Tensile Strength, Elongation, Hardness, and Tensile and Flexural Moduli of Injection-Molded TPS Filled with Glycerol-Plasticized DDGS
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Continuing growth of biofuel industries is generating large amounts of coproducts such as distillers dried grains with solubles (DDGS) from ethanol production and glycerol from biodiesel. Currently these coproducts are undervalued, but they have application in the plastics industry as property modifiers. This research effort has quantified the effects on mechanical properties of adding DDGS and glycerol to a commercial thermoplastic starch (TPS). The methodology was to physically mix DDGS, as filler, with the TPS pellets and injection mold the blends into test bars using glycerol as a processing aid. The bars were then mechanically tested with blends from 0 to 65 %, by weight, of plasticized filler. The test bars were typically relatively brittle with little yielding prior to fracture with elongation between 1 and 3 %. The addition of glycerol enabled molding of blends with high levels of DDGS but did not increase strength. Any presence of filler decreased the tensile strength of the starch, and up to 30 % filler, the tensile strength drops about 15 %. The 20 and 50 % blends (without glycerol) have slightly greater stiffness than pure starch. With some other blends, the presence of plasticized filler degrades the tensile modulus with 35 % filler yielding about 1/3 the stiffness. Changes in the flexural modulus are much more pronounced as 20–25 % filled TPS has a 30 % increase in flexural stiffness. In terms of surface hardness, blends up to 60 % filler are within 20 % of the TPS baseline.
KeywordsDDGS Glycerol Mechanical properties Thermoplastic starch TPS
This material is based upon work supported by the U.S. Department of Agriculture, Agricultural Research Service, under agreement No. 58-5447-0-346. Any opinions, findings, conclusion, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture; mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the United States Department of Agriculture and does not imply approval of a product to the exclusion of others that may be suitable. This work was also supported by U.S. Environmental Protection Agency Grant SU-83473601.
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