Tolylene diisocyanate (TDI) refers primarily to two industrially important aromatic diisocyanates: 2,4‑TDI and 2,6‑TDI, typically marketed as mixtures such as TDI 80/20 or 65/35. These isomers are synthesized via phosgenation of 2,4‑ or 2,6‑toluenediamine, following nitration of toluene and reduction to the diamines. TDI is a clear, colorless to pale yellow liquid with a pungent odor and high reactivity due to the two isocyanate groups.
The history of TDI is closely tied to the development of polyurethane chemistry. In 1937, Otto Bayer and collaborators at IG Farben synthesized the first polyurethanes; by the early 1950s, isocyanates such as TDI became commercially available, and flexible polyurethane foam made from TDI and polyols was introduced in 1954. These innovations revolutionized materials for cushioning, insulation, coatings, adhesives, and elastomers ([ACS Publications][1], [Wikipedia][2]).
TDI gained widespread industrial application in flexible foam production, coatings, adhesives, sealants, and elastomers. In foam manufacturing, its reactivity with polyols and water (as a chemical blowing agent) results in low‑density, open‑cell structures used in mattresses, furniture, automotive seating, and packaging. It is also employed in high‑performance coatings and molded elastomers, where control over crosslink density yields materials with specific mechanical and thermal properties.
With increased recognition of occupational hazards, TDI became the focus of health and safety studies. TDI is classified as a respiratory sensitizer; exposure can lead to occupational asthma, dermatitis, and other respiratory disorders. Industrial hygiene research spanning 2005–2020 across North America and Europe showed that most personal air sampling in foam production facilities recorded TDI concentrations below 5 ppb, although occasional exposures above this threshold emphasize the need for respiratory protection ([ResearchGate][3]).
In consumer safety and environmental assessment, the emission and migration of residual TDI from cured flexible foam have been evaluated. A key study measured TDI emissions and migration from consumer foam products using emission cells and surface migration testing. Despite detectable extractable TDI via solvent methods, no TDI was detected in air or migration tests down to extremely low limits (0.002–0.5 ng g–1 foam), suggesting negligible exposure risks from finished products ([ResearchGate][4]).
A separate toxicological assessment quantified health risks associated with exposure to TDI from flexible foam during typical use scenarios such as sleeping on a mattress. By combining emission data with toxicological benchmarks, the calculated margins of safety ranged from 200 (respiratory) to 3 million (irritation), indicating exposure levels well below thresholds of concern for consumers ([PubMed][5]).
TDI remains a cornerstone of the polyurethane industry due to its cost‑effectiveness and versatility in foam and elastomer production. Regulatory and safety controls continue to evolve, focusing on reducing worker exposure, ensuring product curing, and minimizing residual monomer in final products.
References
Arnold S M, et al. (2012) Risk assessment for consumer exposure to toluene diisocyanate derived from polyurethane flexible foam Regul Toxicol Pharmacol 64(3) 504–515 DOI: 10.1016/j.yrtph.2012.07.006
Vangronsveld E, Berckmans S, Spence M (2013) Toluene diisocyanate emission to air and migration to a surface from a flexible polyurethane foam Ann Occup Hyg 57(5) 650–661 DOI: 10.1093/annhyg/mes105
Donchenko A, Aubin S, Gagné S, et al. (2020) Development of a method for quantification of toluene diisocyanate and methylenediphenyl diisocyanate migration from polyurethane foam sample surface to artificial sweat by HPLC‑UV‑MS J Chromatogr B 1142 122027 DOI: 10.1016/j.jchromb.2020.122027
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