ADVANCES IN SPUN-DYEING OF REGENERATED CELLULOSE FIBERS

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ADVANCES IN SPUN-DYEING OF REGENERATED CELLULOSE FIBERS

BENJAMIN TAWIAH 1 & BENJAMIN K. ASINYO 2

1Key Laboratory of Eco-Textile, Jiangnan University, Ministry of Education, Wuxi, Jiangsu, China 2Department of Textiles, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

ABSTRACT

Spun-dyeing has proven to be very efficient for the coloration of textiles for several decades now. This method of

colored fiber production has unparalleled advantages in terms of environmental safety and color fastness. This review

seeks to highlight the developments in spun-dyeing of regenerated cellulose fibers over the years with emphasis on choice

of colorants and their effect on the fibers produced. Excerpts of results obtained from our research work on the

compatibility of spun-dyed alginate fibers and their thermal/crystalline properties with fluorescent pigments have been

included in this review. It was observed from literature that dissolved dyes have not been appreciably used in spun-dyeing

dyeing due to the high temperature and alkaline nature of the spinning dope usually used in the production of regenerated

cellulose. These perceived challenges however sets the pace for further research into the use of dissolved dyes for fiber

spinning. The possibility of adding other functional finishes such as antimicrobial, antistatic and flame retardant properties

to the spinning dope during the spun-dying process has made it more attractive than ever. However, there is the need for

further research into the compatibility of some of these finishes with the spinning dope and their possible effect on

the microstructure and the tensile properties of the dyed fibers.

KEYWORDS: Regenerated Cellulose, Spun-dyeing, Mass Coloration, Spinning Dope, Colorants

INTRODUCTION

Cellulose, one of the world’s most abundant, natural and renewable biopolymer is extensively present in various

forms of biomasses, such as trees, plants, tunicate and bacteria (Wilkes, 2001; Zhou et al., 2003; Fras Zemljic et al., 2012).

Besides naturally grown cellulose fibers like cotton, hemp or flax, interest in textile fibers made up from regenerated

cellulose has grown over the past few years (Fras Zemljic et al., 2012. A recent study by Transparency Market Research

(TMR) forecasts that the global cellulose fibers market will grow at a CAGR of 9.8% between 2012 - 2018. Out of this

figure the market for rayon fiber alone will grow at a CAGR of 10% over the period 2014-2019. This global cellulose

fibers market has been propelled by the rising demand for skin friendly, eco-friendly, and biodegradable fabrics from the

textiles market. Some of the extensively used man-made cellulose fibers include rayon and its various types like viscose

fibers, triacetate, and acetate.

The production of man-made cellulose fibers involves the application of cheaper and renewable feedstock as

against their synthetic alternatives. Moreover, these renewable biopolymer materials are readily available in nature in huge

quantities, which favors their use as more sustainable material compared to oil-based products. While polyester fibers can

be understood as cost-effective high-performance material, the unique moisture and water-related properties of cotton can

only be substituted by use of cellulose-based fibers, so-called man-made cellulosics (Wilkes, 2001; Manian et al., 2008;

Fras Zemljic et al., 2012).

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66 Benjamin Tawiah & Benjamin K. Asinyo

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Regenerated cellulosic obtained from biopolymer materials are colored by dissolution and incorporation of

colorants followed by reshaping of the cellulose via various physico-chemical processes to obtain colored fibers. (A

glossary of AATCC, 2000; Avinash et al., 2005)

The Case for Spun-dyeing

As substitute to conventional wet-dyeing processing for most technical textiles, spun-dyeing overcomes the

disadvantages of conventional methods and provides its final products with excellent characteristics, such as uniform

coloration, level shade, and is considered as environmentally friendly production process. Its use is not limited to

regenerated cellulose but has become the most prominent and preferred choice of method for coloring most synthetic

fabrics (Wilkes, 2001; Kamide et al., 2001; Kurahashi et al, 2003; Sui et al., 2012). Another characteristic feature of spun-

dyed fibers is their vibrant color and luster, good water-resistance, and excellent color-fastness and light fastness. Spun-

dyed fibers do not only possess outstanding quality of the ordinary fiber, but also reduce the color differences between

batches, and cuts down on environmental pollution (Manian et al., 2008; Fu et al., 2013). Besides, spun-dyeing is cost

efficient, and is therefore mostly preferred choice for coloring synthetic polymers that are otherwise difficult to dye, e.g.

polypropylene (Manian et al., 2007; Kurahashi, 2003). The cost and environmental benefits of spun-dyeing as reported by

Sardana in (table1) (The Rupp Report, 2013) are amazing; and with the recent clamor for eco-friendly productions in some

of the world’s leading producers of textiles such as China, India, Italy, and USA, it has become necessary for further

research to be conducted into spun-dyeing as the next viable alternative to the current environmental mess created by the

conventional dyeing techniques.

Table 1

In a world where water resources are becoming increasingly sparse and disposal of industrial wastewater is been

subjected to stricter environmental controls, spun-dying present a unique opportunity of coloring fibers with very little

water use (Manian et al., 2007). In the coloration of both synthetic and regenerated fibers, spun-dyeing ensure less

environmental damage compared to the conventional bath dyeing.

Challenges of Spun-dyeing

The disadvantage spun-dyeing is speed of reaction to market demands by the fiber producers who have to either

stockpile many different colors of yarns or be prepared to extrude fibers on demand of quixotic fashion and home

furnishing markets (Wilkes, 2001; Kurahashi, 2003; Manian et al., 2008). Depending upon the positioning of the fiber

producer in the supply chain, this can be a major problem and create minor inconvenience. Another disadvantage of mass

coloration is the clean-out required between colors. Extruders, transfer lines, screen packs, and spinneret channels must be

purged from one color prior to starting a run of another color. If the fiber producer is large and diversified, there may be an

outlet for off-color fiber (recycle or using a low-value application). The fiber producer may also reduce waste through

intelligent scheduling of color on spin lines (light colors followed by dark colors). Practically, the clean-out necessities

makes short runs difficult with higher efficiency resulting from longer runs of color (Holme, 2004; Avinash et al., 2005;

Bredereck, 2005)

One of the primary considerations in the spun-dyeing process is to ensure the pysico-chemical compatibility of the

polymer-colorant in the dope mixture (Kurahashi et al., 2003; Fras Zemljic et al., 2012; Wang et al., 2015). Regenerated

cellulosic’s present unique challenges in this regard because their manufacturing processes often involve treatment of the

Advances in Spun-Dyeing of Regenerated Cellulose Fibers 67


cellulose with strong reducing and/or oxidizing agents, which may militate against the stability of colorants or affect the

tensile strength of the ensuing fiber. Despite these perceived challenges, spun-dyeing of regenerated cellulosic’s have been

made possible and various methods for its achievement have been reported in literature (Zhou et al., 2003; Fras Zemljic et

al., 2012). This script therefore seeks to offer a review of the state of the art systems available for mass coloration of

regenerated cellulose fibers.

Applications of Spun-dyed Regenerated Fibers

Previously, most regenerated fiber production capacity serve the technical textiles market especially in the area of

medical textiles for specialized applications and for military uniforms, sportswear and automotive textiles (Zhou et al.,

2003; Fras Zemljic et al., 2012; Avinash et al., 2005). Currently, production of general-purpose textiles have increased over

the past 15 years. For instance, viscose fiber capacity has increased lately to serve the production of general-purpose

textiles. These fibers are increasingly been used as household furnishing and for industrial purposes.

Choice of Colorant for Spun-dyeing Regenerated Fibers

The selection of colorants for a particular regenerated fiber is dependent on many factors with the most critical

one being the compatibility of polymer-color mixture and its possible effect on the mechanical properties of the fiber

(Wang et al., 2015; Fu et al., 2013). Another important aspect worth mentioning is the color performance of the fiber and

its intended end use. As a result, several important factors which can significantly influence the fabric properties ought to

be made in selecting colorants for spun-dyeing. Some of the most defining properties of colors which can significantly

affect regenerated fibers are:

The Limiting Concentration: The limiting concentration of a colorant determines its thermal stability profile in

the chosen polymer. Values for the heat stability of a colorant for instance are usually derived from a pre-determined

concentration i.e. Standard depth 1/3 (Modlich, 1999; Clariant Data sheet 2007). The limiting concentration determines the

lowest dilution at which a colorant is thermally stable at a given temperature. For instance, in a study conducted by Wang

et al., 2015 on thermal behavior of spun-dyed alginate fiber using fluorescent pigment (Figure 1) they observed that the

thermal stability of the fiber was compromised as the content of fluorescent pigment in the polymer matrix increased from

2 to 4%.

Figure 1

Similar phenomenon is observed in most regenerated polymers during spun-dyeing. The limiting concentration

also determines the tensile strength of the fibers to some extent because the ratio of colorant to dissolved polymer can

affect the microstructure and the crystalline alignment of the fiber during extrusion (Fu et al 2013; Wang et al., 2015).

More so, the acidity or alkalinity of the spinning dope can also has a significant effect on the limiting concentration of the

regenerated cellulose because this phenomenon plays a decisive role in in determining whether the pigment in the polymer

matrix behaves as a proton acceptor or donor or otherwise and its dare effect on the stability of pigment particles in the

polymer-color mixture hence the need for a carefully computation of the dope stoichiometry (Fu et al., 2013). It is worth

mentioning that, values obtained for a specific polymer cannot be generalized for all polymers because each polymer has

its unique limit concentration (Modlich, 1999, Shenoy & Aroon 1999).



Particle Size and Its Distribution: In paste and liquid dispersions such as those used for regenerated fibers,

particle size and specific surface area of pigment can significantly influence the rheology of the system (Shenoy & Aroon

1999, Lambourne et al., 1999). The larger the particle size, the lower the specific surface area of a pigment and the

consequential lower viscosity. In spun-dyeing of regenerated cellulose, a pigment with high specific surface area will

require additional “wetting out” in order to obtain an optimum dispersion. A larger particles size in spinning solutions leads

to higher opacity and lower color strength in comparison with a finer milled product (Kunkle et al., 1988; Bilgili et al.,

2004) besides its consequential effect on tensile strength. Particle size distribution is also important factor in obtaining

optimum dispersion in spun-dyeing applications (Maile et al., 2005; Herbst & Klaus, 2006). A narrow band distribution

with a minimum over and undersized particles will more readily disperse in a thermoplastic system particularly when

physical dispersion forces and pigment wetting reach their premium (Günthert, 1989; Fu et al., 2013), but this will not

work for regenerated fibers hence the need for proper dispersion and distribution of the particles before addition to the

spinning dope. The particle size distribution in spinning solution determines the greater extent the crystalline structure and

tensile strength of spun-dyed fibers hence the need to even particle size distribution within the spinning dope in order to

avoid having weak points with the fiber strand.

Color Dispersibility: Optimum colorant dispersion is very essential to the provision of fiber functionality in

everyday use (Parfitt, 1969; Herbst & Klaus, 2006; Fu et al., 2013). A careful selection ought to be made in this regard

especially in the case of spun-dyeing since this can eventually affect the crystalline properties of the fiber.

The Light Fastness: A colorant is primarily determined by its chemistry even though particle size and particle

size distribution can also be influencing factors. Optimal dispersion of mill base, thus pigment and other water insoluble

colorants is critical to the achievement of light fastness properties of particular colorant (Giles et al, 1977; Herbst & Klaus,

2006; El-sayed et al., 2012). It has been suggested that processing parameters can also affect the light fastness properties of

spun-dyed regenerated fibers but this can be minimized to some extent when monitored properly in dope dyeing process.

Pigments and polymer soluble dyes selected for mass coloration of fibers must meet the above-mentioned

requirements and in order to survive the multi-step processing and its end-applications.

Classification of Colorants for Spun-Dyeing of Regenerated Fibers

Vat dyes/leuco Compounds

Spun-dyed fibers are generated by evenly and continually adding the innocuous dye grain of nano-grade colorants

into the spinning solution by a special blending technique by which the dye grains are evenly dispersed into the fiber

(Boerstoel, 2001; Fu et al., 2007)

Several blending techniques have been proposed for spun-dyeing of viscose or cuprammonium rayon, some of

which comprises the addition of vat dyes to spinning dopes, wherein the vat dye is reduced to its leuco form and oxidized

back to its parent form in the course of manufacturing the substrate. Some techniques involve addition of reduced vat dye

to the spinning dope (Ruesch & Schmidt, 1936; I. G. Farbenindustrie 1936; Manian et al., 2008). Others have proposed that

the vat dye should be reduced in the spinning dope either by utilizing the chemical reagents already present in the system (

Kline, 1939) or by the addition of reducing agents such as sodium hydrosulphite (Lockhart, 1932). Similar techniques such

as dispersion of the vat dye in the spinning dope as a pigment to form the regenerated substrate, and treating the formed

substrate with reagents to reduce the vat dye within the fiber (Ruesch & Schmidt, 1936; Batt, 1961; I. G. Farben industrie



1936. In all these techniques, the oxidation of the vat dye back to its parent form is achieved in general by treating the

formed substrate with oxidizing agents.

There are however, some limitations to these techniques. For instance, adding the reduced vat dyes to the spinning

dope may result in the destabilization (Ruesch & Schmidt, 1936) and therefore proper ageing and coagulation of the

spinning dope is hindered, which eventually affects the development of suitable viscosities for fiber/filament spinning.

More so, reduced vat dyes are also predisposed to premature oxidation, which normally results in non-uniform distribution

of dye in the spinning dope thereby creating ‘weak links’ along the length of the spun fiber. (Maloney, 1967). The ‘weak

links’ ultimately create fibers with weak tensile strength with color patches which defeat the purpose for spun dyed fibers.

It is well known that many vat dyes are not reduced under conditions that exist in spinning dopes hence the addition of

reducing agents to the system which in most cases make the dope susceptible to gel formation (Lockhart, 1932; Dosne,

1936). This makes using vat dyes for spun-dyeing a big challenge. As a result, a technique of dispersing vat dyes in the

spinning dope and reducing them in the dyed fiber has been suggested (Lutgerhorst, 1956) but this system has also not

been very successful because other problems like uniform distribution of the dyestuff in the substrate is difficult to achieve,

and besides, not all the dyestuff in the substrate is reduced, causing visible specks of dyestuff particles to remain in and on

the substrate (Boerstoel, 2001; Avinash et al., 2005).

Subsequently, vat acids and their ester derivatives of leuco compounds of vat dyes has been proposed as

alternative technique for successful spun-dyeing regenerated cellulose where these compounds are added to the spinning

dope (Maloney, 1967; Dosne, 1936;). Nonetheless, these leuco compounds and their derivatives are highly susceptible to

oxidation and results in formation of coarse dyestuff particles in the dope thereby affecting the subsequent regeneration

steps (Dosne, 1936; Batt, 1961; Maloney, 1967). This can result in poor tensile strength and color levelness across the

length of the resultant fiber. Despite the perceived challenges to effective use of vat dyes and their derivatives in spun-

dyeing of regenerated cellulose, some success have been achieved lately (Zhou et al., 2003; Fras Zemljic et al., 2012) but

for the environmentally effect of these dyes lately in the wake of cleaner productions.

Dissolved Colorants

Dissolved colorants for mass dyeing must be able to withstand the high temperature of polymer melt (typically in

the region of 150 melt) to give level dyeing. Yet still the dye must not only have a good affinity to the polymer, but also

must not migrate out of the substrate after dyeing (i.e. must not bleed or bloom) (Maloney, 1967; Jones, 1959). Despite the

stringent conditions of spun-dyeing, dissolved colorants in polar water-miscible solvents or in the spinning dope have been

used extensively to spun-dye various regenerated cellulosics (Keil, 1961; Ciba Ltd, 1965, Ciba Ltd, 1966; Ciba Ltd,

191963; Riehen et al., 1971; Wegmann & Booker, 1966). The colorants used in these methods are selected dyes and their

derivatives. The choice of dyestuffs available for this technique is limited by the fact that not all dyestuffs can withstand

the strong alkaline conditions present in the spinning dope or the strong acid treatments imparted to substrates during

regeneration (Maloney, 1967: Steiert et al., 2007). Besides, different polymers behave differently in strongly acidic or basic

medium. Also, it has been established that certain water soluble dyes such as reactive dyes undergo strong hydrolysis

reaction in strong alkaline solution and therefore may not be suitable in polymer solutions that requires strong basic

medium to remain stable for spun dyeing. Moreover, the use of water-soluble dyestuffs in mass coloration of regenerated

cellulosics has been observed to result in poor wet fastness of the resultant fiber (Marcincin, 2002). Despites the perceived

challenges, a method which may be categorized as quasi-mass coloration has been proposed where naphthol dye grounders



are dissolved or mixed in alkaline spinning dope (Manian et al., 2007; Manian et al., 2008) after which the fibers are

treated with coupling components to develop the color. Colored fibers with good tensile strength were achieved using this

approach but color patches easily develop along the fiber strand which results in unleveled dyeing and poor light fastness.

Due to these limitations, the use of dissolved colorants in spun-dyeing is not very popular even though a significant success

have been achieved. Further research is also need in this area to take advantage of large number of dissolved colorants

available on the market.

Dispersed Colorants (Pigments)

The dispersion of superbly pulverized organic or inorganic pigments in spinning dopes has been intimated as a

possible route for mass coloration (Broda et al., 2007; Nypelo et al., 2012; Hao et al., 2012), with additives being

recommended in some cases to improve pigment dispersibility (Fu et al., 2011, Fu et al., 2013). The process of milling

pigments to obtain a suitable particle size is time intensive and accompanied by risks of recrystallization and/or

agglomeration (Fu et al., 2013). Several approaches for milling pigments have been developed lately. Milling pigments

with the aid of polymeric dispersants has been suggested to produce stable pigment dispersions, which builds voluminous

shells to intensify the charges on pigment surface, thus avoiding the flocculation and coagulation of pigment in aqueous

media (Novacel, 1953; Fu et al., 2011).

However, the possibility of poor pigment dispersion in spinning dope is almost a predictable risk with this

technique. This may lead to problems in the regeneration process and that could consequently result in non-uniformity in

color in the spinning dope due to flocculation or coagulation (Novacel, 1953; Marcincin, 2002; Hao et al., 2012). This can

greatly impair the quality of spun-dyed regenerated cellulose fibers substrates (Manufactures de produitschimiques du

Nord, 1956; Ciba Ltd, 1966; Fu et al., 2013). Apart from the problem of flocculation, foam forming in the spinning mass is

believed to be caused by dispersants used in the pigment formulation process (Riehen et al., 1971, Fu et al., 2013). The

colored substrates tend to be opaque (Wegmann et al., 1966), exhibit dull shades and dichroism ((Maloney, 1967: Ciba,

1965). This technique of mass coloration can also have adverse effect on substrate strength and its microstructure (Wang et

al., 2015).

Besides, the use of pigments has been reported in recent times to significantly affect the spinning process, the

microstructure, surface morphology, color performance and the mechanical properties of the regenerated cellulose fibers

due to the large particles sizes and uneven distribution in the spinning dope (Bale, 1941; Mamaza et al, 1996). However,

pigment presents a unique opportunity because it is easily adaptable to several fiber types and problems such as large

particle sizes and uneven distribution can be controlled by the use hyper branched and high molecular weight dispersants

(Fu et al, 2007).

Also, pigment encapsulation technology seem quite appropriate solution to the challenges associated with the

regular approach to pigment application in spun-dyeing of regenerated cellulose due to its perceived advantages as

compared with other methods (Tiarks et al., 2001; Steiert et al., 2007) Unfortunately, this has not been the case due to its

associated effect on tensile strength. Several techniques such as emulsion or miniemulsion polymerization (Lelu et al,

2003; Broda et al, 2007; Fu et al., 2011; Fu et al., 2013) microencapsulation (Schoenbach et al., 1967, Lelu, 2003; El-

Sayed et al, 2012), phase separation (Gomm et al, 1964; Dong et al., 2012) in situ polymerization (Liu, 2007; Roy et al.,

2012), layer-by-layer assembly (Yuan et al., 2008), sol–gel Gomm et al., 1964; Li et al., 2008), and free-radical

precipitation polymerization (Fu et al., 2010) has been proposed.



Out of the several approaches researched above, miniemulsion polymerization has been suggested to be the most

efficient technique due to its attractive advantages (Schoenbach et al., 1967; Fu et al., 2013).

The problem of producing stable pigment/latex still resurfaced because of defect with the emulsifier used during

the process of miniemulsion polymerization (Yuan 2008, Fu et al., 2013). The emulsifier is desorbed from the latex,

especially in highly alkaline solutions at high temperatures thus making it quite unstable for spun-dyeing of regenerated

cellulose fibers (Tiarks et al., 2001, Fu et al., 2013). To this end, the use of polymerizable dispersant as an emulsifier in

miniemulsion polymerization has been suggested (Tiarks et al., 2001, El –Sayed et al., 2012)

This polymerizable dispersant serve as monomer in copolymerization by forming covalent bond on the surface of

the formed latex, thus overcoming the downsides of the common emulsifier (Steiert, 2007; Taniguchi et al., 2008; Fu et al.,

2013-69).

In a recent study conducted by Wang and coworkers, a polymerizable dispersant was used as an emulsifier in miniemulsion

polymerization for encapsulation of carbon black (CB) with latex. The CB/latex composite dispersion showed excellent

stability with superior color yield when used for spun-dyeing of regenerated cellulose fibers. The spun-dyed regenerated

cellulose fiber by CB/latex composite dispersion had enhanced tensile properties with excellent color strength and fastness

(Wang et al., 2013).

The Use of Sulphur dyes

Spun-dyeing of regenerated cellulose fibers using Sulphur dyes have been proposed as an alternative to pigment

dyes but this has not received much research attention since its postulation in 1938 by Whitehead and others. The use of

this approach involved the suspension of Sulphur dyes intermediates in the spinning dopes (Whithead, 1938; Cassella,

1961; Ino et al., 1979) before the addition of dye itself after which the spinning is carried out. Another approach suggested

was to simply mix waste Sulphur dyed cotton textiles with fresh cellulose biopolymer where the mixture is subjected to the

popular xanthation process and spinning to obtain the colored filaments (Hama et al., 1972; Von der Eltz, 1996). This

process however did not receive much attention due to the toxic nature of the xanthation process and the many color and

structural defects of colored fibers (Ino et al., 1979; Bechtold & Manian 2005). There is the need for further research into

the potential of using Sulphur dyes for spun-dyeing of regenerated cellulose.

Spun-dyeing of lyocell

The lyocell fiber has received much research attention in recent times due to its high strength, rigid crystalline

morphology. Lyocell fiber gives higher mechanical modulus which substantially makes it effective material for use in

different biometerials, paper industry, nonwoven fabric for packaging purposes (Kunal Singha, 2012). Lyocell is the

generic name for a biodegradable fabric that's made out of treated wood pulp and commonly sold under the brand name

Tencel, made by Lenzing AG. Lyocell is known for its versatility, durability, and strength when both wet and dry, this

material is used in everything from clothing to cars. Lyocell fibers compared with other regenerated cellulosics is relatively

new being that the first commercial samples appeared in the mid- 1980s with full-scale commercial production beginning

in the early 1990s (Bartsch et al., 1999; Ruef, 2001). Lyocell production is considered as being more environmentally

friendly because the amine oxide used for dissolving the pulp is normally recycled and re-used during the production

process making it a better alternative to viscose production (Bartsch et al., 1999; Bectold & Manian, 2005) as illustrated in

figure 3. Hence, there are only a few methods reported for the mass coloration of lyocell.



Figure 3

Bartsch et al. 1999, suggested that selected inorganic pigments, which contain small amounts of heavy metals that

does not significantly lead to a severe decomposition in temperature of the spinning mass be mixed with the cellulose

solution prior to spinning of lyocell fiber. In a similar work done by (Ruef, 2001), he proposed that colorants or colorant

precursors be mixed with the cellulose solution with the caution that the colorants remain insoluble or sparingly soluble in

amine oxide. The most recent method reported by (Bechtold & Manian 2005), suggested that the cellulose pulp be dyed

with a vat dye where the dyed pulp will be optionally mixed with undyed pulp that will eventually be used for spinning the

lyocell fibers. The disadvantage of this method is that, the fibers produced have lighter shades because the undyed pulp is

mixed with the dyed pulp as illustrated in figure 3.

Figure 3

In the case of spun-dyeing of lyocell using pigment colorants, research has shown that particle size and

distribution in dispersion can significantly impact the color attributes of the resultants fiber (Fu et al., 2010; Mohmmad et

al., 2011). It has been postulated that a small particle size and its even distribution in the polymer matrix results in bright

shade with high tensile strength (Fang et al., 2005 Alexandra & Bermel, 1999; Anton et al., 2004). This assertion has been

collaborated by (Taniguchi et al., 2008; Fu et al., 2010; Mohmmad et al., 2011; Jaturapiree et al., 2011; El-Sayed et al.,

2012) that carbon black dispersion with small particles in lyocell spinning solution minimizes the effect of irregularities in

microstructure, surface morphology and mechanical properties of loycell fibers and as such ensures a continuous spinning

process without problems.

In a study conducted by (Tiarks et al., 2001, Wang et al., 2013), nanoscale carbon black dispersion was prepared and used

to spun-dye lyocell. In their study, a polymerized dispersant was used as the emulsifier in the miniemulsion polymerization

process to enhance the compatibility of the carbon black/latex composite dispersion with the lyocell spinning solution.

Also, they observed that the stability of the color/polymer matrix to pH plays a very important role for successful spun

dyeing of lyocell fiber. They concluded that the stability of the CB/latex composite dispersion decreases slightly as pH

increases from 8 to 14 (Wang et al. 2013). It is worth noting that this phenomenon may not apply to every pigment during

the process of spun-dyeing of lyocell because different pigments behave differently under different processing conditions

before their eventual incorporation into polymer matrixes and therefore, the chemical properties of the specific pigment

ought to be carefully studied in order to successfully incorporate it into the specific polymer matrix.

Spun-dyeing of Alginate Fibers

Alginate fibers are derived from brown algae consisting of -(1-4)- linked-d-mannuronic acid (M) and -l-guluronic

acid (G) segments to form a macromolecule polymer. These fibers have inherently bioactive properties and are highly

biocompatible. Spun-dyeing of alginate fibers is very new because there is basically no literature on it until our research

team (Wang et al., 2015) investigated the compatibility of spun-dyed sodium alginate fiber using fluorescent pigment

dispersion. Below are excerpts of the results; fluorescent pigment dispersion was prepared with styrene maleic anhydride

(SMA) and was then introduced into the sodium alginate fiber spinning solution as shown in the figure 4. (Full manuscript

can be downloaded from dyes and pigment journal)

Figure 4

The fluorescent pigment dispersions was highly compactible with alginate spinning dope with the resultant fiber



having excellent rubbing and light fastness with interestingly high fluorescence intensity (Wang et al., 2015) but

unfortunately, its bioactive properties were not investigated. This sets the pace for further research into the bioactive

properties of spun-dyed alginate fibers and the possibility of using other colorants besides fluorescent pigments.

Future prospects

With increasing oil and cotton prices coupled with the growing preference for bio-based products, especially those

derived from non-food materials, markets for dissolving pulp are well placed to grow in the mere future. The growth in

bio-based products will drive newer technologies and coloration chemistries for these fibers. And with the unparalleled

advantages of spun-dyeing combined with the advancement in color chemistry in recent years; it is certain that spun-dyeing

is the future of the regenerated textile materials. The buoyant environmental prospects of this coloration technique

compared to the traditional method of fiber coloration will create an avenue for achieving fibers with special properties.

The incorporation of such functional elements such as flame retardant finish, antimicrobial properties, antistatic

finishing, and deodorant into structure of the regenerated cellulose spinning dope besides the coloring finishes will even

make it more attractive than ever. With these precursors, it is expected that fibers with specific functions will be produced

through spun-dyeing. The market for spun- dyed regenerated cellulose will expand greatly because spun-dyed fabrics have

superb color quality. The technology for spun-dyeing will in the near future reduce waste generated by 97% compared with

other coloring techniques because “green” approaches for dissolution of cellulosics are being proposed as real alternatives

to the viscose process (Grinshpan et al., 2013).

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Table Legend

Table 1: Process Savings from Using Spun Shades Viscose [The Rupp Report]

Parameters Piece -dyed Spun-dyed Savings (%)

Chemical costs [US$/KG] 0.91 0.24 74 Power costs [US$/KG] 0.04 0.02 50 Water costs [US$/KG] 0.02 0.01 50 ETP Costs [US$/KG]* 0.03 0.01 66 Coal and furnace oil costs [US$/KG] 014 0.08 39 Total costs [US$/KG] 1.13 0.36 68 Total water used (liters/100kg) 9,100 3,100 66

Total Time [min] 575 190 67%



Figure Legend

Figures

Figure 1: Thermal Gravimetric Analysis Curve of Spun-Dyed Alginate Fiber. (Wang et al. 2015)

Figure 2: Lyocell Production Process (Bartsch & Ruef, 1999)



Figure 3: Flow Diagram of Lyocell Coloration Process (Bechtold & Manian, 2005)

Figure 4: Spun-Dyeing Process for Sodium Alginate Fiber. (Wang et al, 2015)

Documents

ADVANCES IN SPUN-DYEING OF REGENERATED CELLULOSE FIBERS