How to determine high growth speeds in polymer crystallization

With the fast crystallizing polymers HDPE and i-PP it is extremely difficult to extend the range of measurements of the growth speed of spherulites to temperatures as low as 80 degrees C. So far the lower limit for these measurements has been about 120 degrees C for both polymers. Several possibilities for this kind of measurements are explored in the present paper. It appears that none of these measurements is without uncertainties. So, only the comparison of results, as obtained with several independent measurements and with theory furnishes a sufficient credibility. Optical measurements, from light scattering to visual inspection, all under very special conditions of heat transfer, are described.