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71.
72.
Zhi-min Zheng Cai-hong Xu Jian Jiang Chang-yu Ren Wei Gao Ze-min Xie Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing China 《高分子科学》2002,(6):559-564
Silicone rubber (SIR) shows superior performance when used outdoors, but its surface can be transformed frominherently hydrophobic to hydrophilic by the adsorption of contaminants. Al(OH)_3, Al_2O_3, quartz powder and active carbonwere selected as authentic contaminants. Hydrophobicity of the surface was determined using contact angle measurement.The results indicate that the adsorbability of the contaminants can strongly affect the hydrophobicity of contaminated SIRsurface. The increasing rate of contact angle of specimens contaminated by Al(OH)_3 was much faster than that by Al_2O_3 andquartz due to the adsorption of migrated low molecular weight (LMW) polydimethylsiloxanes. Specimens contaminated byactive carbon could achieve sunde hydrophobicity within 15 min because active carbon has high adsorbability. Surfaces ofcontaminated ultrapure SIR, polytetrafluoroethylene (PTFE) and glass remain hydrophilic because they contain no mobileLMW components. The addition of oligomeric polydimethylsiloxanes has little effect on the hydrophobicity of contaminantscovered on SIR surface. 相似文献
73.
An investigation of dynamic mechanical, thermal, and electrical properties of housing materials for outdoor polymeric insulators 总被引:1,自引:0,他引:1
The present paper reports the results about a study of mechanical, thermal, dynamic mechanical and electrical properties of housing (weather shed) materials for outdoor polymeric insulators. Silicone rubber, ethylene-propylene-diene monomer (EPDM) and alloys of silicon-EPDM are known polymers for use as housing in high voltage insulators. The result of dynamical mechanical measurement shows that the storage modulus of blends enhances with increase EPDM in formulation. It can be seen from the result of TGA measurement that initial thermal degradation of silicone rubber improves by the effect of EPDM in blends. The blends of silicone-EPDM show good breakdown voltage strength compared to silicone rubber. Surface and volume resistance of silicone rubber improve by EPDM content. The mechanical properties of EPDM such as strength, modulus and elongation at break improve by silicone. 相似文献
74.
T. Kleps M. Piaskiewicz W. Parasiewicz 《Journal of Thermal Analysis and Calorimetry》2000,60(1):271-277
Thermogravimetry was employed to study the changes occurring in rubber vulcanizates during devulcanization carried out by
microwave treatment, a new promising method of recycling rubber waste. The thermogravimetric parameters T
i , T
5 and T
p and the compositions of devulcanizates in comparison with vulcanizates were determined. The results obtained allowed estimation
of the degree of destruction of the polymer chains in response to microwave treatment and permitted establishment of the most
advantageous conditions of devulcanization in order to obtain the best properties of rubber devulcanizates for reuse in rubber
processing.
The results demonstrated that thermogravimetry is a very useful method for investigation and control of the microwave devulcanization
process.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
75.
铂(Ⅳ)—钼酸盐—丁基罗丹明B缔合显色反应的研究 总被引:7,自引:0,他引:7
本文研究在聚乙烯醇(PVA)存在下,铂与钼酸铵和丁基罗丹明B(BRB)形成离子缔合物,该缔合物的最大吸收位于570nm,摩尔吸光系数ε值为9.26×10~5L·mol~(-1)·cm~(-1),服从比耳定律范围0~3.0μg Pt/25ml,缔合物至少稳定3周。测定铂的条件为C_(HClO_4)=1.4mol/L,C_(MoO_4~(2-)=1.1×10~(-3)mol/L,C_(BRB)=3.8×10~(-5)mol/L,0.08%PVA。考察了40多种共存离子的影响,除形成杂多酸的元素外,大多数不干扰。本法已用于催化剂和某些铂矿中铂的测定,结果较满意。 相似文献
76.
C. Decker H. Le Xuan T. Nguyen Thi Viet 《Journal of polymer science. Part A, Polymer chemistry》1995,33(16):2759-2772
Low molecular weight epoxidized natural rubber has been crosslinked within seconds by UV irradiation in the presence of a triarylsulfonium salt. The photoinitiated cationic ring-opening polymerization was studied quantitatively by infrared spectroscopy and shown to proceed with surprisingly long kinetic chains in such solid medium. The high conversion (60%) needed for complete insolubilization, together with the presence of tetrahydrofuran structures, argue in favor of an intramolecular polymerization process involving neighboring epoxy groups. The photoinitiator concentration has a strong influence on the rate and extent of the reaction, as well as on the depth of cure profile. Because of an efficient dark process, close to 100% conversion was reached upon storage of the irradiated elastomer at ambient, with a concomitant increase of the gel fraction and the polymer hardness. The grafting of pendent acrylate groups onto the polymer chain leads to a three-fold decrease of the initial rate of polymerization of the epoxide. The photocuring of natural rubber bearing both epoxy and acrylate groups generates a dual polymer network which combines the properties of the two moieties. © 1995 John Wiley & Sons, Inc. 相似文献
77.
78.
Rita Aparecida Zoppi Maria Isabel Felisberti Marco-Aurelio De Paoli 《Journal of polymer science. Part A, Polymer chemistry》1994,32(6):1001-1008
This work describes the preparation of polypyrrole and EPDM rubber blends, PPy/EPDM, by the sorption of pyrrole (vapor phase) in an EPDM matrix containing CuCl2. We investigated the effect of the oxidant particle-size on the sorption and polymerization equilibrium, electrical conductivity, and mechanical properties of the blends. Independently of the CuCl2 concentration and polymerization time, the polypyrrole weight fraction in the blend, Xppy, increases when the oxidant particle-size in changed from 150–250 μm to smaller than 106 μm. For blends containing 50 phr of CuCl2, obtained following 72 h of exposure to pyrrole, an increase in the Young's Modulus (from 2.2 ± 0.2 to 3.9 ± 0.6 MPa) and an increase in the electrical conductivity (from 10?9 to 10?7 S cm?1) was observed when the oxidant particle-size was decreased. Infrared spectroscopy, thermogravimetric analysis, scanning differential calorimetry, and scanning electron microscopy were used in sample characterization. © 1994 John Wiley & Sons, Inc. 相似文献
79.
N,N-Diethyldithiocarbamate functionnalized 1,4-polyisoprenes were prepared from 1,4-polyisoprenes (natural or synthetic). The syntheses were performed by nucleophilic addition of N,N-diethyldithiocarbamate salts upon oxirane rings of epoxidized units according to a SN2 mechanism with ring opening. Studies on model molecules of epoxidized 1,4-polyisoprene units (1,2-epoxy-1-methylcyclohexane and 4,5-epoxy-4-methyloctane) were previously achieved to develop the procedure. The best yields were obtained at low temperature in polar medium, and more especially in water with sodium N,N-diethyldithiocarbamate (DEDT-Na) as reagent. A diastereospecific addition was noted when reaction was performed in water with DEDT-Na. Afterwards, the developed procedure was successfully generalized to epoxidized synthetic polyisoprenes and epoxidized natural rubber (in THF, then in latex medium). Excellent results were obtained in latex medium with epoxidized natural rubber (ENR) latices. As with the models, a diastereospecific addition of sodium N,N-diethyldithiocarbamate trihydrate onto epoxidized 1,4-polyisoprene units of ENR was observed at the condition to bring the latex medium to pH 8 before introduction of DEDT-Na. Influence of temperature, drc, and DEDT-Na concentration were successively examined to determine the best conditions of the addition on ENR latices. 相似文献
80.
Studies on accelerated sulphur vulcanization of natural rubber using 1-phenyl-2, 4-dithiobiuret/tertiary butyl benzothiazole sulphenamide 总被引:3,自引:0,他引:3
The use of binary accelerators has gained tremendous importance since it increases the production rate of the article made of that elastomer. The authors have analyzed the performance of a novel binary accelerator system in the sulphur vulcanization of natural rubber (NR). The vulcanizates resulting from the binary accelerated process obtained good mechanical properties, ageing and swelling resistance. Network characterization of the mixes was done using swelling measurements, stress-strain analysis etc. The chain entanglement density was measured using dynamic mechanical analysis. However the performance is found to be dependent on the relative proportion of mono, di and polysulphidic linkages in the material. The result of the study points out that the proposed system can be active in NR regardless of the vulcanization recipe and temperature. The performance of the new binary system in filled vulcanizates is also studied. Based on the processing, mechanical and chemical characterization an optimum concentration is suggested for the new system. 相似文献