Banded texture in sheared a semiflexible thermotropic liquid-crystalline polyester and its graft copolymers with polyolefins

The formation of banded texture both in a semiflexible thermotropic liquid- crystalline polyester (SBH 112, synthesized from sebacic acid, 4,4'-dihydro xybiphenyl and 4-hydroxybenzoic acid, from Eniricerche, Milan) and in a ble nd of SBH with graft copolymers, consisting of a polyolefin (polyethylene o r polypropylene) backbone and SBH grafts (COPPE, COPPP) has been studied by polarization microscopy and by scanning electron microscopy. The influence of the preparation conditions upon the perfection, characteristics and the rmal stability of the banded texture has been investigated. The results sho w that the banded texture formed in SBH sheared films possesses greater per fection, smaller band width and larger angle of deviation, and higher therm al stability than the banded texture formed in COPPE and COPPP prepared und er similar conditions. It has been assumed that the chain rigidity of the m acromolecules of the system is mainly responsible for the formation and per fection of the banded texture.