Wool Fibre Detail

Wool Technology and Sheep BreedingVolume51, Issue3 2003 Article 5

Textile properties of wool and other fibres

E Wood∗

∗

Copyright c©2003 Wool Technology and Sheep Breeding. All rights reserved.

Wool Technology and Sheep Breeding, Vol. 51 2003

272 Textile properties of wool and other fibreISSN 0044 - 7875/03 Wool Tech. Sheep Breed., 2003, 51 (3), 272 - 290

Textile Properties of Wool and OtherFibres

Errol WoodEducation, Information and Partnership ServicesCanesis Network LtdChristchurch, New Zealand

Summary

The properties of wool that are of major textile significance are outlined with anexplanation of why each is important in processing and in products. The major manmadefibres that are in competition with, or complementary to wool are described along withtheir advantages and disadvantages. Why and how blending is used in the textile industry(both in wool blends and combining wool with other fibres) is explained.

Keywords: wool properties, man made fibres, blending

Introduction

This paper outlines the properties of wool and its competitor fibres that are of valuein textile processing and products.

Commercially important properties of wool

Wool has a number of physical properties that determine (a) its commercial valueas a textile fibre, (b) the ease with which it can be processed into yarn, and (c) theproducts into which it can be converted. These properties will vary for wools obtainedfrom different

• Parts of the body of a sheep• Individual sheep in the same flock• Strains of sheep within a breed• Ages of sheep within a breed• Breeds• Environments (ie, climate, terrain, pasture etc.)• Farming properties• Shearing regimes (timing, frequency, preparation procedures)• Geographic regions• Seasons of the year

Based on a lecture in WOOL422: Clip preparation and wool marketing unit - UNE

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This list emphasises the fact that wool is a highly variable, natural, textile fibre. Thefollowing sections outline the properties of wool that are significant for its use as amajor textile fibre.

The testing of these properties will not be covered in any detail in this lecture, but avery comprehensive article on wool testing can be downloaded as a PDF file fromAWTA Ltd (awta.com.au). This article (AWTA 2003a) also includes a glossary ofterms relevant to wool testing. The text by Teasdale (Teasdale 1995) and the bookchapter by Teasdale and Cottle (Cottle 1991) are also good general references for theproperties of wool and how they are measured and processed. Many of the paperspresented at “Top-Tech ’96” symposium are also relevant to this lecture and a selectionof these papers have been provided as readings, courtesy of CSIRO Textile and FibreTechnology. Two CSIRO articles (a, b) on how wool growers can meet spinners needsare also very informative.

Fibre Diameter

Fibre diameter is arguably the most important property of wool since it determinesits suitability for certain end-uses (Teasdale 1995). The reason for this ultimately is thatlightweight fabrics desired by the consumer cannot be made from coarser wool. Finerwools produce products with a softer handle. Fibre diameter also controls the finenessto which a yarn can be spun, so finer wools are usually destined for apparel whilecoarser wools are better suited to carpets, outerwear and bedding. The mean fibrediameter determines between 70% and 80% of the price of Australian wool. The cleanprice versus fibre diameter data for Australian and New Zealand wools for auction lotssold in the 2001-2002 season are shown in Figure 1 (Wooltrak 2002, WoolPro 2002).While these curves shift with time, depending on the buoyancy of the internationalwool market, the shape remains more or less the same from season to season; ie, theprice rises very steeply below 20 microns and flattens off to an almost constant levelabove 30 microns.

Fig. 1 Clean price versus fibre diameter for Australian and New Zealandwools in the 2002/2002 selling season

273 Textile properties of wool and other fibres



274 Textile properties of wool and other fibre

Fibre fineness affects processing performance because lower weights of finermaterials can pass through the machinery in a given time. Finer wools are generallymore difficult to spin than coarser wools. They are weaker (because of the smallercross-sectional area) and are more prone to becoming entangled and forming neps.

The unit for fibre diameter is the micron, where 1 micron = 1 millionth of a metre(or one thousandth of a millimetre). The mean fibre diameter of wool in a fleecemostly depends on the breed from which it was obtained, and may range from around16 to over 40 microns. Because of the inherent variability of wool, any sample offibres will have a range of diameters (perhaps from 10–70 microns for individual fibres).Figure 19-2 shows the typical fibre diameter distributions for merino and crossbredwools.

Fig. 2 Typical Fibre Diameter Distributions for Merino and Romney Wools

About 70% of the wool produced globally is consumed in apparel and this tends toconsume the finer wools. The remaining 30%, which comprise mostly coarser wooltypes, is consumed mainly in carpets, upholstery and blankets. Figure 3 shows thefibre diameter requirements for the main products manufactured from wool.

The coefficient of variation of diameter CVD, which is determined from the fibrediameter distribution, is also important. However the actual range of CVD in wool topsis quite limited (Lamb 1997). A good approximation can be calculated using the formulaCVD(%) = 10.5 + 0.5 x D (where D is the mean fibre diameter in microns). For woolsin the range 20-24 microns about 95% of sale lots will have CVD between 19 and 26%.

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Fig. 3 The Fibre Diameter Requirements for the Main Wool Products

In terms of processing performance and product quality, a change in CVD of 5% isequivalent to a change of 1 micron in mean fibre diameter (Lamb 1997). For example,a 21 micron wool with a CVD of 20% can be a substitute for a 20 micron wool with aCVD of 25%. The difference in spinning performance, yarn and fabric properties andnext-to-skin comfort will be negligible.

While the airflow instrument has been the traditional, commercial method formeasuring the mean fibre diameter of wool, it has been superseded by two moderninstruments, Sirolan Laserscan and Optical Fibre Diameter Analyser (OFDA) , both ofwhich provide the full fibre diameter distribution of a wool specimen.

Physics of Fibre Bending and its Textile Implications

Considering a fibre as a flexible rod, the force required to bend it varies as thesquare of the diameter. This means that a fibre with a diameter of 40 microns requiresfour times the force as a 20 micron fibre to bend it to the same extent (assuming thesame length of fibre is involved). The physics of fibre bending, which is governed bythis simple rule, is very important in the flexibility of yarns, and the handle and drape offabrics.





For fabric prickle the mechanism is the buckling of the fibre ends protruding fromthe fabric surface, which is described by Euler’s theory (Naylor and Phillips 1996).Under compression, fibre ends remain vertical until a certain threshold force is reached,but they are unable to sustain a larger force and hence they eventually buckle (Figure4).

Fig. 4 Euler’s theory of buckling

The threshold force at which buckling will occur is proportional to E.D4 / l2, whereE is the Young’s modulus (ie, stiffness) of the fibre material, D is the fibre diameter andl is the length of the protruding fibre end. This relationship indicates that buckling ishighly dependent on the fibre diameter – the coarser the diameter the higher the bucklingforce (Figure 5). However, increasing the length of the protruding fibre ends has theopposite effect - the buckling force is reduced.

Fig. 5 Variation of buckling force with fibre diameter and length

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An indicator, the so-called comfort factor (CF) has been developed for the level ofprickle in fabrics: it is the percentage of fibres finer than 30 microns. A related indicator,the prickle factor (PF), is simply PF = 100% - CF The lower the CF (or the higher thePF) the greater the risk of prickle occurring, and a CF of under 95% (PF over 5%) isgenerally regarded as producing an uncomfortable fabric. However, fabric finishing,where surface fibres may be raised (ie, increasing the lengths of protruding fibre endsl) or removed, can reduce prickle effects, even if the comfort factor predicts thatprickle should be detectable.

For fine Merino wools the mean fibre diameter lies between 18 and 21 microns andfor the risk of prickle is low. At the other extreme, in carpet wool blends, which arecommonly in the 30-38 microns prickle is obviously not an issue. In fact, very coarsewools such as Scottish Blackface and Drysdale are often added to improve the blend.However in the intermediate micron range (halfbreds, Corriedale and Down breeds)of 25-30 microns variation in fibre diameter becomes a significant issue and can affectthe comfort of wearers of garments made from this wool.

The other important textile aspect of fibre diameter, its effect on the spinning limitof yarns, will be discussed in the next lecture.

Fibre length and strength

While fibre diameter is the most important characteristic in fine wools, fibre lengthis of equal importance in coarser wools( Teasdale 1995). Length largely determinesthe processing system on which the wool will be manufactured, and the properties ofthe resulting yarn. Rather than measuring individual fibres, the fibre length and strengthof fleeces is determined by measuring the average length and strength of arepresentative set of staples. Commercial tests that measure the length and tensilestrength (see glossary)of wool staples are available.

Long fibres tend to be easier to spin (eg, give fewer stoppages) and also producestronger and more even yarns. The presence of excessive short fibres in a yarn canlead to surface fuzzing and pilling in garments and fibre shedding from the pile of woolcarpets.

Consequently wools that are short or weak (tender or have low tensile strength)tend to be less desirable in the market than strong (sound) wools. In practice, shortwools are blended with longer wools, with the latter providing most of the cohesionrequired for efficient spinning and for producing a strong yarn.

In a sound wool, with no tender (or break) region, the average fibre length of thefibres when measured after straightening (ie, removal of crimp) may be 20% longerthan the staple length.





Depending on their level of soundness, wools may be reduced in their average fibrelength from 10% to 50% by carding, the most severe processing step (see Figure 6). Inaddition, the longer the initial fibre length the greater the fibre length reduction duringprocessing.

Fig. 6 Fibre breakage in carding

The level of the break region in the staple, called the position of break, is alsoimportant. It indicates where the fibres are most likely to break when subjected tostrong tensile forces, as in carding. There is a tendency for wools with breaks near thetip or butt of the staple to produce higher fibre losses, because the short fibre fragmentsproduced by breakage will be removed by the combing process. On the other hand,wools with breaks near the middle of the staples produce tops (and yarns) with a lowermean fibre length (ie, hauteur). With higher strength wools the position of break has adecreasing influence on processing performance and yarn quality.

Processing requirements

In the worsted process the removal of short fibres by combing improves the meanfibre length and quality of the yarn produced. However, the downside is the reducedprocessing yield that inevitably occurs from the loss of some wool from the batch. Thesemiworsted route, which has no combing step, requires sound, good length, vegetablematter-free wools for efficient processing and acceptable yarn quality.

The woollen processing system is more tolerant with respect to length and strengthrequirements. However, excessively long wools may be rejected because of theproblems they give in carding.

The processed length of wool (usually in the form or a gilled and/or combed topsliver) is mostly quoted as a mean hauteur value (measured in mm). Relationshipshave been developed for worsted processing, the TEAM formulae (Couchman 1996)

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that enable the hauteur of a top to be predicted from the properties of the greasy woolfrom which it is made. The range of fibre lengths, expressed as the coefficient ofvariation of hauteur CVH is also of importance in worsted processing.

CSIRO Textile and Fibre Technology have developed a computer programme, SirolanYarnspec (Lamb and Yang 1997), for predicting what a spinning mill should achievewhen spinning a yarn using a wool top with particular properties. Among the resultsprovided by Yarnspec is the indication that the worsted industry could use longer woolsthan are currently favoured. Currently it is common for limits on CVH to be set, in thebelief that an optimum value around 40-45% exists. Exceeding 45% precludes the useof longer wools in blends for worsted processing; however, it has been shown thatthere is little difference in yarn quality for wools over a CVH range of 30-60%. Usinglonger wools in blends and ignoring the effect on CVH could result in significantreductions in processing costs (see the CSIRO article).

While hauteur is the measure of fibre length used in the worsted processing industry,a related measure, barbe, is used in the woollen and semiworsted processing industries,especially for the specification of crossbred wools for carpet yarns. This is determinedby the length after carding test, which is carried out on samples of scoured wool.

Cotting

Cotting is a serious wool fault, almost always associated with fleece tenderness.The most severe, or ‘hard’, cotts require considerable opening forces to separate thefibres and result in short fibre lengths after carding. For a cott to form there must firstbe a very tender region, giving short fibres in the fleece. New fibres growing in thefollicles may get entangled with adjacent staples and form a matted region. At thesame time, wax and suint (collectively called the yolk) tend to build up at the cottedregion and may yellow and discolour. Cotted wools require a special opening treatmentbefore scouring.

Colour

Poor colour limits the range of shades to which a wool can be dyed, often precludingits use in products requiring light pastel shades (Teasdale 1995). On the other hand,good colour wools can generally be dyed to any shade, and hence have a higher ‘dyeingpotential’. This means that a yellow wool cannot be dyed to a light blue or grey shade,for example, as illustrated in Figure 7. New Zealand wools vary widely in the incidenceof yellowness in an otherwise basically white fibre. On the other hand Australian finewools are well protected from yellowing during wool growth because of the densestructure of a Merino fleece.





Fig. 7 Effect of wool colour on dyeing shade

Merino wools are normally white and bright, while crossbred types are light creamand medullated wools are chalky white. Hence colour is not the major issue in Australiathat it is in New Zealand. The main colour fault in New Zealand wool is permanentyellowness. Some yellow discolorations such as diffuse yellowness, which is mostapparent in late-shorn Crossbred wools grown in warm moist conditions, scour outalmost completely. Others such as canary yellow, which appears after a prolongedperiod of wetness and warmth, are unscourable and hence are heavily discounted. Ahigh level of discolouration often indicates the presence of microbial damage to thewool while it was a fleece. The colour is often in a band across the staple, at or belowa tender or cotted zone.

Naturally coloured (or pigmented) wools, which are commercially insignificant inthe international wool industry, result from sheep genetics, not microbial attack. Isolatedblack fibres associated with some prime lamb breeds, and also stained fibres, areconsidered a very serious fault with apparel wools because of their visibility in a fabric,and hence their presence (even in tiny amounts) lowers the value of the wool appreciably.A top or yarn with more than 100 dark fibres per kilogram may be heavily discounted.Therefore stringent precautions are taken in sheep breeding, selection and in the shearingshed to ensure that the occasional pigmented, stained or foreign fibre does not becomemixed with good wools.

Describing wool colour

The colour test measures the amount of light reflected across the visible spectrumby a prepared sample of wool (Teasdale 1995). The reflectance values for the woolsample in three colour bands of the visible light spectrum: ie, Red (X), Green (Y) andBlue (Z). This trio of measurements is referred to as the tristimulus values, a commonterm used in colour science.

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Two parameters are required to adequately specify the colour of wool. Theinternational wool industry uses the tristimulus results as follows:

• Y: measures wool ‘brightness’ (ie bright as opposed to dull/grey); the higher thebetter;

• Y-Z: measures wool ‘yellowness’ (ie, level of whiteness as opposed to creamyor yellow); the lower the better.

These parameters and the manner in which they vary with wools of different colourare illustrated in Figure 8.

Fig. 8 Wool colour parameters

Crimp and associated properties

The crimp wave, which is most pronounced in merino wools, arises from bilateraldifferentiation in the internal cell structure of the wool fibre. Crimp is the fibrecharacteristic that largely determines the bulk, resistance to compression and lustre ofwool.

The bulk of a wool is related to its crimp characteristics (ie, the crimp spacing orcrimp frequency and its amplitude), and measures its ability to fill space and have aspringy handle. Bulk is a particularly important property in selecting wools for knitwearand machine-made carpets, where good cover is desirable in the pile. Bulk is closelyassociated with wool lustre (or high fibre reflectance); generally the higher the lustrethe lower the bulk. For loose wool or yarns is measured by measuring the volumeoccupied by a sample of standard mass, when a standard (small) pressure is applied.The bulk test is mainly used to assess the suitability of wools for woollen processinginto carpets and knitwear.





Resistance to compression (Teasdale 1995f) is related to bulk, although it is definedand measured differently. It is largely a function of fibre diameter can fibre crimpfrequency. Increasing either of these will increase the resistance of compression. Tomeasure resistance to compression, a sample of wool is compressed to a small, standardvolume and the force that develops is measured. In comparison with bulk measurement,this is a high-compression test which is appropriate for assessing wools for worstedapparel products.

Crimp promotes cohesion between fibres so that higher bulk wools are generallyeasier to process. Also, because air is trapped in the spaces between crimped fibres,products made from high bulk wools tend to provide good thermal insulation and arewarm. However, an increase in crimp frequency (a more closely spaced crimp wave)tends to reduce yarn strength and evenness (Lamb 1997). This is perhaps to be expectedbecause crimp may impede smooth drafting of fibres, resulting in a more irregular (andhence weaker) yarn. There is also some evidence that wools of lower crimp frequencygive fewer breakages in spinning, at least for finer wools.

Higher crimp frequency wools also give rise to a shorter mean fibre length (hauteur)in tops, and shorter tops also give poorer spinning performance and weaker, less evenyarns. Thus higher crimp appears to give rise to a double penalty on spinningperformance. Finally, lower crimp wools provide a discernibly smoother, leaner fabric,and a preferred softer handle.

Because crimp arises from sheep genetic factors, wool bulk is closely associatedwith the breed. Figure 9 shows the staples of (a) low crimp (coarser) wools, whichtend to be of low bulk (ie, low resistance to compression), and (b) highly crimped(finer) wools that tend to have high bulk (high resistance to compression). In the latter,the crimp frequency is so high for the two left-most staples that it is difficult to reproducetheir crimp in the diagram. From their very high crimp frequency it is likely that thesestaples have the lowest fibre diameter, and were probably produced by Merino sheep.

Fig. 9 Wool staples (a) of lower crimp, and (b) higher crimp wools

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It is also evident from Figure 19.9 that:

(a) staples of lower crimp frequency tend to have a higher level of lustre, and

(b) crossbred staples tend to be tapered (or ‘tippy’) while fine wool staples are more rectangular, ie, ‘blocky’.

While mechanical tests have traditionally been used for the measurement of bulkand resistance to compression, fibre curvature measurement techniques using Laserscanand OFDA provide results that correlate closely with the crimp level of wool. Researchon these techniques is proceeding.

Vegetable matter

Vegetable matter consists of burrs, grass seeds, thistles, hard heads, straw, chaffand twigs that adhere to the fleece when the sheep is grazing (Teasdale 1995). Sometypes of vegetable matter are more problematical than others, in terms of (a) thedifficulty to remove them during processing and (b) their potential impact on the qualityof the finished product. The presence of certain types or quantities of vegetable mattermay necessitate carbonising of the wool, in which case the wool becomes downgradedin value and is only suitable for woollen processing.

The shive type of burr (eg, wiregrass, corkscrew, etc.) possibly gives the biggestproblems. They lie parallel to the wool fibres and may slip through the carding andcombing machines to remain as faults in the finished fabric. On the other hand, Bathurstburrs cause minimal inconvenience because their spines fall off quite readily, allowingthe burrs to fall away freely from the wool.

The amount of vegetable matter in a farm lot of wool, as well as the type of vegetablematter present, is determined as part of the IWTO yield test. Here the wool iscompletely dissolved in strong caustic soda solution and the cellulosic residue remainingis vegetable matter. The quantity collected is expressed as a percentage of the originalsample weight.

Medullation

Some wool fibres are not composed of solid keratin but have hollow cells that runalong their length (see Figure 10). This hollow zone is called the medulla and woolswhich contain a significant proportion of these fibres are said to be medullated. Suchwools, which may also be termed ‘hairy’ or kempy, are coarse, harsh-handling and arebrittle. Medullation in wool fibres can occur at various levels – ie, continuous, interruptedand fragmented medullae.





Fig. 10 Medullated wool fibres

Medullation is generally undesirable from a processing point of view, and especiallyfor apparel products. Because of the relatively stiff nature of medullated wool fibres,they tend to break more readily in carding (in comparison with non-medullated fibres),with their fragments being lost as waste. They do not absorb dye to the same extent asnon medullated fibres and tend to produce yarn with a harsh handle and a rough hairyappearance. For these reasons, medullation has been eliminated from most sheep breedsby selective breeding over many years, and medullation is virtually absent from theAustralian merino clip.

Medullated wools do have value in carpets however because of the crisp handleand unique rustic appearance that they impart to the pile. Of the New Zealand breeds,the Drysdale is the most common provider of medullated wool, while Scottish Blackfacewool is often used because of its medullation content and other characteristics, whichare considered to be beneficial in certain styles of carpet. Their stiffness contributesenhanced resilience, which is desirable in carpets, by increasing the force required tocompress the pile and all assisting in the recovery of the pile after compression.

The degree of medullation in wool can vary, with kemps being the most medullatedfibres. In the fleece of a crossbred sheep crutchings are more highly medullated thanthe main fleece and for this reason these types are also often used as a component incarpet blends.

Ranking of wool properties

Greasy wool properties can be ranked according to their processing importance, asshown in Table 1.

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Table 1 Ranking of wool properties according to their processing importance

It is evident that the rankings depend on the process and the nature of the endproduct. For example, colour is very important for light pastel shade products but ismuch less relevant for dark shade products. Although medullation has a ** ranking forboth worsted and woollen (carpet) processing, in for worsted yarn the absence ofmedullation is desirable while for woollen carpet yarn the presence of medullation is amostly a benefit.

Competitor fibres

While wool is still regarded as the bench-mark in terms of quality and versatility, itfaces ongoing competition in the global marketplace from other fibres, especially thehigh-engineered man-made fibres (Woolwise 1999). The opportunities for engineeringthe wool fibre are relatively limited, although the OPTIM development of CSIROTextile and Fibre Technology qualifies as a significant advance in wool fibre modification.Apart from this, most modifications of wool tend to be chemical in nature, eg, to enhancethe natural flame-resist, stain-resist or conductive properties of the fibre. Cotton remainsby far the most widely-used natural fibre, but because of its quite different propertiesand uses, cotton’s relationship with wool tends to be complementary rather thancompetitive.

Manmade fibres, which compete strongly with wool in most market segments, canbe classified as either regenerated or synthetic. Rayon, the most popular regeneratedfibre from wood cellulose, was developed about 1900. Synthetic fibres, which mostlyoriginate from by-products of the petroleum industry, began to appear in the middle ofthe 20th century, beginning with polyamide (nylon) in 1939, polyester in 1940 and acrylicfibres in 1942. The most recent fibre to arrive on the textile scene was polypropylenein 1960.

**** most important *** major importance ** secondary importance * minor importance

Fibre diameterFibre length and strengthColourBulk/resistance to compressionVegetable matter contentMedullation

Wool property Worsted Woollen (apparel) Woollen (carpet)**** **** ** *** ** ***

*** *** *** **

** ** **

*** *** ***

***

*





Table 2 presents the characteristics of other major textile fibres. It emphasises theability of the fibre manufacturers to deliver a wide range of special features that aredifficult or impossible with a natural fibre such as wool. These features include variousdeniers (ie, fibre diameters), cross-sectional shapes (such as the trilobal shape shownin Figure 11), artificial crimp, light scattering, soiling hiding and stain resist features.

Fig. 11 Trilobal cross-sectional shape of polyamide (nylon) fibres

Textile fibre blending

Blending is done primarily to combine the best features of the different fibrecomponents and/or to retain desirable properties at a minimum price. This may involvecombining different types of wool, adding special effect materials such as neps, orblending wool with other types of fibres (both natural and manmade).

Blending of wool types

Wools reaching the market vary in value, quality and properties, with fleece woolsgenerally being more highly valued than the various oddment types. If some latitudeexists in the wool quality required for a particular product, the spinner has flexibility inblend selection. If 100% superior quality fleece wool exceeds the requirements for theproduct in terms of, say, length, strength or colour, some of the batch for spinning canof the batch to the requirements of the process and the product. A topmaker or spinnerwill not want to reduce his profit by producing a top or yarn with properties that greatlyexceed the specification supplied by the customer.

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Poor elasticity and recoveryPoor wet strengthCreases badly, needs care when wetPoor thermal insulation, feels coldBurns readilyCannot resist strong alkalisWeakened by sunlight

Relatively short fibresNot very extensible or resilientAttacked by mildewBurns easilyDamaged by acidsPoor abrasion resistanceFabrics crease badly if untreatedSoils easily

Highly extensible, flexible and resilientAbsorbs water vapour yet water repellentAbsorbed moisture eliminates staticGenerates heat when moisture absorbedReadily dyedReadily set by chemical treatmentResist acids and organic solventsResists burning, ash brushes away

WoolFibre Positive Features Negative Features

Relatively expensiveWeaker and less abrasion resistant

than most man-made fibresDissolved by alkalisDegraded by sunlightAttacked by insectsSurface scales enable entanglement

and felting

(a plant fibre – purecellulose, fibres areflat twisted ribbons whichswell when mercerised)

Cotton Relatively cheapStrong when dry, increases when wetGood conductor of heatReadily absorbs waterNot attacked by insectsHigh resistance to organic solvents and

alkalisDyes readily with a wide variety of dyesNon-static

Viscose rayon(a regenerated

natural polymer,cellulose, with a deeplygrooved surface)

Relatively inexpensive fibreBlends well with other fibresHigh absorbentModerately strongNot prone to staticResists insects and mildewGood dye affinitySurface texture aids spinning

Nylon(a synthetic polymer,

polyamide; smooth fibreusually circular in cross-section and available inother cross-sections, egtrilobal shape)

Very strong and elastic, good recoveryfrom deformation

Excellent abrasion resistanceAbsorbs some water and swells littleThermoplastic, can be textured, heat-setResists alkalisResists insects and mildewDries quickly, scarcely needs ironing

Prone to static unless treatedLow melting point (250oC)Melts rather than burnsDamaged by acidsWeakened by sunlight

Polyester(a synthetic polymer,

smooth fibres available ina wide range of cross-sections)

Very strong, and good recovery fromdeformation

Stiffer than nylonThermoplastic so readily heat-set to

form a permanent creaseSuperior to nylon in resisting sunlightHeat resistant and low flammabilityVirtually non-absorbentResistant to acids, alkalis, mildew, insectsLow water absorption; same properties

wet or dry

Ignites and meltsLower abrasion resistance than

nylon, but still goodInferior resilience to wool and

nylon in carpets

Acrylic(a synthetic polymer

with a slightly lumpysurface, range of cross-sections)

Relatively cheapFairly extensibleAvailable in high-shrink and bi-component

versions to make high-bulk yarnsNon-absorbent so garments dry quicklyResists staining, acids, alkalis, mildew,

solvents, sunlight, weathering

Not as strong as nylon or polyesterLess abrasion resistant than nylonLess receptive to heat setting than

nylon and polyesterVery flammable, releases toxic gases

Available in wide range of strengths andelasticity levels

Chemically inert so resists most chemicals,mildew and insects

High abrasion resistance, less than nylonLow heat conduction so feels warm

Flammable, low melting pointPoor recovery in carpetsMore difficult to dyeSusceptible to soiling and oil-based

stains in carpets

Prone to static unless treated

Polypropylene(a synthetic

polymer, polyolefin,smooth surface, wavyappearance

Table 2 Characteristics of wool and other major textile fibres





Combining a range of wools to form a blend for spinning is normal practice in woolcarpet yarn manufacture, where the wool types can be grouped into three categories.Their proportions in the blend depend on the type of carpet for which it is intended.

1 Mainstream wools are used for their good colour, strength and processingperformance, and their ability to ‘carry’ poorer quality wools. Examples of thesewools are crossbred fleece and second shear body wools. Poor colour Axminster(woven carpet) blends tend to have the lowest proportion of these wools (30%)while tufted carpets generally have 40-60% depending on the pile constructionand texture.

2 Specialty carpet wools are used for their medullation, bulk and springiness, andthe contribution they make to carpet durability and resilience. Examples of thesewools are Drysdale fleece and coarse Romney crutchings. The use of thesewools in carpet blends varies from 10-20%.

3 Filler wools are cheaper types, generally short and with poor colour, and theyare included to reduce blend costs. Lower proportions of these wools should beused where light pastel shades are required. The use of these wools varies from20% to 50%, with the highest proportions being included in Axminster carpets.In some cases recycled waste wool, such as noils from worsted combing andrecovered fabric waste may be used as a cheap blend component. It is commonpractice in some countries to blend inferior ‘local’ wools with superior importedtypes which act as a carrier through the spinning process.

Semi-worsted carpet yarn blends require the use of good length, sound, low vegetablematter wools. For this reason the highest amounts of mainstream wools (~ 60%) tendto be used in these blends.

Blends assembled for worsted processing tend to more homogenous than carpetblends, because of the need for wools of good staple length and strength. For thisreason only virgin wools are used and oddment types are mostly excluded from worstedblends. Instead, these are mostly components for blends destined for apparel via thewoollen spinning route.

Blending wool with other fibres

Mostly, the blending of wool with other fibres is to utilise the respective advantagesof the fibres (Roberts 1996). These advantages may relate to durability, strength,moisture absorbency and comfort, wrinkle resistance, flammability, heat resistanceand chemical behaviour.

For example, a blend of 80% wool and 20% in a carpet gives better durability thana 100% wool carpet while retaining the positive attributes of wool. The following is asummary of the commonly used fibre blends which use wool:

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Viyella: A registered trademark blend of about 55% wool and 45% cotton, used inlight-weight apparel such as nightwear.

Wool/nylon: The inclusion of even a small percentage of nylon significantly increasesthe abrasion resistance of a fabric or carpet. Provided the proportion of nylon is keptbelow 50% the product usually looks and feels like 100% wool. The 80% wool / 20%nylon is a popular fibre combination for carpets.

Wool/polypropylene: This 50/50 combination is used to produce a cheaper carpetthat to some extent retains the desirable features of wool.

Wool/polyester: This blend is suitable for ‘wash-and-wear’ fabrics, especially insuitings, where sharp pleats and creases are desired. These are introduced by ‘heat-setting’ the polyester fibres, which are thermoplastic. Usually the wool or polyestercontent is just over 50%.

CSIRO have developed ‘Total Easy Care’ garments made of wool and polyesterthat have outstanding shape retention, even after repeated machine washing and tumbledrying cycles.

In some wool carpets around 10% of polyester fibre with a low melting point isincluded in the blend. This is to provide inter-fibre bonds which stabilise the yarns,hence improving the initial appearance of the carpet pile and the retention of itsappearance in use.

Wool acetate and wool/viscose: These blends are used to produce a fabric thatappears and handles like wool but which is lower in price. The durability tends to besomewhat lower than the equivalent all-wool fabric.

Wool/elastomeric fibre: Elastomeric fibres such as Lycra have exceptionalextensibility and recovery properties. Even a small amount of these fibres, say 2%, willmake a significant difference to the stretch and recovery performance of a fabric.

References

AWTA Ltd, (2003) Testing the Wool ClipCouchman, R.C., (1996), Commercial use of prediction technology, “Top-Tech ’96, pp

21-27.Lamb, P.R., (1997), Wool quality for spinners, CSIRO Textile and Fibre TechnologyLamb, P.R. and Yang, S., (1997). An introduction to Sirolan-Yarnspec for the prediction

of worsted yarn properties and spinning performance, Report No. 5, Presentedto IWTO Technology and Standards Committee, Boston Meeting.

Naylor, G.R.S. and Phillips, D.G., (1996), Skin comfort of wool fabrics, “Top-Tech ’96,pp 356-361.

Roberts, S., (1996), Blend partners for natural fibres, Wool Record, May 1996, p 57.





Teasdale, D.C., (1995) The Wool Handbook – The A to Z of Fibre to Top, ISBN: 0 64624034 X

Teasdale, D.C.and Cottle, D.J., (1991) Chapter 15 - Wool preparation, marketing andprocessing, in Australian Sheep and Wool Handbook, editor D. J. Cottle,published by WRONZ Developments, ISBN 0 909605 60 2.

Wood, E.J., Flexy fibres, from Tangling With Wool, (2000), published by WRONZ,ISBN 0-908974-22-1.

Wooltrak, Australian Wool Statistics Yearbook – 2001-2002 Season, p 61.WoolPro, Statistical Handbook – 2001-2002, Table 4-9.Woolwise (1999) – Competing Fibres (a Powerpoint presentation by P Auer, available

from www.woolwise.com)

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