Development and characterization of solid and porous polylactide-multiwall carbon nanotube composites

Tailored viscoelasticity of a polymer cellular structure through nanoscale entanglement of carbon nanotubes

A three-dimensional carbon nanotube (CNT) cellular structure presents a unique revelation of microstructure dependent mechanical and viscoelastic properties. Tailored CNT-CNT entanglement demonstrated a direct impact on both the strength and viscosity of the structure. Unlike traditional foams, an increase in the CNT-CNT entanglement progressively increases both the strength and the viscosity. The study reveals that an effective load is directly transferred within the structure through the short-range entanglements (nodes) resulting in an enhanced mechanical strength, whereas the long-range entanglements (bundles) regulate the energy absorption capacity. A three-dimensional structure of entangled CNT-CNT shows ∼15 and ∼26 times enhancement in the storage and loss moduli, respectively. The higher peak stress and energy loss are increased by ∼9.2 fold and ∼8.8 fold, respectively, compared to those of the cellular structures without entanglement. The study also revealed that the viscoelastic properties i.e. the Young's modulus, stress relaxation, strain rate sensitivity and fatigue properties can be modulated by tailoring the CNT-CNT entanglements within the cellular structure. A qualitative analysis is performed using finite element simulation to show the impact of CNT-CNT entanglements on the viscoelastic properties. The finding paves a way for designing a new class of meta-cellular materials which are viscous yet strong for shock absorbing or mechanical damping applications.

Effects of multi-walled carbon nanotubes on flame retardation and thermal stabilization performance of phosphorus-containing flame retardants in polypropylene

Effects of multi-walled carbon nanotubes (MWNTs) on flame retardation as well as thermal stabilization efficiency of two phosphorus-containing flame retardant systems i.e., ammonium polyphosphate/pentaerythritol (APP/PER) and red phosphorus (RP) in polypropylene (PP) have been investigated. Limiting oxygen index, thermo-gravimetric analysis, melt flow index, and tensile tests have been performed in this study. Moreover, the structure of the nanocomposites was characterized by scanning electron microscopy (SEM). SEM images revealed good dispersion of fillers in the polymer matrix. Furthermore, it was shown that the addition of MWNTs alone at a minimum loading level of 4 wt% improves thermal stability of PP considerably without any undesirable effect on its flow-ability and mechanical properties. Moreover, addition of MWNTs alone resulted in a slight improvement of flammability of the polymer. However, comparison between thermal stability and flame retardancy of PP samples containing a combination of MWNTs and APP/PER or RP and those of the samples containing APP/PER or RP alone proved that MWNTs interfere with thermal stabilization and flame retardation efficiency of both APP/PER and RP in the polymer.