A study of all-polymer composites: all-poly(ethylene terephthalate) and all-poly(p-phenylene terephthalamide)

Abstract

Composites are normally composed of two distinct phases: reinforcement and matrix. In recent years, a new class of “self-reinforced” polymer composites or “all-polymer” composites, which are based on similar or identical materials for both reinforcement and matrix have generated increasing interests in both academia and industries due to their advantages in terms of processing, interfacial properties and recyclability. Current research trend in this field is to investigate the potential possibilities of all-polymer composites based on high-performance polymer fibres. In this thesis, all-poly(ethylene terephthalate) composites (Part 1) and all-aramid composites (Part 2) were prepared. In Part 1, Chapter 3 describes the melt spinning and drawing of poly(ethylene terephthalate) (PET) into highly oriented fibres, with moduli of 20GPa and tensile strengths of 925MPa. The effects of spinning and drawing conditions on the mechanical properties of PET fibres were studied. In the following Chapters 4 and 5, all-PET composites were prepared from 1) hot compaction of bi-component multifilament PET yarns; and 2) a film stacking technique, i.e. combining PET tapes unidirectionally with copolyester adhesive films in an alternating “brick-wall” layer-by-layer structure. The effects of processing conditions on mechanical properties were investigated. In Part 2 Chapter 7, all-aramid composites were prepared by a selective surface dissolution method where aramid fibres were partially dissolved to form a matrix phase to bond remaining fibres together into composites. The structure, morphology and mechanical properties were characterized by X-ray diffraction, scanning electronic microscopy, dynamic mechanical analysis and tensile testing. Compared to traditional aramid/epoxy composites, these all-aramid composites show significantly high mechanical properties, even at elevated temperatures. In Chapter 8, the effects of processing conditions on various properties of all-aramid composites were studied and an optimum condition was found. By replacing high concentration sulphuric acid as a solvent, a mild mixed solvent was used to dissolve aramid fibre surfaces in Chapter 9. In this way, all-aramid composites with prolonged immersion times were prepared and characterized. Potential future work including all-PET composites from post-consumer PET waste, microstructural characterization of all-aramid composites and woven all-aramid composites are discussed in Chapter 10.