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Carbon fiber composite is one of the most important materials in aerospace engineering applications. For fabrication of this composite, optimum polymerization and carbonization cycles of phenolic resin were obtained [1]. Then, carbon/phenolic composite was fabricated by mixing different weight percentages of T700 carbon fiber with phenolic resin, and the flexural strength of specimens was examined.The samples were pyrolyzed at 1100°C to form high temperature phenolic matrix. Because of high porosity of samples, the composite was impregnated to increase the density and reduce porosity. The maximum flexural strength of samples was obtained with 40 wt. % of fiber. With addition of TiO2 and ZrO2 nanoparticles to carbon/phenolic composite, thermal and mechanical improvement was measured. The samples were examined by ablation test and microstructures of composites were analyzed by SEM.

Nanocomposites based on phenolic resol and novolac resins and Cloisite 30B were prepared. Different kinds of phenolic resins and clay content were studied with respect to the morphology and mechanical properties of the polymer silicate layers. The phenolic resins, namely resol, novolac and their mixture and four different percentages of clay contents, 0.5, 1, 2 and 5 wt% have been considered. XRD analysis has been used to investigate clay distribution in the prepared polymer matrices. Chopped strand mat glass fiber was impregnated with each phenolic resin solution and after hand-lay-up, specimens were prepared by hot press compression molding. The mechanical properties of the nanocomposites were assessed by tensile, flexural and Izod impact tests. XRD results show that the degree of clay distribution in resol type phenolic resin is more satisfactory than novolac resin. Based on mechanical properties evaluations, the novolac nanocomposites showed better mechanical properties than other systems under study. The mixture of novolac resin and resol showed improved mechanical properties relative to each phenolic system. The final results indicate that nanocomposites with 2 wt% clay content show maximum modulus and tensile strength increased by 23%. Impact test results also show that optimum properties can be achieved with 2 wt% clay content.

In the present work, thermal and mechanical behaviors of phenolic resin are investigated. This polymer can be used as a matrix for carbon-carbon composites. To find out the best heating process, five different cycles are used for curing the polymer and flexural strength of the specimens are obtained. The cycle with maximum strength is used for the next steps. Then, the oxidation behavior of specimens is studied at different temperatures. The results show that the polymer can withstand temperature about 350°C without significant weight changes. Carbonization of phenolic resin is studied by four different cycles at 1100°C. Oxidation of carbon obtained from carbonization cycle is analyzed extensively and shows no weight change until 550°C. The microstructure of specimens is also investigated by SEM. By additining SiC micro particles to phenolic polymer, the strength change is achieved.

Phenolic resins are synthetic low molecular weight thermoset resins which are polymerized and cured to higher molecular weights by condensation method. These resins have high weathering resistance, high oxidative thermal properties and good chemical resistance. Phenolic resins can be cured thermally or by acid curing. The most common method of curing phenolic resin is by thermal curing that takes place in the range of 130-180oC. At room temperature, however, phenolic resins are cured by acid catalysts. In this paper, room temperature curing of resol phenolic resin by para toluene sulphonic acid has been investigated. The acid quantity has been determined for room temperature curing of two types of resols to achieve a reasonable hardness and gelation time. Temperature curing and thermal stability of respective resins have been investigated by DSC and TGA, respectively. A glass-phenolic composite plate has been prepared and cured by these two methods. The results show that the optimum amount of acid is 20% by weight. Optimum mechanical properties, chemical resistance and thermal properties have been achieved for acid cured system. The hot cured resin, however, has better properties.

Fiber-reinforced phenolic resins have been widely used in thermal insulation products. Processability and mechanical properties are the two important characteristics of these compounds. In this research, the flow in spiral mold and tensile strength were considered as indicators for processability and mechanical properties, respectively. B-stage curing time, fiber length and silane treatment effects on flow properties and tensile strength were studied. Spiral flow test results showed that B-stage has a significance effect on flow rates optimized at 85°C for 3 h. Under this condition, resin viscosity increased to a suitable level and improved in transferring and dispersing the fibers. Tensile strength was increased by 3.5 h heat treatment and it was dropped beyond the B-stage. Heat treatment beyond this stage weakened the possible attachment of different components together. Silane treatment increased the tensile strength and based on electron microscopy studies there was improved fiber-resin compatibility with better dispersion of the fibers. Although there were improvements observed in fiber dispersion in silane treatment as well as the B-stage curing, but the effect was greater in the latter case, such that treatment by 3.5 h B-stage produced tensile strength by 130% while the silane treatment effect resulted in 30% greater tensile strength. This may imply that for some applications the silane treatment of the fibers is not sufficient and heat treatment could be considered as a substitute. Tensile strength increased with fiber length which was related to the nature of short-fibercomposites, while the load transfer improved with longer fibers.