(65) Vol. 41, No. 5 (1985) T-211 - JST

(65) Vol. 41, No. 5 (1985) T-211

Technical Section

(Received July 10, 1984)

THE COEFFICIENTS OF FRICTION OF VARIOUS FIBERS

BY ROEDER'S METHOD

By Waichiro Tsuji, Kyoko Yoshida and Shigeko Asahara

(Faculty of Home Economics, Mukogawa Women's University, Ikebiraki-cho, Nishinomiya, Hyogo Pref., 663 Japan)

Synopsis

The static and kinetic coefficients of friction of various fibers were systematically measured by Roeder's method at the velocity ranging from 0 to 20m/min. Fibers tested were viscose rayon, cupra, polynosic, acetate, nylon 4, nylon 6, nylon 11, Nomex, Kevlar, polyester, alkali treated

polyester, polyethylene, polypropylene, vinylon having cocoon-like or circular cross-section, silk, and wool, respectively. In order to confirm the effect of shape of cross-section, the coefficients of friction of polyester and nylon filaments having various shapes such as circular, trilobal, pentagonal,

pentalobal and octalobal were also measured. All fibers tested except wool moved in scale direction, showed similar relation of the coefficient of friction with the circumferential velocity of the cylinder, i.e. the value decreased with increasing velocity at the initial stage and showed a minimum at the velocity 1m/min., gradually increased and levelled off at around 10 to 20m/min. Wool gave different values depending on the direction of rubbing. The effect of alkali treatment of polyester fiber was also examined.

Introduction

The coefficient of friction of fiber is the im

portant property related either to spinning and weaving processes and to the handling touch of textile fiber and fabric. Although various methods of measuring the coefficient of friction have been reported, the method developed by Roeder1)

possesses many advantages as following;(1) The construction of the apparatus is simple.(2) Short staple fiber can be used as sample.(3) The quantity of sample fiber required is small.(4) Both static and kinetic coefficients of friction

can be measured by the same apparatus.

(5) Kinetic coefficient of friction can be measured at various velocities.

(6) Reproducibility of data is high.(7) By selecting the material of the cylinder, the

coefficient of friction of fiber to any other material can be measured. Tsuji2) has already constructed the apparatus,

examined Roeder's method and particularly discussed on the measurement of the static coeffi

cient of friction.

In recent years, many kinds of new fiber have

been developed, however, the coefficient of fric

tion of these new fibers measured systematically

by the same apparatus seems not to be reported.

In this work, the static and kinetic fiber-to-fiber

coefficients of friction of various fibers including

such new fibers were measured using Roeder's

method and effects of fiber structure were dis

cussed.

Experimental

Measurement of the Coefficient of Friction

The experimental apparatus of Roeder's method

used in this research is schematically shown in

Figure 1. The surface of a short cylinder made of

bakelite, diameter of which is 8mm, is covered in

the following way with fibers arranged parallel to

the cylinder axis.

Short cut fibers are arranged parallel on a paper

frame and both ends of the parallel laid fibers are

fixed to the paper frame with adhesive tape. This

parallel fiber layer is wound around the cylinder

T-212 SEN-I GAKKAISHI (•ñ•¶) (66)

Fig. 1. The schematic diagram of the apparatus

of Roeder's method.

and fixed with adhesive tape. This short cylinder,

covered with fibers parallel to the cylinder axis,

is fixed to the end of a shaft which can be rotated

at different velocities by gear change mechanism.

One filament is hung transversely over the

cylinder hanging 100 mg weight on both fiber

ends. The weight of one end is fixed to the hook

of a torsion balance. Test condition was deter

mined referring to JIS L 1074-1977 which desig

nated Roeder's apparatus to measure the coefficient

of friction of synthetic fibers.

For measuring the static coefficient of friction,

the cylinder is not rotated and the arm of the

torsion balance is moved until the filament start

to slip. The indication of the torsion balance

(a mg) is read. For measuring the kinetic coeffi

cient of friction, the cylinder is rotated at the

circumferential velocities of 1, 2, 5, 10 and 20

m/min., and the arm of torsion balance is moved

to keep the hook of the torsion balance at rest.

The indication at this equilibrium state (a mg)

is read.

In this way the static and kinetic coefficient of

friction can be calculated by the classical formula

T1=T0exp(ƒÊƒÆ), where ƒÊ is the coefficient of

friction, ƒÆ=ƒÎ, T1=100mg, T0=(100-a)mg in

this case. In each one series of experiment three

cylinders covered with fibers were used and for

each cylinder ten filaments were tested. Total

number of measurements were thirty, and an

average value and standard deviation were calcu

lated. Most experiments were carried out at about

20•Ž and 55-65% RH.

Experiment on Wool

Sample fibers except wool are long filament,

but wool fiber is too short to hang a single fiber

over the cylinder. Therefore, one filament of Kevlar was attached by adhesive to each end of a wool fiber and carried out the measurement contacting the part of wool with the cylinder and hanging 200mg weight on each end of Kevlar filament. As wool fiber has crimps, it is difficult to cover evenly the cylinder, so in this case the cylinder was covered with degummed silk filaments, and the initial load of 200mg was hung to each end of Kevlar filament to extend the crimps of wool fiber contacting with the cylinder.

As well known, wool fiber has scale on the surface and the frictional force depends on the direction of the rubbing motion (the differential frictional effect). Therefore, in the experiments on wool, the direction of wool fiber hung on the cylinder was reversed after one series of experiment and measurements were repeated.Experiment on Polyethylene Monofilament

As the polyethylene monofilament (50 d) was thick, the initial load of 200mg was applied. The kinetic coefficient of friction could be measured by this apparatus, although the variation of coefficient value was larger than those of other fibers. In the measurement of the static coefficient of friction, the initial load larger than 200mg seemed to be needed to obtain even data, but it was inconvenient to use such a large initial load in this apparatus. Then another method3) was used as follows.

As shown in Figure 2, over the two polyethylene monofilaments parallel laid under tension T, one

polyethylene filament was laid across at right angle and weights T0 were hung at each end. Then the weight at one end was gradually increased by

Fig. 2. The experimental method used for the

measurement of the static coefficient of

friction of polyethylene monofilament.

(67) Vol. 41, No. 5 (1985) T-213

adding additional loads carefully by hand, and the

load T1 was measured at which the filament

started to slip. The static coefficient of friction

was calculated by the following formula.

T1=T0exp(ƒÊƒÎ). In this case, the weights of

20 and 1g were used as T and T0, respectively.

Scouring of the Sample Fibers

Most sample fibers were extracted by benzene

ethanol mixture (wt. ratio 1:1) for 10 hours using

Soxhlet's extractor. Acetate, nylon 4 and poly

ethylene were scoured by benzene-ethanol mixture

at room temperature and in 0.3-1.0% aqueous

solution of Monogen (sodium sulfate of higher

alcohol) at 40•Ž for 1 hour. Polypropylene was

extracted by benzene-ethanol mixture at room

temperature for 6 hours. Wool was scoured with

aqueous solution of Monogen at 40•Ž.

Degumming of Silk

Raw silk was immersed into warm water for

30 minutes and treated with aqueous solution of

soap (15-20% owf, liquor ratio 30-50:1) at

about 95•Ž for 1-2 hours. Further treatment was

given with new aqueous solution of soap (10-15%

owf) at about 95•Ž for 1 hour and washed 2-3

times with 0.1% aqueous solution of sodium

carbonate. The weight decrease in degumming

was 22%.

Causticizing (Alkali Treatment) of Polyester Fiber

As the finishing method to increase the pliability

of the fabric, the treatments with NaOH aqueous

solution at high temperature are sometimes given

to polyester fabrics. The surface of the polyester

fiber is partially hydrolized, the weight of the

fabric decreased and pliability of the fabric in

creased. To examine the effect of this treatment

on the coefficient of friction, polyester filament

(2.5 d) was treated with 5% NaOH aqueous solu

tion at 98•Ž for 10, 20, 30 and 40 minutes. The

weight decreases were 7.50, 12.68, 19.26 and

25.47%, respectively.

Results and Discussion

1. The Coefficients of Friction of Various Fibers

The static and kinetic coefficients of friction

measured by the methods above described are

shown in the following tables and figures.

Rayon and Acetate. As shown in Table 1 and

Figure 3, the coefficients of friction of viscose

rayon, cupra, polynosic and acetate show similar

relation with the circumferential velocity of

cylinder. Minimum value appears at low velocity

(1m/min.). This is presumed to be the result of

the boundary contribution to the friction which

decreases at high velocity, and the viscodynamic

contribution which increases at high velocity.

Similar behaviors are seen in all other following

fibers except wool rubbed in scale direction.

Viscose rayon and polynosic showed nearly the

Fig. 3. Coefficients of friction of rayon and

acetate.

•› Viscose rayon •¢ Cupra

•¬ Polynosic • Acetate

Table 1. Coefficients of friction of rayon and acetate.

a) Tufcel made by Toyobo Co.


Table 2. Coefficients of friction of nylon and polyester fibers.

same values of coefficients of friction. Cupra gave

somewhat higher values. Acetate showed lower

values at low velocity. It may be caused by the

decrease of intermolecular attraction force dues

to the substitution of hydroxyl groups by acetyl

groups.

Synthetic Fibers. The results for various ali

phatic and aromatic nylons are shown in Table 2 and Figure 4. Among three kinds of aliphatic

nylon, nylon 4 gave the highest value of coefficient

of friction and nylon 11 showed the lowest value.

It seemed that the increase of the number of

methylene group contributed to the decrease of

the coefficient of friction.

Aromatic nylons, Nomex and Kevlar, gave lower

values than aliphatic nylon. The results for poly

ester fiber are also shown. The values came

between those of nylon 6 and 4.

Some polyolefin and vinyl fibers gave the results

shown in Table 3 and Figure 5. The coefficients

of friction of polyethylene filament were markedly

Fig. 4. Coefficients of friction of nylon and

polyester fibers.

•› Nylon 4 •œNylon 6 •¬ Nylon 11

•£ Nomex •¬ Kevlar • Polyester

low as was expected. On the other hand, it was

noted that the values for polypropylene fiber

were high.

Acrylic and ordinary vinylon (polyvinyl alcohol

fiber partially acetalized with formaldehyde) fila

ments gave values similar to nylon 6. Vinylon

Table 3. Coefficients of friction of polyolefin and vinyl fibers.

a) The static coefficient of polyethylene monofilament was measured by the hanging weight method 3).b) Pewlon Filament made by Asahi Kasei Co .c) Ordinary vinylon made by Kuraray Co .; the degree of formalization is 27.5 mole%.d) Vinylon filament having circular cross-section made by Kuraray Co. using the coagulating bath

containing alkali and sodium sulfate; formalization is not given.

(69) Vol. 41, No. 5 (1985) T-215

Fig. 5. Coefficients of friction of polyolefin and

vinyl fibers.

•¢ Polyethylene •› Polypropylene

• Acrylic •¬ Vinylon (cocoon-like)

•¬ Vinylon (circular)

Fig. 6. Coefficients of friction of silk and wool.

•¢ Silk (degummed)

•œ Wool (scale direction)

•› Wool (anti-scale direction)

Table 4. Coefficients of friction of silk and wool.

a) Rubbed against the degummed silk filament.

filament having circular cross-section showed lower

values than that of ordinary vinylon which had

cocoon-like cross-section.

The results obtained for silk and wool fibers are

shown in Table 4 and Figure 6. The static coef

ficient of friction of silk is lower than various

nylon and polyester fibers, but the kinetic

coefficients are rather high.

As above described, wool fiber shows the

differential frictional effect. Therefore, in the

experiments on wool fibers sliding on the cylinder

covered with degummed silk, each wool fiber

hung on the cylinder was reversed its direction

and the measurement was repeated. As shown in

Table 4, the values obtained were separated dis

tinctly into high and low values at each cylinder

velocity. Thereupon, it was presumed that the

high values corresponded to the anti-scale direction.

The static coefficient in scale direction is lower

than kinetic coefficient. This is only one ex

ception among all fibers used in this study.

The reason is unknown at present.

The coefficients of variation of the measured

values were generally low (about 5% or less) for

all fibers except polyethylene monofilament, for

which the values exceeded 10% in some case of

measuring the kinetic coefficient as described

above.

2. Causticized (Alkali Treated) Polyester Fiber

Polyester filaments (2.5 d) were treated with

5% NaOH aqueous solution at 98•Ž. The results

obtained are shown in Table 5 and Figure 7.

The coefficients of friction decreased at first

with the increase of the treating time. Minimum

values were seen at the treating time of 20-30

minutes, and afterward the coefficients increased

with the increase of the treating time.

Electron micrographs (Figure 8) show the ero

sion on fiber surface increases with the increase

of treating time. The roughness of the fiber surface

especially increases when the treating time exceeds

30 minutes. Some literature4, 5) described that


Table 5. Coefficients of friction of the causticized (alkali treated) polyester fiber.

a) 5% NaOH aqueous solution at 98•Ž.

Fig. 7. Coefficients of friction of the causticized

(alkali treated) polyester fiber.

Treating times:

•› 0min. •¬ 10min. •¬ 20min.

• 30min. •¢ 40min.

the increase of the roughness of surface decreased the friction. It may be presumed that in above case the roughness of the fiber surface decreases the coefficient of friction until it reaches to some extent. The coefficients of variation of the values of the coefficient of friction increased distinctly at the treating time over 30 minutes (Table 6).3. Polyester and Nylon Fibers Having Different

Shapes of Cross-SectionThe results shown in Table 7 and Figure 9 were

obtained on the polyester and nylon filaments which had various fiber cross-sections.

In both cases, the coefficients of friction remarkably decreased between circular and pentalobal cross-sections, and then the decrease was little in the case of fibers with more complicated cross-section. This roughness effect is seemed to be similar to the case of the alkali treated polyester fiber as above described. The coefficients of variation of the measured values of the coefficient of friction were generally low as shown in Table 8.

Table 6. Coefficients of variation of the coefficient of friction of the causticized

(alkali treated) polyester fiber (%).

a) 5% NaOH aqueous solution at 98•Ž.

(71) Vol. 41, No. 5 (1985) T-217

Fig. 8. Electron micrographs of the polyester filaments causticized (alkali treated) with

5% NaOH aqueous solution at 98•Ž for various minutes. Sample filaments are

the same as described in Table 5 and Fig. 7. (Taken by Prof. Y. Fujiwara at

our faculty).


Fig. 7. Coefficients of friction of the polyester and nylon fibers having different shapes

of cross-section.

a) Dyeable with basic dyes (semidull) .b) Dyeable with disperse dyes (* semidull

, ** superbright).

c) Containing no anti -static agent.d) Containing anti-static agent .

Fig. 9-1. Coefficients of friction of the polyester

fibers having different shapes of cross

section (corresponding to polyester I in

Table 7).

•› Circular •¢ Trilobal • Pentagonal

•ž Pentalobal •¬ Octalobal

Fig. 9-2. Coefficients of friction of the polyester


section (corresponding to polyester II in

Table 7).

•› Circular •¢ Trilobal •ž Pentalobal

•¬ Octalobal

Fig. 9-3. Coefficients of friction of the nylon


section (corresponding to nylon I in

Table 7).

•› Circular •¢ Trigonal (T type, 3d.)

• Trilobal (Y type)

•ž Trigonal (T type, 30d.)

Fig. 9-4. Coefficients of friction of the nylon


section (corresponding to nylon II in

Table 7).

•› Circular •¢ Trigonal (T type)

• Pentalobal

(73) Vol. 41, No. 5 (1985) T-219

Table 8. Coefficients of variation of the coefficient of friction of the polyester and nylon fibers having different shapes of cross-section (%).

a) Dyeable with basic dyes (semidull) .b) Dyeable with disperse dyes (* semidull , ** superbright).

c) Containing no anti-static agent .d) Containing anti-static agent .

Conclusions

The static and kinetic coefficients of friction

of various fibers were measured by Roeder's

method. The circumferential velocities of the small

cylinder covered with fibers laid parallel to the cylinder axis were changed between 0 and 20

m/min. One filament of the same fiber was hung

transversely on the cylinder and the coefficients

of friction of fiber-to-fiber crossed at right angle were measured.

All fibers tested except wool moved in scale

direction showed similar relation of the coefficient

of friction with the circumferential velocity of the cylinder. Minimum value appeared at low velocity

(1m/min.).Acetate showed somewhat low coefficient of

friction at low velocity compared with viscose rayon, polynosic and cupra. Among three kinds

of aliphatic nylon, nylon 4 showed fairly higher

coefficient than nylon 6, and the values for nylon 11 were somewhat lower than nylon 6. Aromatic

nylons, Nomex and Kevlar, gave lower values than

those of aliphatic nylons. The values for polyester fiber came between nylon 4 and 6.

Polyethylene filament showed markedly low

coefficient. On the contrary, polypropylene gave high values. Acrylic and polyvinyl alcohol fiber

with cocoon-like fiber cross-section showed values

similar to nylon 6. The values for polyvinyl alcohol

fiber with circular cross-section were lower than

those.The coefficients of friction of the degummed

silk were lower than polyester and nylon 6 at low

velocity, but were higher at high velocity. The coefficients of wool were divided distinctly into

high and low values at each velocity according to

the direction of rubbing (differential frictional

effect).By the NaOH treatment the coefficients of

polyester fiber decreased at first until the treating time of about 30 minutes, but when the treating time exceeded this, the erosion of the fiber surface

became severe and the coefficients increased. Polyester and nylon fibers having different shapes

of cross-section were examined. The fibers with

circular cross-section showed the highest values of coefficient. The values decreased when the shapes

of fiber cross-section became more complicated.

Acknowledgment: The authors wish to express

appreciation to Toray Co., Kuraray Co. and Toyobo Co. for the presentation of the fiber

samples.

This paper was presented at the Annual Meeting

of the Japan Research Association for Textile End-Use, June 2, 1983, Okayama, Japan.


References

1) H. L. Roeder, J. Textile Inst., 44, T247 (1953).

2) W. Tsuji and M. Imai, Annual Rep. Inst. Chem. Fibers, Kyoto Univ., 14, 53 (1957).

3) I. Sakurada and W. Tsuji, Rayon World

(Jinkenkai), 7, 620 (1939).

4) H. G. Howell, K. W. Mieszkis and D. Tabor,

•g Friction in Textiles•h, Butterworths Scientific

Publications, London, p. 74 (1959).

5) F. L. Scardino and W. J. Lyons, Textile Res. J.,

37, 874 (1967).

レーダー法による種々の繊維の摩擦係数

武庫用女子大学家政学部辻和一郎,吉田恭子,浅原成子

種々の繊維の静的及び動的摩擦係数をレーダー法によ

り, 0～20m/min.の範囲で系統的に測定した。繊維は,

ヴィスコースレーヨン,キュプラ,ポリノジック,アセ

テート,ナイロン4, 6, 11,ノーメックス,ケプラー,

ポリエステル,アルカリ処理ポリエステル,ポリエチレ

ン,ポリプロピレン,まゆ型または円型断面をもつビニ

ロン,絹及び羊毛を用いた。断面の形状効果をみるため

に,種々の形状(円,トリローバル,ペンタゴナル,ぺ

ンタローバル,オクタローバル)をもつポリエステルお

よびナイロン単繊維も測定した。用いたすべての繊維は,

スケールの方向に測定した羊毛を除き,摩擦係数とシリ

ンダー表面速度の間には筒じような関係があった。すな

わち,値は速度の増加とともに初期に減少し, 1m/min.

で最小値を示し,徐々に増加し, 10～20m/min.で飽和

した。羊毛の摩擦方向により値が異った。ポリエステル

繊維のアルカリ処理についても検討した。

(65) Vol. 41, No. 5 (1985) T-211 - JST

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