Colorimetric Analysis to Study the Dyeing Behaviour of Jute Textiles Using Selective Synthetic and Natural Dyes

Abstract

Jute, being a lignocellulosic bast fibre, is dyed with different classes of dyes such as direct, reactive, vat and sulphur which are also used to dye other cellulosic materials such as cotton and viscose. In addition to these, it is possible to dye jute with acid, basic and pre-metallized dyes due to the presence of lignin and gluconoric groups of hemicellulose. Here, a review of the dyeing of jute is done to analyse the dyeing properties of jute fabrics dyed with three classes of synthetic dyes – direct, reactive and acid dyes along with some selected anionic natural dyes. The dyeing process variables, colour strength values and colour fastness properties were analysed and elaborated. The studies have focused on some comparative assessment of the dyeing properties using different synthetic dyes and natural dyes too. The dyeing properties and colour fastness properties of synthetic-dyed and natural-dyed jute materials are also discussed and analysed in detail showing colourimetric analysis and their results.

1. Introduction

The global consciousness for sustainable ecology has gained serious momentum. Consumers want to use greener, ecologically safe products. The textile products made of natural fibres are more eco-friendly than the ones made of synthetic fibres. So, the natural fibre-based textile materials need to be produced more; similarly, they need to be discussed more. Jute among the natural fibres is different in properties and area of application. It is mostly used in packaging. No other natural fibre has more usage in packaging than jute. But, nowadays, the product range of jute is being diversified in home furnishing textiles, upholstery, automotive textiles, carpet, shopping bags, etc. These diversified products need colouration for value addition.

Jute is an important natural fibre grown in South Asia (mainly in the eastern part of India and Bangladesh) for numerous industrial applications [1]. It is the second highest plant-based fibre next to cotton grown in the world. Jute is a multicellular natural fibre, chemically lignocellulosic in nature, having about 60–64% cellulose, 20–24% hemicellulose and 12–14% lignin [2]. Numerous numbers of hydroxyl groups of cellulose and hemicelluloses, besides the glucoronic acid group of hemicelluloses having both –COOH and –CHO groups in it and several phenolic hydroxyl groups and –C=C unsaturation present in lignin, have made jute fibre highly absorptive for different classes of dyes including natural dyes with or without suitable mordants. Direct, reactive, basic and natural dyes are applied on jute. Here, the dyeing properties of various classes of synthetic and natural dyes applied on jute are discussed.

2. Dyeing of jute with direct dyes

Jute fibre, having cellulose and hemicellulose as major constituents, contains an ample amount of hydroxyl and carboxyl groups, thus making the fibre anionic while immersed in water. The anionic nature of the immersed jute fibres can be neutralised by the application of electrolyte, thus rendering the fibres conducive for dyeing with anionic direct dyes.

A few discreet studies are reported on the dyeing of jute with direct dyes [3, 4, 5, 6, 7, 8, 9, 10, 11]. Direct dyes are cheap but do not produce fast colour on jute fibres. Jute fibre having a negative charge in water can be dyed with direct dyes in the presence of an electrolyte which neutralises or reduces the negative potential of jute so that anionic dye molecules are absorbed on the fibre surface. So, application of an electrolyte and pH of the dyebath plays crucial roles in dye uptake of direct dyes by jute fibres. Mondal et al. studied the phenomenon and found that pH 8 is the best condition for direct dyeing of jute [4]. Table 1 shows their results indicating the increase of dye uptake with an increase of pH till pH 8. Also, bleached jute fibres absorb more dye than raw fibres because of the presence of more free carboxyl content in bleached jute fibres.

pH of dyebath →	Dye uptake (%)
	Bleached jute fibre				Raw jute fibre
	4	7	8	10	4	7	8	10
Direct yellow 29	40.5	65.0	78.4	71.5	36.9	61.0	72.4	69.7
Direct orange 31	45.0	70.2	80.5	76.1	40.2	67.8	78.5	75.2
Titan yellow 20	20.5	32.1	46.0	37.5	17.7	28.6	37.8	35.0

Table 1.

Dye uptake of jute fibre dyed with direct dyes under different pH of dye baths.

Jute being a complex heterogeneous structure comprising hemicellulose and lignin intertwined with cellulose matrix shows its multifaceted dyeing characteristics. Ganguly et al., in an interesting study, showed the dyeing behaviour of jute with direct dyes while gradually removing hemicellulose and lignin from it [6]. The equilibrium exhaustion of direct dye and rate of exhaustion of direct dye into jute fibres rise with the gradual reduction of hemicellulose content. The authors derived three reasons for this phenomenon – (a) increase of α-cellulose concentration and primary -OH groups which are responsible for the attachment of direct dye molecules; (b) lowering of copper number, i.e., aldehyde functionality and (c) increase of fibre fineness. However, the study found out that the removal of lignin would bring about the opposite effect of direct dyeing. Dye exhaustion reduces with the reduced concentration of lignin in jute fibres because of an increase in the copper number and carboxyl content in jute fibres.

The curing of dyed textile materials after dyeing has an impact of fixation of dyes into fibres. It was found that curing at 150°C gives the optimum fixation (88%) of direct dyes applied on jute-cotton union fabrics [7]. Panday et al. established a combined method of bleaching and direct dyeing of jute, thus reducing the cost and time of processing [8].

Though there are a few studies on the dyeing behaviour of direct dyes on jute, these studies were all focused on dyeing by a single dye. The behaviour of dyeing done by a mixture of direct dyes on jute was not discussed in those studies. But that is a practical aspect as industrial dyeing is generally mixing two or more dyes altogether. Such a study on dyeing of jute by direct dyes was done by Samanta et al., where six binary mixtures of six direct dyes were applied on jute and their dyeing behaviour and compatibility were studied [9]. The compatibility of dyes was analysed in the conventional method and a new method based on the colour difference index (CDI). It was found that the binary mixture of Direct Green YG (CI Direct Green 513) and Direct Turquoise Blue 2R (CI Direct Blue 199) has the highest compatibility among the pairs for dyeing of jute.

3. Dyeing of jute with acid dyes

Acid dyes generally possess sulphonic acid groups and become negative in water. This dye has relatively low molecular mass. This dye has some structural similarities with direct dye as being DSO₃Na where anionic DSO₃^- generates the colour. However, they have dissimilarities – acid dyeing being nonplanar and smaller in molecular size, while direct dyes being planar and large in molecular size. This dye has been classified into three groups based on the application process:

1. Levelling acid dyes or equalising acid (low molecular weight and strongly acidic)

2. Milling acid dyes (weakly acidic and higher molecular weight than levelling acid dyes).

3. Super milling acid dyes (comparatively high molecular weight and neutral acid dyes).

This dye is substantive to silk, wool, and polyamide and has no substantivity to cellulose. But acid dyes have moderate to good substantivity to jute. This substantivity is attributed to the presence of nonplanar and amorphous lignin structure. However, as reported above, the study by Ganguly et al. found that the gradual removal of lignin affects the acid dye uptake adversely [6]. This is due to the increase of carboxyl content which affects the absorption of acid dyes on jute. But for hemicellulose, it is not so simple. The exhaustion of acid dye is lower than that of dewaxed jute fibre at low doses of removal of hemicelluloses, but it increases at higher removal of hemicellulose. It may be attributed to the high carboxyl content upon low removal of hemicellulose.

Though many studies on acid dyeing of jute are not available, an important study by Bhaumik et al. discussed the role of cationization of jute by the application of soya seed extract on the dyeing of acid, direct and reactive dyes [12]. As these are anionic, the dyebath needs to have an electrolyte to neutralise the negative charge generated on the jute fibre immersed in water. Cationization fulfilled the purposes and neutralised the negative charge, thus enabling salt-free dyeing of jute by anionic dyes.

Most of the acid dyes show poor wash fastness on jute, even by mild rinsing in cold water, though some acid dyes are moderately fast. But metal complex dyes have excellent wash and light fastness and therefore are most suitable for jute. Some metal complex dyes retard photofading of jute under sunlight, by UV quenching action.

4. Dyeing of jute with basic dyes

Basic dyes are cationic in nature. This class of dye is of low cost and provides brilliant shades, but it has poor to medium colour fastness to light. Many basic dyes are destroyed by chlorine, so chlorine-free water must be used in dyeing with basic dyes. This dye needs a suitable retarder for uniform dyeing for having high substantivity to acrylic or wool fibres. The retarder is not essential but is optional for dyeing jute with basic dyes. However, the metal ions present in jute fibres might change the shade of jute material dyed basic dyes, so a chelating agent like EDTA can be used to remove the metal ions present in water or in the jute itself.

A study on the optimum dyeing conditions for dyeing jute with basic dyes has been reported in the literature by Farouqui and Hossain [13].

5. Dyeing of jute with reactive dyes

Reactive dyes though being anionic in nature dye textile fibres in a way different than direct dyes. Reactive dyes react with fibres by forming covalent bonds, thus making the bond strength between the fibre and the dye stronger than the one formed in the dyeing of jute with direct dyes. So, the colour strength and colour fastness properties of the reactive-dyed jute textiles are better than jute textiles dyed with direct, acid and basic dyes.

Several studies have been conducted on reactive dyeing of jute fibres [14, 15, 16, 17, 18, 19, 20]. The effects of electrolytes on the dyeing behaviour have been examined [21]. Aluminium sulphate, alum, sodium sulphate, sodium chloride, etc. have been used for reactive dyeing of jute. Among them, aluminium sulphate is found to have yielded the highest absorption of reactive dyes by jute fibres. Alum, sodium sulphate and sodium chloride followed in succession. Similarly, aluminium sulphate achieves the highest colour fastness to light and wash for the jute material dyed by reactive dyes.

Jute can be dyed with all types of reactive dyes such as hot brand, cold brand, vinyl sulphone and high exhaustion reactive dyes. The choice of type of reactive dye depends on the shade and colour fastness needed. A study by Chattopadhyay et al. analysed the reusability of reactive dyes on jute. It was found that jute fabric can be dyed with good exhaustion if it is dyed in a separate original bath [22]. The exhaustion of dyes at the reused bath is very low for hot brand and high exhaustion reactive dyes.

When the effect of concentration of an electrolyte on the properties of the dyed jute was studied, it was found that Glauber’s salt (hydrated sodium sulphate) at 25 g/L concentration achieved the best dyeing results [23].

The comparative performance of the dyeing behaviour of jute with basic dyes and reactive dyes was studied. It was found that the colour strength of the dyed jute dyed with basic dyes was higher than the one dyed with reactive dyes with the same concentrations of dyes. The reasons for this may be attributed to the higher exhaustion of basic dyes than reactive dyes. However, the colour fastness of jute dyed with basic dyes is lower than the fastness of reactive-dyed jute due to the higher bond strength of fibres and dye.

Several studies have focused on the improvement of dyeability of reactive dyeing of jute [15, 16, 17, 18]. The application of some specific chemicals on jute before reactive dyeing has been found to be productive, enabling the fibres absorb more amount of dyes and achieve higher exhaustion with higher colour strength supported by colourimetric analysis of K/S values and ΔE values. The effect of pretreatment of reactive dyeing of jute was studied by Chattopadyay et al. [19], while the comparative assessment of different reactive dyes on jute and cotton was studied by Sinha and Roy Maulik [20].

Compatibility of soya-based natural aminio acid-modified cationic jute in between a pair of a binary mixture of reactive dyes is also reported in the literature for improving reactive dye exhaustion without salt and colour fastness to washing by Samanta et al. [16].

6. Dyeing of jute with natural dyes

Dyeing of textiles with natural dyes can be carried out in an alkaline bath, acidic bath or neutral bath. There are various reports available on different methods of mordanting and dyeing for the application of natural dyes on different fibres such as cellulosic, protein and synthetic fibres. These studies have been widely available and studied as presented in different literature. Jute is a ligno-cellulosic fibre having different functionalities, but with a high degree of crystallinity and high degree of orientation. These multiple functionalities make jute to be somewhat susceptible to dyeing with natural dyes. Still, application of mordants and modification of jute fibres are essential for better dyeing of jute fibres with most of the anionic natural dyes.

Few reports are available on chemical modifications of cotton textiles for improvement of its dyeability using synthetic and natural dyes [24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38]. However, such studies, particularly for the application of natural dyes on jute or chemically modified jute, are rare and sporadic.

There is a study [25] describing the chemical modification of the jute substrate with acrylamide monomer and post-dyeing treatment with cetyl trimethyl ammonium bromide (CTAB) for investigating their effects on dyeing properties with natural dyes such as turmeric (haldi) and madder (manjistha) substantiated with appropriate colourimetric analysis. A few studies were conducted to analyse the compatibility of dyeing of jute with various natural dyes in binary mixtures. It was found that the decreasing order of the change in chroma values of the pairs is (annatto + pomegranate) > (annatto + marigold) > (annatto + onion) and the decreasing order of the change in hue values of the pairs is (A + O) > (A + M) > (A + P). The wash fastness values for the (A + P) pair for 50:50 and 75:25 proportions are the best results [29]. The after-treatment with chitosan and CTAB improved the wash fastness by 1 grade. The application of 1% benzotriazole improved the light fastness by 1 grade for all three binary pairs. The results of the nonconventional compatibility tests were in good agreement with the results of the conventional method of plot comparisons. As per the RCR system, the compatibility grades of (A + O), (A + P) and (A + M) pairs are poor, fair and fair, respectively.

Another study [33] found that 10% harda (myrobolan) + 10% potash alum dual pre-mordanting of bleached jute fabric has the best results for colour yield (K/S values), dye uniformity (CV% of K/S values) and lower CDI (less variation or minimum dispersion of surface colour values) than that obtained by all other mordant combinations used in this study. After treatments with selective eco-safe chemical cationic dye fixing agents such as CTAB, cetrimide and also Sandofix-HCF (commercially available cationic dye fixer for comparison), it renders ½ to 1 degree of wash fastness rating due to forming salt linkages between natural dye anion in alkaline medium and cationic dye fixing agents, where CTAB is a quaternary ammonium type cation compound, while cetrimide is an amide as a potential cationiser, both of them perform equally good in improving wash fastness for all types of natural dyes applied on dual pre-mordanted jute. However, in some cases, the performance of CTAB is better than CTAB, due to differences in Pka values and cationization potential; both criteria are higher for CTAB than cetrimide. Treatment with 1% benzotriazole as an UV-absorber was reported earlier for both bleached and dyed jute cloth dyed with synthetic dyes (direct and reactive dyes) and is known to improve the light fastness by nearly one unit.

A very recent study on the statistical optimization of dyeing jute fabric with marigold petals has been reported by Chakraborty et al. [2], for obtaining more uniform dyeing on jute using alum and also by suitable double pre-mordanting system, suggesting the reaction mechanism too.

7. Improvement of colour fastness to wash and light by the application of cationic dye-fixing agents and UV-absorbers

Jute materials dyed with natural dyes tend to show poor to moderate colour fastness to wash and light, and this drawback can be corrected to some extent. Materials can be treated with several chemical auxiliaries to obtain high colour fastness to wash and light after dyeing with natural dyes. Several researchers have carried out important studies in this field.

Jute is generally treated with cetrimide, CTAB (cetyl-trimethyl ammonium bromide), for achieving increased colour fastness to wash. These chemicals make a bridge between dye molecules, thus rendering them difficult to leach out during washing. A new study showed the effect of CTAB and chitosan on jute fabrics dyed with annatto seeds. The application of 1% (owf) chitosan improved the colour fastness to washing by ½ grade and 2% CTAB improved the fastness by 1 grade. The application of 1% (owf) benzotriazole (a UV-absorber) improves the colour fastness to light of jute-dyed fabric dyed with different natural dyes by 1 grade [38].

Some chemical treatments before and after dyeing of jute with direct, acid, basic and reactive dyes are reported. Improvement of colour fastness to light of jute fabric dyed with direct dyes through after-treatment with copper sulfate and potassium dichromate is reported by Panday et al. [9], while Sarwaz et al. [11] reported the improvement in colour fastness to washing jute fabric dyed with direct dyes by treating them with various cationic dye-fixing agents. It shows that application of cationic agents after dyeing produces better fastness than the application done before dyeing.

8. Conclusions

Jute as an agro-renewable hard fibre has multiple application areas in technical textiles. Though it is still used mainly in packaging, its properties need to be studied more to bring about more diversified usages of this fibre with the help of proper scientific intervention to produce new products of woven, nonwoven, composites of jute. The fibre is abundantly cultivated in India, Bangladesh, and other South Asian countries.

The present article has shed significant light on the dyeing behaviour of jute and its bottlenecks. Colouration of jute textiles is an important area of research and development for the manufacture of potential end-products in global markets. Dyeing of jute with direct dyes and basic dyes is economic and possesses a wide range of shades, but this suffers from having low colour fastness to wash and light. Some works have been narrated here to overcome the obstacles of these dyes. Reactive dyes being colour-fast and possessing good shades are costlier than direct, acid and basic dyes.

As jute is an eco-friendly fibre, this special aspect of the fibre can only be enhanced if it is dyed with eco-friendly natural dyes. Here, dyeing of jute with natural dyes has been discussed, and suitable after-treatment processes to overcome the low colour fastness associated with natural dyeing have been mentioned.