PU coating for vapor-permeable waterproof textile

Waterproof textile has extraordinarily high use in daily life, from garments to sportswear, camping equipment, etc. Waterproof cloth is often made by polymer surface finishing treatments, coating polymer on one or both sides of a fabric to form a multi-layer polymeric textile material. Polyurethane (PU) resin is one of the most common polymers used for textile material coating. Knowledge of PU resin and its performance working with humidity, liquid, and vapors is essential to understand PU-coated waterproof and water repellent fabric fully.

The PU-coated fabric has high mechanical strength, durability, resistance to aging, flexibility, elasticity, waterproofness, and a non-creasing finish. Most importantly, PU resin may form a porous outer layer, a hydrophilic PU film that allows vapor to be transferred by diffusion. The type and average diameter of the pores are the key factors affecting the waterproof-breathability of the PU layer.
 

Types of pores	Average diameter
- Individual (closed, partially closed, or open) - Distributed in a net	- Macropores (over 50nm; specific surface 0.5-2 m2/g) - Mesopores (2nm~50nm; specific surface 20-150m2/g) - Micropores (<2nm; specific surface 400-900m2/g)

As shown in the diagram above, the tiniest raindrop is fog with dimensions of about 100μm, and water molecules are 0.1-10nm. Therefore, around 2-50nm, the pore dimensions are much lower than the tiniest raindrop to create the waterproof property. But the pore dimensions are bigger than the water molecules, so vapor from the human body can pass through the microporous PU layer. 

In a PU-based coating process, decreasing carbon footprint has been one of the most concerning subjects. Notable mention that TPUCO has been researching and developing two environmental-friendly solutions for the textile coating industry to build a more sustainable supply chain. The first solution is water-based PU dispersions (PUD) for waterproof-breathable coating. General speaking, when the hydrophilic component increases, water vapor penetration increases, and water resistance to water penetration decreases in the PUD coated textile. Furthermore, the second solution is developing recycling technology to lower carbon footprint. While most waterproof-breathable materials are not biodegradable and have ecological issues, TPUCO may recycle the waterproof-breathable cloth made by PU coating on PET fabric to create a greener, lower carbon footprint, and more sustainable supply chain. Don't hesitate to get in touch with our sales representative for more information: pu@taiwanpu.com
 
(Reference: Book “Waterproof and Water Repellent Textiles and Clothing”)

To learn more, visit:
https://www.taiwanpu.com/en/product/PU-Adhesives-and-Hot-Melt/PU-Resin-for-Textile-Waterproof-Coating