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Surface Treatment of Natural Fibers (Chemical Treatment)
Published in Shishir Sinha, G. L. Devnani, Natural Fiber Composites, 2022
Isocyanate is the organic compound with the general formula R−N=C=O, where R is the alkyl group. When isocyanate is treated with a hydroxyl group, a urethane linkage is formed. If di-isocyanate is treated with a compound containing two or more hydroxyl groups, polyurethane is formed (Xue Li et al., 2007). It acts as a coupling agent for surface modification of fiber. It also provides better bonding with the matrix to improve composite properties (Siakeng et al., 2019). The treatment of natural fiber with isocyanate reduces the hydrophilic nature of the fibers and enhances adhesion between fiber and the matrix phase (Xue Li et al., 2007). The reaction between the fiber and isocyanate coupling agent is shown below:
Organic matrices
Published in A.R. Bunsell, S. Joannès, A. Thionnet, Fundamentals of Fibre Reinforced Composite Materials, 2021
R. Bunsell, S. Joannes, A. Thionnet
Polyurethane are polymers which are made by a reaction of an organic isocyanate with a polyol, such as an alcohol, which is any compound containing multiple hydroxyl groups. The general formula for an isocyanate is R–N=C=O in which a reactive, usually large aromatic group. The most widely used isocyanates are toluene diisocyanate (TDI) CH3C6H3(NCO)2 and methylene diphenyl isocyanate (MDI) OCNC6H4CH2C6H4NCO. Isocyanates contain the extremely reactive group – N=C=O. It will react with any hydroxy group –OH and can be combined with many different polymers so that a large range of possibilities exist. It should be noted that, because of the high reactivity of this group, it poses a considerable health risk as inhalation will cause a reaction with the – OH groups in the lung tissue, causing a respiratory illness called isocyanate asthma. Damage can be very debilitating and can be fatal. One variation of isocyanate chemistry was the development of phosgene poison gas which was used in the First World War. However, once made, the resins which are produced have the isocyanate combined with other reactive agents so that after curing they pose no danger. For example, they can be combined with epoxy systems to give resin systems which have continuous in-service temperature capabilities of 200°C.
Polymeric Foams
Published in Kathleen Hess-Kosa, Building Materials, 2017
As for probable emissions from other PU foam, free isocyanates are likely to be residual in the end products. Isocyanates include toluene diisocyanate, (TDI), methylene diphenyl diisocyanate (MDI), and hexamethylene diisocyanate (HDI). As they have no odor, isocyanate exposures offer no warning—other than symptoms. The symptoms of exposure to MDI are eye, nose, and upper respiratory irritation, and MDI can cause dermal sensitization. Although less frequently used in the manufacture of PU foams, TDI symptoms are more serious than that of MDI. TDI is a strong irritant of the eyes, mucous membranes, and skin, and it is a potent respiratory tract sensitizer. HDI symptoms are similar but to a lesser degree to that of TDI.
Investigation on the use of a novel chemical bitumen additive with reclaimed asphalt and at lower mix production and construction temperatures: a case study
Published in Road Materials and Pavement Design, 2021
Nicolás Héctor Carreño Gómez, Markus Oeser
Although concerns about the health risks associated with isocyanates have largely focused on respiratory problems, it has been reported that exposure to isocyanates can cause occupational allergic contact dermatitis, skin sensitisation occurring from a single accidental exposure (Estander et al., 1992; Goossens et al., 2002). This aspect can explain why isocyanate chemistry has not been deeply investigated in asphalt for road pavement. Both the respiratory tract and the skin are potential routes of isocyanate exposure, as this one can occur in the form of a liquid, vapour, or aerosol, depending on the isocyanate species and the industrial process employed (Fleischel et al., 2009). The isocyanate mixture studied in this paper has been designed to overcome such issues when blended and reacted appropriately with bitumen. This reactive isocyanate-modified bitumen solution has been developed in a way to comply with the actual European standard for isocyanate exposure limit (5 ppb) in order to limit the concerns about health risk associated to this particular chemistry.
Costs of isocyanate-related occupational diseases: A systematic review
Published in Journal of Occupational and Environmental Hygiene, 2019
Kristine Kreis, Ines Aumann-Suslin, Andreas Lüdeke, Uta Wegewitz, Jan Zeidler, J.-Matthias Graf von der Schulenburg
As an internationally recognized causative agent of occupational diseases, isocyanates belong to the category of highly reactive, low molecular weight chemicals. They can be classified as mono-, di-, and polyisocyanates depending on the number of isocyanate-groups. The most common type of isocyanates in workplaces are diisocyanates, which contain two isocyanate groups (NCO) and oligomers/polyisocyanates derived thereof. The predominant use of isocyanates (>90%) is in the direct manufacture of polyurethane plastic materials (PUs, also PURs), where diisocyanates are reacted with polyols and/or other nucleophiles like polyamines. Diisocyanates are also utilized in preparations, with the final reaction occurring at a later stage (coatings, adhesives, sealants and binders). In the last 50 years, isocyanates have been increasingly used in the industrial production and application of different kinds of polyurethane foams, flexible and rigid polyurethanes, polyurethane fibers, coatings, elastomers, sealants, and adhesives. Areas of application include inter alia, the automotive industry, autobody repair, construction insulation materials, and metal treatment.[5]
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]