**2.1.2 Disperse dyeable PP fibers**

The advantages of disperse dyeable PP fibers were:


Grafting of dye enhancers to the polyolefin polymer has been reported by Negola et al. [9, 10]. A mixture of amorphous PETG (glycol-modified polyethylene terephthalate) was grafted onto polyolefin. Maleic anhydride was added to increase the cohesion and dispersion of amorphous PETG in polyolefin polymer. A formulation of 50% PP, 48%

Commercially Adaptable Coloration Processes for Generic Polypropylene Fiber 159

While most of the acid dyeable PP fiber versions have failed in the development stage itself due to their lack of commercial viability, some of them have shown limited commercial success. Those which have shown commercial success include acid-dyeable PP fiber from Montecatini (Mercalon D®), Hercules (Herculon® Acid Dyeable), Beaunit, Phillips and Toyobo. Out of these, Mercalon D® was dyeable with almost all anionic dyes up to dark shades. Mercalon D® is presently available as a staple fiber for carpets and knitting yarns. Merkalon D®'s use is increasing because its dyeing profile is similar to that of wool. Merkalon D® has a leveling problem in piece dyeing because of its high affinity to acid dyes and high rate of dyeing. Apart from a few limitations and high cost per pound, Merkalon D® fiber appears to have achieved the status of a commercial, general purpose fiber in the

Arkman et al. [18] reported the mixing of an additive in the PP polymer prior to fiber extrusion. The additive was synthesized by attaching long alkyl chains having substituents such as alkaline nitrogen to a rigid polymer backbone. They found a diffusion coefficient of dyeing in the order of 10-11 m2/s, which indicated very fast diffusion of the acid dye molecules into the modified fiber driven mainly by the electrostatic interaction between the

The use of Koprolene colors (dyes having a metal chelating group) for modified PP fibers containing nickel salt stabilizer has been reported by Baumann et al., [19] and has demonstrated attractive shades with excellent fastness properties to washing, dry-cleaning, crocking, light and gas fading. The scoured yarn or fabric was recommended to be dyed at

Since none of the commercially-dyeable PP fiber was available long enough to explore its dyeing behavior [9], only a few scattered studies were reported. The dyeing of hydrophobic fibers with disperse dyes takes place through the solid solution mechanism, i.e., the dye forms a solution within the amorphous region of the polymer. The dye mass transfer from dyebath to the fiber phase is governed by the partition coefficient of the dye. Bird and Patel [20] have shown that the introduction of additional dye into the dye bath beyond the saturation point of the fiber phase did not increase the amount of dye inside the fiber. Since generic, isotactic PP fiber has only ~30% amorphous mass accessible to dye molecules, the saturation value is low. The encapsulation of a suitable dye receptor additive into the PP matrix causes the amorphous regions of the fiber to increase, leading to the availability of more solvent for the dye to form a solid solution, and thus increasing the saturation values of the fiber. However, the physical properties of the PP fiber, e.g., the percent crystallinity, are lowered when additives are occluded in the solid state structure, and since the cost of the fiber is also increased, both factors detract from use of the modified fiber in

Calogero et al. [21] reported dyeing of unmodified PP fibers using a colloidal emulsion of water plus long-chain, alkyl-substituted anthraquinone dyes dissolved in an organic solvent. Alkyl chains with carbon numbers from 8-18 were described, and the 18 chain length was found as ideal for PP. The ideal dyebath temperature was reported as 90oC. The dyeing resulted in uniform coloration of the PP fibers with excellent fastness to washing,

anionic acid dye and basic dye sites in the polymer contributed by the additive.

carpet and knitting industries.

190 to 200oF for one hour and finally to be washed.

**2.2 Dyeing mechanism of PP fibers** 

textile/carpet products.

**2.3 Dyeing of unmodified PP** 

crocking and dry-cleaning.

amorphous PETG and 2% maleic anhydride was used and the resultant pellets were extruded into fiber form. A 5% disperse dyeable mixture grafted onto 95% PP resulted, which upon dyeing yielded deep shades, whereas a 2.5% disperse dyeable mixture onto 97.5% PP yielded light shades.

Addition of polymeric dye receptors has been investigated by Farber et al. [14] and Dayioglu et al. [15]. Disperse dyeable PP fiber was manufactured to be consumed in the carpet industry. The approach involved addition of selected polymeric compounds into the PP melt prior to extrusion. Certain limitations of using polar polymeric compounds exist:


In relation to the above challenges, the selection of an appropriate PP additive with allround adequate properties becomes difficult. An ideal polymeric additive for PP should possess polar groups lying pendant to its chain, be slightly crystalline in nature, have partial compatibility with PP, have a melting point greater that 140oC and have a glass transition greater than 90oC. Polymers such as saturated linear copolyesters, copolyamides, copolymers of vinyl pyridines with styrene, copolymers of ethylene with vinyl acetate and alkyl acrylate may work as such ideal additives.

In conclusion, disperse dyeable PP fibers are comparatively easy to produce and result in level dyeings, although they are more expensive than the generic fiber (usually >\$1.00/lb. premium). However, the fastness properties of the dyed materials do not meet all the requirements of the textile and apparel businesses, especially due to their poor dry-cleaning fastness to perchloroethlene (PERC). In addition, a similar chlorinated solvent (trichloroethylene) is commonly used as a spot cleaning agent in carpets, both in manufacturing and in residential/commercial use. The shades obtained by acid and basic dyes are also brighter than those obtained with disperse dyes.

FiberVisions recently launched CoolVisions® (a disperse dyeable PP fiber) [16] having a dye receptor as an encapsulated additive in the polymer matrix. The dye receptor additive is an amorphous, low molecular weight copolyester. A compatibilizer is finely distributed and encapsulated in the microstructure of PP [17]. The modified PP fibers are manufactures by sheath-core bicomponent spinning consisting core as dye receptor and sheath material as PP.

#### **2.1.3 Acid dyeable PP fibers**

The advantages of acid dyeable PP fibers include [9]:


While most of the acid dyeable PP fiber versions have failed in the development stage itself due to their lack of commercial viability, some of them have shown limited commercial success. Those which have shown commercial success include acid-dyeable PP fiber from Montecatini (Mercalon D®), Hercules (Herculon® Acid Dyeable), Beaunit, Phillips and Toyobo. Out of these, Mercalon D® was dyeable with almost all anionic dyes up to dark shades. Mercalon D® is presently available as a staple fiber for carpets and knitting yarns. Merkalon D®'s use is increasing because its dyeing profile is similar to that of wool. Merkalon D® has a leveling problem in piece dyeing because of its high affinity to acid dyes and high rate of dyeing. Apart from a few limitations and high cost per pound, Merkalon D® fiber appears to have achieved the status of a commercial, general purpose fiber in the carpet and knitting industries.

Arkman et al. [18] reported the mixing of an additive in the PP polymer prior to fiber extrusion. The additive was synthesized by attaching long alkyl chains having substituents such as alkaline nitrogen to a rigid polymer backbone. They found a diffusion coefficient of dyeing in the order of 10-11 m2/s, which indicated very fast diffusion of the acid dye molecules into the modified fiber driven mainly by the electrostatic interaction between the anionic acid dye and basic dye sites in the polymer contributed by the additive.

The use of Koprolene colors (dyes having a metal chelating group) for modified PP fibers containing nickel salt stabilizer has been reported by Baumann et al., [19] and has demonstrated attractive shades with excellent fastness properties to washing, dry-cleaning, crocking, light and gas fading. The scoured yarn or fabric was recommended to be dyed at 190 to 200oF for one hour and finally to be washed.

#### **2.2 Dyeing mechanism of PP fibers**

158 Textile Dyeing

amorphous PETG and 2% maleic anhydride was used and the resultant pellets were extruded into fiber form. A 5% disperse dyeable mixture grafted onto 95% PP resulted, which upon dyeing yielded deep shades, whereas a 2.5% disperse dyeable mixture onto

Addition of polymeric dye receptors has been investigated by Farber et al. [14] and Dayioglu et al. [15]. Disperse dyeable PP fiber was manufactured to be consumed in the carpet industry. The approach involved addition of selected polymeric compounds into the PP melt prior to extrusion. Certain limitations of using polar polymeric compounds exist: a. Subsequent spinning and drawing operations become difficult because most of the

b. As the polarity of admixing compounds increases, their compatibility with PP decreases. Therefore, polyamides and polyesters with strong polar groups are less

c. The melting point of most polar compounds is higher which requires a high processing

d. Many polymeric additives suitable for processing purposes do not have enough

e. Most of the polymeric additives require amounts over 10% to be incorporated into the PP fiber to achieve satisfactory dyeability. Large quantities of incompatible and partially-miscible additives adversely affect the physical and mechanical properties of

In relation to the above challenges, the selection of an appropriate PP additive with allround adequate properties becomes difficult. An ideal polymeric additive for PP should possess polar groups lying pendant to its chain, be slightly crystalline in nature, have partial compatibility with PP, have a melting point greater that 140oC and have a glass transition greater than 90oC. Polymers such as saturated linear copolyesters, copolyamides, copolymers of vinyl pyridines with styrene, copolymers of ethylene with vinyl acetate and

In conclusion, disperse dyeable PP fibers are comparatively easy to produce and result in level dyeings, although they are more expensive than the generic fiber (usually >\$1.00/lb. premium). However, the fastness properties of the dyed materials do not meet all the requirements of the textile and apparel businesses, especially due to their poor dry-cleaning fastness to perchloroethlene (PERC). In addition, a similar chlorinated solvent (trichloroethylene) is commonly used as a spot cleaning agent in carpets, both in manufacturing and in residential/commercial use. The shades obtained by acid and basic

FiberVisions recently launched CoolVisions® (a disperse dyeable PP fiber) [16] having a dye receptor as an encapsulated additive in the polymer matrix. The dye receptor additive is an amorphous, low molecular weight copolyester. A compatibilizer is finely distributed and encapsulated in the microstructure of PP [17]. The modified PP fibers are manufactures by sheath-core bicomponent spinning consisting core as dye receptor and sheath material as PP.

a. Acid dyes are inexpensive, offering a wide range of shades with bright colors.

polar polymeric compounds lack compatibility with PP.

polarity to give adequate wet- and dry-cleaning fastness.

temperature, resulting in the degradation of PP.

f. The fiber is more costly than the generic version.

alkyl acrylate may work as such ideal additives.

dyes are also brighter than those obtained with disperse dyes.

The advantages of acid dyeable PP fibers include [9]:

compatible with PP than polystyrene and ethylene copolymers.

97.5% PP yielded light shades.

the resulting fiber.

**2.1.3 Acid dyeable PP fibers** 

b. Light fastness is excellent.

Since none of the commercially-dyeable PP fiber was available long enough to explore its dyeing behavior [9], only a few scattered studies were reported. The dyeing of hydrophobic fibers with disperse dyes takes place through the solid solution mechanism, i.e., the dye forms a solution within the amorphous region of the polymer. The dye mass transfer from dyebath to the fiber phase is governed by the partition coefficient of the dye. Bird and Patel [20] have shown that the introduction of additional dye into the dye bath beyond the saturation point of the fiber phase did not increase the amount of dye inside the fiber.

Since generic, isotactic PP fiber has only ~30% amorphous mass accessible to dye molecules, the saturation value is low. The encapsulation of a suitable dye receptor additive into the PP matrix causes the amorphous regions of the fiber to increase, leading to the availability of more solvent for the dye to form a solid solution, and thus increasing the saturation values of the fiber. However, the physical properties of the PP fiber, e.g., the percent crystallinity, are lowered when additives are occluded in the solid state structure, and since the cost of the fiber is also increased, both factors detract from use of the modified fiber in textile/carpet products.

#### **2.3 Dyeing of unmodified PP**

Calogero et al. [21] reported dyeing of unmodified PP fibers using a colloidal emulsion of water plus long-chain, alkyl-substituted anthraquinone dyes dissolved in an organic solvent. Alkyl chains with carbon numbers from 8-18 were described, and the 18 chain length was found as ideal for PP. The ideal dyebath temperature was reported as 90oC. The dyeing resulted in uniform coloration of the PP fibers with excellent fastness to washing, crocking and dry-cleaning.

Commercially Adaptable Coloration Processes for Generic Polypropylene Fiber 161

fibers were employed: Exhaustion, pad-steaming and printing with steam fixation. Burkinshaw et al. [28] investigated dyeing of textile fibers including: segmented polyurethanes, segmented polyurethane ureas and segmented polyetheresters; polyesters including poly(tetramethylene terepthalate); polyamides including poly(hexamethylene adipamide); and polycaprolactam with acid leuco vat dyes utilizing alphahydroxyalkylsufinic acids, their salts and 1, 2, 4-trithiolane as additional reducing agents. The authors reported excellent depth of shade and wash fastness for the dyed materials. Etters et al. [29] reported that several vat dyes in their acid leuco form exhibited substantivity to unmodified, knitted PP fabrics with C. I. Vat Blue 1, Vat Orange 1 and Vat Yellow 2. Gaehr et al. [30] reported that several Colloisol® vat dyes of BASF exhibited good affinity on plasma-pretreated PP fiber in a pigment pad-thermofix process at 120oC. The fixation of pigments was performed in a pad-steam or pad-dry heat process, and the

processes were reported to be applicable for dyeing of fiber mixtures containing PP.

From the literature review, the substantial volume of work conducted by researchers of different laboratories world-wide confirmed that the aqueous dyeing of generic, unmodified PP fiber is of significant importance for textile, carpet, apparel, sportswear and a variety of other product applications. Most of the work carried out by researchers included the modification of PP fiber in some form or another, paths which although they impart dyeability, increase the total fiber costs two to three times above that of generic PP because of utilization of a variety of modifying chemicals, additives, comonomers or components. Another disadvantage of the fiber modification route is that it adversely affects the mechanical and physical properties of the fiber. The low cost and good physical/aesthetic properties, the two basic motivations for utilizing generic PP fiber in textiles and carpets, have been outweighed by the disadvantages and limitations of modifying the fiber solely to

The primary purpose of the aqueous dyeing of PP fiber in its generic, unmodified form is to exploit the advantages this fiber offers to the market place and, at the same time, create new product markets for this inexpensive fiber in high volume consumption areas such as tufted carpets, towels, apparel, sportswear and technical textiles. These product markets are governed today by demand-activated manufacturing, and hence can only be realized by developing flexible, aqueous batch and continuous dyeing processes for generic PP consistent with commercially-established coloration technologies already in use for other

The coloration of cellulosic fibers with vat dyes is well established [31]. However, hydrophobic fibers such as PP are not dyeable by the conventional, aqueous-based methods which are successful for cellulosic fibers in which the alkaline leuco, dianion form (completely water soluble) of vat dyes is utilized. Theoretically, acid leuco vat dyeing analogous to the disperse dyeing of polyester fiber may provide a method to aqueous color unmodified PP fiber. Etters et al. [29] among others [23, 24, 27] reported the acid leuco vat dye route as a potential path to aqueous dyed PP fiber in its unmodified

**3. Literature review summary and scope of the research** 

impart aqueous dyeability.

high-volume, commodity fibers.

**4. Technical approach** 

form.

Vat dyes captured a large part of the dyestuff market in the coloration of cellulosic fibers because they provide excellent all-round fastness, particularly to light, washing and chlorine bleach. Because of their insoluble nature in the oxidized form, vat dyes require a complicated application procedure involving the reduction of the oxidized form into first the leuco form and then with base into the more water-soluble alkaline leuco form. The soluble, reduced alkaline leuco form has high substantivity towards cellulosic fibers, and after levelness is achieved, the dyes are re-oxidized into the original, water-insoluble keto form inside the fibers.

Sodium dithionite and sodium hydroxide produce large amounts of sodium thiosulfate and sulfites as a byproduct, increasing the cost of effluent treatment. Roessler et al. [22] reported electrochemical methods for reduction of vat dyes which are environmentally friendly, thus providing an alternative to the use of sodium dithionite and sodium hydroxide.

A. V. Mishchenko et al. [23] investigated the batch exhaust dyeing of staple PP fiber at 100oC and 80oC with the acid leuco vat dyes thioindigo red S, thioindigo reddish brown Zh and thioindigo red S (actual chemical structures were not revealed). They plotted a dye exhaustion curve (dye adsorption versus dyeing time) and calculated the heat of dyeing and entropy of dyeing. The heat of dyeing was observed as negative, indicating the strong interaction between the acid leuco vat dye and the PP fiber. The measured heat of dyeing of acid leuco vat dye on unmodified PP was of the same order as that in the disperse dyeing of PP fiber.

The authors also investigated the effect of heat treatment [24] on the fixation of acid leuco dyes on PP fiber. The process sequence involved padding of PP fiber with the acid leuco vat dye solution, squeezing, drying and then treating with dry heat for 1 to 10 minutes. The authors noted that the heat treated fibers resulted in better fastness properties, and thus demonstrated that the heat treatment helped in the fixation of dye molecules via diffusion. The rate of dyeing increased on subsequent heat treatment.

Morozova et al. [25, 26] investigated the process of developing the leuco esters of vat dyes on PP fiber by a nitrite method and optimized the development conditions for maximum color yield:

Temperature: 60oC; development time: 40 min.; liquor ratio: 50; liquor composition: 12.5% H2SO4, 2.2 g/l NaNO2. The authors obtained satisfactory light and weathering fastness for the PP dyed with leuco-ester of Vat Brilliant Green S [26].

Bird and Patel [20] studied the dyeing of unmodified PP yarn and film with disperse dyes and concluded that no fundamental difference existed between PP and other substrates in the diffusion mechanism. They showed the Nernst isotherm partition mechanism of dye adsorption between fiber and aqueous phase, which was similar to that followed in the disperse dyeing of polyester fiber. Unmodified PP is more crystalline, nonpolar and hydrophobic than other synthetic fibers [20]. Moreover, the absence of hydrogen bonding groups in PP also precludes the fiber from attaching to the diffused dye molecules, resulting in the poor saturation values. Further, diffusion coefficients of disperse dyes in PP were higher than in cellulose acetate fibers, indicating that diffusion of the dyes inside the PP fiber was not the reason of poor saturation. Weak intermolecular interactions between disperse dyes and PP were concluded to be the reason for the poor saturation values.

According to Ulrich et al. [27], vat dyes when applied in their oxidized or vat acid forms in a colloidal state of dispersion under proper temperature conditions diffuse into highly hydrophobic fibers. Three methods of vat dye application on unmodified polypropylene

Vat dyes captured a large part of the dyestuff market in the coloration of cellulosic fibers because they provide excellent all-round fastness, particularly to light, washing and chlorine bleach. Because of their insoluble nature in the oxidized form, vat dyes require a complicated application procedure involving the reduction of the oxidized form into first the leuco form and then with base into the more water-soluble alkaline leuco form. The soluble, reduced alkaline leuco form has high substantivity towards cellulosic fibers, and after levelness is achieved, the dyes are re-oxidized into the original, water-insoluble keto

Sodium dithionite and sodium hydroxide produce large amounts of sodium thiosulfate and sulfites as a byproduct, increasing the cost of effluent treatment. Roessler et al. [22] reported electrochemical methods for reduction of vat dyes which are environmentally friendly, thus

A. V. Mishchenko et al. [23] investigated the batch exhaust dyeing of staple PP fiber at 100oC and 80oC with the acid leuco vat dyes thioindigo red S, thioindigo reddish brown Zh and thioindigo red S (actual chemical structures were not revealed). They plotted a dye exhaustion curve (dye adsorption versus dyeing time) and calculated the heat of dyeing and entropy of dyeing. The heat of dyeing was observed as negative, indicating the strong interaction between the acid leuco vat dye and the PP fiber. The measured heat of dyeing of acid leuco vat dye on unmodified PP was of the same order as that in the disperse dyeing of

The authors also investigated the effect of heat treatment [24] on the fixation of acid leuco dyes on PP fiber. The process sequence involved padding of PP fiber with the acid leuco vat dye solution, squeezing, drying and then treating with dry heat for 1 to 10 minutes. The authors noted that the heat treated fibers resulted in better fastness properties, and thus demonstrated that the heat treatment helped in the fixation of dye molecules via diffusion.

Morozova et al. [25, 26] investigated the process of developing the leuco esters of vat dyes on PP fiber by a nitrite method and optimized the development conditions for maximum

Temperature: 60oC; development time: 40 min.; liquor ratio: 50; liquor composition: 12.5% H2SO4, 2.2 g/l NaNO2. The authors obtained satisfactory light and weathering fastness for

Bird and Patel [20] studied the dyeing of unmodified PP yarn and film with disperse dyes and concluded that no fundamental difference existed between PP and other substrates in the diffusion mechanism. They showed the Nernst isotherm partition mechanism of dye adsorption between fiber and aqueous phase, which was similar to that followed in the disperse dyeing of polyester fiber. Unmodified PP is more crystalline, nonpolar and hydrophobic than other synthetic fibers [20]. Moreover, the absence of hydrogen bonding groups in PP also precludes the fiber from attaching to the diffused dye molecules, resulting in the poor saturation values. Further, diffusion coefficients of disperse dyes in PP were higher than in cellulose acetate fibers, indicating that diffusion of the dyes inside the PP fiber was not the reason of poor saturation. Weak intermolecular interactions between disperse dyes and PP were concluded to be the reason for the poor saturation

According to Ulrich et al. [27], vat dyes when applied in their oxidized or vat acid forms in a colloidal state of dispersion under proper temperature conditions diffuse into highly hydrophobic fibers. Three methods of vat dye application on unmodified polypropylene

providing an alternative to the use of sodium dithionite and sodium hydroxide.

The rate of dyeing increased on subsequent heat treatment.

the PP dyed with leuco-ester of Vat Brilliant Green S [26].

form inside the fibers.

PP fiber.

color yield:

values.

fibers were employed: Exhaustion, pad-steaming and printing with steam fixation. Burkinshaw et al. [28] investigated dyeing of textile fibers including: segmented polyurethanes, segmented polyurethane ureas and segmented polyetheresters; polyesters including poly(tetramethylene terepthalate); polyamides including poly(hexamethylene adipamide); and polycaprolactam with acid leuco vat dyes utilizing alphahydroxyalkylsufinic acids, their salts and 1, 2, 4-trithiolane as additional reducing agents. The authors reported excellent depth of shade and wash fastness for the dyed materials.

Etters et al. [29] reported that several vat dyes in their acid leuco form exhibited substantivity to unmodified, knitted PP fabrics with C. I. Vat Blue 1, Vat Orange 1 and Vat Yellow 2. Gaehr et al. [30] reported that several Colloisol® vat dyes of BASF exhibited good affinity on plasma-pretreated PP fiber in a pigment pad-thermofix process at 120oC. The fixation of pigments was performed in a pad-steam or pad-dry heat process, and the processes were reported to be applicable for dyeing of fiber mixtures containing PP.
