Accessibility of mercerized, bioscoured and dried cotton yarns - NOPR

Indian Journal of Fibre & Textile Research Vol. 36, September 2011, pp. 259-265

Accessibility of mercerized, bioscoured and dried cotton yarns Igor Jordanova & Biljana Mangovska Faculty of Technology and Metallurgy, Ss. Cyril & Methodius University, R. Boskovic 16, 1000 Skopje, Macedonia Received 29 January 2010; revised received and accepted 29 October 2010 The structure of cotton yarns mercerized, bioscoured using acid and alkaline pectinases and dried at different temperatures has been studied using X-ray diffraction and infrared spectroscopy. The accessibility is investigated in terms of monolayer capacity, moisture regain, water retention values, and diffusion coefficient of the Congo Red dye. It is observed that the drying at 80oC does not change the crystallinity, but type of scouring changes the cotton accessibility towards water and dyes. The temperature of the drying and type of scouring show significant influence on the monolayer capacity, moisture regain and water retention values. Keywords: Bioscouring, Cotton, Water retention

Mercerization,

Monolayer

capacity,

Moisture

regain,

Pectinases,

Scouring,

Introduction The pore volume and surface area of cotton fibre play important role in determining the accessibility, sorption rates and uniformity of reactions involved in dyeing and finishing processes. The pores are interspersed with microfibrillar structure of celluloses and affect the reactivity of celluloses, since they control the accessibility of reagent to the internal sites at which either chemical reaction or physical adsorption by secondary valence forces can occur1. The size of pores is easily affected by intracrystalline swelling agents, like strong NaOH solutions used during mercerization. The extent of changes occurred depends on the processing time, caustic concentration, temperature, degree of polymerization, source of cellulose, slack or tension treatment, degree of applied tension during the treatment and physical state of cellulose 2-6. The temperature of drying after mercerizing also influences the pores size. Samples mercerized and directly dyed adsorb more water and dye than those dried before dyeing1, 7, 8. Higher temperature of drying decreases the size of the pores consequently as well as the dye content and the water absorption2. Mercerization partially removes the non-cellulosic components9. The accessibility of mercerized cotton

can be improved by caustic scouring in the presence of chelating agents and surfactants10. Mercerizedscoured cotton has almost completely removed noncellulosic components, thus increasing accessibility towards dyes and different reagents11, 12. Attempts have been made to replace conventional alkaline scouring with milder enzymatic scouring processes using different enzymes, such as cellulases, pectinases, lipases, proteases, and their mixtures, surfactants, and treatment parameters. Pectinases appear to be the most suitable for this purpose13-24. Properly selected nonionic surfactants and mechanical agitation are also very important for sufficient scouring13. In earlier studies18-24, optimal parameters for alkaline pectinase and acid pectinase scouring treatments have been determined. Alkaline and acid pectinase scouring treatments were performed on mercerized cotton yarns and the cotton cuticle composition was studied after different scouring treatments9. In the present study, an attempt has been made to modify the pores structure with mercerizing, scouring using acid and alkaline pectinases and applying different temperatures of drying.

_____________ a To whom all the correspondence should be addressed. E-mail: [email protected]

2.1 Materials

1

2

Materials and Methods

Plied ring-worsted cotton yarn with a linear density of 30×2 tex and spun with 330 twists/m was used.

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INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2011

BioPrep 3000L (Novozymes), an alkaline pectinase (EC 4.2.2.2) produced by the submerged fermentation of a genetically modified bacillus microorganism, as well as NS 29048 (Novozymes), an acid pectinase, were also used for scouring.

accomplish neutralization. The sample codes of obtained yarns are given below:

2.2 Methods

•

Mercerization was done on Jäegli hank mercerization equipment by rolling the hanks in 23.5% NaOH solution and 1 gdm-3 Subitol MEZ-N (CHT-Germany) wetting agent at 18°C. The hanks were then extended by application of tension to the original length, rinsed with hot (80°C) and cold (18°C) water for 1 min under tension, neutralized and again rinsed. One part of mercerized cotton yarns in the form of hanks was centrifuged and dried at room temperature (20°C), while the other was centrifuged and dried at 80°C. Mercerized cotton yarns in the form of hanks were scoured by alkaline and acid pectinase in an Ahiba Turbomat TM-6 apparatus for laboratory dyeing in the bath with liquor-to-material ratio of 50:1. All scouring procedures were duplicated. The recipes and treatment conditions are shown in Table 1. At the end of all enzymatic scouring, EDTA was added in the bath and the temperature was raised to 90°C for 15 min to stop the enzyme activity. After all treatments, the yarns were rinsed at 90°C for 10 min, at 70°C for 10 min, and several times with cold water to

• • •

• • • • •

Raw—R Mercerized, dried (20°C) —M20 Mercerized, dried (20°C), scoured (NaOH), dried (20°C) —M20SA Mercerized, dried (20°C), scoured (BioPrep 3000L), dried (20°C) —M20SB Mercerized, dried (20°C), scoured (NS 29048), dried (20°C) —M20SN Mercerized, dried (80°C) —M80 Mercerized, dried (80°C), scoured (NaOH), dried (80°C) —M80SA Mercerized, dried (80°C), scoured (BioPrep 3000L), dried (80°C) —M80SB Mercerized, dried (80°C), scoured (NS 29048) and dried (80°C) —M80SN

2.3 Testing and Analysis

Wide-angle X-ray scattering (WAXS) data were collected in the range 8−30º 2θ on a Philips PW 1710 diffractometer equipped with a curved graphite monochromator (working conditions: U = 40 kV, I = 30 mA), using CuKα radiation (λ = 1.5418 Å) and step-scan mode. Scan time and step length were 5 s and 0.05º 2θ respectively. Before data collection, the fibres (m = 0.2 g) were cut in 1-2 mm long pieces and slightly pressed (2 MPa) in about 2 mm thick pellets of 20 mm diameter. Integral crystallinity was determined25 after a full WAXS profile fitting in 8-28º 2θ region. The patterns

Table 1 — Ingredients and conditions of alkaline18, alkaline pectinase18 and acid pectinase scouring19 Scouring

Ingredient

Amount

Alkaline

NaOH

3.2 gdm-3

Kemonecer NI (non-ionic wetting surfactant)

1 gdm-3

Cotoblanc HTD-N (anionic scouring surfactant)

2 gdm-3

Na3PO4

0.15 gdm-3

Alkaline pectinase

Acid pectinase

pH at start

T1, oC

t1, min

T2, oC

t2, min

12

100

60

-

-

9

55

30

-

-

-3

Kemonecer NI,

1 gdm

BioPrep 3000L

0.666 gkg-1

EDTA

0.4 g/dm3

-

-

-

90

15

CH3COOH + CH3COONa

0.5 gdm-3 + 0.5 gdm-3

4

45

30

-

-

-

-

-

90

15

-3

Kemonecer NI

1 gdm

NS 29048

0.625 gkg-1

EDTA

0.8 gdm-3

JORDANOV & MANGOVSKA: ACCESSIBILITY OF MERCERIZED, BIOSCOURED & DRIED COTTON YARNS

were modeled as a series of Voigt peaks located close to the expected diffraction maxima plus a very wide peak representing the amorphous background. The fraction of an amorphous phase was estimated as the ratio of the amorphous integrated diffraction intensity (Iam) to the total integrated diffraction intensity (Itot), as shown below: Integral crystallinity = 100×(1 – Iam/Itot)

… (1)

Structural changes in the treated cotton yarns were measured by FTIR-ATR apparatus Spectrum GX 69876 (Perkin Elmer). The scanning was obtained from 4000 cm-1 to 500 cm-1 and resolution 4 cm-1. All specimens were scanned three times with 16 scans by one scanning. The infrared crystallinity (lateral order index) and conversion of cellulose I to cellulose II were calculated according to a1420/a895, a895/a1420, a895/a1156 and a895/a1025 ratio26-29. Monolayer capacity (MLC)1 was determined by dyeing of cotton yarns for 24 h at 80oC with a liquorto-material ratio of 125:1 at various dye concentrations ranging from 0.1 gdm-3 to 0.9 gdm-3 Congo Red (Direct Red 28; C.I. 22120) with a molar mass of 696.67 g/mol and 2 gdm-3 sodium chloride. The dye bath liquor was allowed to cool to 21oC and diluted for spectrophotometer readings. The amount (in mmol dye/kg) of dye adsorbed by the fibre was determined from the decrease in concentration of the dye solution after dyeing. The Langmuir equation was used to calculate MLC of the cotton fibre. For all adsorption isotherms of Congo Red, the plot of dye concentration in the bath at equilibrium and the ratio of equilibrium concentration in the bath and in the fibre was found to be a straight line. MLC was calculated from the reciprocal value of the tangent of the angle and is given in mmol/kg fibre. Moisture regain (MR) was determined keeping the cotton yarns in the atmosphere of 65% RH at 21°C to constant weight. After that the samples were dried for 4 h at 105°C and reweighed. MR content was calculated using the following relationship: m − m2 … (2) MR(%) = 1 ⋅ 100 m1 where m1 is the weight of yarns conditioned in atmosphere of 65% RH and 21oC; and m2 , the weight of dried yarns. Water retention values (WRV) were determined on dry processed samples which were allowed to swell in water at room temperature for 2 h before centrifugation for 20 min at 3000 rpm. After

261

centrifugation the samples were transferred into tarred weighing bottles and weighed before drying in an air oven for 4 h at 105°C and reweighed. Water retention value was calculated using the following equation: m − m1 … (3) WRV(%) = 2 ⋅ 100 m1 where m2 is the weight of centrifuged wet yarns; and m1, the weight of dried yarns. The diffusion coefficient (D) was evaluated with Congo Red. It was determined spectroscopically on the basis of absorbency measurement of dye solution at maximum absorbency. Dyeing involved constant dyeing conditions of 60oC temperature and 1:200 material-to-liquor ratio by adding 2% dye without electrolyte up to equilibrium. The equipment included an Ahiba Turbomat TM-6 laboratory dyeing apparatus and UV/VIS Lambda spectrophotometer. Diffusion coefficient was calculated by a simplified solution of Fick’s diffusion equation, as shown below: 1/2

Mt  Dt  ≅ 4 … (4)  M∞ π r2  where Mt and M∞ are the dye uptake after time t and at equilibrium respectively; and r, the fibre radius. This equation is used to calculate D by obtaining the time of half dyeing from a plot of dye exhaustion versus time. When dyeing time is relatively short and liquor ratio is high, the quotient F=(A0-At/A0-A∞) is proportional to the square root of time. In the following equation for calculating D, the value b represents the inclination of the straight line dependence of F=f (t1/2): b 2π r 2 … (5) 16 All investigated parameters were analyzed by main effects analysis of variance (ANOVA), considering the type of scouring (variable A) and temperature of drying after mercerizing (variable B) using the STATISTICA 6. ANOVA gives information about the influence of variables on the response of the investigated parameters30, and is based on the Fisher (F) test. Evaluated F values must be higher than those tabulated. The tabulated F test values for significance level of α = 0.05, degrees of freedom ν1=2 and ν2=2, and type of scouring (variable A) is FA (2, 2) = 19.00. The value for different temperatures of drying after mercerizing (variable B) and for degrees of freedom ν1=1 and ν2=2, is FB (1, 2) = 18.51. Coefficients of D=

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INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2011

correlation between investigated parameters were also calculated30. 3

Results and Discussion X-ray diffractograms of the samples R and M20 (Fig. 1) show partial conversion of cellulose I to cellulose II during mercerization. The 002I peak, characteristic for cellulose I, is still present and there is only a smaller peak for 101II with the shoulder. Some previous investigations confirm that tension mercerizing gives mixed cellulose of cellulose I and cellulose II lattices1, 31. Integral crystallinity values of R and RM20 cotton yarns are 70% and 66.2 % respectively. Partial crystallinity of mercerized cotton yarn is 39.8 % for cellulose I and 26.4 % for cellulose II, confirming that tension mercerizing does not converse cellulose I to cellulose II completely. The crystallinity on the differently dried cotton yarns was not measured because the temperature of drying does not have any influence on it1. Characterization of the fine structure, degree of crystallinity, and conversion of cellulose I to cellulose II were also analyzed by infrared spectroscopy. FTIR-

Fig. 1 — X-ray difractograms for (a) raw cotton and (b) mercerized cotton dried at 20oC

ATR spectra of polymorphous modification on cellulose I and II are found to be different (Fig. 2). During mercerizing and conversion of cellulose I to cellulose II, some bands remain the same, some change and some disappear26. The 893 cm-1 band increases, 1105 cm-1 band is transformed to shoulder, and 1429 cm-1 band shifts at 1420 cm-1 (characteristic for cellulose II). Due to the transformation of cellulose I to cellulose II, some researchers introduced ratios of the bands characterizing crystallinity and the degree of mercerizing. Nelson and O’Connor26 defined index of crystallinity as a1372cm-1/ a2900 cm-1 ratio. Hurtubise and Krassig27 defined lateral index order (LOI) before index of crystallinity was defined. Some other ratios that determine the conversion of cellulose I to cellulose II are a895 cm-1/a1156cm-1, a895cm-1/a1025cm-1 and -1 -1 28, 29 a895cm /a1420cm (index of mercerizing) . The results of several ratios applied for this study are given in Table 2. Lower LOI values of the mercerized cotton (independent of temperature of drying) as compared to raw cotton yarns indicate more disordered cellulose chains in mercerized cotton. Degree of mercerization is presented as MI (mercerization index) and other two ratios have similar values for RM20 and RM80, indicating insignificant influence of the temperature of drying on structure of mercerized cotton. Sorption properties also change after mercerization. Mercerized cotton has decreased crystallinity and changed porous and void system. Nitrogen sorption

Fig. 2 — FTIR-ATR spectra of (a) raw cotton and (b) mercerized cotton dried at 20oC


and mercury porosimetry techniques are usually applied for detecting the pores size changes on the dry, non-swollen materials32. Cellulosic substrates are typically processed in the wet state, resulting in a swollen pore structure that is far more accessible to reagents and, in general, differs considerably from that of the dry material. Hence, characterization of the void system of water-swollen substrates is far more relevant. Many researchers33,34 have focused on solute exclusion techniques developed to assess the cellulose pore size distribution. Surface area determinations are based on sorption data using water as a sensor or larger molecules, such as direct dyes, that also physically adsorb but do not chemically react with the substrate. The Langmuir isotherm has been used to calculate internally available surface area for the respective sensor molecules1, 31, 32. Calculated MLC (Table 3) increases in the order: mercerized alkaline < alkaline pectinase scoured < acid pectinase scoured, irrespective of the drying temperature. Alkaline scouring in rigorous alkaline conditions (pH 12 and boiling temperature) completely removes cuticle components and partially destroys the primary wall, thereby decreasing the internal specific surface. Alkaline and acid pectinases remove part of the waxes, thus changing internal specific surface. Hence, M20SB has around 3 % and M20SN has 5 % higher MLC values than that of M20SA. Yarns dried at 80oC have around 6% lower MLC than that of the yarns dried at 20oC. Table 2 — Infrared ratios of raw and mercerized cotton yarns dried at 20 oC and 80oC Sample

a1420/a895 a895/a1420

a895/a1156

a895/a1025

0.662

0.600

0.146

0.473

2.116

0.898

0.197

0.480

2.083

0.924

0.203

LOI

MI

R

1.500

RM20 RM80

263

The influence of the type of scouring (variable A) and the temperature of drying after mercerizing (variable B) on MLC has been analyzed by analysis of variance (ANOVA). The results are given in Table 4 in terms of Fisher F-test values and p-values. Variables have significant influence on the measured properties when p-value is MSN > MSB, irrespective of drying temperature. M20SB yarn has 72% lower and M20SN yarn has 56.5% lower D value than that of

Table 5 — Coefficients of correlation between measured properties Parameter MLC MR WRV WRV/MLC D

MLC

MR

WRV

WRV/ MLC

D

1

0.61 1

0.77 0.73 1

0.61 0.71 0.97 1

-0.15 0.61 0.39 0.54 1

The correlation coefficients above 0.6 are given in bold.

M20SA yarn. Similarly, M80SB yarn has 71.2% lower and M80SN yarn has 60.6% lower D value than that of M80SA yarn. Alkaline scouring was done in high pH media at the boiling temperature inducing high degree of swelling and the highest D. Acid pectinase scoured cotton has slightly higher D value than that of alkaline pectinase scoured cotton, as a result of some pores on the crystallite surface, as well as some defect. Types of scouring has significant influence on diffusion coefficient, and yarns dried at 20oC have higher D values than the same yarns dried at 80oC. Coefficients of correlation among MLC, MR, WRV and D are given in Table 5. MLC, MR and WRV have high correlation between themselves, but D has good correlation only with MR. 4

Conclusion Elevated temperature of drying does not change the index of crystallinity, as measured by FTIR-ATR spectroscopy. o 4.2 Mercerized, dried at 80 C and differently scoured cotton yarns have lower monolayer capacity, moisture regain, water retention values and diffusion 4.1


coefficient values than those of the yarns dried at 20oC. 4.3 Elevated temperature of drying has higher influence on the water retention values than on monolayer capacity and moisture regain. 4.4 Monolayer capacity in both cases of drying increases in the order: MSA < MSB < MSN, while moisture regain decreases in the same order. 4.5 Water retention values increases in the order: MSB < MSA < MSN at both temperatures of drying. 4.6 WRV/MLC ratio shows that MSN yarn at both drying temperatures has smaller pores as compared to other tested yarns. 4.7 WRV/MLC ratio also shows that yarns dried at 80oC have larger pores with dye dimension than that dried at 20oC. 4.8 Types of scouring have significant influence on the monolayer capacity, moisture regain, water retention values and diffusion coefficient values. Acknowledgement Authors gratefully acknowledge the financial support of the Ministry of Education and Science of the Republic of Macedonia for this project (No. 13814/3-05).

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