Y. Agari et al., MEASUREMENT OF THERMAL-DIFFUSIVITY AND SPECIFIC-HEAT CAPACITY OF POLYMERS BY LASER FLASH METHOD, Journal of polymer science. Part B, Polymer physics, 33(1), 1995, pp. 33-42
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.