only one additive, further research on these three additive systems is probably not necessary. Since both systems containing MAPP showed improvement in all properties except impact strength, it is recommended that this additive be studied further, possibly in combination with an impact modifier. More reliable comparisons may be made with control samples if the propor— tions of matrix (less additives) to filler are more similar. 56 APPENDIX 57 LIST OF VARIABLES AR TYPE NAME/DESCRIPTION l numeric treatment 2 numeric replication 3 numeric impact strength CASE CASE NO. 1 2 3 NO 1 2 3 1 1 1 0.732 41 6 l 0 625 2 1 2 0.960 42 6 2 0.598 3 l 3 0.719 43 6 8 0.410 4 1 4 0.921 44 6 4 0.583 5 l 5 0.691 45 6 5 0.651 6 l 6 0.812 46 6 6 0.578 7 1 7 0.844 47 6 7 0.598 8 l 8 0.819 48 6 8 0.542 9 2 1 0.816 49 7 1 0.535 10 2 2 0.823 50 7 2 0.754 11 2 3 0.760 51 7 8 0.635 12 2 4 0.740 52 7 4 0.625 13 2 5 0.719 53 7 5 0.651 14 2 6 0.549 54 7 6 0.736 15 2 7 0.593 55 7 7 0.607 16 2 8 0.734 56 7 8 0 501 17 3 1 0.730 57 8 1 0.629 18 8 2 0.728 58 8 2 0.683 19 3 3 0.798 59 8 3 0.622 2 3 4 0.779 60 8 4 0.501 2 3 5 1.029 61 8 5 0.650 2 3 6 1.038 62 8 6 0.559 23 3 7 0.847 63 8 7 0.656 24 3 8 0.734 64 8 8 0.678 2 4 1 0.656 —————————————————————————————— 26 4 2 0.819 27 4 3 0.740 28 4 4 0.640 29 4 5 0.497 30 4 6 0.810 31 4 7 0.506 32 4 8 0.906 38 5 1 0.535 34 5 2 0.535 35 5 3 0.719 36 5 4 0.505 37 5 5 0.416 38 5 6 0.544 39 5 7 0.551 40 5 8 0.604 Table A1: Individual Results, Impact Strength Data file Title: Function: ANOVA-Z Data case no. 1 Without selection to 58 JideDEKCZTF Impact Strength 64 Two—way analysis of variance over variable 1 treatment with values from replication with values from Variable 3 impact strength A N A L Y S I 8 Degrees of to 8 and to 8 O F Sum of Squares over variable V A R I A N C E Mean Square 2 _._—__‘________——_____-_—__-_‘______‘______-—__———_______¢_____ Freedom Total 63 Variable 1 7 Variable 2 7 Error 49 —————-—————————_—_—————————.————-—-—————————————--——~——————_—————— Non—additivity 1 Residual —~—~-n*—w—-—————.¢—————————u--——-——u-n—-—-——-———-——u—-———~—————————————— Grand Mean: Coefficient of Variation: Means for variable VAR 1 1 MEAN 0.812 VAR 1 7 MEAN 0.631 Table A2: 0.680 Grand 3 for each 2 0.717 8 0.622 15. 0.835 T A B L E F—value Prob 088 8.22 000 007 0 64 011 001 0.07 011 43.505 Total Count: 64 1 4 5 6 0.697 0.551 0.573 Two-Way Analysis of Variance, Impact Strength 59 Data file IMPACT Title: Impact Strength Function: RANGE Data case no. 1 to 64 Without selection Error Mean Square = .011 Error Degrees of Freedom 2 49 Number of observations used to calculate a mean = 8 Tukey’s Honestly Significant Difference Test s_ = 3.708099E—02 at alpha 2 .05 x Original Order Ranked Order Mean 1: 0.81 A Mean 3: 0.83 A Mean 2: 0.72 AB Mean 1: 0.81 A Mean 3: 0.83 A Mean 2: 0.72 AB Mean 4: 0.70 AB Mean 4: 0.70 AB Mean 5: 0.55 B Mean 7: 0.63 B Mean 6: 0.57 B Mean 8: 0.62 B Mean 7: 0.63 B Mean 6: 0.57 B Mean 8: 0.62 B Mean 5: 0.55 B Table A3: Tukey's Test, Impact Strength 60 Data file IMF‘ACT Title: Impact Strength Function: ANOVA-l Data case no. 1 to 64 Without selection One way ANOVA grouped over variable 1 treatment with values from 1 to 8 Variable 3 impact strength A N A L Y S I S 0 F V A R I A N C E T A B L E Degrees of Sum of Error Freedom Squares Mean Square F—value Prob. Between 7 0.6166 0.09 8.61 .000 Within 56 0.5730 0.01 Total 63 1 1896 Coefficient of Variation: 14.88% Var. V A R I A B L E No. 3 1 Number Sum Average SD SE 1 8.00 6.498 0.81 0.10 0.04 2 8.00 5 734 0.72 0.10 0.04 3 8.00 6 683 0 84 0.13 0.04 4 8.00 5 574 0 70 0.15 0.04 5 8.00 4 409 0 55 0.09 0.04 6 8.00 4.585 0.57 0.07 0.04 7 8.00 5 044 0.63 0.09 0.04 8 8.00 4 978 0.62 0.06 0.04 Total 64.00 43.505 0 68 0.14 0 02 Within 0.10 Bartlett’s Test Chi-square = 7.515069 Number of Degrees of Freedom 2 7 Approximate Significance = .3772 Table A4: Orthogonal Contrast, Impact Strength 61 SINGLE DF ORTHOGONAL COMPARISONS (CONTRASTS) FOR CONTRAST # 1 1:—3, 22—3, 3: 1, Sum 0f Squares: Effect: —0.028 Error: 0.007 F value: 14.97 Prob: .000 FOR CONTRAST # 2 1:11;”-2:”:1_Ta”3:_;—1,~4:~1, 5:. l, 6:- 1, 7: Sum Of Squares: Effect: ~0.086 Errorz 0.013 F value: 45.74 Prob: .000 Table A4 (cont'd.) 1, 5: 1, 6: 1, 7: 0.468 62 Data file IMPACT Title: Impact Strength Function: FACTOR Data case no. 1 to 64 Without selection Factorial ANOVA for the factors: Variable 2 with values from 1 to 8 replication Variable 1 with values from 1 to 8 treatment Variable 3 impact strength Grand Mean: 0.680 Grand Sum: 43.505 T A B L E O F M E A N S 2 * 1 * 3 Total 1 * 1 * 0.657 5.258 2 * 1 * 0.738 5.900 3 * 1 * 0.675 5.403 4 * 1 * 0.662 5.294 5 * 1 * 0.663 5.304 6 * 1 * 0.703 5.626 7 * 1 * 0.650 5.202 8 * 1 * 0.690 5.518 1 * 1 * 0.812 6.498 1 * 2 * 0.717 5.734 1 * 3 * 0 835 6.683 1 * 4 * 0.697 5.574 1 * 5 * 0.551 4.409 1 * 6 * 0.573 4.585 1 * 7 * 0.631 5.044 1 * 8 * 0.622 4.978 K value 1 2 Factor 2 1 From 1 1 To 8 8 Table A5: Class Comparison, Impact Strength Total Count: 64 63 7. Randomized Complete Blocks Design (RCBD) A N A L Y S I S O F V A R I A N C E T A B L E Degrees of Sum of F Code Source Freedom Squares Mean Square Valuer Prob 1 Rep 7 0 05 0.007 0 64 2 A 7 0 62 0.088 8 22 000 -3 Error 49 0 53 0 011 Coefficient of Variation: 15.23% s _ for means group 1 = 3 659958E—02 Number of observations 2 8 y s _ for means group 2 : 3.659958E-02 Number of observations 2 8 y Table A5 (cont'd.) 64 Data file TEIJSILE Title: Tensile Strength Function: PRLIST Data case no. 1 to 20 Without selection LIST OF VARIABLES VAR TYPE NAME/DESCRIPTION 1 numeric treatment 2 numeric replication 3 numeric tensile strength CASE NO. 1 2 3 1 l 1 3315 2 1 2 3201 3 1 3 3280 4 1 4 3179 5 1 5 3258 6 2 1 3275 7 2 2 3738 8 2 3 2860 9 2 4 3156 10 2 5 3364 11 3 1 3675 12 3 2 3660 13 3 3 3953 14 3 4 4823 15 3 5 3450 16 4 1 3710 17 4 2 4332 18 4 3 3980 19 4 4 3224 20 4 5 3800 —_—————--——~‘——-——-——-——-——_-——. Table A6: Individual Results, Tensile Strength 65 Data file TEIJSILE Title: Tensile Strength Function: ANOVA—2 Data case no. 1 to 20 Without selection Two-way analysis of variance over variable 1 treatment with values from 1 to 4 and over variable 2 replication with values from 1 to 5 Variable 3 tensile strength A N A L Y S I S O F V A R I A N C E T A B L E Degrees of Sum of Freedom Squares Mean Square F—value Prob Total 19 4058480.55 Variable 1 3 1817700.55 605900.183 3.53 .048 Variable 2 4 182741.30 45685.325 0.2 Error 12 2058038 70 171503.225 Non-additivity 1 12797.19 12797.186 0.07 Residual 11 2045241.51 185931.047 Grand Mean: 3561.650 Grand Sum: 71233 000 Total Count: Coefficient of Variation: 11.63% Means for variable 3 for each value of 1 VAR 1 1 2 3 4 MEAN 3246.600 3278.600 3912.200 3809.200 Table A7: Two-Way Analysis of Variance, Tensile Strength 20 66 Data file TEIJSILE Title: Tensile Strength Function: RANGE Data case no. 1 to 20 Without selection Error Mean Square = 171503 2 Error Degrees of Freedom = 12 Number of observations used to calculate a mean = 5 Tukey’s Honestly Significant Difference Test s_ 2 185.2043 at alpha 2 .05 x Original Order Ranked Order Mean 1: 3246.60 A Mean 3: 3912.20 A Mean 2: 3278.60 A Mean 4: 3809.20 A Mean 3: 3912 20 A Mean 2: 3278.60 A Mean 4: 3809 20 A Mean 1: 3246.60 A Table A8: Tukey's Test, Tensile Strength 67 Data file TENSILE Title: Tensile Strength Function: ANOVA-l Data case no. 1 to 20 Without selection One way ANOVA grouped over variable 1 treatment with values from 1 to 4 Variable 3 tensile strength A N A L Y S I S 0 F V A R I A N C E T A B L E Degrees of Sum of Error Freedom Squares Mean Square F-value Prob. Between 3 1817700.5500 605900.18 4.33 .020 Within 16 2240780.0000 140048.75 Total 19 4058480.5500 Coefficient of Variation: 10.51% Var. V A R I A B L E No. 3 1 Number Sum Average SD SE 4 00 19046 000 3809.20 404 62 167 36 Total 20.00 71233.000 3561.65 462.17 103.35 Within 374.23 Bartlett’s Test Chi-square = 11.67985 Number of Degrees of Freedom 2 3 Approximate Significance = .0085 Table A9: Orthogonal Contrast, Tensile Strength 68 SINGLE DF ORTHOGONAL COMPARISONS (CONTRASTS) FOR CONTRAST # 1 1:—3, 2: 1, 3: 1, 4: 1 Sum Of Squares: 661710.017 Effect: 105.017 Error: 48.313 F value: 4.72 Prob: .045 FOR CONTRAST # 2 1:-14 22-1, 3: 14 4: 1 Sum Of Squares: 1788618.050 Effect: 299.050 Error: 83.681 F’valuezwr"”12f77’"'”" Prob: .002 Table A9 (cont'd.) 69 Data file TENSILE Title: Tensile Strength Function: FACTOR Data case no. 1 to 20 Without selection Factorial ANOVA for the factors: Variable 2 with values from 1 to 5 replication Variable 1 with values from 1 to 4 treatment Variable 3 tensile strength Grand Mean: 3561.650 Grand Sum: 71233.000 Total Count: T A B L E 0 F M E A N S 2 * 1 * 3 Total 1 * 1 * 3493 750 13975 000 2 * 1 * 3732 750 14931 000 3 1 l * 3518 250 14073 000 4 * 1 * 3595 500 14382.000 5 * 1 * 3468 000 13872 000 1 * 1 * 3246 600 16233 000 1 * 2 * 3278 600 16393 000 1 * 3 * 3912 200 19561 000 1 * 4 * 3809 200 19046 000 K value 1 2 Factor 2 1 From 1 1 To 5 4 Table A10: Class Comparison, Tensile Strength 20 7O 7. Randomized Complete Blocks Design (RCBD) A N A L Y S I S O F V A R I A N C E T A B L E Degrees of Sum of F Code Source Freedom Squares Mean Square Value 1 Rep 4 182741.30 45685.325 0.27 2 A 3 1817700.55 605900.183 3.53 —3 Error 12 2058038 70 171503.225 Coefficient of Variation: 11.63% s _ for means group 1 : 207.0647 Number of observations : y s _ for means group 2 2 185.2043 Number of observations : y Table A10(cont'd-) 71 Data file ELOI‘JGAT I Title: Percent Elongation at Break Function: PRLIST Data case no. 1 to 20 Without selection LIST OF VARIABLES VAR TYPE NAME/DESCRIPTION l numeric treatment 2 numeric replication 3 numeric elongation CASE NO 1 2 3 1 1 1 3.23 2 1 2 2.37 3 1 3 2.49 4 1 4 3.14 5 1 5 2.50 6 2 1 2.34 7 2 2 2.66 8 2 3 2.40 9 2 4 2.23 10 2 5 2.74 11 3 1 3.20 12 3 2 2.63 13 3 3 3.14 14 3 4 3.74 15 3 5 2.89 16 4 1 2.67 17 4 2 3.29 18 4 3 2.94 19 4 4 2.48 20 4 5 2.89 ————_——_————-———————--————-— Table All: Individual Results, Elongation at Break 72 Data file ELONGAT I Title: Percent Elongation at Break Function: ANOVA—Z Data case no. 1 to 20 Without selection Two-way analysis of variance over variable 1 treatment with values from 1 to 4 and over variable 2 replication - with values from 1 to 5 Variable 3 elongation A N A L Y S I S O F V A R I A N C E T A B L E Degrees of Sum of Freedom Squares Mean Square F-value Prob Total 19 2.97 Variable l 3 1.07 0.357 2.37 122 Variable 2 4 0.09 0.022 0 15 Error 12 1.81 0.151 Non—additivity 1 0.33 0.330 2.45 146 Residual 11 1 48 0.135 Grand Mean: 2.799 Grand Sum: 55.970 Total Count: 20 Coefficient of Variation: 13.89% Means for variable 3 for each value of 1 VAR 1 l 2 3 4 MEAN 2.746 2.474 3.120 2.854 Table A12: Two-Way Analysis of Variance, Elongation at Break 73 Data file ELONGAT I Title: Percent Elongation at Break Function: FACTOR Data case no. 1 to 20 Without selection Factorial ANOVA for the factors: Variable 2 with values from 1 to 5 replication Variable 1 with values from 1 to 4 treatment Variable 3 elongation Grand Mean: 2 799 Grand Sum: 55 970 T A B L E O F M E A N S 2 * 1 * 3 Total 1 * 1 * 2.860 11.440 2 * 1 * 2.738 10.950 3 * 1 * 2.743 10.970 4 * 1 * 2.898 11.590 5 * 1 * 2.755 11.020 1 * 1 X 2 746 13.730 1 * 2 * 2 474 12.370 1 * 3 * 3 120 15.600 1 * 4 x 2 854 14.270 K value 1 2 Factor 2 1 From 1 1 To 5 4 Table A13: Class Comparison, Elongation at Break Total Count: 20 74 7. Randomized Complete Blocks Design (RCBD) A N A L Y S I S O F V A R I A N C E T A B L E Degrees of Sum of F Code Source Freedom Squares Mean Square Value 1 Rep 4 0 09 0.022 0 15 2 A 3 1 07 0.357 2 37 -3 Error 12 1 81 0.151 Coefficient of Variation: 5 for means group 1 y s _ for means group 2 w Table‘A13(Cont'd.) 13.89% .1943274 'Number‘of observations .1738117 Number of observations Data file ELONGAT I Title: Percent Elongation at Break Function: RANGE Data case no. 1 to 20 Without selection Error Mean Square = .151 Error Degrees of Freedom Number of observations used to calculate a mean Tukey’s Honestly Significant Difference Test s_ = .1737815 X Mean 1: Mean 2: Mean 3: Mean 4: Table A14: at alpha Original Order _ 2.75 A 2.47 A 3.12 A 2.85 A Mean Mean Mean Mean Ranked 3: 3.12 4: 2.85 1: 2.75 2: 2.47 Tukey's Test, Elongation at Break 5 Order 3>3>3> 76 Data file ELOI‘JGATI Title: Percent Elongation at Break Function: ANOVA-1 Data case no. 1 to 20 Without selection One way ANOVA grouped over variable 1 treatment with values from 1 to 4 Variable 3 elongation A N A L Y S I S O F V A R I A N C E T A B L E Degrees of Sum of Error Freedom Squares Mean Square F-value Prob. Between 3 1.0725 0.36 3.01 .061 Within 16 1.9020 0.12 Total 19 2 9745 Coefficient of Variation: 12.32% Var. V A R I A B L E No. 3 1 Number Sum Average SD SE 1 5 00 13.730 2.75 0 41 0.15 2 5 00 12.370 2.47 0 22 0.15 3 5 00 15.600 3.12 O 41 0.15 4 5 00 14.270 2.85 0 31 0.15 Total 20.00 55.970 2.80 0.40 0.09 Within 0 34 Bartlett’s Test -—_——-——‘~—-—-_— Chi-square : 1.750234 Number of Degrees of Freedom : 3 Approximate Significance : .6258 SINGLE DF ORTHOGONAL COMPARISONS (CONTRASTS) FOR CONTRAST # 1 12-1, 2:—1, 3: 3, 4:—1 Sum Of Squares: 0.689 Effect: 0.107 Error: 0.045 F value: 5.80 Prob: .028 Table A15: Orthogonal Contrast. Elongation at Break 77 Data file deDIDLJIJLJES Title: Modulus of Elasticity Function: PRLIST Data case no. 1 to 20 Without selection LIST OF VARIABLES VAR TYPE NAME/DESCRIPTION 1 numeric treatment 2 numeric replication 3 numeric modulus of elasticity CASE NO 1 2 3 1 1 1 183462 2 1 2 229458 3 1 3 217391 4 l 4 187617 5 1 5 191283 6 2 1 236088 7 2 2 250000 8 2 3 239316 9 2 4 234114 10 2 5 227273 11 3 1 232172 12 3 2 244328 13 3 3 235690 14 3 4 227642 15 3 5 241796 16 4 1 229133 17 4 2 236088 18 4 3 233723 19 4 4 234114 20 4 5 239726 Table A16: Individual Results, Modulus of Elasticity 78 Data file MODULUS Title: Modulus of Elasticity Function: ANOVA-2 Data case no. 1 to 20 Without selection Two—way analysis of variance over variable 1 treatment with values from 1 to 4 and over variable 2 replication with values from 1 to 5 Variable 3 modulus of elasticity A N A L Y S I S O F V A R I A N C E T A B L E Degrees of Sum of Freedom Squares Mean Square F—value Prob Total 19 %6595952704.20 Variable 1 3 %4415973678.60 %1471991226.200 16.35 .000 Variable 2 4 %1099513068.70 %274878267.175 3.05 .059 Error 12 %1080465956 90 90038829.?42 _-_*_.———_——————-————_——...——--—————-.—-——-—————————————’_—--— Non-additivity 1 %69374165l.48 %693741651.483 Residual 11 %386724305.42 35156755.038 Grand Mean: 227520.700 Grand Sum: %4550414.000 Total Count: 20 Coefficient of Variation: 4.17% Means for variable 3 for each value of 1 VAR 1 1 2 3 4 MEAN 201842 200237358 200236325 600234556.800 Table A17: Two-Way Analysis of Variance, Modulus of Elasticity 79 Data file MODULUS Title: Modulus of Elasticity Function: RANGE Data case no. 1 to 20 Without selection Error Mean Square : 9.003883E+07 Error Degrees of Freedom : 12 Number of observations used to calculate a mean : 5 Tukey’s Honestly Significant Difference Test s_ : 4243.556 at alpha : .05 x Original Order Ranked Order Mean : 201842.20 B Mean = 237358.20 A Mean 2: 237358.20 A Mean 3: 236325.59 A Mean : 236325.59 A Mean 4: 234556.80 A Mean 4: 234556.80 A Mean 1: 201842 20 B Table A18: Tukey's Test, Modulus of Elasticity 80 muffle MODULUS Title: Modulus of Elasticity Function: ANOVA-1 Data case no. 1 to 20 Without selection One way ANOVA grouped over variable 1 treatment with values from 1 to 4 Variable 3 modulus of elasticity A N A L Y S I S O F V A R I A N C E T A B L E Degrees of Sum of Error Freedom Squares Mean Square F—value Prob. Between 3 4415973678.6000 1471991226.20 10.80 .000 Within 16 2179979025.6000 136248689 10 Total 19 6595952704 2000 Coefficient of Variation: 5.13% Var. V A R I A B L E No. 3 1 Number Sum Average SD SE —-~_——.—-——..———————_-—-———--—_.—_—-——————--——-.———--. 1 5.00 %1009211.000 201842 20 20347.50 5220.13 2 5.00 %1186791.000 237358.20 8329.13 5220.13 3 5.00 %118l628.000 236325.60 6837.85 5220.13 4 5.00 %ll72784.000 234556.80 3852.73 5220.13 Total 20.00 %4550414.000 227520.70 18632.11 4166.27 Within 11672.56 Bartlett’s Test ———_————_—————— Chi—square : 10.32446 Number of Degrees of Freedom : 3 Approximate Significance : .016 SINGLE DF ORTHOGONAL COMPARISONS (CONTRASTS) FOR CONTRAST fl 1 1 -3, 2: 1, 3: 1, 4: 1 Sum Of Squares: %4395902415.000 Effect: 8559.500 Error: 1506.921 F value: 32.26 Prob: .000 Table A19: Orthogonal Contrast, Modulus of Elasticity 81 Data file Title: deDIDIJIBLJES Modulus of Elasticity Function: FACTOR Data case no. 1 to 20 Without selection Factorial ANOVA for the factors: Variable 2 with values from 1 to 5 replication Variable 1 with values from treatment 1 to 4 Variable 3 modulus of elasticity Grand Mean: 227520.700 Grand Sum: %4550414.000 T A B L E O F M E A N S 2 * 1 * 3 Total ———_——.———-————————.——.—_—_————_——————————————————— 1 * 1 * 220213.750 880855.000 2 * 1 * 239968.500 959874.000 3 * 1 * 231530.000 926120.000 4 * 1 * 220871.750 883487.000 5 * 1 * 225019.500 900078.000 1 * 1 * 201842.200 1009211.000 1 * 2 * 237358.200 1186791.000 1 * 3 * 236325.600 1181628.000 1 * 4 * 234556.800 1172784.000 K value 1 2 Factor 2 1 From 1 1 To 5 4 Table A20: Class Comparison, Modulus of Elasticity Total Count: 20 82 7. Randomized Complete Blocks Design (RCBD) A N A L Y S I S O F V A R I A N C E Degrees of Sum of Code Source Freedom Squares 1 Rep 4 %1099513068.70 2 A 3 %4415973678.60 —3 Error 12 %1080465956.90 Coefficient of Variation: 4.17% s for means group 1 : 4744.439 Number ‘4 4243.556 Number 5 _ for means group 2 (d Table A20(cont'd.) Mean Square F %274878267.175 %1471991226.200 90038829.742 ‘of observations of observations T A B L E Value LIST OF REFERENCES LIST OF REFERENCES Agarwal, Bhagwan D. and Lawrence J. Broutman. Analysis and Performance of Fiber Composites. 355 pp. New York: John Wiley & Sons, 1980. Annual Book of ASTM Standards. Section 8: Plastics. Philadelphia, PA: American Society for Testing and Materials, 1988. Beck, Melinda, Mary Hager, Patricia King, Sue Hutchinson, Kate Robins, and Jeanne Gordon. "Buried Alive." Newsweek, pp. 66-76, November 27, 1989. Bigg, D. M. "Mechanical Properties of Particulate Filled Polymers." Polymer Composites, 8(2), 115—122, 1987. B012, Ray E. and George L. Tuve, eds. CRC Handbook of Tables for Applied Engineering Science. 975 pp. Cleveland, OH: The Chemical Rubber Co., 1970. Briston, J. H. Plastice Filme. 3rd Ed. 434 pp. Harlow, Essex, England: Longman Scientific & Technical, 1989. Chand, Navin and P. K. Rohatgi. "Adhesion of Sisal Fibre - Polyester System." Polymer Communications, 27, 157-160, 1986. Crosby, J. M. and T. R. Drye. "Fracture Studies of Discon- tinuous Fiber Reinforced Thermoplastic Composites." Proceedings of the American Society for Composites, First Technical Conference, pp.245—251. Lancaster, PA: Technomic Publishing Company, Inc., 1986. Dalvag, H., C. Klason, and H.-E. Stromvall. "The Efficiency of Cellulosic Fillers in Common Thermoplastics. Part II." International Journal of Polymeric Materials, 11, 9-38, 1985. Giridhar, J., Kishore, and R. M. V. G. K. Rao. "Moisture Absorption Characteristics of Natural Fibre Compo- sites." Journal of Reinforced Plastice and Composites, 5, 141-149, 1986. Gogoi, Binoy K. "Processing-Morphology-Property Relation- ships for Compounding Wood Fibers With Recycled HDPE Using a Twin—Screw Extruder." M.S. Thesis, Michigan State University, 1989. Hull, Derek. An Introduction to Composite Materiale. 246 pp. Cambridge, England: Cambridge University Press, 1981. 83 84 Jindal, U. C. "Development and Testing of Bamboo-Fibres Reinforced Plastic Composites." Journal of Composite Materials, 20, 19-29, 1986. Kalyankar, Varsha. "Mechanical Characteristics of Compo- sites Made From Recycled HDPE Obtained From Milk Bottles." M.S. Thesis, Michigan State University, 1989. Klason, C., J. Kubat, and H.-E. Stromvall. "The Efficiency of Cellulosic Fillers in Common Thermoplastics. Part I. Filling Without Processing Aids or Coupling Agents." International Journal of Polymeric Materials, 10, 159-187, 1984. Lightsey, G. R., P. H. Short, and V. K. K. Sinha. "Low Cost Polyolefin Composites Containing Pulp Mill Wood Residue." Polymer Engineering and Science, 17(5), 305-310, 1977. Maldas, D. and B. V. Kokta. "The Effect of Aging Conditions on the Mechanical Properties of Wood Fiber-Polystyrene Composites: I. Chemithermomechanical Pulp as a Rein- forcing Filler." Composites Science and Technology, 36, 167-182, 1989. McNally, D., W. T. Freed, J. R. Shaner, and J. W. Sell. "A Method to Evaluate the Effect of Compounding Technology on the Stress Transfer Interface in Short Fiber Reinforced Thermoplastics." Polymer Engineering and Science, 18(5), 396-403, 1978. Meylan, B. A. and B. G. Butterfield. Three-Dimensional Structure of Wood. 80 pp. Syracuse, NY: Syracuse University Press, 1972. MSTAT Microcomputer Statistical Program. version 5.0. Michigan State University, 1988. Nieman, Kristine A. "Mechanical Property Enhancement of Recycled High Density Polyethylene and Wood Fiber Composites." M. S. Thesis, Michigan State University, 1989. Owolabi, 0., T. szikovszky, and I. Kovacs. "Coconut-Fiber- Reinforced Thermosetting Plastics." Journal of Applied Polymer Science, 30, 1827-1836, 1985. Pattanakul, Chate. "Characteristic Changes in Recycled HDPE From Milk Bottles." M. S. Thesis, Michigan State University, 1987. 85 Pavithran, C., P. S. Mukherjee, M. Brahmakumar, and A. D. Damodaran. "Impact Properties of Natural Fibre Composites." Journal of Materials Science Letters, 6, 882-884, 1987. Phillips, D. C. and B. Harris. "Strength, Toughness, and Fatigue Properties." Pol er En ineerin Com osites, M. O. W. Richardson, ed., pp. 90-113. London: Applied Science Publishers, Ltd., 1977. Raj, R. G., B. V. Kokta, D. Maldas, and C. Daneault. "Use of Wood Fibers in Thermoplastic Composites: VI. Isocyanate as a Bonding Agent for Polyethylene-Wood Fiber Composites." Polymer Composites, 9(6), 404-411, 1988. Ramirez, Amando Padilla and Antonio Sanchez Solis. "Devel- opment of a New Composite Material From Waste Polymers, Natural Fiber, and Mineral Fillers." Journal of Applied Polymer Science, 29, 2405-2412, 1984. Resource Integration Systems, Ltd. "Market Study for Recyclable Plastics." 111 pp. State of Michigan Department of Natural Resources, 1987. Selke, Susan E. Packaging and The Environment. 179 pp. Lancaster, PA: Technomic Publishing Company, Inc., 1990. Vu-Khanh, T. "Survey of Current Status and Future Trends in Reinforced Plastics Composites." Polymer Composites, 8(6), 363-370, 1987. Wagenfuehr, Rudi. Anatomie des Holzes. 320 pp. Leipzig, GDR: VEB Fachbuchverlag, 1984. Yam, Kit L. "Uses of Recycled Plastics in Composite Materials." Recycled Plastics Applications and Developments: Proceedings of a Seminar, Christopher C. Lai, Kit L. Yam, and Susan E. Selke, eds., pp. 81-90. East Lansing, MI: Michigan State University School of Packaging, 1987. N STQTE UNIV. LIBRARIES L ”‘ij1! «1 Hum“ 4 293008998217