Vitrimers as a solution to improve the viscoelastic and mechanical properties of recycled polymers

Details

Supervisors

Van Ruymbeke, Evelyne

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux, à finalité spécialisée

Abstract

Today, the mechanical recycling of polymers seems to be an essential step to address environmental issues related to plastics as it reduces the need to extract new raw materials and reduces the plastic waste generated. However, due to their poor physical properties, mechanically recycled plastic waste accounts for less than 10% of the feedstock used to manufacture new products in the European Union. To achieve the European Strategy goals of recycling 50% of plastic waste by 2030 requires developing new solutions to ensure that the mechanical and viscoelastic properties of the material are maintained at each life cycle. A possible solution to address this challenge is to use dynamic covalent networks (e.g., vitrimers) which offer the combined advantages of thermoplastics and thermosets. Behaving as crosslinked polymers at low temperature, these materials stay, however, reprocessable at high temperature. Moreover, when added in low concentrations in polymer blends, they could also be used to reinforce the polymer-polymer interfaces, offering a promising way to improve the processing and mechanical properties of recycled polymers. As a first step towards the development of this method, the main objective of this work is to explore the dynamics of well-defined vitrimers in function of different parameters (such as their chemistry, molar mass, crosslinking density, or temperature), which will then be used as compatibilizers in immiscible blends. This approach is investigated on two incompatible polymers: polystyrene (PS) and poly(2-ethyl hexyl methacrylate) (PEHMA), and on their blend. These polymers are specifically selected for their immiscibility translated by poor mechanical properties of their blends. Each thermoplastic as well as the PS based vitrimers and PEHMA based vitrimers are characterized by several analytical methods to understand their mechanical and rheological properties. The Atomic Force Microscopy (AFM) results on the prepared blends without vitrimers show the incompatibility of the selected polymers. The Small Amplitude Oscillatory Shear (SAOS) experiments demonstrate a positive effect on the viscoelastic properties in the samples containing low concentrations of vitrimers.