THE EFFECT OF PHASE HETEROGENEITY ON THE RHEOLOGICAL PROPERTIES OF MELTED COPOLYESTERS AND STRUCTURAL-MECHANICAL PARAMETERS OF RELATED EXTRUDED MATERIALS

The flowability diagrams of homogeneous and heterogeneous melts of the copolyesters between poly(ethylene terephthalate) and acetoxybenzoic acid were studied. The results confirmed that there are two temperatur e regions on the diagrams, corresponding to different structures of th e copolyester melts: a low-temperature region, with high-melting cryst allites occurring in a nematic liquid-crystal (LC) phase, and a high-t emperature region, corresponding to the formation of a homogeneous nem atic LC melt, It is shown that an anomaly in the log(gamma) over dot-l og tau plot and a temporal instability of the viscosity of the heterog eneous melt are caused by the development of processes involving cryst allization and misorientation of the structural elements, The flow cur ves of the LC melt are typical of the viscoplastic systems and show a tendency to limited flowability with decreasing temperature. Materials extruded from a homogeneous melt exhibit a much higher level of molec ular orientation and strength as compared to those of the extrudates o btained from a heterophase melt. The effect of high-melting crystallit es, leading to the structural disordering and decreasing strength of t he extruded material, increases with the proportion of mesogenic fragm ents in the chain.