Devlopment and relaxation of orientation in liquid crystalline polymers : transport properties of liquid crystalline polymer blends

Sammanfattning: In this thesis different types of liquid crystallinepolymers have been investigated with respect to build up andrelaxation of orientation. The potential of making new barriermaterials using liquid crystalline polymer blends was alsostudied. Studies on the relaxation of orientation in injectionmoulded Vectra were performed by subjecting samples ofdifferent degrees of orientations to various thermal treatmentsand different clamping procedures of the sample. Theorientation was assessed by infrared spectroscopy andX-raydiffraction. The oriented samples showed, depending on thethermo-mechanical history, either an increase or a decrease inchain orientation on annealing above and below the crystalmelting range. Highhly oriented samples with ability to changetheir shapes during annealing relaxed quickly from a Hermansorientanon parameter value. f~0.5. to a universal value off~0.2-0.3 at temperatures above 290(C. whereas increasedorientation was obtained for samples with low orientation giventhe same treatment. Slow and gradual heating favoured retainedor increased orientation which persisted far above the meltingregion. It is proposed that this is due to solid staterecrystallization from pseudohexagonal crystals to more stableorthorhombic crystals and to crystal modification II ofpoly(hydroxybenzoic acid). Built-in stresses in injectionmoulded specimens caused curling and shrinkage in orientedsamples at temperatures above 200(C. This behaviour wascorrelated with a noisy baseline and artificial endothermicpeaks during a first heating scan in a differential scanningcalorimeter(DSC). A more reliable method with greatly improvedreproducibility of the heating curves involved either immersionof the sample in silicon oil or placing the sample betweenKapton sheets. This allowed free shrinkage and secured goodthermal contact between the sample and the sample pan. Shearinduced orientation and relaxation of orientation in Vectra wasstudied in a thermo-optical shear cell. The transmitted lightintensity through crossed polarizers increased with increasingshear rate and increasing temperature. Rapid relaxation wasdetected after cessation ofshear at high shear rates. The shortrelaxation times prevented consersation of any appreciabledegrees of orientation by quenching after shearing. Samplessheared and cooled simultaneously showed a high degree oforientation (f~0.7). Infrared rheometry was used to study asmectic side-chain polymer. Steady shear induced a high degreeof perpendicular orientation of the mesogens (f~-0.3). Therelaxation of orientation was slow and not complete after 15h.A lyotropic system of hydroxypropylcellulose in m-cresol wasalso studied using infrared rheomety.Studies reported in theliterature of the molecular orientation for sheared lyotropicsystems have yielded contradictory results. in this work a highorder parameter was achieved in a 50( solution (f~0.55) whereaslower values were obtained in d 45% solution. The relaxationwas in most cases complete within 10 minutes after cessation ofshear. In some cases. After complete relaxation, the orderincreased considerably. Small additions of a liquid crystallinepolymer to a thermoplastic flexible-chain matrix often leads toimproved properties. Transport properties of methanol inVectra/Polyethersulphone blends were investigated with respectto composition.processing technique and orientation. The datawere fitted to a model based on concentration dependentdiffusion. The solubility decreased linearly with LCP content.The zero concentration diffusity was lowest for the compressionmoulded samples where the LCP component formed a continuousphase at lower LCP contents compared to the injection mouldedsamples.Kewords:liquid crystalline polymer; thermotropic;lyotropic; copolyester; Vectra; infrared spectroscopy;orientation; relaxation; thermal behaviour; blends; transportproperties