Pultruded fiber reinforced blocked polyurethane (PU) composites. I. Processability and mechanical properties

Abstract

AbstractThis paper presents a proprietary process developed to manufacture polyurethane (PU) pultruded composites. The blocked isocyanate (NCO)‐terminated PU prepolymer synthesized in this study was prepared from ε‐caprolactam blocked blends of toluene diisocyanate (TDI) and branched polyester. The processability and mechanical properties of various fibers (glass, carbon, and Kevlar 49 aramid fiber) reinforced PU composites have been studied. From the investigation of the pot life of resins, the reactivity of resins, and fiber wet‐out, it was found that the blocked PU prepolymers with chain extender showed excellent processability for pultrusion. Results show that the mechanical properties (i.e., tensile strength, specific tensile strength, flexural strength, specific flexural strength, flexural modulus, and impact strength) increase with fiber content. Kevlar fiber/PU composites possess the highest impact strength and specific tensile strength, whereas carbon fiber/PU composites show the highest tensile strength, flexural strength, specific flexural strength, and flexural modulus. Experimental results of tensile strength of all composites except carbon fiber/PU composites follow the rule of mixtures. The deviation of property of carbon fiber/PU composite is due to fiber breakage during processing. Pultruded fiber reinforced PU composites showed excellent tensile and impact strength compared to other pultruded composites studied.