Polyurethane Dispersions (PUDs) are binary systems of colloids that are formed by the dispersion of particles in the aqueous phase. They have tremendous potential as adhesives and coatings. Recent research has shown that different solvent-based polyurethanes emit organic volatile compounds (VOCs) which are harmful to the environment. Therefore, as an alternative, eco-friendly, versatile water-borne PUDs are being used, to reduce environmental harm.
These dispersions display good adhesion to many different surfaces including polymeric fibers and glass. They are environment-friendly, non-toxic, non-flammable polymers and do not pollute the air or produce wastewater. Polyurethanes, generally, are insoluble in water as they are hydrophobic in nature. Hence, they must be incorporated with hydrophilic monomers (polyurethane ionomers and internal emulsifiers) containing ionic functionality to be dispersed in water.
Water-borne PUDs are usually used in coating and paint applications and are most commonly used in textile and wood coatings. They are also utilized in numerous other industrial applications such as ink, adhesives, glass fibers, paper sizing, synthetic leathers, membranes, packaging films, and biomaterials.
What makes water-borne PUD coatings unique?
Solvent-free / low solvent content Usage of water-borne polyurethane dispersions eliminates the high cost of solvent required when using solvent-borne PUDs. They can also be used on substrates that are sensitive to solvents, such as plastics.
User friendly and less toxic Toxic materials include aromatic solvents, live isocyanate, and NMP (N-methyl pyrrolidone)
Easy handling property
Chemical, abrasion, and scratch resistance
Low viscosity at high molecular weights
Wide range of film hardness
Low-temperature drying
Better adhesion to various polymers
Effective crosslinking chemistry Used in water-borne PUDs but is not possible using solution polymers. Auto-oxidative cross-linking is also easier in water-borne PUDs. Auto-oxidative crosslinking can be used in solvent-based PUDs but needs a smaller starting molecular weight and lesser solids compared to the water-borne polymer. This results in reaching hardness and resistance properties faster than solvent-based or high-solid materials.
Reduced flammability Water-borne PUDs have lower degrees of flammability as the characteristics that decrease the emission of VOCs and odor result in reduced flammability. Few PUD polymers still possess NMP, which has a high degree of flammability and functions as a processing solvent.
Water-borne PUDs in the textile industry are utilized as coating materials that fabricate breathable coatings whose application is formaldehyde-free. They enhance the transient appearance and tensile strength of the textiles.
Depending on the required application of the glass, glass material coatings should have good resistance to scratches, abrasions, solvents, water, and detergents. Compositions of water-borne polyurethane coatings display enhanced hardness, transparency, high impact, better abrasion, and resistance to alkalis, solvents, and water.
The lifespan of water-borne PUDs is up to 10 years, even in exposed areas, due to good UV resistance against cracking, peeling, or yellowing. They are able to penetrate into the substrate easily and provide better bonding with water-borne acrylics. They can be fabricated into glass coatings, clear glossy wood finishes, and anti-corrosive metal coatings. However, despite the numerous advantages of water-based systems, solvent-based PUDs and high solid 2K urethanes are preferred for metal (steel and direct-to-metal) coatings, as they provide strong barrier properties. High solid systems also provide thicker film build and decreased shrinkage. Water-borne PUDs are not used directly in protecting metal substrates, as the hydrophilic segments present in the polymer backbone are significantly susceptible to water and lead to corrosion. Hence, there is still room for improvement regarding water-borne PUDs regarding barrier properties and electrochemical impedance to reach the level of performance of solvent-based anti-corrosion coatings.
C&E Water-Borne Polyurethane Dispersions
C&E offers a wide variety of water-based, eco-friendly PUD technologies under our 'Puthane' range. We strive to create excellence by offering top-quality solutions to meet our customers' requirements. Contact us to understand our water-borne polyurethanes and how our products can be utilized for specific applications.
Article written by Ashni Arun on Jan 28th, 2022