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Step-Growth Polymerization
Published in Anil Kumar, Rakesh K. Gupta, Fundamentals of Polymer Engineering, 2018
In aromatic diisocyanates, such as toluene diisocyanate (TDI), one isocyanate group can modify the activity of the other, and the activity of both groups can depend on the other substituents of the aromatic ring. For a mixture of 2,4, and 2,6 isomers of TDI (industrially, it is difficult to separate the two), 12 reactions with primary and secondary 1OH groups of the polyols have been identified. The rate constants for these reactions have been measured experimentally and are summarized in Table 3.4. Significant differences can be observed in the reactivity of the two –NCO groups; the equal reactivity hypothesis is definitely not followed. There have been several fundamental studies to model the unequal reactivity of functional groups in urethane formation. It has been shown that such reactivity has considerable influence on the polymer formed.
Health and Safety
Published in B. T. Åström, Manufacturing of Polymer Composites, 2018
PURs are the result of a reaction between an isocyanate and a polyol, where the latter has a low level of toxicity. In contrast, most isocyanates and particularly the two most common ones, toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI), are highly toxic and irritating; TDI is a suspected carcinogen. The main danger with isocyanates is inhalation and very low concentrations may cause dryness of throat, tightness of chest, and headache. Repeated and sometimes even a single exposure may lead to sensitization and extremely low concentrations may cause reactions following sensitization. TDI may give rise to cross-sensitization where individuals not only become sensitive to extremely low concentrations of TDI, but also to smells such as perfume, cigarette smoke, automobile exhaust, cold air, etc. Poor warning properties and delayed symptoms make isocyanates particularly deceptive. Although both TDI and MDI have characteristic smells their odor thresholds, 0.1-0.4 ppm and 0.4 ppm respectively, are much higher than concentrations that may cause sensitization. Symptoms from inhalation of isocyanates may in some cases be delayed for several hours, thus easily being mistaken for reaction to something else. Isocyanates are also irritants to skin and may cause permanent eye damage upon direct contact. Isocyanates should clearly be handled with great care using PPE [1,4].
Basics of toxicology
Published in Chris Winder, Neill Stacey, Occupational Toxicology, 2004
There are also specific types of effects that require some attention. Allergic reactions are not uncommon and are of concern with workplace chemicals such as toluene diisocyanate (TDI). Here one individual may become sensitive to TDI, reacting to very low levels, while a workmate remains unaffected. Hypersensitivity or idiosyncratic responses are those seen in particular individuals and are related to some underlying metabolic abnormality. They occur at exposure levels well below those at which the ‘normal’ population would respond. The term is often used to account for otherwise inexplicable observations in particular people. Carcinogenic, genotoxic and developmental effects are specific types of effects that are dealt with in separate chapters.
On site comparison of the OSHA 42, Asset EZ4-NCO, Iso-Chek, DAN and CIP10 methods for measuring toluene diisocyanate (TDI) at a polyurethane foam factory
Published in Journal of Occupational and Environmental Hygiene, 2020
Simon Aubin, El Mekki Hamdi, Audrey Joly, Philippe Sarazin, Jacques Lesage, Livain Breau, Mark Spence, Sébastien Gagné
Toluene diisocyanate (2,4 and 2,6 isomers, TDI) is one of the most commercially produced diisocyanates and a widely used monomer in the manufacture of polyurethane foam (PUF) used in everyday products such as mattresses, upholstery, etc. Like many other isocyanates, TDI is a fast reacting molecule and is recognized as a respiratory sensitizer which can cause occupational asthma (Banks et al. 1986; Mapp et al. 1988; Musk et al. 1988; Vandenplas et al. 1992; Vandenplas et al. 1993; Mapp et al. 1999). Regulatory bodies around the world have set their occupational exposure limits (OELs) to 5 ppb for the diisocyanate monomers (Occupational Safety and Health Administration (OSHA) 1992; National Institute for Occupational Safety and Health (NIOSH) 1996; Swedish National Board of Occupational Safety and Health (SNBOSH) 2000; Quebec (Province) 2014), whereas specific countries such as Australia, Finland, Ireland, and UK have OELs based on the determination of total reactive isocyanate group (TRIG) (Allport et al. 2003; mHealth and Safety Laboratory (HSL) 2014), which is widely accepted as the best approach to protect workers’ health and prevent occupational illness from all forms of isocyanates, including oligomers (Bello et al. 2004). In 2016, the American Conference of Governmental Industrial Hygienists (ACGIH®) recommended a threshold-limit value of 1 ppb based on asthma, pulmonary function and eye irritation (ACGIH 2016). Due to the high reactivity and low limit value of diisocyanates, exposure evaluation has been challenging for industrial hygienists and laboratories.
The future of isosorbide as a fundamental constituent for polycarbonates and polyurethanes
Published in Green Chemistry Letters and Reviews, 2021
Olga Gómez-de-Miranda-Jiménez-de-Aberasturi, Ander Centeno-Pedrazo, Soraya Prieto Fernández, Raquel Rodriguez Alonso, Sandra Medel, Jose María Cuevas, Luciano G. Monsegue, Stefaan De Wildeman, Elena Benedetti, Daniela Klein, Hartmut Henneken, José R. Ochoa-Gómez
Diisocyanates are toxic and hazardous for human health, in special the free species present in the ambient during the polyurethane production process (47). The isosorbide rigid structure opens the possibility for a safe substitution of toxic diisocyanates such as toluene diisocyanate (TDI) or methylene diphenyl diisocyanate (MDI).