LDPE and poly(1-butene) blends: Morphology, crystallinity and rheological properties

In this work, the compatibility and crystallinity of low density polyethylene (LDPE) and polybutene-1 (PB-1) blends were studied. Various blends of LDPE/PB-1 containing 5, 10 and 20 wt.% PB-1 were prepared in a corotating twin-screw extruder and characterized by scanning electron microscopy (SEM), shear oscillation rheology and wide-angle X-ray diffractometry (WAXD). A matrix-droplet morphology was observed in SEM images, indicating incompatibility of the two polymers in the solid state. Compared to neat LDPE, the relaxation spectra of the blends were broadened, and a slight increase in their relaxation times was observed. The relaxation time of the blends was enhanced by increasing PB-1 content, which was further proved by fitting rheological data in the Carreau-Yasuda model. Deviation of Cole-Cole diagrams from circular shape means that the blend samples were not miscible and the positive-deviation behavior of the complex viscosity and storage modulus from the mixing rule revealed the formation of strong interfacial interactions. The crystallinity of both LLDPE and PB-1 was decreased as a result of blending. The peaks attributed to the form II of PB-1 crystals were eliminated and the peaks related to LDPE were obviously weakened, suggesting to prevent crystallinity of polymers which is associated with a reduction in the total crystallinity percentage for the blend. The reduction of crystallinity was more pronounced in PB-1 phase.