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mold temperature by cooling after molding (Plenco 2015; IDI Composites International 2017). Reddy and Yang (2011) employed prolonged slow cooling to molds to obtain soy- wood composites. Likewise, this problem was recognized and was addressed similarly. Composites that contained predominately large wood particles formed an interfacial complex with the “melted” DDGS , which formed a biocomposite that was weaker than the DDGS composite matrix that interacted with smaller wood particles. It was speculated that smaller wood particles interacted better with the DDGS matrix because of the ability of the DDGS to obtain a more fluid molten state that could penetrate the wood of smaller particles. Composites consisting of various particle sizes exhibited different flexural properties, suggesting that two types of interactions were occurring: (1) the wood particles were providing a support role based on their size, which contributed to the composite strength, and (2) the DDGS was interacting differently with the wood particles depending on their size. The < 1700 P m blend produced a composite that exhibited high flexural properties and was the simplest to prepare when compared to the other composites. This PW composite blend was adopted in all further studies (Fig. 8).
Fig. 8. Comparison of composite panels. Top panel consists of 50:50 mixture of DDGS: PW subjected to fast cooling. Note blistering and internal cracking. Middle panel consists of 50:50 mixtures of DDGS:PW subjected to slow cooling. Note absence of disruptive blemishes. Bottom panel is commercial PB locally purchased Effect of Pressure on Flexural Properties The effect of pressure applications on the flexural properties of composites is presented in Fig. 9. Best flexural properties were obtained using the highest pressure tested. The equipment used did not permit higher pressures to be administered. Composites subjected to 5.6 MPa had ) P and ( P values of 41.4 r 0.7 and 6073 r 123, respectively. Composites subjected to 2.1 MPa had ) P and ( P values of 12.6 r 1.0 and 2354 r 286, respectively. ) P and ( P values of composites subjected to 5.6 MPa were 228% and 158% greater than ) P and ( P values of composites subjected to 2.1 MPa, respectively. Similar results have been reported by other investigators (Li HWDO . 2011). Applied pressure had a profound influence on the flexural properties and affected their physical properties, thickness and density. This phenomenon was attributed to the increased densification of the DDGS-PW composite, which resulted in an enhancement in the interfacial binding between particles and thus improving the flexural properties of
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Tisserat et al . (2018). “DDGS - PW fiberboards” B io R esources 13(2), 2678-2701.
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