Submitted to: Journal of Biobased Materials and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 27, 2009
Publication Date: May 25, 2009
Citation: Onwulata, C.I., Thomas, A.E., Cooke, P.H. 2009. Effects of Biomass in Polyethylene or Polylactic Acid Composites. Journal of Biobased Materials and Bioenergy. 3(2):172-180. Interpretive Summary: Using biodegradable and compostable resources reduces the use of petrochemical materials and may reduce the costs of disposing wastes in landfills, and help to prevent environmental pollution. In this study, we combined whey proteins, casein, starch and glycerol to form a new biodegradable material called Dairy-Based Plastic (DBP). The DBP was blended with a plastic, polyethylene (PE) or bioplastic, polylactic acid (PLA) at 5, 10, 20 weight percent (wt %) levels. The blends containing DBP were injection molded into dog-bone shapes specified by the American Society for Testing and Materials (ASTM) method D4065. It was very easy to mold up to 20 wt% DBP with PE, but difficult with PLA which was moldable only up to 10 wt% DBP. The tests showed that material properties such as melting, elongation and flexing strength were maintained with PE blends, but PLA blends fell apart. Our work shows that it is possible to use DBP to help reduce the amount of PE plastic in a formulation. Using DBP will also help to meet U.S. government rule that plastics must contain at least 20% biodegradable materials by the year 2020.
Technical Abstract: Previous studies have shown that compounding Polyethylene (PE) or Polylactic acid (PLA) with a dairy-based bioplastic resulted in composites with good mechanical properties. In this study, mass ratios of a dairy-protein-based material (DBP) ranging from 0, 5, 10 and 20 wt% replaced equivalent masses of PE or PLA in the blends used for injection-molding of ASTM D4065 composite specimens. The PE/DBP composites were moldable up to 20 wt%, but PLA/DBP composites were moldable only up to 10 wt%. Peak melt for PE/DBP composites increased by 2.8 deg C at 5 wt% DBP and by 4.2 deg C at 20 wt% DBP; melt enthalpy decreased by 8.1 J/kg at 20 wt% DBP. Peak melt for PLA/DBP composites increased by 3.7 deg C at 5 wt% DBP and 2.0 deg C at 10 wt% DBP; melt enthalpy did not change. Storage modulus of PE/DBP decreased by 44 MPa at 5 wt% DBP, and increased by 117 MPa at 20 wt% DBP. Storage modulus of PLA/DBP increased by 210 MPa at 5 wt% DBP, but decreased by 190 MPa at 10 wt% DBP. Adding DBP to PE increased elongation at peak, tensile modulus and impact resistance and flexural modulus at 20 wt%, but decreased peak load at break, flexural modulus between 5 to 10 wt%, and impact resistance at 20 wt%. Adding DBP to PLA increased stiffness at 5 wt%, but caused complete failure at 10 wt%. The effect of DBP on PE or PLA depended on the quantity added; PE composite properties were generally less negatively affected.