Poly(ethylene terephthalate) (PET), a widely used engineering thermoplastic for carpet, clothing (fibers), tire cords, soda bottles and other containers, film, automotive, electronics, displays etc., will contribute several billion pounds of waste to landfills this year alone! According to the American Plastics Council, PET packaging was originally used for soft drinks, but packing applications today include other beverages such as water, juice, beer, in addition to other foods such as peanut butter and ketchup and a variety of other household products. The PET market for packaging continues to increase as the popularity of PET-packaged products, such as bottled water, continues to grow. The challenge for PET recycling is to achieve a closed-loop, bottle-to-bottle process, similar to the aluminum industry (65% recycled). The current reuse strategy relies on the reprocessing of PET for use in secondary products such as bulk filled material. The organometallic catalysts used to synthesize PET are based on heavy metals such as antimony, titanium or germanium and remain permanently in the fabricated item. These catalysts are immortal and lead to significant property degradation during secondary melt fabrication process. As a consequence, recovered PET generally ends up in secondary products (carpet, playground equipment, etc.) but ultimately these all find their way to the landfill. In our strategy, which involves a collaboration with a Japanese company, the oil-to-landfill treadmill is circumvented by the use of green organic catalyst that are extremely potent, but with limited lifetime, so that they do not contribute to product degradation during reprocessing. More importantly, processes have been designed by which these new catalyst will allow PET to be chemically broken down into starting or virgin materials. Both strategies provide bottle-to-bottle recycling and would contribute to a world with a constant supply of PET without needing more oil or generating more waste than necessary.
Figure 2. Waste PET is transesterified with methanol (methanolysis) using NHC to DMT and EG starting materials that can be repolymerized using NHC to PET with properties that are invariant with subsequent processing steps.