A MICROHARDNESS TEST TO ANALYZE THERMAL-CHANGE IN GUARGUM, POLYACRYLONITRILE AND THEIR BLENDS

The Vickers microhardness test is found to be a suitable analytical me thod for studying thermal change in thin films of polymers. It is util ised to analyse the effect of thermal pretreatment (annealing and quen ching) on the surface microhardness of guargum (GG); a natural polymer ), polyacrylonitrile (PAN; a synthetic polymer) and their cast blends, guargum-grafted-polyacrylonitrile (GG-g-PAN) and polyacrylonitrile-gu argum (PAN-GG). Annealing at various temperatures reveals the change i n configuration and crystallinity of thin films of polymers. Peak valu es of hardness are found to occur in GG, PAN and. PAN-GG but not in GG -g-PAN. The quenched hardness for GG is found to be nonlinear with tem perature. However, for other polymers quenched hardness decreases, ini tially, up to a certain temperature and then starts increasing; such t emperatures for PAN, PAN-GG and GG-g-PAN are 86, 66 and 86-degrees-C, respectively. The behaviour of polymer blends on quenching can be repr esented by a calculated value of the exponent which is 0.62 and 0.75 f or GG-g-PAN and PAN-GG, respectively.