Effects of Biomass in Polyethylene or Polylactic Acid Composites

There is need for bioplastics to replace some of the total petroleum plastics used in the world, and help alleviate environmental pollution. Compounding bioplastics with Polyethylene (PE) or Polylactic acid (PLA) containing 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%. PE/DBP and PLA/DBP composites placed in 75% relative humidity chambers absorbed less than 1% moisture after 500 h. Peak melt for PE/DBP composites increased by 2.8 C at 5 wt% DBP and by 4.2 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 C at 5 wt% DBP and 2.0 C at 10 wt% DBP; melt enthalpy did not change. Cold crystallization of PLA was at 184.9 C, but with 5 wt% DBP at 104.3 C, and 10 wt% DBP at 99.1 C. 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%. Impact failure was partial for PE/DBP. 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.