ABSTRACT:The effect of the grade, the content, and the particle diameter on the thermal conductivity of high-density polyethylene (HDPE) filled with graphite were studied. The results show an increase of thermal conductivity of the HDPE/graphite composite with increase of graphite content. The thermal conductivity of the HDPE filled with the expanded graphite was larger than that of the HDPE filled with the colloid graphite system. At the same volume content (7%), the thermal conductivity of the former was twice that of the latter one. The particle diameter of the graphite also affected the thermal conductivity of HDPE composites. With increase of the particle diameter of the colloid graphite, the thermal conductivity of the HDPE/graphite increased. However, when the particle diameter of colloid graphite was larger than 15 m, the increase of thermal conductivity of HDPE/graphite changed by inches. Some models proposed to predict thermal conductivity of a composite in a two-phase system could not be applied to HDPE filled graphite powder composites, such as Maxwell-Eucken, Cheng and Vachon, Zieblend, Lewis and Nielsen, Agari and Uno equations. But, according to the increase of thermal conductivity of HDPE composites filled with the colloid graphite, we find that Ziebland equation is suitable except of some constant.
Supertough poly(butylene terephthalate) (PBT) blends were prepared by melting with poly(ethyleneoctene) (POE) and glycidyl methacrylate grafted POE (POEg-GMA), and the toughening mechanism was systematically analyzed. Scanning electron microscopy (SEM) and rheological measurements identified that POE-g-GMA effectively improved the interaction between PBT and elastomer. The compatibility between phases improved gradually, while the notched impact strength increased at first and then decreased with the increase of POE-g-GMA content. The blends containing 10 wt % POE-g-GMA showed the highest impact strength, which was 18.0-fold compared to that of neat PBT. The study of the toughening mechanism indicated that a suitable compatibility was significant for obtaining supertough PBT blends because the good elastomers dispersion and suitable interfacial adhesion can be obtained simultaneously. The weak interface and the large particle size led to unstable crack propagation, while too strong interfacial adhesion prevented interface debonding and arrested matrix shear yielding. Microvoiding generated by both the debonding and internal cavitation of elastomers followed by matrix shear yielding was the main toughening mechanism in toughened PBT blends.
Low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with unimodal polydispersity was synthesized by oxidative polymerization of 2,6-dimethylphenol in the presence of Cu-ethylene diamine tetraacetic acid catalyst in water. A series of low-molecular-weight PPO oligomers with M n ranged from 360 to 3500 were obtained. It was found that the molecular weight and polydispersity were affected by reaction time, reaction temperature, and catalyst concentration. Based on the detector response-elution volume curve and the molecular weight from gel permeation chromatography, a possible molecular weight growth mechanism was proposed. The structure and properties of low-molecular-weight PPO oligomers were characterized by atomic absorption spectroscopy, differential scanning calorimetry, Ubbelohde viscometer, and nuclear magnetic resonance spectroscopy. Compared to the commercial low-molecular-weight PPO, PPO oligomers synthesized in water had a much lower residual copper content. The relationships between T g and M n at relatively low-molecular weight are in good agreement with the equation proposed by Fox and Loshack. V C 2012Wiley Periodicals, Inc. J. Appl. Polym. Sci.
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