Unsaturated bond existing in tetrafluoroethylene-propylene-vinylidene fluoride terpolymer

Infrared and nuclear magnetic resonance (NMR) spectroscopies have been applied for quantitative comparison on unsaturated bonds in tetrafluoroethylene (TFE)-propylene (P)-vinylidene fluoride (VdF) terpolymers. These spectroscopies have led to consistent results while they are based on completely different principles. It is shown that the absolute concentration can be evaluated from NMR measurements. The behavior of unsaturation has been discussed in terms of after-treatment such as wet and dry treatments. The result obtained here can give the important information to improve the performance of fluoroelastomer based on TFE-P-VdF terpolymers.     

STUDIES ON SELF-VULCANIZING FLUOROELASTOMER/PHENOL HYDROXY SILICONE RUBBER BLENDS

Self-vulcanizing blends of phenol hydroxy silicone rubber(PHSR)and fluoroelastomer(FPM)were prepared. Vulcanized rubbers with lower glass transition temperature(T_g)were successfully obtained.The results of dynamic mechanical analysis(DMA)show that the vulcanized FPM/PHSR(10 phr)blend has only one T_g temperature,demonstrating the well compatibility between FPM and PHSR.The thermogravimetric analysis(TGA)demonstrates that the PHSR do little damage to the thermal stability of FPM.The vulcanization charact...     

氟橡胶/改性乙丙橡胶并用胶的热稳定性

采用热分析技术考察了氟橡胶及氟橡胶(FPM)/改性乙丙橡胶(MEPDM)并用胶在氮气中的热稳定性, 通过微分法与积分法两种动力学方法计算出了FPM及FPM/MEPDM并用胶的热分解活化能E和指前因子A. 结果表明, 并用胶的热分解温度稍高于纯的氟橡胶, 但热分解活化能略低于氟橡胶, FPM、FPM/MEPDM(5%)和FPM/MEPDM(10%)的热分解活化能分别为251.74、244.98和219.60 kJ·mol-1; 热分解反应级数n均为0.95. 随着失重百分率的增大, 热分解活化能增大.     

Effect of nanoclays on high and low temperature degradation of fluoroelastomers

High temperature degradation of a fluoroelastomer and its nanocomposites was carried out from room temperature to 700 °C using thermogravimetric analysis (TGA) in nitrogen and oxygen atmospheres. The presence of the unmodified nanoclay enhanced the onset of degradation in both the environments, because of polymer-filler interaction, exfoliation, uniform dispersion and high thermal stability of the layered silicates. In the derivative curve, there was a single T_max, indicating one-stage degradation for all the samples. The non-isothermal activation energy of degradation was determined using the Kissinger and the Flynn-Wall-Ozawa methods. The nanocomposites showed higher activation energy than the neat elastomer. The activation energy of degradation, as observed by isothermal kinetics, was 165, 168 and 177 kJ mol⁻¹ for the neat elastomer, modified and unmodified clay filled samples, respectively. Intrinsic viscosity, measured after low temperature ageing (125-175 °C) showed that the viscosity values were higher for the nanocomposites. The mechanism of degradation is discussed.     

Microstructure to property relations in a family of millable polyurethane fluoroelastomers

A series of segmented polyurethane fluoroelastomers based on perfluoropolyether macromers and functionalized with allyl groups is presented. Their peroxidic vulcanization behaviour was studied on both unfilled and carbon black filled compounds by dynamic rheometry. The optimal amount of allyl groups and peroxy content was determined. Formation of polyphasic structure with phase segregation of a low T_g fluorinated moiety was shown by calorimetric analysis. The low T_g value is not affected by vulcanization which, on the other hand, is effective in the elimination of any residual crystalline order of the urethane phase. The vulcanized compounds were characterized by tensile tests, dynamic-mechanical analysis, solvent swelling, compression tests and non-isothermal stress relaxation measurements. Mastercurves were successfully built based on time-temperature superposition principle. It resulted that polyurethanes based on symmetric diisocyanates show better chemical resistance and low temperature viscoelastic behaviour, and are promising candidates for the development of high performance low temperature sealing materials.     

Aging behavior and thermal degradation of fluoroelastomer reactive blends with poly-phenol hydroxy EPDM

In this paper, the aging behavior of the reactive blends of fluoroelastomer (FPM) with poly-phenol hydroxy ethylene propylene diene monomer rubber (PHEPDM) in hot air was firstly investigated. The aging mechanism was analyzed by the swelling experiment, attenuated total-reflectance Fourier-transform infrared (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The results showed that the aging process increased the crosslinking density and the content of double bond. The O/F or O/C ratios increased and then decreased during aging because of the oxidation reaction of molecular chain and the surface migration of fluoro group. Secondly, thermogravimetric analysis (TGA) was used to study the thermal degradation behavior of the reactive blends. The apparent degradation activation energy (E) of FPM/PHEPDM reactive blends was calculated by the Kissinger and Coats-Redfern methods, respectively. The results showed that the FPM/PHEPDM reactive blends had higher thermal degradation temperature but lower E than FPM. Both the thermal degradation process of FPM/PHEPDM reactive blends and FPM were determined by nucleation and growth mechanism (Am). The general mechanism function was [−ln(1 − α)]^1/m. The optimum value of m was between 1/3 and 1/2 for FPM/PHEPDM reactive blends, but 1/2 for FPM. From the results above, it was deduced that the special structure of PHEPDM made itself surrounded by fluoroelastomer and protected from hot-air aging and thermal degradation.