Properties of poly(lactic acid) and sugar beet pulp green composites. II. Structural and mechanical properties analysis

Authors: Liu, Linshu; Finkenstadt, Victoria; Liu, Cheng Kung; Coffin, David; Willett, Julious; Fishman, Marshall; Hicks, Kevin

Submitted to: Journal of Biobased Materials and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2007
Publication Date: 12/1/2007
Citation: Liu, L.S., Finkenstadt, V.L., Liu, C., Coffin, D.R., Willett, J.L., Fishman, M., Hicks, K.B. 2007. Properties of poly(lactic acid) and sugar beet pulp green composites. II. Structural and mechanical properties analysis. Journal of Biobased Materials and Bioenergy. 1(3):323-330.

Interpretive Summary: Enormous amounts of sugar beet pulp are generated from U.S. beet sugar production that either is subsequently sold as low value animal feed or must be disposed in an environmentally acceptable manner with additional expense. To profitably utilize this biorenewable processing by-product, we have used sugar beet pulp to reinforce poly(lactic acid) to form thermoplastic composite materials using a process called compression-heating. The resultant composites showed suitable mechanical properties for the use as lightweight construction materials and they cost less than materials made with pure poly(lactic acid),(J Agr Food Chem 2005;53:9017-9022). As a continuation of study, this paper explored the possibility of making these useful materials by a different process that can be done more cheaply and on a large-scale commercial basis. This process is called twin-screw extrusion with injection molding. We found that this twin screw extrusion process produced composites that were as good or better than those produced by compression-heating. Sugar beet growers and processors will benefit from this research by the creation of valuable new products from sugar beet pulp that will increase demand and value for this byproduct.

Technical Abstract: Composite materials of sugar beet pulp (SBP) and poly(lactic acid) (PLA) were evaluated for structural, mechanical, and moisture resistant properties. Microscopic analysis revealed that the SBP filler was evenly distributed in the PLA matrix phase. At lower SBP content, the filler was surrounded by the PLA matrix. As the SBP fraction increased, filler particles aggregated in the matrix although PLA remained the continuous phase. Due to the rigid nature of SBP, the PLA-SBP composites showed enhanced stiffness as the SBP fraction increased. However, as characterized by small deformation dynamic mechanical analysis and tensile strength testing, the PLA composites with higher SBP weight fraction were less fracture resistant and more moisture sensitive. Acoustic emission analysis further suggested the role of filler-matrix debonding during fracture at higher SBP content. Thus, the improvement of filler-matrix adhesion is a strategy to enhance the mechanical properties of composites with a higher SBP/PLA ratio.