The objective of BIZENTE project is to develop a multi-step degradation process to degrade thermoset materials at their end-of-life. To do so, BIZENTE partners are working in parallel in order to develop specific enzymes custom designed on the basis of reference resin and also to achieve chemical modification of the reference resins in order to favor enzymatic degradation. Indeed, taking in account the crosslinked nature of the unsaturated polyester, vinylester or epoxy thermosets targeted in this project, a preliminary step by abiotic factors (i.e. mechanical or chemical) must be considered. If not, the penetration of the enzyme in the material bulk will be impossible.
SP role within BIZENTE Project
Within BIZENTE project, SPECIFIC POLYMERS is in charge to propose, develop and implement chemical modifications to the resin in order to ease the targeted biodegradation process. The four reference resins are characterized by different chemical natures (epoxy, vinyl ester, unsaturated polyester) and different specifications (linked to the implementation process and the application). Thus, our chemical modifications strategies are different for each use case. However, in all cases, the enzymatic degradation of thermoplastics can be favored by hydrophilic and non-crystalline polymeric chains, by the introduction of an increase content of biodegradable moieties within the network or finally by the introduction of reversible chemical bonds that can be broken at the materials end-of-life to recover solubility.
BIZENTE – NEW ADVANCES
In the first 24months of BIZENTE project, SP worked first achieved an in-depth characterization of the reference resins to determine the key performance values of each resins. Indeed, all chemical modification achieved each resin must not imply modification of the main properties or performances of the resins. It was then important to define the values to target by analyzing the reference resins. This was achieved thanks to SP’s characterization apparatus.
While these values defined for each resins, SP worked several months on the custom design of resin precursors to achieve resin chemical modifications able to ease the enzymatic degradation. Functional monomers, polymers or building-blocks designed by SP are conceived in order to (i) lower the crystallinity phases within the material, (ii) bring reversible bonds into the network that can be clived at the end-of-life (vitrimer or vitrimer-like strategies) and/or (iii) bring hydrophilicity within the network. While synthesized, first resin formulation trials were achieved in order to evaluate the impact of all chemical modifications on the main resin specifications (Gel-time, curing temp., Glass transition temperature, Tensile modulus) to ensure that the designed alternative resins is still compliant in regards to the process and applicative specifications.
In parallel to the chemical modification, significant work was also achieved to develop a chemical degradation process able to distort crosslinked networks depending on the reversible chemistry used. Main effort were geared toward transesterification, disulfide metathesis and imine metathesis reversible chemistries and degradation conditions could have been identified. Even if the work is still on going on each of these aspects, first conclusion can already be drawn:
– More than 15 different building-blocks were synthesized within the project at lab scale (10-50 grams). The synthesis of the most interesting building blocks was scaled up to 200-300 grams.
– Resin formulation work was achieved and allow introducing required functionalities in the reference resins while conserving the same resin/material properties.
– Chemical degradation processes were set and allow reaching chemical degradation rates in between 30% and 100% depending on the resin chemistry. Enzymatic degradation of pre-treated sample is underway. Improvement are still on-going to reduce degradation time and process sustainability.