The demand for plastic materials is rapidly increasing, and with this rise comes higher requirements in terms of performance and recyclability.
Today, the plastics that are commonly used show their limits and cannot fulfill all those requirements. However, this problem might be solved thanks to vitrimers.
Invented a few years ago by the French researcher Ludwik Leibler and his team, vitrimers are a new class of recyclable organic materials that combine in an extraordinary way for a stronger mechanical strength, thermal and chemical resistance.
The concept of vitrimers has inspired scientists and manufacturers from all over the world to invent materials and functional composites, liquid crystals, or memory-shape elements for example (Figure 1). However, in order to become the plastics of the future, two questions must be answered: can vitrimers be made with the same ingredients as current plastics? And moreover, can they be implemented with the existing industrial tools with the same production rates/speeds?
Figure 1: dynamic chemistry gives plastics a better mechanical strength, thermal resistance and resistance to solvents without compromising their easy implementation and recyclability
This challenge has just been met by researchers from the MMC lab (Matière Molle & Chimie): they’ve discovered a metathesis reaction (Figure 2) that allows atoms to exchange between molecules without breaking existing chemical links. As this reaction is particularly efficient, it becomes possible to turn any polymer with a carbon skeleton (75% of plastics) into a vitrimer. Remarkably, the reaction does not need a catalyst, which gives a serious economical and ecological advantage.
It then becomes very simple to adjust the composition and implementation conditions in order to use plastics transformation methods (injection, molding, blowing, extrusion & thermoforming). On a side note, vitrimers created from polystyrenes, acrylates or polyethylenes have better mechanical strength and thermal resistance than their feedstock without compromising the repair, welding or recycling capacities.
Figure 2: example of a metathesis reaction
Another fact largely unknown is that almost 25% of cracks and breakings of plastic or composite parts can be attributed to the contact with a liquid. Vitrimers are much less susceptible to those attacks: they would thus make an excellent alternative for protective coatings, conduits, glues, organic glass, medical devices or some auto parts (Figure 3).
Figure 3: a polyethylene sample immersed in soapy water cracks after 30h while a polyethylene vitrimer can resists more than 350h
Surprisingly, the metathesis reaction can be effective on surfaces. A strong adhesion between vitrimers made from highly incompatible different plastics can be achieved: this offers promising prospects in many different fields from packaging to tyres.
Regarding plastics recycling, it currently needs the implementation of waste sorting depending on the plastic nature.
The metathesis reaction would allow re-using plastics without needing any waste sorting, or even getting vitrimer alloys with enhanced properties compared to each constituent element (stiffness, shock and tear resistance, solvent impermeability)
Stéphane, Consultant, Leyton France