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Hand-Related Mechanical Behavior of Enzyme-Treated Yarns Part II: Influence of Fiber Disposition P. RADHAKRISHNAIAH, JINGWU HE,

AND

FRED L. COOK

Georgia Institute of Technology, Atlanta, Georgia 30332, U.S.A.

GISELA BUSCHLE-DILLER Auburn University, Auburn, Alabama 36849, U.S.A. ABSTRACT In the second part of our two-part study, we attempt to understand the influence of enzyme treatment on the properties of bicomponent yarns that exhibit systematic differences in fiber arrangement within the yarn. Our results show that the treatment alters the properties of a ring spun, random blended, polyester-cotton yarn more than it alters the properties of a corresponding sheath-core yarn. Results also reveal that the treatment has a different influence on the properties of two friction spun cotton-polyester yarns, one made with a staple polyester core and the other with a multifilament polyester core. The weight losses suffered by the treated yarns are also influenced by the fiber arrangements within the yarn.

In Part I of this work [6], we compared the bending and compression properties of treated and untreated yarns representing ring, rotor, air-jet, and friction spinning systems, and we concluded that the treatment produced desirable property changes in yarns representing all four spinning systems. Thus, Part I looked at the inherent differences in the hand-related mechanical behavior of spun yarns corresponding to different spinning systems, and how these differences are moderated by a cellulase enzyme treatment. In Part II, we attempt to evaluate the impact of enzyme treatment on the hand-related properties of spun yarns exhibiting different fiber arrangements within the yarns. Specifically, we look at the influence of the treatment on the properties of bicomponent yarns representing random fiber disposition and core-sheath construction. We also investigate the effect of using continuous filaments as opposed to cut staple fibers in the core of bicomponent yarns.

Materials and Methods Particulars of the experimental yarns are given in Table I. The two medium count ring yarns (yarns 1 and 2) were made from the same fiber stock with the same amount of twist. They both were knitting yarns with about 18% less twist than that of corresponding warp yarns. Yarns 3, 4, and 5 represented coarse counts (above 60 tex) with twist levels considered appropriate for use Textile Res. J. 75(4), 293–296 (2005) DOI:10.1177/0040517505054841

as warp yarns on high speed shuttleless looms. A DREF-III friction spinning machine was used to produce yarns 4 and 5, where as yarn 3 was made on a rotor spinning machine, mainly because it is not feasible to make a 100% cotton yarn on the DREF-III machine. Yarn 3 was included in the group to understand how the treatment influences the properties of a 100% cotton yarn with approximately the same count as the two friction yarns. All conditions of enzyme treatment except the treatment duration were identical to those described in Part I [6] of this study. The treatment time was 30 minutes for all yarns. We used the Kawabata compression and bending testers to measure the compression and bending properties of the treated and untreated yarns. The test procedures employed and the property parameters measured for the compression and bending tests were identical to those described in Part I. The average breaking load and breaking elongation of the treated and untreated yarns were measured on the Instron tester. Average values were computed on the basis of 30 tests for each yarn. Other test conditions were similar to those described in Part I. We used a scanning electron microscope to observe surface changes in treated yarns and fibers. A Hitachi S-800 scanning electron microscope captured the magnified images of individual fibers on the surface of treated and untreated yarns. © 2005 Sage Publications

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TEXTILE RESEARCH JOURNAL TABLE I. Experimental yarns.

No.

Description of yarn sample

Yarn count, tex

Treatment time, hours

% Weight loss

1 2 3 4 5

Ring spun intimate blend (35P:65C) Ring spun polyester staple core/cotton sheath (35P:65C) 100% Cotton rotor spun Friction spun polyester staple core/cotton sheath (35P:65C) Friction spun polyester filament core/cotton sheath (35P:65C)

21.1 21.1 101.8 83.2 90.8

0.5 0.5 0.5 0.5 0.5

1.03 0.85 1.0 1.9 0.51

Results and Discussion WEIGHT LOSS

OF

TREATED YARNS

The weight losses of the five different yarns are shown in Table I. Of the two ring yarns, one would expect the core-sheath yarn to show a higher weight loss compared to the intimate blend yarn, because of the preferential positioning of the cotton fibers on the surface of the yarn. However, the results indicate that the weight loss of the core-sheath yarn is less than that of the intimate blend yarn. We used the USDA patented ring frame attachment [8, 9] to produce the core-sheath yarn. This attachment wraps a well aligned and compacted ribbon of sheath fibers on the polyester core, thereby forcing the sheath fibers to remain fully extended and in close contact with each other as they are incorporated into the yarn. The sheath fiber wrapping conditions therefore create a very compact sheath with fewer fibers protruding from yarn surface. The close packing of surface fibers and the low hairiness of the yarn appear to be responsible for the lower weight loss shown by the core-sheath yarn. Comparing the weight loss of the ring spun staple-core yarn with that of the friction spun staple-core yarn, we see that the friction yarn accounts for roughly 2.2 times the weight loss of the ring yarn, despite the fact that the friction yarn is much coarser than the ring yarn. While we don’t have any measured data to support the contention that the excess weight loss of the friction yarn may be due to fiber separation, the lack of conditions for effective interlocking of fibers in the friction yarn [5, 1–3] as well as the greater likelihood of fiber breakage in the friction spinning process [2, 3, 5] can be considered to contribute to the greater weight loss of the friction yarn. Comparing the weight losses of the staple-core and filament-core friction yarns, we see that the percent loss suffered by the staple-core yarn is roughly four times that suffered by the filament-core yarn. When we planned this work, we attempted to keep the count and twist of the two friction yarns the same. We managed to keep the wrapping twist of the two yarns the same, but the staplecore yarn turned out to be slightly finer than the filamentcore yarn. While finer yarns can be expected to show a higher percent weight loss, the small difference in fine-

ness of the two friction yarns cannot explain the four times higher weight loss of the staple-core yarn. Thus, substituting cut staple fibers with a twistless multifilament yarn in the core of the bicomponent friction yarn appears to improve its structural integrity, especially the tangling between the sheath fibers and the core yarn. The ends of the sheath fibers trapped between filaments of the core yarn can be expected to be held more firmly than the ends of the sheath fibers held between staple fibers of the core yarn. Also, substituting the staple-fiber core with a multifilament core may be associated with a significant change in the sheath-core contact area. It is not clear from this work which factor or factors contribute to the improved sheath fiber integrity of the filament-core yarn. INFLUENCE OF ENZYME TREATMENT COMPRESSION PROPERTIES

ON

The compression properties listed in Table II suggest that enzyme treatment increases compression energy (WC) and percent thickness compression (EMC%), while reducing the compressive resilience (RC%). This trend in compression properties is in complete agreement with that observed in Part I. Also, past work [4, 7] involving correlations between subjective and objective measures suggests that this trend in compression properties corresponds to an improvement in softness perception. Thus, the measured compression parameters provide a clear indication that enzyme treatment improves the softness of all five yarns. Considering the extent of change in compression properties shown by different yarns, the maximum change, and hence maximum improvement, in compression behavior is associated with the ring spun random blend yarn. Before enzyme treatment, the corespun yarn showed properties indicating greater softness. However, the two yarns showed almost identical compression properties after enzyme treatment, suggesting that the treatment had a greater influence on the softness of the random blended yarn. INFLUENCE OF ENZYME TREATMENT BENDING BEHAVIOR

ON

Table III shows the measured bending rigidity values of the experimental yarns. We have seen that the treat-

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295 TABLE II. Comparison of compression properties of treated and untreated yarns. Intimate blend P/C

PET staple core/cotton sheath P/C

Rotor spun 100% cotton

Friction spun PET staple core/cotton sheath

Friction spun PET filament core/cotton sheath

LC, linearity of load versus thickness curve Untreated Treated 95% Sig.

0.3897 0.37725 no

0.39185 0.36275 yes

0.42485 0.4387 no

0.4237 0.4157 no

0.37075 0.3622 no

WC, g/cm, compression energy (work of compression) Untreated Treated 95% Sig.

0.1424 0.1999 yes

0.160 0.1941 yes

0.2639 0.3379 yes

0.2162 0.2720 yes

0.2307 0.2676 yes

Property

RC%, percent compressive resilience Untreated Treated 95% Sig.

39.69 32.93 yes

35.82 32.71 yes

42.51 39.58 yes

41.08 38.21 yes

38.96 35.07 yes

EMC%, percent thickness reduction Untreated Treated 95% Sig.

39.37 52.47 yes

44.58 54.00 yes

38.13 42.02 yes

38.54 41.01 yes

37.23 43.47 yes

ment accounts for a reduction in bending rigidity of all five yarns, and that the magnitude of change is larger than that observed in Part I. The bending hysteresis value (2HB) does not show a clear trend with respect to enzyme treatment, thus agreeing with the trend in Part I. The reasons for the absence of a consistent trend are the same as those described in Part I. If anything, the yarn surfaces of the treated experimental yarns show more disturbance than seen in Part I yarns. INFLUENCE OF ENZYME TREATMENT TENSILE PROPERTIES

ON

YARN

Measured yarn properties (Table IV) provide an opportunity to arrive at some preliminary conclusions on the applicability of the treatment conditions for different yarns. A comparison of the properties of the treated and untreated yarns reveals the following: First, based on strength loss, the treatment conditions used on the two medium count ring yarns appear to be a little more severe than needed for optimal yarn properties. Second, under identical treatment conditions, the ring yarn representing random fiber distribution shows a greater change in com-

pression, bending, and tensile properties compared to the core-sheath yarn. Therefore, the random blend yarn requires less severe treatment conditions compared to the sheath-core yarn. Third, the rotor spun 100% cotton yarn shows significant improvement in bending and compression properties with a strength loss of less than 10%. The treatment conditions therefore appear to be appropriate for the cotton yarn. Fourth, between the two friction yarns, the staple-core yarn shows more than 10% strength loss, while the strength loss of the filament-core yarn is not statistically significant. This implies that the treatment conditions should be less severe than that used in our study for the staple-core yarn, but they can be more severe for the filament-core yarn. Fifth, the treatment conditions do not lead to a significant drop in the breaking elongation of any of the five experimental yarns. In fact, the breaking elongation of the enzyme-treated cotton yarn shows a 12% increase, and we have no clues at this stage as to what specific factors may be responsible for this increased yarn elongation. Further investigations are needed to understand the factors contributing to the improved breaking elongation of the cotton yarn.

TABLE III. Comparison of bending properties of treated and untreated yarns.

Property

Intimate blend P/C

PET staple core/cotton sheath P/C

Rotor spun 100% cotton

Friction spun PET staple core/cotton sheath

Friction spun PET filament core/cotton sheath

B, g.cm, bending rigidity Untreated Treated 95% Sig.

0.0061 0.0046 yes

0.0278 0.0248 yes

0.0088 0.0059 yes

0.0157 0.0138 yes

0.1379 0.1275 yes

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TEXTILE RESEARCH JOURNAL TABLE IV. Comparison of the tensile properties of treated and untreated yarns. Intimate blend P/C

PET staple core/cotton sheath P/C

Rotor spun 100% cotton

Friction spun PET staple core/ cotton sheath

Friction spun PET filament core/cotton sheath

0.98607 0.7552 ⫺23.41 yes

1.079 0.9219 ⫺14.56 yes

2.2287 2.0245 ⫺9.16 yes

1.874 1.531 ⫺18.17 yes

3.974 3.8165 ⫺3.97 no

Property B L, lb, breaking load Untreated Treated % Change 95% Sig. B E, %, percent breaking elongation Untreated Treated % Change 95% Sig.

MICROGRAPHS

OF

TREATED

AND

11.23 11.29 0.54 no

11.55 11.33 ⫺1.8 no

UNTREATED FIBERS

To ensure that the treatment conditions in this study produce significant surface changes in the cotton fibers, we examined the treated and untreated cotton yarns under a scanning electron microscope. A comparison of micrographs of treated and untreated fibers reveals that the treatment conditions used in Parts I and II of this work cause noticeable changes in the surface condition of the cotton fibers.

Conclusions The direction of change in the compression and bending properties of the treated yarns is similar to that of Part I of this study, with the observed trends being clearer in Part II. The treated yarns show increased compression energy (WC), increased thickness compression (EMC%), and reduced compressive resilience (RC%), all of which indicate an improvement in the compressive softness of the yarns [7]. The treated yarns also show a reduction in bending rigidity (B), which implies that they can be bent with less effort. As expected, finer yarns show larger percent changes in bending, compression, and tensile properties compared to coarser yarns. Between the two ring yarns representing random fiber distribution and core-sheath construction, the yarn with the random fiber disposition is more sensitive to the treatment than the core-sheath yarn. Between the staple-fiber core and filament-core friction yarns, the one with the staple-fiber core loses more strength, suggesting that this yarn may require a less severe treatment compared to the filamentcore yarn.

11.19 12.61 12.67 yes

12.27 12.11 ⫺1.27 no

17.99 17.89 ⫺0.55 no

Literature Cited 1. Klein, W., “The Technology of Short-Staple Spinning, Short-staple Spinning Series,” vol. 4, The Textile Institute, Manchester, U.K., 1987. 2. Klein, W., “New Spinning Systems, Short-staple Spinning Series,” vol. 5, The Textile Institute, Manchester, U.K., 1993. 3. Krause, H. W., Staple-Fiber Spinning Systems, J. Textile Inst. 76(3), 185–195 (1985). 4. Lord, P.R., and Radhakrishnaiah, P., Assessment of the Tactile Properties of Woven Fabrics Made from Various Types of Staple Fiber Yarn, J. Textile Inst. 79(1), 32–52 (1988). 5. Lunenschloss, F. T. I. J., and Brockmanns, K., Mechanism of OE-friction Spinning, Int. Textile Bull. Yarn Form. 31(3), 29 –59 (1985). 6. Radhakrishnaiah, P., He, J., Cook, F. L., and Buschle-Diller, G., Hand-Related Mechanical Behavior of Enzyme Treated Yarns, Part I: Role of the Spinning System, Textile Res. J. 75, 265–273 (2005). 7. Radhakrishnaiah, P., and Sawhney, A. P. S., Low Stress Mechanical Behavior of Cotton/Polyester Yarns and Fabrics in Relation to Fiber Distribution Within the Yarn, Textile Res. J. 66(2), 99 –103 (1996). 8. Sawhney, A. P. S., Robert, K.Q., Ruppenicker, G. F., and Kimmel, L. B., Improved Method of Producing a Cotton Covered/Polyester Staple-Core Yarn on a Ring Spinning Frame, Textile Res. J. 62, 21–25 (1992). 9. Sawhney, A. P. S., Robert, K. Q., and Ruppenicker, G. F., Device for Producing Staple-Core/Cotton-Wrap Ring Spun Yarns, Textile Res. J. 59(9), 519 –524 (1984). Manuscript received August 25, 2003; accepted April 16, 2004.