Vitrimers, invented in 2011 by the group of Leibler, were first based on exchangable links by transesterification and implemented by using classical epoxy chemistry. As epoxies are ubiquitous in high performance composites, a first question addressed here is to examine to what extent the original properties of vitrimer are maintained in materials containing more than 50% by weight of reinforcing fibers. To answer this question, we analyze quantitatively the bond strength of epoxy vitrimer based composite plates made by resin transfer molding and compare them to their non-vitrimer counterparts made of a standard thermoset epoxy,<br/>It is demonstrated that only epoxy vitrimer samples show substantial bond strength and the ability to be repeatedly welded thanks to the exchange reactions which promote improved surface conformity and chemical bonding between the adherands at the joint interface. This opens the way towards joining composite parts without adhesives nor mechanical fasteners.<br/><br/>Polybutylene terephthalate, PBT is characterized by a high degree of crystallinity, a high melting point and rapid crystallization. One of its limitations is that just above the melting point (230°C) any mechanical strength disappears and the polymer tends to drip under its own weight. In demanding applications, it is necessary to use crosslinked PBT but the existing crosslinking processes are complex and the polymer obtained is not recyclable. In the process that we envisioned, PBT is modified by epoxy resins in the presence of a transesterification catalyst, directly into an extruder. To devise an effective formulation we studied in detail the exchange reactions and catalysis in model systems and in the polymer. The polymer thus obtained maintains the essential properties of a semi-crystalline thermoplastic polymer and acquires the new properties of vitrimers such as heat resistance, mechanical strength and solvent resistance. Transformation of ordinary PBT into a vitrimer could open up new areas of application for PBT (Figure).

Epoxy and polyester-based vitrimers and composites

256th National Meeting (2018)

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