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The thermal and mechanical behavior of poly(ethylene terephthalate) fibers incorporating novel thermotropic liquid crystalline polymers
Abstract
This dissertation explores the potential of improving the performance of poly(ethylene terephthalate) fibers by incorporating novel thermotropic liquid crystalline polymers. To determine if a system exhibited desirable characteristics, a screening procedure was developed to assess the various blends. Evaluations focused on blend compositions ranging from 2 to 20 wt.% LCP. Fibers were obtained by melt extrusion and the effect of processing conditions, i.e. spinning temperature, stretch ratio, and post treatment evaluated. The fibers were tested for mechanical performance, dimensional instability (shrinkage), and the development of shrinkage stresses. Test results were used to determine the critical parameters necessary for in-situ reinforcement and to develop strategies for improving LCP architecture and processing techniques. The novel TLCP's incorporated into the PET were mesogenic copolymers containing either alternating or random flexible groups within the polymer backbone. The flexible moieties were used to promote compatibility between the PET matrix phase and the TLCPs. Two systems were found to significantly improve fiber stiffness compared to neat PET fibers. A Random Copolymer based on the reaction of oxyethylene substituted hydroquinone, ethylene glycol, and terephthaloyl chloride was found to effectively enhance the performance of PET fibers. Fibers containing only 5% TLCP exhibited a 50% increase in modulus, while maintaining an ultimate strength equivalent to the PET control. The thermal behavior of the 5% blend, as determined by free shrinkage and force-temperature experiments, was similar to the PET control. A segmented block copolymer consisting of rigid-rod, diad, and flexible coil segments was also found to improve the performance of PET fibers. At a concentration of 20 wt. percent, the alternating block copolymer, Triad2 (2:6:7), increased the tensile modulus of the fibers 40% and decreased free shrinkage by 20% compared to neat PET. The mechanism of reinforcement for these systems is unclear, but morphological, thermal and mechanical evidence suggest that the TLCPs are modifying the PET matrix and not providing true mechanical reinforcement.
Subject Area
Materials science|Polymer chemistry
Recommended Citation
Joslin, Scott Lawrence, "The thermal and mechanical behavior of poly(ethylene terephthalate) fibers incorporating novel thermotropic liquid crystalline polymers" (1994). Doctoral Dissertations Available from Proquest. AAI9420637.
https://scholarworks.umass.edu/dissertations/AAI9420637