Investigation of the mechanical performance of natural fibres and their composites

  • Jose Luis Rudeiros Fernandez

Student thesis: Doctoral Thesis

Abstract

During the last decades, natural fibres, considered to be an environmentally sustainable alternative to some human-made fibres and mineral fillers, have been increasingly used as reinforcements in composite materials. Aspects such as governmental environmental regulations, and increasing social awareness of sustainability, have been driving the increasing interest of these "green" materials, and particularly natural fibre reinforced polymer matrix composites. However, despite the potential of this kind of composite, especially with regards to natural fibre reinforced thermoplastics composites (NFTCs), different issues in relation to their performance and technical applicability have to be resolved before their implementation on a larger industrial scale. This thesis addresses the task of generating a deeper understanding of the processing-structure-performance relationships of natural fibres and NFTCs. The mechanical properties of coir and date palm fibre, along with their thermo-mechanical degradation at thermoplastic processing temperatures have been characterised. Furthermore, the interfacial interaction of coir fibre with polypropylene (PP) and low density polyethylene (LDPE) was investigated. In addition, the mechanical performance of injection moulded coir reinforced PP and LDPE composites was analysed. The complex stress-strain behaviour of date palm and coir fibre was investigated through single fibre testing and direct observation of the fibres' cross sectional area.Two theoretical models were developed, postulating an apparent elastic modulus dependant on the fibres' cross sectional area, which successfully correlated with experimental observations. The thermal degradation of natural fibres was explored within the range of thermoplastic composite processing temperatures, revealing severe degradation of performance in terms of failure strain and tensile strength. The interfacial behaviour of coir-thermoplastic systems, and the effect of maleic anhydride grafted polyolefins (MAPOs), was analysed by pull-out testing at room temperature using a tensile testing machine, and at low and elevated temperatures using a dynamic mechanical analyser (DMA). In general terms, it was found that the addition of MAPOs led to an increase of the apparent interfacial shear strength (IFSS). Furthermore, the analysis based on different theoretical models revealed an apparent dependency of the IFSS on the geometry of the pull-out samples, which was also experimentally observed. In addition, the pull-out study at different temperatures revealed an inverse dependency of the apparent IFSS on the testing temperature. The mechanical behaviour of injection moulded coir reinforced-thermoplastics was investigated through tensile and impact composite testing, along with the observation of fibre morphology, and SEM observation of composite fracture surfaces. The dependence of composite tensile and impact properties on fibre content and interfacial performance was characterised, revealing that enhancement of the apparent interfacial shear strength does not always translate into improved overall composite properties.
Date of Award17 Feb 2017
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorJames Thomason (Supervisor) & John Liggat (Supervisor)

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