Every year, 100 million tonnes of multi-ply plastic waste ends up in a landfill or in an incinerator because it cannot be recycled using conventional methods. American scientists have succeeded in using solvents to separate multilayer plastic and films into the various polymers, which can be reused as raw materials.
Plastic packaging for food and medical goods must meet strict requirements in order to keep humidity, light and oxygen out. Multilayer plastic is the answer, but here comes a recycling problem. Until recently, it was not possible to recycle this type of plastic and foil using conventional methods. This means that the annual production of 100 million tonnes of multi-layer plastic will sooner or later end up in an incinerator or in a landfill.
American engineers were looking for a method to separate the various components of these multi-layer plastics and films and to recycle them back into raw materials for new plastics. They found this with STRAP, or Solvent-Targeted Recovery and Precipitation. Broadly speaking, it comes down to "washing" plastic waste with solvents, based on thermodynamic calculations of the solubility of polymers, in order to arrive at separated polymers. The most common polymers in multi-layer plastics are polyethylene (PE), ethylene vinyl alcohol (EVOH) and polyethylene terephthalate (PET or PETP). These individual polymers can be used to produce new plastic materials.
Specific solvent for specific multilayer plastics
However, the story does not end there. Although most multi-layer plastics and films consist of the three components mentioned above, more complex multi-layer plastics come onto the market, which in turn makes it more difficult to recycle properly. That is why a member of this US team is working on a computer model that will be able "to calculate the solubility of the polymers to be dissolved in mixtures of solvents at different temperatures, thus limiting the number of potential solvents that a polymer could dissolve". Or how the recycling of each type of multi-layer plastic will require a specific (green) solvent.