Indian Journal of Fibre & Textile Research Vol. 25, September 2000, pp. 1 69- 1 76

Influence of spin finish and opening roller speed on the characteristics of OE friction-spun acrylic yams

S Dhamija', G K Tyagi & D Kamar

The Technological Institute of Textile & Sciences, B hiwani 1 27 02 1 , India

K R Salhotra

Department of Textile Technology, Indian Institute of Technology, New Delhi 1 1 0 0 1 6, India and

S K Sett

Institute of Jute Technology, 35 Ballygunge Circular Road, Calcutta 700 0 19, India

Received 17 June 1999; revised received 27 August 1999; accepted 26 October 1999

The influence of composition and level of spin finish and of opening roller speed on the characteristics of OE friction­spun yams spun from acrylic fibres has been studied. It is observed that a change in composition or level of spin finish sig­nificantly affects the yam twist, tenacity, mass irregularity, abrasion resistance and flexural rigidity. An increase in opening roller speed significantly increases the breaking extension but does not cause any systematic variation in other yam charac­teristics except the mass irregularity and flexural rigidity, which show an initial decrease followed by an increase with the increase in opening roller speed.

Keywords : Acrylic yam, DREF-II yam, Fibre friction, Friction-spun yam, Opening roller speed, Spin finish

1 Introduction

The processing behaviour of fibres during different stages of yarn formation largely depends on their sur­face characteristics. These characteristics are, there­fore, of prime importance in a spinning system and friction spinning is no exception to it. Moreover, in friction spinning, twist is generated through frictional contact between fibre assembly and drum surfaces. Hence, higher fibre-to-metal friction and fibre-to­fibre friction are desired for getiing a higher twist level and inter-fibre cohesion. However, a higher in­ter-fibre friction may adversely affect the perform­ance of opening roller in fibre individualization. Fur­ther, more opening roller wrap-ups are encountered when a fibre contains a high lubricant level, while too low a lubricant level causes static problems at card­ingl . One will, therefore, have to be very careful in optimizing the frictional properties of fibres.

In the case of natural fibres, the inherent fibre

a To whom all the correspondence should be addressed. Phone: 4256 1 ; Fax: 09 1 -0 1 664-43728; E-mail : titsintr@nde.vsnI.net.in

properties are generally accepted as such while in the case of man-made fibres, there is an immense choice. As it is well known, a spin finish is applied during fibre manufacture. The ingredients and their propor­tion may vary depending on the type of fibre used and the requirements for processing. However, to improve the processability, it is recoriunended to use addi­tional finish (some effective antistatic agent and lu­bricant) on the fibres during stacking. This may mod­ify the fibre friction and may influence the fibre opening efficiency and rate of twist insertion in fric­tion spinning system. Most of the published work on friction spinning is concentrated on the complex mechanism of yarn formation2-1 1 and its comparison with other systemsI2-17 while a few papers deal with the influence of process variables on the resultant yarn characteristics I 8-20. Although these studies do emphasize on fibre frictional properties, no data re­garding the changes in fibre finish characteristics are reported so far2 1-22. The present work was, therefore, aimed at studying the influence of spin finish (a term used to denote added fibre finish during stacking) and opening roller speed on yarn twist and other charac­teristics of OE friction-spun acrylic yarns.

1 70 INDIAN J.F1BRE TEXT. RES., SEPTEMBER 2000

2 Materials and Methods 2.1 Preparation of Yarn Samples

LV40 and 2 152P, widely used in the spinning mills, were mixed in three different proportions, viz. 1 00:0, 75:25 and 50:50, to get three different compo­sitions of spin finish. Each of these compositions, after dissolving in a fixed quantity of water (4% over the weight of fibres), was sprayed as uniformly as possible on nine batches (5 kg each) of the acrylic fibres (5 1 mm, 1 .67 dtex) at three different levels of 0.2%, 0.4% and 0.6% (owf). All the samples were processed on an MMC card and a Lakshmi Rieter DOI2S drawframe. Three drawing passages were given to the carded slivers and the linear density of drawn slivers was adjusted at 3 ktex. The drawn sliv­ers were then spun into friction yarns of 98.4 tex on DREF-II spinning machine. The spinning particulars are given in Table 1 .

2.2 Measurement of Coefficients of Friction

The coefficients of fibre-to-fibre and fibre-to-metal frictions were measured on an Instron tensile tester by using an extra attachment fabricated by Sengupta et aL.2' . Two fibre fringes with a uniform density of 5 mglcm2, as suggested by Lord2\ were placed one above the other and then a known weight of 40 g was placed on these fringes. The top fringe was attached to the load cell of the Instron by an inextensible cord through frictionless pulley. As the cross-head was made to move, the maximum frictional force devel-

Table I-Spinning particulars

[Yam linear density, 98.4 tex; Friction drum speed, 2650 rpm; Yam delivery rate, 1 30 mlmin; and Friction ratio, 5. 1 ]

Yam ref. Composition Level of spin Opening roller no. of spin finish finish speed

(LV 4012 1 52P) % rpm

S I 1 00 : 0 0.2 2850 S2 1 00 : 0 0.4 2850 S3 1 00 : 0 0.6 2850 S4 75 : 25 0.2 2850 S5 75 : 25 0.4 2850 S� 75 : 25 0.6 2850 S7 50 : 50 0.2 2850 Sx 50 : 50 0.4 2850 S9 50 : 50 0.6 2850 SIO 1 00 : 0 0.2 3400 S I I 1 00 : 0 0.4 3400 S 12 1 00 : 0 0.6 3400 S13 1 00 : 0 0.2 3800 S14 1 00 : 0 0.4 3800 S I� 1 00 : 0 0.6 3800

oped between the fibre fringes at the point of slippage was recorded by the Instron. For measuring the fibre­to-metal friction, a single fringe was made to rest over a bare metal plate and the same operation was re­peated to record the maximum resisting force at the time of slippage. From the values obtained, the coef­ficients of fibre-to-fibre and fibre-to-metal frictions were calculated using the Amontons' Law.

2.3 Measurement of Yarn Twist

Actual twist of OE friction-spun yarns cannot be measured easily and accurately due to their inhomo­geneous twist structure. However, the apparent twist estimated by the commonly used laboratory methods can be used on a relative basis for comparison. This apparent twist of all the yarn samples was measured by detwist-retwist and twist-to-break methods using Eureka single yarn twist tester.

2.3.1 Detwist-Rewist Method

For all the yarn samples, a standard length of 254 mm was taken to measure the yarn twist. A minimum of twenty observations were made for each sample.

2.3.2 Twist-to-break Method

In this method, a yarn of 254 mm length was taken and twisted in the direction of original twist in the yarn. Twisting was continued till the break and the number of turns required to break the yarn (N,) was noted. The test was repeated but this time twisting was done in a direction opposite to that of the original twist and again the number of turns required to break the yarn (N2) was noted . The twist was then calcu­lated by using the following relationship :

Turns/m = (Nz-N1) x 39.37

2.4 Measurement of Yarn Diameter

Yarn diameter was measured using the Projectina (magnification, 28 x). Sixty observations were made for each sample at random.

2.5 Measurement of Tensile Properties

Single yarn tenacity and breaking extension were measured on an Instron Tensile Tester (Model 44 1 1) using 500 mm test specimen and 200 mmlmin exten­sion rate. Fifty observations were made for each sam­ple.

2.6 Measurement of Yarn Unevenness and Imperfections

The yarn unevenness was measured on Uster Evenness Tester (UT-3) with a yarn speed of 1 00

DHAMIJA et al. : FRICTION-SPUN ACRYLIC YARNS 1 7 1

mlmin and evaluation time of 2 min. The sensitivity of spin finish. The two coefficients of friction in-levels used were : Thick places, +50%; Thin places, - crease with an increase in the level of spin finish. 50%; and Neps, + 200%.

3.1 Yarn Twist

2.7 Measurement of Abrasion Resistance Table 3 shows the average twist values of different Resistance to abrasion was measured in terms of

number of abrading cycles to rupture the specimen by Table 2-Influence of composition and level of spin finish on

Custom Scientific Abrasion Tester following the frictional coefficients of acrylic fibres

ASTM standard test method D 3 885. Spin finish Spin finish Coefficient of friction composition level Fibre-to-fibre Fibre-to-metal

2.8 Measurement of Flexural Rigidity (LV 40121 52P) % (llFF) (llFM) Flexural rigidity was measured by using weighted

1 00 : 0 0.2 0.576 0.268 ring-loop method suggested by Peirce24 and modified by Owen and Riding25•

0.4 0.590 0.292 0.6 0.645 0.3 1 1

3 Results and Discussion 75 : 25 0.2 0.635 0.305

Table 2 shows the changes in frictional coefficients 0.4 0.637 0.3 1 6

of acrylic fibres with respect to the composition and 0.6 0.703 0.328

level of spin finish. It is clear that 75:25 composition 50 : 50 0.2 0.595 0.296 of LV 40/21 52P exhibits the highest values of fibre- 0.4 0.6 1 1 0.299

to-fibre friction and fibre-to-metal friction at all levels 0.6 0.654 0.3 1 9

Table 3-lnfluence of spin finish and opening roller speed on characteristics of friction-spun yams

Yam Twist, tEm Diameter Tenacity Breaking CVm Irn�rfections/km Abrasion Flexural

ref. Detwist- Twist-to- mrn gltex extension % Thin Thick Neps Total resistance rigidity no. retwist break % places places (+200%) cycles mN-

method method (- 50%) (+50%) mm2

S ) 436 5 1 6 0.6342 5.67 1 8.85 15. 1 2 1 0 5 29 44 325 1 1 .74 ( 6.44) ( 1 0.29) ( 1 2.83) ( 14.05) ( 9. 1 8)

S2 452 523 0.5797 5.45 1 7.5 1 1 6.97 14 5 36 55 273 1 0.04 ( 5.75) ( 4.9 1 ) ( 1 1 .28) ( 9.52) ( 9.22)

S3 4 1 9 476 0.6474 5.79 1 6.49 22.07 62 6 1 85 208 232 14.21 ( 4.69) ( 1 1 .66) ( 1 2.72) (10.04) ( 1 1 . 1 1 )

S4 437 5 1 7 0.59 1 8 5.60 1 9 . 1 9 1 6.30 9 6 29 43 254 1 8.84 ( 9.09) ( 1 1 .36) ( 1 3.09) ( 1 1 .50) ( 1 3.33)

S5 457 557 0.5546 5 . 1 5 1 6.73 1 9.83 46 23 78 147 246 1 1 .75 ( 7.39) ( 6.84) ( 12.02) ( 1 2.45) ( 1 4.76)

S6 423 490 0.6001 5.55 17.61 22.8 1 96 65 98 259 1 95 22.82 ( 8.98) ( 1 0.93) ( 1 1 .62) ( 8.48) ( 9.58)

S7 4 1 3 478 0.6723 5.76 1 7.59 1 5.74 7 5 25 37 226 14.21 ( 6.0 1 ) ( 7.58) ( 14.5 1 ) ( 7.58) ( 7.68)

S8 435 493 0.5882 5.59 1 8.89 17.64 1 2 1 6 3 9 67 222 1 0.37 ( 4.20) ( 7.38) ( 14.02) ( 7.86) ( 8.86)

S9 356 478 0.6666 5.74 1 8.50 22.78 93 6 1 96 250 1 89 1 5.05 ( 8.74) ( 7.70) ( 1 4.22) ( 1 5.32) ( 7.43)

S)() 447 5 1 9 0.639 1 5.67 1 8.84 1 3 .48 0 7 8 3 1 2 1 1 . 1 8 ( 4. 1 4) ( 7.3 1 ) ( 1 0.07) ( 6.73) ( 6.59)

S) ) 459 534 0.5884 5.74 1 8.72 14.93 7 2 1 2 2 1 277 8.65 ( 6.05) ( 4.85) ( 10.75) (\ 1 .62) ( 8.48)

SJ2 439 497 0.6502 5.76 1 7.09 17.87 6 0 9 I S 1 82 1 0.03 ( 1 1 . 14) ( 5.33) ( 8.56) ( \ 6.69) ( 9.85)

SI3 462 529 0.6205 5.99 1 9.48 12.9 1 0 0 3 3 293 14.21 ( 4.38) ( 9.42) ( 1 0.86) ( 6.86) ( 7.97)

S)4 428 483 0.637 1 5.74 1 8.92 1 8.04 23 I I 47 8 1 1 84 1 1 .60 ( 3.76) ( 9.05) ( 1 1 .35) ( 7.6 1 ) ( 8 . 17)

S)5 407 46 1 0.6652 5.94 1 7.97 20. 14 63 23 90 1 82 1 85 1 6.24 ( 1 0.84) ( 6.99) ( 8.56) ( 7.43) ( 8.34)

Values in Earentheses indicate CV %

1 72 INDIAN J.FlBRE TEXT. RES., SEPTEMBER 2000

yam samples when tested by detwist-retwist and twist-to-break methods. It is observed from Fig. 1 that for both the methods, 75:25 LV40/2 1 52P spin finish yields the maximum yam twist, and there occurs a marginal increase followed by a significant decrease in the apparent twist of OE friction-spun yams with an increase in the level of spin finish, irrespective of composition of spin finish. The decrease in twist val­ues has been found to be significant at both 1 % and 5% levels of significance. An increase in opening roller speed also results in a slight increase in twist followed by a significant decrease in all the cases ex­cept at low level of spin finish (0.2%) where the twist increases continuously (Fig. 2) .

In friction spinning, the amount of twist inserted in the yam depends on the yam delivery rate and the diameter of the fibre sleeve formed at the nip of the friction drums. In the present study, the yam delivery rate was kept constant at 1 30 mlmin while the di­ameter of fibre sleeve was influenced by, apart from the other factors, the stiffness of the fibrous material and the coefficient of friction between the drum and fibrous sleeve. With a higher friction between the two, i .e. larger coefficient of fibre-to-metal friction, the sleeve is pressed into the wedge or nip of the fric­tion drums with a higher force, resulting in a smaller sleevel l . On the other hand, poor fibre individualiza­tion, as a result of increased fibre-to-fibre friction, is expected to lead to a bigger fibre sleeve due to the higher stiffness of the larger fibre aggregates. The higher fibre-to-metal friction would increase the twist while the higher fibre-to-fibre friction would decrease it. Since both fibre-to-fibre and fibre-to-metal fric­tional coefficients are affected by a change in compo­sition and level of spin finish, the effect of composi­tion and level of spin finish is determined by the combination of these two effects. The initial increase in apparent twist with the increase in spin finish level up to 0.4% may be attributed to the increase due to the higher fibre-to-metal friction outweighing the de­crease caused by the higher fibre-to-fibre friction. At higher level of spin finish (0.6%), the lower opening due to the increased inter-fibre friction may be play­ing a more dominant role, decreasing the yam twist. Similar explanation may also be given for the highest twist achieved in case of 75:25 LV4012 1 52P spin finish.

In the case of opening roller speed, the continuous increase in yam twist for low level of spin finish may be due to the better fibre opening at higher speeds,

E

SOOr---------------�----------__ --_, Opening roller speed. 2850 rpm Detwist-retwist mathod .r1.. 4 S 0*-� __ �::::�����������1

�� 4 0 0

3 5 0 -

� 3 00 �--____________ J-______________ � .1ii 600 r-----------------------------. � Opening roUer speed. 2850 rpm'

Twist-to-break mathod S S O

500 �------�----��

4 5 0

400�-------------�--------------� 0. 2 0,4 0.6

Level of spin finish. %

Fig. I -Influence of spin finish level on twist of DREF-II spun yams [LV40121 52P : (-e-) 1 00:0 ; (-D-) 75:25 ; and (-0-) 50:50]

E

5 00r------------------t-V-4-W-2 1-52�P�( 1-0-0:0�)-, Oetwist-retwisrmethOd 480

440L_-----:::::::c

� 4 OO L...-______________ -'-___________ --' .iii "6 00�------------------__,�=::-:::_=_, � LV 40/2152P (100:0)

Twist-to-break method

5 5 0

SOO'L_------:--"'-"---4 50

400� ______________ �-------------�� 2850 3325 3800

Opening roller speed. rpm

Fig. 2-lnfluence of opening roller speed on twist of DREF-II spun yams [Spin finish level : (-e-) 0.2% ; (-D-) 0.4% ; and (-0-) 0.6%)

resulting in smaller sleeve diameter. While in case of higher fibre-to-fibre friction brought about by the in­creased level of spin finish (beyond 0.2%), an in­crease in the opening roller speed beyond 3400 rpm results in the irregular fibre opening accompanied by excessive fibre damage26 and poor fibre alignment. Consequently, the frictional conditions at the surface of friction drums change and may be responsible for the decrease in yam twist.

DHAMIJA et al.: FRICTION-SPUN ACRYLIC YARNS 1 73

3.2 Tenacity

The tenacity values of yarns spun at different levels of opening roller speed and spin finish with different compositions are shown in Table 3 . The weakness in strength of OE DREF-II friction-spun yarns is quite evident from the results. Yarn tenacity varies within a narrow range of S-6 gltex for different spinning con­ditions. An increase in inter-fibre friction, by any means, is expected to increase the yarn strength. Contrary to this expectation, an increase in the spin finish level lowers the strength, the lowest yarn te­nacity being observed at 0.4% level (Fig. 3). Moreo­ver, comparatively stronger yarns are produced with a spin finish containing SO% LV 40 and SO% 2 1 52P instead of 7S:25 (LV40/2 1 52P) combination which has the maximum inter-fibre friction (Table 2). Such a trend is probably associated with the obliquity ef­fect of the fibres at higher values of friction ratio (S . l i n this particular study), considered to be equivalent to twiseo. This may not be apparent from the twist values given by the detwist-retwist and twist-to-break methods. When this twist is converted to actual twist as measured by optical method using the tracer fibre technique, it is observed that at higher twist levels the actual TM is around 7.5 (ref. 27). An increase in twist increases the intensity of the aforesaid obliquity ef­fect, causing a further deterioration in yarn strength while a decrease in twist favours an increase in yarn tenacity.

The effect of opening roller speed on yarn strength (Fig. 4) is not so significant as expected. The yarns spun at a lower speed of 28S0 rpm exhibit somewhat lower yarn strength but an increase in opening roller speed does not show any specific trend.

3.3 Breaking Extension

The influence of spin finish level and opening roller speed on breaking extension is shown in Figs. S and 6 respectively. No trend is observed in relation to spin finish but there is a significant increase in the values of breaking extension with the increase in opening roller speed. This may be attributed to the fact that the fibres SUbjected to higher degree of bending and buckling during assemblage, as a conse­quence of increased decelerating forces at higher opening roller speed, tend to straighten during tensile loading.

3.4 Mass Irregularity

Mass irregularity appears to be the most affected parameter of OE friction-spun yarns by the variables

6.0 r----------:o::-pe-:-:n::::on�g =rol;;:le:-:r s::::pe=ed�.?i28:r.;-50o,r;;;;pm:n1

� '§. 5.6

� c 5.4 {!!

5.2 5.00L.2--------0..J..4--------70.6

Level of spin finish. %

Fig. 3-Influence of spin finish level on tenacity of DREF-II spun yams [LV40121 52P : (-e-) 1 00:0 ; (-0-) 75:25 ; and (-0-) 50:50]

6.5r--------��--��--_.,

� 6.0 'd,

. LV 4012152P (100:0)

Spin finish level ' . -.. 0.2 %

-0- 0.4 % -0- 0.6 %

5.0 L----------:�-------�3800 2850 �325 Opening roner speed. rpm

Fig. 4-Influence of opening roller speed on tenacity of DREF-I1 spun yams

20 r----------���-���� Opening roller speed, 28$0 rpm a: 19 c .2 .. c � 18 '" � � 1 7 III

1 6.�-------........ ---------.J 0.2 0.4 0.6 Level of spin fin1sh, %

Fig. 5-Influence of spin finish level on breaking extension of DREF-I1 spun yams [LV40121 52P : (-e-) 1 00:0 ; (-0-) 75:25 ; and (-0-) 50:50]

20r-----------������ LV 4012152P (100:0) ;Ii. i I9t----------:::t.I===-----4 � ]j 1S 00 � c5 17L_-------�

1 6�:-------_:_:�------___:--I 2&50 ,325 3800 Opening roller speed, rpm

Fig. 6-Influence of opening roller speed on breaking extension of DREF-I1 spun yams [Spin finish level : (-e-) 0.2% ; (-0-) 0.4% ; and (-0-) 0.6%]

1 74 INDIAN J.FIBRE TEXT. RES., SEPTEMBER 2000

under investigation. It increases significantly with the increase in spin finish level (Table 3 and Fig. 7) and out of the three different proportions of LV 40 and 2 1 52 P used, the one (75 :25) which results in maxi­mum fibre-to-fibre friction (Table 2) produces the most irregular yarn. The coefficient of mass variation attains a value as high as 22.8 1 %. Further, as per the expectations, Table 3 and Fig. 8 depict a general im­provement in yam unevenness with an increase in opening roller speed up to 3400 rpm. However, the yam unevenness deteriorates when the speed is fur­ther increased to 3800 rpm except at 0.2% spin finish level at which it continuously improves. The deterio­ration in yam unevenness is obviously due to the inef­ficient and irregular fibre opening either due to the lower opening roller speed or the higher inter-fibre friction on one side, and the poor fibre alignment and the excessive fibre damage at higher opening roller speed on the other side26• The difficulties in fibre re­moval from the wire points of the opening roller at too low speeds28 and high fibre-to-metal friction also contribute to the higher coefficient of mass variation. In relation to the influence of opening roller speed, the results of this particular study agree with the ear­lier findings of Lo and Cheng28 who observed 3400

rpm as the optimum speed for various types of fric­tion-spun yams.

3.5 Imperfections

The measured values of thin places (-50%), thick places (+50%) and neps (+200%) are given in Table 3. It is observed that the imperfection indices follow almost the same pattern as that of coefficient of mass variation. The imperfections achieve their lowest val­ues at the optimum opening roller speed of 3400 rpm in case of 0.4% and 0.6% levels of spin finish. In case of 0.2% level, a speed of 3800 rpm produces the minimum number of imperfections.

3.6 Abrasion Resistance

The results of abrasion resistance (Table 3 and Fig. 9) indicate that 1 00% LV 40 spin finish produces the yams with the maximum resistance to abrasion, irre­spective of spin finish level. However, a significant decrease in the abrasion resistance of OE DREF-II friction-spun acrylic yams is observed with the addi­tion of 2 1 52 P in the spin finish and increase in the level of spin finish. This is probably associated with the coefficient of fibre-to-metal friction. A lower friction between the fibres and a metal , as in case of

24,---------------__ --,

�2 0

.. e {i 16 ..... 100:0 ,-D' 75 :25 -0- 50' :50

1 2�-------�------------�, , 0.2 0.4 0.6

Level of spin finish. %

Fig. 7-Influence of spin finish level on CYrn % of DREF-II spun yarns

24r-----------------�--, LV 4012152P (100:01

* f u 16

1 2��

-----���

------� 2850 3 3 2 5 3600

Opening roller speed. rpm

Fig. 8-Influence of opening roller speed on CYrn % of DREF-I I spun yams [Spin finish level : (-e-) 0.2% ; (-0-) 0.4% ; and (-0-) 0.6%]

3 S0r----------------����__.��__, Opening roller speed, 2650 rpm ':g .lV40 12152P composition � 100:0 ,-D- 75 :25

� 300 8 � � 5�--------------�L

-0- 50 :50

'u; I!! .§ 2 00 e � l S0�--------------�--------------�

0. 2 0.4 0.6 Level of spin finish, %

Fig. 9-Influence of spin finish level on abrasion resistance of DREF-II spun yarns

100% LV 40 spin finish (Table 2), decreases the in­tensity of transmission of frictional force from the abrading surface to the fibres21 which decreases the rate of wear, thus improving the abrasion resistance. As the frictional coefficient of fibre and metal in­creases with the increase in spin finish level, the transmission of friction force improves and predomi­nates over the concominant increase in inter-fibre cohesion which resists the ejection of fibres from the yam body during abrasion, thereby lowering the abra­sion resistance.

DHAMIJA et al.: FRICTION-SPUN ACRYLIC YARNS 1 75

3 5 0 �----

----

--------

----------

----� LV40 121 52P (100:0) .

,------

. I S0 '--__________ _,__---'----------------.....J 2850 3325 3800

Opening roler speed. rpm

Fig. 1 0--Influence of opening roller speed on abrasion resistance of DREF-II spun yams [Spin finish level : (-e-) 0.2% ; (-0-) 0.4% ; and (-0-) 0.6%]

2 5 --------------------���-------, Opening roller speed. 2850 rpm LV40 12152P composition ...... 1 00:0 .{)- 75 :25 ...0- 50 :50

� 1 o·r-----=:::::::��:;:::::;-)( .!1 . u. 5 L-______________ � ______________ �

0.2 0.4 0.6 Level of spin finish. %

Fig. I I-Influence of spin finish level on flexural rigidity of DREF-I I spun yams

It may also be observed from Fig. 10 that the abra­sion resistance does not show any systematic trend with the increase in opening roller speed.

3.7 Flexural Rigidity Table 3 shows that the flexural rigidity is signifi­

cantly affected by the opening roller speed and com­position and level of spin finish. It decreases initially and then increases with the increase in spin finish level and opening roller speed. However, a decrease in the concentration of LV40 from 100% to 50% in the spin finish shows just the opposite trend, dis­playing maximum rigidity at 75% level . This is obvi­ously due to the restricted freedom of fibre movement during bending as a consequence of increased inter­fibre cohesion at higher friction coefficient of single fibres.

Fig. 1 1 shows the lowest flexural rigidity at 0.4% level of spin finish while the corresponding lowest in relation to opening roller speed (Fig. 12) is at 3400 rpm which incidentally is also the optimum speed for various other characteristics of OE friction-spun acrylic yarns.

iOr-------------------�--� __ ��� LV 40121.52P (100: 0) Spin finish level·

...... 0.2% . -0- 0.4% -0- 0.6%

��8�50�------------

3�3�25------

---------3�800 Opening roner speed. rpm

Fig. 1 2-Influence of opening roller speed on flexural rigidity of DREF-II spun yams

Flexural rigidity has also a close association with the yarn geometry. As a result of this, a higher twist in the yarn may result in a lower flexural rigidity in spite of the lower degree of freedom of fibre move­ment as described by Backer29• The variation in flex­ural rigidity as shown in Figs. 1 1 and 1 2 can thus be explained on the basis of variations in yarn twist oc­curring as a result of increase in spin finish level and opening roller speed (Figs. 1 and 2). The corre­sponding changes in yarn diameter (Table 3) com­bined with fibre alignment may explain the trend in flexural rigidity at different levels of spin finish and opening roller speed.

4 Conclusions 4.1 The apparent yarn twist of OE friction-spun yarns changes appreciably with the change in compo­sition and level of spin fin ish. On the other hand, an increase in opening roller speed shows different trends for yarn twist at different levels of spin finish.

4.2 A 50% concentration of 2 1 52P in the spin finish produces comparatively stronger yarns in OE friction spinning system. However, the tenacity of OE DREF­II yarns show a decreasing trend as the spin finish level is increased from 0.2% to 0.4% followed by an increase with the further increase in level of spin fin­ish. The influence of opening roller speed on yarn strength is not so significant. 4.3 In DREF-II yarns, the breaking extension does not show any definite trend with the change in com­position or level of spin finish but it increases signifi­cantly with the increase in opening roller speed. 4.4 Among the different compositions of LV40/21 52P spin finish, 75:25 LV40/2 1 52P displays the maximum unevenness and imperfections for OE DREF-II friction-spun yarns. The irregularity in­creases with the increase in level of spin finish. There

176 INDIAN J.FIBRE TEXT. RES., SEPTEMBER 2000

is an improvement in the yarn evenness accompanied by decrease in imperfection levels with an increase in opening roller speed up to its optimum level (3400 rpm). The unevenness deteriorates beyond the opti­mum level of opening roller speed for most of the friction-spun yarns. 4.5 Increase in the proportion of 2 1 52P in spin fin­ish and that in the level of spin finish considerably decreases the abrasion resistance. 4.6 Change in opening roller speed does not show any systematic variation in the number of cycles to abrade. 4.7 Flexural rigidity is significantly affected by the opening roller speed and composition and level of spin finish. It decreases initially and then increases with the increase in spin finish level from 0.2% to 0.6% and opening roller speed from 2850 rpm to 3800 rpm. However, a decrease in the proportion of LV 40 from 100% to 50% in the spin finish shows just the opposite trend.

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