Chain Extension and Foaming Behavior of Poly(lactic acid) by Functionalized Multiwalled Carbon Nanotubes and Chain Extender

ABSTRACT A nanocomposited biofoam consisting of functionalized multiwalled carbon nanotubes (MWCNTs), a chain extender with multi‐epoxy groups (CEME), and poly(lactic acid) (PLA) was prepared by a batch foam process. First of all, poly(acrylic acid) (PAA) was directly grafted onto the surface of MWCNTs by in situ polymerization. And then, the modified MWCNTs, CEME, and PLA were reacted by melt mixing through the esterification reaction between the epoxy groups of the CEME and the carboxyl groups of PAA or PLA. Finally, the resultant nanocomposites were foamed in a high‐pressure stainless steel autoclave using CO 2 as a physical blowing agent. The functionalized MWCNTs were characterized using Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The crystallization and rheological properties of various samples were examined by a differential scanning calorimeter, rotational rheometer, and torque rheometer, respectively. The foaming properties of various samples were characterized by a scanning electron microscope and densimeter. It was found that the volume expansion ratio of modified MWCNT/PLA foam with a uniform cell size reached nearly 10 times.