Abstract
Bisphenol A epoxy resin is blended with different phenolic novolac resins for property modification. The phenolic resins employed are (a) novolac resins derived from phenol/formaldehyde (PN) and cardanol/ formaldehyde (CDN) condensation and (b) condensation products of cardanol—phenol mixtures with formaldehyde (CPNs). Cardanol is the main constituent of cashew nut shell liquid (CNSL), a renewable resource. Epoxy resins containing 2.5—20 wt% of the above novolacs are prepared and tested for mechanical properties, water absorption, etc. Blends containing 5—10 wt% of novolacs show substantial improvement in properties. These properties show a declining trend with higher novolac loading. The stoichiometric ratio between phenolic material and formaldehyde in the novolacs is optimized (1:0.8) for maximum property enhancement. Among the novolacs studied, those prepared from cardanol—phenol mixtures of different molar ratios (CPNs) yield comparatively higher energy absorption at break and this property increases with increase in cardanol content in the modifier resin up to 40%. The property profiles of these epoxy—novolac blends imply a toughening action by novolac resins, especially phenol—cardanol—formaldehyde resins.
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