A BAROMETER OF CRYSTALLIZATION RATES OF POLYMERIC MATERIALS

A crystallization rate coefficient (CRC) parameter is introduced which has allowed a direct comparison of the crystallization rates of various polymers on a single scale for the first time. Basically, CRC represents a change in cooling rate required to bring about 1-degrees-C change in the supercooling of the polymer melt. For the polymers studied, this value varies between 35 h-1 (poly(ethylene terephthalate)) and 155 h-1 (poly(tetrafluoroethylene)) and jumps to 295 h-1 for indium metal; the precision being better than +/- 5 percent. The reliability of CRC has been tested against the established trends e.g., (i) a large decrease in the crystallization rate of polyethylene terephthalate with increase in molecular weight, (ii) a lower crystallization rate of the "virgin" nylon 6 as compared to the processed nylon 6 resin, (iii) an increase in the crystallization rate of nylon 6 in the presence of nucleating agents, and (iv) a dramatic increase in crystallization rate as we go from poly(ethylene terephthalate) to poly(tetrafluoroethylene) and then from poly(tetrafluoroethylene) to the metals. The significance of the CRC barometer is discussed in the light of prior difficulties in directly comparing the crystallization rates of polymers.