Effect of Zone Drawing, Zone Annealing and Annealing at Constant Length on the Structure and Mechanical Properties of Biends of PET, PBT and Polyamide 6

Abstract

Binary (1:1 by wt.) and ternary (1:1:1 by wt.) blends of polyethylene terephthalate, poly(butylene terephthalate) and polyamide-6 were extruded as strips and ultraquenched from the melt. After zone drawing and subsequent zone annealing or annealing at constant length at temperature T = 220°C for 5 hours in vacuum, the samples were studied by differential scanning calorimetry, wide-angle X-ray scattering, small-angle X-ray scattering and mechanical testing. Substantial improvement of the mechanical properties (increase of Young's modulus and tensile strength) was established after zone annealing, compared to the annealing at constant length. Some proofs are given in the case of zone annealed samples for partial chain unfolding in the crystalline regions and maximal stretching of macromolecules in the non-crystalline regions, i.e., an increase in the number of taut tie molecules is achieved. This leads to a significant improvement of the mechanical properties. Exchange reactions and creation or copolymer layers at the interface between the parent polymers, are believed to occur during the annealing at constant length, playing the role of selfcompatibiliziers. These layers suppress the separation of the homopolymers under the action of external mechanical strains or simply upon aging.