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Eco-Friendly Synthesis of Waterborne Polyurethanes
Published in Ram K. Gupta, Ajay Kumar Mishra, Eco-Friendly Waterborne Polyurethanes, 2022
Pavan M. Paraskar, Vinod M. Hatkar, Ravindra D. Kulkarni
Diisocyanates are one of the essential constituents of PU chemistry. The –N=C=O functional group-containing diisocyanate is a highly reactive compound that plays a vital role in forming the urethane linkage of PU. Usually, based on their chemical constitution, diisocyanates are divided into two types: aliphatic and aromatic. Isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI) are the most commonly used aliphatic diisocyanates. In contrast, methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) are the most commonly used aromatic diisocyanates. High molecular weight di/polyisocyanate adducts like HDI-biuret and HDI isocyanurate have been used to prepare special PUs. This type of isocyanate is beneficial for low volatile applications, such as paints, coatings, adhesives, etc. Thus, as per the application, both types of diisocyanates are employed to modify PUs with required properties [27]. Due to the problems of toxicity and hazards at work arising from the use of these existing diisocyanates, there have been alternative pathways to synthesize isocyanates from renewable raw material, e.g., sugar-based pentamethylene diisocyanate (PDI) [28], 1,7-heptamethylene diisocyanate (HPMDI), DDI (dimer acid-based diisocyanate), ethyl or methyl ester of L-LDI (l-lysine diisocyanate), and cashew nut shell liquid-based diisocyanates [1], etc. Various bio-based isocyanates used for waterborne PUs are shown in Table 4.2.
Isocyanates in Australia: Current exposure to an old hazard
Published in Journal of Occupational and Environmental Hygiene, 2018
Sonia El-Zaemey, Deborah Glass, Lin Fritschi, Ellie Darcey, Renee Carey, Tim Driscoll, Michael Abramson, Si Si, Geza Benke, Alison Reid
Isocyanates are used in a broad range of manufacturing processes and products that are used in domestic and industrial settings.[4] The most common forms of isocyanates are hexamethylene diisocyanates (HDI), isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), and methylene diphenyl diiosocyanate (MDI), which are mostly used to produce paints, coating, flexible foams, and rigid foams, respectively.[5] In a large proportion of product formulations, many diisocyanate monomers have been replaced by their oligomers, which have lower vapor pressure to reduce inhalation exposure.[6] The 8-hr occupational exposure limit for isocyanates in Australia should not exceed 0.02 mg/m3.[7]