Before compounding, wood flour, rice husk and DDGS were dried in an oven for at least 48 h at 105 °C to expel moisture before blending with PP and then stored in polyethylene bags. First, the PP was put in the high-intensity mixer (Papenmeier, TGAHK20, Germany), and the reinforcement was added after the PP had reached its melting temperature. The mixing process took 10 min on average. After blending, the compounded materials were stored in a sealed plastic container. Several formu­lations were produced with various contents of PP, wood flour, rice husk, DDGS and 5% of MAPP in all the samples (Table 12.1). For the extraction of volatile and harmful gases, the hood was open.

For the mechanical property experiments, test specimens were molded in a 33-Cincinnati Milacron reciprocating screw-injection molder (Batavia, OH). The nozzle temperature was set to 204 °C. The extrudate, in the form of strands, was cooled in the air and pelletized. The resulting pellets were dried at 105 °C for 24 h before they were injection-molded into the ASTM test specimens for tensile (Type I, ASTM D 638) and Izod impact strength testing. The dimensions of the specimens for the tests were 120x3x12 mm3 (Length x Thickness x Width).

NORMA-AUREA RANGEL-VAZQUEZ, ADRIAN BONILLA PETRICIOLET, and VIRGINIA HERNANDEZ MONTOYA

ABSTRACT

The development of natural fiber reinforced biodegradable polymer composites promotes the use of environmentally friendly materials. The use of green materials provides alternative way to solve the problems associated with agriculture residues. Agricultural crop residues such as oil palm, pineapple leaf, banana, and sugar palm produced in billions of tons around the world. They can be obtained in abundance, low cost, and they are also renewable sources of biomass.

Among this large amount of residues, only a small quantity of the residues was applied as household fuel or fertilizer and the rest, which is the major portion of the residues is burned in the field. As a result, it gives a negative effect on the environ­ment due to the air pollution. The vital alternative to solve this problem is to use the agriculture residues as reinforcement in the development of polymer composites. A viable solution is to use the entire residues as natural fibers and combine them with polymer matrix derived from petroleum or renewable resources to produce a useful product for our daily applications.

Lignocellulosic materials are renewable resources that can be directly or indi­rectly used for the production of biomolecules and commodity chemicals. However, some of these applications are limited by the close association that exists among the three main components of the plant cell wall, cellulose, hemicellulose and lig­nin. Therefore, it is only through a clear understanding of this chemistry that one

can identify the reasons why lignocellulosics are so resilient to biological processes such as enzymatic hydrolysis and fermentation.

Recently environmental problems caused by the conventional fuel based plastics have become public major concerns. Many countries applied various policies and managements to overcome these problems, for example, recycle reuse and reduce protocol. However, due to the enormous amount of packaging and household plas­tics used every day, such attempt was found to be far from succeeded. Other mod­ern strategy is to replace the conventional plastics with biodegradable plastics such as modified starches, polylactic acids, polyhydroxyalkanoates and such. However, their prices and applications have always been considerated.

Although manufacture of a true biocomposite would demand a matrix phase sourced largely from renewable resources, the current state of biopolymer technol­ogy usually dictates that synthetic thermoplastics or thermosetting materials, such as polyethylene (PE) and polypropylene (PP), are used in commercial biocomposite production. There is still a considerable need for the development of thermosetting materials from renewable resources.

Recent examples of such developments include the use of vegetable oils to build thermosetting resins, which can then be modified to form cross-linkable molecules such as epoxides, maleates, aldehydes and isocyanates.

In recent years, there have been significant breakthroughs in the photoinitiated crosslinking of bulk PE and industrial application of photocrosslinked polyethylene (XLPE) insulated wire and cable. The mechanism and crosslink microstructures of the photocrosslinking of LDPE and its model compounds, the crystalline morpho­logical structures, surface photo-oxidation and stabilization of the XLPE materials, and the photolytic products of benzophenone (BP) as a photoinitiator during the photocrosslinking processes.

Molecular modeling used to be restricted to a small number of scientists who had access to the necessary computer hardware and software. The reliability of the obtained results strongly improved throughout the last decades. During this period Theoretical Chemists developed new strategies to describe the reality and Compu­tational Chemists were able to implement and test models. Nowadays many Experi­mental Chemists, working either in organic or physical chemistry, can easily take advantage of modern commercial software for both research and teaching purposes.

Computational chemistry is a branch of chemistry that uses principles of com­puter science to assist in solving chemical problems. It uses the results of theoretical chemistry, incorporated into efficient computer programs, to calculate the structures and properties of molecules and solids

The analysis techniques used were, FTIR to study this effect and an option to justify the obtained results is using theoretical calculations by means of the com­putational chemistry tools. Using QSAR properties, we can obtain an estimate of the activity of a chemical from its molecular structure only. QSAR have been successfully applied to predict soil sorption coefficients of nonpolar and nonioniz — able organic compounds including many pesticides. Sorption of organic chemicals in soils or sediments is usually described by sorption coefficients. The molecular electrostatic potential (MESP) was calculated using AMBER/AM1 method. These methods give information about the proper region by which compounds have inter­molecular interactions between their units.

The electrostatic potential is the energy of interaction of a point positive charge (an electrophile) with the nuclei and electrons of a molecule. Negative electrostatic potentials indicate areas that are prone to electrophilic attack. The electrostatic po­tential can be mapped onto the electron density by using color to represent the value of the potential. The resulting model simultaneously displays molecular size and shape and electrostatic potential value. Colors toward red indicate negative values of the electrostatic potential, while colors toward blue indicate positive values of the potential.

15.1 INTRODUCTION

Now a days, 80% of the polymer market is occupied by synthetic polymers and most of these polymers are non degradable. The nondegradable nature of polymer causes disturbance in the earth ecosystem. Besides this, the earth has finite resources in terms of fossil based fuel. The escalating increase of price of petroleum based products and alternative disposal method are also a great concern. Hence, the use of fossil-based products is not sustainable. So, there is an urgent need to overcome the dependence on such conventional polymers by using bio-degradable polymers and composites. In order to produce fully renewable and biodegradable composites, both the polymeric matrix and the reinforcement must be derived from renewable natural resources such as agricultural and biological origin. Also, the use of natural polymers, which are normally biodegradable, can pave new direction in designing of newer greener composites and could widen the spectrum of applications in differ­ent sectors such as automobiles, furniture, packing and construction industrial parts.

The process of electrospinning was first investigated by Zeleny in 1914 and was found to be a technique for spinning small diameter fibers.66 Electrospinning is an adaptable technique, enabling the development of nanofiber-biomaterial scaf­folds. These scaffolds can be used for tissue engineering and regenerative medi­cine because they can mimic the fibrous properties of the natural extracellular matrix in tissues. Electrospinning has also been implemented to produce spider silk fibers. In the process, the spinning dope is placed into a syringe fixed to a needle and a high electric potential is applied to a droplet of the solution at the tip of the needle. When the applied electrical force becomes greater than the surface tension of the silk droplet, it results in a charged jet of the silk solution that is ejected in the direction of the applied field. The jet undergoes dehydration as the solvent is evaporated in the air, resulting in dried fibers that can be collected on a receiving conducting mesh. Many more studies have been reported using silk­worm fibroins for electrospinning relative to spider fibroins. To date, nanofibers have been successfully spun from reconstituted natural silk dragline silk as well as recombinantly expressed proteins dissolved in HFIP.67 The diameters of the fibers were several orders of magnitude smaller relative to natural fibers, ranging from 8 to 200 nm, which is similar to other electrospun polymers.68 For the reconstituted spun nanofibers, wide angle X-ray diffraction (WAXD) studies demonstrated the fibers contained orientational and crystalline order comparable to that of natural spider silks.67a Electrospinning has also been used to prepare spider silk fibroins/ poly(D, L-lactide) [PDLLA] composite fibrous nonwoven mats.69 Addition of the spidroins to PDLLA led to improvements in the hydrophilic and mechanical prop­erties of the composite fiber and its biocompatibility. Collectively, the electrospun nonwoven fabrics have promise for scaffolds for tissue engineering, wound dress­ing materials, and carriers for drug delivery because of their high hydrophilicity and porous structure.

Figure 4.22 shows the temperature dependency of E and tan 5 for SPE/QC(1/1.2), SPE/PN(1/0.8), SPE/QC(1/1.2)/WF and SPE/PN(1/0.8)/WF biocomposites mea­sured by DMA. The tan 5 peak amplitude for the biocomposites became weaker with increasing WF content, indicating that amorphous content of the biocompos­ites certainly decreased with WF content. The E curve of at the rubbery plateau region over 120 °C for all the biocomposites was much higher than those of con­trol SPE/QC(1/1.2) and SPE/PN(1/0.8), suggesting a superior reinforcement effect due to the wood fibers. The tan 5 peak temperatures (SPE/QC(1/1.2)/WF20, 30, 40:106.2, 112.7, 107.2 °C) related to Tg for the SPE/QC(1/1.2)/WF biocomposites were significantly higher than that of SPE/QC(1/1.2) (85.5 °C). This trend is marked contrast to the fact that SPE/PN(1/0.8)/WF30 had a lower tan 5 peak temperature (69.9 °C) than that of SPE/PN(1/0.8) did (81.0 °C). Similar lowering of tan 5 peak temperature of WF biocomposite relative to the corresponding cured neat resin had been also observed for GPE/TA/WF biocomposites as was reported by our group.22 Also, the E of the SPE/QC(1/1.2)/WF biocomposites declined at around 90-120 °C due to the glass transition, and then again decreased at around 180-200 °C, probably due to the disappearance of specific interaction between WF and the cured SPE/QC resin. Figure 4.23 shows FT-IR spectra of WF, QC and a mixture of QC/WF 1/1 (w/w) prepared by mixing in THF and drying at 40 °C for 24 h. The band at 1621 cm-1 for QC due to C=C stretching vibration at C-2 and 3 did not shift for QC/WF. In contrast, the band at 1675 cm-1 for QC due to unsaturated carbonyl (C=O) stretch­ing vibration significantly shifted to a lower wavenumber region for QC/WF (1659 cm-1), indicating that there is a hydrogen bonding interaction between unsaturated carbonyl group of quercetin moiety and hydroxy group of lignocellulose component of WF. This interaction is based on the resonance structure of QC generating highly polarized carbonyl group as is shown in Fig. 4.24.

Figure 4.25 shows typical TGA curves of SPE/PN(1/0.8), SPE/QC(1/1.2), SPE/ QC/(1/1.2)WF biocomposites and WF. Since the thermal decomposition tempera­ture of WF was lower than that of SPE/QC(1/1.2), the SPE/QC(1/1.2)/WF com­posite exhibited two-step thermo-degradation. The 5% weight loss temperatures of SPE/QC(1/1.2), SPE/QC(1/1.2)/WF20,30,40 and WF were 342.5, 311.4, 300.8, 299.2 and 295.5 °C, respectively. The SPE/QC showed a comparable 5% weight loss temperature to SPE/PN(1/0.8) (346.3 °C) in agreement with the fact that both QC and PN are aromatic polyphenols. In addition, the cured resin of DGEBA and

QC, both of which are aromatic compounds had a superior 5% weight loss tempera­ture (407.4 °C) as is shown in Table 4.8.

Figure 4.26 shows the relationship between tensile properties and fiber content for SP/QC(1/1.2)/WF composites. The tensile modulus of SPE/QC(1/.12)/WF bio­composites increased with increasing WF content, and SPE/QC(1/1.2)/WF40 had a higher tensile modulus than SPE/PN(1/0.8). However, tensile strength and elonga­tion at break of the biocomposite were lower than those of SPE/QC(1/1.2). Figure 4.27 shows the FE-SEM images of the fractured surface of SPE/QC(1/1.2)/WF bio­composites. The micrograph of WF shows that the fiber length and width of WF are ca. 0.2-0.4 mm and 40-200 mm, respectively. It appeared that the composites are fractured at the interface between WF and the cured resin. As SPE/QC(1/1,2) itself has a high tensile strength (43 MPa), a considerably high interfacial adhesiveness between WF and SPE/QC is necessary to obtain the biocomposite with a higher tensile strength than the cured resin.

FIGURE 4.27 FE-SEM images of WF and the fracture surfaces of SPE/QC(1/1.2) and SPE/ QC(1/1.2)/WF biocomposites.24

In order to apply these jute-based biocomposites in various industrial applications for noise control some of its important properties like mechanical strength, fire re­tardant properties, acoustical properties, chemical stability at extreme temperatures need to be known and understood, among many other important physical properties. Here a brief description of the properties is presented along with some of the values of the properties measured at the various experimental facilities available at the Indian Institute of Technology Kharagpur.

In general, jute fibers have an aspect ratio (length/diameter) above 1000 and thus can be easily woven and can be spun into coarse and strong threads. These fibers are mostly used for fishnets, sacks, bags, ropes and as a filling for mattresses and cushions. In general, bast fibers (skin fiber collected from plants) have good thermal and acoustical insulation properties. There are, however, few drawbacks associated with the application of jute fibers. The primary one is lack of consistency in fiber quality due to presence of hydroxy and other polar groups in various constituents.

Another one is high moisture absorption, which brings the dimensional instability to the composites. The compatibility between matrix and fiber is poor, which require surface or alkali treatment.

Limitation in performance of jute-based fiber composites can be greatly im­proved through chemical modification techniques5.

7.2.1 SHEET FORMING DEVICE FOR DRY TEXTILE REINFORCEMENT

A device presented in Fig. 7.1 was especially designed to analyze the possibility to form reinforcement fabrics. Particularly, the device was developed to examine the local deformations during the forming process64. The device is the assembly of a mechanical part and an optical part. The mechanical part consists of a punch/open die system coupled with a classical blank-holder system. The punch used in this study (Fig. 7.1.b) is a tetrahedron form with 265 mm sides. Its total height is 128 mm and the base height is 20 mm. The edges and vertices possess 10 mm radius for the punch and 20 mm for the die. As the punch possesses low edges radiuses, it is expected that large shear stains take place during forming. A triangular open die (314x314x314 mm3) is used to allow for the measurement of the local strains during the process with video cameras associated to a marks tracking technique65. A piloted electric jack is used to confer the motion of the punch. Generally, the punch veloc­ity is 30 mm/min and its stroke 160 mm. The maximum depth of the punch is 160 mm. A classical multipart blank-holder system is used to prevent the appearance of wrinkling defects during the preforming tests by introducing tension on the fabric. It is composed of independent blank-holders actuated by pneumatic jacks that are able to impose and sense independently a variable pressure. The quality of the final preform may depend on several process parameters such as the dimensions, posi­tions, and the pressure applied by each of the blank-holders can be easily changed to investigate their influence on the quality of the final preform66. Before starting the test, a square piece of fabric is positioned between the die and the blank-holders. The initial positioning of the fabric is of particular importance as it partly conditions the final tow orientations within the part. However, it is not possible to establish be­fore the test their final position at the end of the forming and as a consequence their mechanical stiffness. So, for the tests presented below, it was chosen to align the warp or the weft tows with an edge of the tetrahedron (the opposite edge of Face C (Fig. 7.1.b). To avoid bending of the fabric under its own mass, a draw bead system is used to apply low tensions at the tow extremities. At the end of the performing test, the dry preform can be fixed by applying a spray of resin on its surface so that the preform can be removed from the tools and kept in its final state.

At the end of the preforming test, several analyzes at different scales can be performed. A first global analysis at the macroscopic scale concerning the final state of the preform before removing it from the tool can be performed. It consists in ana­lyzing if the shape is obtained and if the shape shows defects. Another analysis, at the mesoscopic scale, consists in analyzing the evolution of the local strains (shear, tension) during forming.

Using this device, an experimental study to analyze with the tetrahedron shape, the generation of defects (wrinkles, tow buckles, tow sliding, vacancies, etc.) can be performed. The influence of the process parameter and particularly the blank-holder pressures on the generation and the magnitude of defects is also commented and analyzed.

Sugar palm tree is a member of the Palmae family and naturally a forest species.51It belongs to the subfamily Arecoideae and tribe Caryoteae.525 Hyene54 reported that sugar palm have approximately around 150 local names indicating its multiple uses by the villagers. The names includes, Arengapinnata, Areng palm, Black fiber palm, Gomuti palm, Aren, Irok, Bagot and Kaong. In Malaysia, it is known as either enau or kabung. Sugar palm plant was originally from Assam, India and Burma. It origi­nates from an area covering South East Asia up to Irian Jaya in the east of Indonesia. Sugar palm tree are widespread to Malaysia, Indonesia and other South East Asian countries. It is one of the most diverse multipurpose tree species in culture.

Malaysia as a tropical country has ample resources of natural fibers. One of those abundant natural fibers found in Malaysia but has not been widely used in the field of reinforcement is the sugar palm fiber.3 This fiber is traditionally used by the local people to make brooms, brushes, septic tank base filter, door mats, carpet, chair/ sofa cushion, and rope. Although the fiber is popular among locals to have high strength and stiffness, little research has been conducted up to date on the full potential of sugar palm fibers and their composites.3 55 58 Another attractive potential of sugar palms is their ability to produce biopolymers (i. e., starch). The starch ob­tained from the trunks of sugar palm trees can be use to make biodegradable poly­mer which in turn can be reinforced with natural fibers to make green composites. This composite possesses the advantage of being renewable, biodegradable, abun­dantly available (especially in tropical countries like Malaysia) and inexpensive as such they have a promising future in the field of biocomposite materials. Figure 9.11 shows the image of sugar palm fiber and sugar palm starch.

The tensile properties of tensile strength (oU), Young’s modulus (E), and elongation strain at break (%El) of the HDPE-DDGS composites containing various compos­ites are shown in Table 13.2. The flexural strength (ofm), the flexural modulus or modulus of elasticity in bending (Eb), and the notched iZOD impact strength for the various composites are presented in Table 13.3. The average for the five test speci­mens and their standard error is given for each property. Figures 13.2-13.4 graphi­cally summarize the data in Tables 13.2 and 13.3 by normalizing the outcomes to the HDPE control material. For example, the tensile strength of HDPE-MAPE is 96% of the neat HDPE thus the bar graph of the normalized oU for HDPE-MAPE is 96%. This rendering is employed to clearly illustrate the effect of additives.

TABLE 13.3 Flexural and Impact Properties of HDPE and Composites*

Eb °fm Impact Energy

Composition (MPA) (MPa) (J/m)

HDPE 41.4 ± 0.2a 1169 ± 8a 921.8 ± 1.6a

HDPE-MAPE 40.0 ± 0.1b 1125 ± 5a 924.4 ± 1.3a

HDPE-25DDGS 33.7 ± 0.6c 1272 ± 31b 447.8 ± 2.4b

‘Treatment values with different letters in the same column were significant (p £ 0.05). Means and standard errors derived from five different replicates are presented.

All biocomposites containing DDGS exhibited much lower tensile strength but comparable modulus values compared to the neat HDPE or the HDPE-MAPE for­mulations. Refer to Table 13.2 and Fig. 13.2. The %El values were considerably higher in the unextracted DDGS formulation (HDPE-25DDGS) compared to the STDDGS formulation (HDPE-25STDDGS), which is attributed to the presence of residual oils in this composite (HDPE-25DDGS) which acts as a plasticizing agent interacting with the filler and the resin matrix as shown in Table 13.2 and Fig. 13.2. Similarly, Julson et al.,25 reported the poor mechanical performance of PP — and HDPE-DDGS composites when compared to neat PP or HDPE. To improve the

mechanical properties of the HDPE-DDGS composites the coupling agent MAPE was included in the formulations. Adding 5% MAPE to the DDGS composite formu­lation (HDPE-25DDGS-MAPE and HDPE-25STDDGS-MAPE) resulted in a slight increase in oU but a nominal reduction in E values compared to the corresponding DDGS composites without MAPE (HDPE-25DDGS and HDPE-25STDDGS). Re­fer to Table 13.2 and Fig. 13.2.

Unlike in a previous study30 where a marked increase in the tensile strength was observed when using STDDGS versus DDGS in composites (without MAPE), this study showed only a slight improvement in the tensile strength when using STD — DGS. Although, the modulus significantly increases when using the solvent treated DDGS as shown in Fig. 13.2. However, when MAPE was added to the STDDGS
composite (HDPE-25STDDGS-MAPE) verses original untreated-DDGS formula­tions (HDPE-DDGS or HDPE-DDGS-MAPE) resulted in significantly higher oU values than all other DDGS formulations. In addition, the HDPE-25STDDGS — MAPE formulation compared favorably to the neat HDPE and HDPE-MAPE formu­lations. These results shows the importance not extrapolating and overgeneralizing the results conducted in prior studies to current studies.30 In this study, a high melt­ing HDPE, Paxon BA50-120 with a melting temperature of 204°C was employed; in the previous study a much lower melting HDPE, Petrothene LS 5300-00 with a melting temperature of 129°C was employed. In the previous study, the HDPE — STDDGS-MAPE formulations exhibited a significantly higher tensile strength than neat HDPE30 while in this study the HDPE-25STDDGS-MAPE formulation exhib­ited a oU that was slightly lower than the neat HDPE. See Table 13.2 and Fig. 13.2. Nevertheless, similar trends were found between the two studies employing dis­similar HDPE resins.

Removal of extractables in order to obtain a superior filler has been previously documented.7,30,41’49 It is notable that the HDPE-25DDGS formulation exhibited in­ferior mechanical (oU and E) and flexural (ofc and Eb) values compared to the STD — DGS formulations but had significantly higher %El and impact strength values than other formulations. Refer to Tables 2 and 3 and Fig. 13.2. DDGS contains high levels of crude protein («26%), water (»5.5%), hexane extracted oils («14%), and acetone extractables («3%). The solvent extraction treatment removes oils and polar extractables to obtain the modified DDGS filler (STDDGS). Apparently, the oil and extractables in the DDGS composite formulations interacted with the resin matrix acting as plasticizing agents which allow for greater percentage of elongation at break and impact strength. Conversely, they are responsible for the lower oU, E, ofm and Eb values in the composites. Adding 5% MAPE to the solvent treated DDGS formulations results in lower impact strength but higher o^ and a slight reduction in moduli compared to formulations without MAPE. PW formulations were found to exhibit similar trends in mechanical properties as the DDGS formulations previ­ously discussed. Refer to Table 13.2 and Fig. 13.2.

Chemical modification of STDDGS particles through acetylation (A) or acety- lation/malation (AM) prior to blending with HDPE produced HDPE-25STDDG/A and HDPE-25STDDGS/AM formulations. Surprisingly, these formulations exhib­ited lower tensile and flexural moduli, lower flexural strength, and only a modest increase in tensile strength compared to the untreated formulation (HDPE-25STD- DGS). See Tables 13.2 and 13.3 and Fig. 13.2. Further, the %El and impact strength values declined in the acetylated and acetylated/maleate formulations compared to the untreated formulation; refer to Tables 13.2 and 13.3 and Fig. 13.2. The addition of MAPE to the chemically modified formulations (HDPE-25STDDGS/A-MAPE and HDPE-25STDDGS/AM-MAPE) had little effect on changing the mechanical properties compared to the formulations without MAPE.

Although the improvements due to the chemical modifications are small, they exhibit an expected trend. The tensile strength of the HDPE-25STDDGS composite was 73% of neat HDPE and that of the HDPE-STDDGS/A was 80%. When MAPE is added to these formulations, the oU of HDPE-25STDDGS-MAPE composite was 91% of the neat HDPE and the HDPE-25STDDGS/A-MAPE was 91%, respec­tively. These results indicate the improvement is due to the degree of esterification of the hydroxyl groups by the chemical modification treatments, which were further esterified by the presence of the MAPE coupling agent. The net result is an increase mechanical properties.

Solvent treatment of the PW flour to produce the STPW composites (HDPE — STPW and HDPE-STPW-MAPE) had little effect on their tensile, flexural and im­pact strength properties compared to the nonsolvent treated PW composites (HDPE — PW and HDPE-PW-MAPE). See Tables 13.2 and 13.3, and Fig. 13.3. Apparently the extractables in this wood were not as critical factors affecting the mechanical properties of the composites as in the DDGS formulations.

Chemically modified PW formulations (HDPE-25STPW/A, HDPE-25STPW/A — MAPE, HDPE-25STPW/AM, and HDPE-25STPW/AM-MAPE) exhibited similar trends to those seen for the DDGS formulations. Adding MAPE to the formulation had little effect on changing the mechanical properties of the chemically modified filler composites. Refer to Tables 13.2 and 13.3, and Fig. 13.3.

Despite the numerous publications dealing with the chemical modification (acet­ylation) of wood fiber (WF) and lignocellulosic materials in the literature, few me­chanical evaluations have been conducted on the resultant biocomposites containing chemically modified wood or lignocellulosic fibers.8,48,51’56’61’65 In addition, when the mechanical properties have been analyzed on chemically modified composites the results are rather modest or even negative.65 For example, Ichach and Clemons8 re­ported that HDPE-acetylated pine WF composites exhibited o^ and Eb values were -26 and -16%, respectively, compared to HDPE-untreated pine WF composites. However, the acetylated formulation retained its flexural properties better following weathering and fungal treatments when compared to the untreated HDPE-WF com- posite.8 In another study, HDPE-acetylated-WF composites exhibited ои, E, %El, ofm, and Eb values of +12, -22, +8, +6, and -9%, respectively, compared to HDPE- untreated-WF composites.51 Kaci et al.,48 reported that maleic anhydride acetylated — low density PE (LDPE)-olive husk flour composites exhibited ои, E, %El valves of +9, -27 and +15%, respectively, compared to LDPE untreated — olive husk flour composites. Muller et al.,61 reported that Polyvinyl chloride (PVC)-acetylated-WF composites exhibited ои, %El and impact strength values of+19, +22 and +18%, re­spectively, compared to PVC-untreated-WF composites. Previous reports find that acetylation of WF slightly benefits ov but reduces the tensile and flexural moduli in composites compared to untreated-WF composites. This study confirmed this trend with the chemically modified PW and DDGS composites (Table 13.2). The acetyla­tion and malation of solvent treated DDGS (HDPE-STDDG/A and HDPE-STD — DGS/AM) exhibited slightly higher tensile strength and flexural strength values but significantly lower tensile and flexural moduli values compared to the untreated composites (HDPE-STDDGS) as shown in Table 13.2 and Fig. 13.2. When the malation is provided by the matrix, using the MAPE coupling agent, there is a slight improvement in the mechanical strength properties but a slight reduction in the me­chanical moduli values than when chemical modification is done to the fillers. This is seen by comparing HDPE-STDDGS-MAPE to HDPE-STDDGS as shown in Fig. 13.2. Impact strength of DDGS formulations were negatively affected by the mala — tion (HDPE-STDDGS-MAPE) and chemical modification (HDPE-STDDGS/A and HDPE-STDDGS/AM) treatments compared to the untreated control (HDPE — STDDGS). See Table 13.3 and Fig. 13.2. Similar flexural results are mimicked with the maleate (HDPE-STPW-MAPE) and chemically modified (HDPE-STPW/A and HDPE-STPW/AM) PW composites compared to the untreated control PW compos­ite (HDPE-STPW). Inclusion of the coupling agent (MAPE) with the chemically modified DDGS formulations did improve the modulus of rupture or modulus of

elasticity and could significantly decreased the impact strength values compared to chemically modified formulations without MAPE. Clearly, chemical modification of the two fillers has both positive and negative effects of the mechanical properties to the resulting composites.

Semi-empirical quantum chemistry methods are based on the Hartree-Fock formal­ism, but make many approximations and obtain some parameters from empirical data. They are very important in computational chemistry for treating large mole­cules where the full Hartree-Fock method without the approximations is too expen­sive. The use of empirical parameters appears to allow some inclusion of electron correlation effects into the methods. Within the framework of Hartree-Fock calcu­lations, some pieces of information (such as two-electron integrals) are sometimes approximated or completely omitted. As with empirical methods, we can distinguish if: These methods exist for the calculation of electronically excited states of poly­enes, both cyclic and linear.

AM1 is basically a modification to and a reparameterization of the general theo­retical model found in MNDO. Its major difference is the addition of Gaussian func­tions to the description of core repulsion function to overcome MNDO’s hydrogen bond problem. Additionally, since the computer resources were limited in 1970s, in MNDO parameterization methodology, the overlap terms, Ps and Pp, and Slater orbital exponent’s Zs and Zp for 5- and p — atomic orbitals were fixed. That means they are not parameterized separately just considered as Ps = Pp, and Zs = Zp in MNDO. Due to the greatly increasing computer resources in 1985 comparing to 1970 s, these inflexible conditions were relaxed in AM1 and then likely better parameters were obtained.

Optimization of the original AM1 elements was performed manually by Dewar using chemical knowledge and intuition. He also kept the size of the reference pa­rameterization data at a minimum by very carefully selecting necessary data to be used as reference. Over the following years many of the main-group elements have been parameterized keeping the original AM1 parameters for H, C, N and O un­changed.

Of course, a sequential parameterization scheme caused every new parameter­ization to depend on previous ones, which directly affects the quality of the results. AM1 represented a very considerable improvement over MNDO without any in­crease in the computing time needed.

AM1 has been used very widely because of its performance and robustness com­pared to previous methods. This method has retained its popularity for modeling organic compounds and results from AM1 calculations continue to be reported in the chemical literature for many different applications.