Textile Chemistry

Harrick Plasma → Applications → Alter Surface Chemisty → Textile Chemistry

Textile chemistry is important for numerous markets, including clothing, automotive, and outdoor recreation industries.  Plasma treatment is a dry, non-toxic process that can make textiles water-repellent, oil-repellent, or both. In this application note, you will learn about the many ways plasma treatment can be used to alter textile chemistry. These include increasing textile hydrophobicity, extending the lifetime of fiber-polymer composites, improving the adhesion of textile coatings, and creating moisture-wicking channels in fiber-based microfluidic devices.

Hydrophobic textiles

Hydrophobic textiles are essential for many clothing applications, including raingear and sportswear. Researchers frequently use chemical vapor grafting to deposit a hydrophobic layer atop a plasma treated hydrophilic textile (Figure 1). By making the textile hydrophilic during plasma treatment, the subsequent hydrophobic layer bonds well to the underlying textile.

Ramaratnam et. al. used air plasma to treat polyester fibers prior to dip-coating them in PGMA/PVP and applying a solution of silver (Ag), silica (SiO₂), or calcium carbonate (CaCO₃) nanoparticles. Next, Ramaratnam applied a second PGMA/PVP layer to trap the nanoparticles. Finally, a polystyrene (PS) layer was grafted onto the PGMA/PVP, forming polystyrene brushes. Both the deposited nanoparticles and the polystyrene brushes were required to achieve superhydrophobicity (water contact angle > 150°). Fibers containing only the PS brushes had a water contact angle (WCA) of 113°, whereas fibers containing both PS brushes and silver nanoparticles had a water contact angle of 157°. The increased hydrophobicity was due to the increased surface roughness caused by the nanoparticles. Hydrophobicity of fibers coated with SiO₂ or CaCO₃ nanoparticles varied with particle concentration and shape.

Figure 1: Plasma treatment of a substrate, deposition of an intermediate anchoring layer, and chemical vapor grafting of polymer chains onto the anchoring layer.

Fiber Reinforced Polymers (FRP)

Fiber reinforced polymers (FRP) are frequently used in aerospace and construction applications due to their high strength-to-weight ratio, corrosion resistance, and tensile strength. These composites often consist of a polymer matrix surrounding non-plant fibers such as glass or carbon. Efforts have recently been made to create and test FRPs containing natural fibers like coconut or flax. Unlike conventional fibers such as glass or carbon, natural fibers are cheap and widely available.  Enciso et. al. developed a composite containing plasma treated flax fibers embedded in polyethylene.  By plasma treating the flax fibers to make them hydrophilic, Enciso et. al. also achieved better bonding of these fibers to the surrounding polyethylene matrix (Enciso et. al. 2017). Plasma treatment of the fibers significantly increased the Young’s modulus and tensile strength of the composite containing 20% flax; these effects were less pronounced when 30% flax content was used. Plasma treatment is a chemical-free alternative to toxic alkali treatment, as both have been shown to increase the Young’s modulus of natural fibers (Ku et. al. 2011). Polyethylene composites containing plasma-treated flax fibers experienced higher decomposition energy (suggesting longer product lifetimes) than composites containing non-treated flax (Enciso et. al. 2019).

Textiles with novel coatings

Plasma treatment also improves the adhesion of conductive or switchable coatings to textiles. Gao et. al. plasma treated polyester (PET) yarn to make it hydrophilic before adding a highly-conductive PEDOT:PSS coating. The conductive yarn formed electrodes for a yarn-based biobattery.

Zhang et. al. used air plasma to treat cellulose/polypropylene blend textiles before dip coating in a silica nanoparticle solution and functionalizing with bromoalkyl groups via silanization. The textiles were then coated with a P2VP-b-PDMS block copolymer to form a polymer brush layer containing P2VP and PDMS chains. The P2VP chains have oil wettability which varies with pH of the surrounding liquid. At low pH, P2VP is oleophobic, whereas at higher pH, P2VP is oleophilic. Zhang et. al. used these properties to create a switchable filter for a gasoline-water mixture. By initially wetting the filter with low-pH liquid, Zhang extracted water from the gasoline-water mixture. When the filter was wetted with a higher-pH liquid, gasoline was removed from the mixture.

Unique fabric-based microfluidic devices

Plasma treated textiles have also been used in fabric-based microfluidic devices. Unlike traditional microfluidic devices made from the polymer polydimethylsiloxane (PDMS), fabric-based microfluidics can be rapidly manufactured without expensive cleanroom facilities. Nilghaz et. al. recently developed a wax-printing method to create microfluidic devices on cotton, polyester, and silk. After plasma treating these fabrics to make them hydrophilic, Nilghaz printed hydrophobic barriers on the fabric using wax. The hydrophilic fabrics acted as moisture-wicking channels for colorimetric assays.

Xiao et. al. also developed a colorimetric sensor using plasma treated cotton. Plasma treated cotton threads were used to guide human sweat to a paper-based glucose sensor.  During preliminary tests using ink, longer plasma treatments (up to ≈ 1 minute) increased the ink’s flow velocity along the threads. Additionally, longer plasma treatments decreased the threads’ water contact angle (WCA). Together, these findings indicate improved wettability of cotton fabric due to plasma treatment.