Interface phenomena of ecologically scoured cotton material.

Tarbuk, Anita ; Grancaric, Ana Marija ; Markovic, Lea 等

Abstract: The most important phase in textile finishing processes is adsorption of chemical substances and compounds on textile materials surface and wettability as well. Interface phenomena happen between liquid and solid phase, like water solution and textile material, resulting in change of textile material surface free energy. Electrokinetic phenomena, as zeta potential and specific amount of surface charge, characterize electric charge of textile material. In this paper woven cotton fabrics were enzymatically desized, alkali and enzymatically scoured with alkali and neutral pectinases. The influence of these pretreatments to cotton fabric interface phenomena was investigated throughout the change of fabric surface free energy, zeta potential, Isoelectric Point, Point of Zero Charge, and specific amount of surface charge. It is well known the fabrics treated in wet conditions undergo some structural changes; therefore the degree of polymerization, DP for cotton cellulose was determined.

Key words: Cotton material, zeta potential, surface free energy, surface charge.

1. INTRODUCTION

The most important phase in textile finishing processes is adsorption of chemical substances and compounds on textile materials surface and its wettability as well. Cotton scouring process results in hydrophilic cotton material.

Standard procedures of scouring cotton materials involve alkali treatment, usually with NaOH. Those harsh conditions accomplish high effects in textile cleaning of genetic and added impurities such are waxes, protein substances, pectin and other, but also leads to some destruction of cotton cellulose. It is ecologically and economically unfavorable (huge water quantity, high energy, NaOH pollution of wastewater). Therefore, in last few years new agents and technology are intensively studied (Bach & Schollmeyer 1993, Hardin et al. 1997, Hsieh et al. 1998, and Grancariae et al. 2001, 2006). Enzymatic scouring is targeted to degrade only impurities giving an end product with fully intact cellulose including more readily treatable wastewater and energy is saving. Scouring process called "Bioscouring" was recently developed using alkaline pectin lyase BioPrep isolated by Novozymes. Last year BEZEMA released new neutral pectinase Biesol PRO.

This paper deals with interface phenomena of ecologically scoured cotton material. Interface phenomena happen between liquid and solid phase, like water solution and textile material, resulting in change of textile material surface free energy. Electrokinetic phenomena, as electrokinetic (zeta) potential and specific amount of surface charge, characterize electric charge of textile material. Zeta potential is part of the total potential drop occurring in the intermediate surface layer at the boundary of the solid/liquid phases as a result of the ion distribution from the solid surface to the liquid mass. Isoelectric Point (IEP) is a numeric value of pH where electrokinetic surface potential equals zero. Point of Zero Charge (PZC) represents the necessary amount of cationic surfactant added to electrolyte solution to achieve zero charge at a specific pH (pH > 9) (Grancariae et al. 2005, Tarbuk et al. 2006).

Significant influence on the sorption properties of fabrics is the amount of accessible groups (hydroxyl, carboxyl, sulphate and amino groups) and the portion of amorphous regions where the adsorption processes take place. Specific adsorption of ions or dissociation of the surface groups in aqueous solution results with their surface charge. It depends upon their molecular and supramolecular structure, swelling capacity as well as upon ionogenity, structure and concentration of adsorbate (Jachobach 1984, Grancariae 2005). These phenomena characterize material surface. Any change in functional surface group number and dissociation result in different fabric interface phenomena.

2. EXPERIMENTAL

2.1 Material

A plain weave fabric of 100 % cotton and surface mass 135 g/m2 was used. Fabric was enzimatically desized for 3 h at 60[degrees]C in autoclave (Scholl) by pad roll using 3 g/l of amilase Beisol LZV (Bezema) and 2 g/l of wetting agent Kemonetzer NI (Kemo). It was alkali scoured (standard procedure) for 2 h at 100[degrees]C in autoclave (Scholl) by pad roll using 3 % NaOH and 2 g/l Kemonetzer NI. Two sets of samples were enzymatically scoured by exhaustion method in the Linitest (Hanau) using two different pectinases - alkali and neutral one. Fabric was treated with 2 g/l of neutral pectinase Beisol PRO (Bezema) and 1 g/l of wetting agent Felosan NOG (Bezema) at pH 7, for 50 min at 80[degrees]C. Treatment with 0.2 % (owf) of alkali pectinase BioPrep 3000L (Novozymes), was performed in the bath containing 0.5 g/l Kemonetzer NI and buffer ([Na.sub.2]HP[O.sub.4]), pH 9.2 and 65[degrees]C. Labels and treatments are given in Table 1.

For determination of zeta potential and the amount of surface charge the fabrics were specially prepared and finally rinsed to the conductivity of deionised water (2-4 [micro]S/cm).

2.2 Methods

In this paper condition of cotton material after pretreatment was determined through Degree of polymerization (DP) according to DIN 54270. The influence of these pretreatments to cotton fabric interface phenomena was investigated throughout the change of fabric surface free energy, zeta potential, IEP, PZC, and specific amount of surface charge. Zeta ([zeta]) potential was measured by streaming potential/current method using Brookhaven-Paar Electrokinetic Analyzer (EKA) with a rectangular cell designed for textile fabrics. Results were calculated according to the Helmholtz-Smoluchowsky equation (Grancaric et al. 2005). Zeta potential was investigated versus pH resulting in fabric IEP and versus addition of cationic surfactant N-cetylpyridinium chloride (N-CPC) resulting in fabric PZC. Specific quantity of surface charge (q) was calculated after back-titration method with standard polyelectrolyte solution applying Mutek's Partical Charge Detector (Grancaric et al. 2005). In this work PES-Na (sodium salt of polyethylene sulphonic acid) was used as anionic and surfactant solution of N-CPC as cationic polyelectrolyte. Textile surface free energy components were calculated according to thin-layer wicking theory (Chibowski 2000). Acc. to van Oss approach (1984) work of adhesion ([W.sub.A]) can be expressed by this equation:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

from which apolar Lifshitz-van der Waals ([[gamma].sup.LW.sub.S] and polar electron donor ([[gamma].sup.-.sub.S] and electron acceptor ([[gamma].sup.+.sub.S]) components of solid surface free energy can be calculated, if the liquid ones ([[gamma].sup.LW.sub.L], [[gamma].sup.-.sub.L], [[gamma].sup+.sub.L] are known. In these experiments n-heptane was used as an apolar completely spreading liquid and water and formamide as polar non-completely wetting one.

3. RESULTS AND DISSCUSSION

Degree of polymerization is indirect measure of cotton fiber damage caused by scouring conditions. According to results in Table 2, pectinase scoured cotton (ES1, ES2) fabrics have higher degree of polymerization than alkali scoured one (AS). It is to point out that bioscouring with neutral pectinase Beisol PRO is better than with alkali one because those scoured fabrics are less damaged.

It can be seen from Table 2 that all studied fabrics are negatively charged due to the presence of carboxyl and hydroxyl groups. It is obtained that the all scoured fabrics have lower zeta potential than desized and raw one because they have larger number of accessible surface groups. IEP has been not determined for raw and desized cotton fabrics and for scoured is not reliable. Zeta potential of cotton is lower than pH 3 and the results are reliable for pH >3.5, because below pH 3.5, the ionic strength vary significantly. PZC was determined by cationic surfactant (N-CPC) addition to the electrolyte at pH 9 until positive zeta potential values of fabric were achieved. Accessibility of carboxyl and hydroxyl groups in desized and scoured cotton fabrics results in different cationic surfactant adsorption, and the compound used (alkali, enzyme) influence as well. The cotton fabrics have the similar functional groups what results with almost the same specific amount of surface charge (q) (Table 2).

The values of surface free energy components of the studied fabrics, which are calculated from the results of the liquid penetration rates according to thin-layer wicking method, are collected in Table 3.

The liquid penetration rate depended on the liquid properties as well as on the fabric preparation. The highest penetration rate is obtained for n-heptane and the lowest one for formamide irrespective of the fabric preparation. It is also evident that the liquid wicking velocity into the bare fabric differs from that obtained for the pre-contacted one. Since the pretreated fabrics are high wettable by all studied liquids, n-heptane is the only wicking liquid in the case of the hydrophobic fabric R. It can be seen that the fabric R is apolar with [[gamma].sub.S.sup.LW] equals to its total surface free energy, [[gamma].sub.S.sup.tot]. Fabric scouring results in the high increase of the [[gamma].sub.S.sup.-] value, but does not have a significant effect on the increase of [[gamma].sub.S.sup.+]. This suggests that scoured cotton fabrics can be described as monopolar surfaces with a strong electron donor capacity. These results are in good agreement with those of zeta potential and specific surface charge, since carboxyl and hydroxyl groups are strong electron donors. The wettability of scoured cotton with alkali pectinases is very similar to alkali scoured one according to work of spreading ([W.sub.S]). Bioscoured cotton with neutral pectinase has positive [W.sub.S]; no energy is required for wetting. That indicates fabric's great wettability and hydrophility so necessary for all textile finishing processes.

4. CONCLUSIONS

The pre-treatment processes of cotton fabrics causes some kind of modification to the textile surface properties resulting in a great change of its zeta potential, surface charge and surface free energy. Since the pre-treatment leads to a high increase of the [[gamma].sub.S.sup.-] value, this suggests that in contrast to the apolar surface of the raw fabric the pretreated cotton fabrics can be described as monopolar surfaces with a strong electron donor capacity. Ecologic scouring of cotton materials do not damage cotton fibers resulting in great wettability and hydrophility. This confirms the importance of the enzymatic treatment in cotton finishing.

5. REFERENCES

Bach, E. & Schollmeyer, E. (1993). Veregleich des alkalishen Abkochprocesse mit der enzymatischen Entfernung der Begleitsubstanzen der Baumwolle (Comparison of Alkali Scouring and Enzymatic Removal of Cotton Impurities). Textilpraxis International, Vol. 48, No. 3, 220-225, ISSN 0340-5028

Chibowski, E. (2000). Thin layer wicking - Methods for the determination of acid-base energies of interaction. In: Acid-Base Interaction: Relevance to Adhesion Sci. and Technol., Mittal, K.L. (Ed.), Vol. 2, 419-437, ISBN 90-6764-325-4, New Jersez

Grancaric A. M. et al. (2001). The Impact of Treating Cotton with Alkaline Pectinase on Cotton Knitted Fabric Sewability. Tekstil Vol. 50, No. 2, 55-62, ISSN 0492-5882

Grancaric, A.M. et al. (2006). Enzymatic Scouring for Better Textile Properties of Knitted Cotton Fabrics. In: Biotech. in Textile Processing, Guebitz, G. et al. (Ed.), Haworth Press, ISBN 978-1-56022-142-5, New York

Grancaric, A.M. et al. (2005). Electrokinetic Potential of Some of the Most Important Textile Fabrics; Coloration Technol., Vol. 121, No. 4, 221-227, ISSN 1472-3581

Hardin, I.R. & Li, Y. (1997). Enzymatic Scouring of Cotton. Textile Chem. and Colorists, Vol. 29, No. 8, 71-76, ISSN 0040-490X

Jacobasch, H.J. (1984). Oberflachenchemie faserbildender polymerer (Surface Chemistry of Fiber Polymers) Akademie Verlag, Berlin

Tarbuk, A. et al. (2006). Interface Phenomena of Cotton Fabrics--Influence of Pretreatment, Proc. of 37th ISNT, Simoncic, B. et al. (Ed.), ISBN 961-6045-37-7, June 2006, Faculty of Natural Sciences and Engineering, Ljubljana, Slovenia

Table 1. Labels and pretreatments of cotton fabrics

Label Treatment of cotton fabric

R Raw
D Desizing with amilase
AS Alkali scouring
ES1 Enzymatic scouring with alkali pectinase BioPrep 3000L
ES2 Enzymatic scouring with neutral pectinase Beisol PRO

Table 2. Degree of polymerization (DP), Zeta potential ([zeta]),
Isoelectric point (IEP) and Point of zero charge (PZC) of cotton
fabrics

 [zeta] at pH
 10 IEP PZC q
Fabric DP [mV] [pH] [[micro]g/ml] [C/g]

R 2201,02 -11,1 <2,5 94,57 -2,43
D 2159,37 -12,5 <2,5 85,19 -2,40
AS 1987,23 -17,3 2,95 76,82 -2,36
ES1 2056,20 -18,1 2,92 75,68 -2,32
ES2 2151,98 -18,5 2,93 73,21 -2,29

Table 3. Surface free energy components and Work of spreading
([W.sub.s]) according to Chibowski thin-layer wicking method

 [[gamma].sub.S [[gamma].sub [[gamma].sub
 .sup.LW] .S.sup.+] .S.sup.-]
Fabric [mJ/[m.sup.2]] [mJ/[m.sup.2]] [mJ/[m.sup.2]]

R 11,30 0 0
D 47,02 0,37 51,91
AS 56,38 0,01 53,01
ES 1 63,73 0,06 44,52
ES 2 71,98 0,11 45,70

 [[gamma].sub [[gamma].sub
 .S.sup.AB] .S.sup.TOT] [W.sub.S]
Fabric [mJ/[m.sup.2]] [mJ/[m.sup.2]] [mJ/[m.sup.2]]

R 0 11,30 -114,21
D 8,80 55,90 -2,58
AS 0,64 57,03 -1,50
ES 1 3,30 67,03 -1,17
ES 2 4,41 76,39 5,19