Tribological properties of polypropylene composites with carbon nanotubes and sepiolite.

Carbon nanotubes (CNTs) and sepiolite (SEP) were modified in order to improve their compatibility with the polypropylene (PP) matrix. Carboxylic groups were introduced into the CNTs through an oxidative treatment and aliphatic chains were incorporated on SEP by ion exchange of a cationic surfactant. Maleic anhydride grafted polypropylene (PPgMA) was mixed with neat PP to introduce polar groups into the polymer matrix. Composites including modified and non-modified fillers were prepared by melt extrusion. Dispersion and interaction of the CNTs with the PP and PPgMA matrices were evaluated by Raman spectroscopy while a focused ion beam/scanning electron microscopy (FIB/SEM) was used for SEP containing composites. Scratch resistance, microhardness, dynamic friction and wear were determined. Raman spectroscopy shows that the introduction of polar groups into PP matrices has a positive effect on the dispersion of modified CNTs. FIB/SEM results show that the modification of SEP improves its dispersion in the polypropylene matrix; filler clusters found in the PPgMA matrix are much times smaller than those in the neat PP. Despite of SEP agglomerates in the composites, a good interaction between both phases is seen; SEP particles are fully coated and embedded inside the PP matrix. The 'lack of cooperation' between unmodified PP and its fillers results in nanocomposites with larger residual depths; by contrast, PPgMA does 'cooperate' with its fillers so that the nanocomposites in scratch resistance testing have smaller residual depths R(h) than the neat PPgMA. Addition of the fillers to PPgMA also increases the hardness. As for wear rates, some our fillers provide higher and some lower wear rates than PP.

Reinforcement of polymeric latexes by in situ polymerization.

Two silicas with different particle sizes have been synthesized by the Stöber method. The particles have been functionalized with methacryloyl groups. In situ emulsion polymerization of butyl acrylate and methyl methacrylate in the presence of functionalized silica particles was performed. The ratio of butyl acrylate to methyl methacrylate was varied in order to optimize the composition for improvement of tribological and thermophysical properties. The silica particles morphology and functionalization have been determined respectively by scanning electronic microscopy and infrared spectroscopy. The composites were characterized also by thermogravimetric analysis, differential scanning calorimetry, microscratch testing and static light scattering. The latex reinforced with the smallest functionalized silica exhibits higher thermal stability than the non reinforced latex, along with lower penetration depth and higher residual depth in progressive load scratch testing. Thus, the resistance to penetration is increased while viscoelastic healing is hampered by silica particles.