The objective of this study is to investigate the effect of low density polyethylene (LDPE) content in linear low density polyethylene (LLDPE) on the crystallinity and strain hardening of LDPE / LLDPE blends. Three different linear low density polyethylenes (LL-1, LL-2 and LL-3) and low density polyethylenes (LD-1, LD-2 and LD-3) were investigated. Eight blends of LL-1 with 10, 20, 30 and 70 wt % of LD-1 and LD-3, respectively, were prepared using a single screw extruder. The elongational behavior of the blends and their constituents were measured at 150degreesC using an RME rheometer. For the blends of LL-1 with LD-1 the low shear rate viscosity indicated a synergistic effect over the whole range of concentrations, whereas for the blends of LL-1 with LD-3, a different behavior was observed. For the elongational viscosity behavior, no significant differences were observed for the strain hardening of the 10-30% LDPE blends. Thermal analysis indicated that at concentrations up to 20%, LDPE does not significantly affect the melting and crystallization temperatures of LLDPE blends. In conclusion, the crystallinity and rheological results indicate that 10-20%, LDPE is sufficient to provide improved strain hardening in LLDPE. (C) 2003 Wiley Periodicals, Inc.