Quentin-Arthur POUTREL: Enzymatic PLA vitrimers for 3D printed shape changing structures in close loop recyclability

Abstract:
Nowadays, advances in materials science, in addition to developing new sets of properties and applications, must think about sustainability and environmentally friendly materials. With this in mind, the speaker, Dr. Quentin-Arthur Poutrel, would like to present the project "Enzymatic PLA Vitrimers for 3D printed and recyclable closed-loop shape changing structures" as a research theme for the CNRS for a CR position. The seminar aims to introduce Dr. Poutrel's background from previous research topics on the durability potential of epoxy vitrimers network at the University of Manchester, and vitrimer engineering for long latency prepreg carbon fibres at ESPCI Paris. This will be followed by a discussion of his current work between LEMTA and LRGP (Nancy), on thermoplastic vitrimers. These introductions will serve as connecting points to offer a research proposal mixing the two above mentioned points in materials science: sustainable and innovative materials.
Vitrimer networks are adaptable, undergoing covalent bond exchange upon triggers such as heat or light. First demonstrated in 2011, by Leibler et coll. of the ESCPCI Paris, they initially rely on epoxy chemistry to achieve associative exchange between hydroxylester bonds. This allows thermosetting properties such as strength, temperature resistance or chemical resilience to be retained. In addition, when the exchange is triggered, the network can flow like a viscous liquid, making cross-linked polymers reproducible, curable, recyclable and depolymerisable like thermoplastics. In its short 11-year history, vitrimer networks have attracted widespread attention from other researchers, leading to the adaptation of a variety of other base polymers to vitrimer chemistry. Initially focused on thermoset networks, this adaptation has recently reached thermoplastic materials. Indeed, thermoplastics have many advantages, such as ease of processing and recycling but lack of thermal stability at high temperatures and inferior mechanical properties. Thus, the addition of adaptive cross-links in limited quantities (1-2%) allows to obtain thermoplastic materials with improved properties without losing their qualities.
In this context, polyactic acid (PLA) is not yet easily vitrimerised, although it is a very attractive biobased polymer (i.e., low carbon footprint) widely used in 3D printing. Therefore, the use of biocatalysis such as enzymes to achieve PLA vitrimerisation would allow for the production of readily usable PLA vitrimers without the use of petroleum sources. In addition, judicious selection of enzymes can lead to use them not only for vitrimerisation, but also to catalyse covalent bond exchange during the polymer life cycle for processing and repair. Towards the end of the polymer's life, one can envision using the enzymatic activity to chemically depolymerize the thermoplastic vitrimer, and perform a repurposing of the resulting monomers towards closed-loop recyclability.  In terms of the application of these networks, tuning the properties of the polymer networks (i.e., glass transition temperature or Young's modulus) is possible through formulation design (i.e., choice of crosslinker or crosslink density). This would allow 3D printing of PLA vitrimers with complex geometries to achieve reversible shape changing materials.