Morphological study of melt‐crystallized linear low‐density polyethylene by transmission electron microscopy

The morphology of the lamellae in non‐isothermally crystallized linear low‐density polyethylene (LLDPE), conventional high‐pressure low‐density polyethylene (HP‐LDPE), and a high‐density polyethylene (HDPE) sample was investigated by transmission electron microscopy (TEM). LLDPE exhibits clearly two different types of lamellae, i.e., thick, long, and straight lamellae like those of HDPE, and thin, short, and curved lamellae which grow among the former ones. Also LLDPE shows the broadest distribution of the values for the lamella thickness among the three types of polyethylenes mentioned. The average lamella thickness decreases in the order HDPE > LLDPE > HP‐LDPE. Fractions were used to study the effects of the kind and the degree of short chain branching (SCB) and of the molecular weight in the range from 4100 to 3,1·105. SCB has a predominant influence on the lamella thickness as well as on the shape, while the molecular weight does not largely affect lamella thickness but affects the shape of the lamellae. Further it was revealed from TEM observation that the isobutyl branch decreases lamella thickness more effectively than does the ethyl branch. This is in accordance with results from small‐angle X‐ray and differential scanning calorimetry measurements.