Continuous extrusion foaming process of biodegradable nanocomposites based on poly(lactic acid)/carbonaceous nanoparticles with different geometric shapes: An insight into involved physical, chemical and rheological phenomena

Abstract

AbstractOne‐step extrusion foaming process of biodegradable poly(lactic acid) (PLA)‐based nanocomposites in the presence of chemical foaming agent and chain extender has great complexity to control. In this work, PLA‐based nanocomposites containing different carbonaceous nanoparticles with different geometric shapes were obtained through a co‐rotating twin‐screw extrusion process to get insight into the dominant phenomena, which control the structural and final properties of PLA foams. The reactive extrusion foaming of PLA melt was investigated in the presence of carbon black, carbon nanotubes (CNTs), graphene oxide (GO), and a chain extender additive as well as a chemical foaming agent. Nanoparticles affect the continuous extrusion foaming of PLA melt through several phenomena, including providing bubble heterogeneous nucleation sites, intensifying the chemical decomposition of the foaming agent, improving the PLA structural modification reaction, increasing PLA molecular weight and restricting the dissolved gas removal from the melt. By influencing the involved phenomena in process, the nanoparticles at low levels, especially CNT and GO, increased the void content and cell size of PLA foams. The incorporation of CNT and GO nanofillers at the 0.5 phr level increased the electrical conductivity of PLA foams sharply by 9 and 10 orders of magnitude, resulting in lightweight, biodegradable semi‐conductive foams.