Indian Journal of Textile ResearchVol. 2, March 1977, pp. 24-30

Scanning Electron Microscopic Study of WetProcessing of Cotton Fabrics

H. U. MEHTA, P. NEELAKANTAN & J. T. SPARROW.

Ahmedabad Textile Industry's Research Association, Ahmedabad 380015

.Received 18 March 1977 ; accepted 25 March 1977

A poplin fahric was desized and subsequently given different treatments using (i) solvent, (ii) caustic in a kierunder pressure, and (iii) sodium carbonate at atmospheric pressure in the laboratory. The desized sample and the threescoured samples were bleached by mild and severe processes using sodium hypochlorite. All the bleached samples weresubsequently mercerized conventionally in a mill. A scanning electron microscopic study of the above fabrics reveals thatincreasing severity of chemical processing conditions increases fibre damage. The fibre damage appears to be maximumwith the fabric processed under the following sequence: desized-kier boiled-severely bleached-mercerized. The damage wasminimum in the case of a desized.mild bleached-mercerized sequence. Surprisingly, the fibre damage is always restrictedto the warp crown fibres, while the rest of the warp and all the weft fibres appear undamaged under the severest conditionsemployed. The physical properties of the fabric were measured at different stages. Tear strength and flex abrasioncycles decrease considerably with the processing steps, but the tensiie strength does not change significantly. A comparisonof the deterioration in properties suggests that solvent scourlhg and kier boiling operations are more drastic than an opensoda boil, which is obviously more severc than desizing alone.

E ARLIER studies1'2 had shown that severe condi- Using the above treatments, we were able totions of caustic scouring affect the tear strength, investigate the extent of fibre damage to varyingflex abrasion resistance and toughness of a fabric. degree ranging from the mildest treatment, i. e. simply

It can be safely assumed that these changes in physical a desized fabric, to a very severe treatment, viz. aproperties are due to (i) degradation of fibre structure desized, pressure caustic boiled, severely bleached,by chemical action, (ii) mechanical damage to the fibre mercerized fabric.structure before and during the processing treatments,and (iii) a combination of chemical and mechanical Experimental Proceduredamage. A Cambridge Stereoscan S4-] 0 scanning electron

The scanning electron microscope (SEM) offers microscope was used in conjunction with an AEIan easy means of assessing fibre damage, when the vacuum coating unit. The specimens to be examineddamage occurs in the form of changes in the surface in the SEM must be able to withstand the effect ofof individual fibres. With the SEM, fabric samples vacuum and be able to conduct electricity. Cottonare inserted into the instrument and using the wide fabrics are nonconductors of electricity and, therefore,range of magnifications available one is able to view they must be made conductive by the depositiona large area of the fabric at low magnification and through evaporation of a very thin (20-40 p) layerthen examine selected areas at increasing magnification of silver or gold onto the surface of the specimen.until surface detail of a single fibre can be seen. Before coating the fabric samples with metal, they

A systematic study has been undertaken using the are mounted on the SEM mounts using a doubleSEM to determine the extent of fibre damage result- sided adhesive tape and conducting cement. Theing from the effect of various wet processing treat- metal is deposited on the specimen surface in a vacuumments. The results of this SEM investigation and coating unit by thermal evaporation.the physical properties of the fabric are presented in Examination in the SEM is carried out whilethis communication. operating the instrument at 5kV accelerating

The three most common wet processing treatments potential.are scouring, bleaching and mercerization. In this Desizing-A loom-stage grey fabric was desizedstudy, we have examined a fabric without any with a commercial enzyme 0.2 % and salt 2 gpl atscouring treatment, as well as fabrics with all I: 50 ml ratio. Temperature was maintained atcombinations of the above mentioned processes in 50-600 for 2 hr. The fabric was washed, soaped atvarying degrees of severity. Three scouring treat- 85-900 for 45 min with 2 gpl soap and 5 gpl sodaments were used: (i) solvent, (ii) caustic pressure boil, rinsed with hot water, and then with cold water, dried:and (iii) open soda boil. Two bleaching treatments, cut into four pieces and conditioned.mild and severe, were also carried out. The con- Scouring-The desized fabric was extracted withventional mercerization treatment was given. carbon tetrachloride for 6 hr and then with ethyl

alcohol-benzene (40: 60) mixture for 5 hr. Subse-~ .United Nations' Technical Assistance Expert. quently, the fabric was rinsed with ethyl alcohol and

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MEHTA et aI, : SCANNING ELECfRON MICROSCOPIC STUDY OF WET PROCESSING OF COTTON FABRICS

water,and dried. No additives were used in solvent crumpled or pressed.scourIng, Open soda boil-As is observed in the case of

Caustic pressu!e boil-The desiz.ed fabric (about solvent scouring, the fibres appear mostly clean and1.5 kg) was piled 10 a laboratory kler. The liquor undamaged.containing. 4.0 % NaOH, 0,5 % sodium silicate and Pressil~e ca'!stic boil-:-Fig. 4 shows a warp crown0.5% wetting agent (all percentages are based on the of a caustIc boIled fabrIc. It is seen that any adher-weight of fab~ic) was added. The lid was secured, ing material has been totally removed and some ofwater flushed 10 and the contents were boiled at the fibres show small fibrils raised up from their120-1250 under 40 Ib pressure for 5 hr. Then the surfaces. These small fibrils can be considered toliquor was drained out, the fabric washed with hot be the beginnings of fibre damage, even though totalwate~ and then with cold water until free from fibre breakdown has not begun to occur. All thealkali. weft yarn fibres appear clean with virtually no sign

Open soda boil-The desized fabric was boiled in of damage on the surfaces.an open stainless steel vessel using 5 % sodium carbo- BI h.t d 0 5% ' Th '. cac Ingna e an .0 wettIng agent. e materIal to liquorrati<? was I : 6 a~d the time of boiling, 8 hr. The Mild--:In th~ case ?f desized mild bleached fabric,fabrIc was then rInsed free from alkali. the adhe.rI~g resIdual SIze or other material appears

Bleaching-Commercial sodium hypochlorite part~y dlstmtegrated, but not totally removed. Othersol~tion, 'Cali.Chlor' wa~ used after estimating the portions of warp and a;" weft :>:arn fibres appearavaIlable ch~orme. For ~Ild bleachIng, 1.0% chlorine clean and. undamaged. MIld bleachIng of the scouredon the weIght of fabrIc was used and the reaction samples dId not cause any further damage.was continued until more than 90% of it was con- ,Severe-,Fig. 5 shows that severe bleaching of asu~ed. For s.evere bleaching, 2.0% chlorine on the deslze~ fabrIc removes practically the entire adheringweIght of fabrIc was used. The liquor to material materIal.. Warp crown fibres show signs of damageratio was maintained at 50: 1, and the bleaching and e.roslon to some extent. A trend of increasingsolution strength was varied (0.2 gp1 and 0.4 gpl for seve~Ity of damage is observed in solvent scouredmild and severe bleaching respectively). fabr~cs, s<?da boiled fabrics and pressure boiled

Merct;"rization-This was carried out conventionally fabrIcs WhICh have subsequently been given a severeon a chamles.s-padless machine in a local mill using bleach tr~atment. .In th.e solvent scoured fabric and540 Tw caustmg soda solution. soda boIled fabrIc which have had a severe bleach,

damag:e occurs o~ly on the primary wall (Fig. 6), butResults and Discussion ~he prImary Wa;llIS removed and the secondary wall

IS seen on fabrIcs which have had a pressure boil andSEM Studies severe bleach (Figs. 7 and 8).

Fig. I is a scanning electron micrograph of a M . t.d . d f b . k I .fi .,ercerlZa IoneSlze a rIC ta cn at ow magm catIon. The fabrIc ' .,structure is clearly seen. The large depth of focus of MerCerIZatlon fur.ther I~creases the dan;tagethe SEM enables the whole of the warp and weft observed after bleachIng:. FIg. ~ shows a deslzed,yarns to be in focus. Fig. 2 illustrates the appearance seve~ely bleached, t;nercerlzed fa;brIc at a warp crown.of only the crown of a warp yarn. In FIg. 10. the primary wall IS seen. to be partly

The fibres of the warp yarn show deposits of ~emoved and small secondary wall.fibrI,ls are protrud-material over them, The material extends over the mg from the fibre surface. There IS mInor damage toadjoining fibres as if to bond them together. It was the secondary wall.observed that no such deposits are present on weft Slight damage occurs to the primary wall of ayarns, but that the deposits are present only on solvent scoured severely bleached, mercerized fabriccertain warp crowns. Warp crowns on both the at the :-varp crowns (Fig. II). Mercerization of asurfaces of the fabric show such deposits. soda boIled, severely bleached fabric increases the

A sim.ple iodine staining test was carried out on damage at.th~ wa;rp crowns. Loose fibrils begin tothe fabrIc. Only the warp yarns stained the appear, IndIcatIng breakdown of the primarycharacteristic blue colour which is given by iodine wall.in the presence of starch. It can, therefore, be Mercerization of a pressure boiled, severelyinferred that the deposits seen in Fig. 2 are most likely bleached f~bric causes extensive damage at the warpof starch size. However, other impurities, such as crowns (FIgS. 12 and 13). Large amounts of primarywaxes, pectins, etc. could also be present. wall are removed and breakdown of the secondary

The warp yarn 'also appears to be smudged or wall. ~egins to occur. Even under these severeheavily pressed at the crown region (Figs. 1 and 2). co~dltlons, the weft shows no sign of damage

(FIg. 14)Scouring A . I '. .

..scannIng e ectron mIcroscopIC study of varIOUS.Solven!-~ warp crown of a sol,vent scoured fabric fabrIcs reveals that as the severity of chemicalIS shown m FIg. 3. Solvent ~courmg ?as s~rprisingly process~ng conditions increases, fibre damage increasesremoved almost all the deposIts seen m FIg. 3 from at localIzed areas of the fabric, namely the warpthe warp crowns. Warp and weft appear mostly crowns, Fibre damage is almost always located onlyclean, although. th~r~ is no great degree of damage to at the surface Ii bres of warp crowns. The rest of thethe surfaces of IndIVIdual fibres at the warp crown. warp fibres and all the weft fibres show little or noSome of the fibres at the warp crowns appear sign of damage. At the desized stage, some residual

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INDIAN J. TEXT. RES., VOL. 2, MARCH 1977

Fig. 1 - Desized fabric at low magnification showing thewarp and weft yarns (x 100)

Fig. 2 - Desized fabric showing deposits on the warp crown( x 500)

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Fig. 3 - Warp crown of a solvent scoured fabric (x 500)

Fig. 4 - Warp crown of a severely scoured fabric showingfibrillation (x 500)

MEHTA et at. SCANNING ELECTRON MICROSCOPIC STUDY OF WET PROCESSING OF COTTQN FABRICS

Fig. 5 - Warp crown of a desized severely bleached fabricshowing erosion of the primary wall (x 550)

Fig. 6 - Primary wall removal at the warp crown of a solventscoured severely bleached fabric (x 2400)

Fig. 7 -Severely scoured severely bleached fabric showingextensive fibrillation at warp crown (x 900)

Fig. 8 - The fabric in Fig. 7 at the higher magnincationshowing the secondary wall of a single note (x 4500)

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INDIAN J. TEXT. RES., VOL. 2, MARCH 1977

Fig. 9 - Warp crown of a desized, severely bleached andmercerized fabric (x 550)

Fig. 10 - The fabric in Fig. 9 illustrating the removal ofprimary wall (x 2100)

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Fig. J I-A solvent scoured, severely bleached and mercerizedfabric [only minor damage is seen] (x 440)

Fig. 12 - A severely scoured, severely bleached and mercerizedfabric showing extensive damage at a warp crown (x 500)

MEHTA et at. : SCANNING ELECTRON MICROSCOPIC STUDY OF WET PROCESSING OF COTTON FABRICS

Fig. 13 - The fabric in Fig. 12 showing breakdown of thesecondary wall (x 2400)

sizing material appears to be adhering to the warpyarns, which is subsequently removed during scouringor bleaching. Solvent scouring appears least harmfulin comparison with open soda boiling and pressureboiling. Pressure boiling with caustic is the severestoperation which distinctly causes damage to fibresurfaces. Severity of bleaching also affects fibres, butto a smaller extent, while mercerization increasesdamage to the maximum extent. A pressure boiled,severely bleached and mercerized fabric showsdistinctly the secondary walls of warp crown fibres atseveral places.

It is interesting to note that weft yarns are almostalways clean and undamaged even after treatmentunder the severest of conditions. This is illustratedin Fig. 14 which shows the weft yarn of a desized,pressure boiled, severely bleached and mercerizedfabric. The fibres of the yarn are clean and relativelyundamaged. Wherever changes in the fibresurface are observed, they are always at the warpcrowns.

It is difficult to prove or conclude at this stagehow only fibres at the warp crowns form the site ofdamage. However, it can be seen from the variousphotomicrographs presented here that increasingseverity of conditions of chemical processing increasesthe chances of observable damages to the warp crownfibres. Whether the observed damages find theirorigin inherently in the chemical processing or in theprehistory of the fabric during its mechanical proces-sing is yet to be established. If it were only due to

•f

Fig. 14 - The fabric in Fig. 12 showing no damage tofibres in the weft yarn (x 550)

chemicals and severity of conditions of chemicaltreatments, damage would have been expected onwarp and weft to the same extent with no choice ofposition of damage like warp crowns. Apparently,therefore, warp crowns seem to have suffered stressesor damages during the pre-wet processing stages andchemical treatments accentuate the damages, depend-ing on the degree of damage and severity of conditionsof processing. This is the probable explanation fordamage at the warp crowns. Since they are protrudingmore above the fabric surface, they are more proneto any kind of abrasion or mechanical action.

A further study will be undertaken to determinethe reasons for damage to occur only at the warpcrowns.

Physical Properties at Various Stages of ChemicalProcessing

After each stage of chem ical processing, the physicalproperties of the fabrics were determined. Theresults are given in Table 1. The fabrics are groupedaccording to the initial scouring treatment given, i. e.no scour, solvent scour, kier boiled and soda boiled.Within each group, the fabrics are listed according towhat is believed to be increasing severity of chemicaltreatment. By examining the physical properties ofthe fabrics in each group, one can see that there isno significant change in the properties of the fabricwithin a group after the initial scouring treatment.It can be inferred that after the initial scouringtreatment, mild or severe bleaching and mild or severe

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INDIAN J. TEXT. RES., YOLo 2, MARCH 1977

TABLE 1 -EFFECT OF PROCESSING CoNDITIONS ON PHYSICAL PROPERTIES OF COTTON FABRIC (39s/39s/120/72)

Flex abras- Tear strength, Tensile strength, Wax, % FluidityNo. Sequence of DCRA WCRA sion cycles g kg Rhes

processing (W + F) (W + F) Warp Weft Warp Weft Warp Weft

A Desized 190 117 5400 3300 1200 1100 30.4 27.1 0.56 -A-I Mild Bleached 157 109 4800 3400 1200 1100 29.5 26.8 --

Mercerized 172 158 4300 2550 1200 1150 32.1 27.7 -4.1

A-2 Severe Bleached 176 111 3300 3450 1150 1200 26.5 27.4 --

Mercerized 183 160 4550 2850 1200 1050 31.2 28.8 -4.4

AB Solvent scoured 153 141 500 550 700 700 31.5 30.2 0.08 -AB-l Mild bleached 156 125 400 500 750 750 28.5 30.6 --

Mercerized 172 161 500 500 850 650 30.7 28.8 ~ 3.7

AB-2 Severe bleached 162 130 450 550 800 750 29.8 29.8 --Mercerized 171 162 450 650 700 650 31.3 26.1 -4.~

AC Kierboiled 144 129 1300 1600 1050 1150 26.3 26.7 0.44 -AC-l Mild bleached 161 125 650 1000 850 800 28.9 29.5 --

Mercerized 187 163 1450 1100 900 850 30.4 26.3 -3.9

AC-2 Severe bleached 158 119 900 1150 950 850 28.2 26.7 --Mercerized 193 162 1450 1600 1050 1050 30.5 24.0 -4.5

AD Soda boiled 172 123 2000 2000 1100 950 27.3 26.3 0.47 -AD-l Mild bleached 164 123 1350 750 950 850 28.2 26.0 --

Mercerized 183 160 1100 750 1100 1050 31.5 25.6 --' 3.7

AD-2 S~vere bleached 165 133 1400 1500 1100 1000 28.3 27.9 --Mercerized 187 158 1150 1100 1050 1050 32.8 21.1 -4.5

bleaching followed by metcerization does not change treatments accentuate the damage by exposing orthe properties to a great extent. There are of course removing primary or secondary wall layers at theminor changes in the properties, but these will not be warp crown in the fabric. It should be noted thatdiscussed here. only a very small percentage of the fibres in the warp

Examination of the fabrics in the SEM has shown crown show damage. It is assumed that the changethat the fabric which has been damaged the most is in wax content observed for the soda boiled and kierthat which has had a kier boil, severe bleach and boiled fabrics is partly due to the removal of wax atmercerization treatment, while the least damaged the damaged warp crown sites.fabrics are those which have had no scour or aninitial solvent scour. From Table 1 it is evident that Acknowledgementa solve~t proce.ss has.t!te most detrime~t.al effect on the The authors' thanks are due to Dr J. J. Willard,propertl~s. Kler.bolling and soda boiling treatments U. N. Consultant for the U. N~ D. P. Project, Dr

have an intermediate effect. ..N. E. Dweltz, Head, Group of Physics and Shri S. S.AI~ost comI?lete extraction of lubricants and Trivedi, Head, Chemical Technology Division for

cementing materials fro.m the surface layers of .cot~on their suggestions and interest in the progress of thisfibres by solvent scour~ng can. affect pro~ert.les like work. They acknowledge with thanks the helptear strength and abraslo~ res~stance. This IS con- extended by Shri V. K. Bortalavwala, Miss Bhanufirme~ by. the data given In Table 1. The flex Shingala and Shri R. S. Chauhan in the preparationabrasion resls~ance and tear strength for the solve~t of various fabric samples. They would also like to ex-scoured fabrics are seen to have dropped drastl- press their appreciation to the United Nations Deve-

cally. lopment Program for permitting the purchase of theThe effects. of .severe conditions of kler boIling are scanning electron microscope and vacuum coating

to re.duce ~h.e InItial crease recovery, to extract w~es unit under UNDP Project INDj72jO35, "Improve-an~ Impuntles, to red~ce tear stre~gth and abrasion ment of Textile Process and Product Developmentresls~anc.e of the f~brlc and t? dIssolve or to create Facilities at A TIRA ".crevices In the cutIcle and primary wall of cotton

fibres4. Under milder conditions of scouring, thefabric is seen to retain the initial crease recovery, tear References

strength and abrasion resistance, which subsequently 1. MEHTA, H. U., GUPTA, K. C. & BHATT, V. R., Creasehave favourable effects on resin finishingl-3. recovery of untreated and resisn treated cotton fabrics,

Kier boiling and soda boiling etch the surface ATIRA Research Note No. CT/67, March 1975.

fibres, as seen in the scanning electron microscope, 2. MEHTA, H. U., GUPTA, K. C; & BHATT, ,:. R., Crease

b t th t tments do not affect theP ro p erties of recovery .of untreated and resin treated fabrics-Effect of

u es~ rea ..construction and weave, A TIRA Research Note No.

the fabnc as much as solvent extraction. Scouring, CT/73, November 1975.bleach~ng and merc.erization, particul.arly the last 3. MEHTA, H. U., GUPTA, K. C. & BHATT, V. R., Text. Res.Operation, are considered more drastic for fibres J., 44 (1976), 356.which have had a prehistory of surface damage 4. PETERS, R. H., Textile chemistry, Vol. II (Elsevier Publish-caused by mechanical means. The above three ing Co., London), 1967, Ch. 9, 164-186.

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