| dc.description.abstract | The usage of natural fibre composites (NFCs) has been increasing recently to replace traditional composite materials in different sectors due to climate change and sustainability issues. However, natural fibres are hydrophilic, and their composites (NFCs) exhibit inferior performance (i.e., poor durability) in different environmental conditions. Hence, this research aims to study the long-term performance of unidirectional (UD) flax fibre reinforced composites with two selected recyclable polymer matrices in different environmental conditions. The recyclable polymer matrices are (i) a bio-based recyclable epoxy and (ii) an acrylic-based liquid thermoplastic resin (Elium®). The recyclable polymers are chosen to focus on the circularity of the end composite products and sustainability, i.e., to reduce the End-of-Life (EoL) environmental impacts of the studied composite materials in their applications in different sectors, namely, automotive, sports, or wind energy (rotor blades). In addition, a petroleum-based non-recyclable epoxy resin and glass fibre reinforcement were used for comparative purposes in this study. The doctoral thesis consists of a synopsis and Part 1 to Part 3, which includes two peer-reviewed journal articles and one paper submitted. The synopsis consists of the introduction and research objectives of the Ph.D. Research and a summary of the works extracted from Part 1 to Part 3.
Part 1 demonstrates the effects of accelerated weathering on the performance of flax fibre reinforced recyclable polymer composites and makes comparisons with traditional glass fibre composites. Composite laminates were fabricated by compression moulding. The fabricated composites were (i) flax/petro-epoxy (FFRP1), (ii) flax/bio-based recyclable epoxy (FFRP2), and (iii) flax/acrylic thermoplastic (FFRP3) in flax fibre composite series (FFRPs), and (iv) glass/petro-epoxy (GFRP1), (v) glass/bio-based recyclable epoxy (GFRP2), and glass/acrylic thermoplastic (GFRP3) in glass fibre composite series (GFRPs). Then, all composites were exposed to accelerated weathering in a lab-scale weathering chamber for up to 56 days. After ageing, the performance of all the composites was assessed in terms of flexural and viscoelastic properties, surface analysis by Scanning Electron Microscopy (SEM) testing, and visual inspection. It was revealed that FFRPs exhibited significantly poor performance than GFRPs after accelerated weathering of 56 days. In the case of polymers, the bio-based recyclable epoxy revealed similar behaviour to the petro-based epoxy after ageing in both FFRPs and GFRPs. Acrylic thermoplastic-based glass composites (GFRP3) exhibited adequate performance as a function of accelerated weathering ageing.
Part 2 presents the effect of hygrothermal ageing on the performance of the above-mentioned composite materials of Part 1. The ageing environment was distilled water at temperatures of 23, 40, and 60℃. It was revealed that the FFRPs were damaged significantly from the beginning of their ageing period (7 days), with barely noticeable changes, for the ageing up to 56 days. In addition, higher ageing temperatures induced higher degradation in the composites. The GFRPs also experienced damage in their mechanical and viscoelastic properties; however, the magnitude of damage was significantly lower than the FFRPs, after ageing. Similar to the mechanical properties, moisture uptake values were also considerably higher for the case of FFRPs for all the ageing conditions than their glass fibre counterparts. Considering polymers, acrylic thermoplastic-based composites (both FFRPs and GFRPs) exhibited marginally higher moisture resistance.
In Part 3, with a view to improve the durability of flax fibre polymer composites, glass fibres were used fabricating hybrid flax/glass fibre polymer composite laminates. Glass fibre laminas were used as external protecting layers of flax fibres (core), developing flax/glass hybrid (G2F6G2) composite laminates. The fabricated hybrid composites were (i) flax/glass/petro-based epoxy (Hybrid1), (ii) flax/glass/bio-based recyclable epoxy (Hybrid2), and (iii) flax/glass/acrylic thermoplastic (Hybrid3). All hybrid composites were subjected to weathering and hygrothermal ageing for up to 56 days and their performance was assessed at different time intervals, following the approach of Parts 1 and 2. It was found that hybrid composites led to overall, improved flexural properties and storage modulus (E´), compared to neat flax fibre composites while in the case of polymers, the performance order was Hybrid3 > Hybrid2 > Hybrid1. After ageing at weathering and hygrothermal environments, the degradation of mechanical and viscoelastic properties was found to be significant due to the presence of flax fibres in the core of hybrids (G2F6G2). However, marginal improvement in ageing resistance was reported, due to hybridization of flax with glass fibres, compared to their neat flax composites (FFRPs). In the case of polymers, overall performance after 56 days of ageing was reported to be Hybrid2 > Hybrid1 > Hybrid3 (in weathering) and Hybrid3 > Hybrid2 > Hybrid1 (in hygrothermal ageing). Moisture uptake properties were reduced significantly in the case of hybrid composites than their respective flax composites. | en_US |
