Bio-based resins, polymers and composites based on waste vegetable oil valorisation

• Main Author: Cicaroni Fernandes, Felipe
• Format: Dissertation
• Language: English
• Published: University of Warwick 2019
• Subjects: QC Physics; QD Chemistry; T Technology (General)

Historically, energy-intensive materials such as glass fibres and carbon fibres have been applied to reinforce thermoplastic and thermoset matrices from a petrochemical origin. However, recent ecological concerns and latent climate change problems have encouraged the development of environmentally-friendly alternatives for composite industry, creating a new class of materials that bring added technical performance and are produced more sustainably. In this scenario, vegetable fibres have been rediscovered as promising reinforcing agents and bio-based polymers have been developed to attend the demand for greener matrices. In the last decade, vegetable oils have emerged as a key platform to produce bio-based epoxy resins used as matrices for composite laminates, reducing the environmental footprint of composites production. Nevertheless, features such as the intrinsically limited mechanical performance, price and ethical discussions have restricted the applicability of these materials. In this regard, this thesis investigates the utilisation of waste vegetable oil (WVO) as a potential platform to create bio-based epoxy resins and consequently composites in a more sustainable fashion. Investigations have identified the best purification and chemical modification methodologies to enable the polymerisation of these triglycerides. They have also confirmed the possibility of applying such materials as reactive diluents for diglycidyl ether of Bisphenol A (DGEBA), or for the creation of networks exclusively made with waste-based epoxies. Nonetheless, one should ensure that anhydrides are used in excess as hardener to mitigate drops in performance and create networks with Tg above room temperature. Studies also demonstrate the use of resins from WVO for the creation of a library of composite materials reinforced with glass, carbon fibres (virgin and recycled) and flax fibres. To address the challenge of compatibilizing vegetable fibres and the hydrophobic matrix, chemical treatments are explored to enhance the fibre/matrix interaction, with mercerisation leading to the best performance. Materials produced with glass demonstrate to be competitive alternatives for application that require stiffness and impact performance over strength, where the use of WVO-based epoxy also reduced the density of these materials. Finally, laminates reinforced with virgin and recycled carbon fibres reveal that the addition of resins from WVO to commercial formulations can reduce effects associated with barely-visible impact damage (BVID) as investigated in a compression after impact test. Overall, this thesis demonstrates the first developments of a new class of bio-based composites reliant on the exploration of the waste valorisation concept. Despite not being able to completely substitute DGEBA in technical applications, opportunities are explored according to the best features each system, so that WVO can be used as a co-resin in epoxy formulations for tuning (and improving) a number of engineering properties. Finally, these investigations encourage the maturation of WVO as a more environmentally-friendly chemical platform for a more sustainable polymer and composite industries.