(154ae) Recovery of Virgin-like Polypropylene from Mixed Plastic Wastes

Polypropylene (PP) is the most widely produced and used polymer in the world but has an exceptionally poor recycling rate of only about 1%. PP and other polyolefins (i.e., various grades of polyethylene (PE)) are often retrieved together as mixture in a “float” fraction during commercial plastic waste recycling. The recovery of high purity PP from these (and other) mixed plastic streams, is the primary bottleneck that has prevented the recycle and circular economy of PP. In this paper, we present a sustainable approach to selectively dissolve and recover PP from mixed plastic wastes using waste cooking oils or other triglycerides. These “green solvents” are biodegradable, non-toxic, and bio-sourced. Of all the major polymers tested in our study, PP alone was soluble in these solvents while other plastics, including PE, remain insoluble. This exceptional attribute of the triglyceride solvents facilitates the selective recovery of virgin-like PP from virtually any mixed plastic waste. The dissolved PP can subsequently be easily re-precipitated with an anti-solvent. An additional advantage of this unique PP-selective dissolution-precipitation approach is that fillers and pigments, commonly present in commercial PP, can also be separated from the polymer. Finally, the triglyceride solvents can be recovered and reused multiple times without loss in performance.

We have demonstrated high yield (>95%) recovery of high purity, pigment/filler-free PP from a variety of feedstocks, including floats from commercial automotive waste, post-consumer polyolefin waste (i.e. takeout food containers), commercial PET recycling, discarded surgical masks, and multilayer flexible food packaging (Lays chips). These results are shown in the graphic below. Polymer properties of the recovered PP from these various feedstocks will be presented to demonstrate the virgin-like quality of our product.