Effects of carbon nanotubes on dynamic mechanical property, thermal property, and crystal structure of poly(L‐lactic acid)

Abstract

Effects of carbon nanotubes (CNT) on the dynamic mechanical property, thermal property, and crystal structure of poly(L-lactic acid) (PLLA) were investigated. Dynamic mechanical analysis (DMA) found that CNT via grafting modification with PLLA (CNT-g-PLLA) could result in effective reinforcing effects. Tan d of DMA found that CNT-g-PLLA was compatible with the PLLA matrix, giving a single T g of the composite with a higher CNT-g-PLLA loading giving a higher T g of the composite. Wide angle X-ray diffraction (WAXD) data demonstrated that CNT could assist the disorder-to-order (a 0 -to-a) transition in PLLA crystals but did not lead to a more compact chain packing of the crystal lattice in PLLA composites than in pure PLLA. The equilibrium melting temperature (T 0 m ) obtained from Hoffman-Weeks plots were found to increase with increasing CNT-g-PLLA content. Small angle X-ray scattering data revealed that thicknesses of crystal layer and amorphous layer of PLLA both decreased with increasing CNT contents. V C 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: [145][146][147][148][149][150][151][152] 2010

Effects of carbon nanotubes on polymer physics

“…224 In polylactide an increase in the equilibrium melting temperature was reported, but the authors attributed this to a problem with the classical treatment since the equilibrium melting temperature for the pure material was much lower than that presented in the literature. 202 In syndiotactic polystyrene, no change was found for T 0 m , 168 while an increase was found for poly(3-hydroxybutyrate-co-3-hydroxyvalerate). 225 Melting of polyethylene crystals above the equilibrium melting temperature was found for a sample with a very high volume fraction of nanotubes which the authors attributed to melting of surface crystallites, that is, a transition from a nematic liquid crystalline phase to an isotropic phase at the nanotube-polymer interface.…”

“…123 Peaks in small-angle scattering experiments generally shift towards lower angles indicative of thicker crystals with the introduction of nanotubes. 222,226 However, a very detailed analysis of small-angle scattering patterns for polylactide found a decrease in crystal thickness with the introduction of nanotubes 202 while another study also found a decrease in thickness for polybutylene succinate. 184 In a study where the rate of crystallization in an isothermal experiment was much smaller for nanotube-filled polyethylene oxide versus the unfilled polymer, the crystal thickness varied with the level of nanotubes in no obvious pattern.…”

“…148 Finally, the introduction of carbon nanotubes to polylactide caused a rise of 10 C at 5 wt % nanotubes, with 5 C at 1 wt % tubes. 202 Polytrimethylene terephthalate electrospun fibers showed a decrease of 8 C with the introduction of only 0.2 wt % MWCNTs with no further change with the addition of more tubes. 231 As described in ''Dynamics: Glass Transition and Diffusion Coefficient'' section, the introduction of nanotubes to an amorphous polymer can cause the formation of a portion of the material that does not participate in the glass transition.…”

“…168 In polylactide, nanotubes can promote the disorder-to-order transition (a 0 to a) in the crystalline material. 202 An early paper by the present author suggested that nanotubes favored the beta phase in isotactic polypropylene based on multiple endotherms in DSC experiments 203 while other papers suggested the alpha form was favored. [204][205][206][207] Nanotubes can induce complicated melting-recrystallization phenomena, indicating that claims about polymorphism in isotactic polypropylene must be substantiated with X-ray diffraction measurements casting significant doubt on the conclusions reached by the present author in the early paper.…”

Polymer blend nanocomposites based on poly(l-lactic acid), polypropylene and WS2 inorganic nanotubes

“…In other series of experiments, the cooling rate from the melt was increased up to 40 C min À1 for all the samples ( Fig. 8a and b).…”