Encapsulated water as a flame retardant

Lab study tests encapsulating water into polystyrene foam show UL-94 V-0 (4 mm) with 30% water content. Gel emulsions were prepared by high-speed mixing of water with styrene, hydrophobic silicon dioxide and cross linkers/initiators (EGDMA, TMPTMA, AIBN). This emulsion was then polymerised at up to 85°C for several hours, resulting in a cross-linked polystyrene containing trapped water in pores, with final water content of 7 – 70% water by weight. With 30% water, peak heat release was reduced by over 55%, smoke was considerably reduced and UL-94 V-0 (4 mm) was achieved. Based on theoretical modelling of water evaporation from polymers, the authors estimate that by coating the polymer and adding salts to the water, a useful life of 8 years could be achieved. pinfa notes that this inadequate for durable products (EcoDesign), even assuming that it is not reduced by e.g. wear or temperature variations. The impacts of including water into polystyrene, on weight, electrical and insulation properties and corrosion risks in case of any water release, are unfortunately not addressed in the article.

“Encapsulated Water Imparts Unprecedented Flame Retardancy to Cross-Linked Polystyrene Foams”, C. Zhang et al., ACS Appl. Mater. Interfaces 2025, 17, 9971−9980, https://doi.org/10.1021/acsami.4c22309