, ,.Indian JournaJ of TextiJe ResearchVol. 1, June 1976, pp. 37-42

Chemical Treatments for Cotton Yarns to Improve TheirKnitting Performance

K. P. R. PILLAY & N. RAMAN!South India Textile Research Association, Coimbatore 14

Received 1 May 1976; accepted 20 May 1976

The results of an investigation on the influence of chemical finishes on the knitting performance of cottonyarns on warp and weft knitting machines are presented. Three types of treatments, namely (i) synthetic sizes,(ii) waxes, and (iii) finishes that increase interfibre friction without appreciably changing yam to metal friction wereused. It is shown that yarn breaks and fabric defects in knitting can be reduced considerably by chemical finishes.The use of kerosene, Napcostat, Syton and paraffin wax in suitable proportions gives promising results. These treat-ments enable fine counts to be knitted on commercial warp knitting machines and also reduce fabric defects andwaste in garment making.

INrecent years, interest has been growing in theapplication of chemical finishes for spun yarns

. prior to knitting to improve their performanceon the machine and at the same time to reduce the fre-quency of faults in the cloth. A reduced fault rateautomatically reduces knitting costs and also mendingcosts in fabrics where faults are rectified beforedelivery of the cloth.

The main factors limiting the use of spun yarnsin knitting are : (i) slubs and knots, (ii) entangledyarns, (iii) weak spots, and (iv) fibre shedding. Thesefactors are related to the basic yarn characteristics,such as evenness, strength and its variation, breakingelongation, hairiness and friction; the last one isamong the most important factors.

In practical terms, friction of the yarn influencesthe ease with which it can slide over the various guidesand knitting elements during knitting. A higher yarnfriction results in short coarse length in the fabricand causes variation in fabric size. It can be seenth~refo~~, that yarn fri~tion should be low as regard~knittability and consistent for reproducibility offabric sizes and yield.

It follows that there are several approaches whichmay. provide substantial improvements relating toknitting of spun yarns. Perhaps the ideal solutionwould be to combine the best improvements in terms?f yarn properties and yarn treatment. In develop-mg a yarn treatment, it is important to considert~ose chemicals which improve the yarn characteris-tics that are Important for good knitting. A chemicaltreatment for the yarn should be s~c.h as to improveboth strength and elongation, and If It could bind thefibres together, and at the same time lubricate theyarns, sufficient improvement in the knittabilityof the yarn could be achieved.

Th~ objecti.ves of this investigation were : (i) toexamine the Influence of various potential chemicalfin~sh.esand application techniques on yarn charac-teristics and knitting efficiency, and (ii) to suggest~he best.treatmen~ for cotton yarns to improve knitt-ing efficiency by in-plant knitting trials on warp andcircular knitting machines.

Materials and Methods

Chemical treatments - For initial studies on theinfluence of chemical finishes on yarn characteristics,three types of yarn treatments were investigated,each type designed to illustrate a particular effect.

(i) The yarn was treated with synthetic sizes whichbind the fibres in yarn and thus increase yarn strengthand reduce yarn hairiness. Chemicals like carboxy-methyl cellulose, polyvinyl alcohol, polyvinyl ace-tate, sodium carboxymethyl cellulose and acrylicemulsions were used for the purpose. The yarn wasfirst immersed in a bath containing solution of thesize of appropriate concentration, squeezed to about50% pick up and then dried and conditioned, as ina usual pad technique.

(ii) Waxing treatment to reduce the yarn to metalfriction was carried out during winding using thecommercial waxing attachment. The types of waxesexamined included paraffin wax, PEG 1500 andpolywax.

(iii) Treatment with chemicals to increase fibreto fibre friction without appreciably increasing yarnto metal friction was performed by first windingthe yarns on perforated cones and immersing themin selected liquids of appropriate concentration for2 h~. They were then taken out and centrifuged for5 mm to remove excess of liquid. Under these condi-tions, the pick up was about 50%.

The treated yarns were tested for various yarncharacteristics immediately after treatment and afterdrying under laboratory conditions. Some of thechemicals used for this purpose were PEG 200kerosene, .Napcostat LV 40, Cirrasol FPI and poly~wax solution.

Physical characteristics of yarns - The yarnsamples were tested for the following propertiesbefore and after t~~atment.: (i) single yarn strengtha.nd elongation, (n) ~?efficlent of variation (CV) of~mgle yarn str.en~th, (111) y~rn to metal (yarn to knitt-mg needle) friction, and (IV) fibre to fibre friction.

.Method of application of chemicals for knitting-Since large quantities of yarn had to be treated for

37

INDIAN J. TEXT. RES., VOL. I, JUNE 1976

knitting trials, the method of application of chemicalsto yarn was different for warp and circular knitting.

For warp knitting, the chemicals were appliedwhile the warp was in sheet form, the applicationbeing from the hard chrome plated lick-roll coveredwith a felt, rotating in a trough in which the levelof the solution was controlled carefully. The amountof solution applied was controlled by adjusting thespeed of the lick-roller. The warps were stored fora week, except in the case of kerosene, before theywere used for knitting. A special paraffin wax rollerwas prepared and fitted to the warper for waxingthe warp in warp knitting.

For circular knitting, the treatments were given tothe yarn in cone form, as described before. The driedcones were rewound on fresh cones and used forknitting. Paraffin wax treatment alone was givenduring the winding operation. Under this condi-tion, 0.2-0.3 % wax was deposited on the yarnsurface.

Method of determining fibre to fibre friction - Anattachment to the Instron tensile tester was fabricatedto measure fibre to fibre friction. It consisted ofa r++i shaped platform which could be convenientlymounted at the centre of the Instron cross-head. Twotufts of cotton carefully combed and prepared, eachwith a width of I in, were placed one above theother. A known weight was placed on the tufts.Tuft A was secured in its place and one end of tuftB was attached to an inextensible thread; the otherend of tuft B was attached to the load cell through africtionless pulley (Fig. 1).

When the cross-head moved down at a particularspeed (I crn/min), Tuft B slid over tuft A and the

L-.,,,

Inextensiblecord

maximum load recorded by the Instron gave the staticfrictional force between the tufts in grams. If F isthe static frictional force recorded in g, and R, theweight in g placed on the tufts, then the coefficientof friction between tufts, 1.4 = F/ R. A typical curveobtained for the frictional force between the twotufts is shown in Fig. leA).

Method of measuring yarn to metal friction - Tomeasure the coefficient of friction between theyarn and the knitting needle, another attachmentto the Instron was made, as shown in Fig. 2. Theyarn from the package passed through the compen-sating tensioner S, which supplied the yarn to thefrictionless pulleys A, Band C at a constant tension.The pulley B of weight 2Tl hung in the air, thuskeeping the input tension at Tl g until the yarn ente-red the hook of the rigidly fixed knitting needle,

50"""--~

ClI 40

UJUa:011. 30

~z0~ 20ua:11.

10-

o L---'---''--L... __L...-...!.._6 4 2 0

CHART M(,lVEIf.E 1'Ii'T • ernFig. 1A - Curve for frictional force between two tufts [Chart

speed, 5 cm/min; and normal load, lOOgJ

i!,~ I ¢

J j 2T2 cos ¢/1 J. ~"""""I-KNITTJNG

,~i " I '. st.or_ "'oc, , '

~ ~ ..

Fig. 1 - Apparatus for the measurement of fibre to fibre Fig. 2 - Apparatus for the measurement of yarn to knittingfriction needle friction

38

PILLA Y & RAMANI : CHEMICAL TREATMENTS FOR COTTON YARNS

making an angle of wrap 9 (in radians). The yarnfrom the knitting needle passed over another fric-tionless pulley E attached to the Instron load cell.The yarn made an angle of wrap of cp with pulleyE and through the guide F was wound on to the wind-ing drum G. From a knowledge of the input tensionT1, the angle of wrap 9, and the output tension T2

(recorded value in g) . .T3 = 2· - ..... ,the coefficient of fnc-cos cp

tion was calculated using the equation: ~: = e"·. A

typical tracing of the recorded output tension isgiven in Fig. 2 (A).

Knitting trials: (i) Circular knitting - A 17 indiameter, 24 gauge Sinker body machine was usedfor assessing the knitting performance of the treatedand untreated 40s yarns. Knitting trials lasting 2 hrwere made for each treatment using 36 wales and54 courses per inch and the number of fabric defects(holes) produced at 15 min intervals was counted.The error associated with the estimation was about15% of the mean.

(ii) Warp knitting - A 24 gauge, 84 in width Cop-centra warp knitting machine was used for thesetrials. A 40 in pillar stitch fabric of 120 g/sq m wasknitted on the machine using 60s combed cotton yarnsin untreated and treated conditions. The number ofend breaks at 15 min intervals was recorded. Themachine efficiency was also calculated at the end ofthe test. Here again, the error associated with theestimation was about 15% of the mean.

Results and DiscussionEffect of synthetic sizes on yarn characteristics-

The physical characteristics of 20s and 60s yarn treatedwith the most promising of the first group of chemi-

.... 40::Ja.~Ol

0 e-

Z00w-0'"a:zOWut--Wa: 20

0 2 4 6 8 10 12

CHART MOVEMEN em

Fig. 2A - Tracing of the recorded output tension [Chartspeed, 10 em/in; and yarn speed, 60 yd/minl

cals are given in Table 1. It is evident that the chemi-cal treatments tried improve yarn strength by 6-21%,but reduce yarn elongation by 30-70 %. The CV ofyarn strength was reduced appreciably.

Effect of waxing - The effect of treating the yarnwith three types of waxes in solid form is evident fromthe data given in Table 2. It is seen that the waxtreatments lower the yarn to metal friction by 15-23%without influencing other yarn properties like strength.elongation, etc. significantly. Waxing also reducesthe hairiness and fibre shedding tendency of yarns tosome extent, because fibres were laid down on theyarn surface during this process. There was practi-cally no difference between different types of waxesin their ability to lower yarn to metal friction.

Treatments to change inter-fibre friction - A 40shosiery yarn was used in this experiment. Sufficientquantities of this yarn were treated with differentfinishing agents, as described earlier, and the yarncharacteristics were determined. The fibres untwistedfrom treated samples were tested for inter-fibre fric-tion. The results are given in Table 3. These pro-perties were measured immediately after treatmentand also after drying the samples for a week at roomtemperature. It is seen that most of the treatmentsimprove yarn strength and elongation, the range ofimprovement being 3-20% for strength and 2-15 %for breaking elongation. Syton, Cirrasol FPI andPEG 200 at 2.0, 1.5 and 50% concentration res-pectively gave the maximum increase in strength,whereas C-prolube, kerosene and surfasol gave onlyintermediate increase in strength. Polywax solution(l.5 %) reduced yarn strength by about 20 % withoutany appreciable change in breaking elongation.

In the case of breaking elongation, Cirrasol FPI,kerosene, PEG 200 and Napcostat gave the highestvalues. When the treated yarns were dried by keep-ing them for a week under laboratory conditions,small changes in breaking strength and elongationtook place, but even then they were higher than thecorresponding values for untreated yarn.

Data for inter-fibre friction reveal that the increasein the breaking strength of these yarns is most pro-bably due to the increase in inter-fibre friction as aresult of treatment. Data for yarn to metal frictionshow that the change in friction after treatment issmall and cannot be expected to influence knittabilityto any significant level. The increase in inter-fibrefriction would help the fibres to carry a greaterload before fibre slippage and yarn breakage. Hence,it is to be expected that a treatment which increases

TABLE1 - PHYSICALCHARACTERISTICSOF 20s AND 60s YARN TREATEDWITH SELECTEDSYNTHETICSIZES

20s 60sCone. ofsizing agent Breaking Elongation CVof Breaking Elongation CVof

% strength % strength strength % breakingg % g strength

%363.6 7.2 12.7 164.0 6.3 15.2

3.0 387.0 2.0 11.5 193.6 2.1 10.31.0 385.0 3.1 13.2 172.8 2.7 11.13.0 440.4 3.2 9.3 195.6 1.8 12.4

39

Sizing agent

Control (untreated)CMCPolyvinyl acetatePolyvinyl alcohol

INDIAN J. TEXT. RES., VOL. I, JUNE 1976

TABLE2 - EFFECTOF WAXINGON THEPHYSICALCHARACTERISTICSOF YARNS

40s 60sTreatment

Breaking Elongation CVof Yarn to Breaking Elongation CVof Yarn tostrength % breaking metal strength % breaking metal

g strength friction g strength friction% %

Control (untreated) 213.0 6.9 9.4 0.38 147.6 5.5 9.8 0.36Paraffin wax 195.6 6.5 9.2 0.29 149.2 5.2 9.8 0.31PEG 1500 218.4 5.9 9.1 0.31 130.8 4.7 11.5 0.31Polywax (soluble wax) 212.4 6.3 10.7 0.31 143.2 4.8 12.2 0.31

TABLE3 - EFFECT OF SURFACEFINISHESON INTER-FIBREFRICTIONAND YARN PROPERTIES

[Counts, 4Os]

Finishing agent Cone. of Yarn Elongation, CVof Fibre to fibre Yarn tofinishing strength, g % strength, % friction metal friction

agent% A B A B A B A B A B

Control (untreated) 2589 6.6 97 0.31 0.36Syton 2.0 310.2 296.4 6.3 7.2 9.3 10.3 l.00 0.96 0.45 0.38Cirrasol FPI 1.5 310.5 318.0 7.6 7.3 11.8 9.2 0.57 0.46 0.38 0.35C. Prolube 5.0 268.8 271.8 6.7 7.7 8.5 4.9 0.41 0.31 0.43 0.33Kerosene 283.8 264.8 7.2 6.9 8.4 7.8 0.56 0.48 0.36 0.35Surfasol 0.5 288.0 277.2 7.0 7.3 7.8 9.4 0.45 0.33 0.47 0.33Napeostat 1.5 293.4 286.2 7.1 7.9 9.9 9.0 0.52 0.45 0.40 0.35PEG 200 50.0 295.8 292.8 7.4 7.9 7.9 8.4 0.97 0.58 0.33 0.33Polywax soln 1.5 180.8 174.6 6.4 6.9 9.5 10.5 0.45 0.28 0.40 0.31

A, immediately after treatment; B, after one week.

TABLE4 - K.NrrrING PERFORMANCEOF40s YARNONSINKERBODYKNITTINGMACHINE

Sample I Sample IICone. offinishing No. of Improvement No. of Improvement

agent defectsjhr % defectsjhr %%

85 452 97.6 2 95.5

2.0 5 94.1 5 88.82.0 6 92.91.5 7 91.7

10 88.21.5 20 76.4 6 86.6

50.0 22 74.11.5 41 51.7

Finishing agent

Control (untreated)KerosenePYASytonCirrasol FPIParaffin waxNapcostat LV 40PEG 200Polywax

fibre-fibre friction would serve to improve knittabi-lity, provided yarn to metal friction is not changedappreciably and yarn tensile properties are increased.

Effect of yarn treatments on knitting performance -To ascertain whether the improvement in yarn charac-teristics is reflected in the knitting performance, largescale knitting trials were conducted on a Copcentrawarp knitting machine as well as on a Sinker bodycircular knitting machine using 60s and 40s yarnsamples respectively. The results are presented inTables 4 and 5.

It is evident that in both circular and warp knitting,chemical treatments confer significant advantages byreducing the number of fabric defects and increasingmachine efficiency. Kerosene appears to be the bestfinishing agent for both warp and weft knitting. Butthe bad odour of kerosene and the fire hazards infactories during working prevent its commercialapplication. PYA, Syton, Cirrasol and paraffin wax

40

are also very good for warp and weft knitting. Thereis some difference in the performance of some finish-ing agents on warp and weft knitting machines. Thebehaviour of polywax soln is an example. While itwas found to be very good for warp knitting, itsperformance in weft knitting was not very satisfactory.The difference in the performance for the two typesof knitting is probably due to (i) differences in thetensions imposed on the yarns in the two processes,and (ii) differences in the method of application ofthe finishing agent in warp knitting and weft knitting.In the case of warp knitting, the finishing agent wasapplied through the lick-roller during warping, where-as in weft knitting, the cones were immersed in thefinishing agent. In the case of polywax, this differencein treatment might have created large differences inyarn strength. The immersion technique reduced theyarn strength considerably in polywax treatment(Table 4).

PILLAY & RAMANI : CHEMICAL TREATMENTS FOR COTTON YARNS

Since the knitting efficiency may be expected todepend upon a number of yarn characteristics, thevarious factors of yarn quality have been combinedinto a single index called yarn quality index (YQI)in the case of yarns used for knitting. It is defined as :

SxEYQIVx~xUxH

where S is the breaking strength in g; E, the breakingelongation, %; V, the CY of strength i u, yarn tometal friction; U, Uster uniformity, %; and H, hairi-ness of the yarn. However, for this particular study,

SxEYQI has been taken to be equal to ···V - , sinceX ~

hairiness was not measured and the value of U wasfairly constant for all the treated samples.

YQI may be expected to have a positive correlationwith knitting efficiency. YQI values for the yarnsamples treated with different finishing agents aregiven in Table 6. YQI values are plotted againstfabric defects in circular and warp knitting for 40sand 60s yarn in Fig. 3. At a YQI value of about 470,the defects were minimum in circular knitting for40s yarn.

Economic Advantages of Chemical FinishingIn view of the improvement in yarn quality by way

of improved strength and reduced yarn to metalfriction, etc., chemical finishes to yarns could be ex-pected to improve the efficiency of the knitting pro-cess.

TABLE5 - EFFECTOF CHEMICALFINISHINGON THEKNrrnNoPERFORMANCEOF 60s YARN ON WARP K.NrrrING MACHINE

[24 gauge 40 in fabric; count, 60s; speed, 600 cpm]

Finishing agent Cone. of No. of Efficiency YQlfinishing breaks/hr %agent

%Control

(untreated) 27.0 19.6 230.1Kerosene 5.5 95.9 324.9Polywax 1.5 6.5 95.5 192.1Napcostat

7.0 274.7LV 40 1.5 94.6Paraffin wax 9.0 91.8 286.7PYA 2.0 12.0 92.3 282.8Syton 2.0 17.5 88.6 256.3

A preliminary study with normal 60s yarn of2200 CSP on a 24 gauge Copcentra warp knittingmachine, knitting 102 em width fabric showed thatthe knitting efficiency improved from about 80%to 90-95 % when the yarn was given chemicalfinishes. Based on this, for a commercial modelwith 320 em width, chemical finishing could be ex-pected to improve the knitting efficiency and conse-quently the machine production rate considerably.This is because while with the usual yarn, even with2 widths of 102 cm, it was possible only to get anefficiency of about 52 %, with chemically treatedyarns, it was possible to use the full width of themachine and get an efficiency of 60 %. In other words,

,oo~---------------------------------,o

o

00>-u 90zwu::::80w

o o

Warp Knitting

70L- L-__~~ __-J ~ _i ~220 240 260 280 300 320 340

YARN QUALITY INDEX

100r---------------------------------,o;:::> 80oI

o

Circular Knitting

Q:W 60IL

<11I-UW 40u,Wou,o 20oz

oo

o 0

oL-~ __ ~ __ ~ __ _L~=c==~250 350 450 550

YARN QUALITY INDEX

Fig. 3 - Relationship between YQI and fabric defects

TABLE6 - RELATIONSHIPBETWEENYARN QUALITYINDEX AND NUMBEROF DEFECTS/HoURIN FABRIC

[Counts, 4Os]

Finishing agent Cone, of Strength Elongation CVof Yam to No. of YQIfinishing g % strength metal defects/

agent % friction hr%

Control (untreated) 207.2 6.8 9.7 0.38 85 382.2Syton 2.0 231.2 1.4 10.3 0.40 6 426.0Kerosene 227.1 7.4 8.4 0.37 2 540.7Napcostat LV 40 1.5 229.0 7.3 9.9 0.37 20 456.4PEG 200 50.0 224.4 7.1 9.1 0.33 22 530.4Paraffin wax 1.95.6 6.5 9.2 0.29 10 476.5PYA 2.0 240.0 5.6 10.6 0.33 5 470.0Polywax 1.5 155.6 6.9 10.5 0.32 41 319.6Cirrasol FPI 1.5 254.1 7.0 11.2 0.35 1 453.7

41

INDIAN J. TEXT. RES., VOL. I, JUNE 1976

with the application of chemical finishes to the yarn,the production rate in warp knitting could be expec-ted to improve by about 75 %.

In terms of cost, this would help in reducing thecost of production of fabrics from 4 warp knittingmachines by more than Rs 8 lakhs per year. Even ifthe chemical treatments cost 50 paise per kg yarn,there will still be a saving in cost to the extent of atleast Rs 7 lakhs per year. However, more data are tobe collected before a precise estimate of the possiblecost reductions in different counts can be made.

ConclusionsFabric defects can be considerably reduced and

knitting efficiency improved by giving suitable chemi-cal finishes to cotton yarns. Similarly, chemicalfinishing of cotton yarns enables the reduction offabric defects in circular knitting by 90-95 % andthus reduces the number of seconds and waste pro-duced in garment manufacture. The most useful typeof finishing agents appear to be those that increasethe fibre to fibre friction in yarns without appreciablyincreasing the yarn to metal friction. Kerosene

42

appears to be the best agent for this purpose. Butdrawbacks like bad odour and flammability preventits industrial use. Other suitable agents are : PVA1.5%, Syton 2.0 %, Cirrasol 1.5%, Napcostat 1.5%,and paraffin. Application of chemical finishing enableswarp knitting to be carried out on fine counts eco-nomically. It reduces fabric defects and consequentlywaste during garment making.

For a warp knitting unit consisting of four knittingmachines, the adoption of chemical finishing can bringsavings in cost, particularly in fine counts.

Acknowledgement

The authors are indebted to Shri K. Sreenivasan,Director, SITRA, and Mr K. P. Moltu, UNIDOexpert in knitting at SITRA for their valuable sugges-tions and interest during the progress of this work.They are also indebted to Shri K. T. Thomas, Knitt-ing Technologist, Shri R. Ramamurthy, Shri T. M.Krishna Varma and other staff of the Knitting Divisionfor their assistance in carrying out the knittingtrials.