Water repellent fabric | Properties | How to make Water repellent?

Introduction

There have been three types of fabric finishing in general, including water, oil, and soil repellent, the first of which was an attempt to make water-repellent fabrics. Water-repellent is a term related to the wet resistance of a fabric. Here, due to the perforation of the fabric and the permeability of air and water vapor, protection against water under high hydrostatic pressure is not complete and the wearer gets wet in rain if the hydrostatic pressure is high enough. There is another term called waterproof cloth, which has little or even no pores, including complete resistance to the penetration of water under hydrostatic pressure. Recently, Focus has become a waterproof-breathable fabric that meets waterproof requirements and allows higher comfort for the ingress of air and water vapor. The distinction between waterproof and water-repellent fabrics becomes important when considering the final use of fabrics.

Water repellent fabric

Water repellent is the addition of a coating to make it water-resistant (hydrophobic) factory fabrics. Most factory-applied therapies are fluoropolymer-based; these applications are quite thin and not always effective. Water repellents are usually used with a waterproof breathable fabric such as Gore-Tex so that the outer layer of the fabric is not filled with water. This saturation, called 'wet out', can reduce the respiration of the garment and allow it to pass through water. Over time the irritating water stops, and re-treatment is advised if necessary. Many spray-on and wash-in products are available for the treatment of waterproof clothing and lose their water resistance to re-treatment of proof clothing.

High fabric water repellency depends on the following factors:

i. Fine yarn and compact textile structure

ii. A thoroughly prepared fabric free from impurities such as sizes, lubricants, and servants with riveting action

iii. Uniform application of chemical finishes providing a low-energy surface containing less critical surface strength than the surface tension of liquids.

Waterproof fabrics

Waterproofing is the process of making an object or structure waterproof or water-resistant so that it is not relatively affected by water or prevents water from entering under certain conditions. These items can be used in wet environments or at certain depths underwater.

Waterproof fabrics are fabrics that have been treated naturally or to become, resistant to penetration by water and wet. The term waterproof refers to a regulatory specification and compatibility with certain conditions of a laboratory test procedure. These are usually natural or synthetic fabrics that are laminated or coated with waterproofing materials such as rubber, polyvinyl chloride (PVC), polyurethane (PU), silicone elastomers, fluoropolymers, and waxes. Can be fabric during production or can be finished product after production, for example by waterproofing spray. Examples include Mackintosh jackets, sauna suits, and rubberized fabrics used in inflatable boats.

The main differences between water-repellent and water-proof fabrics are below-

i. The holes in the water-proof cloth are filled, when they are open in the water-repellent cloth.

ii. Air and water vapor permeability is negligible in the case of zero or water-proof fabrics, while they are generally higher in the case of water-repellent fabrics.

iii. Water-proof cloth is resistant to penetration by water, on the other hand, water can penetrate water-repellent cloth under external hydrostatic pressure.

Properties of water-repellent fabric

i. Water-repellent fabric pores are relatively open.

ii. It is resistant to water droplets of wetting.

iii.  It permits water passage under the fabric by external hydrostatic pressure.

iv. Air permeability is usually high

v. Water vapor permeability is medium to high.

vi. Comfortable and process cost low.

vii. These are often compact textile structures or common materials treated with hydrophobic chemicals.

How to make water-repellent fabric

To make water-repellent fabric, it is usually coated with some type of waterproofing agent such as wax, rubber, or polyvinyl chloride. Other forms of waterproof fabric are made from synthetic materials that are naturally water-resistant. One of the most common and classic uses for this type of material is the rubberized fabric used to make the conventional British Macintosh rain jacket. This jacket has been around for decades and is one of the first water-resistant jackets to be patented. One of the most important and unique features of water-repellent fabric is that while it prevents water droplets from entering the jacket from the outside, it also allows water vapor to flow from the inside to the outside. This allows a person wearing a waterproof jacket like the Macintosh to stay dry in the rain and prevent him from getting wet from the inevitable accumulation of sweat while walking on a rainy day. In order to properly classify water-resistant fabrics, a standard laboratory testing method has been established so that all manufacturers work to the same standard. Measurements are recorded in millimeters of water.

Mechanisms of repellency

Repellent finishes achieve their properties by reducing the free energy on the fiber surface. If the adhesive interaction between the fibers and a drop of fluid contained in the fiber exceeds the internal connective interactions between the liquids, the drop will spread. If the adhesive interaction between the fiber and the liquid is less than the internal connector interaction between the liquid, the drop will not spread. Surfaces that show less interaction with liquids are called low-energy surfaces. Their critical surface energy or surface tension γC must be less than the surface tension of liquid γL (internal connector interaction) that is repelled. γL of water, at 73 mN m^{− 1}, is two to three times more than oils(20–35 mN m^{− 1}). Therefore, oil repellency is finished with fluorocarbons (γC = 10–20 mN m^{− 1}), always acquiring water antidotes, but fluorine-free products, for example, silicon (C = 24–30 mN m^{− 1}) will not repel oil.

Water-repellent fabric testing

You can take a test to see if the fabric has a water-repellent finish (W.R.) or a waterproof finish (W.P.).

i. Put the cloth on a flat surface and put a few drops of water on it.

ii. If water spills on it, it tells you that there is a W.R. on this side of the fabric now you use your finger to rub in the water. If it does not go the other way, it means that this fabric has W.P. on the other side, however, if it goes the other way, it means it has W.R. on this side.

iii. If water is absorbed and easily moves to the other side (completely wet), it means that the fabric has a “plain finish” not W.R. and not W.P.

iv. If the water does not roll but sticks to the cloth and when you rub it, it does not pass; It tells you that this side of the fabric has a W.P. finish. Most likely, it has W.R. on the other side, because usually, when the fabric has W.P. on the other side. On the other side of it is W.R. To make sure what you think is right, you can turn it around and see if the water is rolling.

v. Another test: if you can breathe with fabric, it’s not W.P. If you can’t breathe with the fabric, it’s W.P.

Conclusion

Water-repellent fabrics are coated with a finish that is resistant but not impervious to water so water-repellent fabrics will keep you dry for a relatively short time when walking in the rain. Thus, the water-resistant fabric will provide some protection against intermittent rain but is not suitable for wearing in rainy or long rainy weather. The biggest advantage of water-repellent pants and jackets is that they somehow match water resistance with their breathability.