Structure and properties of polypropylene/low-density polyethylene blends grafted with itaconic acid in the course of reactive extrusion

This study was concerned with the structural features and mechanical properties of polypropylene (PP)/ low-density polyethylene (LDPE) blends, which after compounding were modified by the free-radical grafting of itaconic acid (IA) to produce [PP/LDPE]-g-IA in the course of reactive extrusion. To analyze the structural features of the [PP/LDPE]g-IA systems, differential scanning calorimetry and relaxation spectrometry techniques were used. The data were indicative of the incompatibility of PP and LDPE in the [PP/LDPE]-g-IA systems on the level of crystalline phases; however, favorable interactions were observed within the amorphous phases of the polymers. Because of these interactions, the crystallization temperature of PP increased by 5-11 degrees C, and that of LDPE increased by 1.3-2.7 degrees C. The rapprochement of their glass-transition temperatures was observed. The single beta-relaxation peak for the [PP/LDPE]-g-IA systems showed that compatibility on the level of structural units was responsible for beta relaxation in the homopolymers used. Variations in the ratios of the polymers in the [PP/LDPE]-g-IA systems led to both nonadditive and complex changes in the viscoelastic properties as well as mechanical characteristics for the composites. Additions of up to 5 wt % PP strengthened the [PP/LDPE]-g-IA blended systems between the glass-transition temperatures of LDPE and PP. (c) 2006 Wiley Periodicals, Inc.