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

Abstract

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

Segmental relaxation and partial crystallization of chain‐extended Poly(l‐lactic acid) reinforced with carboxylated carbon nanotube

“…Before carrying out the DSC and BDS experiments, the morphology of the nanocomposites was characterized by TEM. A homogenous dispersion of carboxylated CNTs in PLLA was observed, whereas aggregation of the nanotubes resulted if nonfunctionalized CNTs is employed . Figure displays TEM micrographs of both PLLA/CNT (panel a) and chain‐extended PLLA/CNT (panel b) nanocomposites.…”

“…Carboxylated CNTs were first prepared through acid oxidation process developed in our previous work . Subsequently, the PLLA/CNTs master batch with 5 wt % MWCNTs was prepared using solution casting.…”

“…The number after CNT shows its weight fraction in the nanocomposite and the upper case at the end of the code indicates reactive (R) or nonreactive (N) melt mixing, for example, PLA/f‐CNT0.5/R corresponds to the nanocomposite containing 0.5 wt % of carboxylated MWCNTs prepared by reactive melt mixing, whereas PLA/f‐CNT0.2/N corresponds to the nanocomposite containing 0.2 wt % of carboxylated MWCNTs during nonreactive melt mixing. The dispersion state of MWCNTs in the PLLA matrix and the effect of chain extension process on the molecular weight and structure of PLLA were discussed in our previous work …”

Nanocomposites based on chain extended poly(l-lactic acid)/carboxylated carbon nanotubes: Crystallization kinetics and lamellar morphology

“…Dispersion state of MWCNTs in the PLLA and the effect of chain extension process on molecular weight and structure of PLLA were discussed in our previous works. 36,38 The studied samples are named by the abbreviation PLLA/x-CNTy/Z. The lower case before CNT indicates pristine (p) or functionalized (f) fillers and the number after CNT shows its weight fraction in the nanocomposite.…”

Simulation of tunneling distance and electrical conductivity for polymer carbon nanotubes nanocomposites by interphase thickness and network density

“…The wonderful levels of mechanical, electrical, thermal, and physical properties of carbon nanotubes (CNT) have motivated the increasing interests for the investigation of composites containing CNT as polymer/CNT nanocomposites (PCNT) . The electrical conductivity of CNT reaches to 10 6 S/m, but the polymer matrices usually show the conductivity of 10 −16 to 10 −12 S/m .…”