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High-temperature Properties (high-temperature + property)
Selected AbstractsPreparation of high-temperature polyurethane by alloying with reactive polyamideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2002Tsutomu Takeichi Abstract A series of novel poly(urethane amide) films were prepared by the reaction of a polyurethane (PU) prepolymer and a soluble polyamide (PA) containing aliphatic hydroxyl groups in the backbone. The PU prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate and then was end-capped with phenol. Soluble PA was prepared by the reaction of 1-(m -aminophenyl)-2-(p -aminophenyl)ethanol and terephthaloyl chloride. The PU prepolymer and PA were blended, and the clear, transparent solutions were cast on glass substrates; this was followed by thermal treatments at various temperatures to produce reactions between the isocyanate group of the PU prepolymer and the hydroxyl group of PA. The opaque poly(urethane amide) films showed various properties, from those of plastics to those of elastomers, depending on the ratio of the PU and PA components. Dynamic mechanical analysis showed two glass-transition temperatures (Tg's), a lower Tg due to the PU component and a higher Tg due to the PA component, suggesting that the two polymer components were phase-separated. The rubbery plateau region of the storage modulus for the elastic films was maintained up to about 250 °C, which is considerably higher than for conventional PUs. Tensile measurements of the elastic films of 90/10 PU/PA showed that the elongation was as high as 347%. This indicated that the alloying of PU with PA containing aliphatic hydroxyl groups in the backbone improved the high-temperature properties of PU and, therefore, enhanced the use temperature of PU. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3497,3503, 2002 [source] Densification of Si3N4 with LiYO2 AdditiveJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2004Branko Matovic This paper deals with the densification and phase transformation during pressureless sintering of Si3N4 with LiYO2 as the sintering additive. The dilatometric shrinkage data show that the first Li2O- rich liquid forms as low as 1250°C, resulting in a significant reduction of sintering temperature. On sintering at 1500°C the bulk density increases to more than 90% of the theoretical density with only minor phase transformation from ,-Si3N4 to ,-Si3N4 taking place. At 1600°C the secondary phase has been completely converted into a glassy phase and total conversion of ,-Si3N4 to ,-Si3N4 takes place. The grain growth is anisotropic, leading to a microstructure which has potential for enhanced fracture toughness. Li2O evaporates during sintering. Thus, the liquid phase is transient and the final material might have promising mechanical properties as well as promising high-temperature properties despite the low sintering temperature. The results show that the Li2O,Y2O3 system can provide very effective low-temperature sintering additives for silicon nitride. [source] Stress-Corrosion Cracking of Silicon Carbide Fiber/Silicon Carbide CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Russell H. Jones Ceramic-matrix composites are being developed to operate at elevated temperatures and in oxidizing environments. Considerable improvements have been made in the creep resistance of SiC fibers and, hence, in the high-temperature properties of SiC fiber/SiC (SiCf/SiC) composites; however, more must be known about the stability of these materials in oxidizing environments before they are widely accepted. Experimental weight change and crack growth data support the conclusion that the oxygen-enhanced crack growth of SiCf/SiC occurs by more than one mechanism, depending on the experimental conditions. These data suggest an oxidation embrittlement mechanism (OEM) at temperatures <1373 K and high oxygen pressures and an interphase removal mechanism (IRM) at temperatures of ,700 K and low oxygen pressures. The OEM results from the reaction of oxygen with SiC to form a glass layer on the fiber or within the fiber,matrix interphase region. The fracture stress of the fiber is decreased if this layer is thicker than a critical value (d > dc) and the temperature below a critical value (T < Tg), such that a sharp crack can be sustained in the layer. The IRM results from the oxidation of the interfacial layer and the resulting decrease of stress that is carried by the bridging fibers. Interphase removal contributes to subcritical crack growth by decreasing the fiber-bridging stresses and, hence, increasing the crack-tip stress. The IRM occurs over a wide range of temperatures for d < dc and may occur at T > Tg for d > dc. This paper summarizes the evidence for the existence of these two mechanisms and attempts to define the conditions for their operation. [source] Modification of bisphenol A dicyanate ester by carboxyl-terminated liquid butadiene-acrylonitrile and its compositesPOLYMER ENGINEERING & SCIENCE, Issue 5 2006Jieliang Wang Cyanate esters with excellent high-temperature properties and easy processing are well known as good resin materials used in aerospace and electrical industries, but the drawback of brittleness limits their usage. In this study, carboxyl-terminated liquid butadiene-acrylonitrile (CTBN) was introduced to improve the toughness of bisphenol A dicyanate resin (BADCy), a typical kind of the cyanate esters. Fourier transform infrared spectroscopy and differential scanning calorimetry were employed to investigate the effects of CTBN on the curing behavior of BADCy; the results indicate that the addition of CTBN has a great influence on the curing behavior of BADCy at lower temperatures, but little at higher temperatures. Data from the thermogravimetric analysis and heat deflection temperature analysis showed that the thermal properties of the modified systems were poorer than that of pristine BADCy resin. On the basis of the scanning electron micrographs of the modified systems, toughening mechanism of the systems was discussed. Mechanical and dielectric properties of the cured resins and glass fiber-reinforced composites were also studied. Modified systems exhibit attractive properties for the future applications in aerospace industries. POLYM. ENG. SCI. 46:581,587, 2006. © 2006 Society of Plastics Engineers. [source] | ||||||||||