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.