**2.2.6.2 Dyeing of textiles based materials**

278 Textile Dyeing

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

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

Surface properties e.g. hydrophobicity, hydrophilicity, abrasion resistance,

Optical properties e.g. improving dyeability, photochromic effect, UV-absorption

Bio-active systems such as biocidal coatings, controlled release systems, immobilization

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

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.,

& Textor, 2008). Sol gel applications for textiles includes manipulation or changing Key textile properties e.g. stiffness, handle, absorbency, permeability etc.

synthetic fibers such as PET, PAN and PA respectively.

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

photocatalytic activity, other barrier functions etc.

And other physical properties e.g. heat resistance, conductivity etc.

of biological materials (enzyme, cells) etc.

properties.

stenter frame.

2011).

**2.2.6.1 The sol gel principle** 

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.


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 dyeability and bringing new functionality together.

**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

Surface and Bulk Modification of Synthetic Textiles to Improve Dyeability 281

cationic mixtures have allowed for facile fabrication of the resultant surface chemistries. To further enhance the viability of the LbL technique for organic polymers, pH-amplified exponential growth LbL self-assembly was implemented for poly(ethylenimine) (PEI) and poly(acrylic acid) PAA as the polycation and polyanion respectively. This technique takes advantage of the synergistic effect of the pH-dependent tunable charge density and weak polyelectrolyte diffusivity. The end result is fast LbL layer formation in a limited number of deposition cycles. This research proved that only three bilayers were necessary to achieve a

PAA

PAA

SiO2

Poly(acrylic acid)

lotus-like superhydrophobic surface (*.cf* **Table 4**) (Sun, Shen, Wang, Fu, & Ji, 2010).

Poly(diallyldimethyl ammonium

poly(allylamine hydrochloride) Inorganic-Organic Hybrids to induce roughness with azofunctional moieties

LbL deposition of polyelectrolytes can also be used to impart a hydrophilic surface to polyolefins. In the case of polyethylene, this would be useful for high performance fibers that might eventually be used for athletic clothing to wick away moisture as well as increase dye receptivity. With a contact angles (dH20) around 70o, polyethylene (PE) surfaces could actually be called slightly hydrophilic. In reality, contact angles below 45o are typically needed for a surface to exhibit facile wetting by a water droplet or hydrophilic behavior. **Table 4** shows a matrix of polymer polyelectrolytes that are used for imparting various finishes to substrates via LbL deposition. Specifically implemented by the Grunlan laboratory to determine the possible hydrophilic coatings onto PE, 2.5 bilayers were needed to achieve a dH20 of 22o when using the system of poly(diallyldimethylammonium chloride) (PDDA-PAA) as compared to other systems comprising 6 or more bilayers. The elevated pH of PAA (pH = 5) created an increased negative charge density and thinner deposition relative to unmodified PAA (pH < 3). Additionally, stopping deposition at half bilayers, where PDDA was at the surface, proved much more hydrophilic than full bilayers due to its

Table 4. Polyelectrolytes for LbL formulations with imparted functionality.

**Property Polycation Polyanion** 

Polyethylenimine

PEI

PDDA

chloride)

PAH

**Super-**

2010)

**Super-**

2011)

**-phobic** 

From

**Hydrophobicity** 

From (Sun et al.,

**Hydrophilicity** 

From (Grunlan,

**Switchable –philic/** 

(Lim et al., 2006)

evaluated for properties that include antimicrobial (Dvoracek, Sukhonosova, Benedik, & Grunlan, 2009; J. H. Fu, Ji, Yuan, & Shen, 2005; J. Fu, Ji, Fan, & Shen, 2006), anti-reflection (Hiller, Mendelsohn, & Rubner, 2002), electrical conductivity (Park, Ham, & Grunlan, 2011), anti-flammable (Carosio, Laufer, Alongi, Camino, & Grunlan, 2011; Li et al., 2010; Li, Mannen, Schulz, & Grunlan, 2011), gas barrier (Priolo, Gamboa, & Grunlan, 2010; Priolo, Gamboa, Holder, & Grunlan, 2010; Yang, Haile, Park, Malek, & Grunlan, 2011), and UV resistance (Dawidczyk, Walton, Jang, & Grunlan, 2008). These films, typically < 1µm thick, are created by alternately exposing a substrate to positively- and negatively-charged molecules, polymer electrolytes, or particles, as shown in **Figure 12**. Steps 1 – 4 are continuously repeated until the desired number of "bilayers" (or cationic-anionic pairs of layers) is achieved. **Figure 12b** provides an illustration of a film deposited with cationic and anionic polymers. Individual layers may be 1 – 100+ nm thick depending on chemistry, molecular weight, charge density, temperature, deposition time, counterion, and pH of species being deposited. The ability to control coating thickness down to the nm-level, easily insert variable thin layers without altering the process, avoid disturbing intrinsic mechanical behavior of the substrate, and process under ambient conditions are some of the key advantages of this deposition technique. In nonwovens, each thread can be individually coated with a uniform LbL nanocoating and still remain soft and flexible.

Fig. 12. a) Schematic of layer-by-layer deposition process used to prepare functional thin films and b) steps 1 – 4 are repeated until the desired number of bilayers are generated on a substrate. From (Jang & Grunlan, 2005)

Surface roughness of materials has been intensely studied over the last decade. When this aspect is coupled with low surface energy components, "rough" materials become superhydrophobic. Olephobicity also comes into play when the material becomes nanoporous, minimizing void volume between molecular substituents, preventing wetting of low surface tension liquids in addition to polar liquid (i.e. water) (Zenerino, Darmanin, de Givenchy, Amigoni, & Guittard, 2010). Designing superhydrophobic surfaces via the layerby-layer assembly method have included covalently bonded interlayers (Amigoni, de Givenchy, Dufay, & Guittard, 2009), integrated organic and inorganic components, and induced micro-roughness from the underlying substrate to mimic the back of the Stenocara beetle where the hydrophilic/ superhydrophobic regions allow self-cleaning surfaces (Garrod et al., 2007; Zhai et al., 2006). Interesting alternating layers of the anionic and

evaluated for properties that include antimicrobial (Dvoracek, Sukhonosova, Benedik, & Grunlan, 2009; J. H. Fu, Ji, Yuan, & Shen, 2005; J. Fu, Ji, Fan, & Shen, 2006), anti-reflection (Hiller, Mendelsohn, & Rubner, 2002), electrical conductivity (Park, Ham, & Grunlan, 2011), anti-flammable (Carosio, Laufer, Alongi, Camino, & Grunlan, 2011; Li et al., 2010; Li, Mannen, Schulz, & Grunlan, 2011), gas barrier (Priolo, Gamboa, & Grunlan, 2010; Priolo, Gamboa, Holder, & Grunlan, 2010; Yang, Haile, Park, Malek, & Grunlan, 2011), and UV resistance (Dawidczyk, Walton, Jang, & Grunlan, 2008). These films, typically < 1µm thick, are created by alternately exposing a substrate to positively- and negatively-charged molecules, polymer electrolytes, or particles, as shown in **Figure 12**. Steps 1 – 4 are continuously repeated until the desired number of "bilayers" (or cationic-anionic pairs of layers) is achieved. **Figure 12b** provides an illustration of a film deposited with cationic and anionic polymers. Individual layers may be 1 – 100+ nm thick depending on chemistry, molecular weight, charge density, temperature, deposition time, counterion, and pH of species being deposited. The ability to control coating thickness down to the nm-level, easily insert variable thin layers without altering the process, avoid disturbing intrinsic mechanical behavior of the substrate, and process under ambient conditions are some of the key advantages of this deposition technique. In nonwovens, each thread can be individually

coated with a uniform LbL nanocoating and still remain soft and flexible.

Fig. 12. a) Schematic of layer-by-layer deposition process used to prepare functional thin films and b) steps 1 – 4 are repeated until the desired number of bilayers are generated on a

Surface roughness of materials has been intensely studied over the last decade. When this aspect is coupled with low surface energy components, "rough" materials become superhydrophobic. Olephobicity also comes into play when the material becomes nanoporous, minimizing void volume between molecular substituents, preventing wetting of low surface tension liquids in addition to polar liquid (i.e. water) (Zenerino, Darmanin, de Givenchy, Amigoni, & Guittard, 2010). Designing superhydrophobic surfaces via the layerby-layer assembly method have included covalently bonded interlayers (Amigoni, de Givenchy, Dufay, & Guittard, 2009), integrated organic and inorganic components, and induced micro-roughness from the underlying substrate to mimic the back of the Stenocara beetle where the hydrophilic/ superhydrophobic regions allow self-cleaning surfaces (Garrod et al., 2007; Zhai et al., 2006). Interesting alternating layers of the anionic and

a) b)

substrate. From (Jang & Grunlan, 2005)

cationic mixtures have allowed for facile fabrication of the resultant surface chemistries. To further enhance the viability of the LbL technique for organic polymers, pH-amplified exponential growth LbL self-assembly was implemented for poly(ethylenimine) (PEI) and poly(acrylic acid) PAA as the polycation and polyanion respectively. This technique takes advantage of the synergistic effect of the pH-dependent tunable charge density and weak polyelectrolyte diffusivity. The end result is fast LbL layer formation in a limited number of deposition cycles. This research proved that only three bilayers were necessary to achieve a lotus-like superhydrophobic surface (*.cf* **Table 4**) (Sun, Shen, Wang, Fu, & Ji, 2010).


Table 4. Polyelectrolytes for LbL formulations with imparted functionality.

LbL deposition of polyelectrolytes can also be used to impart a hydrophilic surface to polyolefins. In the case of polyethylene, this would be useful for high performance fibers that might eventually be used for athletic clothing to wick away moisture as well as increase dye receptivity. With a contact angles (dH20) around 70o, polyethylene (PE) surfaces could actually be called slightly hydrophilic. In reality, contact angles below 45o are typically needed for a surface to exhibit facile wetting by a water droplet or hydrophilic behavior. **Table 4** shows a matrix of polymer polyelectrolytes that are used for imparting various finishes to substrates via LbL deposition. Specifically implemented by the Grunlan laboratory to determine the possible hydrophilic coatings onto PE, 2.5 bilayers were needed to achieve a dH20 of 22o when using the system of poly(diallyldimethylammonium chloride) (PDDA-PAA) as compared to other systems comprising 6 or more bilayers. The elevated pH of PAA (pH = 5) created an increased negative charge density and thinner deposition relative to unmodified PAA (pH < 3). Additionally, stopping deposition at half bilayers, where PDDA was at the surface, proved much more hydrophilic than full bilayers due to its

Surface and Bulk Modification of Synthetic Textiles to Improve Dyeability 283

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

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

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

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

commercial retarding and leveling agent (Gomez & Baptista, 2001).

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

al., 2008).

chains (*.cf* **Figure 14** ).

Fig. 14. Structure of liposome.

high charge density (Grunlan, 2011). They also noticed upon further evaluation, full bilayers of PDDA-PAA (pH = 5) had a contact angle of 11 degrees. This near superhydrophilic value is much lower than the initial screening attributed to a more pristine PE film cleaning and controlled polyelectrolyte deposition. The half bilayer protocol, with PDDA at the film's surface, had contact angles that could no longer be measured (i.e., < 5 degrees), suggesting a superhydrophilic surface. This was shown to be reproducible and unchanging as the assembly was built from 2.5 to 6.5 bilayers.

Another unique utilization of LbL deposition was demonstrated by Cho and researchers (Lim, Han, Kwak, Jin, & Cho, 2006). They formed a nanoporous substrate with microscale roughness through alternating electrostatic deposition of poly(allylamine hydrochloride) (PAH) as the polycation and SiO2 nanoparticles as the polyanion for a substrate with reversible wetting properties. The exposed SiO2 layer was treated with 3- (aminopropyltrichlorosilane) providing reactive binding sites (-NH2) for photo-switchable moieties (7-[(trifluoromethoxyphenylazo)phenoxy]pentanoic acid (CF3AZO)). The CF3AZO moieties in vis (440nm) light are in a hydrophobic *trans* orientation but orient to a *cis* state upon exposure to UV (365 nm) light. After the LbL-CF3AZO fabrication, the surface measured contact angles up to 1560 , as dictated by the number of bilayers (*.cf* **Figure 13a**). In contrast, the contact angle of water for a CF3AZO-functionalized flat film measured 76o (dH2O). The flat surface after exposure to UV light for 10 minutes, demonstrated a contact angle change of 5o, whereas the LbL functionalized surface could switch between being superhydrophobic at 1560 to superhydrophilic at < 5o, for nine bilayers. This reversibility was repeated up to 5 cycles with essentially zero hysteresis (see **Figure 13b**).

Fig. 13. a) the number of LbL bilayers necessary to induce super-hydrophobicity/ super hydrophilicity on CF3AZO-LBL surfaces and b) corresponding reversibility for the nine bilayer surface after UV/Vis exposure. Adapted from (Lim et al., 2006).

To conclude, LbL deposition is a unique surface modifying technique that gives ultimate flexibility for the design of the surface. Challenges for this technique include cost-effective commercial implementation at high on-machine line speeds for continuous operations. Engineering creativity to meet this challenge holds promise for a facile surface treatment technology for textiles.

high charge density (Grunlan, 2011). They also noticed upon further evaluation, full bilayers of PDDA-PAA (pH = 5) had a contact angle of 11 degrees. This near superhydrophilic value is much lower than the initial screening attributed to a more pristine PE film cleaning and controlled polyelectrolyte deposition. The half bilayer protocol, with PDDA at the film's surface, had contact angles that could no longer be measured (i.e., < 5 degrees), suggesting a superhydrophilic surface. This was shown to be reproducible and

Another unique utilization of LbL deposition was demonstrated by Cho and researchers (Lim, Han, Kwak, Jin, & Cho, 2006). They formed a nanoporous substrate with microscale roughness through alternating electrostatic deposition of poly(allylamine hydrochloride) (PAH) as the polycation and SiO2 nanoparticles as the polyanion for a substrate with reversible wetting properties. The exposed SiO2 layer was treated with 3- (aminopropyltrichlorosilane) providing reactive binding sites (-NH2) for photo-switchable moieties (7-[(trifluoromethoxyphenylazo)phenoxy]pentanoic acid (CF3AZO)). The CF3AZO moieties in vis (440nm) light are in a hydrophobic *trans* orientation but orient to a *cis* state upon exposure to UV (365 nm) light. After the LbL-CF3AZO fabrication, the surface measured contact angles up to 1560, as dictated by the number of bilayers (*.cf* **Figure 13a**). In contrast, the contact angle of water for a CF3AZO-functionalized flat film measured 76o (dH2O). The flat surface after exposure to UV light for 10 minutes, demonstrated a contact angle change of 5o, whereas the LbL functionalized surface could switch between being superhydrophobic at 1560 to superhydrophilic at < 5o, for nine bilayers. This reversibility

unchanging as the assembly was built from 2.5 to 6.5 bilayers.

was repeated up to 5 cycles with essentially zero hysteresis (see **Figure 13b**).

Fig. 13. a) the number of LbL bilayers necessary to induce super-hydrophobicity/ super hydrophilicity on CF3AZO-LBL surfaces and b) corresponding reversibility for the nine

To conclude, LbL deposition is a unique surface modifying technique that gives ultimate flexibility for the design of the surface. Challenges for this technique include cost-effective commercial implementation at high on-machine line speeds for continuous operations. Engineering creativity to meet this challenge holds promise for a facile surface treatment

bilayer surface after UV/Vis exposure. Adapted from (Lim et al., 2006).

technology for textiles.
