Isothermal Crystallization of Poly(l-lactide) Induced by Graphene Nanosheets and Carbon Nanotubes: A Comparative Study

Abstract

Low-dimensional nanoparticles have a strong ability to induce the crystallization of polymer matrices. One-dimensional carbon nanotubes (CNTs) and two-dimensional graphene nanosheets (GNSs), both of which are both carbon-based nanoparticles, provide a good opportunity to investigate the effects of differently dimensional nanoparticles on the crystallization behavior of a polymer. For this purpose, respective nanocomposites of CNTs and GNSs with poly(l-lactide) (PLLA) as matrix were prepared by solution coagulation. Time-resolved Fourier-transform infrared spectroscopy (FTIR) and synchrotron wide-angle X-ray diffraction (WAXD) were performed to probe chain conformational changes and to determine the crystallization kinetics during the isothermal crystallization of the PLLA nanocomposites and neat PLLA, especially in the early stages. Both CNTs and GNSs could serve as nucleating agents in accelerating the crystallization kinetics of PLLA; however, the ability of CNTs to induce crystallization was stronger than that of GNSs. On increasing the content of CNTs from 0.05 to 0.1 wt %, the induction period was shortened and the crystallization rate was enhanced, but the reverse situation was found for GNSs nanocomposites. In the case of neat PLLA, −CH3 interchain interactions preceded −(COC + CH3) interchain interactions during the crystallization. Conversely, in the CNTs and GNSs nanocomposites, the conformational ordering began with −(COC + CH3) interchain interactions, which resulted directly in a reduced induction period. Interchain interactions of this type could be explained in terms of surface-induced conformational order (SICO). Finally, the effect of the dimensionality of the nanoparticles on the crystallization behavior of PLLA is discussed.

Effect of carbon black on electrical and rheological properties of graphite nanoplatelets/poly(ethylene-butyl acrylate) composites

“…This can be attributed to the spatial arrangement of the filler particles that limit the possibility of polymer crystallization, as a number of nucleating sites become available for crystallization initiation. The existence of these different nucleation sites has been reported to lead to a decrease in crystallization rate [20,21] The reason for such behavior has been attributed to the two-dimensional nature of the GNP platelets that makes lattice matching the dominant force in the crystallization process. The polymer chains need to be absorbed on the graphitic surface and this will force them to undergo conformational changes that subsequently lead to longer crystal- lization times.…”

Effects of carbon nanotubes on polymer physics

“…145 Geometry may also play a role; the enhancement of crystallization rate in polylactide was much stronger in CNTs than in graphite nanosheets which the authors attributed, with some evidence from X-ray diffraction, to differences in the nature of polymer adsorption. 239 If nanotubes nucleate crystallinity in a given material, then the typical shape of a plot of crystallization half-time versus nanotube content plot (isothermal), or crystallization temperature versus nanotube content (nonisothermal) has a steep increase at low nanotube contents followed by a plateau at high nanotube contents as indicated by the data in Table 2. The Avrami exponent n is also displayed in Table 2.…”

Propriedades mecânicas, tribológicas e térmicas de nanocompósitos de PLLA com nanotubos de carbono de paredes múltiplas

“…A literatura mostra que os NCPM atuam como agente de nucleação para os polímeros [19] , o que não foi observado neste trabalho. Há relatos na literatura que, mesmo que o polímero utilize os nanotubos como núcleo de cristalização, a adesão na interface nanotubo/polímero é da mesma ordem dos cristais normais e/ou da região amorfa.…”