**2.2.8 Micro-encapsulation method to enhance dyeing process**

Microencapsulation is actually a micro-packaging process involving the production of microcapsules. These materials act as barrier walls of different solids or liquids as cores. The wall has the ability to protect the core from hazardous environments, i.e. oxidization, heat, acidity, alkalinity, moisture or evaporation. They are produced by depositing a thin polymer coating on small solid particles or liquid droplets, or on dispersions of solids in liquids. The core contents are released under controlled conditions to suit a specific purpose (Cheng et al., 2008).

The most commonly methods used for preparation of microencapsules are complex coacervation, polymer-polymer incompatibility, interfacial polymerization and in situ polymerization, spray drying, centrifugal extrusion, air suspension coating, pan coating and emulsion hardening method (Cheng et al., 2008). In dyeing of synthetic fibers, the major interest in microencapsulation is currently in the application of dyes as core and liposome as shell. Liposomes are artificially prepared vesicles made of lipid bilayer that can be filled with various materials. They comprise naturally-derived phospholipids with mixed lipid chains (*.cf* **Figure 14** ).

Fig. 14. Structure of liposome.

Gomez and Baptista studied microencapsulation of the dye in liposomes with lecithin from soy as an alternative to retarding and leveling agents. Liposomes were prepared with soy lecithin at different concentrations, containing the commercial acid dye C.I. Acid Blue 113. The effect on the dyeing rate of the microencapsulated dyes was compared with that from common retarding and leveling agents. The influence of surfactants on the stability of the liposomes and hence on the exhaustion curves of the dyeing was also evaluated. Interesting results obtained from exhaustion curves of anionic and non-ionic surfactants compared with commercial retarding and leveling agent (Gomez & Baptista, 2001).

Marti et al. used phosphatidylcholine liposomes instead of synthetic surfactants as dispersing agent for disperse dyeing. They calculated the turbidity ratio to assess the dispersion behavior of different liposome-dispersed dye preparations compared with commercial dye forms. Results indicated that liposomic preparations diminish the aggregation of dye molecules that normally occurs at high temperatures. They also found the potential efficacy of liposomes as natural surfactants which can be applied to disperse dye formulations to dye polyester fibers with good dye exhaustion and washing fastness. This environmentally friendly biological surfactant, phosphatidylcholine, duly structured as

Surface and Bulk Modification of Synthetic Textiles to Improve Dyeability 285

In recent years, synthetic polymer-nanometric filler composites have generated significant attention in diverse applications such as transportation vehicles, construction materials, electronics, sporting goods, packaging, household and textile industries (Sinha Ray & Okamoto, 2003; Leszczy´nska et al., 2007a). The aim is to enhance a wide range of properties including mechanical properties (modulus, stiffness and strength), barrier, flame retardancy, solvent and heat resistance, biodegradability, chemical and thermal stability as well as improvement in dyeability relative to a virgin polymer (Leszczy´nska et al., 2007b, Pesetskii et al., 2007). In order to obtain these specifications, fillers such as cellulose, clay, calcium carbonate, carbon, metal oxides and various forms of silica have been developed by different researchers. In this regard, the geometrical shape of the particles plays an important role in determining the properties of composites (Bhat et al., 2008; Njuguna et al.,

Processing of such polymeric nanocomposites are more difficult compared to the corresponding pure polymers since such inorganic nanoparticles have strong tendencies to agglomerate. To overcome such difficulties, the sol-gel method, LbL deposition, in situ polymerization and melt processing are put into practice. The last method is still the most cost effective, simple, feasible and environmentally benign process for the mass production

Considerable efforts have been devoted to improve various physical, mechanical and barrier properties of PET through mixing it with nanoclays (Phang et al., 2004; Chang et al., 2004; Chang et al., 2005; Jawahar et al., 2005). The layered clays used are mica, fluoro-mica, hectorite, saponite, etc., but one of the most commercially interesting clay is bentonite belonging to a structural family known as the 2:1 phyllosilicates (Calcagno et al., 2007). It is well known that the clay minerals have also been used as adsorbent for removal of acid, reactive, disperse and basic dyes from aqueous solutions due to the fact that they are globally abundant and inexpensive (Xiao et al., 2005). Their inner layers comprise an octahedral sheet, which is situated between two tetrahedral sheets. The substitutions of Al3+ for Si4+ in the tetrahedral layer and Mg2+ or Zn2+ for Al3+ in the octahedral layers result in a net negative surface charge ion in water which cause the repulsion interaction

The dyeability of synthetic fibers depends on their physical and chemical structure. Dyeing process consist of three steps including the diffusion of dye through the aqueous dye bath on to the fiber, the adsorption of dye into the outer layer of the fiber and the diffusion of dye from the adsorbed surface into the fiber interior. It was shown by researchers that functional groups of PET and water molecules play a great role in this process. The terminal carboxylic and hydroxyl groups in PET chains interact with water molecules. This makes a swelled fiber resulting to increase the attraction of disperse dye by these functional groups of fiber

The proportion of crystalline and amorphous regions of polymer is another factor influencing the dyeability. Researchers are concerned with the development and implementation of new techniques in order to fulfill improvement in dyeability of various polymers. Blending of polymeric fibers with nanoclays as inexpensive materials is still claimed as cost effective method to enhance dyeability (Geoghegan & Krausch, 2003). Up to now, only two research articles are focused on dyeing properties of polypropylene- and polyamide 6- layered clay incorporated nanocomposites prepared by melt compounding

**3. Bulk modification of synthetic textiles using nanomaterials** 

of polymeric nanocomposite (Burgentzle´ et al., 2004; Modestia et al., 2007).

with anionic dyes (Parvinzadeh & Eslami, 2011).

2008; Ma et al., 2003).

(Kirk–Othmer, 1998).

liposomes, can substitute high amounts of synthetic dispersing agents in disperse dye formulations (Marti et al., 2011).

Yan et al. suggested microencapsulated disperse dyes to dye PET in the absence of auxiliaries and without reduction clearing. They studied the dyeing behaviors and dyeing kinetic parameters of microencapsulated disperse dye on PET compared with those of commercial disperse dyes with auxiliary solubilization. Their results showed that the dyeing behaviors of disperse dye are influenced greatly by microencapsulation. The diffusion of disperse dyes from microcapsule onto fibers can be adjusted by the reactivity of shell materials and mass ratios of core to shell. The disparity of diffusion between two disperse dyes can be reduced by microencapsulation. In addition, the microencapsulation improves the utilization of disperse dyes due to no auxiliary solubilization (Yan et al., 2011).

#### **2.2.9 Micro surface modification of textiles by aqueous solutions**

Alkaline, acidic and solvents hydrolysis is another method to improve various physical and chemical properties of synthetic fibers (Shcherbina et al., 2008; Park et al., 2009; Veronovski et al., 2009; Barantsev et al., 2007; Konovalova & Rabaeva, 2007; Chapurina et al., 2005; Hou et al., 2009). Alkaline hydrolysis has been studied extensively to overcome some problems of low water absorption properties and softness as alkaline hydrolysis improves the water absorption properties and softness of the PET fiber to give it a character similar to that of natural fibers (Prorokova et al., 2009; Chu et al., 2005). The alkaline hydrolysis of PET fibers is usually carried out with an aqueous alkaline solution, such as sodium hydroxide. In the alkaline hydrolysis process, PET undergoes a nucleophilic substitution. Chain scission of PET occurs, resulting in a considerable weight loss and the formation of hydroxyl and carboxylate end groups, which improves the handling, moisture absorption and dyeability of the fabric with enhanced softness (Mikhailova et al., 2008; Prorokova & Vavilova, 2004; Sohn et al., 2007; Stakne et al., 2003, Akbarov et al., 2006; Pavlov et al., 2001).

The effects of pretreatment reagents on the hydrolysis and physical properties of PET fabrics were investigated under various alkaline hydrolysis treatment and pretreatment conditions by Kim and his colleagues. Solvents used for pretreatment included benzyl alcohol and 2 phenyl ethanol. Results indicated that fabric weight loss, crystallinity, the initial and maximum water absorption increased with increasing hydrolysis time (Kim et al., 2009).

Jain et al. reduced multi-filamentous polyacrylonitrile (PAN) fibers to amino groups using lithium aluminum hydride for immobilization of antibodies and detection of analyte. 24 h reduced fibers gave the most stable and reproducible results on immobilization of antibodies. Modified PAN fibers had a strong potential to be used as matrix for the detection of pathogenic bacteria and medical diagnostics (Jain et al., 2009). Another approach carried out by Cui and Yoon to modify the surface of PET film by treatment with ethoxylated hexylaminoanthraquinones synthesized by the reaction of 1 aminoanthraquinone with poly(ethylene glycol)s via hexamethylene spacer. The ethoxylated hexylaminoanthraquinones were adsorbed only onto the extreme surface of PET and water contact angle was decreased by the adsorption (Cui & Yoon, 2003).

A comprehensive collection of wet-chemical analyses of oxidized surfaces of poly(ethylene terephthalate) or polyolefin was presented by Knittel and Schollmeyer. Advanced oxidation of textile samples has been done using ozone and UV functionalization. They claimed that method presented uses inexpensive equipment and can be done quickly in a normal lab even as a process control (Knittel & Schollmeyer, 2008).

liposomes, can substitute high amounts of synthetic dispersing agents in disperse dye

Yan et al. suggested microencapsulated disperse dyes to dye PET in the absence of auxiliaries and without reduction clearing. They studied the dyeing behaviors and dyeing kinetic parameters of microencapsulated disperse dye on PET compared with those of commercial disperse dyes with auxiliary solubilization. Their results showed that the dyeing behaviors of disperse dye are influenced greatly by microencapsulation. The diffusion of disperse dyes from microcapsule onto fibers can be adjusted by the reactivity of shell materials and mass ratios of core to shell. The disparity of diffusion between two disperse dyes can be reduced by microencapsulation. In addition, the microencapsulation improves

Alkaline, acidic and solvents hydrolysis is another method to improve various physical and chemical properties of synthetic fibers (Shcherbina et al., 2008; Park et al., 2009; Veronovski et al., 2009; Barantsev et al., 2007; Konovalova & Rabaeva, 2007; Chapurina et al., 2005; Hou et al., 2009). Alkaline hydrolysis has been studied extensively to overcome some problems of low water absorption properties and softness as alkaline hydrolysis improves the water absorption properties and softness of the PET fiber to give it a character similar to that of natural fibers (Prorokova et al., 2009; Chu et al., 2005). The alkaline hydrolysis of PET fibers is usually carried out with an aqueous alkaline solution, such as sodium hydroxide. In the alkaline hydrolysis process, PET undergoes a nucleophilic substitution. Chain scission of PET occurs, resulting in a considerable weight loss and the formation of hydroxyl and carboxylate end groups, which improves the handling, moisture absorption and dyeability of the fabric with enhanced softness (Mikhailova et al., 2008; Prorokova & Vavilova, 2004;

The effects of pretreatment reagents on the hydrolysis and physical properties of PET fabrics were investigated under various alkaline hydrolysis treatment and pretreatment conditions by Kim and his colleagues. Solvents used for pretreatment included benzyl alcohol and 2 phenyl ethanol. Results indicated that fabric weight loss, crystallinity, the initial and maximum water absorption increased with increasing hydrolysis time (Kim et al., 2009). Jain et al. reduced multi-filamentous polyacrylonitrile (PAN) fibers to amino groups using lithium aluminum hydride for immobilization of antibodies and detection of analyte. 24 h reduced fibers gave the most stable and reproducible results on immobilization of antibodies. Modified PAN fibers had a strong potential to be used as matrix for the detection of pathogenic bacteria and medical diagnostics (Jain et al., 2009). Another approach carried out by Cui and Yoon to modify the surface of PET film by treatment with ethoxylated hexylaminoanthraquinones synthesized by the reaction of 1 aminoanthraquinone with poly(ethylene glycol)s via hexamethylene spacer. The ethoxylated hexylaminoanthraquinones were adsorbed only onto the extreme surface of

the utilization of disperse dyes due to no auxiliary solubilization (Yan et al., 2011).

**2.2.9 Micro surface modification of textiles by aqueous solutions** 

Sohn et al., 2007; Stakne et al., 2003, Akbarov et al., 2006; Pavlov et al., 2001).

PET and water contact angle was decreased by the adsorption (Cui & Yoon, 2003).

even as a process control (Knittel & Schollmeyer, 2008).

A comprehensive collection of wet-chemical analyses of oxidized surfaces of poly(ethylene terephthalate) or polyolefin was presented by Knittel and Schollmeyer. Advanced oxidation of textile samples has been done using ozone and UV functionalization. They claimed that method presented uses inexpensive equipment and can be done quickly in a normal lab

formulations (Marti et al., 2011).
