Shear rheology and thermal properties of linear and branched poly(ethylene terephthalate) blends

Abstract

Linear poly(ethylene terephthalate) (LPET) was blended with branched poly(ethylene terephthalate) (BPET) by varying the branching comonomer and blend proportion of BPET. The crystallinity and melting temperatures of LPET in blends with BPET was measured using differential scanning calorimetry (DSC). Thermal analysis revealed that the crystallinity and crystallisation/melting temperatures of LPET–BPET blends were increased compared with LPET. The rheological measurements of the blends were conducted using a controlled stress rheometer, with dynamic oscillatory shear, as well as steady shear measurements. The acceleration of the LPET crystallisation was dependent on the blend proportion and on the branching comonomer. The rheological measurements indicated a 50% increase of melt viscosity of LPET when blended with 30mass% of BPET. This was attributed to increasing chain entanglements with the proportion of branching comonomer of the BPETs. Also, blends of LPET with BPET of different branching comonomer were investigated, and the rheology was found to be highly sensitive to composition. Dynamic rheological measurements of the blends were made, and compared with the data for LPET, to evaluate the effect of BPET on the viscoelasticity.