Properties and Structure of Dynamically Vulcanized TPU/EVM Blends

The preparation of dynamically vulcanized TPU (thermoplastic polyurethane)/EVM (ethylene-vinyl acetate copolymer rubber) blends and the effect of two peroxide curing agents, DCP (dicumyl peroxide) and BIPB (bis(tert-butyl peroxy isopropyl)benzene) on the mechanical properties, hot air aging, and oil resistance were investigated. Fourier transform infrared spectroscopy (FTIR), phase-contrast microscopy (PCM), and magnetic resonance crosslink density spectroscopy (MR-CDS) were used to analyze the curing reaction, phase structure, and crosslink density of dynamic vulcanizates. The results showed that the optimum parameters for dynamically vulcanized TPU/EVM by peroxide-DCP or BIPB in a HAAKE rheometer were: mixing temperature 140–150°C and rotor speed 30 rpm. The mechanical properties and oil resistance of these blends were improved by dynamic vulcanization. It was found that BIPB is a better curing agent than DCP for the dynamic vulcanization of TPU/EVM and its optimum content was 0.8 phr in the blend. FTIR spectra showed EVM and TPU could both be cured by peroxide in the blend and the curing reaction occurred at -CH₂- groups that were linked with -C- instead of -O- and -CH₃ groups in the blend. PCM photographs showed that dynamically vulcanized TPU/EVM blends had “sea-island” phase structure when the curing agent content was low and it had “interlocked/co-continuous” phase structure as the curing agent content was increased. The spin-lattice relaxation constant, T_21, measured with MR-CDS proved that the crosslink density of the cured blends increased with increasing curing agent content.     

Kinetic modelling of the thermal oxidation of polyisoprene elastomers. Part 3: Oxidation induced changes of elastic properties

This paper is the third of a series elaborating a non-empirical kinetic model for the thermal oxidation of a sulfur vulcanized polyisoprene. Here, we try to identify kinetic parameters for post-crosslinking and reversion (“decrosslinking”) from torsion measurements, under nitrogen at temperatures ranging from 100 to 160 °C. The kinetic parameters relative to oxidative reversion (selective scissions on sulfur crosslinks) are also determined. Then a system of 13 differential equations is derived from the mechanistic scheme composed of 15 elementary reactions. Diffusion and reactions are coupled in the balance equation of oxygen in order to establish the degradation thickness profiles from which it is possible to determine the modulus profiles. The latter are used, through a composite mechanics model, to predict the global torsion stiffness of a rubber barrel. The results obtained at 100, 110, 130, 140, 150 and 160 °C are in good agreement with experimental data.     

聚丙烯／顺丁橡胶动态硫化增韧的研究

研究了在聚丙烯(pp)与顺丁橡胶(BR)共混过程中加入橡胶硫化剂使共混体系中橡胶相动态硫化交联。研究结果表明,采用动态硫化法可提高共混物的冲击强度和拉伸强度。借助于SEM和DMA,证实了动态硫化使PP/BR共混体系具有相界面粘结良好的多相结构,改善了两相相容性。探讨了动态硫化增韧的机理。     

Dynamically vulcanized ethylene propylene diene terpolymer/nylon thermoplastic elastomers

A thermoplastic elastomer (TPE) of ethylene propylene diene terpolymer (EPDM) and nylon with excellent mechanical properties was prepared by dynamic vulcanization. The effects of the curing systems, compatibilizer, nylon content and reprocessing on the mechanical properties of EPDM/nylon TPEs were investigated in detail. Experimental results indicate that maleic anhydride (MAH) grafted EPR has a better performance in compatibilizing the EPDM/nylon blends compared with other compatibilizers containing acid group. Tensile strength and elongation at break go through a maximum value at a compatibilizer resin content (on total rubber dosage) of 20%. EPDM/nylon TPE using sulfur as curative has higher tensile strength and elongation than that of TPE using phenolic resin or peroxide as curatives. Tensile strength and elongation at break increase with increasing nylon content. Scanning electron microscopy results show that rubber particles distributed at an average size of 1 μm in dynamic vulcanized EPDM/MAH-g-EPR/nylon TPE.     

13X分子筛上硫化促进剂的动态行为研究

采用TPD技术对13X分子筛的表面酸性及3种硫化促进剂在其表面上的动态行为进行了研究。结果表明,13X分子筛具有吸附能量高低不等的多种表面酸性吸附部位。对于吸附型缓释交联剂,有效的表面吸附部位为弱化学吸附位.表观脱附动力学计算结果表明,不同的硫化促进剂从13X分子筛表面有效部位脱出时,其动力学特征亦不同,但均与晶内扩散有关,表观脱附活化能(kJ/mol)分别为51.5(二乙胺)、68.6(环己胺)和78.3(乙二胺)。     

Radiation effect on properties of carbon black filled NBR/EPDM rubber blends

Rubber blend of acrylonitrile butadiene rubber (NBR) and ethylene-propylene diene monomer (EPDM) rubber (50/50) has been loaded with increasing contents, up to 100 phr, of reinforcing filler, namely, high abrasion furnace (HAF) carbon black. Prepared composites have been subjected to gamma radiation doses up to 250 kGy to induce radiation vulcanization under atmospheric conditions. Mechanical properties, namely, tensile strength (TS), tensile modulus at 100% elongation (M₁₀₀), and hardness have been followed up as a function of irradiation dose and degree of loading with filler. On the other hand, variation of the swelling number as a physical property, as a function of same parameters, however, in car oil as well as brake oil has been undertaken. In addition, the electrical properties of prepared composites, namely, their electrical conductivity, were also evaluated. The thermal behavior of the prepared composites was also investigated. The results obtained indicate that improvement has been attained in different properties of loaded NBR/EPDM composites with respect to unloaded ones.     

Dynamic vulcanization of reclaimed tire rubber and high density polyethylene blends

Dynamic vulcanization of reclaimed tire rubber (RTR) and HDPE blends was reported. The effect of blend ratio, methods of vulcanization, i.e. sulphur, peroxide, and mixed system and the addition of compatibilizer on mechanical, thermal, and rheological properties were investigated. The blend with highest impact strength was obtained from 50/50 RTR/HDPE vulcanized by sulphur. Increasing the RTR content to more than 50% resulted in a decrease in the impact strength of blend, most likely due to the increasing carbon black content. For tensile strength, the presence of rubber and carbon black, however, unavoidably caused a drop in this property. Comparing among three methods of vulcanization, sulphur system seems to be the most effective method. Results from solvent swelling ratio, glass transition temperatures and viscosity indicated that the sulphur vulcanization created the highest degree of cross-link and filler-matrix interaction in the RTR/HDPE blend. Morphology of the blends was also assessed by scanning electron microscopy (SEM).     

亚磷酸三乙酯硫化反应历程的GC/MS研究

用气相色谱-质谱联用技术研究了亚磷酸三乙酯和亚磷酸三苯酯与硫反应的机理.研究证明,硫与三价磷化合物的反应只发生在液相状态.     

顺丁橡胶／低密度聚乙烯的共混

比较了未交联和动态交联不同组成PB/LDPE共混物的力学性能。共混物的T_g、T_m和T_d不随组成而变化,表明PB和LDPE不具有相容性。但共混物中PE的γ转变向高温方向位移,说明PE非晶部分的分子短链和PB有界面相互作用。形态研究表明,未交联体系中量多的组份形成连续相,动态交联体系在PB/LDPE≤70/30时,PE呈连续相,交联的PB为分散相。