Pilling on Fi hers

Part 1: Essentials of the Mechanism of Pilling

By Yasushi Omura, Kazuo Wakayama and Tomoichi Inoue, Members, TMSJ

Kyoto University of Industrial Arts and Fibers, Kyoto.

Based on Journal of the Textile Machinery Society of Japan, Transactions, Vol. 21, No. 718, T l 68--178 (1968)

Abstract

Pilling on wool fibers is a serious defect not to be left unnoticed. We have investigated the behaviors of the formation and wearing off of pills on knit goods with the aid of a sponge- and-brush pilling tester. (I) A distinct trait of pilling on wool fibers is that pills form rapidly and have a longer life than pills on other specimens (e.g., acrylic, and their blends). (2) The unit weight of pills fluctuates with the passing of abrasion time. It has a maximum weight point and increase gradually until it reaches that point. (3) The unit weight of pills takes a maximum value when the speed of pill-formation in weight equals the speed of pill-wear off in weight. Until they are equal, the speed of pill- formation in weight exceeds the speed of wear off in weight and helps to increase the weight of pilling. (4) The unit weight of pills is proportional to the amount of fuzz generated on knit goods. (5) The maximum speed of pill-formation in weight arrives slightly later than the maximum amount of fuzz on knit goods. (6) The amount of fuzz generated tends initially to increase sharply as a function of spong- ing time, then levels off as it approaches a nearly horizontal asymptote. Therefore, shearing fuzz in the early stage of abrasion is an efficacious method of pilling control.

KEY WORDS: PILLS, PILLING, WOOL, KNITTED FABRICS, ABRASION, FUZZ, TWIST, PILL WEAR OFF, PILL FORMATION,MICROSCOPIC ANALYSIS

1. Introduction There have been a good many published studies dealing Though used widely as a clothing material, wool fibers with pilling. Many of them concern the mechanism of have some defects, e.g., pilling and shrinking. Pilling is pill formation and discuss preventive measures from the the more defective because it deteriorates clothing appear- viewpoint of the number of pills or the condition of pills allce. on knit or woven fabrics.'-31 A few touch on entangle- Pills as such or in the form of fuzz wear off sooner or ments of fibers. later, because their fibers are poor in tenacity and abrasion We have investigated various phenomena in the whole resistance. However, the period from pill formation to process from pill formation to the wearing off of pills- wearing off is very long, and so the pill formation of wool variations in the unit weight per pill, the generation of fibers is undesirable to the clothing apperance. fuzz by abrasion, the speed of pill-formation and the pill Endowed with many fine characteristics absent in other wear off and the relations among these phenomena. We fibers, wool fibers are widely used as a clothing material have slao made a new attempt to evaluate the weight of in pure or often in mixtures or blends with synthetic fibers pills. which have exceptionally high tenacity and abrasion re- Generally, far more pills form on knit goods than on sistance. Inquiry into the pilling problems with a view to woven. Our experiments were, therefore, confined ex- its solution is, therefore, urgently required. clusively to knit fabrics.

Vol. 15, No. 2 (1969) 45 2. Method of Experiments and Samples Used. to knit goods was also used partly in our test, the pills per 2-1. Pilling Tester in2 of knit fabric being counted and converted, as shown in We have investigated the process from pill formation to the figure, into values per cm2. the wearing off of pills with the aid of a brush-and-sponge 2-3. Fuzz Evaluation pilling tester. The make-up of this tester is shown in Fig. 1. We did not use in our experiment the optical method of The method of testing was as follows: Stick a piece of fuzz evalutaion.~'~ We used a singeing method, because sandpaper on a plate to keep the sample from slipping. we wanted to evaluate fuzz in weight and compare such Hold the sample in place by springs, taking care that the evaluation with an evaluation of pilling in weight. The sample does not crease. Then rub the sample with an ec- method was to singe fuzz generated and remove the tops centrically rotating abradant (2cm in amplitude). The ab- of the singed fibers carefully with a hand brush. Assuming radant we used was cellulose sponge 26-30° in Vicker's that the weight before singeing was W,1 g/cm2 and the hardness. Test the sample under a load of 3.5g/cm2, run- weight after singeing W g/cm2, then the weight (Jg/cm2) ning the abradant at 58 r.p.m. of fuzz generated by abrasion is expressible as follows: In the usual pilling tests, sponging follows after brush- J= W,4 - W1 ing, but we evaluated pilling only by sponging, without WA and W~ denoting the fuzz weight g/cm2 before and brushing. By so doing, it was easy to see the differences after singeing. W;, and W„ were measured in an abso- between pills. lutely dry condition and later amended to obtain a mois- ture regain of 15%. 2-4. Samples A. Sample group I Sample group I was made to check up the distinctive features of pilling on wool fibers. The sample used (wool, acrylic, cotton and their blends) were nearly the same in count and had been manufactured for . The details of sample yarns were given in Table 1.

Table 1 Details of Specimen Yarns

Fig. 1 Mechanism of pilling tester

2-2. Evaluating Pilling There have been two ways to evaluate pilling. One, a "subjective" way , '~6~is to compare samples with a standard specimen and grade them by their visual images. The other, an "objective"~2-41 way, is to count the pills per unit area of the fabric. It has been a practice to use only one or both at the same time. We have tried to investigate the pilling phenomena in The knit goods were double-faced fabrics with 106 their relation to the quantity of fuzz generated and evalu- stitches in wale and 120 stitches in course per 10cm. ated pilling in weight. In other words, after a predeter- B. Sample group II mined number of abrasion cycles, we cut off the pills Sample group II was made for a detailed, quantitative sticking to knit goods with a pair of thin-bladed surgical appraisal of the results obtained from Sample group I. scissors, piled them and weighed them by a precision Sample group II was exclusively used in all the measure- balance. Pills wearing off on knit goods were also weighed ments reported in section 3-3 onward. at the same time. In this way, pills sticking to knit fabrics The raw material of the samples was Australian wool and worn-off pills were distinguished from each other. fibers spun by the worsted system and made into The amount of pills was measured per area of 500 cm2 60s (25 µ in diameter) of mean or nominal counts. The of knit fabric and was converted, as shown in the figure, details of the spun yarns are: into number of pills per cm2. (1) Count 4/18.5 4/118.5 The method of evaluation by counting the pills sticking (2) Number of twists

46 Journal 0 f The Textile Machinery Society of Japan. First twist (Z) 230 tpm each from Sample group I. Pills produced on knit goods 4/18.5 after various cycles of sponging were counted and the re- Final twist (S) 162 tpm lation between the number of pills and the cycles of abra- First twist (Z) 230 tpm sion was clarified. Fig.2 shows the rise and fall of the rate 4//18.5 Final twist (S) of pill formation and of the pill wear off. Fig. 3 is a photo- (3) Moisture regain 15 graphic illustration of pilling on knit goods in this test. (4) Oil content after scouring 0.462 The knit goods were circular rib fabrics with 35 stitches in wale and 42 in course per 10cm. They were left in a chamber of standard condition (20°C, 65 RH) and used unprocessed. The samples were kept and tested in a room of the same standard condition. 2-5. Samples and Data Pills can be counted and worn-off pills in knit fabrics measured continuously by using only one sample. How- ever, to check variations in the weight of pills against the number of abrasion cycles, pills should be cut off for each test. One sample, therefore, cannot be used for all tests which involve checking against the number of abrasion cycles. Therefore, we made a number of samples of uniform condition from the same lot for checking against abrasion cycles differing in number. Accordingly each datum on a curve in the figure is different from each other. Such data were noted in parenthesis. 3. Results and Discussion 3-1. Distinctive Features of Pilling on Wool Fibers. Distinctive features of pilling on wool fibers are discussed here in comparison with acrylic, cotton and their blends, Fig. 2 Number of pills on knit fabric

Fig. 3 Abrasion cycles (time) and time changes in pills

Vol. 15, No. 2 (1969) 47 Wool fibers have the maximum values in number of pills Our investigation has shown that, even with the same which exist over a wide range of cycles. This feature is abrasion, no new pills are generated in the areas where absent in other fibers. Besides, pills are produced on wool pills formed and wore off. This is presumably because fibers by slight abrasion and soon reach stationary state. those areas have no more short fibers needed for pill for- They decrease gradually in number but they have a longer mation. life than pills on fabrics of acrylic, cotton and their blends. There have been a good many works dealing with the Pills on wool fibers are distinctly large and thick but are as behaviors during pill formation. 131 They differ more or small in number as 3 per cm2 or so at a maximum. less among them in dividing the process from pill for- 3-2. Pill Formation mation to the pill off into stages, but the views on pill Wool knit goods were abraded with the pilling tester and formation expressed in those works agree largely with ours. then the behaviors in the process from pill formation to the In our observation, the successive shifts from the first stage wearing off of pills were investigated microscopically. to the third stage are particularly rapid in wool fibers. This The life of pills may be deviled into the following five is a major feature of pill formation in wool fibers. Table 2 stages : shows the average number of abrasion cycles which each (1) Short fibers stick out of knit fabric when the fabrics are fiber undergoes until it reaches the third stage. abraded; (2) The short fibers entangle with one another, Table 2 Abration Cycles Required for Pill-formation but in this stage they cannot be called "pills"; (3) Pills form; (4) Pills grow in size by absorbing near-by short fibers; (5) Pills wear off. Fig. 4 is a photographic illus- tration of the five-stage process.

3-3. Pill Formation and Pill Wear off The samples used in the tests under this heading were the same as sample group 11. Fig. 5 shows variations in the number of pills on a knit fabric with the number of ab- rasion cycles. The curves illustrate strikingly the charac- teristics of pilling behavior in wool fibers referred to in 3-1. The rotations of the tester being constant, abrasion cycles and abrasion time may be thought of as an equivalent element. Taking abrasion cycles to be a time function, the number of pills (N) on a knit fabric is expressible as a function of the speed of pill-wear off in number (dn0 (t) /dt) and the speed of pill-formation in number (dn « (t) /dt) .

Fig. 4 Five stages from pill-formation to wearing off of pills Fig. 5 Number of pills on knit fabric

48 Journal of The Textile Machinery Society of Japan. Accordingly: dno(t)

Fig. 7 Variations in unit weight of pills

In other words, a sample was abraded a given number of times, and out of the pills which had worn off in a 100cm2 area of knit fabric, the largest 40 pills were picked and individually weighed. The unit weight of pills, w, varies with the number of abrasion cycles. The more the abrasion cycles, the gradually heavier the weight of pills. After a pre-determined number of abrasion cycles, the number of pills reaches a maximum value and then decreases gradual- Fig. 6 Relation between abrasion cycles and ly. Posterior to the maximum values, the number of pills integral value of worn-off pills wearing off is not particularly large. This is presumably because the amount of fibers transferring from the yarns Fig. 6 shows the relation between the number of ab- which constitute the knit fabric begins to decrease. With rasion cycles and the integral value of the weight of pills 4/18.5, the number of pills reached a maximum value after which have worn off in a knit fabric. In wool fibers, the 5,200 - 5,500 abrasion cycles in our test. wearing off of pills begins soon after as few as 25-27 cycles Let us call the period preceding 5,200 - 5,500 abrasions of abrasion. Except in the early stage of wearing off, the "Region A" (dw/dt>0) and the period following them "Region B" (d integral value of the weight of pills which wear off in- w/dt <0). In "Region A", pills grow large creases linearly in proportion to the number of abrasion because fuzzes created by abrasion are long and are apt to cycles. Assuming the integral value of the weight of pills be entangled with short fibers, but are slow in the speed of which have worn off to be Wo(t) (g/cm2) and the unit pill wear off in number because the damage of fibers due weight of pills to be (g/a pill), the following equation to the abrasion is slight and there are less chances to wear forms: off. "Region B begins when the generation of fuzz begins d ____ d no (t) , w =constant (exept in the early stage) dt dt to decrease. Therefore, fuzz is comparatively short and is Fig. 5 shows that dn(,(t) /dt is not constant. Accordingly, reduced in strength by abrasion damage, thus limitting the it is believed that the average unit weight of pills, w, varies growth of pills to a small degree and increasing the speed with the number of abrasion cycles. This is easily borne of pill-wear off in number. Accordingly, dWo(t)/dt is out by checking the integral value of pills which have worn believed to be nearly constant in value in both "Region A" off, but it is practically impossible to count them because and "Region B". they are micro-sized. It is believed from the foregoing evidence that fluctu- Fig. 7 shows the approximate unit weight of pills, , ations in the weight of pills on a knit fabric with the obtained on the assumption in the last paragraph but one. number of abrasion cycles are as shown in Fig. 8.

Vol. 15, No. 2 (1969) 49 Fig. 9 shows experimental results, the curves having been obtained from data which vary even on one and the same sample. The curves resemble those in Fig. 8 in point of the maximum value of curves and in point of the number of abrasion cycles. Fig. 8 is based on assumptions based, in turn, on Figs. 5, 6 and 7. Here it is permissible to com- bine curves of the weight of pills on a fabric and curve of pills which have worn off to obtain curves of the total weight of pills forming (see Figs.10 and 11). Fig. 12 shows the speed of pill formation in weight Fig. 8 Estimated weight of pills on knit fabric sought for as a tangent gradient of curves of the weight of pills forming in Fig. 10, 1 l and Fig. 13 shows the curves of

Fig. 9 Variations in weight of pills on the knit fabric as a sequel to the number of abrasion cycles

Fig. 11 Relation between abrasion cycles and quantity of pills

Fig. 10 Relation between abrasion cycles and Fig. 12 Speed of pill-foration and speed of quantity of pills wearing-off relative to weight

50 Journal of The Textile Machinery Society of Japan. maximum. There is a difference only in time lag between samples of 4/18.5 and 4//18.5. Even if the numberof twists (first twists) is made the same, the binding force on re- movable fibers (single fibers convertible into fuzz) differs in degree between doubled and twisted yarns. The pro- perties of doubled and twisted yarns (i.e., the speed of pill-formation in weight and the speed of pill-wear off in weight, the number of pills per unit area, and the unit weight of pills) differ between 4/18.5 and 41/18.5. The characteristic value of doubled yarns exceeded that of twisted . Pills are more likely to be generated on doubled yarns. We have now reached a state, we believe, where we have to consider the fuzz problem. 3-4. Relation between Fuzz and Pilling Fig. 14 shows the relation between pilling and abrasion cycles on the sample of 4/18.5 when the pills and fuzz pro- duced by 300 cycles of sponging were removed from a knit fabric and abrasion was then resumed with no short fibers sticking out of the fabric. (The amount removed was 1.38 Fig. 13 Speed of pill-formation and speed of mg/cm2). Comparing Fig.14 with Fig.10-in which fuzz wearing-off relative to weight the weight of pills wearing off against the abrasion time (cycles), sought for as a tangent gradient of curves of pills wearing off in Fig. 10, 11. The speed of pill-formation in weight and speed of pill-wear off in weight extremely in- creases in the beginning period of abrasion cycles and the former is higher in speed than the latter. The speed of pill- formation in weight gradually decreases in the long run. On the other hand, the speed of pill-wear off in weight reaches the constant stage. The amount of pills on knit fabric is representable by the area covered by the speed of pill- formation in weight and speed of pill-wear off in weight. Its maximum is shown as an integral value from origin to the cross of the two curves. The cross point of the two curves is where the speed of pill-formation in weight and speed of pill-wear off in weight arc egifilibrated. As shown in the figure, in the case of 4/18.5, it is in the range of 5.200 to 5.500 abrasion cycles after the start of abrasion. These figures show that it agrees well with the point show- ing the maximum value of weight of a pill as shown in Fig. 14 Relation between abrasion cycles and quantity Fig. 7. From the period of 5.200-5.500 abrasion cycles of pills on sample shorn of fuzz on, the speed of pill-wear off in weight outruns the speed of pill-formation in weight and the pills on the knit fabric was not removed-we see readily that the amount of fuzz turn into smaller sizes gradually and faded at last. has a bearing on pill formation. Sample shorn of fuzz We have discussed the size of pills on wool yarns of after sponging 300 times will be reduced in the speed of 4/18.5 and their trends from the view point of the speed of pill formation and the speed of pill wear off in weight (the pill-formation in weight and the speed of pill-wear off in tangent grandeint of curves of the weight of pills forming weight. As shown in Figs. 7 and 13, however, the dis- on a knit fabric and curves of the weight of pills wearing cussions done about 4/18.5 will hold true of the wool yarn off relative to time) presumably because the short fibers of 4//18.5. On double wool yarns of 4//18.5, the speed of (fuzz) on the knit fabric decrease in absolute quantity. pill-formation in weight and the speed of pill-wear off in Pilling on a sample shorn of fuzz is small in size and firm, weight make an equilibrium. It was 7,000 abrasion cycles a fact which is presumably related to the length of fuzz on after tha ctart of ahracien that the , iaht of a mill hn~arnn the knit fabric.

Vol. 15, No. 2 (1969) 51 Fig, 16 Effect of singing on unit weight of pills

Fig, 15 Relation between abrasion cycles and amount of fuzz

Fig. 15 shows the relation between the number of ab- rasion cycles and the amount of fuzz generated as a sequel to the number of abrasion cycles. In the figure, the gene- ration of fuzz is markedly heavy in the initial stage of abrasion and then remains nearly constant (strictly speak- ing, it continues to increase slightly) with the generation ratio decreasing gradually. Abrasion produces much more fuzz on doubled yarns than on twisted yarns . Fuzz keeps increasing in amount over a long time and takes long to Fig, 17 Relation between abrasion cycles and amount cease formation (the time it takes fuss to cease formation of fuzz depends somewaht on the number of first twists and final twists, the time for 4// 18.5 being twice as long as for 4/18 .5). This suggests that the coefficient of twists has an important bearing on the number of twists. This aspect is reserved for discussion in a later issue. The effect of fuzz on the size of pills is shown in Fig. 16. The sample involved was sponged 300 times , then shorn of fuzz and abraded, and the pills on it were individually weighed after each abrasion in the same way as in Fig. 7. There are small pills on sample shorn of fuzz than on one with fuzz. This is exactly because there are less fuzz on fuzz-burnt sample. This view holds for the relation be- tween doubled yarns and twisted yarns . Fig. 15 shows that doubled yarns contain much more fuzz than do twisted yarns. This is the reason why pills on doubled yarns are larger in size than those on twisted yarn (Fig . 7). We said in 3-1 that pills on wool fibers were larger in size than on any other fiber. Fig. 2 shows the order in the size of pills on wool, acrylic and acrylic/cotton blends and tendencies in fuzz formation. The amount of fuzz agrees cotton. Fig. 17 is a report of investigation into these well with the order in the size of pills on these fibers.

52 Journal of The Textile Machinery Society of Japan. Accordingly, the mechanical properties of fiber, i.e., ab- (4) The amount fuzz generated by abrasion is in pro- rasion coefficient, Young's modulus, etc. seem to affect portional relation to the unit weight of pills. The amount the size of pills. of removable fibers has an important bearing on the Fig. 18 shows the amount of fuzz on a knit fabric ob- quantity of pills. Accordingly, the size of pills is affected tained from the amount of fuzz-forming in Fig. 15 and the by the mechanical properties related to fuzz generation, amount of pills wearing off in Figs. 10 and 11. It is clear i.e., abrasion coefficient and Young's modulus. from the figures that there is a point where the amount of (5) The point where the speed of pill-formation in weight fuzz on a knit fabric becomes maximum. This point shows is maximum lags behind the point where the amount of up after 1,800 abrasion cycles for 4/18.5 and 2,400 cycles fuzz is maximum. The time lag is presumably the time for 4//18.5, as indicated in 3-3. needed for fuzz to grow into the pills and for pills to absorb This is presumably because the point where the speed of fibers and grow in size. pill-formation in weight is maximum is around the 2,300th (6) Doubled yarns differ in the amount of fuzz gene- cycle for 4/18.5. The point where amount of fuzz is maxi- ration from twisted yarns. This difference makes a dif- mum and the point where the speed of pill-formation in ference in mechanical properties, i.e., the unit weight and weight is maximum are about 600 cycles apart. This time the number of pills, the speed of pill-formation in weight lag corresponds to about l ,000 abrasion cycles for 4//18.5. and speed of pill-wear off in weight, theamount of pill for- This time lag (in cycles) is the first to the fourth stage in the mation and the amount of the wearing off of pills. Each mechanism of pill formation. In other words, it is believed property of doubled yarn is much higher in value than to be between the time from fuzzformation to pill formation that of twisted yarn. Doubled yarns and twisted yarn show and the time when pills absorb other fibers and grow in the same tendency about pilling. size. (7) Fuzz forms heavily at the beginning of abrasion, then 4. Conclusions keeps increasing slightly and takes a nearly constant value. Therefore, if fuzz is burned in the early stage of generation (1) Fuzz generation and pill formation are faster on wool fibers and the pills thereon larger than on acrylic and it will reduce pills effectively in number, size and weight. We thank Prof. M. Ohmori for his guidance and Mr. A. cotton, but the pills wear off more slowly than on a cotton Kanehira of Kyoto University for his cooperation in or acrylic knit fabric. making measurements. (2) The number of pills on wool fibers remain constant in number per unit area by abrasion. The unit weight of Literature cited pills varies with the number of abrasion cycles. The [I] Yoshida, Yamada; J. Fib. Sci. Tech. Japan, 14, 565 variations increase gradually until they take a maximum (1958) value, then decrease gradually. [2] Kuriyama; J. Fib. Sci. Tech. Japan, 14, 418 (1958) (3) The point where the unit weight of pills is maximum [3] D. Gints, E.J. Mead; Text. Res. J., 29, 578 (1959) shows when the speed of pill-formation in weight and the [4] Makishima, Ikeda, Ando; J. Japan Ass. Text. End- speed of pill-wear off in weight are equilibrated. Beforethe Uses, 3, 263 (1962) unit weight of pills becomes maximum, the speed of pill- [5] Suzuki; Text. Mach. Soc. Japan, Symposium on Fiber formation in weight exceeds the speed of pill-wear off in Entanglement (May 1964) weight. After the unit weight of pills becomes maximum, [6] Sada ; J. Japan Res. Ass. Text. End-Uses, 8, 69 (1967) the two get the other round, thus reducing the weight of [7] Kubota; J. Text. Mach. Soc. Japan, 18, 123, 431 (1965) pills.

Vol. 15, No. 2 (1969) 53