Why is Polypropylene (PP) So Troublesome to Recycle?

Polypropylene (PP) is without doubt one of the most typical plastic varieties on the earth. Within the U.S., PP plastic is marked with the quantity 5 plastic resin identification code on the underside of packaging. It’s the second most manufactured plastic after polyethylene, composing round 17% of annual international plastic manufacturing. As a food-safe plastic with excessive flexibility and puncture resistance, PP has intensive functions in snack and medicine packaging in addition to manufacturing.  

Regardless of the various functions and demand for PP, its recycling price is extremely low. At simply 3%, PP’s recycling price is dwarfed by that of high-density polyethylene (10%) and polyethylene terephthalate (15%). 

Acronym checklist: PET – Polyethylene Terephthalate, HDPE – Excessive Density Polyethylene, PVC – Polyvinyl Chloride, LDPE – Low Density Polyethylene, PP – Polypropylene, and PS – Polystyrene. Sort 7 excluded resulting from problem in tracing and excessive variation in class of plastic. 

PP recycling presents a number of challenges that the incumbent plastic recycling expertise (mechanical recycling) is solely not ready to deal with. As PP is delicate to excessive warmth, it typically loses important chemical integrity, power, and suppleness in the course of the extrusion strategy of mechanical recycling. Past this, recycled PP typically has a substandard melt-flow price (MFR), molecular weight, and thermal stability in comparison with virgin PP, resulting from contamination or degradation in the course of the recycling course of.  

Because of the excessive regulatory requirements for food-safe plastic, this recycled PP is commonly unsuited for many market functions. Some corporations add virgin PP or components to enhance the standard of recycled plastic, however these options don’t reverse the fabric degradation of PP. Inside 2-3 recycling cycles, the unique PP could be unusable in practically all functions. This isn’t a round useful resource neither is it true recycling. 

Past chemical degradation, the economics of recycling PP stay daunting. The value of recycled PP is round 80% larger than virgin PP. Major value drivers right here embody the intensive testing/components wanted for food-grade certification, non-existent economies of scale for PP recycling, and costly sortation.  With corporations unwilling to pay such a excessive premium, PP recycling has but to learn from massive, devoted recycling services and their economies of scale. Whereas sortation is bettering throughout plastic varieties, PP’s poor efficiency in mechanical recycling has stored it from being a spotlight of waste sortation innovators. A real hen or egg situation: for PP to obtain improved feedstocks, novel recycling applied sciences should show profitability.  

Fortunately, solvent dissolution goals to fill that precise position for PP and several other different plastics.  

Innovation of Curiosity: Purecycle 

Purecycle is an revolutionary American start-up using supercritical butane, a brand new class of solvent capitalizing on properties of each liquids and gasses to enhance plastic recycling. Solvent dissolution takes a number of kinds however removes goal substances from a selected polymer.  

Purecycle licensed Proctor & Gamble’s expertise eradicating impurities from PP. Whereas Proctor & Gamble stay lively within the solvent dissolution house, it’s in a analysis capability as they lately inked a joint settlement with Dow Chemical substances to discover polyethylene recycling utilizing solvents. Purecycle has gone on to ascertain the U.S.’ first commercial-scale solvent dissolution recycling plant in Ohio. With ongoing development on a second, bigger plant in Georgia to course of a billion kilos of plastic per 12 months, Purecycle goals to consolidate their maintain over America’s recycled PP output. 

With Europe’s extra strong plastic recycling infrastructure, it’s not shocking to see business ventures in solvent dissolution from APK (lately acquired by LyondellBasell) and Saperatec. With out the strong European sortation networks, Purecycle aggregated options to convey their supercritical butane solvent expertise to business scale. They recognized and expanded low cost, low competitors, typically contaminated PP feedstock to fulfill excessive demand for recycled PP. Supercritical butane grew to become the right match for this uncared for feedstock. Capable of maximize diffusion charges because of a low viscosity, supercritical butane is tuned with temperature and strain to selectively take away contaminants from PP.  

Whereas they continue to be costly from a capital value perspective, supercritical fluids are poised to essentially redefine perceptions on plastic recycling. Educational analysis has explored the usage of supercritical water in depolymerization of polyethylene terephthalate or supercritical CO2 as a delamination expertise for multilayer plastic. 

Solvent dissolution gives one of the best path for commercialized plastic recycling that achieves true useful resource circularity for PP. Enhancing on the incompatibility with mechanical recycling, Purecycle gives an answer able to recycling contaminated and combined variations of PP whereas retaining the plastic’s chemical purity for all business functions virgin PP is used for. Already commercialized within the U.S., the corporate is now exploring patent licensing agreements with a few of Asia and Europe’s greatest chemical gamers together with Mitsui, SK, and TotalEnergies.