Plastics,Rubber and Composites: Macromolecular Engineering

Tensile and flexural strengths of single and double gated polybutylene terephthalate and polycarbonate (PBT/PC) reinforced with 0–30 wt-% short glass fibres were investigated. Results showed that tensile and flexural strengths of single gated mouldings conform to modified rule of mixtures with overall fibre efficiency parameter η_σ of 0·128 for tensile strengths and 0·132 for flexural strengths. The presence of weldlines in double gated mouldings significantly reduced strength of PBT/PC composites but had a minor effect on the strength of the unreinforced PBT/PC matrix. Results indicated that the flexural strengths of both single and double gated mouldings were always greater than tensile strengths. The weldline integrity factor for both strengths decreased with increasing fibre concentration in a linear manner and was independent of the test method. The strength data for both specimen types and test methods were found to fit a two parameter Weibull distribution reasonably well. The Weibull modulus m for single gated composites was found to be independent of the test method and fibre concentration (m≈48) and was higher than the value for the unreinforced matrix (m≈30). The presence of weldline in double gated composites reduced the value of m quite significantly. The m value for double gated mouldings decreased with increasing fibre concentration. Analysis showed that the variation in strength values with test method cannot be explained solely by the two parameter Weibull distribution model.

Hybrid glass/polytetrafluoroethylene (PTFE) fabric composites filled with micrometre Synfluo 180XF wax (SFW) and nano-SiO₂ were prepared by dip coating of hybrid glass/PTFE fabric in phenolic adhesive resin containing the particles to be incorporated and successive curing. The friction and wear behaviours of these hybrid composites sliding against AISI-1045 steel in a pin on disc configuration were evaluated on a high temperature friction and wear tester. The composite structures and the morphologies of the worn surfaces were analysed by means of scanning electron microscopy. The results show that the addition of SFW and nano-SiO₂ can improve the wear resistance and friction reduction in the hybrid composite, and the addition of nano-SiO₂ endows the composite with best triboperformance. The improved triboperformance of nano-SiO2 or SFW filled hybrid glass/PTFE fabric composites can be attributed to the self-lubricating properties of filler, the improved structural stability and the special characteristics of transfer film.

The effect of molecular structure of polyethylene (PE) [low density PE (LDPE), linear LDPE and high density PE] and silane/peroxide concentration on the grafting level and gel content in silane crosslinking process has been studied. The effect of incorporation of ethylene vinyl acetate (EVA) copolymer on the rate of crosslinking and thermal properties of PEs has been reported. The order of gel content was LDPE>linear LDPE>high density PE. With the incorporation of EVA, the rate of crosslinking increased. The degree of crystallinity did not change with crosslinking significantly. However, the shape of melting and crystallisation peaks changed, and two regions due to gel and sol parts were formed. In EVA/PE blends, two melting points were observed for both crosslinked and uncrosslinked samples. The SEM images showed the droplet matrix morphology with the EVA as the dispersed phase, especially for EVA/LDPE blend. The EVA/PE blends failed in hot set test, while the origin of PEs passed the hot set test successfully.

Three different types of environmently friendly blowing agents (HFC 365mfc, HFC 245fa and water) have been used to fabricate rigid polyurethane foams from crude methylene diphenyl diisocyanate and polypropylene glycols. Water induced the earliest bubble, temperature and pressure rises, whereas HFC 365mfc gave the slowest reactivity. Water blown foams showed the largest cell and the lowest density and compression strength, together with the highest glass transition temperature and the greatest dimensional stalibility at high temperature. With the combined effects of large cell and large thermal conductivity of CO₂, water blown foam gave the highest conductivity of the foam. On the other hand, HFC 365mfc gave the smallest cell size, the greatest foam density and compression strength, whereas HFC 245fa gave the intermediate values, except the lowest thermal conductivity of the foam.

Natural rubber (NR) based nanocomposites were prepared by incorporation of a hybrid filler system, organoclay and carbon black (CB), through melt compounding. The hybrid filler exhibited more significant reinforcing effect over the same loading of CB on NR matrix, as revealed by mechanical tests and dynamic mechanical analysis. Wide angle X-ray diffraction, transmission electron microscopy and scanning electron microscopy were used to study the microstructure of NR nanocomposites. Dynamic rheological tests were performed to elucidate the mechanism of reinforcement in order to explain the superior performance of NR containing the hybrid filler. The storage modulus G′ of uncured rubber composites exhibits a three order increase in magnitude for rubber filled with 15 parts per hundred parts of rubber CB and 10 parts per hundred parts of rubber organoclay as compared with gum rubber, leading to a solid-like low frequency behaviour. The findings suggest that the reinforcement is due to a more developed filler network formation in hybrid filler system than that in single phase filler.