**2. Man made fibres**

### **2.1 Polyester**

Polyester fibers have attained a major position in the textile and non-textile uses, although polyester fibers have several drawbacks vis. low moisture regain (0.4%), a tendency to accumulate static charges, pick up soil dirt during wearing, difficulty of cleaning during washing, pill formation, thus spoiling fabric appearance and flammability. Modifications of polyester fibers can have an effect to overcome these disadvantages and can promote its permeability, hydrophilicity, hand and thermal properties (1, 2). Modification of polyester fibers is carried out via its treatments with alkalies, combined thermal and alkali, mono or multifunctional amines, organic solvents and acids as well as enzymatic hydrolysis. Thermal treatment of polyester fibers is a well known and important method in modification of the polymeric structure of the fibers. The purposes have increased to concern and cover the specific physico-chemical changes of the fiber structure to induce a certain tendency of crystallinity and orientation.

Pretreatment of Proteinic and Synthetic Fibres Prior to Dyeing 309

cleaved chain at the carbonyl group distal to the free end group of the chain. The free end groups consist of either terephthalate anion or the hydroxyl ethyl group. The reactions leading to elimination of the terephthalate dianion or ethylene glycol by "un- zippering" (i.e., the progressive reaction of the chain with hydroxide ion, beginning at a free end group) occur at locations that may be solvated, and hence can be expected to have rates that are faster than the rates of chain cleavage. Hydrolysis at the end group produces one molecule of either ethylene glycol or the terephthalate dianion for the reaction of each hydroxide ion. Consequently, this sort of reaction is first order in hydroxide concentration, while chain cleavage may be either first order or second order in hydroxide concentration. Neither the density, the intrinsic viscosity, nor the number of carboxyl end groups changes appreciably as compared to the untreated one after treatment with 10% solution of aqueous caustic at 60ºC for 2h, as the reaction does not occur in either regions of low order or high order and the attack is at the ends of the polymer (23, 24). A theoretical model has been developed to describe the kinetics of polyester fiber dissolution in alkaline solutions. The model is based on the surface reaction concept. The rate of dissolution is taken as being proportional to the surface area of fibers and to the concentration of OH- ions raised to a certain power(order of reaction: 0, 1, or 2). Integrated forms of rate laws are derived for all possible orders of dissolution reactions. According to the results, the weight loss is not a simple linearfunction of time, as usually accepted. The kinetics of the process is characterized by the rate constant,

**Alkali Treatment in Aqueous Medium:** Hydrolysis of polyester fabrics with sodium hydroxide was found to improve the hydrophilicity and other comfort-related properties of fabrics. Effect of the reaction parameters such as treatment time, sodium hydroxide concentration, and temperature on the extent of hydrolysis is examined. The modified fabrics are evaluated for their physical, mechanical and physico-mechanical properties (29, 30). Improved moisture absorbency of polyester fibers can be achieved by introducing hydrophilic block copolymers (31). In addition, penetration of water into the interior of the fibers has not been clearly shown to improve perceived comfort. Surface modifications can have an effect on hand, permeability, and hydrophilicity. Polyester fibers are susceptible to the action of bases depending on their ionic character. Ionizable bases like caustic soda, caustic potash and lime water only affect the outer surface of polyester fibers. Primary, secondary bases and ammonia can diffuse into polyester fibre and attack in depth resulting in breaking of polyester chain molecules by amide formation (32). The action of strong base leads to cleavage of ester linkages on the fibre surfaces (33, 34). The result is the formation of terminal hydroxyl and carboxylate groups on the fibre surface. Hydrolysis is believed to

Some methods are involved to overcome the low water absorption of polyester fibers to improve its dyeability. The compactness of the structure of polyester fibers minimizes the rate of the dye diffusion. To overcome this difficulty, swelling agents or high temperature treatments are used. Preswelling and plasticization of polyester fibers promote their physico-mechanical properties, moisture regain, as well as dyeability characteristics. Treatment of polyester fabric with ethanolic sodium hydroxide solution showed a significant improvement in the absorbency behavior of the polyester fabric, such as the decrease in wicking time and relative increase in the moisture regain percentage, as

, fibers, and water in the

which is, for a given system, independent of the content of OH-

increase the number of polar functional groups at the fibre surface.

**Caustic treatment in organic solvent medium** 

system (25-28).

Unevenness is one of the major drawbacks in their dyeing. Drastic dyeing conditions are usually performed to overcome unevenness, to promote colour homogeneity and depth, which however endanger the properties of the fibres. The lower barré effect appears from the application of dyes having high diffusion efficiency in polyester fibres. It is an oversimplification to deem that polyester is a solid solvent for disperse dyes and other hydrophobic molecules (3). Some relationships exist between the rate of dye diffusion, temperature, steric structure of the dye, size of voids in the substrate and elasticity of the amorphous regions. Ensuring the benefits of chemical modifications of polyester fibres in order to introduce new possibilities by changing its dyeing characteristics was done (3 ,4). It is nearly impossible for a dye molecule to diffuse into the polyester structure at low temperature; adequate rates are only achieved when dyeing temperature exceeds the glass transition temperature of the fibre. Satisfactory dyeing of polyester fibres can be carried out by loosening the fibre structure. This can be achieved by high temperature treatments; or during high temperature –high pressure dyeing or via carrier dyeing. High temperature and carrier dyeing methods succeed in opening the fibre structure. As the fibre is being heated thermal motion of the polymer chains increases, thus allowing dye molecules to diffuse in. Dyeing begins in the least oriented regions of the fibres. The orientation of polymeric, chains directly determines the rate of diffusion and dyeing rate. Treatment with organic solvents increases the dyeability of polyester in spite of a significant increase in crystallinity. Preswelling and plasticization of polyester fibres promote its physico-mechanical properties as well as dyeability characteristics. Plasticizing effects occur due to carrier attack on polyester fibres resulting in larger and more accessible channels and voids giving more porous fibre into which dye and water molecules can diffuse more rapidly and uniformly(5-13).

#### **2.1.1 Treatment with alkali**

Alkaline hydrolysis has been used since several years to modify the physical properties of polyester. It is well established that the alkaline hydrolysis of polyester fibers using aqueous sodium hydroxide is confined to the polymer surface (3, 4). When using sodium hydroxide in alcoholic media, the attack is found to be more severe and weight loss occurs more rapidly. Sodium alkoxides form alkyl ester end groups during the ester interchange reaction with polyester, resulting in a more rapid loss in weight than using aqueous sodium hydroxide. Alkali treatment of polyester fibers in glycolic media was also tried. Combined thermal and alkali treatment was carried out (14-21).

**Theory of Alkali Hydrolysis:** Two separate kinds of chain cleavage may occur. The first may involve the reaction of single hydroxide ion with the chain to produce a carboxylate anion and hydroxyl end groups of the shortened chain. This reaction does not produce a weight loss directly but may increase the weight due to the addition of hydroxide ion. The second reaction involves the attack of two hydroxide ions essentially simultaneously some distance apart along the same polymer chain backbone (22). In this case, a low molecular weight segment of the chain is removed as a single unit, resulting in a loss in weight from the polymer. Further reaction of these low molecular weight segments occur in liquid phase and do not contribute further to the weight loss of polyester, but it does contribute to depletion of the caustic concentration of the solution. Both of these reactions occur at the interface between the caustic solution (liquid phase), and the fibre surface (solid phase). At the moment of reaction, molecular solvation of the polymer must be minimal. Accordingly, this step of the reaction must be slow. Another kind of reaction is a scission of an already-

Unevenness is one of the major drawbacks in their dyeing. Drastic dyeing conditions are usually performed to overcome unevenness, to promote colour homogeneity and depth, which however endanger the properties of the fibres. The lower barré effect appears from the application of dyes having high diffusion efficiency in polyester fibres. It is an oversimplification to deem that polyester is a solid solvent for disperse dyes and other hydrophobic molecules (3). Some relationships exist between the rate of dye diffusion, temperature, steric structure of the dye, size of voids in the substrate and elasticity of the amorphous regions. Ensuring the benefits of chemical modifications of polyester fibres in order to introduce new possibilities by changing its dyeing characteristics was done (3 ,4). It is nearly impossible for a dye molecule to diffuse into the polyester structure at low temperature; adequate rates are only achieved when dyeing temperature exceeds the glass transition temperature of the fibre. Satisfactory dyeing of polyester fibres can be carried out by loosening the fibre structure. This can be achieved by high temperature treatments; or during high temperature –high pressure dyeing or via carrier dyeing. High temperature and carrier dyeing methods succeed in opening the fibre structure. As the fibre is being heated thermal motion of the polymer chains increases, thus allowing dye molecules to diffuse in. Dyeing begins in the least oriented regions of the fibres. The orientation of polymeric, chains directly determines the rate of diffusion and dyeing rate. Treatment with organic solvents increases the dyeability of polyester in spite of a significant increase in crystallinity. Preswelling and plasticization of polyester fibres promote its physico-mechanical properties as well as dyeability characteristics. Plasticizing effects occur due to carrier attack on polyester fibres resulting in larger and more accessible channels and voids giving more porous fibre into which dye and water molecules can diffuse more

Alkaline hydrolysis has been used since several years to modify the physical properties of polyester. It is well established that the alkaline hydrolysis of polyester fibers using aqueous sodium hydroxide is confined to the polymer surface (3, 4). When using sodium hydroxide in alcoholic media, the attack is found to be more severe and weight loss occurs more rapidly. Sodium alkoxides form alkyl ester end groups during the ester interchange reaction with polyester, resulting in a more rapid loss in weight than using aqueous sodium hydroxide. Alkali treatment of polyester fibers in glycolic media was also tried. Combined thermal and

**Theory of Alkali Hydrolysis:** Two separate kinds of chain cleavage may occur. The first may involve the reaction of single hydroxide ion with the chain to produce a carboxylate anion and hydroxyl end groups of the shortened chain. This reaction does not produce a weight loss directly but may increase the weight due to the addition of hydroxide ion. The second reaction involves the attack of two hydroxide ions essentially simultaneously some distance apart along the same polymer chain backbone (22). In this case, a low molecular weight segment of the chain is removed as a single unit, resulting in a loss in weight from the polymer. Further reaction of these low molecular weight segments occur in liquid phase and do not contribute further to the weight loss of polyester, but it does contribute to depletion of the caustic concentration of the solution. Both of these reactions occur at the interface between the caustic solution (liquid phase), and the fibre surface (solid phase). At the moment of reaction, molecular solvation of the polymer must be minimal. Accordingly, this step of the reaction must be slow. Another kind of reaction is a scission of an already-

rapidly and uniformly(5-13).

**2.1.1 Treatment with alkali** 

alkali treatment was carried out (14-21).

cleaved chain at the carbonyl group distal to the free end group of the chain. The free end groups consist of either terephthalate anion or the hydroxyl ethyl group. The reactions leading to elimination of the terephthalate dianion or ethylene glycol by "un- zippering" (i.e., the progressive reaction of the chain with hydroxide ion, beginning at a free end group) occur at locations that may be solvated, and hence can be expected to have rates that are faster than the rates of chain cleavage. Hydrolysis at the end group produces one molecule of either ethylene glycol or the terephthalate dianion for the reaction of each hydroxide ion. Consequently, this sort of reaction is first order in hydroxide concentration, while chain cleavage may be either first order or second order in hydroxide concentration. Neither the density, the intrinsic viscosity, nor the number of carboxyl end groups changes appreciably as compared to the untreated one after treatment with 10% solution of aqueous caustic at 60ºC for 2h, as the reaction does not occur in either regions of low order or high order and the attack is at the ends of the polymer (23, 24). A theoretical model has been developed to describe the kinetics of polyester fiber dissolution in alkaline solutions. The model is based on the surface reaction concept. The rate of dissolution is taken as being proportional to the surface area of fibers and to the concentration of OH- ions raised to a certain power(order of reaction: 0, 1, or 2). Integrated forms of rate laws are derived for all possible orders of dissolution reactions. According to the results, the weight loss is not a simple linearfunction of time, as usually accepted. The kinetics of the process is characterized by the rate constant, which is, for a given system, independent of the content of OH- , fibers, and water in the system (25-28).

**Alkali Treatment in Aqueous Medium:** Hydrolysis of polyester fabrics with sodium hydroxide was found to improve the hydrophilicity and other comfort-related properties of fabrics. Effect of the reaction parameters such as treatment time, sodium hydroxide concentration, and temperature on the extent of hydrolysis is examined. The modified fabrics are evaluated for their physical, mechanical and physico-mechanical properties (29, 30). Improved moisture absorbency of polyester fibers can be achieved by introducing hydrophilic block copolymers (31). In addition, penetration of water into the interior of the fibers has not been clearly shown to improve perceived comfort. Surface modifications can have an effect on hand, permeability, and hydrophilicity. Polyester fibers are susceptible to the action of bases depending on their ionic character. Ionizable bases like caustic soda, caustic potash and lime water only affect the outer surface of polyester fibers. Primary, secondary bases and ammonia can diffuse into polyester fibre and attack in depth resulting in breaking of polyester chain molecules by amide formation (32). The action of strong base leads to cleavage of ester linkages on the fibre surfaces (33, 34). The result is the formation of terminal hydroxyl and carboxylate groups on the fibre surface. Hydrolysis is believed to increase the number of polar functional groups at the fibre surface.

#### **Caustic treatment in organic solvent medium**

Some methods are involved to overcome the low water absorption of polyester fibers to improve its dyeability. The compactness of the structure of polyester fibers minimizes the rate of the dye diffusion. To overcome this difficulty, swelling agents or high temperature treatments are used. Preswelling and plasticization of polyester fibers promote their physico-mechanical properties, moisture regain, as well as dyeability characteristics. Treatment of polyester fabric with ethanolic sodium hydroxide solution showed a significant improvement in the absorbency behavior of the polyester fabric, such as the decrease in wicking time and relative increase in the moisture regain percentage, as

Pretreatment of Proteinic and Synthetic Fibres Prior to Dyeing 311

Differentiating of the previous equations (y`) that represent the tangent of the curve at any point, it is found that y`x=0.1 = 1.9 and y`x=0.2 = 1.3 for the untreated sample, whereas the corresponding values for the pretreated sample with propoxide are 4.4 and 2.9 and that for the pretreated polyester with ethoxide are 4.8 and 3.2, respectively. These results indicate that the rate of tan α (y`) is found to decrease by increasing the dye concentration. This would enhance the evenness of the dyed pretreated polyester fabric despite increasing the

Fig. 2.3. Dependence of tan α value on the concentration of dye used in dyeing of polyester Ethylene glycol is examined as an accelerating agent, but the improvement is not as good as methanol. Ethylene glycol and glycerin are used to replace the conventional water treatment of the alkaline solution. Both hydrolysis and glycolysis may shorten the treatment time and increase the hydrophilicity and dyeability of polyester (18). Treatment of polyester fibers with sodium hydroxide using propyl alcohol, propylene glycol and glycerol as a solvent was tried. The degradation rate in both propyl alcohol and propylene glycol is found to increase rapidly. The effect of treatment on some properties of polyester fabric are given through measurements of tensile strength, drapability, permeability, density gradient, crystallinity, moisture regain, and scanning electron microscopy. The use of this treatment can greatly shorten the treatment time to achieve results similar to those with the conventional aqueous system. The effect of concentration of sodium hydroxide in mono-, di- and tri-hydric alcohols on the weight loss of treated polyester fabric is illustrated in Fig. 2.4. The loss in weight resulted from treating of polyester fibres with sodium hydroxide in mono-hydric alcohol (propanol) more than di-hydric alcohol (propylene glycol) more than tri-hydric alcohol (glycerol). The loss in weight is about 10% in case of using propylene glycol corresponds to about 2% in case of glycerol, while using propanol as a medium of alkali hydrolysis leads to complete dissolving of polyester fibres after about 45 min at 65C with

0.5 M sodium hydroxide (19).

rate of dyeing, as proved by the above-mentioned mathematical analysis (38).

compared with the untreated mate (35-40). It can be noticed from the scanning electron micrographs (Figs 2.1 and 2.2) of the untreated and treated polyester fabric with sodium ethoxide that there is a change on the surface of the polyester fabric without whole-fiber damage. This may be due to the use of alkoxide solutions causing a reduction in the wholefiber swelling and thus imparting beneficial effects on the fiber surface (38).

Fig. 2.1. SEM of untreated polyester fabric (16).

Fig. 2.2. SEM of treated polyester fabric with ethoxide (16).

The dyeability of the pretreated polyester fabric with disperse dye shows some progressive improvements with lowering the dyeing temperature and/or decreasing the time of dyeing. Ethoxide is found to be more effective in enhancing the dyeability of polyester fabric than either methoxide or propoxide. A decrease in the half dyeing time and an increase in the rate of dyeing of the pretreated polyester as compared with the untreated one are noticed (38). The influence of the variation of dye concentration in the solution on the extent of dyeing is studied by plotting rate of dyeing (tan α) against the dye concentration. This relation is illustrated in Fig. 2.3. The resultant curve is found to rise moderately at low dye concentration up to 0.2 g/L, and then the increase of tan α is slowed down by increasing the dye concentration up to 0.4 g/L for both dyed untreated and pretreated polyester fabric. The assumed equations of the curved line in Fig. 2.3 are:

> Y = -2.9369x2 + 2.4799x for untreated polyester fabric; Y = -7.3587x2 + 5.8675x for pretreated polyester with propoxide; Y = -7.8556x2 **+**6.4022x for pretreated polyester with ethoxide

compared with the untreated mate (35-40). It can be noticed from the scanning electron micrographs (Figs 2.1 and 2.2) of the untreated and treated polyester fabric with sodium ethoxide that there is a change on the surface of the polyester fabric without whole-fiber damage. This may be due to the use of alkoxide solutions causing a reduction in the whole-

The dyeability of the pretreated polyester fabric with disperse dye shows some progressive improvements with lowering the dyeing temperature and/or decreasing the time of dyeing. Ethoxide is found to be more effective in enhancing the dyeability of polyester fabric than either methoxide or propoxide. A decrease in the half dyeing time and an increase in the rate of dyeing of the pretreated polyester as compared with the untreated one are noticed (38). The influence of the variation of dye concentration in the solution on the extent of dyeing is studied by plotting rate of dyeing (tan α) against the dye concentration. This relation is illustrated in Fig. 2.3. The resultant curve is found to rise moderately at low dye concentration up to 0.2 g/L, and then the increase of tan α is slowed down by increasing the dye concentration up to 0.4 g/L for both dyed untreated and pretreated polyester fabric. The

> Y = -2.9369x2 + 2.4799x for untreated polyester fabric; Y = -7.3587x2 + 5.8675x for pretreated polyester with propoxide; Y = -7.8556x2 **+**6.4022x for pretreated polyester with ethoxide

fiber swelling and thus imparting beneficial effects on the fiber surface (38).

Fig. 2.1. SEM of untreated polyester fabric (16).

Fig. 2.2. SEM of treated polyester fabric with ethoxide (16).

assumed equations of the curved line in Fig. 2.3 are:

Differentiating of the previous equations (y`) that represent the tangent of the curve at any point, it is found that y`x=0.1 = 1.9 and y`x=0.2 = 1.3 for the untreated sample, whereas the corresponding values for the pretreated sample with propoxide are 4.4 and 2.9 and that for the pretreated polyester with ethoxide are 4.8 and 3.2, respectively. These results indicate that the rate of tan α (y`) is found to decrease by increasing the dye concentration. This would enhance the evenness of the dyed pretreated polyester fabric despite increasing the rate of dyeing, as proved by the above-mentioned mathematical analysis (38).

Fig. 2.3. Dependence of tan α value on the concentration of dye used in dyeing of polyester

Ethylene glycol is examined as an accelerating agent, but the improvement is not as good as methanol. Ethylene glycol and glycerin are used to replace the conventional water treatment of the alkaline solution. Both hydrolysis and glycolysis may shorten the treatment time and increase the hydrophilicity and dyeability of polyester (18). Treatment of polyester fibers with sodium hydroxide using propyl alcohol, propylene glycol and glycerol as a solvent was tried. The degradation rate in both propyl alcohol and propylene glycol is found to increase rapidly. The effect of treatment on some properties of polyester fabric are given through measurements of tensile strength, drapability, permeability, density gradient, crystallinity, moisture regain, and scanning electron microscopy. The use of this treatment can greatly shorten the treatment time to achieve results similar to those with the conventional aqueous system. The effect of concentration of sodium hydroxide in mono-, di- and tri-hydric alcohols on the weight loss of treated polyester fabric is illustrated in Fig. 2.4. The loss in weight resulted from treating of polyester fibres with sodium hydroxide in mono-hydric alcohol (propanol) more than di-hydric alcohol (propylene glycol) more than tri-hydric alcohol (glycerol). The loss in weight is about 10% in case of using propylene glycol corresponds to about 2% in case of glycerol, while using propanol as a medium of alkali hydrolysis leads to complete dissolving of polyester fibres after about 45 min at 65C with 0.5 M sodium hydroxide (19).

Pretreatment of Proteinic and Synthetic Fibres Prior to Dyeing 313

and hydrazine hydrate (5-20 % v/v) solutions are used in this study as pretreatment reagents by padding technique then squeezed up to 100 % pick up, followed by thermal treatment at 160ºC for 15 min in air under slack conditions. The pretreated fabric is dyed at the boil with disperse dye without using carriers. Treatment of polyester fabric with hydrazine hydrate before thermal treatment led to high enhancement of the fibre dyeability with disperse dyes as well as decreasing the setting temperature of polyester to 160ºC. Applying the padding technique in treatment of PET may decrease the consumption of chemicals in the dyeing process as well as reducing the pollution impacts (40, 48). The effect of pretreatment of polyester fibers with some amines such as methylamine, ethylamine and

0 5% 10% 15% 20% 30%

ethanolamine followed by thermal treatment is shown in Table 2.1 (40).

PET sample Color intensity (K/S)


Treatment: 160ºC, 15 min, Dyeing: 1% (owf) C.I. Disperse Red 60, 100 ºC, pH 4.5, L.R. 1:100.

methoxybenzophenone are reported to be 63º, 68 º and 63º C respectively (40).

Table 2.2. Dye depth and glass transition temperature of polyester fabric.

Polyester sample Dye depth in cross section % Tg °C -untreated 38.4 72 -hydrate hydrazine treated 46.5 70 -Steam treated 39.5 69.0

amines.

**2.1.2 Enzymatic hydrolysis** 

Table 2.1. Dyeability of pretreated polyester fabric with various concentrations of some

The depth of disperse dye inside the interior structure of pretreated PET fabrics increases by the effect of steam and hydrazine hydrate treatments (Table 2.2). Polyester fabrics pretreated with steam have lower Tg values. The chemical/thermal pretreatment of polyester fabrics with hydrazine hydrate causes a decrease in Tg. The glass transition temperatures of pretreated polyester fabric with ethanolamine, ethylene glycol and 2-hydroxy-4-

Application of biotechnology to textile finishing is an example of more environmentally compatible processes. Enzymes are produced from fermentation of microorganisms (renewable resources) and are biodegradable. Amylases and cellulases hydrolyze starch and cellulose respectively and can be used in desizing of textiles. Hydrolases are capable of hydrolyzing fatty acids or carboxylic esters. Lipases have been reported to biodegrade polyesters. The insoluble nature of polyester fibers in an aqueous medium may limit enzymatic hydrolysis to the surface, thus improving the fibre wettability. The water wetting contact angle of the untreated polyester is evaluated as 75.8º. Polyester fabrics are immersed in the buffer solution (organic and inorganic) at 35ºC for 1h. The organic buffer, tris (hydroxyl methyl)-aminomethane, lowers the wetting contact angle of polyester fabric to

Fig. 2.4. Concentration of sodium hydroxide/ loss in weight of PET fibers, Treatment: 65°C, 45 min, L. R. 1: 25, x-x glycerol, o-o propylene glycol, Δ-Δ propanol

#### **Combined thermal and alkali treatment**

In textile processing, polyester fabric is usually heat set to improve dimensional stability and prevent creases during wet processing and handling. Heat setting of polyester fibers is processed to make a change in the fine structure and consequently dyeability and chemical reactivity (39- 49). The effect of heat setting temperature on the hydrazinolysis of polyester fibers was studied. Polyester partially oriented yarn (POY) is heat set at 100° to 220°C in a fixed state and then treated with hydrazine. Relatively smaller amines, such as hydrazine, swell the less ordered regions of the fibre and attack ester linkages in the molecular chain effectively. The weight loss of thermally treated POY is found to be minimum at 120°C and increased with increasing treatment temperature up to 220°C , while it is recorded to be 160°C for regular polyester because of the difference in the fine structure of the fibers. Hydrazinolysis with 40% aqueous solution of hydrazine monohydrate at 60°C for 120 min incorporates a hydrazide group at the end of the fibre's molecular chain. Hydrazinolysis builds inactive sites for adsorption acid dyes by modified polyester fibers. The crystallinity of the heat-set POY fibers increases with hydrazinolysis as well as the heat setting temperature. Scanning electron microscopy (SEM) photographs of the hydrolyzed POY fibers show appearance of cracks on the fibre surface which differs with variation of heat setting temperature and becomes deeper in the inner regions. Polyester fibre is heat set at 100°-220º C and then hydrolyzed with 10 % aqueous sodium hydroxide solution at 90 ºC for 1 and 2h. The disperse dye exhaustion of the heat set/ alkali hydrolyzed polyester is found to decrease with increasing the temperature up to 180 ºC. The amorphous/ crystalline ratios are the controlled parameters in dyeing of PET fibre with disperse dye and consequently the applied method in thermal treatment (20). Other attempts were carried out to improve the dyeability of polyester fabric with disperse dyes at the boil without using carriers or using HT/HP dyeing technique. Some alkyl and/or alkylol amines as well as hydrazine hydrate treatments are carried out by padding technique at room temperature prior subjecting it to the thermal treatment in air and slack conditions. Methylamine, ethylamine, ethanolamine

Fig. 2.4. Concentration of sodium hydroxide/ loss in weight of PET fibers, Treatment: 65°C,

In textile processing, polyester fabric is usually heat set to improve dimensional stability and prevent creases during wet processing and handling. Heat setting of polyester fibers is processed to make a change in the fine structure and consequently dyeability and chemical reactivity (39- 49). The effect of heat setting temperature on the hydrazinolysis of polyester fibers was studied. Polyester partially oriented yarn (POY) is heat set at 100° to 220°C in a fixed state and then treated with hydrazine. Relatively smaller amines, such as hydrazine, swell the less ordered regions of the fibre and attack ester linkages in the molecular chain effectively. The weight loss of thermally treated POY is found to be minimum at 120°C and increased with increasing treatment temperature up to 220°C , while it is recorded to be 160°C for regular polyester because of the difference in the fine structure of the fibers. Hydrazinolysis with 40% aqueous solution of hydrazine monohydrate at 60°C for 120 min incorporates a hydrazide group at the end of the fibre's molecular chain. Hydrazinolysis builds inactive sites for adsorption acid dyes by modified polyester fibers. The crystallinity of the heat-set POY fibers increases with hydrazinolysis as well as the heat setting temperature. Scanning electron microscopy (SEM) photographs of the hydrolyzed POY fibers show appearance of cracks on the fibre surface which differs with variation of heat setting temperature and becomes deeper in the inner regions. Polyester fibre is heat set at 100°-220º C and then hydrolyzed with 10 % aqueous sodium hydroxide solution at 90 ºC for 1 and 2h. The disperse dye exhaustion of the heat set/ alkali hydrolyzed polyester is found to decrease with increasing the temperature up to 180 ºC. The amorphous/ crystalline ratios are the controlled parameters in dyeing of PET fibre with disperse dye and consequently the applied method in thermal treatment (20). Other attempts were carried out to improve the dyeability of polyester fabric with disperse dyes at the boil without using carriers or using HT/HP dyeing technique. Some alkyl and/or alkylol amines as well as hydrazine hydrate treatments are carried out by padding technique at room temperature prior subjecting it to the thermal treatment in air and slack conditions. Methylamine, ethylamine, ethanolamine

45 min, L. R. 1: 25, x-x glycerol, o-o propylene glycol, Δ-Δ propanol

**Combined thermal and alkali treatment** 

and hydrazine hydrate (5-20 % v/v) solutions are used in this study as pretreatment reagents by padding technique then squeezed up to 100 % pick up, followed by thermal treatment at 160ºC for 15 min in air under slack conditions. The pretreated fabric is dyed at the boil with disperse dye without using carriers. Treatment of polyester fabric with hydrazine hydrate before thermal treatment led to high enhancement of the fibre dyeability with disperse dyes as well as decreasing the setting temperature of polyester to 160ºC. Applying the padding technique in treatment of PET may decrease the consumption of chemicals in the dyeing process as well as reducing the pollution impacts (40, 48). The effect of pretreatment of polyester fibers with some amines such as methylamine, ethylamine and ethanolamine followed by thermal treatment is shown in Table 2.1 (40).


Treatment: 160ºC, 15 min, Dyeing: 1% (owf) C.I. Disperse Red 60, 100 ºC, pH 4.5, L.R. 1:100.

Table 2.1. Dyeability of pretreated polyester fabric with various concentrations of some amines.

The depth of disperse dye inside the interior structure of pretreated PET fabrics increases by the effect of steam and hydrazine hydrate treatments (Table 2.2). Polyester fabrics pretreated with steam have lower Tg values. The chemical/thermal pretreatment of polyester fabrics with hydrazine hydrate causes a decrease in Tg. The glass transition temperatures of pretreated polyester fabric with ethanolamine, ethylene glycol and 2-hydroxy-4 methoxybenzophenone are reported to be 63º, 68 º and 63º C respectively (40).


Table 2.2. Dye depth and glass transition temperature of polyester fabric.

#### **2.1.2 Enzymatic hydrolysis**

Application of biotechnology to textile finishing is an example of more environmentally compatible processes. Enzymes are produced from fermentation of microorganisms (renewable resources) and are biodegradable. Amylases and cellulases hydrolyze starch and cellulose respectively and can be used in desizing of textiles. Hydrolases are capable of hydrolyzing fatty acids or carboxylic esters. Lipases have been reported to biodegrade polyesters. The insoluble nature of polyester fibers in an aqueous medium may limit enzymatic hydrolysis to the surface, thus improving the fibre wettability. The water wetting contact angle of the untreated polyester is evaluated as 75.8º. Polyester fabrics are immersed in the buffer solution (organic and inorganic) at 35ºC for 1h. The organic buffer, tris (hydroxyl methyl)-aminomethane, lowers the wetting contact angle of polyester fabric to

Pretreatment of Proteinic and Synthetic Fibres Prior to Dyeing 315

process was studied in the ranges 85—125°C and 400—550 kg/m3. The dye saturation concentration in the polyester increased and the distribution coefficient decreased with temperature, the latter showing a logarithmic dependence on the reciprocal of temperature. Increasing the fluid density led to an increasing saturation concentration and a decreasing distribution coefficient. When the right temperature and solvent density were chosen for the supercritical process, the same dye concentration could be attained as in aqueous dyeing. The experiments showed that the dyeing was exothermic, with a negative change of entropy. The thermodynamic characteristics of supercritical and aqueous dyeing were concluded to be roughly the same, with similar saturation concentrations, thermodynamic affinities and heats and entropies of dyeing (71). One-bath dyeing of polyester/cotton blends with reactive disperse dyes is investigated using supercritical carbon dioxide (SC-CO2) as a solvent in the range of 353 to 393° K and 10 to 20 MPa. The dyeing behavior is compared with the thermosol dyeing method using the same dye. Samples are subjected to a color fastness test and colorimetric measurements. Good color intensity and wash fastness are obtained by the SC-CO2 dyeing method at 393 K and 20 MPa. The color fastness properties of fabrics dyed in SC-CO2 are superior to those of fabrics dyed by the thermosol dyeing method (72). Supercritical carbon dioxide is a suitable solvent for dyeing even for the most sensitive textiles up to 140°C. The treatment time at 160°C should not be longer than 1 hour (73). Supercritical dyeing can be an interesting alternative to traditional dyeing due to the unquestionable advantage of the use of a clean solvent that can be easily recovered and separated from the excess dye at the end of the process. Set up a pilot plant of supercritical

dyeing could be performed with yarn bobbins for polyester textiles (74).

difficult disperse dyes (75, 76).

**Dyeing with Carriers:** Carrier dyeing is a method of dyeing polyester materials that is used when necessary. Although usage of carriers in dyeing enables the dyeing of polyester materials at atmospheric pressure, the undesirable properties of the carriers are drawbacks. Disperse dyes are classified under different energy levels and the dyeing methods and color and fastness properties of dyed materials are associated with this classification. Carriers can be used when dyeing at higher temperatures than 100°C to promote the leveling of the more

**Dye Absorption after Thermal Treatment:** Thermal treatment of polyester fibers can lead to variation in the absorption behavior as appeared in its dyeing properties, iodine sorption as well as swellability. The rate of dyeing of polyester is dependent on temperature, time and thermal history of the polyester fibers. The dye uptake of disperse dyes by thermally- set polyester initially decreases as the temperature of pre-heating is raised. At higher temperatures the dye uptake increases with temperature and can be greater than that of the untreated polyester fibers depending also on the dye molecule (77). The variations in dyeing properties of polyester fibers in terms of structure is described using two- phase theory of structure involving crystalline and amorphous regions. The competition between crystallization (with reduction of rate of dyeing) and disorientation of the amorphous region (leading to increased dye uptake) explains the variations of dyeing behavior of polyester fibers with heat setting. The effect of heat setting at various temperatures and draw ratios on the diffusion of disperse dyes into polyester fibers is studied in relation to the measurements of the dynamic loss modulus of the fibers. The diffusion is controlled by the chain mobility of polymer as indicated by measuring the glass transition temperature (Tg). The diffusivity and dye saturation values depend on the difference between the dyeing temperatures and glass–transition temperature. The dye molecules penetrate the polymeric fiber structure upon movement of the chain segments producing spaces suitable to the size

67.5º. The inorganic buffer, sodium phosphate, increases the contact angle to 81.9º. Any improvement in surface wetting can be due to the hydrolyzing action of the lipase. Some types of lipases are found to decrease the water wetting contact angle to 57.4º without significant change in breaking tenacity and strain of pretreated polyester fabric. The lipase hydrolysis resulted in better wetting surfaces than aqueous alkaline hydrolysis. The improved wettability due to enzyme treatment is accompanied by full strength retention compared to the significant reduced strength and mass from alkaline hydrolysis. The water contact angle is found to decrease from 75.8º to about 52º. As the contact angle decreases, the wettability increases and consequently the dyeability is improved (50-56).

#### **2.1.3 Other trends in dyeing**

**Organic Solvents:** The solvent treatment of synthetic fibres influences strongly dyediffusion characteristics as well as the equilibrium dye-uptake. Interaction of solvents with synthetic fibres can affect fibre swellability, segmental mobility, irreversible structural changes, shrinkage and shifts in glass-transition temperature. Small amounts of organic solvents such as alcohols were added in the aqueous dyeing baths of synthetic and natural fibres to assist the dyeing process (5-13). The effect of plasticizing of benzyl alcohol /chloroform (6: 4) mixture on polyester is presumed to increase the degree of crystallinity and the perfection of the apparent size of the crystallites. This effect might occur by reducing the forces of entanglement points between the macromolecular chains. Chain segments thereby acquired relatively sufficient free movement into a crystal arrangement. Part of the amorphous region remains intact and tends slowly to crystallize at an extremely slow rate. The solvent molecules were expelled from the crystal, but still persist to influence the amorphous portion, which exhibited some mobility. Change in the tendency of the modified polyester to uptake disperse dyestuff was also noticed. Polyester structure modification due to binary solvent interaction showed some promising improvement in the accessibility of the substrate to dyeing (57, 58). Treatments of polyester fibres were performed with non-hydrogen bonded solvents vis. 1, 4-dioxan, N, N'-dimethylformamide, cyclohexanone and with hydrogen-bonded reagents such as formic and monochloroacetic acids (59). The non-hydrogen bonded-type of solvents were found to be more efficient in improving the colour intensity than the pretreatment with some hydrogen-bonded solvents. Adsorption behaviour of these modified polyester fibres is examined via studying the nature of the dye, maximum adsorption temperature, and dipole moment of the dye molecules (60-64).

**Acids:** Moderate treatment of polyester and Quiana polyamide fibers with sulfuric acid solution is studied (65). Significant improvements in the dyeabilities of both fibers with cationic dyes below the boiling point, without appreciable reduction of the fabric dimension are attained. Kinetic characterization of the dyeing process reveals that the time of half dyeing decreased pronouncedly in case of the modified substrates and, consequently, the specific dyeing rate constant increases. A rapid decrease in the relative diffusion coefficient of the sulfuric acid pretreated substrates is observed upon increasing the temperature of dyeing. The dye affinities increase and the corresponding heats of dyeing practically decrease for both modified fibers. The kinetic reactions between both polyester and Quiana polyamide fibers and sulfuric acid were studied (66). The moisture regain and dye uptake of treated polyester increased (67-70).

**Super Critical CO2**: The dyeing of polyester textile in supercritical carbon dioxide is investigated experimentally. The influence of temperature and density of the SC-CO2 on the

67.5º. The inorganic buffer, sodium phosphate, increases the contact angle to 81.9º. Any improvement in surface wetting can be due to the hydrolyzing action of the lipase. Some types of lipases are found to decrease the water wetting contact angle to 57.4º without significant change in breaking tenacity and strain of pretreated polyester fabric. The lipase hydrolysis resulted in better wetting surfaces than aqueous alkaline hydrolysis. The improved wettability due to enzyme treatment is accompanied by full strength retention compared to the significant reduced strength and mass from alkaline hydrolysis. The water contact angle is found to decrease from 75.8º to about 52º. As the contact angle decreases, the

**Organic Solvents:** The solvent treatment of synthetic fibres influences strongly dyediffusion characteristics as well as the equilibrium dye-uptake. Interaction of solvents with synthetic fibres can affect fibre swellability, segmental mobility, irreversible structural changes, shrinkage and shifts in glass-transition temperature. Small amounts of organic solvents such as alcohols were added in the aqueous dyeing baths of synthetic and natural fibres to assist the dyeing process (5-13). The effect of plasticizing of benzyl alcohol /chloroform (6: 4) mixture on polyester is presumed to increase the degree of crystallinity and the perfection of the apparent size of the crystallites. This effect might occur by reducing the forces of entanglement points between the macromolecular chains. Chain segments thereby acquired relatively sufficient free movement into a crystal arrangement. Part of the amorphous region remains intact and tends slowly to crystallize at an extremely slow rate. The solvent molecules were expelled from the crystal, but still persist to influence the amorphous portion, which exhibited some mobility. Change in the tendency of the modified polyester to uptake disperse dyestuff was also noticed. Polyester structure modification due to binary solvent interaction showed some promising improvement in the accessibility of the substrate to dyeing (57, 58). Treatments of polyester fibres were performed with non-hydrogen bonded solvents vis. 1, 4-dioxan, N, N'-dimethylformamide, cyclohexanone and with hydrogen-bonded reagents such as formic and monochloroacetic acids (59). The non-hydrogen bonded-type of solvents were found to be more efficient in improving the colour intensity than the pretreatment with some hydrogen-bonded solvents. Adsorption behaviour of these modified polyester fibres is examined via studying the nature of the dye, maximum adsorption temperature, and dipole moment of the dye

**Acids:** Moderate treatment of polyester and Quiana polyamide fibers with sulfuric acid solution is studied (65). Significant improvements in the dyeabilities of both fibers with cationic dyes below the boiling point, without appreciable reduction of the fabric dimension are attained. Kinetic characterization of the dyeing process reveals that the time of half dyeing decreased pronouncedly in case of the modified substrates and, consequently, the specific dyeing rate constant increases. A rapid decrease in the relative diffusion coefficient of the sulfuric acid pretreated substrates is observed upon increasing the temperature of dyeing. The dye affinities increase and the corresponding heats of dyeing practically decrease for both modified fibers. The kinetic reactions between both polyester and Quiana polyamide fibers and sulfuric acid were studied (66). The moisture regain and dye uptake of

**Super Critical CO2**: The dyeing of polyester textile in supercritical carbon dioxide is investigated experimentally. The influence of temperature and density of the SC-CO2 on the

wettability increases and consequently the dyeability is improved (50-56).

**2.1.3 Other trends in dyeing** 

molecules (60-64).

treated polyester increased (67-70).

process was studied in the ranges 85—125°C and 400—550 kg/m3. The dye saturation concentration in the polyester increased and the distribution coefficient decreased with temperature, the latter showing a logarithmic dependence on the reciprocal of temperature. Increasing the fluid density led to an increasing saturation concentration and a decreasing distribution coefficient. When the right temperature and solvent density were chosen for the supercritical process, the same dye concentration could be attained as in aqueous dyeing. The experiments showed that the dyeing was exothermic, with a negative change of entropy. The thermodynamic characteristics of supercritical and aqueous dyeing were concluded to be roughly the same, with similar saturation concentrations, thermodynamic affinities and heats and entropies of dyeing (71). One-bath dyeing of polyester/cotton blends with reactive disperse dyes is investigated using supercritical carbon dioxide (SC-CO2) as a solvent in the range of 353 to 393° K and 10 to 20 MPa. The dyeing behavior is compared with the thermosol dyeing method using the same dye. Samples are subjected to a color fastness test and colorimetric measurements. Good color intensity and wash fastness are obtained by the SC-CO2 dyeing method at 393 K and 20 MPa. The color fastness properties of fabrics dyed in SC-CO2 are superior to those of fabrics dyed by the thermosol dyeing method (72). Supercritical carbon dioxide is a suitable solvent for dyeing even for the most sensitive textiles up to 140°C. The treatment time at 160°C should not be longer than 1 hour (73). Supercritical dyeing can be an interesting alternative to traditional dyeing due to the unquestionable advantage of the use of a clean solvent that can be easily recovered and separated from the excess dye at the end of the process. Set up a pilot plant of supercritical dyeing could be performed with yarn bobbins for polyester textiles (74).

**Dyeing with Carriers:** Carrier dyeing is a method of dyeing polyester materials that is used when necessary. Although usage of carriers in dyeing enables the dyeing of polyester materials at atmospheric pressure, the undesirable properties of the carriers are drawbacks. Disperse dyes are classified under different energy levels and the dyeing methods and color and fastness properties of dyed materials are associated with this classification. Carriers can be used when dyeing at higher temperatures than 100°C to promote the leveling of the more difficult disperse dyes (75, 76).

**Dye Absorption after Thermal Treatment:** Thermal treatment of polyester fibers can lead to variation in the absorption behavior as appeared in its dyeing properties, iodine sorption as well as swellability. The rate of dyeing of polyester is dependent on temperature, time and thermal history of the polyester fibers. The dye uptake of disperse dyes by thermally- set polyester initially decreases as the temperature of pre-heating is raised. At higher temperatures the dye uptake increases with temperature and can be greater than that of the untreated polyester fibers depending also on the dye molecule (77). The variations in dyeing properties of polyester fibers in terms of structure is described using two- phase theory of structure involving crystalline and amorphous regions. The competition between crystallization (with reduction of rate of dyeing) and disorientation of the amorphous region (leading to increased dye uptake) explains the variations of dyeing behavior of polyester fibers with heat setting. The effect of heat setting at various temperatures and draw ratios on the diffusion of disperse dyes into polyester fibers is studied in relation to the measurements of the dynamic loss modulus of the fibers. The diffusion is controlled by the chain mobility of polymer as indicated by measuring the glass transition temperature (Tg). The diffusivity and dye saturation values depend on the difference between the dyeing temperatures and glass–transition temperature. The dye molecules penetrate the polymeric fiber structure upon movement of the chain segments producing spaces suitable to the size

Pretreatment of Proteinic and Synthetic Fibres Prior to Dyeing 317

various redox systems were incorporated in the dyebath vicinity. Redox systems have been utilized to induce covalent fixation of dye moieties on proteinic and polyamide fibres. Radical formation is usually the consequence of a bimolecular reaction between oxidant and reductant. Its rate can be adjusted almost by suitable variation of reactant concentration. The organic substrate may participate in a two-electron transfer process without radical formation (1-5). Introduction of glyoxal- hydrogen peroxide as a redox system to accelerate the polyamide dyeability with acid dyes is performed. An increase in colour intensity of the substrate dyed in the presence of the redox system as well as rapid exhaustion of the dyebath was observed. Time of half dyeing, specific dyeing rate constant and diffusion coefficient show some advancement as compared with the untreated polyamide. The activation energy of dyeing of the pretreated substrate decreased (1). Addition of 2 % alcohols to the pretreatment bath reveals nearly complete exhaustion of the dyebath after 30 min. at 70°C. The alcohol effectiveness can be ordered methanol > ethanol > propanol. Complete dye exhaustion at lower dyeing temperature and time can save energy, time as well as minimize pollution effects. Half dyeing time at 60ºC decreased by the applied treatment from 13.5 min for untreated sample to 2.5 min for glyoxal pretreated sample in methanol/water (2:98), as compared with the given t ½ at 80ºC which decreased from 6 min to 1 min. Both dyeing rate constant (k`) and diffusion coefficient (D) at 60ºC and 80ºC have

Type of Sample t 1/2 (min) K' D (cm 2 sec –1) x10-4

1- Untreated 13.5 6 0.01 0.0245 0.176 0.291


Table 2.3. Half dyeing time (t ½), dyeing rate constant (K'), and diffusion coefficient (D) of

1- Untreated 41.5 2- Pretreated with glyoxal in: methanol / water 24.9 ethanol / water 26.9 propanol / water 26.9

Table 2.4. Activation energy (E) of dyeing for pretreated polyamide 6 fibres

Treatment: 0.5 g glyoxal / 100 g fibre, solvent / water ratio 2: 98, 50ºC, 1h, Dyeing: 1 % (o.w. f.) C. I.

The activation energy decreased from 41.5 kJ/g mol for untreated one to 24.9 kJ/g mol for pretreated polyamide 6 fabric with glyoxal/H2O2 in methanol/water (Table 2.4). The decrease in the half dyeing time and the activation energy and the increase in dyeing rate constant and diffusion coefficient led to saving in time. The colour intensity was improved

Samples E (kJ/ g mol)

60ºC 80ºC 60ºC 80ºC 60ºC 80ºC

increased by the same pretreatment (Table 2.3).

2-Pretreated with glyoxal in:

Red 41, pH 4.5, liq ratio 1: 100, 0.3 % H2O2

polyamide 6 fibres dyed with C. I. Acid Red 41.

upon applying continuous dyeing technique.

Acid Red 41, pH 4.5, liq ratio 1: 100, 0.3 % H2O2

of the dye molecules. The larger the dye molecule, the higher might be the dyeing temperature to permit the formation of spaces of sufficient size by the segmental motion of chains (78, 79). The physical characteristics of polyester fibers such as solubility, dyeability and iodine absorption are related to the orientation and crystallinity of fibers. The absorption of iodine by polyester fibers decreases on increasing the thermosetting temperature from 180° to 220° C. Increasing the applied tension on the fiber during thermal treatment hinders the iodine absorption due to better microstructure orientation (80- 82). The dyeability of the microdenier polyester fabric is compared with the normal denier polyester. The rate of dyeing is found to be higher in the case of micro denier polyester. The fastness property has not been influenced by the rate of heating during dyeing with disperse dyes (83, 84).

#### **2.1.4 Plasma treatment**

Polyester (PET) swatches are treated with electrical discharge plasma of a reactive atmosphere (tetrachlorosilane) to graft chlorosilane groups, subsequently hydrolyzed to very hydrophilic hydroxysilane groups. The results show that the surface parameters are considerably modified by the treatment (85). Low-pressure glow discharges are efficient in generating uniform plasmas. They have been applied in the surface modification of a variety of materials. Through the discharge of mixture of argon and oxygen, Ar-O2 (10:1), polyester fabric is continuously modified. The results reveal that the dyeability of the polyester fabric is dramatically improved. The improvement of dyeability is attributed to the introduction of functional groups on the surface during the treatment (86). Polyester fabrics are treated with radio-frequency plasma (in air) at different power levels and time intervals, and moisture content and surface resistivity behavior. The surface resistivity of polyester is dramatically reduced after plasma treatment. The fabrics are subjected to further plasma initiated grafting of acrylamide and acrylonitrile. Polyester has a moisture content of up to 3% after plasma initiated grafting. The surface resistivity of polyester is drastically lowered after grafting (87). Polyester fabrics are dyeable and printable with disperse dyes. Since the dyeability of PET fabric has been related to hydrophilicity and/or increase of micro roughness and surface area therefore, plasma treatment can improve the colouration of fibres (88). The printability of treated fabric with plasma/Al2O3 at 1.3 watt for 2 min was tried. The colour intensity of treated sample increased from 13.4 for untreated sample to 15.2 for treated one. The washing fastness properties of coloured treated samples are almost the same as the untreated one (4-5).

#### **2.1.5 Microwave irradiation**

Microwave drying is substantially more effective than convection oven drying. Microwave exposure has no effect on the elongation of polyester (89). Aliphatic polyesters have been studied mainly for medical applications. High energy radiation induced processing is an established technique that is used in polymer science. Radiation is used to initiate radical polymerizations and for modifications such as degradation, cross-linking, and graftcopolymerization (90).

#### **2.2 Polyamide**

Prospects of low waste or clean technology in textile dyeing can be realized by preserving the quality of both fibres and dyeing during processing. To meet new demands for energy conservation, high production rates (1, 2) and strengthening the dye-fibre bond formation,

of the dye molecules. The larger the dye molecule, the higher might be the dyeing temperature to permit the formation of spaces of sufficient size by the segmental motion of chains (78, 79). The physical characteristics of polyester fibers such as solubility, dyeability and iodine absorption are related to the orientation and crystallinity of fibers. The absorption of iodine by polyester fibers decreases on increasing the thermosetting temperature from 180° to 220° C. Increasing the applied tension on the fiber during thermal treatment hinders the iodine absorption due to better microstructure orientation (80- 82). The dyeability of the microdenier polyester fabric is compared with the normal denier polyester. The rate of dyeing is found to be higher in the case of micro denier polyester. The fastness property has not been

Polyester (PET) swatches are treated with electrical discharge plasma of a reactive atmosphere (tetrachlorosilane) to graft chlorosilane groups, subsequently hydrolyzed to very hydrophilic hydroxysilane groups. The results show that the surface parameters are considerably modified by the treatment (85). Low-pressure glow discharges are efficient in generating uniform plasmas. They have been applied in the surface modification of a variety of materials. Through the discharge of mixture of argon and oxygen, Ar-O2 (10:1), polyester fabric is continuously modified. The results reveal that the dyeability of the polyester fabric is dramatically improved. The improvement of dyeability is attributed to the introduction of functional groups on the surface during the treatment (86). Polyester fabrics are treated with radio-frequency plasma (in air) at different power levels and time intervals, and moisture content and surface resistivity behavior. The surface resistivity of polyester is dramatically reduced after plasma treatment. The fabrics are subjected to further plasma initiated grafting of acrylamide and acrylonitrile. Polyester has a moisture content of up to 3% after plasma initiated grafting. The surface resistivity of polyester is drastically lowered after grafting (87). Polyester fabrics are dyeable and printable with disperse dyes. Since the dyeability of PET fabric has been related to hydrophilicity and/or increase of micro roughness and surface area therefore, plasma treatment can improve the colouration of fibres (88). The printability of treated fabric with plasma/Al2O3 at 1.3 watt for 2 min was tried. The colour intensity of treated sample increased from 13.4 for untreated sample to 15.2 for treated one. The washing fastness properties of coloured treated samples are almost the same as the

Microwave drying is substantially more effective than convection oven drying. Microwave exposure has no effect on the elongation of polyester (89). Aliphatic polyesters have been studied mainly for medical applications. High energy radiation induced processing is an established technique that is used in polymer science. Radiation is used to initiate radical polymerizations and for modifications such as degradation, cross-linking, and graft-

Prospects of low waste or clean technology in textile dyeing can be realized by preserving the quality of both fibres and dyeing during processing. To meet new demands for energy conservation, high production rates (1, 2) and strengthening the dye-fibre bond formation,

influenced by the rate of heating during dyeing with disperse dyes (83, 84).

**2.1.4 Plasma treatment** 

untreated one (4-5).

copolymerization (90).

**2.2 Polyamide** 

**2.1.5 Microwave irradiation** 

various redox systems were incorporated in the dyebath vicinity. Redox systems have been utilized to induce covalent fixation of dye moieties on proteinic and polyamide fibres. Radical formation is usually the consequence of a bimolecular reaction between oxidant and reductant. Its rate can be adjusted almost by suitable variation of reactant concentration. The organic substrate may participate in a two-electron transfer process without radical formation (1-5). Introduction of glyoxal- hydrogen peroxide as a redox system to accelerate the polyamide dyeability with acid dyes is performed. An increase in colour intensity of the substrate dyed in the presence of the redox system as well as rapid exhaustion of the dyebath was observed. Time of half dyeing, specific dyeing rate constant and diffusion coefficient show some advancement as compared with the untreated polyamide. The activation energy of dyeing of the pretreated substrate decreased (1). Addition of 2 % alcohols to the pretreatment bath reveals nearly complete exhaustion of the dyebath after 30 min. at 70°C. The alcohol effectiveness can be ordered methanol > ethanol > propanol. Complete dye exhaustion at lower dyeing temperature and time can save energy, time as well as minimize pollution effects. Half dyeing time at 60ºC decreased by the applied treatment from 13.5 min for untreated sample to 2.5 min for glyoxal pretreated sample in methanol/water (2:98), as compared with the given t ½ at 80ºC which decreased from 6 min to 1 min. Both dyeing rate constant (k`) and diffusion coefficient (D) at 60ºC and 80ºC have increased by the same pretreatment (Table 2.3).


Treatment: 0.5 g glyoxal/ 100g fibre , solvent/ water ratio 2:98 , 50ºC, 1h.,Dyeing: 1% (o.w.f.) C. I. Acid Red 41, pH 4.5, liq ratio 1: 100, 0.3 % H2O2

Table 2.3. Half dyeing time (t ½), dyeing rate constant (K'), and diffusion coefficient (D) of polyamide 6 fibres dyed with C. I. Acid Red 41.

The activation energy decreased from 41.5 kJ/g mol for untreated one to 24.9 kJ/g mol for pretreated polyamide 6 fabric with glyoxal/H2O2 in methanol/water (Table 2.4). The decrease in the half dyeing time and the activation energy and the increase in dyeing rate constant and diffusion coefficient led to saving in time. The colour intensity was improved upon applying continuous dyeing technique.


Treatment: 0.5 g glyoxal / 100 g fibre, solvent / water ratio 2: 98, 50ºC, 1h, Dyeing: 1 % (o.w. f.) C. I. Acid Red 41, pH 4.5, liq ratio 1: 100, 0.3 % H2O2

Table 2.4. Activation energy (E) of dyeing for pretreated polyamide 6 fibres

Pretreatment of Proteinic and Synthetic Fibres Prior to Dyeing 319

Where Q is the heat required, Cp is the specific heat of matter to be warmed up, W is the weight of the material to be warmed up; and Δt is the temperature difference involved, An initial temperature of 20oC is assumed for water. The heat loss by radiation and by other means can be calculated by assuming that the total heat is twice the heat required for heating up (12). Table 2.6 shows the cost of heat energy per kg of fabric. It is clear that the

Dyeing process Energy/cycle Kcal Cost/cycle Cost/kg

Table 2.6. Cost of energy consumption for the different dyeing process in (LE)

497280 372960 29.8368 22.3776 0.0995 0.0746

0.031 0.0325 0.034

9.283 9.772 10.262

154716 162876 171036

In addition to the expenditure on dyes, chemicals, water and energy, the layout on the equipment and operating personnel carrying out the dyeing process have to be considered, besides the general costs and overheads. The general costs have to be a common item not to

The suggested dyeing processes have to be compared with the conventional one. The price of Jet machine is considered as one million Egyptian pounds. For suggestion of dyeing methods, a stainless steel tank of 4m3 is required for preparation and storing the pretreatment solutions of either acetaldehyde or glyoxal. A stainless steel pump (5 Hp) is also required. The total cost of the pump and the storage tank is assumed to be about 10.000

<sup>X</sup>cost of machine

**Labour** /kg fabric = (Man hour x no. of hours/shift x no. of shifts/day x no. of

Table 2.7 represents the total fixed operating costs/kg fabric for all dyeing processes in this study. It can be noticed that the investigated pretreatments led to decreasing the operating

Table 2.8 illustrates the total production cost/kg fabric. Glyoxal/H2O2 pretreated fabric attained a lower production cost than both conventional dyeing method and that pretreated fabric with acetaldehyde. It can be noticed that pretreatment of PA-6 fabric with redox system (glyoxal/H2O2) led to a decrease in the total production cost/kg fabric in the range of 7-11% as well as increasing the production rate/year and decreasing the pollution

production rate (kg/year)

glyoxal / H2O2 pretreated fabric attained the lowest value.

LE, supposing the use of two Jet machines in this study.

10

labours/shift) ÷ (no. of batches/day x Production rate/ batch)

impacts without impairing the tensile properties of the fibre.

costs as well as increasing the production rate.

Conventional dyeing Method Pretreated with acetaldehyde. Pretreated with glyoxal/H2O2 and dyed at: 60oC 70oC 80oC

Assuming that 106 Kcal energy = 60 LE

be included in the calculations.

**Depreciation** for 10 years as: <sup>1</sup>

**Interest** =10 % of the capital cost. **Repairs** = 5 % of the capital cost.

**Fixed costs** 

**Machinery** 
