The interaction between fiber and matrix considerably influences the mechanical properties of reinforced composites.

The mechanical properties of biocomposites depend on a number of factors such as the quantity and type of fiber added to the material, nature and amount of polymer matrix has been pointed as the most important parameters, but also the distribution and orientation of reinforcing fillers, nature of filler-matrix interfaces, interphase region and temperature of production influences the mechanical properties of the biocomposites. The amount of coupling agents (required to make the adhesion be­tween surface of fiber and matrix) in the composite is dependent on the fiber content and type and also influences the mechanical and other physical properties of the composites.

The water absorption behavior of the cellulose reinforced chitosan films was fol­lowed by gravimetrically exposing the films to the moisture at relative humidity (RH) from 55 to 100% or by immersing in deionized water and sometimes the mechanical properties dependence up on moisture absorption. The water uptake at equilibrium of nanocomposite films in water was reduced from 71 to 40% linearly with CNC loading up to 30 wt.%.40 A similar trend in the reduction in the water up­take was also observed with even 4 times shorter nanocrystals and the longer NFCs are used to prepare nanocomposites when the films were incubated in water and at RH 75%, respectively.36 The reduction in water uptake can be attributed to the in­crease in highly crystalline cellulose which lesser hydrophilic than chitosan matrix and a strong interfacial interaction between them. Due to the reduced water uptake, the moisture-dependent mechanical properties chitosan-cellulose nanocomposite films were less affected in comparison of neat chitosan. However, the water uptake can be still reduced by covalently linking the cellulose and chitosan as represented in Fig. 16.4 that compares the unmodified CNC and surface modified CNCs.37

Contrarily, the cellulose-chitosan nanocomposites systems can be tuned to ab­sorb higher amount of water for biological and sanitary applications, when required. The in-situ grafting of acrylic acid onto chitosan in presence of CNCs (10% w/w) has led to a super absorbent hydrogel materials. The superabsorbent materials ex­hibit an improved the swelling capacity in ca.100 units, from 381 to 486 with faster equilibrium. In this case, the averaged dimension of pores was increased by the in­corporation of CNCs to increase the porous capacity.46 These hydrogels can be used as functional pH/ionic materials.

Hydroxyapatite (HAp) has been widely used as an artificial bone substitute because of the its high biocompatibility and good bioaffinity, as well as osteoconductabil — ity. HAp powders have been produced using bio products like corals11, cuttlefish shells12, natural gypsum13, natural calcite14, bovine bone15, eggshell1617, etc. Chemi­cal analysis has shown that these products which are otherwise considered as bio­waste are rich sources of calcium in the form of carbonates and oxide.

Several papers reported to produce the materials for implant or prosthesis pur­poses with chemical characteristics similar to HAp18-21. Eggshell is a nonexpensive and environmental friendly material for HAp production. The eggshell is consist­ing of a three-layered structure, namely the cuticle, the spongeous layer and the lamellar layer. The cuticle layer represents the outermost surface and it consists of a number of proteins. Spongeous and lamellar layers form a matrix constituted by protein fibers bonded to calcite-calcium carbonate crystals. The eggshell repre­sents the 11% of the total weight of the egg and is composed by calcium carbonate 94%, calcium phosphate 1%, organic matter 4% and magnesium carbonate 1%22. Bone replacements are frequently required to substitute damaged tissue due to trauma, disease or surgery. Resorbable porous bioceramics, such as P-tricalcium phosphate (P-Ca3(PO4)2, P-TCP) and hydroxyapatite (Ca10(PO4)6(OH)2, Fig. 2.1) have been widely used as bone defect filling materials due to their remarkable bio­compatibility and close chemical similarity to biological apatite present in bone tissues23,26.

Figure 4.39 also shows the temperature dependency of E’ and tan 5 for SPE/ PGVNC(1/2.65)/WF composites measured by DMA. The E’ at the rubbery pla­teau region over 150 °C for the composites was much higher than that of SPE/ PGVNC(1/2.65), suggesting a superior reinforcement effect due to the wood fibers. The tan 5 peak temperature related to Tg for the composites was a little lower than that of the corresponding neat resins. The reason is not clear, but it is thought that hydroxy groups of WF reacted with epoxy groups of SPE and the stoichiometry of epoxy and hydroxy is deviated.

Figure 4.40 also shows the tensile properties for SPE/PGVNC(1/2.65)/WF com­posites. The SPE/PGVNC(1/2.65) composites showed higher tensile modulus than SPE/PGVNC(1/2.65) in agreement with the result of storage modulus by DMA. Tensile strength also improved by the addition of WF. Figure 4.41 shows SEM im­ages of WF and fracture surfaces of SPE/PGVNC(1/2.65) and SPE/PGVNC(1/2.65)/ WF20. The photograph of WF shows that the fiber length and width of WF are ca. 0.2-0.4 mm and 40-200 mm, respectively. Although some voids due to vaporiza­tion of THF were observed in the microphotograph of SPE/PGVNC(1/2.65), the cured resin itself is homogeneous, suggesting that SPE was homogeneously cured with PGVNC. In case of SPE/PGVNC(1/2.65), it appeared that WF was tightly in­corporated into the crosslinked epoxy resins and their interfacial adhesion is good. This result may be attributed to the fact that the structures of guaiacyl and pyrogallol moieties of PGVNC resemble that of lignin of WF. The fact that tensile strength and elongation at break did not decrease by the addition of WF should be related to the good affinity of SPE/PGVNC and WF.

Figure 4.42 shows TGA curves of WF, SPE/PGVNC(1/2.65), SPE/PN(1/1), SPE/PGVNC(1/2.65)/WF composites. Since the thermal decomposition tempera­ture of WF was lower than that of SPE/PGVNC(1/2.65), the SPE/PGVNC(1/2.65)/

WF composite exhibited two-step thermo-degradation, and the 5% weight loss temperatures decreased with increasing WF content (0 wt.%: 319.2 °C, 10 wt.%: 312.1 °C, 20 wt.%: 301.8 °C, 100%: 293.2 °C). The 5% weight loss temperature of SPE/PGVNC(1/2.65) (319.2 °C) was lower than that of SPE/PN(1/1) (346.3 °C). The feed ratio of 1/2.65 for SPE/PGVNC was selected based on the highest tan 5 peak temperature. In order to get the cured material with higher thermal stability, the epoxy/hydroxy ratio should be approached to 1/1, as is obvious from Table 4.9. Regarding the biodegradability, it is supposed that SPE/PGVNC and SPE/PGVNC/ WF are fairly resistant to both aerobic and anaerobic biodegradation because their materials contain highly crosslinked aromatic structure, which is similar to that of lignin.80,81

4.6 CONCLUSION

The biocomposites composed of bio-based epoxy resins (GPE, PGPE, SPE, and ESO), bio-based polyphenol hardeners (TA, QC, TPG, and PGVNC), lignocellu — losic fibers (WF and MFC) were prepared and their thermal and mechanical prop­erties were investigated. Tan 5 peak temperatures and tensile properties of all the biocomposites are summarized in Table 4.10. Among the bio-based epoxy resins cured with TA, SPE/TA(1/1) showed the highest tan 5 peak temperature (95 °C), and

PGPE/TA(1/1) showed the highest tensile strength and modulus (63.5 MPa and 2.71 GPa). Among the SPE cured with various bio-based polyphenol hardeners, SPE/ PGVNC(1/2.65) showed the highest tan 5 peak temperature (148 °C), and PGPE/ TA(1/1) showed the highest tensile strength and modulus. Regarding the biocom­posites with WF, although the tensile modulus increased with increasing WF, tensile strength rather decreased by the addition of WF for all the WF biocomposites ex­cept for GPE/TA(1/1)/WF. In case of GPE/TA(1/1)/WF biocomposites, the tensile modulus and strength were improved by the addition of WF. The GPE/TA(1/0.8)/ WF60 had the highest tensile modulus (5.22 GPa) among the all biocomposites, and had a superior tensile strength (54.9 MPa). The tan 5 peak temperature of all the WF biocomposites except SPE/QC(1/1.2)/WF biocomposites were lower than those of the corresponding cured neat resins. When QC was used as a hardener, the tan 5 peak temperature considerably increased, probably due to a hydrogen bond­ing interaction between WF and QC. Although the maximal fiber content of MFC biocomposite (ca. 10 wt.%) was much lower than that of WF biocomposite (ca. 60 wt.%), the tensile strength and modulus increased with increasing MFC content. Tan 5 peak temperature also increased a little with increasing MFC content. Among all the biocomposites, SPE/TA(1/1)/MFC10 showed the highest tensile strength (78.6 MPa) and a superior tan 5 peak temperature (108 °C). As a whole, it can be said that WF biocomposites are suitable to get the materials with a higher tensile modulus, and that MFC biocomposites are suitable to get the materials with a higher tensile strength and Tg than the corresponding cured neat resins.

KEYWORDS

Bio-based Epoxy Resins Bio-based Polyphenols Biocomposites Microfibrillated Cellulose Wood Flour

ASTM D570 standard covers method of determination of swelling in water of jute composite8. This test was done to determine the hydrophilic nature of 3 cm x 2.7 cm x 0.4 cm jute-based natural rubber composite. The average of the three values
obtained for the change in thickness expressed as a percentage of the original aver­age thickness is reported as the swelling value.

Thickness of swelling in water was measured as per Eq. (5),

Swelling Thickness, T s= ——— xl00 (5)

Ti

where T1 is initial thickness and T2 is the final thickness after water absorption. Table 6.4 gives the percentage of thickness swelling of samples in water at 24 h. The saturation point occurs at 24 h and thickness swelling is approximately l00%.

6.5.1.1 BIODEGRADATION

This test was done to evaluate microbial biodegradation activities of jute composite by burying in soil9. Sample dimensions: 10 cm x 5 cm * 0.4 cm of the jute compos­ite was used for the test. Weight of l0 pieces of rectangular shaped samples were measured and buried in soil mixture containing garden soil, cow dung and sand (2:1:1, w/w). After 15 and 30 days the samples were removed, cleaned properly and finally kept in oven at 100°C till a constant weight was obtained. The weight loss of the samples after 15 days was 3.74% and 30 days was 6.28%.

As indicated in Section 7.3.2.1, the raise of the blank holder pressure may have for consequence to also increase the tension in the fabric. Close to the basis of the shape, sliding of tows may appear when high blank holder pressures are applied therefore limiting the sliding of the fabric between the blank holder and the die. This phenomenon is shown in Fig. 7.12. The tow-sliding defect cannot obviously be accepted when manufacturing a composite part because the homogeneity of the reinforcement does not remain.

This type of defect also depends in a large extent of the complexity of the shape to be formed as well as the cohesion of the woven fabric. As an example, it is in­teresting to note that the tow sliding phenomenon appears for uniform blank holder pressures higher than 2 bar for reinforcement 1whereas it only appears for pressure higher than 5 bar for reinforcement 2.

The location of the phenomenon also depends on the orientation of the fabric. For reinforcement 1 at orientation 0°, tow sliding starts at places where tows are very tight (at the basis of Face C and at the bottom of Edge 1) as shown by Fig. 7.12.

For orientation 90°, the tow sliding phenomenon takes place on the basis of the faces A and B at the bottom of the buckle line where the tows seem to be the tightest (Fig. 7.13).

For reinforcement 2, the tow-sliding phenomenon only appears when the blank holder pressure is higher than 5 bar. This therefore means that the cohesion of this reinforcement is higher than the one of reinforcement 1. However, the phenomenon also takes place for orientation 0° at the bottom of the buckle line as shown by Fig. 7.14

The appearance of the tow sliding phenomenon shows that it is particularly im­portant to well control the blank holder pressure when a complex geometry is con­cerned and that it may not be possible to apply too high pressure if the cohesion of the reinforcement does not allow it. This may be a limitation of a fabric as increasing
the blank holder pressure may be useful to get rid of tow buckles (reinforcement 2) or suppress small wrinkles by increasing the tension of the whole membrane.

It was found that the fiber loading increased thermal stability of the biocomposite. The first mass loss, in the range 31-100°C, is due to evaporation of moisture. Then the mass loss between 150°C and 380°C for SPF/SPS biocomposites, are due to the decomposition of the three major constituents of the natural fibers; hemicellulose, cellulose and lignin.94 In general, the thermal decomposition of these fibers consists of four phases. The first phase was decomposition of hemicelluloses, followed by cellulose, lignin and lastly their ash.9596 Yang et al.97 reported that hemicelluloses decompose at 220°C and substantially completed at 315°C. As soon as hemicel­luloses had completely decomposed, the decomposition of cellulose will take place as the second phase of decomposition. Because of its highly crystalline nature of their cellulose chain than amorphous, cellulose has relatively thermally stable. It does not start to decompose until hemicelluloses had completely decomposed which normally starts at higher temperature at about 315°C.97 This is supported by Kim et al.98 where they reported that the critical temperature of decomposition of crystal­line cellulose is 320°C. The third phase was the decomposition of lignin. It is the most difficult to decompose compared to hemicelluloses and cellulose. Although the decomposition of lignin had started as early as 160°C, it decomposes slowly and extends its temperature as high as 900°C to complete its decomposition.97This is contributed by lignin which is very tough component and known as the compound that gives rigidity to the plant materials. Finally, when the lignin had completely decomposed, the component that is left is inorganic material in the fibers which can be assumed as ash content. This is due to the presence of inorganic materials such as silica (silicon dioxide, SiO2) in the fiber which can only be decomposed at a very high temperature of 1723°C. The increase of fibers increased the lignin and ash content, compared to pure plasticized SPS. It was found that the lignin and ash content of SPF was 31.5% and 4%, respectively.99 The large degradation at 310 °C appears for plasticized SPS are due to the elimination of the polyhyroxyl groups, accompanied by depolymerization and decomposition in starch.100

BRENT TISSERAT, LOUIS REIFSCHNEIDER, DAVID GREWELL, GOWRISHANKER SRINIVASAN, and ROGERS HARRY O’KURU

There is a need to identify usable lignocellulosic materials that can be blended with thermoplastic resins to produced commercial lignocellulosic plastic compos­ites (LPC) at lower costs with improved performance. The core objectives of this study are to: i) evaluate the use of dried distillers grain with solubles (DDGS) and Paulownia wood (PW) flour in high density polyethylene-composites (LPC); ii) as­sess the benefit of chemically modifying DDGS and PW flour through chemical extraction and modification (acetylation/malation); and iii) to evaluate the benefit of mixing DDGS with Pine wood (PINEW) in a hybrid LPC. Injection molded test specimens were evaluated for their tensile, flexural, impact, environmental durabil­ity (soaking responses), and thermal properties. All mechanical results from com­posites are compared to neat high-density polyethylene (HDPE) to determine their relative merits and drawbacks. HDPE composites composed of various percentage weights of fillers and either 0% or 5% by weight of maleate polyethylene (MAPE) were produced by twin screw compounding and injection molding. Chemical modi­fication by acetylation and malation of DDGS and PW fillers prior to compounding was done to evaluate their potential in making an improved lignocellulosic mate­rial. Composite-DDGS/PINEW mixture blends composed of a majority of PINEW were superior to composites containing DDGS only. Composites containing MAPE

had significantly improved tensile and flexural moduli compared to neat HDPE. Impact strength of all composites were significantly lower than neat HDPE. Chemi­cal modification substantially improved the tensile, flexural, water absorbance, and thermal properties of the resultant composites compared to untreated composites. Differential scanning calorimeter and thermogravimetric analysis were conducted on the HDPE composites to evaluate their thermal properties as this may indicate processing limitations with conventional plastics processing equipment due to the exposure of the bio-material to elevated temperatures. Finally, because exposure to the moisture in the environment can affect the physical and color properties of wood, changes in the size and color of test specimens after prolonged soaking were evaluated.

Contact information: a) Functional Foods Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, United States Department of Agriculture, 1815 N. University St., Peoria IL 61604, USA; b) De­partment of Technology, College of Applied Science and Technology, Illinois State University, Normal IL 61790, USA; c) Polymer Composites Research Group: Ag­ricultural and Bio systems Engineering, College of Agriculture and Life Science, Iowa State University, Ames, IA, 50011, USA; d) Bio-oils Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, United States Department of Agriculture, Peoria, IL 61604, USA; Corresponding author: Brent. Tisserat@ars. usda. gov

13.1 INTRODUCTION

The U. S. wood plastic composite (WPC) industry is projected to increase 13% a year to amount to $5.3 billion by 2015 and is likely thereafter to continue to increase at a similar rate in the foreseeable future.1-3 There is an ever increasing need to improve the quality of lignocellulosic plastic composite and WPC in order to obtain more useful, reliable and inexpensive commercial products.410 The most common type of LPC is WPC, which uses wood flour fillers derived from wood waste materials such as shavings and sawdust generated from lumber processing.61012 WPC thermoplas­tics typically include polyethylene (PE), polypropylene (PP), and polystyrene and are mixed with up to 50% wood flour (w/w) depending on the desired mechanical and physical properties and industrial acceptance.61112 Cost is the most important consideration in the commercialization of any LPC/WPC products. Generally, wood flour fillers are used without elaborate chemical preparations; however, the fillers are sized (sieved) and dried to enhance their processing. The price of LPC is dictated by the price of petroleum and the cost of wood/lignocellulosic fillers. Currently, PE and PP sell for ~$1.85 to $2.27/kg ($0.91 to $1.12/lb.) and ~$2.23 to $2.47/kg ($1.10 to $1.22/lb.), respectively.213 Commercial hardwood flour blends are derived from lumber milling byproducts is composed of various tree species (e. g., maple, birch, ash) and sells for ~$0.18 to $0.48/kg ($0.08 to $0.22/lb.).u Wood waste mate­rial prices fluctuate on the basis of availability (housing demand) and the demand for their utilization.14 For example, in 2006-2008, when the US housing market con­tracted, sawdust prices quadrupled due to a lack of supply.14 Biomass energy us­age competes with LPC/WPC filler availability and price. Currently, 85% of wood waste is consumed for energy production (fuel pellets and direct combustion).15 The Energy Independence and Security Act of 2007 mandates that 36 billion gallons of biofuels be produced by 2022 and woody biomass materials will be increasingly used to achieve this goal.16 A number of government subsidy programs are diverting the woody biomass into bio-energy facilities from their traditional markets. Changes in the cost, availability, and utilization of the biomass and wood waste markets are in flux.16 As previously noted, since the demand for wood flour needed by the WPC in­dustry will also increase and its cost will undoubtedly increase due to the bio-energy mandates, new sources of woody biomass are clearly needed.

Alternative woody biomass sources to provide wood flour are being devel — oped.71719 Small-diameter trees obtained from forest under-stories or brush condi­tions offers a source of woody materials to satisfy both the bio-energy as well as wood flour for WPC.1718 Short-rotational woody crops using “fast-growing trees” grown in coppicing plantations are another option to obtain woody materials.20 Mar­ginal land utilization has been suggested as the potential site for planting large acre­ages of bio-energy woody tree crops.52021

Paulownia elongate S. Y. Hu, family Paulowniaceae, a native to China, is an ex­tremely fast-growing coppicing hardwood that is cultivated in plantations in China and Japan. Paulownia wood (PW) is highly valued in the construction and furniture industries.2223 There are several attributes of Paulownia wood that favor using it as a feedstock for WPC: a Paulownia plot containing 2000 trees per hectare can yield up to 150 to 300 tons of wood within 5 to 7 years, growth rate of heights up to 3.7-4.6 m and diameters of 3 to 5 cm a year are common, Paulownia trees are amenable to being established on marginal lands and have deep taproots, which make them drought resistant, PW is light weight, insect resistance, highly durable, and heat re­sistance. Paulownia species such as P elongate, P kawakamii, and P tomentosa, are currently being grown and evaluated in the United States for their commercial wood properties.2324 For example, recent studies conducted at Fort Valley State University, Fort Valley, GA show that two to four-year-old trees can grow to a diameter of 16.5 cm and achieved a height of 10 m.24 In addition, Paulownia could serve as a short — rotational woody crop that could be harvested frequently over a 10 year period. Therefore, in this study the utilization of juvenile wood materials harvested from 3 year old trees were used as a reinforcement materials with thermoplastic resins.

In many cases, lignocellulosic flour cost is less than wood flour; sometimes costing only a few cents a pound, thereby making it a very economically attrac­tive material to be developed as a filler for LPC.2526 Ag-waste materials generated from processing seeds have not been vigorously exploited as possible fillers in bio­composites. In the U. S. Midwest, dried distillers grains and soluble (DDGS) offers an abundant, available and inexpensive lignocellulosic flour for biocomposites.27’31 DDGS are processed corn seeds left over after the distillation of alcohol to generate the bio-based ethanol fuel.31,32 Approximately, 25 million metric tons of DDGSs are produced annually in North America with this figure expected to increase further in the next few years.29,31,33 Currently, DDGS is used almost entirely as an animal feed although other uses have been sought.26,27,29 DDGS sells for about $0.06 to $0.10/kg ($0.03 to $0.05/lb.) which makes it an attractive bio-filler to blend with thermoplas­tic resins. However, to date, studies employing DDGS as a filler with thermoplastic resins have produced composites that have poor mechanical properties compared to the neat thermoplastic resin.30,33,35 Further research is required to produce a DDGS material that has improved mechanical properties in order to become an acceptable filler material.

In addition, there are also numerous other seed residues (seed meals or press cakes) generated from seeds after their oil processing (soybean, cottonseed, penny — cress). Roughly half of the oil seed’s harvest mass remains as a press cake after oil extraction by pressing.36 In 2012, 472 million tons of oil seeds were harvested glob­ally to provide for culinary (e. g., edible oils and food additives) and industrial (e. g., soaps, cosmetics and biodiesel) products.37 Many press cakes are used as an animal feed or fertilizer, when appropriate.38 However, there is much interest in finding higher value uses for press cakes. Also, “new” oil energy-crops, such as jatropha (Jatropha curcas L.) and pennycress (Thlaspi arvense L.) containing even higher oil compositions than current oil seeds crops and are being developed to address the world’s fuel needs.36,39,40 In the U. S. Midwest, pennycress has a promising future as a bio-diesel crop. It contains more oil than soybeans and is unique in that it is a winter annual that can be grown on the same land used for soybeans without competition since their planting and harvesting dates do not coincide.36,39,40 However, pennycress press cake cannot be used as animal feed since it contains high levels of toxic gluco — sinolates.40 Therefore, alternative uses for pennycress press cakes are sought in or­der to maximize the utilization of this oil seed crop.41 In the tropical and subtropical regions, jatropha is becoming a prominent bio-diesel crop. Likewise, its seed meal is also toxic due to the presence of phorbol esters and is not available to be used as an animal feed or fertilizer. Employment of these press cakes as a filler in LPC could be an ideal utilization. Press cakes price between a range of $0.09 to $0.55/kg ($0.04 to $0.25/lb.) depending on the species and extent of their preparation, which makes press cakes an attractive bio-filler to be blended with thermoplastic resins.42 How­ever, press cakes composition differs substantially from other lignocellulosic flour fillers because they contain high concentrations of extractives which includes re­sidual vegetable oil (» 8-15%) and protein (» 20-35%) while having a low cellulose (» 11-25%) and lignin concentration (» 3-15%).36 DDGS is composed of 25-33% protein, 39-60% carbohydrates, 5-12% oils and 2-9% ash.33 In contrast, PW flour contains: water and solvent extractives (» 3-12%), protein content (» 1-2%), cel­lulose (45-50%), hemicellulose (22-25%) and lignin (20-25%).4,43,44 Few published reports have dealt with using press cakes as a lignocellulosic flour filler.45 Attempts to employ press cakes has resulted in composites with relatively poor mechanical properties when compared to neat thermoplastic resins.45

Chemical modification (acetylation and malation) of lignocellulosic and wood flour fillers is a common method to improve their physical and mechanical proper- ties.6,8,11,12,33,46,53 Chemical modification of a lignocellulosic material is defined as a chemical reaction between a reactive portion of the lignocellulosic material (hy­droxyl group) and a chemical reagent, with or without a catalyst, to create an ester group.6,8,11,12,33,46,52 Acetylation is the most common method to chemically modify lignocellulosic materials.8,51,54,55 Acetylation offers a number of benefits to WPC/ LPC compared to nonacetylated WPC/LPC including superior weathering resis­tance,8,53 greater thermal stability,51 and enhanced mechanical properties.56 Because there is no accepted method to administer acetylation and/or chemical modification treatments to lignocellulosic and wood flours there are a myriad of acetylation/mala — tion techniques presented in the literature.8,47,48,50,51,53,55,68 Generally, however, chemi­cal medication by acetylation involves the treatment of lignocellulosic and wood flour particles by soaking or coating with a coupling agents (e. g., acetic anhydride) in order to reduce the presence of hydroxyl groups in exchange for esterification linkages (i. e., covalent bonds between the wood and the reagent).8,47,53 In this study, chemical modifications were made on both Paulonia wood flour and DDGS prior to their blending with HDPE to determine if a chemical modification techniques could improve the mechanical properties of these lignocellulosic materials in the resulting composites.

There are three core objectives of this study. The first is to perform an assess­ment of the mechanical properties of thermoplastic composites made with DDGS. The methods developed to produce a usable DDGS composite that exhibits high mechanical properties can be transferred to the development of composites contain­ing seed press cake residues from various species. This is a reasonable assumption due to the chemical compositional similarity between the DDGS and press cakes. Lignocellulosic materials are polar (hydrophilic) due to the occurrence of hydroxyl groups and are not compatible with thermoplastic resin polymers, which are non­polar (hydrophobic). In order to obtain a LPC/WPC with superior physical and me­chanical properties a coupling agent is often employed to aid in the binding of the lignocellulosic materials to thermoplastic resins.50 A variety of different types of couplings agents are blended with LPC/WPC but maleate polyolefins are the most common due to their cost, performance and acceptability.6,11,12,33,46,49,50,52 Since inclu­sion of a coupling agent is typical in WPC,6,11,12 the effects of employing a commer­cial maleate polyethylene (MAPE) on the mechanical properties of HDPE-DDGS composites is included in this study. Residual oils in DDGS may adversely affect the performance of DDGS composites due to their lubricating effect. Therefore, a solvent extracted DDGS material was tested to assess the benefit of oil extraction.

In addition, DDGS was subjected to chemical modification treatments in order to obtain an improved DDGS composite.

The second core objective was to evaluate the mechanical, physical, and thermal properties of WPC obtained from blending Paulownia wood flour with high density polyethylene because there have been relatively few studies of the use of Paulownia wood (PW) as a fiber reinforcement for thermoplastics.10,43,44’69 There is interest in using Paulownia wood flour derived from juvenile trees since small diameter short — rotation woody crop trees are likely to be a source of woody biomass needed by the US in the future. This study used PW flour derived from juvenile tree biomass (i. e., 36-month-old). The use of a maleate PE was employed as part of the scope of the project. Further, because chemical modification through acetylation or malation of filler materials may affect the performance of reinforcement, the mechanical and flexural properties of WPC derived from PW that had been acetylated and acety — lated/maleate was examined.

The third core objective was an evaluation of the physical and mechanical prop­erties of “mixed” composites composed of DDGS mixed with pine wood (PINEW) was conducted due to their relatively unique chemical make-up. The mechanical and flexural properties of these composites were benchmarked to formulations con­taining just PINEW or DDGS as well as to neat HDPE. The mechanical property outcomes were normalized to the control HDPE for ease of assessing the benefit of various filler treatments.

Because bio-composites are subject to degradation by water, water immersion tests were administered on tensile bars composites to evaluate their environmental durability. Weights, thickness, and mechanical properties were measured before and after the immersion tests. Finally, because bio-fiber materials are sensitive to heat exposure during processing, differential scanning calorimetry and thermogravimet­ric analysis were conducted on DDGS, PW, and PINEW composites to evaluate their thermal properties to assess any implications of processing on these materials.