**4. Results and discussions**

#### **4.1 Morphological studies**

Nylon fabric was treated with nitrogen and oxygen plasma. It can be seen from Figure 2 that the surface morphology changed after the plasma treatment. The untreated nylon fibres are smooth as shown in Fig. 2 (a) and (b). The etching, roughening effect of oxygen plasma on the surface (Fig. e and f) is more as compared with the nitrogen plasma as shown in Fig. 2 (c) and (d). It is probably due to oxygen is more reactive than nitrogen. The treated surfaces look damaged or abraded. This is due to the removal of some material by etching. Similar abraded surface topography for plasma processed wool and cotton fibers, respectively, was observed by Karahan and Ozdogan (Karahan et al., 2009; Ozdogan et al., 2009). In the case of wool fibers this helped to impart anti-felting properties to the fabrics due to loss of the scales. Significant fiber surface roughness was also observed by McCord et al. for nylon and polypropylene fibers with He and He+O2 atmospheric plasmas (McCord et al.,2002 ). It may be of interest to try to understand the morphology and mechanism of the etching process. It has been confirmed through various studies that only the amorphous portion gets degraded and etched away in the initial stage (Bhat and Deshmukh, 2002; Thomas et al., 1998; Yoon et al.,1996). The plasma process is such that the electrons and ions attack the amorphous portion, as it is loosely bound. On the other hand, the crystalline regions are more compact and hard as compared to amorphous regions and therefore the amorphous region gets removed easily in the plasma etching. As a result, the percentage crystallinity increases to some extent. This has been concluded by previous studies using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) for silk (Bhat and Nadiger, 1978). Navaneetha and Selvaraj have also observed that the effect of plasma on the amorphous zone is more predominant than the crystalline zone of the cotton fabrics (Navaneetha and Selvaraj, 2008.).

Similarly when nylon fabric was subjected to the plasma polymerization of acrylic acid (PPAA), we observed deposition as shown in Fig. 2 (g) and (h). This deposition leads to decreased capillaries present in the texture. The choice of acrylic acid monomer was based on its hydrophilic properties.

O.D. of original solution – O.D. of exhausted solution % Dye exhaustion <sup>100</sup>

Nylon fabric was treated in O2 and N2 plasma for different durations of time. Similarly plasma polymerization of acrylic acid was carried out onto the nylon fabric for different durations of time. These samples were tested for their hydrophilicity, FTIR, dyeabilty and surface morphology. In order to study the characteristics of plasma polymerized acrylic acid film, KBr disc was kept in the plasma chamber while carrying out deposition onto the fabrics. Such deposited film was used for FTIR study. The wettability of the untreated fabric was measured by contact angle measurement with respect to water and for treated samples; the time required for water drop to disappear was measured and recorded as wetting time. Average of 5 readings is reported here. The shorter is the average wetting time, better is the fabric wettability. The surface energy of untreated sample was calculated from the contact angle data using the equation given by Deshmukh and Shetty (Deshmukh and Shetty, 2008).

Nylon fabric was treated with nitrogen and oxygen plasma. It can be seen from Figure 2 that the surface morphology changed after the plasma treatment. The untreated nylon fibres are smooth as shown in Fig. 2 (a) and (b). The etching, roughening effect of oxygen plasma on the surface (Fig. e and f) is more as compared with the nitrogen plasma as shown in Fig. 2 (c) and (d). It is probably due to oxygen is more reactive than nitrogen. The treated surfaces look damaged or abraded. This is due to the removal of some material by etching. Similar abraded surface topography for plasma processed wool and cotton fibers, respectively, was observed by Karahan and Ozdogan (Karahan et al., 2009; Ozdogan et al., 2009). In the case of wool fibers this helped to impart anti-felting properties to the fabrics due to loss of the scales. Significant fiber surface roughness was also observed by McCord et al. for nylon and polypropylene fibers with He and He+O2 atmospheric plasmas (McCord et al.,2002 ). It may be of interest to try to understand the morphology and mechanism of the etching process. It has been confirmed through various studies that only the amorphous portion gets degraded and etched away in the initial stage (Bhat and Deshmukh, 2002; Thomas et al., 1998; Yoon et al.,1996). The plasma process is such that the electrons and ions attack the amorphous portion, as it is loosely bound. On the other hand, the crystalline regions are more compact and hard as compared to amorphous regions and therefore the amorphous region gets removed easily in the plasma etching. As a result, the percentage crystallinity increases to some extent. This has been concluded by previous studies using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) for silk (Bhat and Nadiger, 1978). Navaneetha and Selvaraj have also observed that the effect of plasma on the amorphous zone is more predominant than

the crystalline zone of the cotton fabrics (Navaneetha and Selvaraj, 2008.).

Similarly when nylon fabric was subjected to the plasma polymerization of acrylic acid (PPAA), we observed deposition as shown in Fig. 2 (g) and (h). This deposition leads to decreased capillaries present in the texture. The choice of acrylic acid monomer was based

Where, O.D. is the optical density at the maximum absorption wavelength.

Surface morphology was studied using SEM.

**4. Results and discussions** 

**4.1 Morphological studies** 

on its hydrophilic properties.

O.D. of original dye bath (1)

Fig. 2. SEM micrograph of (a) and (b) Untreated Nylon fabric, (c) and (d) 4 min. N2 plasma treated Nylon fabric, (e) and (f) 4 min. O2 plasma treated Nylon fabric, (g) and (h) 4 min. PPAA deposited on Nylon fabric.

Pretreatments of Textiles Prior to Dyeing: Plasma Processing 47

<sup>1710</sup>carbonyl group of acrylic acid, C=O stretching absorption band

2800 to 3800 a broad OH stretching absorption band due to monomeric and

It has been observed that our result of plasma polymerization of acrylic acid is in relevance with the literature. PPAA incorporates considerable amount of polar functional groups such as hydroxyl, carbonyl, carboxylic acid, etc. The peak intensity increases with the deposition

The contact angle of untreated nylon fabric was observed to be 830 (±2). Its surface energy comes to be 33.6 mJ/m2. Fig. 4 shows the photograph of water droplet taken on untreated

(a) (b)

However, we could not measure contact angle for any plasma processed samples. It shows that the surface energy of all the samples increases rapidly after the plasma processing.

Fig. 4. Water droplet on the nylon fabric. (a) untreated, (b) Oxygen plasma treated.

Therefore we have measured wetting time of the samples as given in Table 2.

between 1828 to 1559 cm-1 with maximum at ~1710 cm-1

Frequency, cm-1 Peak Assignment

Table 1. IR peak assignment of PPAA

and 4 minute oxygen plasma treated nylon fabric.

time.

**4.3 Wettability study** 

<sup>814</sup>O-H out of plane bending vibration of carboxylic acid 1265 C-O stretching of carboxylic acid 1425 O-H bending of carboxylic acid

dimeric C(O)OH

#### **4.2 FTIR study**

Polar functional groups are incorporated onto the polymer film during the plasma treatment. These polar groups are readily detected by ESCA (XPS), but are often missed by ATR-FTIR spectroscopy (Wu S, 1982). XPS is the best technique to study such modified surfaces. Several studies showed that air, N2, O2, NH3, etc. plasma incorporates hydrophilic functional groups onto the polymer surfaces thereby increasing wettability and surface energy (Bhat et al., 2011; Navaneetha et al., 2010; P´chal and Klenko, 2009). It has been reported that the treatment carried out in inert gases like Ar introduces oxygen moieties onto the polymer surface because of post plasma exposure of samples to atmosphere (Deshmukh and Bhat, 2003(b); Gupta et al., 2000). Therefore, IR spectra of N2 and O2 plasma treated nylon samples is not given here. The IR spectra of plasma polymerized acrylic acid (PPAA) is given in Fig. 3 below.

Fig. 3. FTIR spectra of PPAA (A) 2min. deposition, (B) 4min. deposition.

The FTIR spectrum of a PPAA film prepared using the technique of plasma polymerization was very similar to the spectrum of Poly (acrylic acid) prepared by conventional polymerization techniques and it shows all the characteristic bands. In particular, the FTIR spectrum shows that the film contains a high density of C(O)OH groups. The absorption peaks assignment is given in table below (Alaa et al., 2011; Cho et al., 1990; Chilcoti and Ratner, 1993; Eun-Young Choi and Seung-Hyeon Moon, 2007; Jafari et al., 2006; Mirzadeh et al., 2002).


Table 1. IR peak assignment of PPAA

It has been observed that our result of plasma polymerization of acrylic acid is in relevance with the literature. PPAA incorporates considerable amount of polar functional groups such as hydroxyl, carbonyl, carboxylic acid, etc. The peak intensity increases with the deposition time.
