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.

Natural-synthetic hybrid polymers developed via electrospinning: the effect of PET in chitosan/starch system.

Chitosan is an amino polysaccharide found in nature, which is biodegradable, nontoxic and biocompatible. It has versatile features and can be used in a variety of applications including films, packaging, and also in medical surgery. Recently a possibility to diversify chitosan properties has emerged by combining it with synthetic materials to produce novel natural-synthetic hybrid polymers. We have studied structural and thermophysical properties of chitosan + starch + poly(ethylene terephthalate) (Ch + S + PET) fibers developed via electrospinning. Properties of these hybrids polymers are compared with extant chitosan containing hybrids synthesized by electrospinning. Molecular interactions and orientation in the fibers are analyzed by infrared and Raman spectroscopies respectively, morphology by scanning electron microscopy and thermophysical properties by thermogravimetric analysis and differential scanning calorimetry. Addition of PET to Ch + S systems results in improved thermal stability at elevated temperatures.

Tribological properties of epoxy + silica hybrid materials.

Various amounts of nano size silica particles prepared by a sol-gel process were added to epoxy+ amine systems. We have investigated tribological properties including friction and sliding wear resistance of hybrids so obtained, and also relationships between different tribological properties and surface topography. The thermal degradation behavior and thermal stabilities were determined by thermogravimetric analysis (TGA). The introduction of silica into bisphenol-A type epoxy resins does not affect significantly char formation in the epoxy resins; relatively small improvements in thermal stabilities is seen. At the same time, results from a pin-on-disc tribometer show that silica addition causes lowering of friction already at 1 part per hundred (phr) and very significant lowering of wear at 2 or more phr. We have found finer waves of the worn surface in the hybrids than in the neat epoxy. SEM results demonstrate that the silica particles improve the wear resistance by hindering crack propagation.