Soil Compostability of Ester-based Thiol-ene Photopolymer Networks

Photopolymer materials are used in many commodity applications, including adhesives, overprint varnishes, packaging materials, and disposable medical devices such as contact lenses. The vast majority of photopolymer materials directly contribute to landfill waste, as they are not recyclable or capable of biodegradation. To address this problem, we design a series of photopolymers leveraging thiol-ene click chemistry to incorporate ester groups into the backbone, including the ones found in biodegradable polymers, such as oligo-caprolactone and adipate. We investigated the degradability of these photopolymer networks and found that over 28 days, thiol-ene photopolymers containing oligo-caprolactone groups were susceptible to 55-83% biodegradation through biochemical oxygen demand (BOD) testing with activated sludge. We were able to completely disintegrate these polymers in compost at 58 degrees C and 76 +/- 1% humidity through soil disintegration testing adapted from international standards (e.g., ISO 14851, ISO 20200, and OECD 301D). Our work demonstrates for the first time that ester-based thiol-ene photopolymers are biodegradable alternative materials for photopolymer applications.