Waterborne polyurethane applications

Figure 4.10 Synthesis and properties of BPLP and biodegradable BPLP-based biodegradable waterborne polyurethane (BPLP-WPU). (a) Synthesis of BPLP. (b) Structure and application of BPLP-WPU. (c) Emission spectra of BPLP-WPU excited at wavelengths of 335, 365, 380, 425,455, and 485 nm. (d) Particle size distribution of BPLP-WPU dispersed in water.

Lei L, Zhong L, Lin X, Li Y, Xia Z. Synthesis and characterization of waterborne polyurethane dispersions with different chain extenders for potential application in waterborne ink. Chem Eng J 2014 253 518-25. 

An example of the application of blocked polyisocyanate technology is polyurethane powder coatings. These coatings typically consist of a solid, blocked isocyanate and a solid polyester resin, melt blended with pigments and additives, extruded and then pulverized. The block polyisocyanate technique can also be used to formulate waterborne polyurethane coatings [8]. 

For information on the chemistry of two-component waterborne polyurethane technology, the reader should see the review of Wicks et al. [ 16]. A very good review of the effects of two-component waterborne polyurethane formulation on coating properties and application is available from Bassner and Hegedus [11]. 

Lopez A, Degrandi E, Cretan C, Canetta E, Keddie JL, Asua JM. Waterborne polyurethane-acrylic hybrid nanoparticles by miniemulsion polymerization applications in pressure-sensitive adhesives. Langmuir 2011 27 3878-3888. 

Adhesion properties of the waterborne polyurethane adhesives are greatly determined by the polymer, so formulation is generally simple and generally only includes small amounts of a thickener and an emulsifier. When formulating the adhesives, the application conditions (heat activation, contact bond time, pressure) and substrate type must be taken into account. 

C Hegedus, D Lawson, D Lindenmuth. Two component, waterborne polyurethane coatings chemistry and application. Proceedings of Twenty-fifth International Waterborne, High-Solid, and Powder Coatings Symposium, New Orleans, 1998, pp 391-408. 

The coatings industry has developed waterborne paints and coatings that greatly reduce VOC emissions. Some applications include automotive coatings, interior latex paints, and polyurethane coatings (Sherman et al., 1998). 

Paint consists of a mixture of pigments which gives body and colour, and a resin or binder which is the actual film-forming component and acts as a glue to hold the pigment together and stick them to the surface. Binders include synthetic resins such as acrylics, polyurethanes, polyesters and epoxies and can be a combination of resins, e.g. epoxy/ acrylic and polyurethane/acrylic. To adjust the curing properties and reduce the viscosity so that the paint can be easily applied, a solvent or carrier is used. These evaporate after application and do not form part of the paint film. In waterborne paints, the carrier is water. With solvent-borne paints, also called oil-based paints, the carrier is a solvent such as acetone, turpentine, naphtha, toluene, xylene and white spirit. 

These two-pack cold-cure solvent-borne coatings have excellent durability and abrasion resistance. They are designed for spray applications on steel, aluminium and light alloy surfaces wMch have been suitably pretreated. Base and hardener are mixed in 3 1 or 5 1 ratios as recommended by the manufacturer and the pot life is around 2 hours under normal working conditions (20 C) and should not be used after the stated time. Polyurethane/acrylic resin combination is also available. Two-pack polyurethanes are widely used in veMcle body repair and can contain isocyanate which is a basic constituent in the production of polyurethane and is the most common cause of industrial asthma and it is also a skin irritant. It should be easily identified by a label on the container which should say contains isocyanates, harmful by inhalation and in contact with skin . Waterborne two-pack polyurethane finishes are available. 

As discussed in the Introduction, in addition to hot-melt adhesives, one of the most important forms of adhesives for the future is the waterborne system. In general, an advantage of the waterborne system is that it is free from the solvent-pollution problem. For this reason, we shall describe several new waterborne systems in detail acrylics, modified ethylene-vinyl acetate, polyurethanes, phenolics, epoxies, isocyanates, and tackifiers. Applications of these systems range from PSA s contact adhesives, and laminating adhesives to wood adhesives. 

Thomas P (ed.) (1998) Waterborne and Solvent Based Surface Coating Resins and their Applications, vol. Ill, Polyurethanes. Chichester Wiley. 

An overview is presented on the merits of polyurethane dispersions in waterborne paint formulations. In addition to the characteristics listed which they impart to coatings, such binders can offer an even wider range of properties by means of blending or copolymerisation, producing binders which are tailor made for specific applications, it is stated. 

Conveyor belt and moving web reactors give a piston-flow reaction environment. The polymer layer is usually thin enough so that heat transfer is not a serious issue, but the confinement of vapors to meet environmental requirements can be expensive. Thus waterborne or condensation polymerizations without by-products (eg polyurethanes) are preferred. Ultraviolet and electron beam curing is common. Applications include photographic and xerographic films, breathable fabrics, coated abrasives, and printed films, as well as polymers manufactured on belt flakers. 

Adhesives for Plastic Floor Covering. Solvent-free adhesives based on acrylic and vinyl acetate - ethylene - acrylic emulsions are used for bonding vinyl, synthetic rubber, and polyolefin flooring. Solvent-containing contact adhesives (rubber- or polychloro-prene-based) still are used for some applications (e.g., stairs). When water resistance is required, reactive polyurethane or epoxy resin adhesives are preferred to waterborne emulsions. 

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