Morphology and crystallization of blends of linear low density polyethylene with a semiflexible liquid crystalline polymer

Abstract

The morphology and the crystallization behavior of blends of linear low density polyethylene (LLDPE) with an experimental sample of a semiflexible liquid crystalline polymer (SBH 1∶1∶2 by Eniricerche, Italy) have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The blends possess a two-phase morphology, due to immiscibility of the two components. SEM observations show that dispersion of the minor SBH phase is favored at low (<ca. 15%) SBH concentration. At higher concentrations, the dimensions of the dispersed particles increase strongly. Non-isothermal and isothermal DSC measurements have shown that the LLDPE crystallization rate is strongly enhanced by the addition of SBH. The maximum effect has been found for an SBH concentration of ca. 10% w/w. POM observation shows that the LLDPE spherulite size decreases by ca 50% in the presence of SBH. These results have been interpreted on the basis of a heterogeneous nucleation played by the crystallized SBH particles on the molten LLDPE matrix. The interpretation of the non-isothermal and isothermal data in terms of the Avrami exponents indicates that the nucleation mechanism is not altered by the presence of a dispersed SBH phase. The relationship between blends morphology and nucleation phenomena have been discussed.