High-density polyethylene-based nanocomposites were prepared through a melt compounding process by using surface functionalized fumed silica nanoparticles in various amounts, in order to investigate their capability to improve both mechanical properties and resistance to thermal degradation. The fine dispersion of silica aggregates led to noticeable improvements of both the elastic modulus and of the stress at yield proportionally to the filler content, while the tensile properties at break were not impaired even at elevated filler content. Thermogravimetric analysis showed that the selected nanoparticles were extremely effective both in increasing the decomposition temperature and in decreasing the mass loss rate, even at relatively low filler loadings. The formation of a char enriched layer, limiting the diffusion of the oxygen through the nanofilled samples, was responsible of noticeable improvements of the limiting oxygen index, especially at elevated silica loadings. In contrast with commonly reported literature results, cone calorimeter tests also revealed the efficacy of functionalized nanoparticles in delaying the time to ignition and in decreasing the heat release rate values. Therefore, the addition of functionalized fumed silica nanoparticles could represent an effective way to enhance the flammability properties of polyolefin matrices even at low filler concentrations.
Effect of hydrolysis time on molar mass, glass transition temperature, crystallinity, and resistance to thermooxidation at
elevated temperatures was analyzed for Estanes 54600, 54610, and 54650. Kinetics of the hydrolysis can be plausibly described
in terms of the first-order reaction with an average induction period of about 7 days. Reduction of molar mass induced by
hydrolysis brings about an appreciable decrease in glass transition temperature, fraction of crystalline domains of soft segments,
and thermooxidative stability. The latter effect is manifested by shortening of the lifetimes (related to 5% mass loss) the
temperature dependence of which obeys the Arrhenius plot. The observed differences in hydrolysis resistance of Estanes can
be related to their chemical composition.
The effect of the deformation temperature on the energy stored in post-yield deformed poly(butylene terephthalate) PBT, was
studied by means of DSC tests. Deformed specimens were rapidly cooled after unloading, in order to avoid the energy relaxation
processes occurring before the DSC measurements. Cooling revealed to have a significant contribution on the whole stored energy,
as shown by DSC tests conducted on undeformed PBT specimens conditioned at various temperatures. This work is aimed at separating
the effects due to cooling and those ascribed to deformation on the energy storage and release processes, permitting to better
understand previous findings on post-yield compressed PBT.