Depolymerisation: back to basics

Regained optical quality for PMMA

PMMA (polymethylmethacrylate), better known by its commercial names Altuglas® and Plexiglas®, is a thermoplastic polymer known for its transparency. It is used in a wide variety of applications, from optical instruments to car taillights, countless decorative objects, illuminated signs, POS displays, parapets and LCD flat screens.
LCD screens are an innovative technology that has been a dazzling success for more than ten years. Although they have a satisfactory lifespan, users do not keep them for long because they like to replace their equipment quite frequently. Thousands of screens are scrapped every year. What can be done with them? The idea of chemically recycling the PMMA from these screens is not new. Until recently, this was done by placing them on a bed of molten metal. The PMMA then returns to its original monomer. Although this technique is effective, it does have one limitation: it cannot guarantee that a polymer offering very high optical quality will be obtained, which prevents it from being re-used to manufacture new LCD screens.

Liquid crystal displays are a boon for our daily lives. Created using PMMA, they were until recently very complicated to recycle. The MMAtwo process, although still at the research stage, looks promising in this regard, especially as it could be relatively easy to duplicate.

 Faced with this observation, a European consortium was created in 2018. Christened MMAtwo, it brings together 13 partners from 6 different countries, including Arkema, one of the world's leading PMMA manufacturers, as well as recyclers, processors and even a university. The aim is to regenerate a high-purity monomer from all types of waste: electrical and electronic products, car taillights, noise barriers, agricultural greenhouses and screens.
Two years after the launch of MMAtwo, the first results are already in. Although still at the development stage, the process is based around an extruder that is heated to high temperatures (around 400°C). The monomer obtained is more than 99% pure, a quality almost equivalent to that of a virgin material.
The results are very encouraging, and the consortium is now seeking to raise awareness throughout the industry in order to better collect end-of-life PMMA and, in a few years' time, to be able to supply several recycling units throughout Europe.

PET: the best in mechanical and chemical recycling

Recycling PET (polyethylene terephthalate) is often the first example that comes to mind when talking about polymer recycling. Its emblematic proponent: the water or soda bottle. To date, it is the only polymer with European approval for mechanical recycling for use in food packaging and it is by far the most recycled. This is satisfactory but not enough because, like all polymers and most materials, PET is not infinitely mechanically recyclable. In addition, some PET products (e.g. opaque or highly coloured trays and bottles) create issues for mechanical recycling processes.

PET is one of the most recyclable polymers. New depolymerisation processes allow it to return to its original monomer state. All beverage manufacturers are keeping a close eye on technological advances so that they will soon be able to offer bottles made from recycled PET.

Hence the idea of recycling it back to the basic monomer through the chemical process of depolymerisation. Dutch company Ioniqa has achieved this by using a reagent based on water and glycol. It has mainly succeeded in recycling coloured bottles that mechanical recycling cannot process because of the presence of dyes. At Ioniqa, PET is first depolymerised after being heated and then decolourised using a magnetic system (a proprietary technology).

From an economic standpoint, the challenge was to make the process competitive, based on the principle that it should not be more costly than manufacturing virgin PET, while emitting less CO2. Many beverage manufacturers, including major ones such as Coca-Cola, have already approached the Dutch company to produce bottles from recycled PET.

Another highly original solution is that developed by French company Carbios, which uses enzymatic depolymerisation to recycle PET. This involves soaking the polymer in a bath of enzymes that break the polymer chains. A promising solution that continues to evolve, since Carbios has managed to considerably improve the depolymerisation time. Its technology is now capable of depolymerising 90% of a volume of PET in about ten hours, whereas little time ago it took several weeks to degrade 1%!

A royal road for polystyrene

Many industries, such as the automotive, electronics, healthcare, construction and packaging industries, use styrenics, including polystyrene, for their versatility. They are also prime candidates for depolymerisation.

Ineos Styrolution, the world leader in styrenics, has published the final results of its three-year ResolVe research project (2017-2020) funded by the German Federal Ministry of Education and Research (BMBF) aimed at exploring the recycling of polystyrene by depolymerisation.

Led by Ineos Styrolution and the research company Neue Materialien Bayreuth, in collaboration with the University of Aachen, the report concludes that depolymerisation is a very appropriate recycling solution for polystyrene which promises to produce recycled polystyrene that meets food contact standards. The project proves the feasibility of converting post-consumer waste into a valuable raw material, thus creating the possibility of a circular economy for polystyrene.

Polystyrene is also a prime candidate for depolymerisation. This plastic, once recycled, could find many applications, particularly in the automotive industry which is always seeking to increase the amount of recycled plastics in its production processes.