Waterborne Polyurethanes

Chem. Descrip. Aliphatic silicone-modified polyester polyurethane waterborne disp. with n-methyl pyrrolidone cosolv. 

Crystalline polyesters are highly important as adhesive raw materials. They are normally crystalline waxes and are highly symmetrical in nature, which can aid the crystallization process [26]. Poly(hexamethylene adipate) and poly(caprolactone), shown in Table 2, are only two of the many crystallizable backbones. Poly(ethylene adipate) and poly(letramethylene adipate) are also commonly used in urethane adhesives. The crystalline polyesters are used in curing hot melts, waterborne polyurethanes, thermoplastic polyurethanes, and solvent-borne urethane adhesives. The adipates are available mostly as diols. The poly(caprolactones) are available as diols and triols. 

Polyurethane dispersions (PUD s) are usually high-performance adhesives based on crystalline, hydrophobic polyester polyols, such as hexamethylene adipate, and aliphatic diisocyanates, such as methylene bis(cyclohexyl isocyanate) (H12MDI) or isophorone diisocyanate (IPDI). These PUD s are at the more expensive end of the waterborne adhesive market but provide excellent performance. 

The chain extension step may then take place in the water phase. Hydrazine and ethylene diamine are commonly used chain extenders for waterborne urethane dispersions. The isocyanates react with the diamine chain extenders much faster than with the water, thus forming polyurea linkages and building a high molecular weight polymer. More detailed information regarding the synthesis and process of making waterborne polyurethane dispersions is found in Dieterich s review article [58]. 

Fig. 5. Viscosity versus time — bonding process for a waterborne polyurethane dispersion.

Two-component waterborne urethane dispersions are similar to the one-component PUD s in that a polyurethane dispersion comprises one of the two components. The second component is usually a crosslinker from the following classes of materials (a) polyisocyanates, (b) aziridines, (c) polycarbodiimides, and (d) epoxies. Many of the crosslinkers are not inherently water-soluble or water-dispersible. Therefore, they must be modified with surface active agents themselves, so as to become emulsifiable in water. 

Fig. 8. Crosslinking reactions of carboxylated waterborne polyurethane dispersions.

Chandalia, K. et al.. In Storey, R. and Thames, S. (Eds.), Proceedings of 28th International Waterborne, High-Solids and Powder Coating Symposium. New Orleans, LA, 2001, p. 77. Woods, G., The ICI Polyurethanes Book. Wiley, New York, NY, 1987. 

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. 

Turner, S. Richard, 1 Two-component (2-K), nonsagging, polyurea structural adhesive, preparation of, 255-256 Two-component (2-K) systems, 238-241 Two-component (2-K) waterborne polyurethane coatings, 206 preparation of, 254-255 Two-shot cast elastomer, preparation of, 249-250... 

Acidification of chloramine T with sulfuric acid produces the formation of dichloramine T (DCT) and hypochlorous acid (HCIO), species which react with C=C bonds of the butadiene units. The effectiveness of the treatment is ascribed to the introduction of chlorine and oxygen moieties on the mbber surface. A decrease in the pH of the chloramine T aqueous solutions produced more extended surface modifications and improved adhesion properties in the joints produced with waterborne polyurethane adhesive (Figure 27.9). The adhesive strength obtained is slightly lower than that obtained for the rubber treated with 3 wt% TCI/MEK, and its increases as the pH of the chloramine T solution decreases (Figure 27.9). A cohesive failure in the rubber is generally obtained. 

Waterborne coatings, 7 127-128, 10 443 Waterborne coating technologies, 10 349 Waterborne contact adhesives, phenolic resins in, 18 784 Waterborne polyamides, 10 400 Water-borne polyurethane coatings,... 

J.Y. Kwon, H.D. Kim, Preparation and properties of acid-treated multiwalled carbon nanotubes/waterborne polyurethane nanocomposites, Journal of Applied Polymer Science, vol. 96, pp. 595-604, 2005. 

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). 

Waterborne polyurethanes that have the performance of solvent-based systems can be made via tailored emulsion polymerization (Hagernrother and Ruttmann, 1990). 

Waterborne UV curable polyurethane dispersions have been developed that yield excellent performance when tested for exterior weathering. They... 

In addition to continued emphasis on reservoir capacity, we will shift our attention to other important specialty characteristics of polyurethane the abilities to be colonized by living cells and to attach active ligands. More specifically, this chapter will illustrate how polyurethanes are used to address environmental problems. The problems we will discuss are different in nature from the problems discussed in the last chapter. This chapter focuses on the treatment of waterborne human waste. 

Several hybrid epoxy emulsions have been commercially prepared. An epoxy emulsion blended with waterborne aliphatic urethanes exhibited peel strength on aluminum of 10 lb/in—1.5 times greater than with the polyurethane itself. The optimum concentration of urethane in the final emulsion was about 50 percent by weight.13 Epoxy-phenolic dispersions have also been developed to provide waterborne adhesive systems with high glass transition temperature and chemical resistance. 

Howarth, G.A. and Manok, H.L. (19%) Zero VOC and high solids waterborne polyurethane dispersions. Coatings World, 10(1), 18-22. 

Niax PWB-1200. [Union Carbide] Polyether polyol us to mfg. waterborne polyurethane coatings and adhesives. 

An important class of waterborne coatings is the family of polyurethane dispersions (PUDs). lonizable groups (usually carboxyl) incorporated to the PU backbone allow the polymer to be dispersed in water after neutralization with amines. The properties can be varied substantially depending on the structure of the polyol and diisocyanate used to prepare them. Aliphatic and cycloaliphatic isocyanates are preferred because of their low reactivity with water and... 

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