MEASUREMENT OF THERMAL-DIFFUSIVITY AND SPECIFIC-HEAT CAPACITY OF POLYMERS BY LASER FLASH METHOD

We measured thermal diffusivity and heat capacity of polymers by laser flash method, and the effects of measurement condition and sample siz e on the accuracy of the measurement are discussed. Thermal diffusivit ies of PTFE films with thickness 200-500 mum were the same as those da ta that have been reported. But, the data for film thickness less than 200 mum have to be corrected by an equation to cancel thermal resista nce between sample film and graphite layers for receiving light and de tecting temperature. Thermal diffusivity was almost unaffected by the size of area vertical to the direction of laser pulse, because heat fl ow for the direction could be negligible. Specific heat capacity of po lymer film was exactly measured at room temperature, provided that low absorbed energy (< 0.3 J) and enough sample mass (> 25 mg) were satis fied as measuring conditions. Thermal diffusivity curve of PS or PC ve rsus temperature had a terrace around T(g), whereas that of PE decreas ed monotonously with increasing in temperature until T(m). Further, we estimated relative specific heat capacity (RCp) by calculating ratios of heat capacities at various temperatures to the one at 299 K. RCp f or PS obtained by laser flash method was larger than that obtained by DSC method, whereas the RCps for PE obtained by the both methods agree d with one another until T(m) (305 K). RCp for PS decreased linearly, with increase in temperature after it increased linearly until T(g) (3 89 K), showing similarity to temperature dependency of thermal conduct ivity. RCp for PE also decreased until T(m), similar to thermal conduc tivity. (C) 1995 John Wiley & Sons, Inc.