The Modification of Commercial Epoxy Resin Using Cardanol - Formaldehyde Copolymers

Abstract

ABSTRACT Unmodified epoxy resins based on bis-phenol A exhibit brittleness and low elongation after cure. Hybrid polymer networks of DGEBA resin and phenolic resol type resins were prepared from phenol (PF) and cardanol (CF), the main constituent of cashew nut shell liquid (CNSL), a renewable resource. The modified epoxy resins were found to exhibit improved elongation and energy absorption at break. Bisphenol A-epoxy resins containing 2.5 to 20 wt% of phenolic resols were prepared and tested for mechanical properties, water absorption, and so on. Blends containing 5 to 10 wt% of PF resin show substantial improvement in properties such as tensile strength, elongation, and energy at break, and these properties show a decline with higher resol loading. However, epoxy-CF blends show decreased tensile and compressive strengths. Resol resins made from cardanol–phenol mixtures (CPF) have improved energy absorption at break and this property increases with increase in CF content in the modifier resin. DGEBA/CPF blend containing cardanol and phenol in the mole ratio 3:2 is found to be superior in energy absorption at break. The property profiles of these blends imply a toughening action by resol type phenolic resins, especially cardanol–formaldehyde resins. The blends, however, show higher water absorption with only marginal improvement in certain other mechanical properties and surface hardness.