Cure characteristics of alkali catalysed cashew nut shell liquid-formaldehyde resin

Cashew nut shell liquid (CNSL) is a naturally occurring chemical monomer co nsisting four alkyl substituted phenols. Its phenolic nature makes it suita ble for polymerisation into resins by formaldehyde using sodium hydroxide ( NaOH) as a catalyst and hexamethylenetetramine (HMTA) employed as a hardene r. There is intense interest in understanding the cure characteristics and properties of CNSL-based resins. In this work the DSC technique has been ap plied to study the change in the glass transition temperature of the oven-c ured resin with and without HMTA in order to monitor the extent of cure. Th e glass transition temperature was found to rise when the alkaline catalyse d resin was subjected to higher curing temperatures regardless of the conce ntration of formaldehyde used. The mode of cure of the NaOH-catalysed CNSL- formaldehyde resin has been found to be more regular with HMTA hardener. FT -IR spectroscopy has been used to study the neat CNSL and polymerised CNSL- formaldehyde resin with and without HMTA. The use of the DSC and FT-IR tech niques to elucidate the extent of cure of CNSL resins is a valuable step to wards the production of commercially successful CNSL-natural fibre composit es. (C) 2001 Kluwer Academic Publishers.