Polyurethanes isocyanate-based coatings

STRUCTURE 4.2 Example of polyfunctional cyclic carbonate-tricyclic carbonate on the base of propoxylated glycerin. (Reprinted from O. Figovsky and L. Shapovalov, Cyclocarbonate-Based Polymers Including Non-Isocyanate Polyurethane Adhesives and Coatings, in Encyclopedia of Surface and Colloid Science, ed. P. Somasundaran, vol. 3, 1633-1653. New York Taylor Francis, 2006. With permission.)... 

O. Figovsky and L. Shapovalov, Cyclocarbonate-Based Polymers Including Non-Isocyanate Polyurethane Adhesives and Coatings, in Encyclopedia of Surface and Colloid Science, ed. 

Major polyurethane products today include cellular materials such as water-blown flexible foams or fluorocarbon-blown rigid foams, elastomers, coatings, and elastic fibers, which are described subsequently. Closely related to polyurethanes is an isocyanate-based product called isocyanurate foam. 

Aircraft coatings normally consist of two coats. The topcoat used for civil aircraft is a high-gloss two-pack polyurethane product, cured with aliphatic isocyanates. Single-coat systems based on thermoplastic acrylic resins have been used for military aircraft, but are being replaced by polyurethane topcoats [11.10]. 

Example 9. Two-Component Waterborne Polyurethane Coating. This example utilizes the PUD from Example 8 in a two-component, waterborne coating formulation. An HDI-based, water-dispersible isocyanate is also prepared. 

Isosorbide polyurethanes, especially those based on aliphatic isocyanates, may be useful in the same applications as conventional polyurethanes i.e. thermoplastics, coatings, and foams. In fact, excellent rigid foams have been obtained from P(I-MDI)(5). Isosorbide has a low melting point of 61°C and it is suitable for use in reactive injection molding processes alone or in the form of a mixture with other conventional diols. In addition, its polymers may also find specific applications due to the anticipated high complexation ability of the two tetrahydrofuran rings in their isosorbide units. 

The prepolymer used for this study was an MDI-based preparation (Suprasec 1002) from Huntsman PU, Brussels, Belgium. Immobilization of the enzyme was accomplished by coating the inside structure of a reticulated foam with an acetone solution of a hydrophilic polyurethane prepolymer. A 45-pore/in. reticulated foam cut into sheets 0.25 in. thick was used. The coated reticulated foam was immersed in a catalase solution (5 pg/ml) at 4°C and left in the solution for 1 hour to ensure a complete solution. It is known that both the water and some functionality in the catalase react with the isocyanate groups to cause polymerization (the water-isocyanate reaction) and chain termination (the catalase reaction). Controlling the relative concentrations and temperature permits control of the physical properties of the composite and the ability of the foam to function as an enzyme. 

Linear polyurethane is used for coating paper. The abovementioned diols and polyethers based on ethylene oxide and propylene oxide with free hydroxyl groups, adipic acid, phthalic acid and the isocyanates indicated in c) may be used as starting materials. 

By the year 1956, more than 100 cases of illnesses and four cases of death due to poisoning by TDI were reported (Baader, 1956). In view of the increased use of isocyanates, the National Institute of Occupational Safety and Health, USA, projected as early as 1978 that approximately 50,000 to 100,000 workers would be exposed to these chemicals within 2 years (NIOSH, 1978) this estimate was based on exposure at the workplace in polyurethane production, upholstery work, wire coating, and spray painting in the absence of any accidental spill (Axford et al, 1976 Editorial, 1966 Fuchs and Valade, 1951 Hill, 1970 Williamson, 1965). 

Pitch-polyurethane coatings are two-component materials containing polyol as the base resin and an isocyanate curing agent. They cure satisfactorily at temperatures as low as 0°C (BSC, undated). 

Aqueous polyurethane systems have been developed which are considered to be safe from a health and safety point of view. They do not contain harmful isocyanates. The major application of this type of system is for coatings and floor finishes. Aqueous systems are based on single-pack, clear-water-based polyurethane. Two-pack and pigmented systems are also available. 

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