Book Review

200-201 Nanosols and Textiles by B Mehltig and T Textor (World Scientific Publishing Co. Pte. Ltd, Singapore 596224), 2008</smarttagtype

Atmospheric pressure glow discharge plasma and its applications in textile

83-98Plasma, a partially-ionized gas generated by an electrical discharge or high temperature, is of different types and can be classified based on pressure, temperature, source of energy and type of gases. Cold plasma is generated by electric discharge at near-ambient temperatures and can be used for surface modification of textile substrates. This paper reports a brief review of the various plasma and their applications for textile modifications. For textile modifications, atmospheric pressure glow discharge cold plasma is more suitable because it can be designed for continuous treatment of textile. However, the main challenge in atmospheric plasma is to obtain a stable glow (filament-free) discharge over a large surface area suitable for the safe treatment of textile. At IIT-Delhi, uniform glow discharge plasma at the atmospheric pressure over large surface area has been developed by optimizing reactor design and process parameters. Using this plasma, polyester (PET) and nylon fabrics were treated for 10-60 s under different gasses. The treatment significantly enhanced the water absorbency and surface energy of both the nylon and PET fabrics. In nylon-6, the properties imparted by plasma treatment did not change even after 25 days. However, in PET, the absorbency and surface energy were found to reduce slowly with time of storage. The samples did not degrade during plasma treatment and showed insignificant change in mechanical properties. The atmospheric pressure glow discharge plasma can effectively and safely be used to modify surfaces of textile substrates at reduced process and environment cost

Sol-gel derived titanium dioxide finishing of cotton fabric for self cleaning

443-450Nano- TiO₂ coatings have been applied to cotton fabric by sol-gel process without any crosslinker or binder. The characteristics of coatings derived from two different approaches by sol-gel process are compared. It is revealed from the Fourier transform infrared spectroscopy that the TiO₂ sol particles have the similar spectra as observed for commercial TiO₂ (Degussa P25). The nano-TiO₂ particles are applied to cotton fabric using 1 wt% acrylic binder and cured. The photo-catalytic activity of the finished fabric has been investigated and a comparison is made between the commercially available TiO₂ sample and the nano-sol coated samples. The self-cleaning action of nano-crystalline TiO₂ coated cotton has been quantified by measuring the photo-catalytic degradation of stain due to visible light irradiation. Nano-sol derived TiO₂ particles with smaller particle size of <10 nm (prepared using nitric acid) show significantly better activity than the commercial TiO₂ sample of the particle size 25nm. The titanium coatings on fabric also act as anti-bacterial photocatalyst

Thermoresponsive smart textile

52-65The developments in temperature-sensitive copolymers have been reviewed critically and an attempt has been made to synthesize a series of temperature-sensitive random linear and crosslinked copolymers of N-tert-butyl acrylamide (NTBA) and acrylamide (Am) in varying proportion from 80:20 mol % to 20:80 mol % with transition temperature varying between 2°C and 58°C. Linear copolymer with 40:60 feed ratio of NTBA and Am with actual incorporation of NTBA to the extent of 27 mol% was processed into mechanically strong films of 10-200 μm thickness. The transition temperatures of the crosslinked films are found to shift towards the lower temperature from 37°C (in linear copolymer) to ~ 22-25°C. In thin films of 10 μm, the swelling percentage increases to 4200 and the response time reduces to 5 min from 680% and 120 min respectively of the polymerized gel samples (2 mm disc) of the same composition. Reversible transition was also observed over repeated cycling. These copolymers were chemically integrated to the textile substrates for developing smart textile materials. Cotton yarns coated with this copolymer show a broad transition in the temperature range 15-30°C, and an equilibrium volumetric swelling of ~ 4500% in about 5 min and deswelling within 10 s. A model fabric, fabricated using the coated cotton yarns, exhibited temperature-responsive percentage cover (100% at 6°C and 43% above transition temperature)

Simple and fast method for purifying single-walled carbon nanotubes

374-376A fast and efficient method for purification of single-walled carbon nanotubes has been reported in this paper. It is observed that the use of an inorganic acid in conjugation with an organic solvent can effectively remove the metal catalyst particles from the single-walled carbon nanotubes. This treatment technique has been compared with the conventional method employing concentrated nitric acid using high resolution transmission electron microscopy and energy dispersive X-ray studies

Synthesis and characterization of non-fluorinated copolymer emulsions for hydrophobic finishing of cotton textiles

264-271Non-flouro copolymers containing a hydrophobic alkyl acrylate monomer (butyl acrylate/2-ethylhexyl acrylate/ lauryl acrylate) and a reactive monomer (maleic anhydride) have been synthesized using emulsion polymerization technique. The copolymer emulsions have been applied on to cotton fabric by a pad-dry-cure process and the water repellency of the fabrics before and after vigorous washes compared. The effect of chain length of hydrophobic monomer on the water repellency has been compared and the comfort properties of the coated fabrics such as air permeability and bending length evaluated. It is observed that the copolymers prepared using long alkyl chain acrylates show promising alternatives to the repellent agents based on perfluoroalkyl chains for water repellency

Effect of emulsion preparation method on microencapsulation of <i>n</i>-octadecane using melamine-formaldehyde pre-polymers

101-106The microcapsules containing n-octadecane as the core material and melamine-formaldehyde resin as the wall material have been synthesized by in situ polymerization method. A systematic study has been carried out to investigate the effect of the method used in the preparation of reaction emulsion mixture, and the curing conditions used during the encapsulation process on the properties of microcapsules. The microcapsules so obtained are characterized for their core content, encapsulation efficiency, mean particle size distribution, and thermal & solvent stability. Using the modified encapsulation process with a formaldehyde-to-melamine molar ratio of 8 and core-to-wall ratio of 2, microcapsules with a high core content of 70% and a heat storage capacity of >160 J/g could be obtained. The capsules are found to be stable at temperatures more than 80 °C and to cyclohexane wash

Hydrophobic functionalization of cellulosic substrate by tetrafluoroethane dielectric barrier discharge plasma at atmospheric pressure

Hydrophobic functionalization of cellulosic fabric (viscose) was carried out using helium/tetrafluoroethane (He/ TFE) plasma, a commercially available fluorocarbon gas, at the atmospheric pressure. By selecting suitable plasma parameters, He/TFE plasma was produced and maintained in glow state so that the various fragments of TFE in plasma zone could react covalently with the cellulose. After the plasma treatment, the highly hydrophilic cellulosic fabric turned into superhydrophobic fabric with a water absorbency time of >> 60 min, a water contact angle of 153 degrees and a water rolling angle of 5 degrees. The functionalization was found to be wash durable to 25 laundry cycles. From the analyses of species present in plasma zone by optical emission spectroscopy (OES), gas chromatography-mass spectrometry (GC-MS), and the chemical nature of the functionalized substrate by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS), a possible mechanism involved in the reaction of TFE fragments with cellulose macromolecule was arrived at. Further, it could be inferred that the modification took place only at the surface of the fibres at the nanometre level. The study postulates that it is possible to elucidate reactions undergoing in plasma zone and to control them to achieve desirable modification of substrates