Indian Journal of Fibre & Textile Research Vol . 3 1 , September 2006, pp. 376-380

Tensile properties of various cotton and Dyneema ® blend yarns

L B Kimmel, A P S Sawhnel & C D Delhom

Southern Regional Research Center, Agricultural Research Service, U S Department of Agriculture, New Orleans, LA 70 1 24, USA

Received 17 February 2005; revised received alld accepTed 9 June 2005

A series of ring- and rotor-spun yarns has been produced from the low-level blends of Dyneema®, a gel-spun ultra-high molecular weight, high-density polyethylene fiber (HOPE) of varied types, with selected white and naturally colored cottons and the tensile properties of blended yarns studied. The Dyneema® fiber is commonly referred to as high performance polyethylene (HPPE) due to its exceptionally high strength. The addition of small quantities of certain HPPE fibers substantially increases the yarn tenacity and breaking elongation of certain cotton blended yarns, particularly those made from natural ly colored cottons. The resultant yarn tenacity appears to be influenced by the fineness of the constituent fibers and the level of yarn twist. The effect is more pronounced for the colored cottons than for the H PPE blends with white cotton. Whereas the yarn strength tends to increase for the pure brown and white cottons as the twist increases, it decreases in the green cotton yarns with the increase in twist within the range studied. However, the addition of small quantities of HPPE fiber results in substantial increase in tenacity for all at a constant level of twist. Finer H PPE fibers provide a greater improvement in yarn strength as compared to coarser H PPE fibers. The different frictional properties and geometries of the constituent cottons and synthetic fibers play a role in their blending and associated resultant yarn strength. The use of small quantities of I -denier HPPE fiber significantly increases the strength and elongation of cotton blended yarns, particularly those made from brown cotton, with the minimal change in observed color. Such cotton and Dyneema® blends may find application in special purpose denims, where pure cotton yarns (whether white or naturally colored) or the traditional cotton­rich blends with conventional synthetics may not meet the performance requirements for fabric strength.

Keywords: Cotton, Dyneema®, H igh performance polyethylene, Yarn strength IPC Code: l nt. CI.8 001 0, D02G3/00

1 Introduction Despite stiff competition from popular synthetic

fibers such as polyester and nylon, cotton retains a very significant market share i n the apparel sector worldwide, mainly because of i ts excellent comfort (abil i ty to absorb, transport and dissipate moisture) and substrate properties . However, pure cotton fabrics tend to exhibit deficiencies such as h igh shrinkage, low strength and durabi l i ty , lack of easy-care properties, and i nferior laundered appearance. Smith I , Hamburger2, and Peirce3 were the earliest scientists who studied the i mportance of i nherent properties of the basic fibers of which text i le structures of desired functional performance are made. Hamburger2

demonstrated the effect of blending two fibers of different mechanical characteristics (mainly strength and extensibil i ty) on the mechanical behavior of the blended yarn composed thereof. He was one of the earliest investigators to study the i mportance of stress­strain relationships of different fiber blends for

"To whom all the correspondence should be addressed. E-mai l : apsingh@srrc.ars.usda.gov.

industrial applications. He calculated the "strength efficiency" of constituent fibers of a composite/blend yarn to demonstrate the benefi ci al i mportance of blending different fibers to ach ieve texti le structures of desired attributes. However, since then many good studies on blending ( intimate, draw-frame, or double­roving) of fibers of different types and / or quali ties have been reported. In fact, i ndustrial blending of cotton with polyester and other strong synthetic fibers has been popular for decades to reduce some of the above stated fabric deficiencies and to produce blended fabrics that are much stronger than those made from pure cotton. However, such blended fabrics typically contain 65% polyester and 35% cotton, although 50:50 polyester/cotton blends are also common. These fabrics obviously do not provide the appearance, comfort and excellent substrate properties of 1 00% cotton fabrics. For some texti le applications such as special ty denims, i t i s desirable to maintain the appearance and comfort of cotton, thereby requiring h igher percentages of cotton in the blends. However, the specific h igh strength requirements of the fabrics cannot be met with low

KIMMEL el al . : TENSILE PROPERTIES OF COTION & DYNEEMA BLEND YARNS 377

levels of the popular synthetic fibers. To meet the challenge of attammg superior durabi l i ty of predominantly cotton fabrics, Sawhney et al.4 demonstrated that the addition of merely 1 0% ultra gel-spun polyethylene (PE) Dyneema® staple fibers to cotton significantly i ncreases the tensi le and tear properties of the blended fabric. In this paper, the effects of blending nominal percentages of Dyneema®

of varied geometry with white as wel l as naturally colored cottons has been reported. The use of colored cottonS has been curtailed by its relative weakness, despite increasing consumer demand for such ecological materials that do not require chemical dyeing. Al though the present production of colored cotton in the United States is mini mal, there is a substantial and growing market6 especially in Western European countries for colored cottons grown in Peru, China, Israel and a few other countries .

2 Materials and Methods

Dyneema® gel-spun h igh performance polyethylene (HPPE) staple fiber was obtained from DSM H igh Performance Fibers , Netherlands. This material is of high molecular weight, and extremely h igh molecular orientation, strength and modulus. The specifications of HPPE fiber used are shown in Table 1 . The properties of cotton fibers were measured by HVI as per the ASTM standards4 and are shown in Table 2. The HPPE fibers were blended in 1 0, 1 5 and 20% proportions by weight with Delta and Maxxa varieties of white cotton and with naturally colored green and brown cottons.

The fibers were processed into yarn on laboratory­scale commercial equipment using standard procedures. Cotton control yarns contain ing no HPPE fiber were spun from each fiber across the range of twist. For the experimental yarns, the cotton and Dyneema® fibers were separately opened and careful ly blended i n a SpinLab Opener/Blender i n the designated proportions by weight. The blended materials were processed i nto 37 tex (Ne 1 61 1 ) yarns. The ring yarns were spun at 3 .6, 4.2, and 4.8 TM and the rotor yarns at several twist levels between 3.0 TM and 6.0 TM. Numerous series of yarns were spun reflecting each cotton in different blend levels of a variety of HPPE fibers. Al l the yarns were tested on an Uster Tensorapid 3 i nstrument i n accordance with ASTM7 procedures and the selected results are reported.

Table I-Properties of high performance polyethylene (HPPE) Dyneema® fiber as provided by supplier

Fiber code Denier! filament Staple length Strength inch g/tex

Dyneema® H I 1 .0 1 .00 270.27

1 .0 1 .25 270.27

1 .0 1 .50 270.27

Dyneema® H2 2.0 1 .00 270.27

2.0 1 .25 270.27

2.0 1 .50 270.27

Table 2- Fiber properties (HVI) of various cottons

Fiber UHM Uniformity Strength Micronaire i nch % g!tex

Delta 1 . 1 1 4 8 1 .9 24.0 1 4.3

Maxxa 1 . 1 2 83.6 28.85 4. 1

Brown 1 4 1 .0 1 8 1 .8 25.8 1 4.2

Green 1 4 0.9 1 77.9 1 6.34 2.9

3 Results and Discussion The tenacities of the pure cotton ring and rotor

yarns as a function of twist are shown in Figs 1 and 2 . The ring yarns show maximum twist strength i n the vicinity of 4.2 TM for the brown and white cottons and at <-3.6 TM for the very fine, low micronaire green cotton. The only plausible explanation for the green fiber (weakest) producing the strongest yarn at a relatively low TM is that the extreme fineness or the lowest micronaire (2.9) of the fiber permit relatively the h ighest number of fibers (green) in the yarn cross­section, resulting in comparatively greater overall i nter-fiber cohesion and consequently greater yarn tensi le strength. The impurity content (honey dew sugars, waxes, minerals, etc.) of the various fibers, which possibly could also have had some influence in the processing and ul timately on the yarn strength, has not been i nvestigated in this study. The rotor- spun yarns show i ncreasing strength with added twist for the brown and white cottons but no discernable trend for the green cotton. The ring and rotor yarns approach s imi lar levels of maximum tenacity although the latter require more twist for comparable strength. A set of yarns spun from the same cotton with greater quantities of the same HPPE fiber generally shows increasing yarn strength . Where 1 0% blends of I -denier HPPE fiber may cause considerable improvements in strength, 1 5% blends of the same fibers may i mpart dramatic increase in strength. However, 20% levels of I -denier HPPE derive l i ttle or no added benefit . The addition of

378 INDIAN J. FIBRE TEXT. RES. , SEPTEMBER 2006

181,---------------------------------------­D = Drown Colored COlloll

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Fig. I - Tenacity of pure cotton ring-spun control yarns as a function of varied TM or twist level

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Fig. 2 - Tenacity of pure cotton rotor-spun control yarns as a function of varied TM or twist level

suitable HPPE fiber tends to benefit the Maxxa cotton more than the Delta cotton. Selective data are shown in Figs 3-7. In general, the longer HPPE fi bers produce stronger yarns at comparable blend levels of the same fibers in the ring yarns (Fig. 3), but these tend to be associated wi th relat ively greater variabi l i ty (Fig. 4). The shortest HPPE fibers produce relatively more uniform yarns. Additional trials were focused on the I -inch cut length staple HPPE fiber for the two levels of fineness . The coarser 2-denier HPPE fiber i s proved t o be much less effective i n i mproving yarn strength, and actually decreased yarn strength in some fiber/blend combination yarns. For example, among the 1 0% I -inch staple HPPE blended yarns, the finer I -denier HPPE fiber enhances the strength of the brown, white, and green cotton blends, but the coarser 2-denier HPPE fibers actually reduces the strength of the brown cotton blended yarns and the low-twist white cotton blended yarns. The tenac i ty of ring-spun yarns (Fig. 5) i s found to be more consistent than the rotor-spun yarns, whose sl ivers lost varying amount of HPPE fiber to the opening rollers (precise fiber

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"

White Cullon BIt.'nds

Fig. 3 - Average ring-spun yarn tenacity of white cotton blends with HPPE (Ne 1 6s, 4.2 TM, 100 single strand breaks)

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rl I H­�-�ll-- j ---:--+H-t---+- -1---

Fig. 4 - Average rotor yarn tenacity and variability ( 1 00 single strand breaks ± 2 standard deviations)

B Bwwn (\1\1(111: f) - Whik' Ddla ('olton: ( i = (in..'..:n COIlI.n: I I I "" 1 [ )�'I\iC'r ( 1 5%); 1 12 -:: 2 1 kni�'r { 1 5%): -XX = SuUix clenotes Yarn TJ\\

rirnmJHillIllliU�J��j \I; rl 00 -.0 ('I X -c. r-I oc ...c ("I 00 ...c ("I XI -0 ("I en ..c (" ' 00 � ("I 00 ..::; (" % � � � � � � � � � � � � � � � � � � � � � � � � � � i 6 � � 6 6 � � � � � 6 � 6 0 6 0 � 0 � 6 ± 6 6 6 � � �

- - - _ _ _ _ _ _ '"'I (" I (" I (""I ("'I ("" I r l ("'I ("' = = I I = = = = = I = = = = = I = =

Fig. 5 - Average ring-spun yarn tenacity as a function of blend component and twist

waste data not avai lable). Figures 6 and 7 show the comparison of cotton/HPPE blended ring-spun yarns with their respective cotton contrfll yarns. The changes were most dramati c for the brown cotton, increasing tenacity between -20% and 50% among the 3 .6, 4.2, and 4.8 TM yarns. The trends for the change i n elongation were s imilar for a given set of yarns.

Fiber properties and/or yarn geometry may also play a part in the differential changes in tenacity of the white, brown, and green cotton blended yarns. I n general, the improvements b y the addit ion o f HPPE are notable for the white cotton blends and very

KIMMEL el al. : TENSILE PROPERTIES OF COTTON & DYNEEMA BLEND YARNS 379

I I I ; l oenier Pcr filament; 1 12 � 2 nenier Per Filament

1\ ; Brown ('otton _ D ; White Delta Cotton c::::J (j ; Green Cotton _

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Fig. 6 - Change i n tenacity of pure cotton control and 1 0% HPPE blended ring-spun yarns (al l yarns are nominal Ne 1 6s)

I I I = I Denier Per filament; H2 ; 2 Denier Per Filament

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Fig. 7 - Change in elongation of pure cotton control and 1 0% blended ring-spun yarns (al l yarns are nominal Ne 1 6s)

significant for the brown cotton blends, even at only 10% level of HPPE fiber. The respectable strength of the pure green cotton (control) yarns may argue against the inclusion of HPPE fibers, although their addition st i l l provides modest i mprovement i n yarn strength. The extreme fi neness of these fibers probably called for reducing twist rather than the usual i ncrease to ach ieve greater yarn tenac i ty . The high wax level and low frictional resistance of green cotton8 may induce i rregular draft ing in the green cotton/HPPE blends, andlor al low greater sl ippage among constituent fibers of the yarns under loading. Unfortunately, the specific stress-strain relationships of the yarns' const i tuent fibers, which were not thoroughly i nvestigated in this particular study, could also be significant factors in this aspect . Interestingly, the strength of the pure colored cotton yarns i s found to be greater than the strength of the whi te cotton controls. Previous work8 also has witnessed the

"compensatory effect" of more and finer colored fibers in yarns of matched l inear density.

I n general, above experimental findings appear consistent wi th those of other researchers who studied the blending of cotton fibers. More uniform blends of fiber length and fineness have been found9- 1 3 to be associated wi th more un iform products, although a defi n i t ive relationship between fiber i rregularity and yarn irregularity has yet to be established. Greater uniformity of the blends i s presumed to contribute to the generally higher strength and greater uniformi ty of the cotton blended yarns contai ning shorter and finer HPPE fibers. S ince the greater uniformity of color in colored cotton blended yarns has been shown to be an indicator of the uniformity of blending, color readings of the result ing yarns may provide some additional i nsight. The ring yarns tend to be stronger and show more predictable trends than the rotor yarns. The rotor yarns tend to be weaker and are not necessarily more uniform, perhaps due, i n part, to the variable losses of HPPE fiber during spinning or the i nherently low coeffic ients of friction of the constituent fibers (coefficients of friction of Dyneema® and green cotton are -0. 1 6 and 0.2 1 respect ively) or the factors of fiberlyarn geometry.

4 Conclusions

The use of low percentages of suitable high performance gel-spun polyethylene Dyneema® staple fiber can dramatically improve the yarn tenacity in blends with both whi te and naturally colored cottons. In general , the longer HPPE fibers result in stronger but less uniform yarns, whereas the shorter staple and finer HPPE fibers produce substantial increase in tenacity wi th relatively greater uniformity . The i mproved yarn tenaci ty and uniformity of the blended yarns are partly attributed to the degree of homogeneity of the fiber mixtures within the associated yarns.

The merit of using these very h igh strength HPPE fibers differ for the differen t cottons they are blended with . Whereas the brown cotton derives great benefit from the Dyneema® fibers, the white cottons are benefited less. The variation i n yarn strength may be an indication of the mass variabi l i ty or blend non­uniformity of the consti tuent fibers in these blends. By contrast, the green cotton blends with HPPE generally gain less strength wi th less consistency in the ranges of blend and twist wi tnessed. Thi s probably was because of the variabi l i ty imposed during

380 INDIAN 1. FIBRE TEXT. RES., SEPTEMBER 2006

process ing due to the known low frictional characteristics of both fibers. Unfortunately, such outcomes cannot be preci sely explained or predicted except by repeated experimental trials, which s imply could not conducted due to the time and budget constraints for the project.

The improved tensile strength of the Dyneema®j cotton blended yarns, the brown cotton in particular, may reveal up new applications for these cottons; although more expensive, these yarns provide an attractive and environment-friendly alternative to white cotton. Selective natural ly colored cotton blends with Dyneema® staple fiber may be useful in those appl ications where the appearance, texture and comfort pure cotton are essential along wi th the high fabric strength and durabi l i ty . V isual comparisons evidenced very l i ttle if any perceivable change i n color with the addition o f HPPE fiber i n blends. One possible appli cation might be colored denims, where comfort and durabi l i ty are crit ical and the hue, softness, luster, and ecological appeal of naturally colored cottons may provide an economic and marketing advantage.

Acknowledgement The authors gratefully appreciate the assistance,

support, and cooperation of personnel from with in and outside SRRC, including government, academic, commercial, and private parties. Thanks are also due to the National Program Staff of ARS for providing financial support. They are particularly thankful to the personnel of the Cotton S tructure & Quality and Cotton Chemistry & Uti l ization Units of SRRC for the help during the study.

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