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Title: Sugar beet pulp and poly(lactic acid) composites using methylene diphenyl diisocyanate as coupling agent

item Liu, Linshu
item Coffin, David
item Liu, Cheng Kung
item Cooke, Peter
item Hicks, Kevin

Submitted to: Polymers Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2008
Publication Date: 11/1/2008
Citation: Liu, L.S., Coffin, D.R., Liu, C., Cooke, P.H., Hicks, K.B. 2008. Sugar beet pulp and poly(lactic acid) composites using methylene diphenyl diisocyanate as coupling agent. Polymers Research Journal. 2(2):115-126.

Interpretive Summary: Billions of pounds of low valued sugar beet pulp (SBP) are generated yearly as a byproduct of the U.S. beet sugar industries. These residues are generally sold, at low or no profit as animal feeds. Finding new uses for this biodegradable, agricultural byproduct is critical for the long term economic viability of U.S. agribusiness. In this study, SBP was used to make composite structural materials by extrusion with another biomass-derived compound, poly(lactic acid), and a few percent weight of a popular chemical cross-linker, methylene diphenyl diisocyanate (pMDI), which has a long safe history in the use for the manufacturing of sealants and biomedical materials. The resultant composites were able to retain the tensile strength of the original PLA and were stiffer than the samples extruded from pure PLA, even at SBP content as high as 50% of the total mass. Therefore, the novel composites could be used as light weight-bearing construction materials. If these materials are commercialized, it would develop new, higher value uses for sugar beet pulp which would benefit sugar beet growers and beet sugar processors.

Technical Abstract: Composites from sugar beet pulp (SBP) and poly(lactic acid) (PLA) were extruded in the presence of polymeric methylene diphenyl diisocyanate (pMDI). SBP particles were evenly distributed within the PLA matrix phase as revealed by confocal fluorescence microscopic analysis. The resultant composites were evaluated for mechanical properties and acoustic emission simultaneously, and examined by scanning electronic microscopy for the structures of the fractural surfaces after the destructive tests. The results showed that the inclusion of pMDI enhanced the inter-phase adhesion of the filler phase SBP to the matrix phase. Thus, the pMDI-containing composites were able to retain the tensile strength similar to that of extruded pure PLA and had higher Young’s modulus than PLA. The results from this study indicated an effective approach for preparation of environmentally friendly, useful structural materials from low cost biomass.