Effects of Surface Treatment on Weld Strength of Fiber-Reinforced Polycarbonate Produced by Injection Molding.

Abstract

Effects of surface treatments with coupling agents and a binder on mechanical properties and processabillities were examined for fiber-reinforced polycarbonate produced by injection molding. Moldings with a weldline were used for the evaluation of the mechanical properties. Polycarbonates and glass fibers treated with a series of surface-treatment agents including three types of silane coupling agents and one type of urethane binder were compounded with a twin screw extruder into pellets for injection molding. Dumbbell test bars with or without a weldline were injection-molded and subjected to tensile test. Molecular weight of polycarbonate, average length of glass fibers and bar-flow length of the compounds in an injection mold were measured. The non-weld strengths of the materials, whose fibers were treated with a silane coupling agent and/or a urethane binder, were improved remarkably as compared with that of the untreated material. An amino silane, which was the most effective amongst three types of silanes, improved the non-weld strength up to 40% higher than that of the untreated material. This result was due to the higher strength of the fiber/resin interface and the longer fiber legth maintained during the processing. As the weld strength was not influenced by the fiber length, it depended only on the interface strength. The weld strength of the material treated with the amino silane increased to a value 25% higher than that of untreated one. The effect of the amino silane was attributed to the hydrogen bond between the amino groups and the carbonyl groups, because thermoplastics such as polycarbonate form no strong chemical bonds with the silanes. The urethane binder was not effective for the adhesion with polycarbonate, but promoted the adhesion of the silanes.