Nonwovens

Cotton for Nonwovens A Technical Guide

FOREWARD
This publication provides technical information about cotton that should be useful to nonwovens manufacturers who have an interest in providing cotton products. Cotton products that fall under the nonwovens description are absorbent or personal care items. Radical improvements have been made in fiber selection, mechanical cleaning, bleaching and fiber finishing that make cotton nonwoven roll goods production commercially viable. Cotton is the fiber of consumer choice. Its current market share is 56 percent of all fibers sold in the U.S. in apparel and home furnishings, excluding carpets. Independent consumer studies have shown that most purchasers of personal care items prefer cotton over synthetic fibers for these products.

Cotton Incorporated is pleased to provide this manual which presents technical information on the use of cotton in nonwoven products. The manual has been prepared in response to the many requests for information on this subject. In brief, the following subjects are covered:

• U.S. cotton production
• Cotton's physical properties
• Preparation and bleaching procedures
• Cellulose chemistry and fiber morphology
• Methods for producing cotton nonwoven products

Cotton Incorporated, the fiber company of American cotton producers, is available to provide assistance to those interested in developing, producing and marketing cotton nonwoven products. Our services include marketing research, technical research, product development and implementation and marketing. More information on the scope of each service appears later.

Top

The cotton plant is a warm season, woody perennial shrub that is grown as an annual field crop. Since the plants are grown in different environments, the cotton farmer has a choice of many varieties of cotton seeds that are bred to be productive in various environmental and cultural conditions. After the seeds are planted and the plants begin to grow and develop, they must be protected from insects, diseases and weeds. After flowering, the cotton fibers (lint) develop in the boll in three periods. The first period is the elongation period in which the thin primary wall is developed with a large vacuole (0-27 days). During the second period (15-55 days), the protoplast shrinks (circumferentially) progressively while, at the inside of the primary wall, a mass of almost pure cellulose is deposited as a secondary wall. By the time of boll maturation, the third period, the secondary wall fills the major part of the cell volume, leaving the lumen, the small central cavity containing the cytoplasm and the vacuole. As the boll opens, quick desiccation occurs and the tubular cells collapse longitudinally and assume a ribbon-like form with twists called convolutions. Prior to harvesting, the plants are defoliated, thus reducing large amounts of foliage on the cotton plant that might interfere with mechanical harvesting. Approximately 85 percent of the total U.S. crop is machine picked and the remaining 15 percent, primarily from Texas and Oklahoma, is machine stripped.

Machine pickers harvest cotton from open bolls and leave unopened bolls and empty bolls on the plant. This is accomplished by revolving spindles that pluck the fiber out of the boll. Machine strippers strip the entire plant of opened and unopened bolls. The fiber removed from the plant also contains the cotton seeds and is referred to as seed cotton. After harvesting, the seed cotton is transported to the gin.

Ginning, in its strictest sense, is the process of separating cotton fibers from the seeds which is what Eli Whitney's invention of the cotton gin accomplished in 1794. But today's modem cotton gin is required to do much more. To convert mechanically harvested cotton into a marketable product, gins have to dry and clean (remove plant parts and field trash) from the seed cotton, separate the fiber from the seed, further clean the fibers and place the fiber into an acceptable package, while preserving the quality of the fiber. American Upland cotton is saw ginned, which is a process different from roller ginning used for American Pima cotton. Saw gin stands can operate at capacities as high as 12 (480 lb.) bales per hour. The saw gin removes the fiber from the cotton seeds using a cylinder that has saw teeth around its circumference. There are approximately 1600 gins located throughout the cotton belt. In the U.S., roller ginning is limited to the areas of West Texas, New Mexico, Arizona and California that produce Pima cotton.

After the ginning process, the output fiber is compressed into bales. At this stage, the fiber is referred to as raw cotton. Samples are taken from both sides of every bale produced and sent to the USDA for classing. However, the cotton gin actually produces two products with cash value - raw cotton and the cotton seed. The cotton seeds removed during ginning are shipped to cotton oil mills. Short fibers (known as linters) that were not removed by ginning remain on these cotton seeds. At the oil mill the linters are removed from the seeds by delinting machines, employing the same principles as saw gins. The seeds can be run through a delinting machine once, in which case the linters produced are known as mill run linters. Most mills run the seed through twice and produce first-cut and second-cut linters. First-cuts consist of longer, more resilient fibers and are used in a number of nonwoven products. Second-cuts are made up of short fibers and are used to produce high grade bond paper and as a source of cellulose in the chemical industry. After removal of the linters, the remainder of the cotton seed is converted into food for people, feed for livestock, fertilizer and mulch for plants.

Another by-product of the gin is motes. Motes are small, immature seeds with attached fiber that are removed at a different stage of the gin stand than the mature seeds. The fiber can be removed from the motes using a delinting machine. This fiber is called gin mote fiber and is used in nonwoven products.

Top

Cotton classification, or classing, is the process of describing the quality of cotton in terms of grade, staple length and micronaire. In the past, this classing has been done with the hand and the eye. Micronaire determinations are performed with an airflow measurement which indicates fiber fineness.

Classification is essential to the cotton pricing systems, but additional testing is required for high level quality control in textile production. Therefore, an instrument was developed to measure most fiber properties. This instrument is referred to as the High Volume Instrument (HVI) and is manufactured by Zellweger Uster, Inc. Its classification system currently consists of instrument measurements for fiber length, strength, length uniformity, micronaire, trash and color. Since 1991, 100 percent of the U.S. crop is graded by the HVI.

The three cotton properties most often referred to in nonwovens are micronaire, length and strength.

A. Micronaire

Micronaire is an airflow measurement that is performed on a 2.34 grams test specimen which is compressed to a specific volume in a porous chamber. Air is forced through the specimen and the resistance to the airflow is proportional to the linear density of the fibers (expressed in micrograms per inch) - The micronaire range for Upland cotton is 2.0 to 6.5. Since denier is equal to micronaire divided by 2.82, Upland cottons ordinarily range from 0.7 to 2.3 denier.

Top

B. Length

Cotton fiber length varies genetically and has a fiber length array or length distribution ( Figure 1). The HVI reports fiber length as the upper half mean length in hundredths of an inch. The lengths of linters and comber noils are less than 0.5 inches. U.S. Upland raw cotton is normally between 0.9 and 1.2 inches. Pima cotton can be as long as 1.6 inches.

Figure 1. Fiber Length Array

C. Strength

Fiber strength is measured by HVI using 1/8 inch spacing between clamp jaws and reported in terms of grams per tex. A tex unit is equal to the weight in grams of 1000 meters of fiber. Therefore, the strength reported is the force in grams required to break a bundle of fibers one tex unit in size.

Top

D. Neps

Neps sometime detract from visual appearance. A nep is a small tangled knot of fiber often caused by mechanical processing. Neps can now be measured by an AFIS nep tester and are reported as total neps per 0.5 gram of cotton and average diameter in millimeters. Properly equipped and set machinery will minimize nep formation during processing.

The AFIS equipment can now be used to measure fiber length and trash content as well as neps. It is very effective at measuring any small amount of residual trash present in bleached cotton. Table I lists the data obtained by the AFIS-M.

Table 1. Zellweger Uster AFIS-M

• Neps
  • Count/g
  • Diameter, mm
• Length Distribution (by weight and number)
  • Length, in. and UQL
  • Short Fiber Content, %
• Trash
  • Count/g
  • Mean Size, mm
  • Trash (Greater Than 500 micrometers), count/g
  • Dust (Less Than 500 micrometers), count/g
  • Visible Foreign Matter, %

Another instrument useful in measuring non-lint content of bleached cotton is the Zellweger Uster MDTA-3. This instrument uses a 10 gram fiber sample and separates the lint and reports the non-lint at percent trash (greater than 500 micrometers), percent dust (less than 500 micrometers) and percent fiber fragments (Table II). Each of three components is collected for visual inspection.

Top

Table II. Zellweger Uster MDTA-3

• Lint, %
• -Trash (greater than 500 micrometers), %
• -Dust (less than 500 micrometers), %
• -Fiber Fragments, %

Raw cotton (gin output) contains cotton fiber as well as small plant parts and field trash that are not removed by the ginning process. The cotton fiber at this stage has a coating of oils and waxes that make it hydrophobic. Raw fiber is suitable for making nonwovens to be used in industrial products where absorbency and aesthetics are not important. In some cases, fabrics made with raw fiber can be wet processed in the same manner as woven and knitted fabrics.

Top

Cotton must be scoured and bleached for many nonwovens where absorbency, whiteness and purity are desired.

Two techniques of commercial scouring and bleaching are kier and continuous. Both processes accomplish the same results by the same chemical interactions but with different mechanical handling. Figure 2 is a schematic diagram of the various operations involved in cotton bleaching for nonwoven applications.

Scouring is accomplished by saturating the cotton fiber with a caustic soda (sodium hydroxide) solution. The alkali solution is allowed to remain on the fiber at elevated temperatures to speed chemical reactions. During this time the natural oils and waxes are saponified (converted into soaps), the plant matter is softened, pectins and other noncellulosic materials are suspended so they can be washed away. After a predetermined amount of time to allow for complete scouring, the alkali, saponified waxes and suspended materials are rinsed away with water.

At this point a bleaching solution is applied to the fiber. A stabilized oxidizing agent, hydrogen peroxide or sodium hypochlorite, is used in the bleaching liquor to whiten the fiber by the destruction of natural coloring matter. In the U.S., hydrogen peroxide is the most widely used agent in the bleaching of raw cotton in fiber form. This bleaching solution remains on the fiber at elevated temperatures for a fixed amount of time to allow for proper removal of the color bodies, then the bleaching solution is rinsed away. Cotton bleached with hydrogen peroxide contains no dioxins because lignin and chlorine are both absent.

After scouring and bleaching all impurities have been removed and the cotton fiber is in the form of pure cellulose. If properly done, this fiber will meet the demands for pharmacopeia purified cotton. The requirements for the United States Pharmacopeia are shown in Table III.

Top

Figure 2. Cotton Bleaching Stages

Top

Table III. U.S. Pharmacopeia Requirements for Purified Cotton

Currently available bleached cotton from U.S. sources has been processed in batch kiers where both high temperatures and high pressures are used. Special opening equipment is required for processing bleached cotton going into such quality roll goods as coverstock.

Cotton Incorporated developed a continuous bleaching system - and advanced bleaching methodology - which included several patented elements. After the first continuous bleaching line was built and its ability to provide superior bleached cotton in terms of fiber openness and freedom from natural and foreign contaminants had been demonstrated, the technology was licensed to Edward Hall Ltd. of England. This company is marketing continuous bleached fiber under the name Luxicot.

Cotton Incorporated has continued efforts to upgrade bleached cotton quality as a route to increasing market share in nonwoven products. In 1990, Veratec Natural Fibers Group, a unit of International Paper, adopted fiber opening technology developed by Cotton Incorporated. This technology is used by Veratec to produce their Easy Street super opened cotton. The use of this improved technology has been restricted to high quality bleached staple and is not used with such fiber by-products as comber, motes or mill waste. Customers using this improved fiber are nonwoven roll goods manufacturers.

Top

Continued efforts by Cotton Incorporated to improve kier bleached cotton for use in nonwoven roll goods led to the development of an advanced fiber opening/cleaning machine. The LINTMASTER(TM) Opener/Cleaner was built to Cotton Incorporated's description by John D. Hollingsworth on Wheels specifically for processing kier bleached cotton (Figure 3). This machine not only opens the fiber and removes residual non-lint particulate, it performs these operations at 300 kg/hour and higher without adding to nep content or causing appreciable fiber damage.
Figure 3. LINTMASTER(TM) Opener/Cleaner

Top

A. Increased Production

To eliminate fiber recirculation at high production rates, the doffing roll was removed and replaced with a newly designed air-doffing system for removing the fiber from the main cylinder. The increased production rate was achieved by using a steel cylinder capable of operating safely at 1000 rpm.

B. Opening

Fiber opening occurs by carding action supplied by four stationary card plates situated around the main cylinder. For additional opening, a carding segment was installed under the lickerin roll (Figure 3, #18).

C. Cleaning

Features that contribute to the cleaning efficiency of the LINTMASTER^TM Opener/Cleaner include a special main cylinder that allows speeds up to 1000 rpm and a lickerin roll speed of 1600 rpm. High centrifugal forces cause heavier trash particles to move further away from the rolls where they are removed. The LINTMASTER^TM Opener/Cleaner produces the following three waste streams that take advantage of this principle.

• Two mote knives have been installed under the lickerin (Figure 3, #16-#l7) to shave away most of the heavy trash particles.
• Three vacuum slots are provided between the four stationary flats referred to as the Cleanmaster trash removal system. Small trash and fiber fragments are removed at these points.
• A Trashmaster cleaning segment (a knife blade with a vacuum take-away) is installed to remove additional trash that is thrown from the main cylinder at the exit end of the machine. Additional small trash particles are removed at this point.

  ---

  Top

Table IV shows test data obtained from kier bleached cotton as currently provided to nonwoven manufacturers before and after LINTMASTER^TM Opener/Cleaner processing. Fiber length was reduced and short fiber content was increased, but these changes were at a moderate level. Non-lint removal of fifty percent for bleached cotton fiber is very dramatic. Also, the fact that this type opening and cleaning took place on a one meter width machine with production of 300 kg/hour without causing an increase in neps was most unusual. High cylinder speed (850 rpm) coupled with air doffing of the fiber minimized work on the fiber that usually results in damaged fiber and nep formation.

Table IV. LINTMASTER™ Opener/Cleaner
Performance Evaluations on Kier Bleached Fiber

Property	Kier Bleached	LINTMASTERTM
Length (in)	0.99	0.93
Short Fiber	16.7	19.8
Neps (per g)	677	648
Non-Lint (%)	0.14	0.07

---

Top

Since post-cleaning the bleached cotton is much more difficult than pre-cleaning raw fiber, the LINTMASTER^TMOpener/Cleaner was tested as a pre-cleaner. Cleaning the fiber before bleaching is preferred because the remaining non-lint should be small particles that are easily bleached.

A study using the most common commercial cleaning machines available was conducted on a blended lot of raw fiber. The cleaning efficiencies and nep formation results are shown in Table V.

Table V. Cleaning Equipment Comparisons

NOTE: Production rate was 300 kg/hr for all trials.

The LINTMASTER^TMOpener/Cleaner compared favorably in cleaning efficiency with two other cleaning machines but was superior in terms of neps created.

A yield trial was conducted using spinning quality fiber of 1.04 inches length with a micronaire of 3.9. The fiber was processed through the LINTMASTER(TM) Opener/Cleaner at 300 kg/hr. The cleaning efficiency for the trial was 83%, derived from 1.404% visible foreign matter (VFM) being reduced to 0.261% as measured by the AFIS instrument. The nep content was increased only 6% by the LINTMASTER(TM) Opener/cleaner. The yield data - 497 pounds of input fiber - are shown in Table VI.

Top

Table VI. LINTMASTER^TMOpener/Cleaner Yield Data
(Spinning Grade Fiber)

NOTE: Production rate was 300 kg/hr.

The LINTMASTER^TM Opener/Cleaner is being utilized for pre-cleaning raw cotton before kier bleaching. The data shown in Table VII were obtained for fiber produced after a typical 20,000 pounds of production.

Top

Table VII. LINTMASTER^TM( Opener/Cleaner
Efficiency in Processing Raw Cotton

These data show that the LINTMASTER^TM Opener/Cleaner reduced nep content while maintaining a 70% cleaning efficiency. It also reduced the short fiber content which resulted in an increase in average fiber length.

Bleached cotton processed in this manner is marketed by Barnhardt Manufacturing Company as High-Q(TM) cotton.

Top

Selection of the proper fiber finish is essential when considering bleached cotton fiber as a raw material for making nonwoven webs. Bleaching removes the natural finish, therefore bleached cotton has high fiber-to-fiber friction. To allow the bleached cotton to be processed through the high production web-forming equipment common for nonwovens, a lubricant and antistatic agent are needed.

Over the years, such different finishes as soap, glycerine and Tween (ethoxylated sorbitan esters) products have been used with limited success. Cotton Incorporated discovered the value of butoxyethyl stearate (BES) as the current fiber finish of choice. This chemical finish provides a satisfactory degree of lubricity without interfering with absorbency. The finish has good acceptability from a toxicity standpoint which is a more important concern than improved physical properties. A recommended fiber finish system for most bleached cotton includes add-on levels of I .0% BES and 1.0% sodium acetate. The addition of the salt provides antistatic benefits during mechanical processing as shown in Table VIII.

Top

Table VIII. Bleached Cotton Carding Data

Cotton Incorporated has performed extensive fiber finish evaluations on various bleaching practices and the most useful test, with the exception of Carding, was found to be a sled test from I.C.I(1). The apparatus used in this test is shown in Figure 4. Following is an example of the test procedure.

(1) The fiber sample was prepared for testing by carding 450 grains of fiber through a Shirley Card and collecting the web bv lavering on a turning cylinder. To insure sample uniformity, the web was removed from the cylinder and carded a second time.

(2) The card web was pulled apart and removed from the cylinder. Test specimens were cut four inches square from a single web thickness. Individual web specimens were then placed on the apparatus for testing.

(3) The sled was placed on top of the fiber sample and a 2 kg weight was placed on top of the sled. The sled was connected to the load cell with a wire.

(4) The rate of pull by the tensile tester was 25 mm/in and the force was recorded on a chart. The friction force value was taken when the chart reached a steady level and was recorded in grams.

Top

Figure 4. Sled Test Apparatus

(1) Imperial Chemical Industries PLC. The method is based on ANSI/ASTM D 1894-78, Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting.

Top

After scouring and bleaching, cotton is 99% pure cellulose. Cellulose is a macromolecule made up of anhydroglucose units united by 1, 4, oxygen bridges (Figure 5.) The anhydroglucose units are linked together as beta-cellobiose; therefore, anhydro-beta-cellobiose is the repeating unit of the polymer chain. The number of these repeat units that are linked together to form the cellulose polymer is referred to as the degree of polymerization (dp).

Figure 5. Chemical Structure of Cellulose

Top

Table IX. Average Degree of Polymerization for Cellulosic Fibers

Source: Joseph, M., Introduction to Textile Science, 5th Edition, 1986

It can be noted that wood pulp, rayon and cellophane (all three derived from wood cellulose) are also constructed of cellulose polymers. Cotton cellulose differs from wood cellulose primarily by having a higher degree of polymerization and a higher degree of crystallinity. Crystallinity indicates that the fiber molecules are closely packed and parallel to one another. Table IX shows the average degree of polymerization for cellulosic fibers and Figure 6 shows the average crystallinity of cellulose fibers. Higher crystallinity and degree of polymerization in polymers are associated with higher strengths.

Top

Figure 6. Amorphous and Crystalline Areas of Polymers

The cellulose chains within the cotton fibers tend to be held in place by hydrogen bonding. These hydrogen bonds occur between the hydroxyl groups of adjacent molecules and are more prevalent between the parallel, closely packed molecules in the crystalline areas of the fiber.

The three hydroxyl groups, one primary and two secondary, in each repeating cellobiose unit of cellulose are chemically reactive groups. These groups can undergo substitution reactions in procedures designed to modify the cellulose fibers or in the application of dyes and finishes for crosslinking.

The hydroxyl groups also serve as principal sorption sites for water molecules. Directly sorbed water is firmly chemisorbed on the cellulosic hydroxyl groups by hydrogen bonding.

Of particular interest in the case of cellulosic fibers is the response of their strength to variations in moisture content. Generally, in the case of regenerated and derivative cellulosic fibers, strength decreases with increasing moisture content. In contrast, the strength of cotton generally increases with increased moisture. The contrast seen between the fibers in their response to moisture is explained in terms of intermolecular hydrogen bonding between cellulose chains and their degree of crystallinity (Tables X, XI).

Top

Table X. Average Crystallinity Measured by
X-Ray Diffraction for Cellulosic Fibers

Source: Shirley Institute

Top

Table XI. Fiber Strength (g/tex)

Thermoplastic fibers melt at elevated temperatures and have a glass transition temperature (Tg) below the polymers' melting point. At the glass transition temperature, a thermoplastic fiber becomes brittle and loses its elasticity. Cotton is not a thermoplastic fiber, therefore it has no glass transition temperature and remains flexible even at very low temperatures. At elevated temperatures, cotton will decompose instead of melting. Long exposure to dry heat above 300o'F will cause cotton fibers to decompose gradually, and temperatures greater than 475oF will cause rapid deterioration.

Top

Figure 7 shows a schematic structure of a mature cotton fiber with the six parts identified and defined.

Figure 7. Cotton Fiber Structure

1. The cuticle is the outer waxy layer which contains pectins and proteinaceous materials. It serves as a smooth, water resistant coating which protects the rest of the fiber. This layer is removed from the fiber by scouring.

2. The primary wall is the original thin cell wall. It is mainly cellulose made up of a network of fine fibrils (small strands of cellulose). This makes for a well organized system of continuous, very fine capillaries. It is well known that fine capillaries rob liquids from coarse capillaries. The fine surface capillaries of each cotton fiber contribute greatly to cotton's wipe-dry performance.

3. The winding layer is the first layer of secondary thickening (also referred to as the S, layer) - It differs in structure from either the primary wall or the remainder of the secondary wall. It is an open netting type pattern of fibrils that is aligned at 40 to 70 degree angles to the fiber axis.

4. The secondary wall consists of concentric layers of cellulose which constitute the main portion of the cotton fiber (also called the S, layer). After the fiber has attained its maximum size during the growth period, a new layer of cellulose is added to the secondary wall. The fibrils are deposited at angles of 70 to 80 degrees with points where the angles are reversed along the length of the fiber. The fibrils are packed close together again forming small capillaries.

5. The lumen wall separates the secondary wall from the lumen and appears to be more resistant to certain reagents than the secondary wall layers (also called the S Layer).

6. The lumen is the hollow canal that runs the length of the fiber. It is filled with living protoplast during- the growth period. After the fiber matures and the boll opens, the protoplast dries up and the lumen will naturally collapse. This leaves a large central void or pore space in each fiber.

Throughout the fiber structure there are variously sized pores or capillary spaces between the variously sized fibrils in each of the six fiber parts. Consequently the cotton fiber can be viewed as a physical microscopic sponge with a complex porous structure. This internal structure makes cotton fibers accessible to liquids and vapors. The capillary action of the fibrils in the fiber pull in the liquids by capillary action where it is held in pores between the fibrils. This accounts for cotton's wickability and its unique absorbing capacity.

The cotton fiber when observed in its entirety, is a flat twisted ribbon which has 50-100 convolutions per inch. The fibers are tapered on one end and fibrillated on the other end where they were joined to the cotton seed. This provides the fiber with a soft touch or feel since there are no sharply cut ends as there are with synthetic staple fibers.

Top

Such absorbent products as surgical sponges, sanitary napkins, tampons and cosmetic pads and puffs can be satisfactorily made from by-product cotton fiber, i.e., gin motes, comber noils and other mill waste. Most of these products evolve from a bleached cotton coil ( an oversized sliver) that needs little integrity (fiber-to-fiber cohesion). However, roll goods from lightweight webs made by carding or air forming require textile grade fiber. Recommended fiber properties and suggested methods of testing are shown in Table XII. This table lists certain other performance criteria that bleached cotton must satisfy to meet the demands for manufacturing roll goods that can be used in coverstock for diapers and feminine pads as well as fabrics for protective clothing and home product areas.

Table XII. Bleached Cotton Properties for Nonwoven Roll Goods

• Micronaire: greater than or = 4.9
• Length: greater than or = 0.95 inches
• Uniformity: greataer than or = 81.0 percent
• Strength: greater than or = 23.0 g/tex
• Non-Lint Content 0.8% Maximum (MDTA-3)
• Fiber-to-Fiber Cohesion, 1700 g force Maximum (ICI Fiber Cohesion Test)
• Fiber Openness Equal to 100 cc/gram Minimum (ITT Test Method)

Fiber length and strength are important in the manufacture of lightweight roll goods for obvious reasons. However, good fabric appearance is more important than fabric strength in certain nonwoven products, and fiber micronaire plays a major role in these items. An undesirable component is nep content. High micronaire cotton tends to have lower nep content after ginning and is less prone to form additional neps in subsequent processing.

To study the influence of micronaire on certain nonwoven production criteria, three bales of cotton of both high and low micronaire were selected using high volume instrument data. Properties of the selected cottons are shown in Table XIII. Care was taken to keep other fiber variables constant to obtain a true reading on micronaire influences.

Top

Table XIII. Fiber Properties for High and Low Micronaire Cottons

The bales were bleached at a commercial operation using normal production procedures and the nep content was determined at various stages of processing using the Zellweger Uster AFIS-Tester. Table XIV shows the nep comparisons for the two cottons. The high micronaire cotton shows some increase in nep content resulting from bleaching. This increase is most likely attributed to the fiber opening stages before and after drying. Substantial increases in neps were noted for the low micronaire cotton during bleaching and during nonwoven web formation. The benefits for using higher micronaire cotton are dramatic.

Table XIV. Influence of Processing High and Low
Micronaire Cotton on Nep Formation

	AFIS Neps/Gram
Sample Location	High Mic	Low Mic
Original Bale	375	574
Mechanical Cleaned	354	860
Bleached	520	1140
Card Web	540	2406

---

Top

Cotton staple is readily processed to form carded, air laid or carded/crosslapped webs that can be bonded by a variety of techniques to form useful nonwoven materials. Some suggestions that should be considered for web consolidation (bonding) are:

A. Needlepunched Nonwovens

Regular length staple cotton should be considered for needlepunching since longer lengths perform better. Even though cotton staple has random length distribution, enough long fiber is present in regular staple to form strong fabrics. Fiber finish is critical in needling. Bleached cotton with good lubricity is needed to prevent fiber damage and needle breakage. Raw cotton (unbleached) also needles extremely well with proper needle selection. Recommended needle selections are:

• Foster Needle - 15 x 18 x 40 x 3HDB, FBST 206-18-2B/CC
• Groz-Beckert - 15 x 18 x 40 x 3, F222 G92919
• Singer - 15 x 17 x 40 x 3 RB22, A 27/04/06 B222 PL5 0/6-4 Con.

As shown in Table XV, choosing a fiber with a high micronaire allows the production of a stronger needlepunched fabric, providing all other factors remain equal.

Table XV. Needlepunched Fabric Properties
High vs. Low Micronaire Cottons

Fiber Type Micronaire	Mullen Burst (lb./sq in)	Tensile Strength (lb.)
High	33	15
Low	23	12

---

Top

B. Spunlaced (Hydroentangled) Nonwovens

The spunlaced, or hydroentangled, method of web consolidation is highly attractive with cotton because it preserves the pure fiber condition which is conducive to making products with high absorbency. Spunlaced fabrics have many characteristics that are similar to woven cotton fabrics, i.e., they are easily dyed and finished using conventional textile methods because they have good strength characteristics.

Special consideration must be given to water filtering in a hydroentangling operation. Cotton Incorporated has worked with Valco Chemical Co., Krofta Engineering Corporation and Valmet/Honeycomb Inc., to design suitable water recycling processes. Information can be provided to interested parties on request.

C. Resin Bonded Carded Fabrics

Cotton webs can be bonded by spraying, foaming, gravure roll padding or by printing with aqueous binder systems. Chemical suppliers have knowledge of the different techniques of application and can make recommendations for binders based on web weights and end product performance needs. Printed patterns confer fabric integrity without imparting objectionable stiffness to the bonded material.

Top

D. Thermal Bonded Carded Fabrics

Lightweight fabrics suitable for coverstock can be made by blending cotton with polyolefin, polyester or bicomponent fibers then subjecting the web to heat and pressure using heated calender rolls. Generally, an engraved calender roll with at least 30 percent bonding area is needed for blends of cotton and polypropylene (Table XVI) - Unbleached cotton cannot be effectively bonded in the typical low-melt synthetic fiber blends due to the natural waxes present on raw fiber which interfere with the adhesion expected of thermal bonding. Increasing the cotton content of thermal bonded fabrics decreases the number of bonding points, therefore reducing the fabric strength. As shown, a fabric containing 60% bleached cotton in the coverstock weight range still has good strength properties (Table XVII).

Table XVI. Thermal Bonding of Bleached Cotton/Polypropylene Hercules Type 196

Table XVII. Strength of Thermal Bonded Cotton and Polypropylene

Fiber Content Cotton/Polypropylene	Breaking Strength Machine	(g/in) Cross Machine
0/100	3330	690
25/75	2200	400
50/50	1300	280
60/40	1200	270

---

Top

E. Stitchbonded Nonwovens

Arachne and Maliwatt type warp knit machines are used to produce stitchbonded nonwovens. Typically, a filament type yam is used for stitching purposes, but it has been demonstrated that cotton yarn in counts from 18's to 30's Ne will stitch a cotton web. This is an approach being investigated for a new cotton industrial wrapping material. As with some of the other bonded webs, stitchbonded cotton can be wet processed in fabric form much like conventional textiles.

Cotton Incorporated is interested in providing assistance to those involved in the development, production or marketing of cotton nonwoven products.

Top

A. Market Research

Market research can be done through Cotton Incorporated's Marketing Research group in New York. Consumer studies have been effective in demonstrating awareness and preferences on a nationwide consumer scale. The Seal of Cotton is one of the most recognized trademarks in the retail market. Recent studies' have shown that the presence of the Seal increases consumers' intention to purchase products in the diaper, wipes and feminine care categories. The Seal can be used on nonwoven products sold in the U.S. and Canada, provided certain conditions are met.

B. Technical Research and Development

Cotton Incorporated contracts many research activities outside, but essential in-house capabilities are available to conduct developmental studies and provide technical assistance for cotton customers. Some of these facilities are:

Complete physical and analytical testing:

• Fibers - High Volume instrument, Advanced Fiber Information System, Micro Dust Trash Analyzer
• Yarns - Complete Profile Yarn Properties and Imperfections
• Fabrics - Tensile, Tear, Abrasion Resistance, Appearance Retention and Washing Performance

Complete fiber processing through spinning - all short staple systems:

• Knit and woven Cad/Cam designing and fabrication
• Chemistry research
• Commercial scale dyeing and finishing facilities
• Nonwovens equipment located at the College of Textiles, North Carolina State University (NCSU), allows cooperative developments
• Research is conducted also at John D. Hollingsworth on Wheels and the University of Tennessee.

Top

C. New Program Development

It is Cotton Incorporated's goal to increase cotton's market share. The combination of partnership research, product implementation and marketing activities will accomplish this objective.

NOTE: Bleached cotton is exempt from OSHA cotton dust regulations.

Top

• Figure 1. Fiber Length Array
• Figure 2. Cotton Bleaching Stages
• Figure 3. LINTMASTER^TM; Opener/Cleaner
• Figure 4. Sled Test Apparatus
• Figure 5. Chemical Structure of Cellulose
• Figure 6. Amorphous and Crystalline Areas of Polymers
• Figure 7. Cotton Fiber Structure

• Table I. Zellweger Uster AFIS-M
• Table II. Zellweger Uster MDTA-3
• Table III. U.S. Pharmacopeia Requirements for Purified Cotton
• Table IV. LINTMASTER^TM Opener/Cleaner Performance Evaluations on Kier Bleached Fiber
• Table V. Cleaning Equipment Comparisons
• Table VI. LINTMASTER^TM Opener/Cleaner Yield Data (Spinning Grade Fiber)
• Table VII. LINTMASTER^TM Opener/Cleaner Efficiency in Processing Raw Cotton.
• Table VIII. Bleached Cotton Carding Data
• Table IX. Average Degree of Polymerization for Cellulosic Fibers
• Table X. Average Crystallinity Measured by X-Ray Diffraction for Cellulosic Fibers
• Table XI. Fiber Strength (g/tex)
• Table XII. Bleached Cotton Properties for Nonwoven Roll Goods
• Table XIII. Fiber Properties for High and Low Micronaire Cottons
• Table XIV. Influence of Processing High and Low Micronaire Cotton on Nep Formation
• Table XV. Needlepunched Fabric Properties High vs. Low Micronaire Cottons
• Table XVI. Thermal Bonding of Bleached Cotton/Polypropylene Hercules Type 196
• Table XVII. Strength of Thermal Bonded Cotton and Polypropylene

  ---

  Cotton Incorporated is the research and promotion company representing cotton producers. Operating from world headquarters in New York City, Cotton Incorporated utilizes research, advertising and promotions to build demand for cotton worldwide. Through its Raleigh Research Center in North Carolina, extensive work in fiber quality, fiber processing, agricultural research and textile research keeps mills abreast of developments in cotton.
  
  Cotton Incorporated is a source for all information regarding cotton, but does not produce or sell fiber or fabrics. Offices in New York, Raleigh, Los Angeles, Dallas, Atlanta, Basel, Switzerland, Osaka, Japan, Singapore and Mexico City supply information to textile mills, manufacturers, designers, retailers and the press regarding fashion forecast information, marketing research studies, agricultural developments, new product introductions and technical advancements.

  ---

  The statements, recommendations and suggestions contained herein are based on experiments and information believed to be reliable only with regard to the products and/or processes involved at the time. No guarantee is made of their accuracy, however, and the information is given without warranty as to its accuracy or reproducibility either expressed or implied, and does not authorize use of the information for purposes of advertisement or product endorsement or certification. Likewise, no statement contained herein shall be construed as a permission or recommendation for the use of any information or product that may infringe any existing patents. The use of trade names does not constitute endorsement of any product mentioned, nor is permission granted to use the name Cotton Incorporated or any of its trademarks in conjunction with the products involved.

  ---

  Description: Cotton for Nonwovens: A Technical Guide - This page is the online copy of a technical report that provides technical information about cotton that should be useful to nonwovens manufacturers who have an interest in providing cotton products. The Diagrams/Figures Index lists the illustrations in this guide. The Tables Index lists all tables contained in this guide.

Top