Biofillers Improved Compression Modulus of Extruded PLA Foams

Abstract

Foams produced with biobased materials, such as poly(lactic acid) (PLA), cellulose, starch, and plant oil-based polyurethanes, have become more and more important in the circular economy. However, there are still significant challenges, including inferior performance and higher cost. The use of low-cost filler material has the potential to reduce the cost and alter the composite properties of biobased foams. By selecting biofillers derived from plant material, we can reduce the cost without sacrificing the compostability. This study explored the impact of landfill-diverted biofiller material, ground coffee chaff and rice hulls on the physical properties of biobased foams. Both biofillers were extrusion compounded with PLA, then extruded into rigid foams using a physical blowing agent. A filler concentration up to 10 weight % rice hull or 5 weight % coffee chaff could be incorporated without a significant increase in density, in comparison to the regular PLA foam. The thermal conductivity was similarly unaffected by biofiller loading, with values ranging between 71.5 and 76.2 mW/m-K. Surprisingly, the filler composite foams possessed impressive mechanical properties with all compressive moduli above 300 MPa. Only 5 weight % loading resulted in the doubling of compressive modulus, compared to the regular PLA foam. These results indicate that landfill-diverted fillers can strengthen foam mechanical properties without impacting thermal insulation performance, by forming reinforcing networks within the cell walls.