STABILITY OF BLENDS OF THERMOTROPIC LIQUID-CRYSTALLINE POLYMERS WITH THERMOPLASTIC POLYMERS

Breakup of fibers of a thermotropic liquid crystalline polymer (TLCP) above the melting temperature in various ordinary polymers has been st udied by capillary instability experiments on single TLCP fibers and b y annealing experiments on extruded TLCP/thermoplast blends. The TLCP was an aromatic copolyester, Vectra A900, the matrix polymers were PP, PS, PC, PEI, PES, and PEBT. Both types of experiments show that the f iber/matrix morphology is, in general, highly unstable in the molten s tate. The TLCP fibers break up into droplets by a combination of Rayle igh distortions, end-pinching and retraction, depending on the system and shape of the fiber. Fibers of a thickness of similar to 1 mu m can break up in a few seconds. Breakup times of fibrous blends and indivi dual fibers are in agreement provided size effects are accounted for. Rayleigh distortions develop exponentially in time up to relative dist ortions of 0.5 to 0.6. Breakup occurs within a range of wave numbers r ather than at one distinct dominant wave number, which is shown to be the consequence of relatively large initial distortions. Apparent valu es for the interfacial tensions calculated with Tomotika's theory turn ed out to be of the correct order of magnitude, ranging from 7 mN/m fo r Vectra/PES to 24 mN/m for Vectra/PP and to yield correct values of t he interfacial tensions of PP/PS, PP/PC, and PS/PC using Antonow's rul e.