Pilling on Wool 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 Textile 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, cotton 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 yarns used (wool, acrylic, cotton and their blends) were nearly the same in count and had been manufactured for knitting. 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 spinning 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.