http://trj.sagepub.com/Textile Research Journal

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 DOI: 10.1177/004051758405400405

1984 54: 242Textile Research JournalWilton R. Goynes, Jarrell H. Carra and Ralph J. Berni

Changes in Cotton Fiber Surfaces Due to Washing  

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lifetime of the filter cloth may be limited to ^-1 yearat these high filtration velocities.

ACKNOWLEDGMENTS

We wish to acknowledge the assistance given in thisproject by G. H. Michell and Sons Pty. Ltd., Adelaide,Australia. We are particularly grateful for the help givenby Mr. Richard Lee and his staff during the runningof the experiments.

Literature Cited

1. Boucher, D. F., and Alves, G. E., Fluid and ParticleMechanics, in "Chemical Engineers Handbook," 4thed. R. H. Perry and C. H. Chilton, Eds., McGraw Hill,New York, 1963, pp. 5-11.

2. Dennis, R., and Klemm, H. A., Modelling Concepts forPulse Jet Filtration, J. Air Pollut. Control Assoc. 30, 38-43 (1980).

3. Dennis, R., Wilder, J. E., and Harman, D. L., PredictingPressure Loss for Pulse Jet Filters, J. Air Pollut. ControlAssoc. 31, 987-992 (1981).

4. Ellenbecker, M. J., Pressure Drop in a Pulse Jet Fabric

Filter, Doctoral thesis, Harvard School of Public Health,1979.

5. Ellenbecker, M. J., and Leith, D., The Effect of DustRetention on Pressure Drop in a High Velocity Pulse-Jet Filter, Powder Technol. 25, 147-1.54 (1980).

6. Humphries, W., Influences of Cloth Structure on DustDislodgement from Fabric Filters, Powder Technol. 28,189-194 (1981).

7. Leith, D., Ellenbecker, M. J., First, M. W., Price, J. M.,Martin, A., and Gibson, D. G., Performance of a HighVelocity Pulse Jet Filter II, Environmental ProtectionAgency, Report EPA-600/7-80-042, 1980.

8. Leith, D., and First, M. W., Performance of a Pulse-JetFilter at High Filtration Velocity, I: Particle Collection,J. Air Pollut. Control Assoc. 27, 534-539 (1977).

9. Leith, D., and First, M. W., Performance of a Pulse-JetFilter at High Filtration Velocity, III: Penetration byFault Processes, J. Air Pollut. Control Assoc. 27, 754-758 (1977).

10. Leith, D., First, M. W., and Feldman, H., Performanceof a Pulse-Jet Filter at High Filtration Velocity, II: FilterCake Redeposition, J. Air Pollut. Control Assoc. 27, 636-642 (1977).

Manuscript received April 4. 1983; accepted June 10, 1983.

Changes in Cotton Fiber Surfaces Due to WashingWILTON R. GOYNES, JARRELL H. CARRA, AND RALPH J. BERNI

U.S. Department of Agriculture, New Orleans, Louisiana 70179, U.S.A.

ABSTRACT

Several "washing" procedures have been applied to harvested cotton fibers in at-tempts to remove byssinogenic agents before processing. These procedures includedwashing at various temperatures, scouring, and bleaching. Microscopical examination,by both transmission electron microscopy and scanning electron microscopy, of cottonfiber surfaces showed a reduction in the number of loose surface particles present.Changes were also observed in the nature of the coatings on the fiber surfaces. Naturalcoatings appeared to have been removed in some cases, and heavier deposits werefound on some surfaces. The nature of these deposits could not be determined sincefinishes had been added in the final bath of all washing processes.

Harvested cotton fibers contain dusts that becomeairborne during processing of the fibers into textiles.Inhalation of these dusts is believed to be related tothe development of the respiratory disease, byssinosis.Extensive research has been carried out in efforts tocharacterize and eliminate cotton dusts. One methodfor removal of dust from fibers is washing. Sasser [6]

and Perkins [4] reviewed the changes in fiber propertiesdue to various washing processes. They found thatwashing has an effect on noncellulose fiber constituents,dust levels, and processing quality.

Muller el al. [3] reported on changes in chemicalcontent of cotton after various washing treatments.Fischer [1] showed that significant decreases in gram

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negative bacteria and endotoxin levels occurred withprecleaning-and washing of cotton. Gibbs et al. [2]stated that washed cotton has lower respirable dustand endotoxin levels and elicits smaller decreases inhuman lung function than unwashed cotton.

Fiber processing properties are influenced by thenature of the fiber surface. Natural surface coatingmaterials (waxes, sugars, etc.) can be removed or re-distributed during washing, depending on washingconditions [5]. We used transmission and scanningelectron microscopy to study fibers from washing pro-cesses intended to remove or deactivate dusts or other

byssinogenic agents from the fibers. We compared dif-ferences in amounts of particles present and changesin surface coating.

’

’

ExperimentalMATERIALS

Cotton fibers from 10 different washing methodswere studied microscopically. Treatments are shownin Table I. Cottonmaster’ batts were used in treatmentsB through G and bale stock was used in treatments Iand K.

z

MICROSCOPICAL METHODS

Transmission Electron MicroscopyFiber surfaces were studied with the transmission

electron miccroscope (TEM) using a surface replicationprocedure. Although this is an old method for studyingsurfaces and is much more tedious and time consumingthan scanning electron microscopy (SEM), it providesbetter resolution for seeing areas of exposed fibrils onthe fiber surface. To prepare the replicas a two step

procedure was used. A methacrylate film approxi-mately ’/2 to 1 mm thick was prepared by spreading athickened prepolymerized mixture of 3 parts methyland 2 parts butyl methacrylate on a clean glass mi-croscope slide. The film was covered with a cover glassand heated at 65-70°C on a warming table for 2-3hours. After the film hardened, the cover glass andslide were removed by freezing or by dipping in icewater. The edges of the film were then trimmed.A small bundle of fibers was placed on the film and

clamped between two glass slides with light, even pres-sure. The slide composite was placed in an oven at100°C for 6-10 minutes, then removed and allowedto cool. (Fibers should make an impression in film butshould not be embedded so deeply that they cannotbe removed easily.)

Fibers were removed from the film with fine pointedtweezers while being viewed under a wide field mi-croscope. The film was placed, impression side up, ina vacuum evaporator and carbon was evaporated froma vertical position onto the film.The carbon coated replica was placed face down on

TEM sample grids on filter paper squares. Filter paperwas wet with methyl ethyl ketone (2-butanone).To remove the methacrylate, the filter paper con-

taining the replica and grids was placed on a gauzepad saturated with methyl ethyl ketone in a Petri dish.The surface of the replica film was wet with methylethyl ketone and allowed to stand in a closed desiccator(no desiccant or vacuum) for approximately 2 hours.Grids were carefully moved to clean filter paper andPetri dishes with clean gauze saturated with methylethyl ketone, left in the desiccator approximately 12hours, and moved again. After 24 hours grids wereplaced under an optical microscope to check for rye-

°

moval of methacrylate and to find the best replica.Replicas were shadowed with platinum for observationin the TEM.

’ Use of a company or product named by the Department doesnot imply that approval or recommendation of the product to theexclusion of others may also be suitable.

TABLE I. Fiber treatments.

Samples B-G processed in a chemical line processor that included five water baths and two steam processors.

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Scanning Electron MicroscopyFor surface viewing in the SEM, fibers were attached

to adhesive coated specimen stubs and sputter coatedwith gold/palladium for electrical charge suppression.

RESULTS AND DISCUSSION

When cotton fibers are subjected to purificationprocesses such as scouring or solvent extraction, surfacecoating materials are removed. If the treatment is ex-tensive the fibrillar structure of the primary wall canbe seen. Figure 1 is a surface replica of a cotton fiberafter thorough scouring and bleaching. In this treat-ment, waxes, pectic materials, and other noncellulosicsubstances have been removed and the cellulose fibrilsare apparent. Removal of these materials changes boththe chemical and physical nature of the surface of thefiber. Washing treatments designed to remove byssi-nogenic agents from cotton fibers are not strenuousenough to remove surface coating materials completely;however, microscopical evidence indicates that in someinstances the coatings have been disturbed enough tochange the fiber surface character.

Figure 2a shows a TEM replica of an unwashed,natural cotton fiber, and Figure 2b shows the SEMimage of an unwashed fiber. Natural ridges andcompression marks as well as some particles attachedto the surface can be seen in these micrographs.

. Microscopical surface studies of the sample washedat 93°C indicated the removal of some coating ma-terial. The surface replica of this sample shown inFigure 3 has a roughened grainy appearance, probably

FIGURE 1. TEM surface replica of a thoroughly scoured andbleached cotton fiber. Distance between marks equals I ~m.

due to the network fibrils of the primary wall showingthrough the thinned coating. Not all fibers in this sam-ple exhibited this graininess; therefore, degree of coatingremoval was not uniform throughout the sample.Scanning electron micrograp s of this sample showedthat surfaces of approximately half the fibers viewedwere splotched with clusters of &dquo;soft&dquo; particulates thatappeared fused onto the surface. These particles weredifferent from the trash particles sitting on surfaces ofunwashed samples. Figures 4a and b show SEM viewsof these &dquo;soft,&dquo; particles. The source of these depositsis unknown but they can be attributed to (a) rede-

FIGURE 2.(a) TEM surface replica of natural surface of a cotton fiber. Distance between marks equals I Am.(b) SEM image of natural surface of a cotton fiber.

-

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FIGURE 3. TEM surface replica of a fiber washed at 93°C (arrowindicates grainy area). Distance between marks equals I ~m.

position of coating materials removed from other areasof the fiber, (b) clumping of finishing materials addedin the last bath of the washing process, or (c) depositsfrom fungi growing on the fibers. While clumping offinishing materials may be the most likely of thesesources, more of these deposits were found on thefibers from the high temperature wash than on anyother sample, even though all samples were given afinish after washing.A sample washed at 60°C, MQ 101 C, closely re-

sembled the unwashed sample except that it had fewerparticles scattered over the fiber surfaces. This sampleis illustrated in the scanning micrograph in Figure 5.Occasional &dquo;soft&dquo; deposits were seen on some fibersurfaces resembling those on the fibers washed at 93°C.TEM replicas showed some slightly roughened areas

~ _ _

FIGURE 5. SEM view of fiber washed at 60°C.

that may indicate some removal of surface coating.Deposits found on sample MQ 101 K, Rome batchwash, were similar to those seen on fibers from thehigh temperature wash, though individual depositswere not as heavy or as extensive throughout thesample.Of the samples studied, the scoured sample, MQ

101 D, had more areas of exposed fibrils than anyother. Figure 6 shows a surface replica of an area ofa fiber with fibrils partially exposed. Although we foundthese exposed fibrils on several surfaces, most surfaceswere similar to the unwashed sample. In the SEM,surfaces of these fibers appeared very clean, and somesurfaces had a grainy appearance that could be areaswhere the impression of underlying fibrils is seen (Fig-ure 7). The other two scoured samples had even lessindication of removal of surface coating. Sample MQ101 G, low temperature scour, had only occasionalsurfaces that showed fibrillar patterns, and sample MQ

FIGURE 4. (a and b) SEM of two fibers washed at 93°C showing presence of &dquo;soft&dquo; particulate coating.

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FIGURE 6. TEM surface replica of a fiber scoured with 6% NaOH.Distance between marks equals I ~m.

101 K, Rome batch scour, showed some graininessbut no fibrils.A bleached sample, MQ 101 E, showed no evidence

of fibril exposure; however, we found small holes inthe surface of most fibers. This is illustrated in themicrograph in Figure 8. We studied a duplicate samplebleached under the same conditions but saw no holes;therefore, we could not determine the reason for theholes in sample MQ 101 E.

FIGURE 7. SEM view of surface of a fiber scoured with 696 NaOH.

Conclusions

Microscopical examination of cotton sampleswashed under three different conditions, scoured underthree different conditions, and bleached in two differentbatches has shown that fiber surfaces changed duringwashing procedures. While we found some areas ofexposed or nearly exposed fibrils in some washed sam-ples, none of the washing processes removed largequantities of the surface coating. We found clumps ofcoating and particulate materials on some fibers, espe-cially on those from the high temperature washing andthe Rome batch wash. Since a surface finishing chem-ical was added to all samples in the final rinse, it is

FIGURE 8. SEM view of surface of a fiber bleached with 0.9% HzOI.

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247

not possible to determine whether these clumped de-posits are relocated natural coating materials or poorlydeposited finish. Nevertheless these surface changes inboth areas where fibrils are exposed and those whereexcess materials are deposited might account for

changes in the natural processing properties of the cot-ton fiber. All washed fibers contained fewer surface

particles. The removal of these particles could accountfor the reduction of loss--of lung function in humansubjects exposed to processing dusts from these washedcottons.

ACKNOWLEDGMENTS .

We express our appreciation to Joseph B. Cocke,Cotton Quality Research Station, Clemson, S.C., forsupplying the washed cotton samples and to HenryPerkins, Cotton Quality Research Station, Clemson,S.C., and Bob Jacobs, Bill Rearick, Byron Leslie, ChuckAllen, Larry Porter, and Preston Sasser, Cotton In-corporated, for processing the cottons for these co-operative studies.

Literature Cited

1. Fischer, J. J., Evaluation of Cleaning Processes for CottonFiber, Part VII: Microbiological Evaluation, Textile Res.J. 50, 93-95 (1980).

2. Gibbs, A. H., McKenna, F. P., Riser, W. H., Rogers,W. B., Jr., Ross, S. E., and Trexler, J. E., Washed Cotton,A Review of Manufacturing, Properties, and Processing,in "Proceedings, Beltwide Cotton Production ResearchConference," P. J. Wakelyn, Ed., 1980, pp. 19-21.

3. Muller, Linda L., Piccolo, Biagio, and Bemi. Ralph J.,Chemical Characterization of Washed Cotton, in "Pro-ceedings, Beltwide Cotton Production Research Con-ference," P. J. Wakelyn, Ed., 1982, pp. 47-51.

4. Perkins, Henry H., Jr., Effects of Washing on FiberProperties, Dust Generation, and Processing Quality ofCotton, Textile Res. J. 51, 123-127 ( 1981 ).

5. Rollins, Mary L., The Cotton Fiber, in "The AmericanCotton Handbook," Vol. 1, Dame S. Hamby, Ed., In-terscience Publishers, New York, 1965, pp. 44-81.

6. Sasser, P. E., Evaluation of Cleaning and Washing Pro-cesses for Cotton Fiber, Part I: Introduction and CottonProperties, Textile Res. J. 50, 61-63 (1980).

Manuscript received May 6. 1983, accepted July 11, 1983.

- Fatigue of Aramid Cords in Conveyor Belts

M. FRANSSON, B. WIBERGER, AND B. OLOFSSON

Department of Textile Technology, Chalmers University of Technology, Gothenburg, Sweden

ABSTRACT

A theoretical study of strains and stresses in cycling of conveyor belts strengthenedby two layers of high modulus cord (Kevlar®) was performed. Experimental beltswere then built with cords of varying twist and their behavior in fatigue investigated.The significance of cord compression was especially clarified, but the results yieldmuch further information on engineering these fiber composite products.

Several industrial fibers have been used through theyears for arming cords in rubber type composites, e.g.,conveyor belts [ 1 ]. Because of their high modulus andstrength, aramid fibers might be profitable because highcost is balanced by small quantity [4, 5]. Among themechanical properties, the repeated extension andcompression makes fatigue most important, and espe-cially the relationships between fatigue and twist [2,3]. Our work is a rather fundamental study in thisarea.

Experimental .

The fiber used was a high strength intermediatemodulus KevlarO 29 fiber with the following charac-teristics : density-1.44 g/cm3, tensile strength-2760MPa, tensile modulus-59 GPa, elongation to break-4.0%, filament diameter-12 ~m, and linear density-0.17 tex. Single strands were constructed by Z-twistingthe filaments, and then were cords made by plyingthree strands together with an S-twist. The cords were

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