Examination of Flow-Induced Crystallization Precursor Structures in Polyethylene Blend Films by Reversed Melting Method

\textit{In-situ.} SAXS (small-angle X-ray scattering) and WAXD (wide-angle X-ray diffraction) techniques were used to investigate melting behavior of the confined blown films that consist of structures formed during film blowing. The PE blend consisted of 95wt {\%} LLDPE ($\bar {M}_{\mbox{w}} \sim $116 Kg/mole) and 5wt {\%} HDPE. The HDPE possessed a bimodal molecular weight distribution with 80 {\%} of low molecular weight fraction (LMW-HDPE, $\bar {M}_{\mbox{w}} $\textit{$\sim $}99 Kg/mole) and 20 {\%} high molecular weight fraction (HMW-HDPE, $\bar {M}_{\mbox{w}} $\textit{$\sim $}1,100 Kg/mole), respectively. Thus, the final blend contained 1 wt {\%} of HMW-HDPE in the range of the overlap concentration, 0.5 wt {\%}. The study was for examining the evolution of flow-induced crystallization precursors and their thermal stability. The results of the blend compared to neat LLDPE showed that the HMW-HDPE species in the blend significantly improved the crystal orientation. We speculate that the HMW-HDPE formed a network of extended-chain crystals due to their long relaxation times, which, subsequently, generated a scaffold of the oriented nuclei that defined the final morphology.