Aqueous Polyurethane Systems

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. 

Shao, C. H., Huang, J. J., Chen, G. N., Yeh, J. T., and Chen, K. N., Thermal and combustion behaviors of aqueous-based polyurethane system with phosphorus and nitrogen containing curing agent, Polym. Degrad. Stab., 1999, 65, 359-371. 

Wang, T. Z. and Chen, K. N., Introduction of covalently bonded phosphorus into aqueous-based polyurethane system via postcuring reaction, J. Appl. Polym. Sci., 1999, 74, 2499-2509. 

Figure 224 Scheme for an aqueous, anionically stabilised polyurethane dispersion. Source Klein H.P. and Schwab, M., Aqueous polyurethane dispersions - an environment friendly alternative for high quality paint systems, Resin News, number 29 (July) published by Hoechst AG, Frankfurt, 1993... 

Dieterich et al. (147. 148) reviewed in depth aqueous ionic and nonionic polyurethane systems and described different methods for the preparation of these polymers. 

In formulating polyurethane/urea systems using ultra-low monol PPG polyols, it was found that polyol MWD has a major effect on polymer properties. A broadened MWD is required to achieve a property profile similar to a PTMEG-based system. The MW-distribution effect is illustrated using TDI prepolymers cured with MBOCA, TDI moisture-cured prepolymers and aqueous polyurethane/urea dispersion coatings. 

Witcobond, Pol)uirethane latices, aqueous polyurethane dispersiotts, Witco corp.. Performance Chemicals Group Woku, Quick mold change system. Unitemp Wollastocoat, Chemically surface-modified wollastonite, Nyco Minerals, Inc. 

Polycarbodiimides react with carboxylic acid and slowly enough with water so that they can be used in waterborne systems. The product of the reaction with a carboxylic acid is an AT-acylurea. Polycarbodiimides cross-link carboxylic acid-functional resins, including aqueous polyurethane dispersions and latexes (196, 197). Cross-linking occurs within several days at ambient temperature and faster with heat. 

Aqueous two-component polyurethane systems for automotive topcoats are under development. Currently the automotive topcoats are made from solvent-based two-component or blocked one-component systems based on HDI trimer (Desmodur N) or IPDI trimer (Desmodur Z) or both in conjunction with an acrylic polyol. The polyurethane topcoats provide the vehicles with a tough and durable finish with excellent long-lasting glossy appearance ( wet look ) One-component aqueous dispersions are already used in electrodeposition primers and pigmented base coats. Soft-feel polyurethane coatings are increasingly used for instrument panels and seat covers. 

Aqueous polyurethane dispersions are not new they have been available since the early 1970s. However, environmental concerns and impending legislation are in favour of non-solvent containing materials and reduction of VOCs making these systems commercially available nowadays. Performance of new aqueous dispersions has reached the point that they exceed the performance of some solvent-based systems [16]. These urethane dispersions can also often be processed with the same or similar equipment as solvent systems. They may be used as the sole resin or blended with other resin systems, such as acrylics. 

The development of chip resistant water-borne primer-surfacers has benefited from the use of predominantly water-borne polyester and polyester-polyurethane resins. Polyesters which are dissolved or dispersed in water by neutralizing acid groups with amines are crosslinked with a suitable melamine resin. Aqueous polyurethane or acrylic modified polyurethane systems are also slowly entering the primer market. 

The prime advantage of aqueous polyurethane and polyacrylate dispersions over solvent-containing systems is that recovery or disposal of significant amounts of solvent is unnecessary. In the packaging industry, potential for residual solvent traces in the adhesive and subsequent migration into food are also major concerns. Therefore, solvent-containing adhesives have already been replaced by environmentally friendly water-borne adhesives in a number of applications. 

Two-shot techniques for acyclic diene metathesis, 435-445 for polyamides, 149-164 for polyimides, 287-300 for polyurethanes, 241-246 for transition metal coupling, 483-490 Anionic deactivation, 360 Anionic polymerization, 149, 174 of lactam, 177-178 Apolar solvents, 90 Aprotic polar solvents, 185, 338 Aprotic solvents, low-temperature condensation in, 302 Aqueous coating formulations, 235 Aqueous polyoxymethylene glycol, depolymerization of, 377 Aqueous systems, 206 Ardel, 20, 22... 

The following fluoropolymers are commercially available in aqueous systems PTFE, PFA, MFA, FEP, ETFE, PVDF, THV Fluoroplastic, fluorocarbon elastomers, fluoroacrylates, and fluorinated polyurethanes. 

This reaction yields surfactants in which the polar group is linked to the silicone through an SiOC linkage. These materials have found widespread use in nonaqueous applications such as manufacture of polyurethane foam (PUF) but in an aqueous system the SiOC linkage hydrolyses (rapidly away from pH = 7). 

The surface activity of silicones is often exploited by using them as additives. For this reason, aspects of the two most important additive forms, copolymers and surfactants, are also included in this discussion. These two classes come together in the relatively low molecular weight PDMS-poly(alkylene oxide) block and graft copolymers that are commonly used as polyurethane foam stabilizers. Other short-chain silicone surfactants designed for aqueous systems and other silicone-organic copolymers are also available. 

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