Waterborne Polyurethane Introduction

Waterborne Polyurethane Introduction
 
Waterborne polyurethane is a type of coating and adhesive technology that utilizes urethane polymer particles dispersed in water. One commonly used technique for achieving this dispersion is through the use of "self-dispersing ionomeric PU prepolymers." In this process, Dimethylolpropionic acid (DMPA) is frequently employed as a component to react with a PU prepolymer, resulting in the synthesis of an ionomeric prepolymer for water-based polyurethane dispersions, known as PUD.
 

Brief about Waterborne Polyurethane Chemistry

The chemistry behind the formation of waterborne polyurethane involves the reaction of a stoichiometric excess of isocyanate with hydroxy groups and a specific moiety. The structures of the polyol and isocyanate in waterborne polyurethane prepolymers can vary significantly depending on the desired application and requirements of the waterborne polyurethane. For instance, isocyanate-terminated prepolymers are typical for waterborne polyurethane, but hydroxyl-terminated prepolymers are used in the formulation of two-component waterborne polyurethane systems.
 

Production of Waterborne Polyurethane

Prior to the water-dispersing process, the carboxylic acid groups in the prepolymer must be neutralized with a strong base to convert them into carboxylate groups. This neutralization step enables the urethane particles to disperse and stabilize in water. Following base neutralization, the aqueous dispersion process must be initiated promptly. During this process, a chain extender, such as primary or secondary polyamines, is added to the waterborne polyurethane to convert the remaining isocyanate groups into the final polymer within the particles. Primary or secondary polyamines are chosen as chain extenders due to their higher reactivity towards isocyanates compared to water. Once all the reactions are complete, the final products of the reaction consist of ionomeric prepolymer and residual monomeric isocyanate.
 

Waterborne Polyurethane Outlook

The formulation and application of waterborne polyurethane have experienced significant growth in recent years. This growth is primarily driven by the need to comply with environmental and occupational safety regulations, which aim to reduce exposure to organic solvents. Waterborne polyurethane coatings and adhesives are now widely used in various industries, including footwear, textile fibers, fiberglass, leather goods, automobiles, and floor polishes. Particularly in well-developed countries like those in North America and the European Union, solvent-based coatings and adhesives are being phased out in favor of waterborne polyurethane systems. These water-based alternatives are VOC-free, safe for human health, environmentally friendly, and possess properties comparable to solvent-based polyurethane systems.

 
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