Water adsorption
The graph was plotted between the time for water absorption by the samples of cotton fabric treated with Corona discharge and untreated as well as of the samples before and after frequent washing procedures against the applied concentration of cationic softener as shown in Figure 3, where data points are presented with a standard error. As it can be seen by comparing the two charts Figure 3a and Figure 3b that the time required for the water droplet to be absorbed in the surface of the cotton fabric samples after treating with Corona discharge significantly decreases.
The time of water absorption by cotton fabric sample not treated with Corona is 27.4s whereas it reduced to 1.52s for the sample treated with Corona discharge. Corona discharge treatments cause surface modification of cotton physically and chemically that can be observed [2, 10]. By the increasing amount of cationic softener from 1% to 4%, the time for Water absorption by the fabric sample untreated by Corona discharge was 51.4s to 126.0 s which was then decreased significantly to 2.07s to 3.87s respectively after Corona treatment.
It can also be observed that the time for water absorption by the cotton fabric samples not treated with Corona discharge more sharply increases against the addition of cationic softener as compared to those samples which were treated by the Corona discharge. The application of cationic softener on Cotton fabric samples untreated with Corona consequently produces a hydrophobic layer on the surface. While cationic softener penetrates the fibers in the samples treated with Corona due to the modification of the surface, which ultimately affects water absorption very less.
The results of water absorption time by the sample after 5 times repeated standard home washing procedure are also shown in Figure 3a and Figure 3b. As it can be seen, after finishing with a cationic softener, the time for water absorption of samples untreated with Corona has significantly decreased. Based on the fact it can be said that the cationic softener particles that are present on the surface of the fibers are removed from the surface by repetitive washing, while the samples after Corona treatment, little difference was observed in the time for absorption of water after washing and this is because of penetration of the softener molecules into the fiber structure. Corona discharge surface modification treatments peel the fiber surface. Thus vents are created through which chemicals are absorbed and surface modification of cotton fibers elaborates the phenomenon in the SEM images shown in Figure 5-B.
These results correspond with the researchers who studied the effect of dye on polyester modified with plasma at different levels. In this way, the plasma causes the fiber surface modification and uptake of dye by the polyester fiber increased [18]. Malik, Carneiro, and his co-worker also showed that plasma and Corona surface modification of cotton results in water and dye absorption. [2, 21]. Therefore it can be interpreted that, this research has resulted in more absorption of cationic softener in the fibers.
Bending length
The bending length of the samples treated with cationic softener and repetitive standard washing procedure are presented in Table 1.
In general overview, it can be perceived that by increasing the amount of cationic softener to the cotton fabric, the bending length decreases remarkably for all the samples both in warp and weft directions regardless of washing. The woven fabric has often contained less weft density as compared to the warp fabric sample is more flexible in the weft direction compared to the warp direction [22]. A similar trend of having lesser bending length in the direction of weft can be observed in this experiment too.
Repetitive washing procedure influenced the drape ability of the fabric a lot causes an increase in the bending length to some extent no matter the samples were Corona treated or not. This is because of the removal of cationic softener from the fiber surface during the washing procedure. The removal of cationic softener is more pronounced in the samples which were not treated by Corona discharge, i.e. the bending length increases up to 0.3” in warp and 0.18” in weft direction when 4% cationic softener was applied. In comparison, bending length increases less significantly for the samples which are treated by Corona demonstrated by 0.1” in the warp and same figure in weft direction with the same concentration of cationic softener.
As the results of water adsorption show, the effect of Corona discharge treatment on physical modification of the surface, the time for water absorption reduced. It can also be said that the effect on the uptake of cationic softener is also evident [2, 21], and increasing the amount of cationic softener on the fiber causes the reduction in bending length of the fabric sample.
Crease recovery angle
Crease recovery angles of the sample applied with Cationic softeners treated and untreated with Corona discharge as well as before and after frequent washing are shown in Figure 4. It can be observed that the crease recovery angle of samples applied with cationic softener and untreated with Corona increases from 218° to 241° and for Corona treated from 225° to 251° against the concentration of applied cationic softener from 0 to 4% respectively.
In samples that are applied with a cationic softener but not treated with Corona discharge, the particles of softener do not penetrate the fiber surface and remain on the surface without interaction. In contrast, the surface modification treatment with Corona causes the physical revamping of the fibers that help the better penetration of the cationic softener particles which ultimately increase resilience and crease recovery properties. The particles of the cationic softener penetrate the cracks present in the fiber surface generated by the Corona treatment, act as a filling material in the spaces between fibers and molecules in the fiber structure, and hence upsurges the wrinkle recovery of the fabric sample [23, 24]. It can also be insinuated that after repetitive washes, the crease recovery angles for the samples which are applied with cationic softener and untreated with Corona, however slightly decrease.
Surface morphology characterization
The SEM images of samples applied with cationic softener at a concentration of 4% on cotton fabric sample treated with Corona and untreated with Corona as well as of the control sample are Shown in Figure 5. Figure 5(a) represents the SEM image of the cotton fiber sample not treated with Corona as well as without application of cationic softener at the magnification of 2500 and depicts that the untreated cotton fiber surface is smooth. Figure 5(b) denotes the SEM image of a sample of a cotton fiber treated with Corona at the magnification of 2500. Micrograph indicates fractures and gaps appeared on the surface of cotton fiber as a result of physical modification by the Corona treatment. In this operation, high-energy electrons collide with the molecules present at the surface of the fiber, and consequently cracked surface is created. Also, the high energy produced during the Corona treatment could burn the surface of the fiber which leads to the converse results and prohibits the penetration of water and chemicals into the surface of the fiber [25, 26]. As the results of this study formerly suggested an increase in the rate of water absorption and chemical softener, it can be said that cracks on the fiber surface cause the absorption of softener and confirms the earlier statement. As revealed in Figures 5(c) and 5(d) that cationic softener has somewhat filled the cracks on the surface of cotton produced after Corona treatment.
Spectroscopy ATR-FTIR
Figure 6 represents the spectrum of ATR-FTIR of cotton fabric samples treated and untreated with Corona discharge. The absorption by the Cotton fiber untreated with Corona in the region of 3291 cm-1 due to stretching of alcohol OH and 1000-1200 cm-1 for the O-C stretching confirms the presence of hydroxyl groups. Corona treated cotton fabric sample absorption in the area of 1000-1200 cm1-due to O-C stretching and 3200-3600 cm1- (H-O stretching), endorses the presence of Hydroxyl groups.
Therefore, it can be understood that the cotton surface has been modified with Corona discharge and cause the creation of functional groups and chemical change. The sharp absorption in the region of 2889 and 3345cm-1 is evident in the presence of hydroxyl groups and hydrophilic cotton. The intensity of the absorption bands in the spectrum of the cationic softener impregnated cotton is low, indicating a hydrophobic surface which can be due to the coating of the cotton fiber by the softener molecules.
Figure 8 shows the ATR-FTIR spectrum related to cotton treated by Corona and applied with the cationic softener. The results show that, with the addition of softener, the intensity of absorption bands in the region of 3291cm-1 is increased proves the increase in the number of hydroxyl groups. The increase in the absorption intensity is more significant in the samples which are not Corona treated and applied with cationic softener compared to cotton after treatment with Corona discharge and cationic softener application, therefore, verifies less affected fiber surface. Hence the results of ATR-FTIR are consistent with the results of water absorption.