W. Brostow
Laboratory of Polymers and Composites, Department of Materials Science, University of North Texas, Denton, TX 76203-5308
ABSTRACT
Polymer Liquid Crystals (PLCs) show superior properties over conventional thermoplastic polymers with regard to chemical resistance, low flammability and high modulus.1 In addition, their low isobaric expansivity combined with their low viscosities at processing temperatures combine to assist in the development of high tolerance parts. PLCs achieve these properties due to their unusual phase behavior during temperature variations. In conventional semi-crystalline thermoplastics, three kinds of relaxational phenomena are seen:
(i) Low temperature solid state transitions (often related to side group chain conformational changes).
(ii) An alpha transition region in which the segmental mobility of the polymer chains results in the polymer changing from glassy to rubbery.
(iii) A high temperature melting transition to ensure flow.
Since PLCs have additional phase behavior due to their mesophases, understanding their phase behavior is vital to their use. In the past we reported on the mechanical behavior and phase diagram of the transition temperatures versus the mole fraxtion x of a series of PET/xPHB PLCs, where PET = poly(ethylene terephthalate) and PHB = p-hydroxybenzoic acid.2 To study the effects of blending PLCs with cheaper thermoplastics in order to obtain higher strength plastics at a lower cost, we continue to study systems of the engineering plastics (EP) + PLC type.3-5 Rheological experiments show that EP viscosity decreases upon addition of a PLC, making processing easier while reinforcing the EP at the same time.5
1. W. Brostow, Polymer, 1990, 31, 979.
2. W. Brostow, M. Hess, B.L. López, Macromolecules, 1994, 27, 2262.
3. W. Brostow, M. Hess, B.L. López and T. Sterzynski, Polymer, 1996, 37, 1551.
4. W. Brostow, B.L. López and T. Sterzynski, in preparation.
5. W. Brostow, T. Sterzynski and S. Triouleyre, Polymer, 1996, 37, 1561.