Why Plasma Processing ?
Surface modification of textile/polymeric substrates is important for different industrial applications. Among the available surface modification techniques, plasma processing of textile is gaining area of research interest due its ecological and economical advantages over conventional chemical processing of textile substrates. High-value added product with new functionalities such as water/stain and oil repellency, permanent hydrophillicity, bio-compatibility, flame-retardancy, abrasion resistance, improvement in dyeing/printing and adhesion can be achieved by nano-scale surface engineering of fibre and fabric surface.
What is Plasma ?
Plasma, the fourth state of matter is partially-ionized gas containing a mixture of ions, electrons, neutral and excited molecules and photons. Matter within the universe is most commonly found in the form of plasma rather than solid, liquid or gas. This state of matter was first identified by Sir William Crookes in 1879, and named "plasma" by Irving Langmuir in 1928.
Different types of Plasma
Plasma can be classified in various ways such as based on temperature, pressure inside the reactor and electric signal. On basis of temperature of the ions and electrons, and degree of ionization plasma can be classified in two ways (i) Hot plasma (ii) Cold plasma. There is (i) Atmospheric pressure plasma and (ii) Low pressure plasma when plasma is classified on basis of pressure. Also, plasma can be classified into A.C. and D.C. based on electric power sources used. Among the various kinds of plasma, only cold plasma can be used for the textile modification.
Challenges in Atmospheric Pressure Plasma Reaction
· Generation of glow plasma
o Over a large surface area
o In presence of liquid and gaseous precursors
· Carry out In-situ plasma reaction with textile substrates
· Achievement of durable functional finishes
· Carry out continuous plasma reaction
Current area of Research
The research group is working on textile modification using indigenously developed atmospheric pressure glow discharge cold plasma reactor. The reactor has also been modified for continuous treatment of textile substrates. Current research fields are hydrophobic to superhydrophobic finishing, improvement in hydrophilicity, adhesion, dyeability and printability of the textile materials, in-situ synthesis of nano particles and eventually achieving novel properties on textile.
Alteration in dye behavior of wool fabric using He plasma.
Figure 1: Dye uptake of untreated and plasma treated wool fabric
Dye uptake of wool fabric increases
after helium plasma treatment.
Hydrophobic functionalization of cellulosic textile using He/non-fluoro carbon compound plasma treatment.
Fluorocarbon compound is known compound for hydrophobic plasma treatment but it is hazardous to health and environment. Our group has been used different nonfluoro compound like butadiene, styrene, dodecyl acrylate and hexa methylene di siloxane to make the surface of textile from hydrophilic to hydrophobic in nature.
Figure : Water drop shape on (a) untreated (b) plasma treated–soap washed fabric.
After treatment hydrophilic fabric shows water absorbency time of more than 1 h and water contact angle in the range of 130o-150o
Hydrophobic functionalization of viscose fabric was carried out using long chain hydrocarbon compound dodecyl acrylate (DA). The treatment was carried out in-situ using DA/helium atmospheric pressure plasma at low frequency. After the treatment, the water absorbency time of the substrate was more than 1 h and water contact angle was 143°. The functional property developed after the treatment was durable to both solvent and soap washing. Effect of various parameters such as concentration of precursor, helium flow rate, discharge voltage, discharge frequency and treatment time on functionalization was investigated.
Figure: Images of water droplet on plasma treated (a) solvent washed (b) solvent and soap washed fabrics.
Table: Water absorbency time & water contact angles of viscose fabric treated at different discharge frequencies Table: Effect of discharge voltage on water absorbency time and water contact angle of plasma treated viscose fabrics.
Functionalization of Cotton by In-Situ Reaction of Styrene in Atmospheric Pressure Plasma Zone
Cotton fabric was treated using styrene/helium glow plasma at the atmospheric pressure. After the treatment, the substrate was found to turn into a highly hydrophobic material showing water drop disappearance time of 60 min and water contact angle of 133o. The treatment was found to be durable even after vigorous washing. The effect of various parameters, such as discharge voltage and frequency, on fragmentation of styrene inside plasma zone was investigated using optical emission spectroscopy and GC–MS.
Figure: Scheme of possible fragmentation of styrene in styrene/He plasma
Figure Water contact angle of a drop placed on a as-prepared b washed cotton fabric sample after plasma treatment at frequency of 18.94 kHz and at voltage (1) 1.55 kV, (2) 1.73 kV, (3) 2.36 kV (4) 6.0 kV
Improvement in water and oil absorbency of textile substrate by atmospheric pressure cold plasma treatment
With an aim to improve water absorbency of the textile substrates, nylon and polyester fabrics were treated continuously in an atmospheric-pressure-glow-discharge-plasma produced in presence of different gases. After plasma treatment, time taken in spreading a water droplet over a pre-defined area was found to decrease significantly.However, the rate of oil absorption (a hydrophobic fluid) was also found to increase to a great extent. Spreading time for mustard oil droplet over a specified area was observed to decrease significantly from 152 s in an untreated fabric to 52 s in He plasma treated fabric for nylon, whereas, it decreased from 28.6 min in untreated fabric to 2.8 min in the treated fabric for PET samples. The effect of plasma treatment on the rate of oil absorbency was further confirmed for cotton fabrics, where the time for oil absorbency decreased from 59.5 s in the untreated sample to 30.4 s in the treated sample.
Antistatic Effect of Atmospheric Pressure Glow Discharge Cold Plasma Treatment on Textile Substrates
Hydrophobic synthetic textile substrates, nylon and polyester fabrics, were continuously treated in an atmosphericpressure-glow-discharge-cold-plasma reactor using He and air. The samples were evaluated for antistatic properties by measuring the static charge build-up and half charge decay time. The 60 sec air-plasma treated nylon fabric produced only 1.53 kV of charge and showed a significantly smaller half decay time of 0.63 sec compared to static voltage of 2.76 kV and a half decay time of 8.9 sec in the untreated nylon fabric. In comparison, the He plasma treated nylon fabrics showed relatively less improvement by producing static charge built-up of 2.12 kV and half charge decay time of 1.1 sec. Similar improvements were obtained for polyester (PET) fabrics as well. The treated samples showed good antistatic properties even after five laundry wash cycles.The results revealed that the improvement on antistatic properties are attributable to increase in the surface energy of the fabrics due to the formation of hydrophilic groups and increase in the surface area due to the formation of nano-sized horizontal and vertical channels on the fibre surface.
Atmospheric Pressure Plasma Polymerization of 1,3- Butadiene for Hydrophobic Finishing of Textile Substrates
In this study, a stable glow plasma was generated at atmospheric pressure in the mixture of gaseous reactive monomer-1,3-butadiene and He and was made to react with cellulosic textile substrate. After 12 min of plasma treatment, the hydrophilic surface of the cellulosic substrate turned into highly hydrophobic surface. The hydrophobic finish was found to be durable to soap washing. After soap washing, a water drop of 37 μl took around 250 s to get absorbed in the treated sample compared to < 1 s in the untreated samples. The plasma modified samples showed water contact angle of around 1340. Both top and bottom sides of the fabric showed similar hydrophobic results in terms of water absorbency and contact angle. The results may be attributed to chemical reaction of butadiene with the cellulosic textile substrate.