Submitted to: Polymers and the Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/4/2007
Publication Date: 2/20/2008
Citation: Finkenstadt, V.L., Liu, C., Cooke, P.H., Liu, L.S., Willett, J.L. 2008. Mechanical Property Characterization of Plasticized Sugar Beet Pulp and Poly(lactic acid) Green Composites using Acoustic Emission and Confocal Microscopy. Polymers and the Environment. 16(1):19-26. Interpretive Summary: Polymer composite materials may be used in non-durable and short-term applications. Green composites use agricultural-based polymers and biodegradable plant-based fillers. Poly (lactic acid) (PLA) is a hydrophobic polymer prepared from renewable agriculture-based feed stocks which are fermented to lactic acid and then polymerized. PLA is biodegradable in soil, compost or water, and the degradation products of PLA are non-toxic to the environment. The use of renewable and biodegradable fillers is desirable to provide cost-competitive polymer composites. Sugar beet (Beta vulgaris) is grown as a commercial crop and is the source of about one-third of the world supply of sugar. Sugar beet pulp (SBP) is usually used as low value animal feed or disposed of at additional cost. The work reports on the formation of a co-continuous phase of plasticized sugar beet pulp (SBP) and poly (lactic acid) fabricated by twin-screw extrusion and injection molding. Earlier work showed that SBP functions as a non-reinforcing filler in PLA. The composites are biodegradable and competitive in cost with comparable non-sustainable petroleum based products currently in the marketplace. The manuscript discusses the results from acoustic emission and confocal microscopy as they relate to the mechanical properties. The current study presents a new way to utilize agricultural by-products for the future profitability of the agriculture industry.
Technical Abstract: Sorbitol and glycerol were used to plasticize sugar beet pulp-poly (lactic acid) green composites. The plasticizer was incorporated into sugar beet pulp (SBP)at 0, 10, 20, 30 and 40% w/w at low temperature and shear and then compounded with PLA using twin-screw extrusion and injection molding. The SBP:PLA ratio was maintained at 30:70. As expected, tensile strength decreased by 25% and the elongation increased. Acoustic emission showed correlated debonding and fracture mechanisms for up to 20% w/w plasticizer and uncorrelated debonding and fracture for 30-40% sorbitol and 30% glycerol content in SBP-PLA composites. All samples had a well dispersed SBP phase with some aggregation in the PLA matrix. However, at 40% glycerol plasticized SBP-PLA composites exhibited unique AE behavior and confocal microscopy revealed the plasticized SBP and PLA formed an a co-continuous two phase system.