ile 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.
3.3. Adjustment of Curing Time and Power Setting
Time and power settings of the microwave irradiation were investigated with a view of their adjustment. As shown in Table 2, gain in whiteness index percent increases by increasing the curing time from 10 to 15 seconds. Further prolongation of time has no perceptible increase in gain in whiteness index. The same holds good for the loss in color strength. The implication of this is that the time of curing should not exceed 15 second. Within a time ranging from 10 - 15 second highly acceptable self-cleaning properties could be achieved without strength, roughness and wettability deterioration.
Table 3 shows the effect of microwave power on selfcleaning properties of CA fabric loaded with nano-sized TiO2 particles and the impact of this on other technical properties of CA fabrics. Obviously, gain in whiteness index and loss in color strength, as a measure of selfcleaning ability of the nano TiO2-loaded fabric; display the most appropriate values at a microwave power of 90%. A microwave power of 100% produces similar results but with the certainty that other technical properties, notably, tensile strength decreases. Indeed, elevating the microwave power from 80% to 100% leaves the elongation at break, roughness and wettability practically intact. This indicates that the microwave power causes stabilization of CA fabric through gel formation/fixation of titania cluster and, in so doing, imparts self-cleaning properties without harming other technical properties. Nevertheless a microwave power of 90% is advocated for the next experiments as given below.
3.4. Effect of Exposure Time to UV Irradiation
CA fabrics were treated at optimum conditions, viz. TiO2 nano particles (0.75 g/100g fabric), at a power of 90%
Table 1. Effect of TiO2-nano sol concentration on the self-cleaning ability and its onset on other technical properties of CA fabrics.
Table 2. Dependence of gain whiteness and loss in color strength (K/S) as measure of self-cleaning on time of curing and the onset of this on strength properties, roughness and wettability of CA fabric loaded with nano-sized TiO2 particles.
and curing time of 15 seconds. The so treated fabrics were then stained with coffee and exposed to UV irradiation using a UV light lamp for different times (30, 60 and 90 minutes) at room temperature. At this end, the UV irradiated fabrics were monitored for the said technical properties. Results obtained are given in Table 4.
It is clear (Table 4) that W.I gain percent and K/S loss percent, as a measure of self-cleaning properties, increase by increasing time of exposure to UV irradiation and in turn, higher UV dose the absorption of which causes photo-decomposing of coffee stain on nano-TiO2- loaded fabric surface. It is also clear that strength properties and wetting time marginally decrease and roughness degree slightly increases upon prolongation of the UV exposure time. This could be associated with changes in the molecular structure of nano TiO2-loaded CA fabrics under the influence of UV irradiation.
3.5. Incorporation of Binder during Nano-TiO2 Sol Treatment
Table 5 shows the effect of incorporation of the binder (1%) in the nano-TiO2 sol finishing formulation on self-cleaning and other technical properties of CA treated fabrics. Properties of the latter but in absence of the binder are shown in the same table for comparison. Results of Table 5 signify that fabrics finished with solution containing nano-sized TiO2 particles at a concentration of 0.75 g/100g fabric) in presence of the binder exhibit excellent self-cleaning properties, expressed as W.I gain percent, K/S loss percent. Other properties, namely, strength properties, wettability and roughness call for good performance, reflecting the role of binder in fixation of the deposits of TiO2 nanoparticles within the molecular structure of CA fibers. A more clarified picture could be obtained when the values of the technical properties of fabrics treated in presence of the binder are compared with those obtained without binder. The technical properties, notably those expressing the self-cleaning properties, are by far, superior in presence then in absence of the binder.
3.6. Microwave Fixation Process Vis-À-Vis Conventional Thermal Fixation
Table 6 summarizes the results of whiteness index gain
Table 3. Effect of microwave power on self-cleaning and other technical properties of CA fabrics treated with nano-TiO2 sol as per the pad-dry-cure method.
Table 4. Variation of self-cleaning and other properties of CA fabrics loaded with nano-sized TiO2 particles with exposure time to UV irradiation.
Table 5. Effect of incorporation of binder during treatment of CA fabrics with TiO2 nano-sol on major performance properties of the treated fabrics.
Table 6. Microwave Fixation process vis-à-vis conventional thermal fixation.
and color strength loss as a measure of self-cleaning ability of CA fabrics loaded with nano-sized TiO2 particles along with other technical properties, namely, strength, roughness and wettability. These results are obtained when CA fabrics were subjected to these finishing treatments.
Treatment 1 involves padding the CA fabrics which were not pretreated with H2O2 in nano-TiO2 sol, drying, curing using microwave then exposed to UV radiation as detailed in the footnote of the table.
Treatment II entails the same consecutive sequence but the CA fabrics were pretreated with H2O2.
Treatment III comprises the steps of treatment II but curing was effected thermally rather than by microwave. A close examination of the results of Table 6 would reveal:
a) That pretreatment of CA fabric prior to the finishing treatment under investigation is absolutely necessary to have better self-cleaning properties without adversely affecting the other technical properties.
b) That curing by making use of the microwave can eerily replace conventional thermal curing by virtue of the very comparable technical properties obtained in both cases.
The much lower values of whiteness index gain % and loss in color strength % obtained with CA fabrics processed as per treatment I suggest that the interaction of titania with the CA hydroxyls are favoured by treatment of CA with H2O2 prior to finding using nano-TiO2 sol. Beside cleaning and purifying the CA fabrics, H2O2 treatment may hydrolyze some of the acetyl groups of CA and, in so doing, creates additional hydroxyl groups in the molecular structure of CA fabrics thereby enhancing interaction of CA hydroxyls with titania hydroxyls.
3.7. SEM Images
SEM was used to clarify morphological changes in CA fabrics by finishing using nano-TiO2 sol in presence and absence of binder. Fixation of the finish was expedited through microwave irradiation or thermally.
Figure 1(a) shows the SEM image of the untreated CA fabric. The latter is characterized by a rough surface
Figure 1. SEM images of CA fabric.
along with some deposits and protruding fibres. On the contrary, the treated CA fabrics as shown by Figures 1(b) and (d) acquire a smooth surface as compared with Figure 1(c) indicating the formation of a uniform continuous titania layer but with the certainty that microwave fixation brings about smoother surfaces than does the thermofixation. Presence of the binder has no effect on surface smoothness of CA fabric finished using nanoTiO2 sol.
CA fabrics were first treated with H2O2 then subjected to TiO2-nanosol treatment as per the pad-dry-cure method. This was done to render the CA fabric self-cleaning treatment with TiO2-nanosol was carried out under different conditions. Most appropriate conditions for application of the TiO2-nanosol to CA fabrics were found to be as follows: concentration of nanosol, 0.75 g/100g fabric; curing time, 15 seconds; microwave power, 90%. In addition, exposure time to UV radiation of up to 90 minute is a must in order to achieve self-cleaning properties while preserving technical properties such as strength, roughness and wettability. The use of binder along with TiO2-nanosol pad-bath was advantageous in stabilizing the TiO2 deposit H2O2 pretreatment of CA fabrics was essential to guarantee excellent self-cleaning ability. The microwave technique produced self-cleaning fabrics the properties of which were very comparable. At any event, however, fabrics containing TiO2 deposits would be expected to find wide applications in apparel, domestic and technical textiles.