enzymatic finishing of wool fabrics

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Enzymatic Finishing of WoolFabricsDr. Ascensión Riva a , Inés Algaba a & RemediosPrieto aa Instituto de Investigación Textil de Terrassa ,Universidad Politécnica de Cataluña , Colón 15,E-08222, Terrassa, SpainPublished online: 08 Oct 2008.

To cite this article: Dr. Ascensión Riva , Inés Algaba & Remedios Prieto (2006)Enzymatic Finishing of Wool Fabrics, Journal of Natural Fibers, 3:2-3, 209-227

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Enzymatic Finishing of Wool Fabrics:Effects of Different Treatments

with a Protease on Physical and ChemicalParameters of the Fabric

Ascensión RivaInés Algaba

Remedios Prieto

SUMMARY. The objective of the present work is to evaluate the actionof a protease when applied on a high quality wool fabric to obtain an im-proved touch and drape on the fabric as well as to decrease its shrinkageand pilling propensity.

The effectiveness of the enzymatic treatment as well as the intensityof the attack to the wool fibre are evaluated by determining several me-chanical and chemical parameters. [Article copies available for a fee fromThe Haworth Document Delivery Service: 1-800-HAWORTH. E-mail address:<[email protected]> Website: <http://www.HaworthPress.com>© 2006 by The Haworth Press, Inc. All rights reserved.]

Prof. Dr. Ascensión Riva (E-mail: [email protected]), Ind. Eng. Inés Algaba(E-mail: [email protected]), and Tech. Eng. Remedios Prieto (E-mail: [email protected]) are affiliated with the Instituto de Investigación Textil de Terrassa,Universidad Politécnica de Cataluña, Colón 15, E-08222 Terrassa, Spain.

The authors thank the Spanish company Artextil (Sabadell) for the fabric supplyand the carrying out of the industrial finishing process, and the Danish company NovoNordisk for the enzyme supply. The authors want to express their special gratitude toMrs. P. Ferrer for her cooperation in the experimental work.

[Haworth co-indexing entry note]: “Enzymatic Finishing of Wool Fabrics: Effects of Different Treat-ments with a Protease on Physical and Chemical Parameters of the Fabric.” Riva, Ascensión, Inés Algaba,and Remedios Prieto. Co-published simultaneously in Journal of Natural Fibers (Food Products Press, an im-print of The Haworth Press, Inc.) Vol. 3, No. 2/3, 2006, pp. 209-227; and: Biotechnology in Textile Process-ing (ed: Georg M. Guebitz, Artur Cavaco-Paulo, and Ryszard Kozlowski) Food Products Press, an imprint ofThe Haworth Press, Inc., 2006, pp. 209-227. Single or multiple copies of this article are available for a fee fromThe Haworth Document Delivery Service [1-800-HAWORTH, 9:00 a.m. - 5:00 p.m. (EST). E-mail address:[email protected]].

Available online at http://www.haworthpress.com/web/JNF© 2006 by The Haworth Press, Inc. All rights reserved.

doi:10.1300/J395v03n02_14 209

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KEYWORDS. Wool, finishing, enzyme, protease, softness, compress-ibility, flexural stiffness, bending, dimensional stability, pilling, tensilestrength, abrasion resistance, alkaline solubility, urea-bisulphite solubility

INTRODUCTION

The use of enzymes in the textile industrial processes is a field of bio-technology in which remarkable results have been already obtained andnew medium and short-term developments are still expected (Nilsson &Ainaga, 1996; Cegarra, 1999; Briera & Nubiola, 1998; Heine & Hoecker,1995; Roessner, 1995; Uhlig, 1998; Cavaco-Paulo & Gübitz, 2003).

Particularly, the application of enzymatic treatments in the finishingof wool fabrics to improve some of their properties is a topic in whichresearch has been intensified in the last years. One of the main aims isthe study of finishing processes more environmentally respectful thanthose traditionally used (Riva, 1995; Levene et al., 1996; Heine et al.,1998; Breier, 2000).

Concretely, the application of proteases has been efficient in the de-crease of shrinkage as well as in the improvement of the touch, handleand drape of the fabrics. Regarding this topic, the authors have studiedthe action of several proteases applied on wool fabrics in order to reducetheir felting shrinkage and to improve their drape (Riva et al., 1993;Cegarra et al., 1992; Cegarra et al., 2003). They have studied as well therepercussion of the enzymatic treatment on the later tinctorial behaviourof wool, analysing the dyeing kinetics and the colour levelling (Riva etal., 1991, 2002, 2003). In other research works, the authors have fo-cused on the study of the effects of the enzymatic treatments on the col-our quality (colour change and colour fastness of fabrics dyed withdifferent dyestuff types) when the enzymatic treatment is applied ondyed articles (Riva et al., 2001). They have as well tested the possibili-ties of application of enzymes as dyeing auxiliaries (Riva et al., 1999).

In all these research works, the effectiveness of the enzymatic treat-ment as well as the attack on the fibre have been found to vary apprecia-bly in terms of the type of protease used. It suggests that it is necessaryto carry on with the research to find out the more suitable enzymes, foreach desired finishing, and to optimise the application conditions. In thepresent research work a high quality 100% wool fabric is treated with aprotease. The main objective is to obtain an excellent touch and drapeon the fabric, as well as to decrease its shrinkage and pilling.

210 BIOTECHNOLOGY IN TEXTILE PROCESSING

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The effectiveness of the enzymatic treatment is evaluated by deter-mining the following physical and mechanical parameters: softness,compressibility, flexural stiffness, bending, dimensional stability andpilling. The possible negative effects of the treatment are evaluated bydetermining physical parameters of the wool fabrics, such as tensilestrength and abrasion resistance, together with chemical parameters ofthe wool fibre, such as alkaline solubility and urea-bisulphite solubility.

The optimal conditions for the treatment could be defined by com-parison of the results obtained on the untreated fabrics with those ob-tained on the fabrics treated without and with different enzyme con-centrations.

EXPERIMENTAL

Material

To carry out the study a 100% worsted wool fabric, usually applied inhigh quality garments, was used. The structural characteristics of thisfabric are:

• Weight: 228 g/m2

• Weave: step twill• Thread count: warp, 30 yarns/cm; weft, 25 picks/cm

The fabric preparation operations have been the following:

• Scouring-milling, in a industrial machine of the type scourer-full-ing mill, with a solution of sodium carbonate and non-ionicdetergent

• Rinsing and final acidulating to pH 5• Drying in a three floor rame, suitable for wool articles

Enzymatic Treatment

Enzyme

For the enzymatic treatment, the enzyme Novolan T granulated wasused. This enzyme is a protease produced by fermentation of a geneti-cally modified microorganism of the type Bacillus. According to thetechnical information (“Novo Nordisk,” n.d.), it is especially suitable

Riva, Algaba, and Prieto 211

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for improving the handle of wool fabrics, providing a soft touch and aspecial drape, as well as to minimise the hairiness of the surface andpilling. The proteolytic activity of the enzyme Novolan T is 1000NWPU–evaluated by the manufacturer according to a Novo Nordisk as-say and expressed in Novo Wool Protease Units. The recommendeddosage of the enzyme is between 2 and 4% o.w.f. The maximum rela-tive activity of the enzyme is achieved at pH 8.5 and temperature 55°C.

Application Conditions of the Enzymatic Treatment

Before the enzymatic treatment the wool was pre-treated in order toregulate the wool internal pH as well as to maintain the pH of the enzy-matic bath during the treatment. The pre-treatment was carried out un-der the following conditions:

• Sodium carbonate: 1% o.w.f.• Temperature: 50°C• Time: 30 minutes• Liquor ratio: 1/10

At the end of the pre-treatment the fabrics are centrifuged and driedon a plain surface. The enzymatic treatment was carried out in the con-ditions shown in Table 1.

For the application of the enzymatic treatments a Linitest apparatuswas used. After the enzymatic treatment, in order to denaturalise the en-zyme, the fabrics are treated for 5 minutes in an aqueous bath at a tem-perature of 90°C and pH lower than 4, adjusted with sulphuric acid.After the enzyme denaturalisation, the fabrics are rinsed three timeswith cold water to eliminate the enzyme remains and free fibres removedin the treatment. Finally, they are centrifuged and dried into the air.


TABLE 1. Conditions of the enzymatic treatment

Enzymatic treatment conditions

Soft (S) Medium (M) Intense (I)

Enzyme concentration (% o.w.f.) 1 3 5

Temperature (°C) 45 50 55

Time (min) 15 30 45

pH (sodium carbonate) 8.5 8.5 8.5

Liquor ratio 1/10 1/10 1/10

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Finishing of the Fabrics

The fabric finishing was carried out by a company specialised inwool finishing, so that the process would be identical to that whichwould be industrially applied to a fabric with the characteristics of thefabric used in this study. Thus, the finishing was a completely industrialprocess. It consisted of the following finishing operations:

• Shearing: to eliminate free fibres from the fabric surface• Flat setting: to eliminate wrinkles and obtain a flat surface free of

wrinkles• Continuous fixing: to fix the fabric dimensions• Free vaporising: to provide a fluffy characteristic• Decatising in KD: to complete the process providing a completely

flat surface without the wrinkles that were produced during the en-zymatic treatment

DETERMINED PARAMETERS

The following parameters were determined:

Parameters Indicating the Effectiveness of the Treatment

Test of softness, according to INTEXTER MO B9.1/08/24

Compressibility, according to the Compression Tester method KES-FB3

Conventional flexural stiffness, according to ISO 4604:1978

Bending, according to the Pure Bending Tester method KES-FB2

Dimensional stability, according to IWS TM n° 31 (25) and ISO6330

Pilling resistance, according to UNE-EN ISO 12945-2, Martindalemethod

Parameters Indicating the Degree of the Fibre Degradation

Tensile strength, according to UNE-EN ISO 13934-1:1999

Abrasion resistance, according to UNE-EN-ISO 12947-2, Martindalemethod


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Solubility in alkali, according to ISO 3072:1975

Solubility in urea-bisulphite, according to IWTO 11-62

RESULTS AND DISCUSSION

In the enzymatic treatments, the fabrics are likely to undergo someshrinkage as they are subjected to a mechanical action in a wet environ-ment. For this reason, the results of the fabrics treated with enzyme arecompared with the untreated fabric as well as with a fabric treated withoutenzyme (under the medium conditions but without addition of enzyme).

Parameters Indicating the Effectiveness of the Enzymatic Treatment

Softness

The softness of a fabric is associated with a great number of physicalproperties. Several of these properties were determined in this study,such as bending and compression. Nevertheless, despite the existenceof a number of methods for evaluating the softness of fabrics, none ofthem accounts for the highly subjective sense of what is or is not soft.Therefore, the evaluation of this property has been carried out by a sub-jective test, in which 11 experts in the evaluation of the feel of fabricsparticipated.

The methodology was as follows: equal-sized samples of all the fab-rics were prepared. Each evaluator compared all the possible binarycombinations of these samples. The evaluation was carried out only bytouch, as the evaluators were not allowed to see the samples. A table ismade with the evaluation of the order of softness given by each evaluator.The order of softness of the fabrics is the result of computing the num-ber of times that each sample was chosen as softer by each evaluator.Table 2 shows the results.

The table shows the choice of each person for every possible combi-nation of pairs of samples. The symbol “equal” (=) means that the per-son asked in the survey has not been able to distinguish between the twosamples.

According to Table 2, the order from the softest to the least soft fabricis as follows:

I > M > W > U > S


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Results show that the fabric treated with enzyme under the most in-tense conditions has been considered to be the softest one, followed bythe fabric treated with enzyme under the medium conditions. The fabrictreated without enzyme and the untreated fabric are evaluated with amedium softness. Curiously, the fabric treated with enzyme under thesoft conditions has been evaluated as the least soft.

Summarising, in the subjective evaluation of softness, the enzymatictreatment has shown its effectiveness to provide a softest touch to thefabric, when the treatment conditions are medium or intense. An im-provement of the softness has not been seen when the fabric is treatedwith the lowest enzyme concentration.

Compressibility

Table 3 shows the results obtained from the compression curve givenby the Compression Tester of Kawabata. The values are the average ofthe measurement of three samples.


TABLE 2. Test of softness (U: untreated fabric; W: fabric treated without en-zyme; S: fabric treated with enzyme soft conditions; M: fabric treated with en-zyme medium conditions; I: fabric treated with enzyme intense conditions)

Binary combinations of the fabrics

U-W U-S U-M U-I W-S W-M W-I S-M S-I M-I

Evaluator Fabric chosen as the softest

1 U U U I W M W M I M

2 W U U U W W I M I I

3 W U U I S M I S I M

4 U S M I S M I M I I

5 W S M I W M W S I I

6 U U M I W M I S I I

7 W U M U W W I M I I

8 W S M I S M I M I M

9 W S M = W M I M S I

10 U U U U S M I S I I

11 = U U U W W W M I M

Softestfabric

W U M I W M I M I I

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Results show that the linearity of the compression curve follows anorder in agreement with the intensity of the enzymatic treatment. Thus,the fabric treated under the intense conditions is the one with lowest lin-earity, followed in increasing order by the fabrics treated with enzymeunder the medium and soft conditions, the fabric treated without en-zyme and the untreated fabric. A lower linearity means that the fabriccan be compressed more easily at small increases of pressure.

Regarding the compressional energy, results show that the highestvalues are obtained for the fabrics treated with enzyme.

The compressional resilience of the fabric varies with the enzymatictreatment as well. The lowest resilience values correspond to the fabricstreated under the more intense conditions.

It must be taken into account that the compressibility values are re-lated to the variation of the fabric thickness. From the values shown inthe table, it is deduced that the fabrics treated with enzyme as well as thefabric treated without enzyme are thicker than the untreated fabric. Thecompression rate is also higher for the treated fabrics.

Flexural Stiffness

The simplest conventional procedure is based on the determinationof the projection length needed to have a settled flexion angle betweenthe free end and the horizontal plane. The flexural stiffness is calculatedby the following formula:

Flexural stiffness = 0,1 P c3 (mg � cm)


TABLE 3. Compressibility (LC: linearity of compression-thickness curve; WC:compressional energy; RC: compressional resilience; TO: thickness of the fab-ric at a pressure of 0.5 cN/cm2; TM: thickness of the fabric at a pressure of 50cN/cm2; EMC: compression rate)

Fabric LC WC(gf cm/cm2)

RC(%)

TO(mm)

TM(mm)

EMC(%)

Untreated 0.729 0.409 63.66 0.757 0.531 29.87

Treated without enzyme 0.669 0.440 63.52 0.803 0.540 32.78

Treated with enzyme: Soft 0.665 0.453 64.13 0.869 0.596 31.54

Treated with enzyme: Medium 0.646 0.441 60.69 0.852 0.578 32.17

Treated with enzyme: Intense 0.622 0.446 59.50 0.868 0.581 33.05

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P: weight of the fabric (g/m2)C: curvature length of the fabric

The total flexural stiffness is the geometric average of the flexuralstiffness in the direction of the warp (Ru) and the weft (Rt).

Total flexural stiffness = Ru Rt

To calculate the flexural stiffness, the weight per surface unit of thefabrics is needed. The results on this parameter, together with the resultson flexural stiffness, are shown in Table 4. The values are the average ofthe measurement of two samples.

The flexural stiffness of the fabrics is a parameter related to the drapeof the fabrics. The relation is inverse, that is, the lower the flexural stiff-ness, the better the drape is.

It can be observed that the fabric treated without enzyme has a higherweight than the untreated fabric. That is a usual consequence of shrink-age of the fabric caused by the wet treatment together with mechanicalaction. The fabrics treated with enzymes have also undergone a wettreatment with mechanical action. As said previously, their thicknesseshave increased when compared to the untreated fabric, in a similar orderthan the fabric treated without enzyme. It seems that the treated fabricsundergo a similar compaction, but their weight per surface unit de-creases by the enzymatic treatment. This decrease is, logically, moreoutstanding when the treatment intensity increases, indicating a partialelimination of the keratin material.

An increase of the warp flexural stiffness of the fabric treated withoutenzyme when compared with the untreated fabric is observed. This isdue to its more compacted structure, a consequence of the shrinkage of


TABLE 4. Weight and flexural stiffness

Fabric Weight(g/m2)

Flexural stiffness (mg cm)

Warp Weft Total

Untreated 228 105 110 107

Treated without enzyme 237 128 105 116

Treated with enzyme: Soft 228 115 96 105

Treated with enzyme: Medium 225 113 93 103

Treated with enzyme: Intense 221 109 83 95

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the fabric produced in the wet treatment. All the fabrics treated with en-zyme exhibit lower warp flexural stiffness than the fabric treated with-out enzyme, that is, they have a better drape. The warp flexural stiffnessdecreases when the intensity of the treatment increases.

Regarding the weft flexural stiffness, the fabrics treated with enzymealso present the lower values of flexural stiffness. Once again the flex-ural stiffness decreases when the intensity of the treatment increases.

Summarising, the enzymatic treatment is efficient in improving thedrape of the fabrics. The effectiveness increases when the intensity ofthe enzymatic treatment increases.

Bending

The bending behaviour, determined by the “Pure Bending Tester” ofKabawata, is deduced from the KES Standard Chart and expressed bythe following parameters:

B: rigidity per length unit (gf � cm2/cm)–average of the inclina-tions Bf (bending face) and Bb (bending back)

2HB: moment of hysteresis per length unit (gf � cm/cm)–average ofthe hysteresis 2HBf (face) and 2HBb (back)

Results are shown in Table 5. The values are the average of the mea-surement of two samples.

The table shows that, in the weft direction, the fabric that exhibits thelowest rigidity, that is, the fabric that can be bent more easily, is the fab-ric treated with enzyme under the intense conditions, followed by thefabric treated under the medium conditions. Although they can not beconsidered very different compared with the previously mentioned val-


TABLE 5. Rigidity B and hysteresis 2HB

FabricB (gf cm2/cm) 2HB (gf cm2/cm)

Warp Weft Average Warp Weft Average

Untreated 0.1325 0.1225 0.1275 0.0775 0.0525 0.0650

Treated without enzyme 0.1375 0.1138 0.1256 0.0625 0.0388 0.0506

Treated with enzyme: Soft 0.1675 0.1242 0.1459 0.0793 0.0468 0.0630

Treated with enzyme: Medium 0.1413 0.1100 0.1265 0.0708 0.0425 0.0562

Treated with enzyme: Intense 0.1385 0.1063 0.1224 0.0650 0.0460 0.0555

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ues, the values obtained for the other three fabrics place the fabrictreated without enzyme in a intermediate position, giving the untreatedfabric and the fabric treated with enzyme under the soft conditions asomewhat higher rigidity.

These results are in agreement with the subjective evaluation of thesoftness. The fabrics evaluated as the softest are also the most flexiblefabrics.

In the direction of the warp the values seem to be less coherent. Theuntreated fabric, the fabric treated without enzyme and the fabric treatedwith enzyme under the intense conditions show the lowest rigidity val-ues. The values are very similar among these fabrics. The fabric treatedunder the soft conditions has, once again, the highest rigidity. Regard-ing the values of hysteresis, the order of the fabrics is very similar to theabove mentioned for the values of rigidity, in the direction of the warpas well as in the direction of the weft.

Dimensional Stability

The dimensional stability to laundering has been carried out accord-ing to the TM31 of the IWS. Firstly, the fabrics undergo a washing cycle7A according to ISO 6330 to allow them to relax. The conditions of the7A washing cycle are:

Weight 1 kg

Detergent ECE 1 g/l

Temperature 40°C

Volume of bath (high level) 25 l

In this relaxation shrinkage cycle, the tensions of the previous weav-ing and finishing operations are eliminated and the fabrics are preparedto undergo the test for the determination of the felting shrinkage.

The results on the relaxation shrinkage test are very similar for all thefabrics. It means that all the fabrics had similar residual tensions. Thevalues of the shrinkage area were around 4%, being mainly caused bythe shrinkage in the warp direction.

After the relaxation shrinkage the fabrics underwent a washing cycle5A, according to ISO 6330, to determine the felting shrinkage. The con-ditions of the 5A cycle are:


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Weight 1 kg

Detergent ECE 0.3 g/l

Temperature 40°C

Volume of bath (high level) 25 l

The shrinkage test was carried out in a Wascator FOM 71 machine.Results of the felting shrinkage are shown in Table 6. The values are

the average of the measurement of two samples.Results show that the fabrics treated with enzyme have lower felting

shrinkage than the untreated fabric and the fabric treated without en-zyme, in the warp as well as in the weft directions. The shrinkage de-creases when the intensity of the enzymatic treatment is increased.

Pilling Resistance

The results on pilling resistance are shown in Table 7. The values arethe average of the measurement of four samples.

Results of the tendency of pilling formation at the beginning of thetest show some pilling formation in the fabrics with a few rubbing cy-cles. In all the fabrics the pilling formation increases until the testreaches 1000-2000 rubbing cycles. From this point the pilling de-creases, that is, all or a part of the pilling is released. The fabrics thathave a higher propensity to pilling are the untreated fabric and the fabrictreated without enzyme.

Analysing the evaluation at the 5000 of rubbing cycles, that is thenumber of cycles that is taken usually as the end of the test, the untreatedfabric exhibits a “not bad” pilling rate. The fabrics treated with enzyme


TABLE 6. Felting shrinkage

FabricShrinkage (%)

Warp Weft Area

Untreated 8.0 5.0 12.6

Treated without enzyme 7.5 4.5 11.6

Treated with enzyme: Soft 6.8 4.9 11.3

Treated with enzyme: Medium 6.1 3.6 9.5

Treated with enzyme: Intense 5.2 3.5 8.5

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and the fabric treated without enzyme show a better behaviour than theuntreated fabric. The fabrics treated with enzyme under the medium andintense conditions show an excellent mark, that is, no pilling is observedin the fabric surface.

Parameters Indicating the Damage Produced to the Fibre

Tensile Strength

Results on tensile strength are shown in Table 8 and results on break-ing elongation are shown in Table 9. The values are the average of themeasurement of five samples.

The enzymatic treatment produces, as expected, a decrease of thetensile strength of the fabrics, which indicates that the fibres have beenattacked. This decrease is more appreciable when the intensity of thetreatment increases and can be even considered as excessive for themore intense treatment conditions.


TABLE 7. Pilling resistance

Fabric

Evaluation

Number of cycles

125 500 1000 2000 5000

Untreated 2-3 1-2 1 1 3

Treated without enzyme 4 3 1-2 1 4

Treated with enzyme: Soft 3-4 3 2-3 3 4

Treated with enzyme: Medium 3 2 1-2 2-3 5

Treated with enzyme: Intense 3 2-3 2-3 3-4 5

TABLE 8. Tensile strength

FabricTensile strength (kg)

Warp Weft

Untreated 36.2 29.1

Treated without enzyme 31.7 28.5

Treated with enzyme: Soft 35.7 30.2

Treated with enzyme: Medium 30.4 27.1

Treated with enzyme: Intense 25.1 23.9

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The values of the breaking elongation also decrease when the inten-sity of the treatment increases.

Abrasion Resistance

The results on abrasion resistance are shown in Table 10. The valuesare the average of the measurement of four samples.

The abrasion resistance is, together with the tensile strength, one ofthe physical parameters that better represent the damage that the fibresundergo.

The table shows that the enzymatic treatment produces a decrease onthe abrasion resistance that is more and more appreciable when the in-tensity of the enzymatic treatment increases. The loss of resistance inthe fabrics treated with enzyme under the medium and intense condi-tions must be considered as important.

Solubility in Alkali

The results on this parameter are shown in Table 11. They are the av-erage of three replicates.


TABLE 9. Breaking elongation

FabricBreaking elongation (%)

Warp Weft

Untreated 35.5 28.5

Treated without enzyme 35.6 31.5

Treated with enzyme: Soft 32.1 29.3

Treated with enzyme: Medium 29.5 25.2

Treated with enzyme: Intense 24.3 22.1

TABLE 10. Abrasion resistance

Fabric Abrasion resistance(number of cycles)

Untreated 34750

Treated without enzyme 33500

Treated with enzyme: Soft 31000

Treated with enzyme: Medium 24250

Treated with enzyme: Intense 23500

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The solubility in alkali of the untreated fabric has a value of 15.5%,which is normal for untreated wool.

The fabric treated without enzyme and the fabric treated with enzymeunder the soft conditions exhibit the same solubility in alkali than theuntreated fabric.

The fabrics treated with enzyme under the medium and intense con-ditions have higher solubility in alkali. That means that an attack on thewool fibre has been produced, resulting in the shortening of the poly-meric chain.

Solubility in Urea-Bisulphite

The results on solubility in urea-bisulphite are shown in Table 12.They are the average of three replicates.

From the obtained results, it has firstly to be pointed out that the solu-bility in urea-bisulphite of the untreated fabric is low in excess, as theusual values for a scoured wool are higher than 45%. This behaviour isproduced when the wool has undergone an alkaline treatment, so it islikely that the fibre had already been damaged to a certain extent in thealkaline preparation treatments.


TABLE 11. Solubility in alkali

Fabric Solubility in alkali (%)

Untreated 15.5

Treated without enzyme 15.4

Treated with enzyme: Soft 15.5

Treated with enzyme: Medium 16.6

Treated with enzyme: Intense 17.1

TABLE 12. Solubility in urea-bisulphite

Fabric Solubility in urea-bisulphite (%)

Untreated 30.5

Treated without enzyme 25.5

Treated with enzyme: Soft 33.1

Treated with enzyme: Medium 38.5

Treated with enzyme: Intense 38.7

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The fabric treated without enzyme shows a considerable decrease ofits solubility in urea-bisulphite compared with the untreated fabric. Thedegradation initiated in the alkaline pre-treatments could have been in-tensified in the treatment without enzyme, which is carried out atalkaline pH.

The fabrics treated with enzymes present higher solubility in urea-bisulphite. This parameter increases when the intensity of the treatmentincreases. This fact suggests that the disulphide bond is not broken dueto the enzymatic treatment, and therefore the treatment does not nega-tively affect the fibre reticulation.

These results, together with the results obtained in the solubility in al-kali test, show that the attack produced on the fibre by the enzymatictreatment has mainly broken peptide bonds of the fibre, producing theshortening of the polymeric chain. In previous works (Cegarra et al.,1992) it was found that the enzymatic treatment with proteases causesan increase of the terminal amino groups, which means that the peptidebonds were broken. Thus, the enzymatic attack with the studied prote-ase has an effect on the length of the polypeptide chain, while the fibrereticulation degree is not affected by the treatment.

CONCLUSIONS

• The enzymatic treatment with the studied protease produces animprovement of the softness of the fabrics when the treatment iscarried out under the medium and intense treatment conditions.

• The fabrics treated with enzyme show better compressibility thanthe untreated fabrics. The effect is more notorious when the inten-sity of the treatment increases. The resilience, on the contrary, de-creases when the fabrics are treated with the enzyme.

• The enzymatic treatment produces a decrease of the flexural stiff-ness of the fabrics; that is, they promote a better drape. This im-provement is more outstanding when the intensity of the treatmentincreases.

• The bending properties are improved by the enzymatic treatmentunder the medium and intense conditions.

• The dimensional stability increases when the intensity of the enzy-matic treatment increases.

• The pilling resistance is also improved by the enzymatic treatment.The treatment under medium and intense conditions produces anexcellent pilling resistance.


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• The tensile strength values decrease notably with the increase ofthe enzymatic treatment intensity. The treatment under the me-dium and intense conditions produces an excessive loss of tensilestrength.

• The abrasion resistance decreases as well with the enzymatic treat-ment. The decrease is considerable on the fabrics treated under themedium and intense conditions.

• The solubility in alkali values of the fabrics treated with enzymeunder the medium and intense conditions is higher than the valuesof the untreated fabrics. This fact means that a shortening of thepolypeptide chains is produced.

• The solubility in urea-bisulphite is not decreased by the enzymatictreatment. On the contrary, it presents a slight increase. It meansthat the enzymatic treatment does not produce a breaking of thedisulphide bonds.

Summarising: the enzymatic treatment with the studied protease hasshown to be effective in improving the softness, handle and drape of thefabrics, as well as in increasing their dimensional stability and pillingresistance, when the treatment conditions are intense enough. However,under these treatment conditions a notorious attack to the fibre is pro-duced, which means excessive losses on mechanical properties such astensile strength and abrasion resistance.

REFERENCES

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Cavaco-Paulo, A., & Gübitz, G.M. (2003). Textile processing with enzymes. Cam-bridge: Woodhead Publishing Ltd.

Cegarra, J. (1999). Biotecnología aplicada a los procesos de química textil. Revista dela Industria Textil, 365, 52-69.

Cegarra, J., Pepió, M., Naik, A., & Riva, A. (2003). Modello di influenza delle proteasisulle proprietà fisiche di un tessuto petinato. Tinctoria, 100(12), 42-49.

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Heine, E., Hollfelder, B., Lorenz, W., Thomas, H., Wortmann, G., & Hoecker, H.(1998). Enzymes for wool modification. In Eriksson, K.E.L. & Cavaco-Paulo, A.


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KES-FB-2 Manual (1997) Kao tech & Co. Ltd., Kyoto, Japan.KES-FB-3 DC Manual (1997) Kao tech & Co. Ltd., Kyoto, Japan.Levene, R., Cohen, Y., & Barkai, D. (1996). Applying proteases to confer improved

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Riva, A., Cegarra, J., & Prieto, R. (1993). The role of an enzyme in reducing woolshrinkage. J.S.D.C., 109(5/6), 210-213.

Riva, A., Cegarra, J., Algaba, I., & Prieto, R. (2001). Wirkung der Enzymbehandlungauf gefärbte Wollgewebe. Melliand Textilberichte, 82(9), 726-729.

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enzymatic finishing of wool fabrics

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