Indi an Journal o f Fibre & Textile Research Vol. 29, March 2004, pp. 12- 18

Relationship between USDA calibration cotton properties and yarn strength/unevenness

K P Chell amani", V Thanabal , Arindam Basu & T V Ratnam

The South Ind ia Textile Researc h Associat ion, Coimbatore 64 1 0 14 , Indi a

Received 2 Decelllber 2002; accepled 8 April 2003

N ine cottons di ffering widely in fibre properti es have been spun on a set of modern machinery to di ffe rent counts rang ing from 20s to 100s to estab li sh the re lat io nshi p between the fibre properties and the ya rn strength/yarn unevenness. For assessing fi bre properti es, HVI (high vo lume in struments) test syste m and fo r assess ing yarn properties. lea strength tester, s ing le ya rn strength tester and evenness tester were used. T wo ex pressions, one for predicting Rkm value and the o ther for pred ic ting yarn irregulari ty , from newer fi bre length ;md strength parameters measured on HVI t ,~s t i n g system using HVI test mode have been deri ved. T he overa ll fib re quality in HVI mode has been fo und to be about 2.2S times of that obtained in ICC mode.

Keywords : Cotto n. Fibre propert ies, Rkm va lue. Tw ist Illult ipl ier, Yarn hairi ness IPC Code: Int. C l. 7 D02G 3/00

1 Introduction Evo lving workable predi cti on fo rmul ae to relate

fibre properties to yarn quality has been an interesting field of study by several research workers for more than three decades 1-5 . However, during the last decade there has been a spectacul ar improvement in the technological perfo rmance of spinning machinery, such as improved opening and effec ti ve separation of heavy particles in modern blow room lines, and better carding plus effi cient fibre control during drafti ng in preparatory and spinning machinery.These advances in machinery des ign h:1Ve contributed to improvement in yarn quality. This is also substanti ated by SITRA's qual ity surveys conducted in member mill s.

SITRA has developed ex pressions fo r predi cting yarn quality fro m fibre properti es measured by HVI test system6

. However, in these ex pressions, fibre properties like 2.5 % span length and uniformity ratio were taken into consideration. Of late, USDA calibration cottons were supplied with upper half mean length (UHML), uniformity index (UI), bundle strength , elongati on and micronaire value. Therefore, when USDA cottons are used fo r calibration, fibre properties for cotton samples could be evaluated only in terms of new measuring parameters. In view of the fact that fibre properties like 2.5% span length and

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uniformity ratio won' t be avail able whil e using USDA calibration cottons, the present study was undertaken to establi sh relationshi p between the newer fibre pw perties and the yarn quality (s trength and unevenness). Nine cotton vanetl es widely differing in fibre properti es have been spu n to different counts ranging from 20s to 100s using a set of modern machinery. This will broadly help the mills to evaluate their spinning performance and determine the cotton fibre properties to be used in spinning a desired quality yarn.

2 Materials and Methods Nine different cottons, VI Z . V 797, RCH, LRA ,

MECH, S 6, LK, DCH 32, MCU 5 and SUVIN, differing widely in fibre properti es were spun on a set of modern machinery. The major properti es of these cottons (newer fibre properties) as measured by HVI test system using USDA calibration cotton are given in Table I.

Each cottOIl was spun into different counts and each count at three different twist multi pli ers (TM). In all , about] 25 spinning tri als were made.The various counts spun and their respecti ve twi st values are given in Table 2.

The yarn samples were tested for Rkm value & elongation characteristics by Uster tensorapid tester and for yarn unevenness & hairiness by Uster-3 tester.

CHELLAMAN I el al.: RELATIONS HI P BETWEEN COTTON PROPERTI ES & YARN STRENGTH/UNEVENN ESS 13

Table I - Fibre properties of different cottons

Cotton variety

Upper half mean length

mill

Uniformity index

Mean length Bundle strength Micronaire value

flgli nch

SUVIN

DCH 32

MCU5

S6

LK

MEC H

LRA

RCH

V 797

35.8

34.6

32.2

28 .8

29.9

25.8

24.8

24.0

23.0

85.4

84.1

82.6

82.4

84.0

80.3

8 1.7

8 1.0

80.3

Table 2- Counts spun from different cottons and twist mult ip liers employed

Cotton Count Twist multi plier variety Ne

SUVIN 100,80,60,50,40,30,20 3.6, 4.0, 4.4

DCH 32 80,60,50,40,30,20 3.8, 4.2, 4.6

MCU5 90,80,60,50,40.30,20 3.9,4.3, 4.6

LK 60,50,40,30,20 4.0,4.4, 4.9

S6 60,50,40,30.20 4.0, 4.5, 5.0

MECH 50,40.30,20 4.1 ,4.6, 5.0

LR A 40,30,20 4.2, 4.7, 5.1

RCH 30,20 4.3, 4.8, 5.3

V 797 30,20 4.4, 4.8, 5.3

3 Results and Discussion

3.1 Relationship between Fibre Quality and Rkm Value

The yarns were spun w ith quality attributes and the fo llowing express ions have been deri ved for the Rkm value (g/tex) achievable at optimum twist multiplier under good working conditi ons:

Rkm value, g/tex= I . I JFQI + 4.0-[ 13 CI 150] ... ( I)

(for carded counts)

and

Rkm value, g/tex

(for combed counts)

=I.I[JFQI + 4.0- ( 13 ClI50)]

x [ I + (W/I 00)] ... (2)

FQI (Fibre quality index) = [LSlf]

where L is the mean length (mm) measured in HVI mode; S, the fibre bundle strength (g/tex) measured in . HVI mode;.f, the micronaire va lue ; C, the yarn count ; and W, the comber noi l (Ok ).

mm g/tex

30.6 33.8 2.8

29. 1 32.9 2.8

26.6 3 1.6 3.0

23 .7 26.5 4.0

25. 1 3 1.7 3.7

20.7 23.7 3.4

20.3 24.9 3. 1

19.4 22.7 4. 1

18.5 19.4 4.7

25

. . . . r = 0.969 ..

10 10 15 20 25

Predicted Rkm (g/tex)

Fig. I-Actual and pred icted Rkm values

The prediction express ion g ives a very close fit with the actual Rkm with a high correlation of 0.969 (Fi g. 1) . The error of predicti on was fo und to be 1.5 g/tex at 95% confi dence limit.

It can be observed that the yarn Rkm va lue decreases by about 0 .087 units fo r an increase of every one count. This would mean that in long and ex tra long staple cottons, the re lati ve drop in Rkm fo r unit increase in count would be lower. Fo r example, in cotton with FQI value of around 350, the drop in Rkm value will be 0 .45% and that with FQI o f around 120, the fall in Rkm value will be around 0 .60%.

3.2 Relationship between Fibre Quality and Yarn Unevenness

For cotton counts, it has been shown earlier that the yarn irregul arity tS given by the fo llow ing relationship:

U2= [(QC + a) (d-l )] + Ur2 ... (3 )

where U is the yarn unevenness; C, the roving hank; d, the ring fra me draft; Ur, the rovi ng unevenness; Q,

14 INDIAN J. FIBRE TEXT. RES., MARCH 2004

the factor depending on the drafting property of cotton, which, in turn, is associated with some physical properties of the fibres; and a, the measure of performance of ring frame i.e. the extent of control exercised on fibres during drafting. This depends on the mechanical conditions of ring frame drafting system.

The factor a, taken as the contribution by the ring frame to yarn irregu larity, was found to be (by least square estimate) 4.1 wh ich is significantly different from zero. Using thi s value of a, the best estimate value of Q was obtai ned for different cottons (Table 3) .

To relate Q with fibre properties, a model of the form as shown below is suggested:

. .. (4)

where f is the micronaire value in ~g/in. ; and L, the mean length in mm (measured in HVI mode). The best least square fit was found for K value of 137 which is a constant infl uencing the drafting quality of cotton. The p and r consist of a value of 2 each and Q is fou nd to be

Q = 137 (J /L)2 ... (5)

T he Q expected from Eq . (5) is found to be very close with Q estimated from the Eq. (3) (Table 3), the r value between the two bei ng 0 .99 (Fig. 2).

Hence, the final expression for yarn irregularity is :

U2=137(J/L)2[(d-l )/d] Ne + 4.1 (d- I) +Ur2 . . . (6)

A high correlation of 0.990 was obtained between the actual and predicted values of yarn unevenness (Fig. 3) . The error of estimate was fou nd to be about 0 .8 U% at 95% confidence limit.

It is observed from the above that about 42% of the total yarn irregulari ty is due to the cotton quali ty, 40% due to the condition of ri ng frame & draft employed, and the remaini ng due to the roving quality.

Using the prediction expression, it can be deduced that a unit increase in Q the fibre quality, d the ring frame draft, a the ring frame parameter, and Ur the roving unevenness (U %) would increase the yarn unevenness (U%) approximate ly by

Ne a d -1 Ur 2U' 2U' 2U' U respectively.

To illustrate, in a spinn ing mi ll , for the spinning of 40s carded yarn with an average evenness value of 14.5 U% (roving unevenness 5 U%), an improvement of 0 .5 U% in yarn evenness could be achieved either by (i) decreas ing Q by 0.36 units, (ii) lowering the ri ng frame draft by 4 numbers, (iii) reducing a by 0.6, or (iv) using of more even roving by 1.5 U %.

Table 3 - Expected and ac tua l va lues of Q for different cottons

Cotton QV:1l ue variety Actual Expected

SUV IN 1.148 1.23 1

DC H 32 1.271 1.397

MCU 5 1.743 1.830

LK 2.970 3.099

S6 3.900 4.169

MECH 3.704 4.246

LRA 4.563 5.094

RCH 5.542 6. 166

V 797 8.45 1 8.733

10 /' •

8 // 9 '7

/

"0 6 ~ u (!)

4 0.. ><

lLl / 2 ~

0 t---------- t--

0 2 4 6 8 10

Actual 'Q'

Fig. 2 - Actual and expected Q values

20 ./ . r = 0.990 •

8 8 12 16 20

Actual U%

Fig. 3 - Actual and expected U% values

CHELLAMANI ef al.: RELATIONSHIP BETWEEN COTION PROPERTIES & YARN STRENGTH/UNEVENNESS IS

* c: 6 .~ 0; 00 c: o

a:i 00 c:

:;;: co ~ 4

o:l

e SUVIN

~MCU5

6

4

7

IreH

I ~V 797

+ LRA

6

5 ~ 4 ~ O L-~-------L------~~

20s 305 405 50s 60s 205 305 405 50s 60s 80s 20s .lOs 40s

Count (Ne)

Fig. 4 - Break ing elongation for LK, S 6, MECH, SUVIN, MCU 5, DCH 32, RCH, V 797 and LRA cottons

3.3 Factors Influencing the Breaking Elongation of Spun Yarns

3.3.1 Effect of COllllt

The breaking elongation of yarns spun from a given cotton could be expected to be influenced by the linear density of yarn spun. To ascertain this, an analysis was made regarding the fall in elongation for the increase of everyone count. The breaking elongation values for different counts spun from 9 different yarn cottons are given in Fig. 4 .

Yarn breaking elongation is found to be a function of cotton progressively decreasing with the cotton quality. It is highest for the yarns spun from DCH 32, about 7% lower for SUVIN and MCU 5 yarns, 15% less for LK yarns, 18% lower for RCH yarns, 25% lower for S 6 and MECH yarns, and only about two­third for V 797 yarns (Fig.5).

On an average, the yarn elongation drops by about 0.43% (absolute values) for every increase of 10 counts.The drop is slightly on the higher side for coarse and medium counts by 0.47% and on the lower side for fine and super fine counts by 0.38% (Fig. 4) .

3.3.2 Effect of Twist

The influence of twist on yarn elongation is given in Table 4 for SUVIN cotton where the micronaire value is 2.8.

On an average, for the increase of every 1 TM, the yarn elongation improves by about 0.5%, except in very fine counts (80s Ne) where the improvement is only marginal. During tensile testing, the contracted length of yarn has to be straightened first before the yarn is subjected for loading. Higher the yarn contraction, greater will be the measured value of yarn elongation and vice versa.

8' 100

:r: u 90 e

>< ., 11 80 c .S:

'" 00 70 -c: o

iJ3 ,;..

0 N <'l

:r: u 0

Z lr\ ::.::: <t: :r: \0 :r: r-

:> ~ -l e::: u Vl U 0-r-u -l e::: U.J

~ :::2 :::2 > Vl

Cottons

Fig. 5 -Elongation index of different coltons

Table 4 - Breaking elongation at different twi st levels

Count Twist Breaking Ne multiplier elongation

%

20s 3.5 6. 17 3.9 6.27 4.3 6.44

30s 3.5 5.42 3.9 6. 13 4.3 6.10

40s 3.5 5.53 3.9 5.69 4.3 6.11

50s 3.5 5.00 3.9 5.31 '4.3 5,28

60s 3.5 5.10 3.9 5,50 4.3 5,70

80s 3.5 4.80 3.9 4.86 4.3 4.92

16 INDIAN J. FIf3RE TEXT. RES., MARCH 2004

3.4 Factors Influencing Hairiness of Spun Yarns

3.4. J Effect of Count

Hairiness index exhibits progressive increase as the cotton quality level decreases. Comparing the counts normally spun from a colton of a given quality, the hairiness index shows an overall increase of about 50% between cottons. SUVIN cotton yarns have the lowest level of hairiness (Fig. 6). Yarns spun from DCH 32 and LK cottons show 12% more hai riness, MCU 5 and S 6 cottons about 20% higher, MECH , RCH and V 797 cotLOns 33% greater, and LRA cotton the highest level s, ' ~' S()% more.

In general. as count becomes fin er, the hairiness vn lue ge ts reduced. Thi s is due to the decrease in total number of fibres in the yarn cross-section as the cou nt becomes finer. On an average, the hairiness index decreases by about 10% for the increase of every 10 counts.

3.,/.2 Effect of Twist

Twist has very sign ificant influence on yarn hairiness. On an average, the hairiness decreases by about II % for the increase of every I TM . The hairiness values for different counts at various twi st levels are given in Table 5.

3.5 Relationship betw(!CJl Fihre Properties Measured by HVI and ICC Modes

While using high volume instrument test system for cotton quality evaluation, testing can be carried out in HVI mode (using HV I ca libration cotton) as well as in ICC mode (using international calibration cotton) . The fibre quality attributes of cottons obtained while using HVI mode and ICC mode are given in Table 6.

150.------------------,

o o

Z 130 :> ::::> C/) '-"

C/) C/)

Cl)

t:: 110 ·c .~

:r:

0 1 I Z N :.:: :> ...... ...l :r: ;::J u VJ ,:::)

1 I 1 1 I V) 'D :r: « :r: r-;::J VJ U ~ U 0"-

r-u w.l ...l ~

:2 :2 >

Cottons

Fig. 6--Hai riness index of difFerent coltons

Table 5 - Hairiness index for different coun ts

Colton variety

SUVIN

MCU 5

DCH 32

LK

S6

MECH

LRA

RCH

V 797

Co unt Ne

205 30s 40s 50s 60s 80s 1005

205 305 40s 50s 60s 80, 90s

20s 30s 40s 50s 60s 80s

205 305 40s 50s 60s

20s 305 40s 50s 60s

205 305 40s 50s

205 305 405

205 305

205 305

Hairiness in dex

7.05 5.66 4 .63 4 .33 3.7 1 3.59 3.09

6.1 5 5.75

.17 4 .8 1 4 .51 4 .20 :;.99

5.88 5. 51 4 . 5 4 .66 4 .28 3.83

6.59 5.98 5. 13 4.68 4.39

6.46 5.87 5.44 5.06 4 .70

6.98 6.33 5.87 5.57

8. 15 7.28 6 .47

7.39 6.52

7.60 6.44

Table 6 - Fibre properties obtained in HVI mode and ICC mode

Testing mode

HVI

ICC

Fibre properties obtai lied

Upper half mean length (UHML) Uniformity index (U I) Bundle strength and e longation Fineness

2.5 % span length (2.5 % SL) UniFormity ratio (UR) Bundle strength and e longation Fineness

CHELLAMANI et al.: RELATIONSHIP BETWEEN COTION PROPERTIES & YARN STRENGTH/UNEVENNESS 17

Table 7 - Ratios of fibre properties measured using HVI and ICC modes

Cotton Ratio of fibre I2rol2erties variety Mean length (HVI) / Bundle strength (HVI) / Fineness (HVI) / FQI (HVI) /

50% Span length (lCC) Bundle strength (ICC) Fineness (ICC) FQI (lCC)

V 797 1.73 1.37 0.98 2.21

RCH 1.90 1.34 1.07 2.19

LRA 1.65 1.22 0.95 2.35

MECH 1.67 1.1 2 1.00 2.49

S6 1.80 1.23 1.00 2.39

LK 1.84 1.32 1.06 2.14

DCH 32 1.92 1.31 1.04 2.16

MCU5 1.76 1.29 0.97 2.28

SUVIN 1.77 1.17 0.97 2.09

Average 1.79 1.26 1.00 2.24

Mean length (ML) - Upper half mean length x Uniformity index 50% Span length - 2.5 % span length x uniformity ratio

It is of interest to know how the fibre properties measured using ICC mode are related with that measured using HVI mode, as shown by the following three ratios :

(i) Mean length (HVI)

50% Span length (ICC)

(ii) Bundle strength (HVI) , and Bundle strength (ICC)

(iii) Fineness (HVI)

Fineness (ICC)

The values obtained for all the 9 cottons studied are given in Table 7.

Mean length and bundle strength by HVI mode are found to be higher on an average by 80% and 25 % respectively as compared to 50% span length and bundle strength by ICC mode. However, there was no difference in fibre fineness values measured in both the modes.The overall fibre quality (FQI) obtained in HVI mode is found to be 2.25 times greater than that obtained in ICC mode.

4 Conclusions 4.1 Two expressions, one for predicting Rkm value and the other for predicting yarn irregularity, from newer fibre length and strength parameters measured on HVI testing system using HVI test mode have been derived.

4.2 The actual and predicted values for both Rkm and unevenness are found to be very close, the correlation coefficient being 0 .969 in case of Rkm and 0.990in the case of yarn irregularity . 4.3 The Rkm value at optimum twi st decreases at the rate of 0 .55% for unit increase of count for short and medium staple cottons and 0.35 % for long and extra long staple cottons. 4.4 The square of micronaire value divided by the square of mean length (obtained in HVI mode) is highly correlated with the contribution of fibre properties to yarn irregularity . in view of this , the factor [fIL] which would approximately depend on the ratio of fibre diameter to fibre length can be taken as measure of cotton quality with regard to yarn irregularity. 4.5 Of the total yarn irregularity, 42% is due to cotton quality, 40% due to condition of ring frame & draft employed and the remaining 18% due to roving quality. 4.6 Breaking elongation of spun yarn is greatly influenced by the count spun , twi st and cotton employed. On an average, increase of every 10 counts reduces elongation by 0.43% (absolute values) and the increase of every I TM (from the optimum value with regard to yarn strength) improves elongation by about 0 .5%. 4.7 Yarn elongation varies between cottons by about 33%, being the highest for DCH 32, about 7% lower for SUVIN and MCU 5, 15% less for LK, 18% lower for RCH, 25 % lower for S 6 and MECH and 33% for V 797 .

18 INDI AN 1. FIBRE TEXT. RES ., MARCH 2004

4.8 Yarn hairiness decreases with count and twist but exhibits progressive increase of about 50% with lower quality cottons. 4.9 SUVIN cotton yarns show the lowest level of hairiness followed by DCH 32 and LK (12% more), MCU 5 and S 6 (20% higher), and MECH, RCH and V 797 (33 % greater). For a given cotton, hairiness decreases by about 10% each fo r every increase of 10 counts and 1 TM (from the optimum levels with regard to strength). 4.10 The overall fibre quali ty (FQI) in HVI mode was found to be about 2.25 times o f that obtained in ICC mode.

Acknowledgement The authors are thankful to Ms. Indra Doraiswamy,

Research Advisor, S ITRA, for her guidance at vari ous stages of work .

References 1 Ratnam T V, Seshan K N & Govindarajulu K, J Texl 111.1'1, 65

(2) (1 974) 6\.

2 Turner A J, Emp COl/on Gr Rev, ( I) ( 1924) 107.

3 Subramaniam T A & 8 andyopadhyay S, An equati on fo r predicting the lea strength of ring spun cotton yarns, Proceedil/.gs, the J 3,h Joint Technological Conference of A T1RA, BTRA & SITRA (ATlRA, Ahmedabad), 1972, 83.

4 Ratnam T V, Indra Dorai swamy & Chellamani P, Fibre quality-yarn strength relationships and spin ning performance, SITRA Research Reporl , 34 (6) September 1989.

5 Chellamani K P, Ravindran M S & Ratnam T V, Factors influencing imperfec ti ons in cotton yarns, SITRA Research Reporl, 43 ( 11 ) December 1998.

6 Ratnam T V, Indra Doraiswamy, Chellaman i K P, Gnanasekar K & Ravindran M S, Fibre and yarn re lat ionships using HVIIFMT measured fi bre propert ies, J Federalion Asian Professional Texl Assoc, 3 (1 ) ( 1995) 42 .