Rheology,morphology and tensile properties of thermotropic liquid crystalline polymer/polypropylene in‐situ composites

Blends of various grades of polypropylene (PP) with a thermotropic liquid crystalline polymer (TLCP), namely a copolymer of p‐benzoic acid and ethylene terephthalate (60/40 mole ratio) were prepared as extruded films. A thermoplastic elastomer styrene (ethylene‐butylene) styrene (SEBS) was used as a compatibilizer. Melt viscosities of all specimens were measured using a plate‐and‐plate rheometer with oscillating mode in the shear rate region of 1 ‐ 200 rad/s. Addition of SEBS compatibilizer resulted in an increase of the blend viscosity. Observation of the blend morphology revealed an improvement of TLCP dispersion. The TLCP fiber aspect ratio (length to diameter) in the extruded film also increased after addition of SEBS. As a result, the film modulus in extrusion direction was enhanced. The tensile strength of the film specimen was also increased due to an improvement of interfacial adhesion.     

Preparation and photoinduced isomerization study of a homopolymer and a copolymer based on 4′‐(6‐acryloxy)hexyloxy‐4‐methoxyazobenzene and acrylic acid

The synthesis and characterization of a copolymer based on 4′‐(6‐acryloxy)hexyloxy‐4‐methoxyazobenzene (MAB6) and acrylic acid (AA) are reported. A reaction was carried out by free‐radical polymerization, yielding an MAB6 homopolymer and an AA–MAB6 copolymer with an MAB6 concentration of 16–80%. A nematic phase was observed in the copolymer when the MAB6 content was 44% or higher. Both nematic and smectic phases were observed in the MAB6 homopolymer. All of the polymers were investigated for trans–cis–trans isomerization in a solid film. The samples were irradiated with nonpolarized ultraviolet light (385 nm) before absorption measurements were taken with an ultraviolet–visible spectrometer. The copolymer and homopolymer exhibited a thermal cis–trans isomerization, which could be described by a double‐exponential relaxation process (fast and slow). The relaxation experiment suggested that the hydrogen bonding may have hindered the slow process but had no effect on the fast process. A film of a copolymer sample with a high MAB6 content could be optically aligned by the exposure of the sample to polarized light (385 nm). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 4017–4024, 2003     

Effect of melt viscosity of polypropylene on fibrillation of thermotropic liquid crystalline polymer in in situ composite film

 Various grades of polypropylene were melt blended with a thermotropic liquid crystalline polymer, a block copolymer of p-hydroxy benzoic acid and ethylene terephthalate (60/40 mole ratio). The blends were extruded as cast films at different values of draw ratio (slit width/film thickness). Fibrillation of TLCP dispersed phase with high fiber aspect ratio (length/width) was obtained with the matrix of low melt flow rate, i.e., high viscosity and with increasing film drawing. Melt viscosities of pure components and blends measured using capillary rheometer were found to decrease with increasing shear rate and temperature. Viscosity ratios (dispersed phase to matrix phase) of the systems being investigated at 255 °C at the shear rate ranged from 10² to 10⁴ s⁻¹, were found to lie between 0.04 and 0.15. The addition of a few percent of elastomeric compatibilizers; a tri-block copolymer SEBS, EPDM rubber and maleated-EPDM, was found to affect the melt viscosity of the blend and hence the morphology. Among these three compatibilizers, SEBS was found to provide the best fibrillation. Received: 10 January 2000/Accepted: 24 January 2000