No abstract

Poly(tetrafluoroethylene) (PTFE) scraps were recovered as a filler material for low-density polyethylene (LDPE) after they were degraded by Co-60 ␥-rays under atmospheric conditions to make small-size powder. The powder PTFE, which was called secondary PTFE (2°-PTFE), was melt mixed with LDPE and then extruded to obtain 200 m films. The mechanical and thermal properties and also the morphology of the fractured surface of these 2°-PTFE-filled LDPE were studied. It was found that the addition of 2°-PTFE resulted in thermofilm property of LDPE but it slightly decreased the thermal oxidative temperature of LDPE. The tensile strength and ultimate elongation of LDPE were found to decrease with the addition of 2°-PTFE. However, when it is compared to the addition of virgin PTFE into LDPE, 2°-PTFE shows better mechanical properties due to the presence of oxy groups which are capable of interacting with the main matrix. A further improvement in mechanical properties was achieved by silane coupling agent treatment of 2°-PTFE. Silane coupling agents were found to enhance the interfacial adhesion between 2°-PTFE and LDPE. The study on the fractured surfaces by scanning electron microscope revealed this adhesion between these two polymers.

This study covers the preparation of noncrosslinked and crosslinked solvent-cast blend films of ultrahigh molecular weight polyethylene (UHMWPE) and polyisoprene rubber (PIR) and their mechanical, thermal, IR spectroscopic, and morphological characterizations. Solvent-cast films of polymer blends with 0, 10, 20, 35, 50, and 65% PIR composition were prepared by vigorous stirring from a hot decalin solution. The films were crosslinked chemically by using acetophenone as a crosslinking agent under UV radiation. The mechanical properties, measured as ultimate properties and tensile modulus, were found to decrease with PIR content but crosslinking was found to enhance the ultimate strength and tensile modulus. DSC results revealed that melting point of UHMWPE remains almost constant in blends. However, upon crosslinking, the melting point of UHMWPE is depressed almost 5ЊC. We observed a similar trend in the enthalpy change of the melting of UHMWPE and the variation of percent crystallinity in UHMWPE. Scanning electron microscopy (SEM) studies on the fractured surfaces of the blends showed that the fibrillar texture is present in both crosslinked and noncrosslinked blends. The crosslinking appeared to be through oxygen linkages, which are preferentially conjugated to double bonds, in addition to the possible carboncarbon crosslinks.

Ultraviolet (UV) stability of ␥-irradiated poly(tetrafluoroethylene), 2°-PTFE, powder-filled low-density polyethylene (LDPE) was studied in this work. The mechanical and thermal properties of 2°-PTFE powder-filled LDPE were discussed in our previous work (Akınay and Tinçer, 1999). It already has been shown that silane coupling agents (SCAs) result in improvements in mechanical properties. The UV stability of these samples was followed by a comparision between strain at break measured after UV irradiation and the initial strain at break, in terms of their ratio defined as residual elongation. The development of carbonyl index was also determined by infrared measurements. To get further UV stability, a hindered amine light stabilizer (HALS) was also used. Whereas addition of 2°-PTFE slightly enhanced the UV stability of LDPE, mercapto type silane (A-189) treatment appeared to increase the UV stability compared with the other types of silane treatments. HALS highly improved the UV stability of untreated and silane-treated 2°-PTFE-filled LDPE at given UV irradiation time. Although we observed some fluctuations in the experimental data of HALS and SCA treated 2°-PTFE-filled LDPE, the coaddition of HALS and SCAs showed synergetics effects in the UV stability compared with the separate additions.