Rigid amorphous phase and constrained polymer chains in poly(L‐lactide) nanocomposites with carboxylated carbon nanotubes prepared via reactive melt mixing

Evaluation of constrained polymer chains and the glass transition behavior of the nanocomposite constituted by poly(L‐lactide) (PLLA) and functionalized carbon nanotubes (f‐CNTs) have been carried out. To control thermal degradation, nanocomposites were prepared via reactive melt mixing taking advantage of the capacity of carboxylic groups of both PLLA and f‐CNTs to participate in chain extension reactions. At low f‐CNT content (e.g., 0.2 and 0.5 wt%), a good dispersion of f‐CNTs was observed due to scarce bonds established between both components (i.e., the polymer matrix and the nanofiller), whereas at higher f‐CNT content (e.g., 1 wt%), a greater number of epoxy groups of the chain extender were bonded to carboxyl groups of f‐CNTs, giving rise to a highly significant crosslinking of CNT and a lower molecular weight of PLLA. Crystallinity, glass transition temperature and both the rigid polymer chains and constrained polymer chains were influenced by the dispersion state of f‐CNTs after reactive melt mixing and the thermal history (e.g., cooling rate form the melt) of samples. For evaluation of interphases between poly(lactic acid) and f‐CNTs, a simple method was developed for the considered tube‐like nanoparticles. Specifically, thicknesses of the generated interphases were calculated from DMA experiments. POLYM. COMPOS., 39:E1280–E1293, 2018. © 2018 Society of Plastics Engineers