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Title: Performance enhancement of a Poly(lactic acid) and sugar beet pulp composites by improving interfacial adhesion and penetration

item Liu, Linshu
item COOKE, PETER - USDA/ARS 1935-
item Hicks, Kevin

Submitted to: Journal of Industrial and Engineering Chemical Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2008
Publication Date: 9/17/2008
Citation: Chen, F., Liu, L.S., Cooke, P., Hicks, K.B., Zhang, J. 2008. Performance enhancement of a Poly(lactic acid) and sugar beet pulp composites by improving interfacial adhesion and penetration. Journal of Industrial and Engineering Chemical Research. 47:8667-8675.

Interpretive Summary: Forty million tons of sugar beet pulp (SBP) are generated yearly by U.S. beet sugar industries and most of it is used as low value animal feeds. Finding new uses for this biodegradable, agricultural byproduct is critical for the long term economic viability of the U.S. sugar industry. In this study, we developed composite structural materials from SBP by co-extrusion with another biomass-derived compound, poly(lactic acid), and a popular chemical cross-linker, methylene diphenyl diisocyanate (pMDI), which has a long safe history of use in sealants and biomedical materials. The resultant composites were able to retain the mechanical properties of the original PLA even at SBP content as high as 50% of the total mass. The mechanism of the composite formation was studied and methods to prepare such types of composites with > 50% SBP content were developed. The novel composites can function as light weight-bearing construction materials, which would use a large volume of SBP and benefit sugar beet growers and beet sugar processors.

Technical Abstract: Polylactic acid (PLA) and sugar beet pulp (SBP) composites were prepared using a twin screw extruder. The phase structure, thermal properties, mechanical properties and water resistance of the composites were studied. The molecular weight change of PLA in the composites was also studied. Polymeric diphenylmethane diisocyanate (pMDI) was used as a coupling agent and resulted in significant increases in mechanical properties and water resistance. The tensile strength of the PLA/SBP (70/30 w/w) composite was only 56.9% that of neat PLA, but it was increased to 80.3% with the addition of 0.5% pMDI and further increased to 93.8% at 2% pMDI. With 50% SBP and 2% pMDI, the tensile strength of the composite was 87.8% of that of neat PLA. The microstructure of the composites indicated that the addition of pMDI greatly improved the wettability of the SBP particles by PLA and increased the penetration of PLA into the porous SBP. Consequently, the failure of the composites in mechanical testing changed from extensive debonding without pMDI to progressive rupture of the SBP particles with pMDI.