Isocyanate handling

Some of these isocyanates are commercially available in derivatized form, such as biurets and carbodiimides, to provide materials having improved handling or processing characteristics. 

The most overlooked hazard and contaminant is water (99). Water reacts with isocyanates at room temperature to yield both ureas and large quantities of carbon dioxide. The presence of water or moisture can produce a sufficient amount of CO2 to overpressurize and mpture containers. As Httle as 30 mL of water can result in 40 L of carbon dioxide which could result in pressures of up to 300 kPa (40 psi). For these reasons, the use of dry nitrogen atmospheres is recommended during handling. If a plant air system must be used, purification equipment, such as oil traps and drying beds, should be installed between the source and the isocyanate vessel. 

Temperature control is important in the handling and storage of isocyanates. Storage at inappropriate temperatures can cause product discoloration, viscosity increases, and dimerization. Handling personnel should consult the technical data sheets for the recommended storage temperature of the specific isocyanate product. 

Some of the chemicals used in the production of polyurethanes, such as the highly reactive isocyanates and tertiary amine catalysts, must be handled with caution. The other polyurethane ingredients, polyols and surfactants, are relatively inert materials having low toxicity. 

Isocyanates. Isocyanates in general are toxic chemicals and require great care in handling. Oral ingestion of substantial quantities of isocyanates can be tolerated by the human body, but acute symptoms may develop from the inhalation of much smaller amounts. The inhalation of isocyanates presents a ha2ard for the people who work with them as weU as the people who Hve in the proximity of an isocyanate plant. Adequate control of exposure is necessary to achieve a safe working environment. The suppHers Material Safety Data Sheets (MSDS) have to be consulted for the most current information on the safe handling of isocyanates. 

There are a multitude of governmental requirements for the manufacture and handling of isocyanates. The U.S. Environmental Protection Agency (EPA) mandates testing and risk management for TDl and MDl under Toxic Substance Control Administration (TSCA). Annual reports on emissions of both isocyanates are required by the EPA under SARA 313. 

The principal additive shrink-resist treatment uses the polymer Synthappret BAP (Bayer AG) which is a polypropylene oxide polyurethane containing reactive carbamoyl sulfonates (or isocyanate bisulfite adduct groups, —NHCOSO —Na" ). An aqueous solution of this polymer is padded onto woven fabrics, which are immediately dried. Other polymers may be appHed at the same time to modify the handle. 

There is persisting interest in nylon-RIM materials as alternatives to polyurethane-RIM. Advantages of the nylon materials are the better shelf life and lower viscosity of the reaction components, ability to mould thick-walled articles, absence of a need for mould lubrication and the ability to avoid using isocyanates with their associated hazards. The main disadvantages of nylon-RIM are the need to have heated storage tanks and elevated temperature reactions, difficulties in catalyst handling and the high water absorption of the product. Possible markets include exterior car body components and appliance and business machine components. 

Alkyl and aryl isocyanates react with anhydrous hydrogen fluonde to give carbamyl fluorides [J, 55], the more conveniently handled pyridinium poly(hydro-gen fluoride) reagent can also be used, although the yields tend to be poorer [9] (equation 10). 

Isocyanates are quite toxic materials and need careful handling. They affect mainly the respiratory tract causing breathing difficulties, sore throats and, in extreme cases, bronchial spasms. Once they have been allowed to react, for example to form foams, they undergo complete conversion and appear to leave no toxic residues. 

The reaction rates of diisocyanates are strongly influenced by their molecular structure. The reactivity of isocyanate groups is enhanced by adjacent electron-withdrawing substituents. Aromatic rings are very effective electron withdrawing groups, and it is for this reason that the majority of commercial diisocyanates are aromatic. Many of the diisocyanates used commercially consist of mixtures of isomers. Some of the more important commercial diisocyanates are illustrated in Fig. 25.6. Diisocyanates must be handled carefully to avoid exposing workers to their hazardous vapors. 

This handbook provides detailed working procedures for those exposed to isocyanates and other chemicals used in flexible foam manufacture, supplying hazard data for individual chemicals and recommending handling practices. This second edition provides the most up-to date information regarding topics covered in the first edition and also includes a code of practice for the manufacture of polyurethane elastomers using MbOCA. 

Spruce meal and beech blocks were modified by using a mixture of perfluoroalkyl ethanol and MDI. Improved dimensional stability and water repellency were reported (Engonga etal., 1999). In order to avoid the handling problems associated with the use of most isocyanates, the generation of isocyanates within the wood by thermal rearrangement of acyl azides has been studied (Gdrardin etal., 1995) (Figure 4.8). This is potentially a... 

Most of the work reported in the literature employs sodium lactamate salt as catalyst and isocyanate/lactam adducts as initiator. Gabbert and Hedrick [14] preferred to work with acyllactam as the initiator and Grignard salts of caprolactam as the catalyst in view of their ease of handling and fewer side reactions compared with the sodium lactamate and isocyanate system. 

Graham JD. 1980. Simplified sample handling procedure for monitoring industrial isocyanates in air. J Chromatogr Sci 18(8) 384-387. 

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