Ana E. Leiderman, Manager, Specialty Products, Textile Research & Implementation, Cotton Incorporated

Cotton accounts for 48% of the total fiber consumption worldwide and 59% of all fibers consumed in apparel and home furnishings in the United States today. However, when it comes to cotton rugs and carpets, cotton accounts for less than 1% of all the fibers used in the floor coverings industry. Even though cotton is widely used in bath and throw rugs, it is a new and unknown fiber to most broadloom and large area rug makers, who are used to manufacturing products either out of synthetic fibers or wool.

Cotton differs in many ways from traditional rug and carpet fibers. Unlike synthetic fibers and wool:

• cotton does not melt
• cotton has no glass transition temperature
• cotton has little crimp
• cotton can absorb many times its weight in water

Cotton is a short staple fiber. Its length ranges between 1.0 and 1.6 inches depending on the variety. It is also a very fine fiber, with a thickness between 1.5 and 8.5 micronaire (0.5 to 3.0 denier). In comparison, synthetic carpet fibers are available in a number of different lengths and denier, while wool has a staple length of 3+ inches and an average 37-38 microns in thickness.

Cotton fiber properties require a different manufacturing approach that must be considered when making decisions in the production of quality rugs and carpets. The following will provide useful guidelines for new makers of cotton floor covering products.

Cotton Fiber Selection

As mentioned before, cotton differs in many ways from synthetic fibers and wool. So what constitutes a good cotton fiber?

Nearly 100% of the cotton crop is tested by the USDA each year and graded visually and through high volume instruments. The fiber characteristics tested are: length, strength, micronaire, color, and trash or leaf content. This data is available directly from the USDA or from the cotton merchant.

The appropriate cotton fiber for carpet should have the following properties:

Length:
Longer than 1", with a short fiber content of no more than 15%. A high percentage of short fiber will cause the carpet to pill and shed.

Strength:
Higher than 24.0 grams/Tex. Strong fibers are necessary to make yarns that will withstand the rigors of processing.

Micronaire:
A micronaire of 5.0 or higher is appropriate. Cotton is a very fine fiber. Using the thickest fibers available will improve the resiliency of the final product.

Color and Trash Content:
Cotton should be clean and contain little trash or leaf particles. A grade of Strict Low Middling (41) or better is recommended.

Spinning
The short staple length of cotton fiber requires that it be spun on different equipment than that used for longer fibers like wool or staple synthetics. In general, the process to make a cotton yarn is very similar to that of other yarns. Unlike synthetics, cotton requires additional cleaning stages to remove trash and short fibers. Short staple machinery is almost identical in shape and function to long staple equipment, but of smaller dimensions.

Fiber Preparation
The process begins with the opening of bales and blending of fibers to ensure a homogenous mix. During blending, the cotton is separated into small tufts and larger trash particles are removed.

The next stage is carding, where the fibers are combed and paralleled by a rotating cylinder covered with wire teeth that carry the fibers past slower moving flats, also covered with wire. This forms the fibers into a web structure that is then condensed into a large diameter rope-like structure called sliver. The card not only parallels the fibers, but also removes smaller trash particles and fiber fragments. The fragile sliver, which has little twist, is coiled into cans, ready for drawing.

In drawing or drafting, several ends of sliver are fed through sets of rollers and stretched. Since the sliver has no twist, fibers slide easily past each other. This straightens the fibers, improves the homogeneity of the fiber mix and the evenness of the sliver. Sliver is drawn several times, usually in an even number of processes.

From drawing, the process can continue one of two ways: Directly to open end (rotor) spinning or to further preparation for ring spinning.
If the fiber is to be ring spun, sliver must first be drawn to a smaller diameter in a process called roving. The roving frame consists of rollers similar to a draw frame that stretch the sliver to reduce its linear density. This makes the bundle of fibers finer (about as thick as a pencil), therefore harder to handle. For handling, the drawing frame then inserts some twist to improve cohesion of the fibers and winds the roving onto large bobbins.

Of the many spinning methods available for cotton today, the most suitable for making cotton yarns for rugs and carpets are open end (rotor) spinning and ring spinning.

In ring spinning, the roving (described above) is drafted into a fine stream of fibers through rollers. Twist is inserted by a rotating spindle inside a ring: The spindle rotates, dragging a clip or traveler on the ring, which in turn twists the fibers as they exit the draft roller area. The yarn made is continuously wound on a bobbin that sits on the spindle.

Rotor spinning does not require the preparation of roving. Sliver is fed directly from a can to a set of drafting brushes. These feed the fibers into a concave rotor. Centrifugal force collects the fibers along the inside of the rotor. When a starter yarn is inserted and then quickly removed from the rotor through a navel, it catches the bundle of fibers that twists on itself through the action of the rotor. Yarn is made by the continuous feeding and removal of fibers into and from the rotor and is wound onto a package outside the yarn formation area.

Besides the fact that open end spinning requires less preparation than ring spinning, it has the advantage of out-producing it 10:1, reducing yarn costs. However, the ring spun look and quality cannot be duplicated through open end spinning and are well worth the cost in certain applications.

Twisting and Cabling
Because of the short staple length of cotton and the capabilities of the available spinning equipment, there is a limit to the size of single yarns that can be produced. The resultant or effective count (linear density, denier, decitex) can be increased through plying or twisting single yarns together.

Fiber Blends
Cotton can be blended with other fibers at several stages during the spinning process. The first place blending can be accomplished is during bale opening. Fiber proportions are weighed out and fed into the hoppers for an intimate blend. Blending can also be achieved at the draw frame, where sliver ends of different fibers are drawn together in the same operation. This is called a draw blend. The third opportunity for blending cotton with other fibers comes after spinning, where yarns of different composition can be plied or cabled together.

Engineering Cotton Yarns for Resiliency and Appearance Retention
There are many factors that influence carpet yarn resiliency. Among them are fiber denier, fiber crimp, yarn twist, and carpet construction. Man-made fibers can be made in a variety of deniers and cross sections. The thermoplastic characteristics of synthetic fibers also allow the modification of crimp and the setting of twist in permanent configurations. Wool has natural crimp and is available in varying thicknesses. Cotton has little natural crimp and cannot be permanently modified through heat treatment. However, certain procedures can be used to improve cotton yarn resiliency.

Cotton can be blended with a small percentage of thermoplastic fiber--such as low melt synthetics--during the spinning process. Later, after plying, the yarn can be heat treated using conventional heat setting equipment to melt the thermoplastic fiber. In a second method, 100% cotton yarns can be plied with a thermoplastic filament and heat set using conventional heat setting equipment.

Cotton Incorporated has evaluated low melt polyester at 10-15% blend level and a 210 denier/34 filament polypropylene twisted with 3/1 Ne yarns with good results.

The use of low melt synthetic fibers accomplishes several objectives:

1. The thermoplastic fibers act as an adhesive, 'gluing' the fibers together and creating the effect of increased fiber denier. The fine fibers act together as one, mimicking thicker fibers and improving resiliency.
   
2. The thermoplastic fibers melt and hold the cotton yarn in the desired twisted configuration, something similar to synthetic crimp or twist setting through heat. This prevents tuft 'blooming', improving tuft definition, resiliency, and appearance.
   
3. Heat setting holds the yarn bundle together, reducing fiber removal and pilling during the life of the carpet.

It is important to verify that the low melt fiber is melted throughout the entire yarn bundle to ensure good yarn performance.

Although yarns created by these methods contain synthetic material, they can still be labeled 100% cotton. The labeling pertains exclusively to fiber content. The synthetic material loses its fiber configuration and becomes an adhesive during processing and can be classified as a finish. ^*he use of the described methods will produce the best performing yarns for cut and loop pile carpets, but sometimes the use of low melt fibers is not desired due to cost or processing constraints. In those cases, there are other options that can be considered :

1. Use longer staple cotton to decrease fiber removal and pilling.
   
2. Increase the number of plies in the yarn, maintaining the resultant yarn size constant.
   
3. Use an enzyme wash to clean up the yarn surface after piece dyeing in paddle, rotary drum, beck or jet dyeing machines.
   
4. Tuft tight, dense constructions, where tufts can support each other.

Other Considerations
The production of a quality yarn depends on the strict adherence to the previous recommendations. The use of low quality fiber or a high percentage of trash and short fiber will result in an inferior product that will not meet performance standards.

Coloration Methods
Cotton, like other fibers, can be colored at many stages during the production cycle. It requires dyes, chemicals, and procedures different from those typically used for wool, nylon, or polyester. There is a coloration method appropriate for each particular operation.

Stock Dyeing
Like the highest quality wool carpets, cotton can be dyed in fiber form and then spun to make a colored yarn. This offers several advantages:

• streak free carpet for solid colored styles
  
• styling flexibility through the use of color blends
  
• flexibility in yarn color inventory
  
• large, evenly colored lots
  
• elimination of wet processing after tufting

Yarn Dyeing
Cotton can be package (bobbin) or skein (hank) dyed offering:

• flexibility in yarn color inventory
  
• suitable for patterned carpets where dye unevenness will not be apparent
  
• shortened lead time
  
• elimination of wet processing after tufting

Piece Dyeing
Smaller rugs can be piece dyed using paddle or rotary drum machines. Larger rugs and carpet can be dyed in becks or jet dyeing machines. The main advantages of piece dyeing are:

• flexibility in finished product color inventory
  
• shortened lead time

Continuous Dyeing
Although continuous dyeing requires reduced speeds because of the time required to dry cotton and cotton-containing carpet, it is possible to dye continuously using a variety of dye systems and existing equipment.

Dye Selection
Cotton can be dyed using direct, fiber reactive, sulfur, vat, and naphthol dyes. Direct, reactive, sulfur, and vat dyes are widely used in the industry.

There is a correct dye for each type of cotton product. The best dye system for a product will be one that provides the necessary light and wash fastness characteristics, and whose processing requirements match the production practices and equipment in the plant.

Direct dyes generally have poor wash fastness and medium to good light fastness. They are also sensitive to chlorine. They are suitable for smaller rugs that can be laundered in a washing machine, where color change will occur overall. Direct dyes are not suitable for broadloom or large area rugs where spot cleaning might be necessary. Spot cleaning solutions and vigorous rubbing can cause the removal of dye or a color change in the cleaning location, resulting in damage to the product.

Fiber reactive dyes are available in brilliant colors and have good wash fastness and fair light fastness; however, they can be very sensitive to chlorine in certain cases. Like direct dyes, fiber reactive dyes are suitable for smaller rugs where spot cleaning is not an issue. Selected chlorine-resistant reactive dyes can be used for larger rugs in some cases.

Sulfur dyes exhibit good light and wash fastness; however, they are very sensitive to chlorine.

Vat dyes have excellent wash fastness, light fastness, and are resistant to mild solutions of chlorine, such as those present in some spot cleaning agents. This makes them suitable for broadloom products and large area rugs, since spot cleaning can be performed without discoloration. Vat dyes are most easily processed in enclosed equipment.

In conclusion, vat dyes have the best properties for the coloration of cotton rugs and carpets.

Soiling, Staining, and Cleaning
As mentioned before, cotton is a hydrophilic fiber that can hold many times its weight in water. The same hydrophilic characteristics allow for the easy penetration of water and cleaning solutions to remove soils and stains.

Common household laundering is appropriate for cleaning smaller bath and throw rugs. Larger cotton rugs and carpets can be cleaned using commercially available products and services. Products and procedures that minimize the absorption of water are preferred because of the length of time required to air-dry cotton carpet. As usual, the manufacturers' instructions and recommendations should be followed carefully to avoid any damage to the carpet.

Spot cleaning of stains can be accomplished through the use a mild solution of household ammonia and peroxide. If cotton is dyed with the appropriate dyes, tough stains such as coffee and mustard can be removed with no discoloration.

Cotton carpets can also be treated with stain guards such as fluorocarbon topical sprays during product finishing to prevent the absorption of soils and stains.>

Addressing Flammability
Cotton carpet must meet strict standards governing the flammability of household textile products. To accomplish this, the carpet can be made flame retardant by spraying a phosphorous compound solution during finishing. The compound is catalyzed and cured during drying to make it permanent to cleaning and laundering. The amount of flame retardant necessary will vary depending on the construction of the carpet and the amount of cotton present.

Flammability can also be reduced by modifying the carpet construction or fiber blend. Increasing the pile density can reduce the amount of oxygen available to the flame, making the carpet inherently flame retardant. Blending the cotton with flame retardant synthetic fibers or wool can also reduce flammability.

Summary
Cotton Incorporated has conducted extensive rug and carpet research over the last ten years. Depending on the needs of the consumer, we can meet all requirements necessary to produce quality value-added products.

The Technical Services group of Cotton Incorporated can assist you at your facilities to produce performing rugs and carpets to be added to your existing product line.

"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 express 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, product or process 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."