Study On Heat Resistant Wave-transparent Composites Based On Cyanate Ester Resin

Advanced wave-transparent composites are"structural-heat resistant-wave transparent"composites, which are the main components of"eyes"for spacecrafts. With the repaid developments of aviation and aerospace industries, the Mach number of spacecrafts is increasing, so the wave-transparent composites should have more and higher properties, they are outstanding thermal resistance, excellent dielectric property, good processing characteristics and mechanical properties.Property of the matrix is the key factor of determining the main properties (such as dielectric, thermal and moisture properties) of a composite, so high performance matrix should be employed for developing advanced wave-transparent composites.Based on outstanding integrate properties of both cyanate ester (CE) and phosphate aluminum (AlPO₄), a novel kind of composite (AlPO₄/CE) was designed and prepared in this thesis by employing the"composite technology", the effects of the interfacial nature and AlPO₄ content on the properties of the new composite are discussed; in order to improve the toughness and moisture-resistance of AlPO₄/CE composite, a ternary composite made up of epoxidized methyl phenyl silicone epoxy (E-Si), AlPO₄ and CE were developed, the influence of E-Si content on properties of AlPO₄/CE are evaluated; a mixture of some kinds of aluminum phosphates with a pH value of 3-4 and good adhesion, s-AlPO₄, was synthesized by grinding phosphoric acid, aluminum hydroxide and water, and glass fiber cloth reinforced composites (s-AlPO₄/CE/EW-210) were prepared, then the mechanical and dielectric properties of s-AlPO₄/CE/EW-210 composites were emphasized. By the investigations of this thesis, new theory and technology for developing new kinds of high performance resins and wave-transparent composites are set up preliminarily.Three kinds of coupling agents (KH-550, KH-560 and H-2) were used to surface treat AlPO₄. The chemical nature of coupling agents on the properties of aluminum phosphate/CE composites were discussed, Results show that different coupling agents have different effects on the curing behavior and the interfacial adhesion of aluminum phosphate/CE composites. AlPO₄(KH-550) and AlPO₄(KH-560) have bigger effects than AlPO₄(H-2),so AlPO₄(KH-550)/CE has the optimum properties among three composites. The properties of AlPO₄(KH-550)/CE composites are closely related with AlPO₄(KH-550) content. The thermal-decomposition of AlPO₄(KH-550)/CE composites can be divided into 3 steps, while that of CE resin is 2 steps. With the increase of AlPO₄(KH-550) content in composites,both the thermal conductivity and storage modulus increase, but dielectric loss (tanδ) and glass transition temperature (Tg) decrease,while water absorption almost does not change. AlPO₄(KH-550)/CE composite with desirable AlPO₄(KH-550) content has better properties than CE resin.Comparing to AlPO₄/CE composite, E-Si/AlPO₄/CE composites have effectively improved impact strength, for example, the impact strength of the ternary composite with 15wt% E-Si is improved about 50%. In addition, the ternary composite has higher initial decomposition temperature; its thermal decomposition still has 3 steps, but the first temperature of the maximum decomposition temperature shifts to low temperature, and the char yield (Yc) decreases. On the other hand, the dielectric constant and water absorption of E-Si/AlPO₄/CE composites are lower than AlPO₄/CE composites.Comparing to CE/EW-210 composites,S-AlPO₄/CE/EW-210 composites show higher mechanical properties due to increased the interfacial effect by the addition of S-AlPO₄. For example, the impact strength, flexible strength and modulus as well as interfacial shear strength of S-AlPO₄/CE/EW-210 composite with 15% S-AlPO₄ increase about 38%, 6%, 32% and 45%, respectively, while the thermal expansion coefficient of the latter is only about 50% of that of the former. In addition, the ternary composite has the lowest dielectric constantε(3.353)and highest tanδ(0.0133). Although the addition of S-AlPO₄ into CE/EW-210 changes the shapes of damping factor in dynamic mechanical analyses, which does not decline Tg values.