Charge distribution and crystalline structure in polyethylene nucleated with sorbitol

The charge distribution in samples under direct current electrical field wa s measured by the pulsed electro-acoustic method, which showed that the spa ce charges were greatly decreased and field distribution tended to be unifo rm in low-density polyethylene (LDPE) by adding 0.3 wt % bis-(p-ethylbenzyl idene)sorbitol. The crystalline structures of LDPE and LDPE/sorbitol were s tudied. The non-isothermal crystallization kinetics were investigated by di fferential scanning calorimetry, which showed that sorbitol increases cryst allization temperature and crystallinity, but lowers the Avrami exponent of crystallization. The results of wide-angle X-ray diffraction (WAXD) and sm all-angle light scattering (SALS) experiments show that the crystal form do es not change, whereas the perfection of spherulites degrades in the presen ce of sorbitol. In addition to the obvious difference in crystalline morpho logy, 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 spherulit es. The decrease of space charges can probably be attributed to the uniform distribution of impurities in the whole material, with smaller and imperfe ct spherulites. (C) 2001 John Wiley & Sons, Inc.