Water Repellent Finish. (For Textile Processing)

Water Repellent Finish. (For Textile Processing)

Introduction 

Waterproofing is defined as the property of a material not to be penetrated by fluids. Water repellent textiles are often high-density woven materials made of very fine yarns or common materials with hydrophobic surface treatment. 

Water repellency is therefore a step up from water resistance. This means that water can't easily penetrate the material. Water repellents are chemical finishes that retains textile material from wetting and also protect the other comfort ability. The droplet of water molecules tends to spread out over the fabric mainly depends on the contact angle between water molecule and fabric surface. Actually, this property adds on the fabric by providing a thin layer on the fabric surface that abstains water droplet from fabric wetting. 

Chemistry 

Compounds formed by reacting Stearic Acid (C18H35O2) and Formaldehyde (CH2O) with Melamine (C3H6N6) constitute another class of water-repellent materials. The hydrophobic character of the Stearic Acid groups provides the water repellency, while the remaining N-methyl groups can react with cellulose or with each other (crosslinking) to generate permanent effects. 

Mechanism 

Repellent finishes achieve their properties by reducing the free energy at fiber surfaces. If the adhesive interactions between a fiber and a drop of liquid placed on the fiber are greater than the internal cohesive interactions within the liquid, the drop will spread. If the adhesive interactions between the fiber and the liquid are less than the internal cohesive interactions within the liquid, the drop will not spread. Surfaces that exhibit low interactions with liquids are referred to as low energy surfaces. Their critical surface energy or surface tension ƴC must be lower than the surface tension of the liquid ƴL that is repellent. critical surface energy or surface tension γC must be lower than the surface tension of the liquid γL (the internal cohesive interaction) that is repelled. 

 Applications: 

1.Rainwear. 

2. Waterproof outdoor sports clothing. 

3.Tents. and other applications. 

 Written by: Md Enamul Haque (Sajib) References: 1. Principles of Textile Finishing by Asim Kumar Roy Choudhury. 2. Waterproof and Water Repellent Textiles and Clothing Edited by John Williams. 3. Textile Engineering-An Introduction Edited by Yasir Nawab. 4. Google.