In order to study the effect of chemical reactions on the properties of poly(butylene terephthalate)[PBT] by reactive blending with liquid crystalline polymer[LCP], blend of PBT with the copolyester of PHB60/PET were prepared and investigated.
Several characterization of pure PBT and LCP were performed to understand the physical properties and characteristics of PBT/LCP blends. From the DSC study, PBT showed an endotherm peak around at 223℃ and recrystallization was not observed due to its inherent fast crystallization from melt state. PBT was degraded beyond 260℃ during isothermal time sweep of rheological measurements. LCP has biphasic structures over the wide range of temperatures and the rheological response was strongly affected by the relative fraction of nematic and isotropic phase.
From the study on reactive blend of PBT/LCP system under various blending conditions, the molecular weight distribution progressively shifts toward lower molecular weight with increasing reaction temperature during 1 hour blending. Based upon the GPC and NMR analysis, the direct evidence for intermolecular exchange reaction between PBT and LCP were monitored. From the thermal analysis, crystallization of PBT in PBT/LCP blends during the cooling scan was delayed with increasing LCP content as a result of transesterification between PBT and LCP.
Polarized light microscopy revealed that the reactive blends exhibited weaker depolarized light intensity compared with corresponding simple blends indicating lowered liquid crystallinity because of PHB-PHB sequence of LCP, which is closely related to liquid crystallinity, was destructed due to transesterification between PBT and LCP. SEM morphology showed the general tendency of decreasing LCP domain size with increasing blending temperature in reactive blend.
The presence of the molten second component physically hinders the transport of the crystallizing PBT molecule, thereby adversely affecting crystal growth. In the presence of the molten second component, factors such as miscibility, relative melt viscosity, and inherent crystallizability all influenced the complex crystallization behavior. From the time sweep of rheological measurements at 210℃, simple blends exhibited delayed crystallization of PBT in the presence of LCP phase which retards crystallization of PBT. But crystallization of PBT in reactive blends prepared at 240℃ was promoted compared with corresponding simple blends due to the reduced obstructing effect of the second phase on spherulite growth. Moreover, isothermal time sweep at 210℃ for reactive blend prepared at 260℃ showed no crystallization behavior due to the severe structural irregularity of PBT chain sequence caused by the transesterification between LCP and PBT. From the frequency sweep at 240℃, the reactive blend at 240℃ exhibited higher complex viscosity than that of corresponding simple blends due to morphological state caused by decrease in LCP droplet size. On the contrary, the reactive blend with PBT70/LCP30 composition prepared at 260℃ exhibited lower complex viscosity than that of simple blend due to decrease in molecular weight caused by chain scission.
The plot of logG' versus logG" showed different morphological state for PBT, LCP and blends. Even if there was no appreciable difference in slop of logG' vs. logG" plot between two types of blends, careful observation showed enhanced homogenization for transesterified blend.
