Melting and crystallization behavior of partially miscible high density polyethylene/ethylene vinyl acetate copolymer (HDPE/EVA) blends

• HDPE/EVA blends undergo phase separation, making it an interesting topic to investigate the relationships between miscibility and crystallization.
• Influences from blending on the crystallization kinetics were successfully evaluated by Friedman's and Khanna's method.
• X-ray diffraction studies revealed that blending with EVA the unit length of the unit cell of the HDPE increases.
• Thermal fractionation method was successfully used to characterize the co-crystallization in HDPE/EVA blends.

Crystallization studies on HDPE/EVA blends and the individual components were performed with differential scanning calorimetry (DSC) technique and wide angle X-ray scattering (WAXS). Influences of blending on the crystallization kinetics of each component in HDPE/EVA mixture were evaluated by Friedman's activation energy and Khanna's crystallization rate coefficient (CRC). The addition of more HDPE into the EVA matrix causes more heterogeneous nucleation while the addition of EVA would hinder the nucleation of HDPE at the beginning of cooling process. Inter-molecular interaction in the melt facilitated the crystallization of both EVA and HDPE components. X-ray diffraction studies revealed that HDPE and EVA have orthorhombic unit cell. Blending with EVA did not affect the crystalline structure of HDPE. In addition, a little shift of (1 1 0), (2 0 0) and (0 2 0) crystalline peaks toward lower 2θ values of samples indicating a little increase of unit cell parameters of the orthorhombic unit cell of polyethylene. Thermal fractionation results showed that co-crystallization took place in the HDPE/EVA blend. All those results indicated that the polymer pair we choose was partially miscible.