PVC is versatile in its properties and can be described as durable, resistant, light and insulating. In addition, these properties can be manipulated by adding additives, such as plasticisers. These plasticisers make the polymer softer and more flexible, and thus make it suitable for additional applications. In contrast to normal “hard” PVC, this “soft” PVC is suitable for applications such as vinyl flooring, flexible hoses and artificial leather (fig. 1). PVC is the third most widely used plastic worldwide and has a production volume of 5 million tonnes in Europe.
In the Netherlands, the objective is to handle plastics with greater responsibility. In the Netherlands alone, for example, 64 kt of PVC waste is produced. When one speaks of the recycling of the plastic PVC, one mainly speaks of the recycling of the hard form. Unfortunately, this is still impossible for the soft form of PVC due to the presence of the aforementioned plasticisers. Unfortunately, some of these plasticisers are harmful to health. The majority of the global market for plasticisers is used in the production of soft PVC. This soft PVC can then contain up to 60% plasticisers, making it suitable for numerous applications such as vinyl flooring, flexible hoses and artificial leather. These plasticisers often come in the form of phthalates (fig. 2). Until recently, the phthalate DEHP was the most commonly used plasticiser in PVC, but in 2008 it was put on the SVHC list as a substance of very high concern. This resulted in a general European ban on the use of DEHP in 2015.
Unfortunately, this substance, as well as countless other so-called Legacy Substances including even more phthalates, is still present in old PVC that people would like to recycle. Ecoras is investigating new recycling methods together with TRH Recycling B.V., Deepgrooves B.V. and the University of Groningen. It is important for all parties to find an alternative to the incineration of PVC waste, because the dioxins and hydrochloric acid vapours released during this process are very harmful to health and the environment. In addition, many valuable raw materials are lost. There is also a financial interest because the cost of disposing of PVC waste using current methods is at least five times higher than the original production cost of the PVC. In early 2021, the SIA governing body will have approved the grant application required for the future development of this research project.
A method currently under investigation in the soft PVC recycling process is extraction of plasticisers by means of supercritical CO2. The extraction of these plasticisers is made possible by exposing the soft PVC to supercritical CO2. This supercritical phase is achieved by putting the CO2 under high pressure (>74 bar) and to high temperature (>31˚C). In this phase, the CO2 behaves as a gas and a liquid at the same time, so that the properties of both phases can be brought about. This makes it possible for the CO2, as a gas, to reach deep into small spaces, while as a liquid it can act as a solvent. When these two functions are combined, the removal of the phatalate plasticizers can be efficiently achieved. In addition, CO2 is interesting as a solvent, since it is predominantly more environmentally responsible than other solvents.