Effect of molecular weight distribution and structure of LDPE on its deformation behavior in a high‐temperature region

Abstract

AbstractThe effect of molecular weight distribution (MWD) (the low‐molecular weight “tail” in particular) on the deformation behavior of low‐density polyethylene (LDPE) during uniaxial stretching was studied over the temperature range from 293 K to the melting point. Four types of film samples were used: untreated polyethylene (PE), the same PE subjected either to solvent extraction or to thermal degradation, and PE with extracted fractions replaced by a low‐molecular weight paraffin analog. Graphs of elongation at break εb versus temperature always exhibited a minimum that occurred in the neighborhood of 370 K. The shape of the curve, the amount that εb decreases with increasing temperature, as well as the absolute values of εb strongly depend on the type of sample. The εb for a degraded PE is markedly lower than that for an untreated one. On the other hand, the extraction of low‐molecular weight fractions leads to a higher εb, especially in the premelting region. The low‐molecular weight “tail” has a different effect from that of added paraffin. This appears to be due to the plasticizing effect of the latter. The effect of temperature is much more pronounced on the work of deformation (Ad) than on εb. The results obtained were interpreted on the assumption that structural (phase) inhomogeneity of LDPE is the key factor determining the deformation behavior of polymer over the studied temperature range.