International Nonwovens Journal Home Page

The physical characteristics and performance attributes of absorbent gauze and spunlaced nonwovens used formedical/surgical applications are reviewed. Because the manufacturing lines for spunlacing are versatile and highlyproductive, nonwoven products from this process are highly engineered and may have superior performancecharacteristics relative to gauze products. Dressings made from spunlaced materials are rapidly gaining in the woundcare products market, which was once exclusive to woven gauze. A few microscopic images and SEMphotomicrographs of a gauze made with two dissimilar technologies are included to show structural differencesbetween the two, which otherwise are difficult to detect visually. IntroductionThe primary use for woven and nonwoven medical/surgical materials is in wound care. Wounds have traditional beencovered by gauze to absorb exudate, protect from external contamination and cushion from further trauma. Woundsmay occur from trauma, burns or surgical procedures and produce varying amounts of wound exudates that providean environment for infection and bacterial growth. Gauze in the form of sterile dressings, sponges and bandage rollshave been used for decades to cover, protect, absorb body fluids and support wounds. While absorbent woven gauze has been widely used for wound care, the newer spunlaced nonwovens are anattractive alternative to woven gauze for medical/surgical use. Construction and salient features of both gauze andnonwoven materials will be discussed. Woven Absorbent GauzeGauze has been the preferred material for the making of medical dressings, sponges and bandages for over a hundredyears. "Absorbent Gauze" is described in the United States Pharmacopoeia (USP) [1] as follows: "Absorbent Gauzeis cotton or a mixture of cotton and not more than 53%, by weight, of rayon, and is in the form of a plain weave clothconforming to the standards set forth in USP." Because gauze is converted into dressings and bandages for wound care, the standards of construction and chemicalpurity are well defined in the USP Absorbent Gauze monograph. [1] Absorbent gauze must meet specific standardsof construction, chemical purity and absorbency to be labeled as USP gauze. Gauze is a thin, sheer-woven, open-mesh, low-count, plain weave, soft fabric. [2,3] This fabric is manufactured by atextile process known as weaving. Weaving consists of interlacing the lengthwise warp yarns with the crossing orfilling yarns. Figure 1 shows a plain weave cotton gauze USP Type III. As seen, cotton yarns are hairy. Becausecotton warp yarns are subjected to considerable tension they are first coated with starch or other sizing to prevent thewarp yarns from breaking during weaving. Twenty years ago, the typical cotton loom speed was 180 picks perWoven and Nonwoven Medical/Surgical Materials file:///D|/WWW/inda/subscrip/inj99_1/medsurg.html (1 of 7) [3/21/2002 5:44:50 PM] Figure 1100% COTTON WOVEN GAUZEUSP TYPE III 35 G/M2minute. This means that 180 filling yarns are interlaced with warpyarns each minute. For USP gauze type VIII with a thread count of 12x 10 (i.e., 12 warp and 10 filling threads per inch) 18 inches (0.5 yard)of fabric can be woven in a minute. On the latest multisheds SulzerRuti M8300 airjet loom, for a maximum reeded width of 1,900 mm (75inches) with capability of 2,800 picks per minute, 280 inches (7.7yards) of fabric may be produces in a minute. To improve productivity, the machine manufacturers are attempting toaccelerate the speed of the looms and increase the width of the wovenfabric. In the airjet field, the Sulzer Ruti's L5200 loom will have a reedspace of 3,300 mm (130 inches). Among the conventional orsingle-shed machines, the Tsudakoma ZAX-390-4C-C8, at only 800picks/minute, is often used because it is a very wide machine (3800mm or 150 inches) with a reeded width of two cloths of 1,830 mm each, and a fill-insertion rate of 2,930 m/min. [4]Since weaving productivity is mainly a function of pick density, production capability of the looms will be relativelyreduced for weaving gauze that has a density greater than 10 picks per inch. Performance of high-speed loomsdepends on good quality cotton yarns, since inferior quality yarns cause excessive breaks. Gauze in the greige or loom state is nonabsorbent. Chemical processing steps of desizing, scouring and bleaching ofgauze are necessary to make the fabric absorbent, soft and free from natural and added impurities. The preliminarystep in the preparation of gauze for leaching consists of desizing. Desized fabric is subsequently scoured andbleached. Bleached gauze must meet specific standards of chemical purity (Table 1) to be labeled as USP gauze. Table 1PURITY STANDARDS FOR USP GRADE ABSORBENT COTTON GAUZE* TestSpecification Justification AbsorbencyLess than 30 To maximize absorption of fluids.SecondsAbsorbency increases with decreasing timeof wetting.% WaterMax 0.6%Gauze should be free from waterExtractables (owf)extractables. Theoretically, waterextractables should be almost zero.Ignited Residue Max 0.16%To test the purity of cotton. Ignited(owf)residue is high when the impurities arenot thoroughly removed during bleaching.AshMax 0.12%Ash is high when the impurities are(owf)not thoroughly removed during bleaching.Ether Extract Max 0.7% (owf) Theoretically there should be little etherextractable waxesEther extractables reduce absorbency.AlkalinityNegativeAlkalinity on gauze can irritate wounds.AcidityNegativeAcidity on gauze can irritate wounds.StarchShould not be Starch is added before weaving to protectpresentthe wrap. Removal of starch (desizing)from the gauze is the first step in thebleaching process.pH range6.0 to 7.5Should be neutral or near neutral. *specifications are established as per USP test procedures (1);Woven and Nonwoven Medical/Surgical Materials file:///D|/WWW/inda/subscrip/inj99_1/medsurg.html (2 of 7) [3/21/2002 5:44:50 PM] owf = on weight of the fiber Gauze bleaching by high volume healthcare product manufacturers is carried out in open-width on multi-beams inhuge kiers. A few of these manufacturers have an additional advantage in that the converting operations (of makingsurgical gauze products, dressings, sponges and bandage rolls) packaging and sterilizing are at the same location(Savings in shipping costs). Smaller bleacheries carry out 4-to-6 layered gauze bleaching in conventional rope form.The rope of several layers of gauze is opened to full width on a water-mangle before drying. In the following pages it will be shown that 15 or more highly productive Tsudakoma looms (or 220 typical 20year-old looms) are required to match the production capability of a spunlacing operating at a modest speed of 100meters per minute. The spunlacing lines are capable of operating at 350 meters per minute. Thus the economics ofproduction are heavily in favor of spunlacing. Quality and versatility are also in favor of spunlacing. It has beenrealized that the conventional weaving of gauze for specific medical products may be best left to developingcountries with low labor costs. Johnson & Johnson and Smith & Nephew decided to start a phase out of gauzeproduction in favor of spunlaced nonwovens in 1991 and 1994, respectively, [5,6] and will be sourcing woven gauzefrom the Far East. Another reason for the shift is that low labor rates and modern plants in Asian countries along withreasonable long-distance shipping costs give many commodity products made in developing countries a costadvantage over the U.S.-made gauze products. Despite all the technological advancements in nonwoven products,gauze products likely will always have an assured medical market. Doctors and nurses have developed proceduresand techniques for using woven gauze products and tend to be reluctant to change. [7] Spunlaced NonwovensDuring World War II, a shortage of gauze and other raw materials led engineers to search for new ways tomanufacture lightweight fabrics. They sought production methods that were more efficient than weaving and lessdependent on quality yarns. Researchers focused on producing textile fabrics from the fibrous webs that are createdduring the carding process. They strengthened the web with an adhesive binder to produce nonwoven fabrics. Later,they developed a nonwoven fabric made from a web that was strengthened by hydroentanglement without a binder.The term spunlaced nonwovens is also sometimes used because nonwovens that are formed by entangling fiber webswith water initially had lace like patterns. During the past 10 years, fabrics based on hydroentanglement have reached sales and production levels that challengethe previous use of woven gauze. [7, 8, 9] Spunlaced fabrics often have better aesthetic and physical characteristicsthan traditional woven gauze products. They are safe, cost competitive and provide functional advantages notprovided by gauze or to other types of nonwoven fabrics. Because spunlaced fabrics do not use yarns, they are oftenless expensive to manufacture than woven or knit fabrics. In the hydroentanglement process, fine, high-speed, high-pressure waterjets impact a fibrous web. This causes thefibers to curl, entangle and knot each other. Figure 2100% SPUNLACED GAUZE, 60 G/M2Figure 2 shows the structure of a spunlaced 100% cotton fabric(60g/m2). Figures 3a and 3b show a 50/50 polyester/cotton spunlacedfabric, at two magnifications. Figures 4a and 4b show micrographs ofa 100% polyester fabric at comparable two magnifications having anidentical pattern as in Figure 3. Thus, binder-free nonwovens are produced for applications wherechemicals are not desired, especially in hospital operating rooms. [10]Because the waterjets in spunlacing perforate the web, the producttakes on a aesthetically pleasing woven appearance. This appearancecan be controlled or changed by supporting the web on a perforated orpatterned screen, plate or drum so that the fibers become entangled andthe product assumes the pattern of these web supporting devices. [11,12, 13, 14] Cotton, polyester, and rayon are the most frequently used fibers and they are often blended to obtaincertain desired physical and functional characteristics.Woven and Nonwoven Medical/Surgical Materials file:///D|/WWW/inda/subscrip/inj99_1/medsurg.html (3 of 7) [3/21/2002 5:44:50 PM] Figure 3a50/50 COTTON/POLYESTER SPUNLACEDGAUZE,38 G/M2 VIEWED USING A WIDEFIELD STEREO MICROSCOPE AND DIGITIZEDFigure 4a100% POLYESTER SPUNLACED GAUZE, 38G/M2 VIEWED USING A WIDE FIELD STEREOMICROSCOPE AND DIGITIZED Figure 3bSEM OF 50/50 COTTON/POLYESTERSPUNLACED GAUZE, 38 G/M2 20XFigure 4bSEM 100% POLYESTERSPUNLACED GAUZE, 38 G/M2 20X The broadening of the spunlacing market results essentially from technological improvements, and especiallyimprovements in manufacturing costs [15]. Spunlaced fabrics made with bleached cotton are being produced aroundthe world, with significant quantities produced in Japan. [16] The Japanese company Unitika manufactures aspunlaced cotton nonwoven called "Cottace." Production of Cottace has been 2000 tons per year [17] and Unitika iscurrently considering increasing production capacity by about 50%. [18] Spunlaced fabrics for medical devices are produced in the U.S. by DuPont, PGI, Veratec and others. Finishedsponges and bandage rolls are converted and sold by Allegiance, Johnson & Johnson, Kendall Healthcare, AmericanThreshold Industries and others for the hospital, dental, consumer and other institutional markets. Spunlaced fabricsare also produced in Europe and the Far East for a variety of medical and industrial uses. Presently there are 54commercial producers of spunlaced fabrics in the world. A dramatic expansion is underway in this sector: the marketis expected to grow approximately 8% per year for the next several years. [19] The worldwide capacity of spunlacingis increasing. For example, Sontara Technologies (DuPont) expanded its activities in Spain with the start-up of aspunlacing line in late 1998. The new line is able to manufacture spunlaced nonwovens at twice the industry averagespeed. A huge, full-scale production Miratec line began in December, 1998 at Polymer Group's Benson, NC plant.The Miratec line has some of its technology based on spunlacing. The line is projected to produce $26 million inannual sales. [20] Keeping pace with the increasing production capacity are a wide range of new improved hydroentangling productionsystems. ICBT Perfojet, France, and Honeycomb Systems, U.S., jointly developed the Jetlace 2000 machine capableof making hydroentangled nonwovens weighing up to 400 gsm. These fabrics are characterized by relatively hightensile strength and abrasion resistance, with softness, drape and conformability approaching that of woven fabrics,.Woven and Nonwoven Medical/Surgical Materials file:///D|/WWW/inda/subscrip/inj99_1/medsurg.html (4 of 7) [3/21/2002 5:44:50 PM] The hydrolace model developed by Courtaulds Engineering makes fabrics weighing up to 600 gsm. Courtaulds, U.K.,in collaboration with Orsa, of Italy, have developed the Hydrolace twin drum hydroentangling unit which operates atspeeds of over 100m/min. The versatile Aquajet system with the advanced manifold of Fleissner GmbH, is designedfor high pressure of 250 bars, with a rapid exchange system of wire mesh covers, permitting minimum downtime.The Aquajet system can be adapted to manufacture spunlaced nonwovens for medical as well as industrial uses. [21]The production plant capabilities are being continuously upgraded with improved quality control for manufacturinghigh-quality spunlaced fabrics at speeds higher than 150 m/min. Market data show a 20-25% dollar penetration of spunlaced fabrics into a medical market that formerly used wovengauze exclusively. Medical sponges and bandage rolls utilize approximately one billion square yards of woven andnonwoven fabrics in the United States. The continued increase use of hydroentangled fabrics demonstrates theacceptance by medical professionals and other consumers who have recognized the unique fabric features, desirablefunctional attributes and economics of spunlaced sponges and bandage rolls. Table 2CONSTRUCTION OF DIFFERENT TYPES OF USP WOVEN GAUZE