The Foam of Polyurethane
Polyurethanes (PU) are part of a broad class of polymers that are used, among many other things, to make rigid foams for insulation, flexible foams for footwear, spandex and artificial leather for apparel and furniture, and in various coatings such as deck varnish.
Polyurethanes are most commonly made by reacting poly alcohols (polyols) with isocyanates. Both polyols and isocyanates are usually derived from petroleum. Of these two, isocyanates are the more concerning class - they can be potent sensitizers, and are made using a highly toxic chemical called phosgene, which has also been used in the past as a nerve agent in chemical weapons.
To make polyurethanes more sustainable we could use renewable feedstocks, use alternative chemistry to phosgene, and make them compostable.
Biobased polyols have been available in the past five to ten years, are often derived from plant or algae oils, and can account for 40% to 70% of the final polyurethane by weight. Switching to renewable polyols improves the carbon footprint of the resulting PU, but still relies on the isocyanate chemistry and often costs more. Several companies including Checkerspot, Elevance, and Covestro have been leading the development of biobased polyol chemistry.
Algenesis, is a San Diego-based company that is working to make a biobased and degradable PU. The company claims to make biodegradable polyurethane, using a mixture of biobased polyols and isocyanates that biodegrade under some environmental conditions. Algenesis is also working on a way to make the biobased isocyanates using a less toxic alternative to the phosgene chemistry.
Algreen and Matereal are making biobased PU using carbonates and amines as alternative chemical classes to polyols and isocyanates. These companies are identifying new feedstocks and formulations that make a wider range of PU materials possible. Specifically making foams from isocyanate-free PU has been difficult. It will be exciting to see what all these young companies develop.
PVC or Not So Lucky Number 3
The derailment of a train carrying vinyl chloride monomer in East Palestine, Ohio in February was a reminder of the impact the production of certain plastics can have on human health and the natural world. We know from subsequent reporting that releases of vinyl chloride monomer can happen at polyvinyl chloride (PVC) production facilities, for example in 2021, over 400,000 pounds of vinyl chloride were released.
Best known for the ubiquitous white pipes, PVC is among the most hazardous compared to other plastics. PVC is made of vinyl chloride, a known carcinogen, neurotoxin, and reproductive toxin. PVC is often made with antimony catalysts, and relies on phthalate plasticizers and toxic UV stabilizers. PVC has one of the longest rates of environmental persistence. PVC has the potential to release toxic byproducts when heated or burned and can interfere with the recycling of other plastics.
Plastics are part of our modern way of life, however, we should focus on reducing the use of some of the most harmful ones, such as PVC.
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