**2.2.2 Supercritical carbon dioxide technique**

270 Textile Dyeing

Ozone self-decomposes rapidly in water producing free radicals, a stronger oxidant than ozone itself (Hoigne & Bader, 1976). This property was utilized to produce hydrophilic and highly reactive high-density polyethylene (HDPE) films (Gu et al., 2009). The O2 gas rate in this study was about twelve times higher with exit ozone concentrations ranging between

**Figure 7** illustrates the difference of ozone treatment in the aqueous phase versus the gas phase. While initially there is no apparent difference in the media treatment, the peroxide generation (as measured by the iodometric method (Kokatnur & Jelling, 1941)) is greater and faster for ozonation in the aqueous phase. For all samples, it was demonstrated that the stability of the generated peroxides lasted at least 15 days with no change in concentration. The subsequent grafting of acrylamide on the aqueous ozone treated samples was successful but its performance in terms of surface energy was not contrasted to acrylamide graft

> 1.0 wt% ozone in distilled water 1.0 wt% ozone in gas phase 3.7 wt% ozone in distilled water 3.7 wt% ozone in gas phase

Ozone oxidation time (hour)

Fig. 7. Peroxides generated after different ozonation times in different media (Gu et al., 2009) Specific to fabrics, chemical modification via gas-phase ozone treatment was performed on nylon 6 taffeta, polyester taffetas (Lee et al., 2006), cationic dyeable polyester (CDP) and poly(butylene terephthalate) fibers (Lee et al., 2006, 2007). The surface analysis via ESCA was very comparable to the plasma studies by others (Fujimoto et al., 1993), the reader is referred to previous methods for process conditions (Wakida et al., 2004). Notable is that the processing time was only 10 minutes with similar surface chemistries for operations at atmospheric pressure and 0.1 MPa. The ozone-modified fabrics were treated with Disperse Red 60 and Disperse Blue 56 dyes in batch immersion at 100oC for up to 120 hours. The authors found that the internal structure of the fibers increased in crystallinity (as measured by a density gradient column and X-ray diffraction), wettability and moisture uptake upon ozone treatment. These characteristics of the modified fibers were attributed to the increase in dye uptake rate, especially for polyester fibers. The equilibrium dye uptake increased for PBT fibers, polyester taffeta and nylon 6 taffeta but remained unchanged for CDP fibers.

1-3.7 weight percent.

polymerization on gas-phase ozone treated samples.

C peroxide (mmol/ m2)

In recent years, waterless dyeing in supercritical carbon dioxide (scCO2) fluid has been gaining much interest to textile chemists. This process is deemed an environmentally safe solvent as opposed to the traditional solvent of choice, water. Application of these techniques can result in reducing waste and cost for the entire dyeing process of synthetic textiles (Kikic & Vecchione, 2003).

The possible advantages of this process are


**Figure 8** shows the supercritical carbon dioxide apparatus which is usually used for dyeing of synthetic fibers. Fabric and dye are put in the container before starting the process. The apparatus is then sealed and heated to a pre-selected dyeing temperature and CO2 is pumped simultaneously to the set pressure. The dyeing is carried out on textile depending on the type of fiber and then the pressure is slowly reduced to atmospheric at isothermal conditions (Li-qiu et al., 2005).

Fig. 8. The supercritical carbon dioxide apparatus used for dyeing of synthetic fibers 1. Liquid CO2, 2. Pump, 3,5,9. Pressure-control valves, 4. Manometer, 6.Autoclave, 7. Temperature sensor, 8. Dyepot, 10. Adjust valve (Li-qiu et al., 2005)

Bach et al. dyed PP fibers in scCO2 with different disperse dyes. They showed that disperse azo dyes with a naphthalene moiety gave much deeper colors on PP versus benzo-azo or anthraquinone dyes. They stated that improvement in dyeability is due to the changes in the crystal network of PP by the treatment in CO2 as contrasted with PP dyed in water or air (Bach, 1998).

Surface and Bulk Modification of Synthetic Textiles to Improve Dyeability 273

coating thickness improved electrical conductivity (.*cf* **Figure 9)**. The coated textiles also showed considerable improvement in UV and visible light shielding as examined by

Covalent bonding of a molecule to most non-reactive synthetic surfaces such as polyolefins typically requires surface activation via one the physical methods described earlier. To this extent, graft peroxide-initiated polymerization of acrylamide (AAm) proceeded successfully on the ozonated surfaces described in Section 2.2.1. The SEMs in **Figure 10** clearly show the progression of the surface treatment to the final brush-like topography of AAm-grafted HDPE film (Gu et al., 2009). FTIR confirmed the presence of the amide groups with peak intensity at 1667 cm-1 increasing for the samples exposed longer to ozone treatment. Finally contact angle of the samples proceed from 74.92o for virgin HDPE to 38.55o for the AAmgrafted HDPE (*cf.* Inset of **Figure 10** ). Grafting of AAm to the PU and PE films by Fujimoto et al. was favorable although the methodology was different (Fujimoto et al., 1993). In this case, thermal activation of the peroxide for AAm grafting occurred at lower temperature (60oC versus 85oc) for less time (3 hr versus 24 hr). The end result was still an outermost layer of polyacrylamide on the PU film as measured by FTIR, optical microscopy, and graft density determination by the ninhydrin method (150 g·cm-1). It was also demonstrated, however, that the grafting efficiency was reduced when the procedure was performed on PE film. This is attributed to lower levels of peroxides incorporated to the more chemicallyresistant PE film as compared to PU film (Gu et al., 2009). These two surface modifications are categorized as *"grafting from"* methods as the peroxide initiator was tethered to the fiber surface prior to the polymerization reaction. When polymer chains are absorbed (and then subsequently reacted) to a solid surface, the correct term is "*grafting to*". A thorough

UV/Vis spectrometer (Wei et al., 2008).

overview of this subject is provided by Minko (Minko, 2008).

a) = 74.92o b) = 69.71o c) = 38.55o

Fig. 10. SEM images of the morphology of the film surfaces (x 5000): a) Virgin HDPE film, b) HDPE film after ozonation in distilled water at 3.7 wt% for 1 hour, and c) AAm-grafted HDPE film ozonated in distilled water at 3.7wt% for 1 hour. Adapted from (Gu et al., 2009). Polymerization processing parameters for the grafting of 4-vinyl pyridine to PET fiber was done to increase wettability and heavy-metal capture from aqueous media (Arslan, Yigitoglu, Sanli, & Unal, 2003). Similar to previous work (Hebeish, Shalaby, & Bayazeed, 1979; Shalaby, Allam, Abouzeid, & Bayzeed, 1976; Shalaby, Bayzeed, & Hebeish, 1978), benzoyl peroxide was used as the initiator. The researchers pre-swelled the fibers in dichloroethane to aid in the absorption of initiator and monomer prior to polymerization. They evaluated monomer concentration, initiator concentration, reaction temperature and

**2.2.4 Surface grafting** 

FTIR and NMR results obtained from Nylon 6,6 fabric samples that underwent scCO2 dyeing of with a disperse-reactive dye confirmed a covalent bond with the fibers. Wash and light fastness of the fabrics showed satisfactory results. Their results indicated that fabric immersed in scCO2 does not undergo any fiber damage (Liao et al., 2000). Shim et al. studied sorption of disperse dyes in PET and PTT textiles in the presence of scCO2. They found that the dyeing rate increased monotonically with pressure at isothermal conditions and increased with temperature isobaric conditions (Shim et al., 2003). Generally, this method plasticizes the polymeric fibrous chains enhancing dye diffusion rates and increasing the ease of solvent removal. Moreover, it replaces water in dyeing processes, overcoming the problem of wastewater treatment.

#### **2.2.3 Textile surface functionalization by vapor deposition methods (VDM)**

Sputter coating is a significant technique producing functional nanostructured fibers. These functionalized fibers are essential for realizing their applications in microelectronic elements, photonics devices, and medical implants (Wei et al., 2006). Wei et al. used magnetron sputter coatings to generate functional nanostructures on polymer fiber surfaces. Conducting aluminum (Al) film, piezoelectric aluminum nitride (AlN) film, and ceramic film of aluminum oxide (Al2O3) were deposited onto PET fibers at low temperature. These nanostructured fibers have great potential for applications ranging from conductive shields, packing, and protective materials to electronic sensors.

Fig. 9. Surface morphology of textile fiber: (a) original polypropylene fiber; (b) 20nm copper coated polypropylene fiber; (c) 50nm copper coated polypropylene fiber; and (d) 100nm copper coated polypropylene fiber (Wei et al., 2008).

Copper (Cu) nanocomposite textiles were prepared by magnetron sputter coating as discussed by other researchers. The surface conductivity of the textiles coated with Cu nanostructures showed a significant increase compared to the uncoated ones. The increased coating thickness improved electrical conductivity (.*cf* **Figure 9)**. The coated textiles also showed considerable improvement in UV and visible light shielding as examined by UV/Vis spectrometer (Wei et al., 2008).

#### **2.2.4 Surface grafting**

272 Textile Dyeing

FTIR and NMR results obtained from Nylon 6,6 fabric samples that underwent scCO2 dyeing of with a disperse-reactive dye confirmed a covalent bond with the fibers. Wash and light fastness of the fabrics showed satisfactory results. Their results indicated that fabric immersed in scCO2 does not undergo any fiber damage (Liao et al., 2000). Shim et al. studied sorption of disperse dyes in PET and PTT textiles in the presence of scCO2. They found that the dyeing rate increased monotonically with pressure at isothermal conditions and increased with temperature isobaric conditions (Shim et al., 2003). Generally, this method plasticizes the polymeric fibrous chains enhancing dye diffusion rates and increasing the ease of solvent removal. Moreover, it replaces water in dyeing processes, overcoming the

**2.2.3 Textile surface functionalization by vapor deposition methods (VDM)** 

Sputter coating is a significant technique producing functional nanostructured fibers. These functionalized fibers are essential for realizing their applications in microelectronic elements, photonics devices, and medical implants (Wei et al., 2006). Wei et al. used magnetron sputter coatings to generate functional nanostructures on polymer fiber surfaces. Conducting aluminum (Al) film, piezoelectric aluminum nitride (AlN) film, and ceramic film of aluminum oxide (Al2O3) were deposited onto PET fibers at low temperature. These nanostructured fibers have great potential for applications ranging from conductive shields,

Fig. 9. Surface morphology of textile fiber: (a) original polypropylene fiber; (b) 20nm copper coated polypropylene fiber; (c) 50nm copper coated polypropylene fiber; and (d) 100nm

Copper (Cu) nanocomposite textiles were prepared by magnetron sputter coating as discussed by other researchers. The surface conductivity of the textiles coated with Cu nanostructures showed a significant increase compared to the uncoated ones. The increased

problem of wastewater treatment.

packing, and protective materials to electronic sensors.

copper coated polypropylene fiber (Wei et al., 2008).

Covalent bonding of a molecule to most non-reactive synthetic surfaces such as polyolefins typically requires surface activation via one the physical methods described earlier. To this extent, graft peroxide-initiated polymerization of acrylamide (AAm) proceeded successfully on the ozonated surfaces described in Section 2.2.1. The SEMs in **Figure 10** clearly show the progression of the surface treatment to the final brush-like topography of AAm-grafted HDPE film (Gu et al., 2009). FTIR confirmed the presence of the amide groups with peak intensity at 1667 cm-1 increasing for the samples exposed longer to ozone treatment. Finally contact angle of the samples proceed from 74.92o for virgin HDPE to 38.55o for the AAmgrafted HDPE (*cf.* Inset of **Figure 10** ). Grafting of AAm to the PU and PE films by Fujimoto et al. was favorable although the methodology was different (Fujimoto et al., 1993). In this case, thermal activation of the peroxide for AAm grafting occurred at lower temperature (60oC versus 85oc) for less time (3 hr versus 24 hr). The end result was still an outermost layer of polyacrylamide on the PU film as measured by FTIR, optical microscopy, and graft density determination by the ninhydrin method (150 g·cm-1). It was also demonstrated, however, that the grafting efficiency was reduced when the procedure was performed on PE film. This is attributed to lower levels of peroxides incorporated to the more chemicallyresistant PE film as compared to PU film (Gu et al., 2009). These two surface modifications are categorized as *"grafting from"* methods as the peroxide initiator was tethered to the fiber surface prior to the polymerization reaction. When polymer chains are absorbed (and then subsequently reacted) to a solid surface, the correct term is "*grafting to*". A thorough overview of this subject is provided by Minko (Minko, 2008).

Fig. 10. SEM images of the morphology of the film surfaces (x 5000): a) Virgin HDPE film, b) HDPE film after ozonation in distilled water at 3.7 wt% for 1 hour, and c) AAm-grafted HDPE film ozonated in distilled water at 3.7wt% for 1 hour. Adapted from (Gu et al., 2009).

Polymerization processing parameters for the grafting of 4-vinyl pyridine to PET fiber was done to increase wettability and heavy-metal capture from aqueous media (Arslan, Yigitoglu, Sanli, & Unal, 2003). Similar to previous work (Hebeish, Shalaby, & Bayazeed, 1979; Shalaby, Allam, Abouzeid, & Bayzeed, 1976; Shalaby, Bayzeed, & Hebeish, 1978), benzoyl peroxide was used as the initiator. The researchers pre-swelled the fibers in dichloroethane to aid in the absorption of initiator and monomer prior to polymerization. They evaluated monomer concentration, initiator concentration, reaction temperature and

Surface and Bulk Modification of Synthetic Textiles to Improve Dyeability 275

**Water** 

a = 77o

a = 62o

a = 72o

a = 63o

a = 39.4o @minutes **%C/ %O/ %N** 

**(XPS)** 

r = 55o 71.5/ 28.5

r = 16o 69.9/ 30.1

r = 32o 70.7/ 29.3

r = 25o 69.1/30.9

75.0/ 21.0/ 4.3 @ 180 minutes

**Reaction or molecule Contact Angle of** 

a) Virgin PET surface

b) Modification via Hydrolysis

c) Modification via Reduction

d) Modification via Glycolysis

e) Modification via Aminolysis

1998) and e) from (Nissen et al., 2001).

Table 1. Chemical reactions to the surface of PET film or fiber with corresponding

the test methods utilized for their characterization and performance.

wettability (as measured by DCA) and XPS results; a)-d) adapted from (Chen & McCarthy,

In this section, we summarize how enzymes can be used to increase the hydrophilicity of selected synthetic polymers. Increase in hydrophilicity often leads to improved dyeability of the textile products. Enzymes are also used for the synthesis, surface functionalization and grafting of polymers that are used as textile fibers, however it is beyond the scope of this book chapter. We will discuss both the enzymes for hydrolysis of synthetic fibers as well as

time to determine the optimum grafting conditions for a maximum yield of 70%. The incorporation of 4-vinyl pyridine resulted in a 40% increase of water absorption at the maximum graft yield. The chemical initiator immersion technique for benzoyl peroxide and ammonium persulphate was implemented for grafting acrylic acid onto polylactide fibers. Both techniques for grafting were inefficient to produce significant improvement in dyeability. They do note that layer-by-layer deposition provided surprising results in that the alternative barrier layer impeded the diffusion of oxygen thus prevention of polymer (PLA) degradation fibers. Dyeability as observed by K/ S values was also the highest for the layer-by-layer modification technique.

**Table 1** contrasts four chemical reaction schemes to modify PET surfaces without physical modification (Chen & McCarthy, 1998; Nissen, Stevens, Stuart, & Baker, 2001). PET modification by glycolysis was determined most effective as measured by percent concentration of hydroxyl groups. The quantity of hydroxyl groups was assessed by X-ray photoelectron spectroscopy (XPS), dynamic contact angle (DCA) and labeling reactions. The labeling reactions combined with DCA are key results to conclude the increase effectiveness of glycolysis over hydrolysis and reduction of PET surfaces for incorporating hydrophilicity. Although XPS is surface sensitive to the first 100 angstroms, it is also performed in vacuum. Functionalizing the surface with non-polar moieties (fluorine) insure that their preferred orientation state is at the non-polar interface (air then vacuum) versus buried beneath the polymer surface. One final chemical reaction to be discussed for PET modification is aminolysis (Nissen et al., 2001). This reaction forms amide groups through the reaction of polyester's carbonyl with a primary amine. This reaction was done in the early 1960's to improve wettability, reduce static electricity and increase dyeability (Farrow, Ravens, & Ward, 1962; Kim & Ko, 1989). This reaction can be quite severe to the fibers with complete degradation as a result. To temper fiber degradation, long chain multifunctional amines such as tetraethylenepentamine (TTEPA) has been employed with favorable results (Nissen et al., 2001). While XPS showed no difference in % nitrogen content with reaction time, titration and DCA methods show an optimum wettability or amide content at 180 minutes. This indicated that the reaction was proceeding through the depth of the fiber which can also positively impact the diffusion of a dye throughout the fiber.

#### **2.2.5 Enzyme surface modification of textiles**

Processing with enzymes is one of the best environmental friendly applications of biotechnology in textile industry (Cavaco-Paulo & Gubitz, 2003; 2008; Agrawal et. al., 2008; Parvinzadeh et. al., 2009). Enzymes are biological catalysts that mediate virtually all of the biochemical reactions that constitute metabolism in living systems. They accelerate the rate of chemical reaction without themselves undergoing any permanent chemical change.

All known enzymes are proteins and consist of one or more polypeptide chains. The influence of many chemical and physical parameters such as salt concentration, temperature and pH on the rate of enzyme catalysis can be explained by their influence on protein structure. Some enzymes require small non-protein molecules, known as cofactors, in order to function as catalysts (Palmer & Bonner, 2007). Enzymes differ from chemical catalysts in at least two ways. Enzymes have far greater reaction specificity than chemically catalyzed reactions rarely forming by-products. In contrast to chemical catalysis, enzymes catalyze reactions under milder reaction conditions (temperatures way below 100°C), at atmospheric pressures and at neutral pHs (Cavaco-Paulo & Gubitz, 2003).

time to determine the optimum grafting conditions for a maximum yield of 70%. The incorporation of 4-vinyl pyridine resulted in a 40% increase of water absorption at the maximum graft yield. The chemical initiator immersion technique for benzoyl peroxide and ammonium persulphate was implemented for grafting acrylic acid onto polylactide fibers. Both techniques for grafting were inefficient to produce significant improvement in dyeability. They do note that layer-by-layer deposition provided surprising results in that the alternative barrier layer impeded the diffusion of oxygen thus prevention of polymer (PLA) degradation fibers. Dyeability as observed by K/ S values was also the highest for the

**Table 1** contrasts four chemical reaction schemes to modify PET surfaces without physical modification (Chen & McCarthy, 1998; Nissen, Stevens, Stuart, & Baker, 2001). PET modification by glycolysis was determined most effective as measured by percent concentration of hydroxyl groups. The quantity of hydroxyl groups was assessed by X-ray photoelectron spectroscopy (XPS), dynamic contact angle (DCA) and labeling reactions. The labeling reactions combined with DCA are key results to conclude the increase effectiveness of glycolysis over hydrolysis and reduction of PET surfaces for incorporating hydrophilicity. Although XPS is surface sensitive to the first 100 angstroms, it is also performed in vacuum. Functionalizing the surface with non-polar moieties (fluorine) insure that their preferred orientation state is at the non-polar interface (air then vacuum) versus buried beneath the polymer surface. One final chemical reaction to be discussed for PET modification is aminolysis (Nissen et al., 2001). This reaction forms amide groups through the reaction of polyester's carbonyl with a primary amine. This reaction was done in the early 1960's to improve wettability, reduce static electricity and increase dyeability (Farrow, Ravens, & Ward, 1962; Kim & Ko, 1989). This reaction can be quite severe to the fibers with complete degradation as a result. To temper fiber degradation, long chain multifunctional amines such as tetraethylenepentamine (TTEPA) has been employed with favorable results (Nissen et al., 2001). While XPS showed no difference in % nitrogen content with reaction time, titration and DCA methods show an optimum wettability or amide content at 180 minutes. This indicated that the reaction was proceeding through the depth of the fiber which can

Processing with enzymes is one of the best environmental friendly applications of biotechnology in textile industry (Cavaco-Paulo & Gubitz, 2003; 2008; Agrawal et. al., 2008; Parvinzadeh et. al., 2009). Enzymes are biological catalysts that mediate virtually all of the biochemical reactions that constitute metabolism in living systems. They accelerate the rate of chemical reaction without themselves undergoing any permanent chemical change. All known enzymes are proteins and consist of one or more polypeptide chains. The influence of many chemical and physical parameters such as salt concentration, temperature and pH on the rate of enzyme catalysis can be explained by their influence on protein structure. Some enzymes require small non-protein molecules, known as cofactors, in order to function as catalysts (Palmer & Bonner, 2007). Enzymes differ from chemical catalysts in at least two ways. Enzymes have far greater reaction specificity than chemically catalyzed reactions rarely forming by-products. In contrast to chemical catalysis, enzymes catalyze reactions under milder reaction conditions (temperatures way below 100°C), at atmospheric

also positively impact the diffusion of a dye throughout the fiber.

pressures and at neutral pHs (Cavaco-Paulo & Gubitz, 2003).

**2.2.5 Enzyme surface modification of textiles** 

layer-by-layer modification technique.


Table 1. Chemical reactions to the surface of PET film or fiber with corresponding wettability (as measured by DCA) and XPS results; a)-d) adapted from (Chen & McCarthy, 1998) and e) from (Nissen et al., 2001).

In this section, we summarize how enzymes can be used to increase the hydrophilicity of selected synthetic polymers. Increase in hydrophilicity often leads to improved dyeability of the textile products. Enzymes are also used for the synthesis, surface functionalization and grafting of polymers that are used as textile fibers, however it is beyond the scope of this book chapter. We will discuss both the enzymes for hydrolysis of synthetic fibers as well as the test methods utilized for their characterization and performance.

Surface and Bulk Modification of Synthetic Textiles to Improve Dyeability 277

Enzymes such as proteases, amidases and cutinase can hydrolyse PA (*.cf* **Table 2**). A model substrate (adipic acid bishexyl-amide) has been developed for screening PA hydrolysis activity of given enzymes. It has been found that protease from *Beauveria sp*., an amidase from *Nocardia sp.* and a cutinase from *F. solani pisi* can degrade the model substrate and correlated with PA hydrolysis activity (Heumann, et. al., 2006). For actual PA substrates; it has been demonstrated by Parvinzadeh et.al (2009) that protease treated Nylon 66 fabrics shows higher dye bath exhaustion with reactive and acid dyes. The intensity of major peaks in FTIR spectra of the protease treated samples is in favor of chemical changes of the polypeptide functional groups in the fabric. The results of color measurements showed that there is a direct co-relation between the concentrations of enzyme against the darker shade of the dyed fabric. In a separate study performed by the same researchers, it was confirmed that acid and disperse dyes showed higher exhaustion on the protease (Parvinzadeh, 2009)

> **Key Analysis Methods**

XPS, HPLC, NH3 formation, dye-binding assay

XPS, NH3 formation, dye-binding assay [2]

XPS, FTIR, SEM, dyebinding assay [5]

Release of oligomers, reactive dye-binding assay, hydrophilicity

FTIR, SEM, UV-vis spectrophotometer, thermal, dyeability, hydrophilicity [8-10].

[1,3,4]

[3,7]

EC 3.5: enzymes acting on carbonnitrogen bonds, other than peptide

Nitrile hydrolase

Nitrilase [5]

bonds

[2]

[4, 9] Amidase [7]

[1] = Vertommen et. al., 2005; [2] = Tauber et. al., 2000; [3] = Wang et. al., 2004; [4] = Battistel et al., 2001;

**2.2.5.3 Enzymatic hydrolysis of polyamides (PA)** 

EC 3.1: enzyme acting on ester bond

Cutinase [1] Lipase [3] Serine esterase [4]

Cutinase [3]

Lipase [9]

Table 2. Enzymatic modification of synthetic polymers

Polyacrylonitrile Cutinasea [6] -

**Key Synthetic Fibers** 

**PAN –** 

**PET –** Polyethylene terephthalate

**PA** – Polyamide

& lipase (Kiumarsi & Parvinzadeh, 2010) treated Nylon 6 samples.

**EC 3: Hydrolase class of enzymes** 

EC 3.4: enzymes acting on peptide bond


Proteases

aPAN co-polymer with 7% vinyl acetate, FTIR: Fourier-transform infrared spectroscopy, SEM: scanning electron microscopy, HPLC: High Performance Liquid Chromatography,

[5] = Fischer-Colbrie et. al., 2006; [6] = Matama, et. al., 2006 ; [7] = Heumann, et. al., 2006; [8] = Parvinzadeh, 2009; [9] = Kiumarsi & Parvinzadeh, 2010; [10] = Parvinzadeh et. al., 2009

#### **2.2.5.1 Enzymatic hydrolysis of polyesters / PET**

Enzymes are potential tools for PET hydrolysis (Vertommen et. al., 2005). As illustrated in Table 2, PET hydrolyzing enzymes belong to the hydrolase class (EC 3.1) such as cutinases, lipases and esterases (Vertommen et. al., 2005; Wang et. al., 2004; Battistel et al., 2001). PET was hydrolyzed by cutinases from organism *F. solani, F. oxysporum* and from *Pencillium citrinum*. Other PET-hydrolyzing enzymes are lipases, such as those from *Humicola sp., Candida sp., Pseudomonas sp.* and *Thermomyces lanuginosus* (Gubitz & Cavaco-Paulo, 2008). In addition to enzymatic hydrolysis, the simple adsorption of enzyme protein to the polymer can also increase the hydrophilicity of PET owing to the hydrophilicity of the protein. High crystallinity of PET polymers negatively affects the ability of the enzymes to hydrolyze which has already been shown for enzymes from *F. solani* and from *T. fusca* (Vertommen et. al., 2005; Cavaco-Paulo & Gubitz, 2008).

#### **2.2.5.2 Enzymatic hydrolysis of polyacrylonitrile (PAN)**

PAN (*.cf* **Figure 11**) is a collective name for all polymers that consist of at least 85% acrylonitrile monomer (BISFA, 2009). The homopolymer (100% acrylonitrile) is difficult to process and dye thus is only for industrial applications. The co-monomers in acrylic fibers are selected for fiber specific properties, such as dyeability with sodium methallyl sulfonate, sodium sulfophenyl methallyl ether, etc (Cavaco-Paulo & Gubitz, 2003).

Acrylic fibers comprising negative groups can be dyed with basic (cationic) dyes under carefully controlled conditions. Dyeing is usually performed in the presence of a retarder, which decreases the dyeing process rate for uniform shade reproduction. Finishing processes for PAN are limited since desirable properties can be more easily incorporated by copolymerization or by modification on the fiber level. For example, highly absorbent fibers are made by inclusion of a hydrophilic co-monomer which is subsequently removed by hydrolysis.

Fig. 11. Polyacrylonitrile 89-95% homopolymer, R = CN and up to 10% copolymer, R = vinyl acetate, COOH, SO3H, OSO3H etc

It has been shown that bacterial strains, such as *Micrococcus luteus,* can degrade PAN fibers. During this process, poly(acrylic acid) is released from PAN as confirmed by NMR analysis (Fischer-Colbrie et al., 2007). The release of poly(acrylic acid) from PAN, together with the formation of ammonia, was also shown for commercial nitrilases (Matama et. al., 2007). Several researchers converted the nitrile groups of PAN to the corresponding acids or amides by nitrilases or by an enzyme system comprising nitrile hydratase and amidase, respectively resulting in major increases in hydrophobicity (Tauber et. al., 2000; Fischer-Colbrie et al., 2007) (*.cf* **Table 2**). These changes in surface properties corresponded to an 80% increase in the surface oxygen-to-carbon (O/C) ratio attributed to enzymatic hydrolysis of the nitrile groups (Matama et. al., 2007). Commercial PAN-based materials usually contain around 7% vinyl acetate to reduce rigidity of the polymer. The vinyl acetate moieties in PAN can be hydrolyzed by cutinases and lipases, making this approach applicable to most commercially available PANs (Matama, et. al., 2006).

#### **2.2.5.3 Enzymatic hydrolysis of polyamides (PA)**

276 Textile Dyeing

Enzymes are potential tools for PET hydrolysis (Vertommen et. al., 2005). As illustrated in Table 2, PET hydrolyzing enzymes belong to the hydrolase class (EC 3.1) such as cutinases, lipases and esterases (Vertommen et. al., 2005; Wang et. al., 2004; Battistel et al., 2001). PET was hydrolyzed by cutinases from organism *F. solani, F. oxysporum* and from *Pencillium citrinum*. Other PET-hydrolyzing enzymes are lipases, such as those from *Humicola sp., Candida sp., Pseudomonas sp.* and *Thermomyces lanuginosus* (Gubitz & Cavaco-Paulo, 2008). In addition to enzymatic hydrolysis, the simple adsorption of enzyme protein to the polymer can also increase the hydrophilicity of PET owing to the hydrophilicity of the protein. High crystallinity of PET polymers negatively affects the ability of the enzymes to hydrolyze which has already been shown for enzymes from *F. solani* and from *T. fusca* (Vertommen et.

PAN (*.cf* **Figure 11**) is a collective name for all polymers that consist of at least 85% acrylonitrile monomer (BISFA, 2009). The homopolymer (100% acrylonitrile) is difficult to process and dye thus is only for industrial applications. The co-monomers in acrylic fibers are selected for fiber specific properties, such as dyeability with sodium methallyl sulfonate,

Acrylic fibers comprising negative groups can be dyed with basic (cationic) dyes under carefully controlled conditions. Dyeing is usually performed in the presence of a retarder, which decreases the dyeing process rate for uniform shade reproduction. Finishing processes for PAN are limited since desirable properties can be more easily incorporated by copolymerization or by modification on the fiber level. For example, highly absorbent fibers are made by inclusion of a hydrophilic co-monomer which is subsequently removed by

Fig. 11. Polyacrylonitrile 89-95% homopolymer, R = CN and up to 10% copolymer, R = vinyl

It has been shown that bacterial strains, such as *Micrococcus luteus,* can degrade PAN fibers. During this process, poly(acrylic acid) is released from PAN as confirmed by NMR analysis (Fischer-Colbrie et al., 2007). The release of poly(acrylic acid) from PAN, together with the formation of ammonia, was also shown for commercial nitrilases (Matama et. al., 2007). Several researchers converted the nitrile groups of PAN to the corresponding acids or amides by nitrilases or by an enzyme system comprising nitrile hydratase and amidase, respectively resulting in major increases in hydrophobicity (Tauber et. al., 2000; Fischer-Colbrie et al., 2007) (*.cf* **Table 2**). These changes in surface properties corresponded to an 80% increase in the surface oxygen-to-carbon (O/C) ratio attributed to enzymatic hydrolysis of the nitrile groups (Matama et. al., 2007). Commercial PAN-based materials usually contain around 7% vinyl acetate to reduce rigidity of the polymer. The vinyl acetate moieties in PAN can be hydrolyzed by cutinases and lipases, making this approach applicable to

**2.2.5.1 Enzymatic hydrolysis of polyesters / PET** 

al., 2005; Cavaco-Paulo & Gubitz, 2008).

acetate, COOH, SO3H, OSO3H etc

most commercially available PANs (Matama, et. al., 2006).

hydrolysis.

**2.2.5.2 Enzymatic hydrolysis of polyacrylonitrile (PAN)** 

sodium sulfophenyl methallyl ether, etc (Cavaco-Paulo & Gubitz, 2003).

Enzymes such as proteases, amidases and cutinase can hydrolyse PA (*.cf* **Table 2**). A model substrate (adipic acid bishexyl-amide) has been developed for screening PA hydrolysis activity of given enzymes. It has been found that protease from *Beauveria sp*., an amidase from *Nocardia sp.* and a cutinase from *F. solani pisi* can degrade the model substrate and correlated with PA hydrolysis activity (Heumann, et. al., 2006). For actual PA substrates; it has been demonstrated by Parvinzadeh et.al (2009) that protease treated Nylon 66 fabrics shows higher dye bath exhaustion with reactive and acid dyes. The intensity of major peaks in FTIR spectra of the protease treated samples is in favor of chemical changes of the polypeptide functional groups in the fabric. The results of color measurements showed that there is a direct co-relation between the concentrations of enzyme against the darker shade of the dyed fabric. In a separate study performed by the same researchers, it was confirmed that acid and disperse dyes showed higher exhaustion on the protease (Parvinzadeh, 2009) & lipase (Kiumarsi & Parvinzadeh, 2010) treated Nylon 6 samples.


aPAN co-polymer with 7% vinyl acetate, FTIR: Fourier-transform infrared spectroscopy,

SEM: scanning electron microscopy, HPLC: High Performance Liquid Chromatography,

[1] = Vertommen et. al., 2005; [2] = Tauber et. al., 2000; [3] = Wang et. al., 2004; [4] = Battistel et al., 2001;

[5] = Fischer-Colbrie et. al., 2006; [6] = Matama, et. al., 2006 ; [7] = Heumann, et. al., 2006;

[8] = Parvinzadeh, 2009; [9] = Kiumarsi & Parvinzadeh, 2010; [10] = Parvinzadeh et. al., 2009

Table 2. Enzymatic modification of synthetic polymers

Surface and Bulk Modification of Synthetic Textiles to Improve Dyeability 279

Currently, we are observing an intensive increase in the production of textiles made of synthetic polymers. Synthetic fibers have high mechanical properties and are extremely rigid apart from other properties such as having low porosity and lower swelling etc. These properties are directly related to low dyeability with the standard dyeing technology. Synthetic fibers normally have a high glass transition temperature which makes it impossible for the dye molecule to penetrate into the fibers, especially when using water (H2O) as a solvent. In some cases, it is possible to use other solvents or other fiber-swelling compounds to reduce the glass transition temperature of fibers. **Table 3** illustrates some key examples of sol gel method applied on textile based materials to improve it dyeability.

**Fabric Dye(s) Technique / key results Reference** 

Dyes immobilized modified silica sol to reduce dye leaching from the substrate.

trimethoxysilyl propyl methacrylate in isopropanol with supporting chemicals

Functionalization of the titanosilicates with ethylenediamine groups was carried out via the sol gel process, using the hydrolytic route followed by dyeing.

Sol was prepared by hydrolysis of tetraethoxysilane (TEOS) in presence of HNO3 and H2O, for deposition of porous

SiO2 film on polyester fabric.

(water, HCl, benzoyl peroxide).

The sol–gel consisted of 50% tetraethoxysilane (TEOS) and 50% methyltriethoxysilane (MTEOS) (w/w).

Table 3. Improving dyeability of various textile based materials using sol gel method.

In the surface treatment of polymer structures, it is necessary to use hybrid layers based on a mixture of inorganic and organic polymer compounds, which are connected at the end of the process to a single macromolecular network (.*cf* **Table 3**). The inorganic part is linked with chemical, mechanical and thermal stability. The application of sol gel technology for improving dyeability is still at relatively early stage of development. However, looking at the trends, it is expected that sol gel technology will play important role towards improving

**2.2.7 Nano-modifications of textiles surfaces using layer-by-layer deposition methods**  A variety of functional thin films can be produced using the layer-by-layer (LbL) assembly technique (Ariga, Hill, & Ji, 2007; Decher, 2003). LbL-based thin films are currently being

The sol is the blending of 3-

**(**Nedelčev et. al., 2008)

(Barabi et. al., 2010)

**(**Chládova, et. al., 2011)

(Ismail, et. al., 2011)

(Marc¸al, L. et. al., 2011)

**2.2.6.2 Dyeing of textiles based materials** 

Rhodamine B, Naphthol Blue Black, Metanil Yellow & Bismarck Brown R

Total 12 dyes belongs to cationic dyes, disperse dyes & metal complex dyes

pH sensitive dye methyl red (MR), tropaeolin (TO) and

dyeability and bringing new functionality together.

bromocresol green (BCG).

Titanosilicates Azo dye Orange II

(PET) Disperse Blue 56

**Materials/** 

Polyester /Viscose

Polyester

Glass fibers

Glass

To conclude, in coming years, the textile industry will go towards sustainable technologies and developing environmentally safer methods for textiles processing. One way is the processing with enzymatic system, rather than conventional chemical methods. There are several ways to improve the dyeability of any synthetic fibers. However, enhancement of the hydrophilicity of synthetic polymers is a key requirement for better dyeability. Enzymes have proved to be environmental friendly tools for hydrolysis of synthetic polymers, specifically on the polymer surface, without compromises in polymer bulk properties. In general hydrolases class of enzymes (EC 3.1: cutinase, lipase, esterase, EC 3.4: protease and EC 3.5: nitrilase, nitril hydrolase, amidase etc) are used for improving hydrophilicity of synthetic fibers such as PET, PAN and PA respectively.

## **2.2.6 Modification of textile surfaces using sol-gel technique**

A sol-gel technology is probably one of the most important developments in material science during the last decades. The sol-gel technique offers far reaching possibilities for creating new surface properties. Scientific literature demonstrates a wide array of functionalities that have been achieved by application of sol-gel coatings on textile surfaces. Its inorganic nature makes sol–gel layers very strong with nanometer-thick layers (Mahltig & Textor, 2008). Sol gel applications for textiles includes manipulation or changing


Sol-gel technology offers the possibility of tailoring surface properties to a certain extent, and combining different functionalities into a single material. The added advantage is that the application of sols can be carried out with techniques commonly used in the textile industry such as, a simple dip or padding process followed by a thermal treatment in a stenter frame.

#### **2.2.6.1 The sol gel principle**

The preparatory material or precursor used to produce the "sol" usually consists of inorganic metal salts or metal organic components, such as metal alkoxides (Mahltig & Textor, 2008; Chládová1, et. al., 2011). These precursors are subjected to a series of hydrolysis and polymerization reactions to create a colloidal suspension or "sol". This sol is deposited on the surface of materials, transferred into a gel and finally into a layer of oxide by heat treatment. In production and for research purposes, SiO2 and TiO2 layers are deposited most often. Also, layers of many other compositions containing Al2O3, B2O3, ZrO2, PbO and other oxides are often prepared. Next to the clearly inorganic layers, hybrid inorganic-organic layers have also been developed (production terms ORMOCER, ORMOSIL and NANOMER), which contain both chemical bonding of organic substances and functional groups next to silicon, titanium, zirconium and oxygen (Chládová, et. al., 2011).
