Disperse dyeing of wool/polyester blend fabric

Disperse dyeing of wool/polyester blend fabric

Smita Honade, Jayant Udakhe, Neeraj Shrivastava and Dr R V Adivarekar

Abstract

Blends of wool with polyester represent an attempt to achieve a combination of desirable features of both fibres, allowing the production of fabrics with good wear properties and dimensional stability, yet which retain an attractive handle and drape reminiscent of pure wool. Wool/polyester blended fabrics are usually dyed with dyestuff mixtures having acid or metal complex dyes for wool and disperse dyes for the polyester component.

These two classes of dyes can be applied onto wool polyester blend separately in two bath process or together in a single bath process with addition of wool protective agents. Time and cost saving is the main advantage of the single bath process for dyeing wool polyester blends. The present research is attempted towards developing a single bath dyeing system for wool/polyester blend by surface modification of fibre using plasma technology followed by disperse dyeing of both polyester and wool components simultaneously without adversely affecting the fastness properties and strength of the fabric.

  1. Introduction

Wool/polyester blend fabric represents an attempt to achieve a combination of desirable features of both fibres, allowing the production of fabrics with good wear properties and dimensional stability, yet which retain an attractive handle and drape reminiscent of pure wool. The most important end uses for wool/polyester blends are outerwear especially men’s suiting, as well as women’s suiting, dresses and skirts. Wool/polyester blend dyeing is always directed towards solidity rather than differential effects and these blended fabrics are usually dyed with dyestuff mixtures having acid or metal complex dyes for wool and disperse dyes for the polyester component.

These two classes of dyes are applied onto wool polyester blend separately in two bath process or together in a single bath process with addition of wool protective agents. Other method ie one-bath dyeing method has established itself in practice because it saves time, money and energy and also ensures minimum tendering of the wool fibre but in this process, most of the disperse dyes causes staining of wool at boil. High temperature dyeing methods which are normally used for polyester dyeing cannot be used for blend dyeing because of the susceptibility of the wool fibre to damage. To overcome the above difficulties, present research work was attempted towards developing a single bath dyeing system which use only disperse dye for dyeing both polyester and wool components simultaneously without adversely affecting the fastness properties and strength of the fabric. For this study we have selected few disperse dyes which shows high staining on wool component at low dyeing temperature.

Plasma technique is used widely to modify textile materials as it is a dry process and involves no chemicals or water8)9). Plasma technology is well known for imparting functional finishes to textile materials which could be achieved by altering process parameters such as supply frequency, discharge power, treatment time, type and pressure of gas. Several surface phenomena such as absorption, desorption, etching, cleaning, surface activation and cross-linking occur singly or in combination on exposure to plasma. In wool application, plasma treatment has been found to affect the lipid layer and surface cuticle of wool without affecting its bulk properties, thus it could help to improve the shrink proofing properties and enhance the dyeability. Today, the low temperature plasma (LTP) treatment is one of the most commonly used physical methods to replace chemicals for treating wool fibres. The treatment improves wettability and also increases dye uptake, leading to an enhancement in the depth of shade and evenness.
Current research work aims at developing a single bath dyeing system using disperse dyes for plasma treated wool/polyester blend fabric without adversely affecting the fastness properties and strength of the fabric. In the present work polyester rich wool/polyester blend fabrics were treated on both sides with DBD plasma at different electrode spacing and plasma exposure time. After plasma treatments, blend fabrics were dyed using selected disperse dyes – which shows high staining on wool in single bath and colour strength and fastness properties of dyed fabrics were assessed. Tensile strength, relaxation and felting shrinkage and morphology of the modified treated fabrics were also analysed.

2.Material & Methods

2.1 Materials

35/65 and 45/55 wool/polyester blend fabrics (22.5 micron wool and 2.5 denier and 1.5 denier polyester fibre respectively) were obtained from Raymond, Vapi. Disperse Yellow 64, Disperse Red 92, Disperse Blue 73 were procured from Dystar India Pvt Ltd. Other chemicals such as nonionic surfactant (Imerol PC liq, Clariant), dispersing agent (Lyocol RDN, Clariant), levelling agent (Eganal PS liq, Clariant), acidic buffer (Opticid PBI, Clariant) were procured from Clariant India Ltd.

2.2 Methods

2.2.1 Plasma treatment

Plasma treatment of 35/65 wool/polyester blend fabric was done on a dielectric barrier discharge (DBD) plasma reactor. It was carried out at atmospheric pressure using 2-5 mm electrode spacing, 5 KV voltages and 0.8 A current across the electrodes. Air was used as the non-polymerizing gas for plasma treatment. Different parameters used for plasma treatments are given in (Tables 1 and 2).

disperse-TABEL1

disperse-TABEL2

 

Dyeing of plasma treated P/W blend fabrics

Plasma treated 35/65 wool/polyester blend fabrics (fabric treated at various plasma treatment time and various electrode spacing) were dyed with three disperse dyes (Disperse Yellow 64, Disperse Red 92, Disperse Blue 73) with 1% shade in Infracolor laboratory dyeing machine (from R. B. Electronics & Electrical Pvt. Ltd.). Dyeing was carried out in a liquor ratio of 20:1 at 110˚C (2˚C/min rate of rise) for 60 min in presence of dispersing agent, levelling agent at 4.5-5.0 pH (pH was adjusted with acetic acid and acidic buffer). After dyeing all samples were soaped at 80˚C for 20 min in 1 gpl nonionic surfactant solution followed by two rinsing and drying. Fastness properties of dyed fabrics were evaluated. Plasma treatment parameters of plasma treated and dyed fabric samples were optimized based on the K/S values measured at wavelength of maximum absorbance. Further 35/65 and 45/55 Wool/Polyester blend fabrics were given plasma treatment at optimized parameters and then dyed with three disperse dyes (Disperse Yellow 64, Disperse Red 92, Disperse Blue 73) in three shades i.e. 0.2%, 1%, 4%.

2.3 Measurement and analysis

Colour strength

The colour strength of the dyed specimen, expressed as K/S, was measured at wavelength of maximum absorbance using reflectance spectrophotometer (Colour i7 from X- rite)

Fastness properties

Washing, light and sublimation fastness properties of wool/polyester dyed fabric were evaluated by standard test method such as ISO 105-C10, ISO 105- BO2, ISO P01 respectively.

Alkali solubility

Alkali solubility of wool/polyester blend is an indication of the extent of damage to the epicuticle layer. The epicuticle layer is major hindrance to penetration of chemical species and thus protects native wool fibre from damage. To quantify the damage to the epicuticle, alkali solubility of untreated and plasma treated fabrics was studied using IWTO TM-4-00 standard test method. The values were calculated as a percentage of the original mass.

Wetting time

The wetting time for untreated and plasma treated wool/polyester blend fabric was tested using standard test method AATCC 79-2010. Since the fabrics are plasma treated, the surface characteristics of the fabrics tend to change. The smaller the average wetting time, the more absorbent is the textile. Five seconds or less is generally considered to represent adequate absorbency. If the average time is more than five seconds, the textile is considered to have poor absorbency.

Whiteness index

Whiteness and yellowness index of untreated and plasma treated wool/polyester blend fabric was measured by ASTM and CIE method using Colour i7 Spectrophotometer (from X- rite).

Morphological study

The surface morphology of the untreated and plasma-treated samples was investigated by scanning electron microscope (SEM). Wool/polyester blend fibre samples were coated with gold using JEOL JEC-550 twin coater before scanning electron microscopy. JEOL JSM-5400 scanning electron microscope was used for studying the surface morphology of untreated and plasma treated fabric samples.

Tensile strength

Tensile strength of untreated and plasma treated fabric samples was studied using ASTM D5035-95 (2003) (2R-E) method using Shimadzu tensile strength tester.

Relaxation and felting shrinkage (TM 31)

Relaxation and felting shrinkage of wool/polyester blend fabrics were tested using Electrolux Wascator (Model FOM 71 CLS) laboratory washing machine. Testing was performed using TM 31 standard test method. Relaxation shrinkage was tested using 7A washing programme and felting shrinkage was tested using 5A washing programme.

3.Result & discussion

3.1 Effect of plasma treatment time on K/S values

The K/S values of disperse dye dyed P/W blend fabrics are found to increase significantly after the DBD plasma treatment as seen in Figure 1 where 5 min plasma exposure time is sufficient to obtain significant increase in K/S values. Therefore, DBD plasma treatment on P/W blend fabric can be considered as an effective method to promote it’s disperse dye dyeability.

Figure1

3.2 Effect of plasma reactor electrode spacing on K/S values

The K/S values of disperse dye dyed 35/65 P/W blend fabric (Figure 2) are found to be decreasing significantly with increase in electrode spacing of plasma reactor and maximum colour yield is obtained at 2 mm electrode spacing. Based on the results obtained, it can be concluded that efficiency of plasma treatment is inversely proportional to the electrode spacing and that clearly reflects in colour yield of dyed fabric; provided that all other parameters like voltage and current remains same.

Figure2

3.3 Study of disperse dyeing of various wool/polyester blend fabric at optimized plasma treatment parameters

Results obtained under section 3.1 and 3.2 clearly demonstrates that the disperse dyeability of wool/polyester fabric after plasma treatment is enhanced as plasma treated wool/polyester blend fabric shows higher colour yield compared to untreated fabric after dyeing with disperse dye. The best results in terms of increased K/S values are obtained at 5 min plasma treatment time and 2 mm electrode spacing. Therefore, for further study of effect of plasma treatment on disperse dyeability of 35/65 and 45/55 wool/polyester blend fabric, the optimized plasma treatment conditions i.e. 5 min plasma treatment time & 2mm electrode spacing are maintained. After plasma treatment, untreated and plasma treated fabrics are dyed with three disperse dyes used in previous study at 3 different shades i.e. 0.2%, 1.0% and 4.0%.

TABEL3

K/S values and increase in K/S (%) values are mentioned in Table 3. From the K/S values obtained, it is observed that Disperse Red 92 shows higher difference in K/S values of untreated and plasma treated dyed samples compared to other two dyes. On 35/65 wool polyester blend, red dye shows 27.47% and 22.38% increase in K/S values for 0.2% & 1.0% shade respectively but for 4.0% shade magnitude of increase in K/S is less. For all three dyes % increase in K/S values of plasma treated samples decreases with increase in shade. So it can be concluded that effect of plasma treatment on colour yield of disperse dyed wool/polyester blend is significant for light and medium shade. Similar results are obtained for 45/55 wool polyester blend fabric. Increase in % of K/S values of untreated and plasma treated blend fabric for 35/65 wool/polyester blend fabric are higher than 45/55 wool polyester blend.

3.4 Fastness properties of untreated and plasma treated dyed wool/polyester blend fabrics

Washing, light and sublimation fastness of plasma treated blend fabric has not shown any significant enhancement when compared to untreated fabric

3.5 Alkali solubility and wetting time

The alkali solubility of the plasma treated blend fabric was tested and compared with the untreated sample. For undamaged wool fibres reported alkali solubility values are between 9 and 15% [Atav R, Yurdakul A, 2011, (Standard test method for alkali solubility of wool, ASTM D 1283, 1985)]. In current study the alkali solubility of untreated wool fabric is found to be 9.46% and for 35/65 wool/polyester blend fabric it is 4.10%. For 5 min plasma treated wool sample alkali solubility is 12.29% whereas for wool/polyester it is 5.39%. The increase in alkali solubility of the plasma treated wool and wool/polyester fabric is due to removal of 18-MEA from the epicuticle and generation of more hydrophilic sites on the fibre surface.

From SEM images (given further) it is observed that, plasma treatment creates pores on the fibre surface, creating a pathway for the penetration of caustic species into the fibre during the alkali solubility test. Untreated and plasma treated polyester fibre shows negligible change in alkali solubility values. Therefore, it can be concluded that increase in alkali solubility of wool/polyester blend is mainly because of wool component of blend. The increased hydrophilicity of plasma treated fabric is shown in terms of decreased wetting time of treated sample compared to the untreated fabric. Water absorbency time decreases from non-wettable for untreated fabric to 0.45 sec after 1 min plasma treatment. This sharp decrease in water absorbency time after plasma treatment can be explained by an increase in surface hydrophilicity due to formation of micro cracks and damage of scales on wool fibre surface. This plays an important role in increasing the moisture adsorption.

3.6 Whiteness index

Changes in whiteness or yellowness of wool/polyester blend fabric after plasma treatment is also studied. From W.I. and Y.I. values studied it is observed that whiteness of plasma treated sample increases up to 10 min plasma treatment after that W.I. decrease for 15 and 20 min plasma treatment time. During plasma treatment various active species are bombarded onto wool fibre surface causing surface etching. Etching may cause removal of surface impurities resulting in increased whiteness.  It is also observed that with increase in electrode spacing W.I. value decreases gradually as intensity of plasma reduced with increasing electrode spacing.

3.7 Surface morphology

The SEM images of plasma treated wool/polyester blend fabrics (with special emphasis on wool fibre surface modification) are shown in Figure 3.

Figure3

Figure4

Surface morphology of undyed and plasma treated dyed wool/polyester blend fabrics is also studied using Scanning Electron Microscope and the SEM images obtained are shown in Figure 4. It can be seen in Figure 4 a & b that the surface of some fibres is completely smooth. These smooth fibres are polyester and the other fibres with scales are wool. After plasma treatment wool fibre shows significantly reduced scale sharpness whereas polyester fibre surface doesn’t show any noticeable changes.

3.8 Tensile strength

Tensile strength of the plasma treated fabric is found to be higher than untreated fabrics. In the tensile strength test, a load is applied to cause the fabric breakage. In general, the fabric breakage depends not only on the nature of the fibre but also on the fabric construction. When considering the fabric construction, the inter-yarn and inter-fibre friction plays an important role in the tensile strength properties of the fabric. With the use of plasma treatment, it is believed that such techniques do increase the inter-yarn and inter-fibre friction as confirmed by the roughening effect generated on the textile surface. Hence more forces must be required to overcome the inter-yarn and inter-fibre friction before the occurrence of fabric breakage resulting in higher breaking load.

3.9 Relaxation and felting shrinkage

The area relaxation and felting shrinkage (%) of untreated and plasma treated wool/polyester blend fabric is mentioned under Table 4. Felting shrinkage of the fabric is measured up to three 5A washing cycle. From the results obtained it is observed that, plasma treatment reduces relaxation as well as felting shrinkage of fabric. Plasma treatment reduces sharpness of wool fibre scale (Can be observed in above mentioned SEM images) which could result into less fibre entanglement with each other during washing. Therefore, plasma treated wool/polyester blended fabric shows reduced felting tendency during washing.

TABEL4

The results indicate that the disperse dyeability of wool/polyester blend fabric is enhanced after plasma treatment as plasma treated wool/polyester blend fabric had shown higher colour yield (K/S values). Plasma treatments of wool/polyester blend fabric also results in improvement in fabric wettability, tensile strength and reduction in felting tendency.

  1. Conclusion

In recent years, considerable R&D efforts have been devoted to develop ecofriendly cost effective single stage blend dyeing techniques. With selective disperse dyes and optimum dyeing parameters, single-stage disperse dyeing of wool/polyester blend can be established in practice as it saves time, money and energy and also ensures minimum tendering of the wool fibre. In this respect plasma surface treatments show distinct advantages because they are able to modify the surface properties of textiles without any chemical or water consumption. In current study, the disperse dyeability of wool/polyester fabric after plasma treatment is enhanced. The result obtained indicates that plasma treated wool/polyester blend fabric shows higher colour yield (K/S values) and best results are obtained at 5 min plasma treatment time & 2 mm electrode spacing. Washing, Light and sublimation fastness of plasma treated blend fabric doesn’t show any significant enhancement. Plasma treatments of wool/polyester blend fabric also results in improvement in fabric wettability, tensile strength and reduction in felting tendency.

 

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