Morphology of blends of linear and short-chain branched polyethylenes in the solid state by small-angle neutron and X-ray scattering, differential scanning calorimetry, and transmission electron microscopy

Differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and small-angle neutron and X-ray scattering (SANS and SAXS, respectively) have been used to investigate the solid-state morphology of blends of linear (high-density) and model short-chain branched (linear-low-density) polyethylenes (HDPE/LLDPE). SANS indicates that the mixtures are homogeneous in the melt for all compositions when the ethyl branch content in the copolymer is low(i.e., <4 branches/100 backbone carbon atoms for a molecular weight of M-w similar to 10(5)). However, due to the structural and melting point differences between HDPE and LLDPE, the components may phase segregate in the solid state. The degree of separation is therefore controlled by the crystallization kinetics. DSC, TEM, SAXS, and SANS experiments have been used to investigate the solid-state morphology as a function of component composition, the thermal history, and the rate of cooling. It is shown that the combination of scattering, microscopy, and calorimetric techniques can provide detailed insight into the compositions of the various populations of the lamellar crystals and the amorphous regions that surround them.