Abstract

AGRICULTURE, AGROBUSINESS AND BIOTECHNOLOGY

A biological treatment technique for wool textile

Xiao-Wei Yu; Wen-Jun Guan; Yong-Quan Li^* * Author for correspondence ; Ting-Jing Guo; Ji-Dong Zhou

College of Life Science, Zhejiang University; Hangzhou310027; P. R. China

ABSTRACT

A biological treatment technique for wool textile was carried out by enzymes degradation coupled with H₂O₂ oxidation. The results demonstrated that the technique had ideal effects on wool textile such as better softness, plump and less loss of bursting stress. Because of mild reaction conditions, less textile damage and less environmental pollution, this technique for wool textile treatment could have promising prospect.

Key words: Wool textile decrement, oxidation pretreatment, enzyme degradation, L86 enzymes

INTRODUCTION

It is necessary for the wool industry to use more environmentally friendly finishing processes due to the pollutant in the process of chemical treatment. Wool mainly consists of scaly layer and cortex layer, both adhering to each other through cellular matrix carboxymethyl cellulose (CMC). Scaly layer is composed of surface layer, outer layer and inner layer, which is approximately 10% of total wool weight (Word et al., 1993; Messinger et al., 1994). During the processing the scaly layer of wool is peeled off partly or completely by digestion in order to raise the wool fineness shine, softness and elasticity. Surface layer and outer layer of wool contain abundant keratin protein, which are too tight to be degraded; whereas inner layer contains non-keratin protein, which are easy to be digested by protease; cellular matrix CMC is similarly easy to be degraded by cellulase (Leeder et al., 1968).

Traditional oxidizers such as NaClO and KMnO₄ are used to break the surface layer and outer layer of the scaly layer by oxidizing the disulfide bond in keratin proteins. However, their strong oxidations are always difficult to control and often result in disproportion of the treatment. Moreover, NaClO reaction with wool produces halogenide. Thus, chemical oxidizes are not suitable. Experimental results in this paper proved that H₂O₂ was a suitable oxidizer, since it could give oxygen smoothly with moderate oxidization. The mechanism of oxidation is shown in scheme 1.

Therefore, less aggressive chemical processes and environmentally friendly methods such as enzyme based processes, as well as combination treatments have gained widespread acceptance (Cortez et al., 2002; Jose et al., 1996; Manjrekar, 1995; Shridhar et al., 1995), which impart desirable properties, such as improving handle properties and imparting shrink-resistance and produce less pollution (Breier et al.,1999; Bishop et al.,1998; Heine et al.,2001).^.Generally H₂O₂ is applied to break the surface layer and outer layer of the scaly layer; Then, Aspergillus usamii L86 enzymes including acid protease and CMCase (Yongquan Li,2001) are added to degrade inner layer and outer layer in order to peel off the scaly layer effectively.

MATERIALS AND METHODS

Experimental Materials

Knitted fabric was made from 100% Australia wool, whose size was 22cm*16cm, transverse 54 needles/cm and longitudinal 78 lines/10cm.

Process of treatment

After H₂O₂ oxidation pretreatment, the wool textile was degraded with L86 enzymes, followed by neutralization with alkali, washing and aminosilicone oil Umd softening treatment (18g/L of Umd, pH5-6, 20-30ºC for 10min), and finally, the treated wool textile was washed and dried at 80ºC.

H₂O₂ oxidation

All experiments were carried out under the conditions of the dissolvent proportion of 1:30 and 2.0g/L of penetrate reagent. For observing influence of H₂O₂ oxidation on wool textile, reaction temperature and pH were at 20ºC, pH 4.0 for 40 min; H₂O₂ concentration 40g/L, pH 4.0 for 40 min, and at 20ºC, H₂O₂ concentration 40g /L and ratio at 6.0%.

Biological treatment with respectively enzymes

Under the conditions of dissolvent proportion of 1:30, reaction temperature 40ºC and pH 4.0 according to the enzymatic characteristics of acid protease and CMCase (Xinghua,Wen, 1999), the L86 enzymes containing acid protease and CMCase were added to degrade the inner layer, and add NaHSO₃ at the same time.

Acid protease measurement

Folin method was applied in the enzyme activity assay (Yongquan Li, 1999). Under the conditions of pH3.0 and 40ºC, one unit of acid protease was defined as 1g tyrosine produced by hydrolysis of casein per minute.

CMCase measurement

CMC saccharimetry was applied in the enzyme activity assay (Shuzheng Zhang, 1984). Under the conditions of pH5.0 and 50ºC, one unit of CMCase was defined as 1µg CMC hydrolyzed per minute.

Bending stiffness

Bending stiffness was measured with Instron 1122 Strength Electronic Instrument.

Bursting Strength

The strength of wool textile (measure unit N/cm²) was determined with Textile Bursting Strength Instrument.

Decrement ratio

Untreated wool textile was dried at 105ºC. Then, it was treated with decrement and dried. The decrement ratio was calculated:

Each test was conducted at least three times. Data are the means of three replications. Significantly different from replications was at p<0.05.

RESULTS AND ANALYSIS

Technique of oxidation pretreatment

The relationships between the concentration of H₂O₂ and bursting strength loss ratio, decrement ratio are illustrated in Fig. 1. The results indicated that when the concentration of H₂O₂ was between 40 and 50g/L, the decrement ratio arrived was 6-8% with the textile bursting strength loss ratio within 10% and the wool textile was soft, plump and smooth.

The experiment about effect of reaction temperature on decrement ratio showed (Fig 2) that the speed of H₂O₂ oxidation was slow below 20ºC.

However, the reaction speed was increased above 20ºC, but it damaged the strength of wool textile intensively and made the wool textile fragile and faint, so the temperature should be controlled strictly at 20ºC in pretreatment process.

Fig. 3 showed the pH effect on pretreatment reaction. The results revealed that the H₂O₂ oxidation reaction was hardly processed at pH>6.5. While at pH<2.0, H₂O₂ reaction finished completely within 20 min (decrement ratio at 6.0%); and if the reaction time was beyond 30 min, the effects of the treatment were not fairly proportioned (decrement ratio>10%, bursting strength loss ratio>12%). However, controlling pH 4.0 and reaction time 45min, the decrement ratio also could reach at 6.0%. Thus, the pretreatment condition was selected as 40g/L of H₂O₂ concentration, reaction time 45 min and pH 4.0.

Enzymatic degradation

The supernatant from Aspergillums usamii L86's fermentation broth containing acid protease (10000U/ml) and CMCase (3600U/ml) was used as treating reagent. After the oxidation pretreatment at the conditions of 40g/L of H₂O₂, pH 4.0, 20ºC and 45min of reaction time, the L86 enzymes containing acid protease and CMCase were added to degrade the inner layer. CMCase acted on the cellular matrix between scaly layer and cortex layer, which could help peeling off the scaly layer, so as to reinforce the effect of acid protease degradation. In order to optimize the enzyme degradation process, an L9 (3⁴) orthogonal test was carried out, in which the amount of enzyme solution, the concentration of NaHSO₃ and the reaction time were taken as experimental parameters.

The results are shown in Table 1, which showed that reaction time influenced the results most significantly and the enzyme concentration followed. The reaction time represented the influence of enzyme degradation on the decrement ratio, the longer the treatment time, the stronger the degradation reaction.

While it was treated for 60 min, the effect of decrement was quite good, but too much loss of textile strength, so the suitable reaction time was selected as 45 min. NaHSO₃ in solution had two functions, one was to decompose the disulfide bond in the wool, which would raise the speed of enzyme degradation; the other was to reduce residue of H₂O₂ in the solution, because the residue of H₂O₂ would injure the wool gradually and influence the whiteness of textile. The results demonstrated that the suitable concentration of NaHSO₃ was 60g/L, and increasing the concentration of protease could increase the textile decrement ratio with bursting strength decreased. However, there was a two-phase reaction of solid-liquid on wool surface, when the enzyme concentration reached at a certain amount, the wool surface was saturated and reaction was efficiency. By adding more enzymes into solution, the reaction speed could not be increased. Considering the reaction effect and the material cost, the suitable amount of enzymes was selected as 1.5 ml of per liter solution.

The optimum conditions of enzyme degradation process were 1.5ml of enzymes of per liter solution and its final concentration arrived at 15U/ml of acid protease and 5U/ml of CMCase, 60g/L of NaHSO₃, the reaction time 45min, dissolvent proportion 1:30, 40ºC, pH 4.0.

Contrast experiment

In order to show the characteristics of enzyme degradation coupled with H₂O₂ oxidation, the contrast experiment about enzyme degradation, H₂O₂ oxidation pretreatment and enzyme degradation coupled with H₂O₂ oxidation were carried out and the decrement ratio, bending stiffness and bursting strength were selected as responsive values. The test conditions and results are shown in Table 2.

Apparently the coupled treatment process provided better decrement effect with satisfying decrement ratio, bursting strength and softness than that of H₂O₂ oxidation or enzyme degradation alone. Furthermore, after coupling treatment, washing and drying, the treated wool textile showed good strength and softness, and clear printing pattern. While treated with H₂O₂ oxidation or enzyme degradation alone, the textile showed relatively bad strength, softness and feel of handle.

After the treatment by enzyme degradation coupled with H₂O₂ oxidation, the wool textile should be washed, avoiding the peptides and carbonaceous matters adhering to textile, which were produced by enzyme degradation. Then, temperature should be raised to 80ºC so as to deactivate enzyme and dry wool textile. When the scaly layer of wool was peeled off, the wool textile showed plump and softness but bad elasticity, and the cortex layer would be influenced easily by many chemistry reagents and weather conditions, therefore softener with affinity to wool, amino-silicone oil Umd, had to use to form a protective membrane covering the wool surface.

The technique of biological treatment was studied according to the subtle structure of wool. The enzyme degradation had mild reaction conditions and could be controlled easily. The enzymes from strain Aspergillums L86, whose components (two enzymes) interrelated with the structure of wool closely and had the same pH of decrement process, improved the effects of treatment remarkably (Yongquan Li, 2001). Hence the effect of coupling treatment process was better than that of traditional chemistry treatment. For example, it greatly improved the quality of treated textile, and produced less environment pollution.

Since H₂O₂ oxidation and enzyme degradation required the same pH, when these two processes were combined, the solution needed not be changed during process. Thus, using this technique could cut down the material cost and manpower.

ACKNOWLEDGEMENTS

This work was supported by Science Research Plan of Zhejiang Province in China (No.99-3-031).

Received: December 08, 2003;

Revised: June 26, 2004;

Accepted: June 08, 2005.

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