MICROFIBRILLAR REINFORCED COMPOSITES FROM BINARY AND TERNARY BLENDS OF POLYESTERS AND NYLON-6

Binary (1:1 by weight) and ternary (1:1:1 by weight) blends of poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), and Nylon 6 (PA 6) as well as the homopolymers are extruded as strips and ultraquenched from the melt. After zone drawing and additional annealing at T(a) = 220 or 240-degrees-C for 5 or 25 h with fixed ends in vacuum, the samples are studied by DSC, WAXS, solubility, and mechanical testing. It is found that all components in the blends are oriented and perfection of the structure is observed at T(a) = 220-degrees-C. At T(a) = 240-degrees-C isotropization of PBT and PA 6 takes place in their blends with PET, the orientation of the latter being preserved; i.e., microfibrillar reinforced composites are obtained. Their mechanical properties are comparable to those of glass fiber reinforced PBT and PA 6. During prolonged thermal treatment, in addition to isotropization, chemical interactions (additional condensation and exchange reactions) take place at the interfaces, resulting in the formation of copolycondensates playing the role of compatibilizers. The initially multiblock copolymers randomize with the progress of annealing, losing their crystallization ability, as proved by DSC, WAXS, and solubility measurements. Finally, the entire amounts of PBT and PA 6 become involved in the copolymers, converting in this way the starting homopolymer matrix of the microfibrillar reinforced composite into a copolymer one. This change in the chemical composition affects the overall behavior of the composites.