Finishing using TiO 2-nanosol treatment of cellulose acetate (CA) fabrics before and after the latter were pretreated with H 2O 2was undertaken with a view to impart unique properties to CA fabrics, notably, self-cleaning. Finishing was performed as per the pad-dry-cure method. The finishing treatment involved dispersing the nano-sized TiO 2particles in a mixture of water and ethylene glycol (1:1) and application of the dispersions to CA fabrics was made under a variety of conditions. Self cleaning ability of the fabrics is favored by 1) increasing the concentration of TiO 2-nanosol to certain limit; 2) prolongation of curing time up to 15 second; 3) raising the microwave power from 80% to 100% but with the certainty that power of 90% is the most proper. Besides, exposure time-to UV radiation-up to 90 minutes is essential to have remarkable self cleaning properties while keeping other technical properties, namely, strength, roughness and wettability practically unaltered. Incorporation of binder in the finishing pad-bath helps stabilizing the deposition of TiO 2 with excellent self-cleaning. Pretreatment of CA fabrics with H 2O 2 is a pre requisite to guarantee excellent self-cleaning ability. Thermofixation and microwave fixation produces fabrics with very comparable technical properties.
Self-cleaning is a unique textile property which caught imagination of the consumer. Nanotechnology provides a new concept for production of self-cleaning textiles particularly by incorporation of TiO2 nanoparticles in the textile structure [
It is anticipated that self-cleaning of fibrous materials such as cellulose acetate (CA) fabrics are important for their value added. To impart durable self-cleaning property to CA by applying TiO2 nanoparticles, it is a must to improve the adhesion between TiO2 and CA through alteration of the physical and chemical characteristics of CA surface. Laser irradiation pretreatment of CA surface is one technique to improve the bond-ability of TiO2 on CA fibers [
Sol-gel coating on textiles has been used to provide textiles with new properties, e.g. colouration, UV protection and medical applications [
Preparing nano-crystalline TiO2 and nano-crystalline anatase by sol-gel techniques to use them for coating the textiles was studied [
We undertake current work with a view to produce self-cleaning cellulose acetate fabrics through treatment of the latter with TiO2-nano-sol. Thus nanoparticles of TiO2 were dispersed in a mixture of water and ethylene glycol (1:1) and the treatment was performed as per the pad-dry-cure method. The treatment was carried out under a variety of conditions including concentration of TiO2-nanosol, curing time, microwave power, exposure time to UV radiation, incorporation of binder, pretreatment of CA fabrics with H2O2 prior to finishing treatment and comparison between fixation using microwave and thermofixation. Fabrics so treated were monitored for gain in whiteness index and loss in color strength as a measure of self-cleaning along with other properties, notably strength, roughness and wettability.
White secondary cellulose acetate (CA), satin weave, of density 1.32 g/cm3 and of 38.5% acetyl content was used. The fabric was cleaned in an aqueous solution containing 2 g/l of nonionic detergent (Hostapal CV, Clariant) at 60˚C for 20 min followed by warm and cold rinsing. The fabric was dried under ambient conditions.
Titanium dioxide nano-powders of size <100 nm was supplied from Aldrich (Germany). All other used chemicals such as ethylene glycol, acrylate binder were of reagent grade.
Hydrogen peroxide (50%) was of laboratory grade chemicals. Egyptol® (nonionic wetting agent based on ethylene oxide condensate) was of technical grade chemicals. Commercial coffee used as received.
Cellulose acetate fabrics were treated in ultrasonic bath using a solution containing H2O2 (10g/l) along with an nonionic wetting agent (0.5 g/l) and sodium silicate (2 g/l). The treatment was carried out at 30˚C and pH 9 for 3 min. using a material to liquor ratio 1:20. The pH was adjusted using dilute orthophosphoric acid to avoid any possible degradation of treatment ingredients previously added. After every bleaching condition, the fabrics were subjected to thorough washing with water then dried at ambient conditions [
H2O2 treated CA fabric was dried at 100˚C for 5 min to remove the moisture content present in the fabric. CA samples were immersed in a mixture of water and ethylene glycol (1:1) containing the nanoparicles of TiO2 for 5 min. The nanoparicles concentration ranged from 0.5 to 1.5 g/100g fabric). Nanoparicles of TiO2 were dispersed in a mixture of water and ethylene glycol (1:1). The padded samples were then squeezed to a pick up of 100% and the dried at 70˚C for 10 min.
Titanium dioxide treated CA samples along with the untreated sample were subjected to microwave irradiation as a means of curing using microwave oven [KOR-131 G(Olympic electric, Korea), 2450 MHz, 220 - 240 V, 50 Hz, microwave input power: 1350 W, microwave energy output: 1000 W, capacity 32 L]. The oven was operated at various power settings (80%, 90%, 100%) for different lengths of time (10, 20 and 30 sec). The cured fabric samples were rinsed (with distilled water) to remove the extra and unattached TiO2-nanoparticles followed by drying.
CA fabrics loaded with nano-TiO2 particles and those without these particles were stained by coffee and dried at 70˚C for 10 min. The fabrics were then exposed to UV irradiation using a UV light lamp (Philips TLO58W with a maximum intensity, wavelength (λ max at 365 nm). Irradiation was performed for different times (30, 60 and 90 minutes) at room temperature.
Changes in whiteness index (W.I) of fabrics loaded with TiO2 nanoparticles and stained were measured before and after exposure to UV light, as a function for self-cleaning efficiency. Whiteness measurement was carried out using Ultra Scan PRO-Hunter Lab spectrophotometer according to AATCC test method 153 (1985) [
where W.I1 is the whiteness index before exposure to U.V irradiation;
W.I2 is the whiteness index after exposure to U.V irradiation.
Fabric tensile strength test was conducted according to ASTM method 1682 (1994), which is a standard method for breaking force and elongation of tensile fabrics [
Roughness degree of the treated (nano-TiO2 loaded) and untreated fabrics was measured using a surface roughness measuring instrument SE 1700 α (Japan). The device consists of two parts; one is connected to a digital screen and the second is connected to a movable sensor, the sample is fixed manually under the sensor; which moves on the sample surface for a distance of 4 mm and then records the mean result. This operation is repeated on different places for the same sample.
Wettability, expressed as wetting time, of the treated samples was performed according to the standard method WT, AATCC Test Method 39 (1980).
The color intensity, expressed as K/S value, of the stained samples before and after exposure to sun light was, as a function for self-cleaning efficiency, determined spectrophotometrically using Ultra Scan PRO-Hunter Lab spectrophotometer. K/S was calculated by applying the Kubelka-Munk equation [
where K/S1 is the color intensity before exposure to U.V irradiation;
K/S2 is the color intensity after exposure to U.V irradiation.
All the determinations in this work were done in triplicate and the results present mean values.
The surface morphology of untreated and treated fabric was investigated by using SEM, JSMT-20, JEOL-Japan. Before examination, the fabric surface was prepared on an appropriate disk and coated randomly by a spray of gold. SEM was carried out in National Research Centre (Egypt).
According to previous reports [8,17-19] preparation of TiO2-nanosol and the gel formation/fixation of titania cluster onto cotton fabric involve a number of interacttions that may be categorized and represented as follow:
1) Preparation of TiO2-nano sol [
and/or
where R: is an organic group, and, Ti-O-Ti is a colloidal oxide network in the sol form.
2) Gel formation/fixation of titania-cluster onto cotton fabric [
With the above mechanism in mind, parameters affecting the self-cleaning ability of CA fabrics loaded with nano-TiO2, expressed as gain of whiteness index and loss of color strength, are herein presented. Furthermore the onset of such Parameters include TiO2 nano sol concentration, curing time, microwave power, time of UV irradiation, incorporation of binder and microwave fixation. On the other hand, technical properties examined encompass strength properties, roughness and wettability.
The foregoing concludes that CA fabrics loaded with TiO2 nanoparticles display self-cleaning properties, expressed as gain on whiteness index and loss in color strength (K/S). This is most probably owing to the high photo catalytic activity of the nano-sized TiO2 particles which enables generation of highly oxidative radicals onto titania film. In subsequent step, these radicals induce photodecomposition of the coffee stains on fabric surface loaded with nano-sized TiO2 particles and thus prevent them from built up [17,18].
Variations in tensile strength, elongation at break and roughness as well as wettability are a manifestation of the formation of nano-sized titania film on the fabric surface. This results in increments in both stiffness and covalent bonding between the uncondensed hydroxyl groups of titania and the hydroxyl groups of cellulose [11,14]. Indeed the observed decreased wettability by increasing TiO2-nano sol concentration is in conformation with thus.
Time and power settings of the microwave irradiation were investigated with a view of their adjustment. As shown in