Charge distribution and crystalline structure in polyethylene nucleated with sorbitol

The charge distribution in samples under direct current electrical field was measured by the pulsed electro-acoustic method, which showed that the space charges were greatly decreased and field distribution tended to be uniform in low-density polyethylene (LDPE) by adding 0.3 wt % bis-(p-ethylbenzylidene)sorbitol. The crystalline structures of LDPE and LDPE/sorbitol were studied. The non-isothermal crystallization kinetics were investigated by differential scanning calorimetry, which showed that sorbitol increases crystallization temperature and crystallinity, but lowers the Avrami exponent of crystallization. The results of wide-angle X-ray diffraction (WAXD) and small-angle light scattering (SALS) experiments show that the crystal form does not change, whereas the perfection of spherulites degrades in the presence of sorbitol. In addition to the obvious difference in crystalline morphology, observed by scanning electron microscopy, the spherulites in the LDPE/sorbitol sample are smaller in size and more in number than those of LDPE. It is well known that in semicrystalline polymers, impurities are expelled from crystalline regions into amorphous regions or interfaces of spherulites. The decrease of space charges can probably be attributed to the uniform distribution of impurities in the whole material, with smaller and imperfect spherulites. (C) 2001 John Wiley & Sons, Inc.