Structural Change in Mercerized Cotton Fibers on CellulaseTreatment

T. HAGA,1 T. TAKAGISHI2

1 Faculty of Education, Hirosaki University, Bunkyocho, Hirosaki, Aomori 036-8560, Japan

2 College of Engineering, University of Osaka Prefecture, Gakuencho, Sakai, Osaka, 599-8231, Japan

Received 1 March 2000; accepted 28 July 2000Published online 16 March 2001

ABSTRACT: Cotton fibers treated with liquid ammonia and sodium hydroxide werehydrolyzed with crude cellulase. The structural change in the fibers due to the cellulasetreatment was examined in relation to the apparent affinity of Congo Red. The celluloseIII crystalline structure collapsed and generated intermediate-molecular-ordered re-gions on cellulase treatment. Adsorption of Congo Red occurred on the crystallitesurfaces of cellulose II and cellulose III that was transformed from cellulose II. Thefiber, the dominant crystallite phase of which was cellulose III that was transformedfrom cellulose II, had a considerably increased apparent affinity after cellulase treat-ment. The intermediate structure on the crystallite surface was associated with theadsorption of Congo Red in the cases of cellulose II and cellulose III. © 2001 John Wiley& Sons, Inc. J Appl Polym Sci 80: 1675–1680, 2001

Key words: cotton fiber; cellulase; hydrolysis; crystallinity; crystallite; affinity ofCongo Red; intermediate-molecular-ordered region

INTRODUCTION

Liquid ammonia (ammonia) treatment rendershigh resilience and good shape retention in cottonfabrics,1 whereas sodium hydroxide treatmentprovides cotton fabrics with a deep shade and agood luster. On the other hand, cellulase treat-ment is markedly effective for improving the me-chanical and aesthetic properties of cellulose fab-rics. Therefore, the combination of cellulase andalkaline treatments is promising for improvingthe performance of cotton fabrics.

We reported that crystalline regions of cottonfibers, which were mercerized with ammonia andsodium hydroxide, were hydrolyzed by cellulase

treatment in the first step of hydrolysis.2 We alsoelucidated that water sorption was closely relatedto the surface of the crystallites, irrespective ofthe fiber species treated with cellulase.2

It is well known that the crystalline structureof cellulose I is transformed to those of celluloseIII1 and cellulose II3 by ammonia and sodiumhydroxide treatments, respectively. The struc-tural transformation of cellulose III to cellulose Iand that to cellulose II by respective treatmentswith hot water and sodium hydroxide were veryeffective in improving the softness of cotton fab-rics.4 We studied the structural changes in themercerized cotton fibers caused by cellulase treat-ment, using infrared spectroscopy, X-ray diffrac-tion, and a method involving the apparent affinityof Congo Red.

The extent of the ordered regions evaluated byinfrared spectroscopy has a better correlation

Correspondence to: T. Haga.Journal of Applied Polymer Science, Vol. 80, 1675–1680 (2001)© 2001 John Wiley & Sons, Inc.

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with the accessibility obtained by water sorptionthan with the crystallinity evaluated by the X-raymethod.5 The accessibility obtained by watersorption corresponds to the number of hydroxidegroups, which are sufficiently free from neighbor-ing molecules.5 The criterion of fine structure forthe accessibility evaluated by water sorption andthe ordered regions evaluated by infrared mea-surement is at the molecular level or short-dis-tance order rather than at the level of larger unitsof the crystallites in the X-ray method.5

The dyeing of Congo Red occurs in disorderedregions which have enough space to adsorb largemolecules of the dye. The adsorption of direct dyessuch as Congo Red requires planar and linearconfigurations of cellulose molecules in order forthe dye molecule to be proximate to the polymerchain.6 This suggests that the structure of theshort-distance order detected by infrared adsorp-tion is an effective dyeing site of Congo Red.

The structure of short-distance order, detectedas crystalline regions by infrared measurement,5

is divided into two regions: One exists outside ofwell-grown crystallites and has an intermediate-molecular-ordered structure. The other is in-cluded in well-grown crystallites detected by theX-ray method. The intermediate-molecular-or-dered structure outside the crystallites is an im-portant subject in the study dealing with thestructural changes in cotton fibers caused by cel-lulase treatment.

The amount of bound water, which was esti-mated from the exotherm peak of different scan-ning calorimetry, was decreased by cellulasetreatment.7 The cellulase-treated cuprammo-nium rayon fiber increased the peak temperatureof tan d,8 based on the segmental movement of thecellulase chain in disordered regions. The inter-mediate-molecular-ordered structure plays a rolein reducing the amount of bound water, which isa measure of the accessibility, and in increasingthe peak temperature of tan d to restrict themovement of the cellulose chain.

We also focused our attention on the influenceof the sequence of combined treatment, whichconsists of ammonia (sodium hydroxide) treat-ment and subsequent sodium hydroxide (ammo-nia) treatment. We observed that the subsequenttreatment had a marked effect on the final fiberformation, even though the crystallinity and af-finity of Congo Red are dependent on the firsttreatment.

EXPERIMENTAL

Materials

The cotton fibers were purified in the same man-ner described in our previous article.2 The fiber(original 1 fiber) was dipped in liquid ammonia for2 s, then squeezed and dried for 10 s at 130°C ina hot drum. It was then steamed for 1 min tocompletely eliminate ammonia.2 The original 1fiber was treated with an 18% sodium hydroxidesolution at 20°C for 10 min and then rinsed thor-oughly in water. Mercerization treatment wasperformed in the relaxed state. The unprocessedfiber described in our previous article9 was alsoexamined (original 2 fiber).

The crude cellulase (Meiselase) used waskindly offered by Meiji Seika Ltd. (Tokyo, Japan);it is from Trichoderna viride. The carboxymeth-ylcellulase activity of the cellulase was 233,000units/g, determined in the same manner as thatin our previous article.10 One unit of carboxym-ethylcellulase was defined as the amount of en-zyme which liberates 10 mg glucose equivalentsper 10 min.

Cellulase Treatment

The fibers were treated with an enzyme concen-tration of 0.2% (w/v) at 40°C and pH 4.5. Theliquor-to-sample ratio was 1:100. The treatmentsolution containing the substrate was inactivatedby immersing it in boiling water after the treat-ment. Weight-loss values were obtained by com-paring fabric weights before and after treatment.

X-ray Diffraction Measurement

The crystallinity and the crystallite size weremeasured using an X-ray diffractometer (SRAM18XHF; MAC Science Co.) under the same con-ditions as those in our previous article.2 Crystal-linity was defined as the ratio of the integratedcrystallite scattering intensity to the total scat-tering intensity ranging from 10 to 26°. The dom-inant crystalline phase of the ammonia-treatedfiber and the sodium hydroxide- and subsequentlyammonia-treated fibers is cellulose III, whereasthat of the sodium-hydroxide-treated fiber andthe ammonia- and, subsequently, sodium hydrox-ide-treated fiber is cellulose II, as described pre-viously.2 It was confirmed that the crystallinephase of the original fiber is cellulose I.

1676 HAGA AND TAKAGISHI

Dyeing Method

The fibers were dyed to equilibrium with CongoRed at 80°C. Other dyeing conditions were de-scribed previously.10 The apparent affinity (affin-ity) of Congo Red to cotton fibers was calculated inthe same manner described previously,10 basedon the assumption that the effective volume termfor the dyeing of cotton fiber is 0.22 L/kg. Thechange in the apparent affinity calculated reflectsthe change in the amount of the inner surface ofthe fibers in which dye adsorption takes place.

Measurement of Infrared Spectrophotometry

The adsorptivity ratio of 1372–2900 cm21 wasobtained as the crystallinity index,5 using an in-frared (IR) spectrophotometer (FTS-30, Bio-RadCo.). Measurement was performed by means of adiffuse reflection method11 using a mixture of cutfiber segments and potassium bromide. The ab-sorptivity ratio was estimated according to theliterature.5

RESULTS AND DISCUSSION

Collapse of Crystallites

The relationship of the crystallinity index to theweight loss of the fibers examined is shown in

Figure 1. The crystallinity index of the original 2fiber first increased, reached a maximum, andthen decreased with an increasing weight loss.The crystallinity index of the ammonia-treatedfiber and the sodium hydroxide- and subsequentlyammonia-treated fiber first increased and thenreached a maximum in a manner similar to thatshown by the original 2 fiber with an increasingweight loss. The amount of the increase of thesodium hydroxide- and subsequently ammonia-treated fiber was greater than that of the ammo-nia-treated fiber. In contrast, the crystallinityindex of the sodium hydroxide-treated and theammonia- and subsequently sodium hydroxide-treated fibers first decreased, reached a mini-mum, and then increased with an increasing weightloss.

The crystallinity index versus crystallinity plotsfor the fibers treated with cellulase are shown inFigure 2. The crystallinity index increased withdecreasing crystallinity for the ammonia-treatedfiber and the sodium hydroxide- and subsequentlyammonia-treated fiber. Cellulase treatment gen-erally decreased the crystallinity and increasedthe crystallinity index of these fibers.

It was found that cellulase treatment of theammonia-treated fiber and the sodium hydroxide-

Figure 1 Change in crystallinity index with increas-ing weight loss for mercerized fibers after cellulasetreatment. The reagents indicated were used for mer-cerization treatment.

Figure 2 Relationship between crystallinity indexand crystallinity for fibers mercerized using the re-agents indicated. The encircled plots correspond to fi-bers which were not treated with cellulase. A straightline of the original fibers was obtained based on all dataof the two original fibers.

COTTON FIBER STRUCTURAL CHANGE WITH CELLULASE 1677

and subsequently ammonia-treated fiber causedthe cellulose III crystalline structure to collapse,such that the extent of the intermediate-molecu-lar-ordered structure outside the crystallites wasincreased, which was detected as an increase ofthe crystallinity index. The initial increase of thecrystallinity index with weight loss shown in Fig-ure 1 was caused by the collapse of crystallineregions in both the ammonia-treated fiber and thesodium hydroxide- and subsequently ammonia-treated fiber.

The negative slope of the crystallinity indexversus the crystallinity of the ammonia-treatedfiber was smaller than that of the sodium hydrox-ide- and subsequently ammonia-treated fiber.This indicated that the amount of transformationof the well-ordered structure to the intermediate-molecular-ordered structure was greater for thesodium hydroxide- and subsequently ammonia-treated fiber than for the ammonia-treated fiber.

The sodium hydroxide-treated fiber and theammonia- and subsequently sodium hydroxide-treated fiber exhibited a decrease in both the crys-tallinity index and the crystallinity during cellu-lase treatment. This trend suggested that thecrystallites of these fibers were hydrolyzed withno collapse during cellulase treatment. The posi-tive slope of the crystallinity index versus thecrystallinity of the ammonia- and subsequentlysodium hydroxide-treated fiber was almost thesame as that of the sodium hydroxide-treated fi-ber. It was found that the cellulose II crystallinestructure formed from cellulose III was hydro-lyzed in a manner similar to that of cellulose IIformed from cellulose I.

Cellulase treatment of the original fibers in-creased both the crystallinity and the crystallin-ity index. This is because the hydrolysis occurredonly in the disordered regions, as indicated by theinitial increase in crystallinity. It was assumedthat the initial increase in the crystallinity indexwas not caused by the collapse of the crystallineregions, but was due to the increase in the pro-portion of the crystalline regions, compared to thedisordered regions for the original fibers. Thiswas consistent with the assumption that the cel-lulose I structure is more stable under cellulasetreatment than are the cellulose II and III struc-tures.2

Affinity of Congo Red

The affinity of Congo Red was plotted against theweight loss of the cellulase-treated fibers and

compared with the original fibers in Figure 3. Theaffinity of the dye for the original fibers decreasedwith increasing weight loss because of the de-crease in the extent of disordered regions. In ad-dition, the affinity of the dye for the mercerizedfibers decreased with increasing weight loss, ex-cept for the sodium hydroxide- and subsequentlyammonia-treated fibers, for which the affinity ofthe dye increased on cellulase treatment.

The relationship between the affinity of the dyeand the crystallinity index is shown in Figure 4.The affinity of the dye for the original fibers ex-hibited a tendency to decrease with an increasingcrystallinity index. This was due to the increasein the proportion of crystalline regions comparedwith disordered regions.

In contrast, the affinity of the dye increasedwith an increasing crystallinity index for all alka-li-treated fibers. Concretely, the sodium hydrox-ide-treated and the ammonia- and subsequentlysodium hydroxide-treated fibers decreased inboth the affinity of the dye and the crystallinityindex after cellulase treatment, in contrast withthe decrease in the extent of crystalline regions,as shown in Figure 2. The cellulase treatmentclearly increased both the affinity of the dye andthe crystallinity index of the sodium hydroxide-and subsequently ammonia-treated fiber.

It was concluded that the adsorption of the dyein the mercerized fibers was closely related to

Figure 3 Affinity of Congo Red with increasingweight loss of fibers mercerized using the reagentsindicated.

1678 HAGA AND TAKAGISHI

intermediate-molecular-ordered regions on thecrystallite surface. This is because Congo Red waspreferably adsorbed in planar and linear configu-rations of cellulose molecules related to the crys-tallinity index on the crystallite surface.

It was reported that the sodium hydroxide- andsubsequently ammonia-treated fiber was muchmore effective for achieving a soft fabric handcompared with the ammonia-treated fiber.12 Thecellulose III crystallite surface of the sodium hy-droxide- and subsequently ammonia-treated fiberwas easily changed into intermediate-molecular-ordered regions on cellulase treatment. The sur-face regions of cellulose III may have a possiblerole in the improvement of the fabric softnessmentioned above.

The relationship between the affinity of CongoRed and the crystallite size is shown in Figure 5.Because dye adsorption took place in the disor-dered regions and the crystalline regions are notdirectly related to the adsorption of Congo Red inthe original fibers, the data for the original fibersare not shown in this figure.

Small crystallites are thermodynamically un-stable and it is thought that their surfaces easilyadsorb dye molecules. The mercerized fibers, ex-cept for the ammonia-treated fiber, exhibited a

decrease in the affinity with increasing crystallitesize, as shown in Figure 5. This trend is reason-able and indicates the occurrence of dye adsorp-tion on the crystallite surfaces in these fibers.

Slopes of the affinity of Congo Red plottedagainst the crystallite size for mercerized fibersare shown in Table I. The slopes of water sorptionplotted against the crystallite size for mercerizedfibers were calculated based on our previouslyreported results2 and are also shown in Table I. Itwas clear that the dye adsorption of the sodiumhydroxide- and subsequently ammonia-treated fi-

Figure 4 Affinity of Congo Red against crystallinityindex of fibers mercerized using the reagents indicated.Encircled plots correspond to fibers which were nottreated with cellulase. A straight line of the originalfibers was obtained based on all data of the two originalfibers.

Figure 5 Change in affinity of Congo Red with crys-tallite size due to cellulase treatment for fibers mercer-ized using the reagents indicated.

Table I Regression Coefficients of the LinearRelationship of Affinity of Congo Redand Water Sorption to Crystallite Sizefor Mercerized Cotton Fibers

Fibers

Regression Coefficient

Affinity ofCongo Red

WaterSorption

Ammonia 0.011 0.083Sodium hydroxide 20.063 21.063Sodium hydroxide and then

ammonia 20.421 1.301Ammonia and then sodium

hydroxide 20.057 20.227

COTTON FIBER STRUCTURAL CHANGE WITH CELLULASE 1679

ber exhibited a decrease with increasing crystal-lite size. This trend of dye adsorption was differ-ent from that of water sorption, which increasedwith increasing crystallite size.2 The contradic-tion is because the molecular size of Congo Red ismuch larger than that of a water molecule. It wasassumed that the surfaces of large crystallites ofcellulose III, which were formed from cellulose IIand treated with cellulase, were finely split andeasily penetrated by water molecules but not byCongo Red molecules. This trend was probablygreater with larger crystallites.

The dependence of dye adsorption on the crys-tallite size of the ammonia-treated fiber wasweak, similar to water sorption,2 compared withthe other mercerized fibers, as shown in Table I.The extent of disordered regions was thought tocontribute considerably to dye adsorption and wa-ter sorption for the ammonia-treated fiber.

CONCLUSIONS

Four mercerized cotton fibers were treated withcrude cellulase. The cellulose III crystalline struc-ture progressively collapsed and generated inter-mediate-molecular-ordered regions. This trendwas considerable for cellulose III transformedfrom cellulose II. Cellulose II crystallites werehydrolyzed with no collapse of the crystallinestructure. Adsorption of Congo Red occurred onthe crystallite surfaces of cellulose II and cellu-lose III transformed from cellulose II, while thecrystalline regions of the original fiber were un-

related to dye adsorption. The extent of the inter-mediate-molecular-ordered structure on the crys-tallite surface was closely related to the amountof Congo Red adsorption for all mercerized fibers.

The authors express deep thanks to Prof. T. Wakida ofGifu Woman’s College and Prof. R. Mori of HirosakiUniversity for providing helpful suggestions and con-venience.

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