Optimization of Tensile Strength of Phenolic-Glass Compound for Compression Molding Process

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-fiber composites، while the load transfer improved with longer fibers.