- The new coating technique makes natural fabric water-repellent, and it works better than existing methods.
- The fabrics have passed repeated washing tests and harsh abrasion tests without any degradation and damage to the coating.
Waterproof fabrics are usually synthetic fibers that are coated or laminated with waterproofing materials like silicone elastomer, polyvinyl chloride (PVC), fluoropolymers, and wax. They are essential for almost everything from military tents and inflatable boats to sauna suits and rainwear.
The traditional waterproofing treatments raise health and environmental concerns, and thus likely to be phased out for safety purposes. This leaves a large slot to be filled if scientists can discover a better alternative.
Now, MIT researchers have come up with a new, effective technique to make natural fabrics (like silk and cotton) water repellent. It actually works better than existing techniques.
Most of the waterproof fabrics that we use today are ‘water-resistant’, which means ultimately water will get through. The aim is to make fabrics ‘water repellent’ that can bounce back water droplets. The new technique does the same.
How It Works?
The existing coating methods use long polymers with perfluorinated side-chains. Since they’re liquid based, fabrics must be submerged into a specific liquid and then dried out. This drying process clogs fabric’s pores, leaving fabrics unable to breathe.
In order to reopen these pores, air is blown through the fabric in the next step. This makes the water-protection feature less effective and adds manufacturing costs.
In this study, researchers combined 2 things:
- Chemically enhanced short-chain polymer (perfluorinated compound) that shows hydrophobic effects.
- Recently developed coating process known as iCVD (initiated chemical vapor deposition).
Unlike existing coating techniques, the iCVD isn’t based on any specific liquid and can be performed at low temperatures. It uniformly spreads on the fibers, forming a thin layer without clogging pores.
Droplets on coated vs non-coated surface | Credit: Varanasi and Gleason research groups
Therefore, the process doesn’t require any further manufacturing step to reopen the pores. However, a process called surface sandblasting could be added as an option to enhance its water repellency tendency.
For researchers, the toughest task was to find the perfect spot where iCVD’s compatibility and durability could function together to yield the best performance.
They observed that for blasting particle sizes of 4 micrometers and below, drops stopped gliding down the specific slop and eventually remained pinned on the fabric. For blasting particles of 11 micrometers and above, all drops were able to bounce off and detach from the coated material (fiber diameter of 10 micrometers).
Standard rain-repellency test | Credit: Varanasi and Gleason research groups
The researchers subjected the coated materials to a standard rain test and a variety of lab tests. Not only they tested the material by bombarding water, but also other liquids like sodium hydroxide, ketchup, coffee, and different acids and bases. The coated fabric repelled all of them.
Moreover, the coated materials passed repeated washing tests (10,000 repetitions) and harsh abrasion tests without any degradation and damage to the coating.
This technique works on a variety fabrics, including linen, nylon and cotton. In fact, it could be applied to some non-fabric materials like paper, which opens a wide range of potential applications.
The researchers plan to further optimize the chemical formula to achieve the maximum possible water-repelling capability. Meanwhile, they will license this technology (patent pending) to big fabric and clothing manufacturers.