A qualitative assessment of long chain branching content in LLDPE, LDPE and their blends via thermorheological analysis

Abstract

ABSTRACTVarious blend systems having controlled level of long‐chain branching were prepared by melt mixing of different amounts (5, 10, 25, 50, 75, and 90 wt %) of low‐density polyethylene (LDPE) with a linear low density polyethylene (LLDPE). Analysis of the branching structure in the blends as well as in the neat components was carried out via thermorheological method. For this purpose six methods including time–temperature superposition (TTS), Cole–Cole plot, van Gurp–Palmen curve, phase angle (δ) versus reduced frequency curve, and activation energy as a function of the δ were employed. The results of all these methods (except TTS) indicated a complex thermorheological behavior for the neat LLDPE and LLDPE/LDPE blends. The extent of complexity was intensified by increasing LDPE content of the blends. However, using TTS method, Ea(δ) and δ(ω) curves resulted in simple thermorheological behavior for neat LDPE. The simple thermorheological behavior of LDPE having high content of long‐chain branches (LCB) was attributed to small differences in its branch structures. The zero‐shear rate viscosities of all samples deviated from the power‐law equation of linear PEs which confirmed the presence of LCB in all the systems. This study shows that thermorheological assessment can be used as an alternative powerful rheological tool for analysis of the branching structures in PE blends. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3240–3250, 2013