THERMAL EFFECTS DUE TO POLYMER CRYSTALLIZATION

The problem of dissipation of latent heat of fusion by thermal conduct ivity in polymer crystallizing in bulk is discussed. It is shown that the liberation of latent heat of fusion causes the increase of the tem perature at the crystallization front. The increase of thermal conduct ivity and diffusivity of a polymer due to phase transition decreases w hile the presence of another crystallization front increases the tempe rature elevation. The temperature buildup is limited by the decrease o f growth rate with temperature, directly related to the release of lat ent heat of fusion. The thermal effects due to crystallization of nume rous spherulites in a plate are also estimated. It is shown that the c rystallization causes a significant increase of the temperature inside the material as the crystallization proceeds, which slows the rate of conversion of melt into spherulites. The temperature increase in the interior of material depends on the initial temperature and on the sam ple sizes. The predictions were confirmed by the measurements of the t emperature in bulk samples of isotactic polypropylene during crystalli zation at isothermal ambient conditions. (C) 1997 John Wiley & Sons, I nc.