In the last decades environmental concerns regarding petroleum-based synthetic polymers have been growing, which has facilitated the development of new strategies in the field of polymer science. Indeed, plastic materials and especially thermoset polymers, thanks to their versatile and multifunctional properties, are widely used for many applications and especially in fibers reinforced polymer composites, a market with an enormous growth the last decades. Thermoset matrices in such composites include epoxies, polyesters, vinyl esters, phenolics,cyanate esters, bismaleimides, and polyimides. However, epoxies currently are the dominant resins used for high-performance composites at low and moderate temperatures (up to 200 °C) thanks to the superior mechanical performance, lighter weight and resistance to environmental degradation in comparison to the other thermoset resins. On the other hand, fundamental chemicals for the production of epoxy resins, like bisphenol A or epichlorohydrin, have been found toxic. Furthermore, epoxy resins derive from petroleum, contributing both to the rapid depletion of nonrenewable fuel sources and to the related environmental problems. Indeed, like the other thermosets, epoxy resins show a strong permanent covalent network which preclude flow, even at high temperatures, which makes mechanical and chemical recycling challenging. As a result, most thermosets are incinerated or landfilled at the end of their lifetime. All these issues can be potentially solved by biobased vitrimers, a new class of polymers which makes the thermosets meet the thermoplastics thanks to the presence of dynamic bonds which allow for easily reprocessing and recycling of covalently crosslinked polymers. Indeed, these revolutionary thermosetting polymeric material are, recyclable and malleable like thermoplastic but still maintain their outstanding properties awarded by crosslinked network structure. During the first part of my PhD, a new vitrimer resin for carbon fibre reinforced composites, based on epoxidized linseed oil and dithiol boronic ester cross-linker was synthetized. As a continuation of that research a series of new low melting or even liquid boronic ester cross- linkers were developed which allowed for a room temperature curing. Crosslinkers with several functional groups, like thiol, hydroxyl, carboxyl and amino group were successfully synthesized following green chemistry principles. The most promising one containing amino groups was used together with phloroglucinol triglycidyl ether, a biobased epoxy from brown algae to fabricate a new, room-temperature curable vitrimer resin. The synthetized vitrimers were used to produce fibre-reinforced composites and tested in comparison to a commercial epoxy-based composite. Moreover, the vitrimers were found to be mechanically recyclable through techniques typically employed for thermoplastics polymer as well as chemically recyclable through hydrolysis in aqueous ethanol as a green solvent. The chemical recycling gives the possibility, at the end of their lifetime, of recovering the components of the composite, therefore bringing environmental and economic advantages. Besides, the new materials showed also signs of biodegradability in sea water, which is important to prevent the vitrimer accumulation in the marine environment in case of an accidental release into the environment. For all these reasons, the developed vitrimers and composites can address many challenges facing conventional polymers and thermosets composites.
Novel Boronic Ester Cross-linkers and Biobased Vitrimers for Fibre-reinforced Composites
SANGALETTI, DAVIDE
2024-05-15
Abstract
In the last decades environmental concerns regarding petroleum-based synthetic polymers have been growing, which has facilitated the development of new strategies in the field of polymer science. Indeed, plastic materials and especially thermoset polymers, thanks to their versatile and multifunctional properties, are widely used for many applications and especially in fibers reinforced polymer composites, a market with an enormous growth the last decades. Thermoset matrices in such composites include epoxies, polyesters, vinyl esters, phenolics,cyanate esters, bismaleimides, and polyimides. However, epoxies currently are the dominant resins used for high-performance composites at low and moderate temperatures (up to 200 °C) thanks to the superior mechanical performance, lighter weight and resistance to environmental degradation in comparison to the other thermoset resins. On the other hand, fundamental chemicals for the production of epoxy resins, like bisphenol A or epichlorohydrin, have been found toxic. Furthermore, epoxy resins derive from petroleum, contributing both to the rapid depletion of nonrenewable fuel sources and to the related environmental problems. Indeed, like the other thermosets, epoxy resins show a strong permanent covalent network which preclude flow, even at high temperatures, which makes mechanical and chemical recycling challenging. As a result, most thermosets are incinerated or landfilled at the end of their lifetime. All these issues can be potentially solved by biobased vitrimers, a new class of polymers which makes the thermosets meet the thermoplastics thanks to the presence of dynamic bonds which allow for easily reprocessing and recycling of covalently crosslinked polymers. Indeed, these revolutionary thermosetting polymeric material are, recyclable and malleable like thermoplastic but still maintain their outstanding properties awarded by crosslinked network structure. During the first part of my PhD, a new vitrimer resin for carbon fibre reinforced composites, based on epoxidized linseed oil and dithiol boronic ester cross-linker was synthetized. As a continuation of that research a series of new low melting or even liquid boronic ester cross- linkers were developed which allowed for a room temperature curing. Crosslinkers with several functional groups, like thiol, hydroxyl, carboxyl and amino group were successfully synthesized following green chemistry principles. The most promising one containing amino groups was used together with phloroglucinol triglycidyl ether, a biobased epoxy from brown algae to fabricate a new, room-temperature curable vitrimer resin. The synthetized vitrimers were used to produce fibre-reinforced composites and tested in comparison to a commercial epoxy-based composite. Moreover, the vitrimers were found to be mechanically recyclable through techniques typically employed for thermoplastics polymer as well as chemically recyclable through hydrolysis in aqueous ethanol as a green solvent. The chemical recycling gives the possibility, at the end of their lifetime, of recovering the components of the composite, therefore bringing environmental and economic advantages. Besides, the new materials showed also signs of biodegradability in sea water, which is important to prevent the vitrimer accumulation in the marine environment in case of an accidental release into the environment. For all these reasons, the developed vitrimers and composites can address many challenges facing conventional polymers and thermosets composites.File | Dimensione | Formato | |
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