Technical textiles are functional fabrics that have various applications across different industries such as agriculture, automotive, construction, infrastructure, civil engineering, industrial safety, oil, petroleum, healthcare, and personal protection. As the superior functionality of technical textiles is understood, the consumption of these versatile products will increase vastly.
Being environmentally friendly, as they do not emit volatile organic compounds, water-borne PUDs are attracting attention in today’s world. While retaining the tremendous qualities of solvent-borne PUDs, such as low temperature, fatigue resistance, and good flexibility, water-borne PUDs are also eco-friendly, energy-saving, safe, and easy to process.
Technical textiles are coated with water-borne PUDs without the use of other solvents. These coatings are sustainable and water-based, yet waterproof, which allows the escape of water vapor. They are abrasion-resistant, flexible, breathable, and have superior elongation and tensile properties. They can be used on their own, or in association with acrylic emulsions (thickeners, defoamers, wetting agents), to obtain the optimum performance for the required application. Crosslinking of water-borne PUDs can be carried out for textile coatings resins to enhance their properties. The characteristics of water-borne PUDs depend on the type/functionality/hydroxyl value of the polyol, nature of the isocyanate, type of emulsifier, and chain extender. When the hydrophilic component increases, both the permeability values of water vapor, as well as the water penetration resistance increases.
Many water-borne PUD coatings are not thermoplastic because of additional crosslinking, which is required to attain favorable properties such as wash fastness at higher temperatures. The numerous characteristics that can be attained through water-borne PUD coatings for technical textiles include resistance to fuels, heat, ozone gas, UV, extreme weather conditions, abrasion, tears, chemicals, oils, acids, alkalis, flame, and other solvents. Gas permeability, good tensile strength and flexibility, low/high friction (depending on required condition), improved stretchability and elongation, low cost, hard/soft nature (depending on required condition), increased rigidity and water repellency are a few other important characteristics to be addressed, to obtain performance properties for technical textiles. Coating compounds can be customized with different additives, such as flame retardants, fluorocarbon, and PTFE so that each one imparts different properties to the final coated textiles, for usage in textile coatings. Various technical textiles are being manufactured with specialized characteristics such as heat generating, cooling, antimicrobial, quick-dry, breathable and waterproof nature.
Technical textiles use a specialized coating technology, such as air knife, roller coating, or foam coating in which many layers of a high polymer adhesive are coated on the surface of the fabric, so as to form a film. This improves the hydrophilic characteristics of the fabric and allows water vapor to be removed quickly. The numerous hydrogen bonds present in the polyurethane structure lead to strong intermolecular forces which helps maintain strong adhesion.
Water-borne PUDs have various applications in the technical textile coating industry, such as footwear, agrotextiles, automotive applications, geotextiles, medical textiles, tents, luggage etc. For example, waterproof behaviour and elasticity are the main performance requirements of textiles used for tents. PUD coating textiles are highly elastic and the resulting surface film formed is waterproof. For technical outerwear, breathability, water repellency, scratch and wear resistance are important requirements, and the polyurethane film protects the inner layer from extreme weather conditions.
To make sure the fabricated water-borne PUD coating textiles have favourable characteristics, the following conditions should be taken into consideration.
After mixing, adhesives should be filtered- undissolved contaminants will result in an unfinished coating layer.
Additives that are added on the surface of the textile will affect the quality of the coating.
Reduce amounts of bubbles formed during the coating process, as bubbles decrease the strength of water pressure resistance. The addition of antifoaming agents during the blending of adhesives can aid the reduction of bubbles.
Decrease the generation of CO2 gas; polyurethanes produce CO2 gas during the drying process. Slowly increase the oven temperature at a low temperature to decrease bubbles formed during the processes of coating and drying.
Viscosity should be controlled above 10000 cps/25°C. Adhesives will be absorbed easily into textile fibres during coating if the viscosity is not enough. This hinders surface film formation, and hence poor resistance to water pressure.
Water-borne PUDs enhance and improve the tensile strength and transient appearance of technical textiles. We, at C&E provide environment-friendly, water-borne PUDs under our 'Puthane' 5000 range, which are preferred for technical textile coatings. We aim to create excellence by enhancing the technical performance of your textiles and exceeding customer expectations.
Article written by Ashni Arun on Feb 3rd, 2022
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