REAL-TIME SMALL-ANGLE X-RAY-SCATTERING DURING ANNEALING OF POLYMER SINGLE-CRYSTALS

Experiments at the Cornell high energy synchrotron source have shown that it is possible to obtain 2-D-small-angle x-ray scattering patterns from single crystal mats of high density polyethylene with a time resolution of 0. 3s. However, it took up to 5s to heat the 0. 1-mm-thick specimen to the annealing temperature. A logarithmic increase of long spacing was quickly established, after an induction time of less than 2s at the higher annealing temperatures. At lower temperatures the original reflection remains, weakening, while a continuous scatter to smaller angles builds up. At 10-20s annealing time a new maximum becomes clear, and then the logarithmic increase of long spacing begins. The intensity of this reflection is initially low and increases with annealing time. On cooling it decreases again. It seems that here one can directly observe two mechanisms of lamellar thickening, melting and then recrystallization at short times and diffusional thickening at long times.