Recyclable thermosets based on modified epoxy-amine network polymers

Anderson, Lynn (2023) Recyclable thermosets based on modified epoxy-amine network polymers. Doctoral thesis, Northumbria University.

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Abstract

With growing interest in recyclable polymer materials, due to environmental concerns, attention has been aimed towards substantially reducing waste generation through prevention, reduction, recycling and reuse. In response to recycling polymer waste, the emerging field of covalent adaptable networks (CANs) has provided solutions to the reduction of thermoset polymer waste by utilising dynamic bonds to form three dimensional architectures. In particular, boronic esters provide a desirable associative CAN mechanism, for high-performance applications, plus a reversible route by hydrolysis or boronic esterification mechanisms. This offers routes to recycling in materials of this class.

This research investigates a novel dioxazaborocane crosslinking mechanism in epoxyamine thermoset polymers for use as a CAN, creating an opportunity to form high performance, recyclable materials from established molecular building blocks, common to the plastics, composites, coatings and adhesive industries. This work establishes a practical methodology of fabricating polymer networks of this class as well as the subsequent analysis and characterisation of their thermal and material properties, through Tg analysis and procurement of ultimate tensile strengths, to assess the suitability as a high-performance material for aerospace and wind turbine applications. Most notably, an efficient and low-cost process for the chemical recycling (disassembly and dissolution) of the thermoset material is demonstrated via two complementary synthetic processes, using either pinacol (diol) or mono-functional phenylboronic esters. Mechanical recycling has also been realised due to the facile topological rearrangement due to dynamic boronic ester bond exchange mechanisms.

This research demonstrates the value of designing chemical recyclability into the molecular architecture for a sustainable outlook on future thermosets.

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