Two teams searched for safer alternatives to two very common and effective, but worrisome, chemicals used in two very different manufacturing sectors: apparel (footwear) and additive manufacturing (3D printing).
The first target chemical, dimethylformamide (DMF) is used extensively as a solvent and “texturizer” in the manufacture of polyurethane-based synthetic leather used in sport shoes and partner Nike wished to explore ways to reduce or eliminate the chemical from its production line.
DMF is a known liver toxicant and is associated with several other severe health outcomes. DMF can be easily absorbed by the dermal and respiratory systems, whereafter the liver is the primary target organ. Overall, DMF is a high or moderate hazard for the endpoints of carcinogenicity and mutagenicity, developmental and reproductive toxicity, endocrine activity, neurotoxicity, and skin and eye irritation. It is also a very effective solvent, however, and is used extensively because of its miscibility with water and operational range of temperature and pressure among other factors.
The DMF team focused on three strategies for intervention: drop-in solvent replacement, production process change and functional material change, and were able to recommend five drop-in replacements, suggest a strategy toward water-borne polyurethane (PU) dispersions, and one toward the use of mycelium-based material substitutions.
The second target chemical was actually a group of chemicals, acrylates, some of which are used as very effective cross-linkers in the polymerization of liquid resins used in stereolithography (SLA) printing. When UV light is shown on reactive monomers or oligomers in the liquid resins, they bond together to form a solid object and a typical SLA printer will build up a solid object, layer by layer, using this chemical reaction.
Acrylates and methacrylates present some human and environmental health problems, however. In use in the baseline study resin these chemicals were shown to be skin and eye irritants, skin sensitizers and aquatic toxicants.
The SLA team identified five strategies to reduce or replace (meth)acrylates in SLA printing resins: the employment of functionalized biopolymers, the use of click chemistry, pH-induced photo-polymerization, the photo-polymerization of unmodified proteins, and novel encapsulation techniques.
For each strategy, the team proposed a photopolymerization process and gave example materials for use in resin formulas. They also considered additional steps that could be taken to enhance the properties of objects printed with their proposed strategies; for instance, using post-print curing or additives to enhance strength. Finally, they provided an overview of how each strategy addressed human health and environmental criteria while promising adequate technical performance, and proposed steps that industry leaders could take to further develop these strategies.
Both teams presented to their partners, Nike, Inc. and Region 9 of the US EPA, and the general public on December 10. The presentation videos, slide decks and final reports are below.