Development of crystalline structure during tubular film blowing of low‐density polyethylene

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Abstract
Development of crystalline structure during the tubular film blowing of low‐density polyethylene was investigated, using wide‐angle X‐ray diffraction technique, low‐angle light scattering, and scanning electron microscopy. In the study, commercial grades of both high‐pressure low‐density polyethylene (HP‐LDPE) and low‐pressure low‐density polyethylene (LP‐LDPE) (also, commonly referred to as linear low‐density polyethylene, LLDPE) were used. The applied stresses at the freeze line were determined using theoretical expressions derived in an earlier publication [C. D. Han and T. H. Kwack, J. Appl. Polym. Sci., 28, 3399 (1983)]. The applied stresses, S11F and S33F, at and above the freeze line in the machine and transverse directions were expressed in terms of the tension at the take‐up device, take‐up ratio, blow‐up ratio, and the pressure difference across the film of the bubble. These applied stresses were used to interpret the crystalline axes' orientation in the tubular blown films. It was found that the magnitude of S11F is an important process parameter for the crystalline axes' orientation and that the biaxial stress ratio (S11F/S33F) appears to be a determining factor in the distribution of fibrillous nuclei and crystalline texture, as well as film anisotropy.

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