Kenaf as a Textile Fiber:

Processing, Fiber Quality, and Product Development

Gita N. Ramaswamy and Catherine R. Boyd

Kenaf is a bast fiber crop that has been used for a long time as cordage, ropes, etc. in other countries. Studies with kenaf in the United States have been mostly concerned with production. While some of the research of the 1970's and 1980's related to use of kenaf in newsprint, the commercialization of kenaf into various products has become the main focus in more recent projects, especially since 1986.

The possibility of extracting fibers from kenaf was investigated using established retting methods. The kenaf stalk, when decorticated, offers the opportunity to extract fibers that may be used in various textile end­products. The fiber extraction process affects fiber properties which are important for the making of textiles, both woven and nonwoven structures. Fibers can be extracted by either bacterial or chemical retting process.

Bacterial retting experiments were conducted with decorticated stalks being placed in water at room temperature. Staggered retting was done with the bases of stalks being immersed initially and then the whole stalks. This method wasused to prevent over­retting of the upper stalk portion. Following the retting, which can take from 5 to 22 days, stalks were washed in hot water to remove the remaining green slime residue. Air drying and brushing or combing were done as final steps in obtaining the fiber.

Chemical retting was done using an established procedure with some modification to suit kenaf processing. The decorticated stalks were boiled for one hour in a weak alkali solution. Fibers were washed in hot water upon removaland then immediately neutralized. The material was then washed in hot water again. Air drying was followed by combing or brushing to obtain the fibers.

Although the natural retting process is lengthy, the resulting fibers have many desirable characteristics. The chemical retting process is quick but affects several properties, including a loss in tenacity, color, and luster when compared to the bacterially­retted fibers. It was found that the retting time could be reduced by a combination of the methods without great effects on fiber quality.

Data were collected on the following characteristics to examine differences in the fibers extracted by the two retting methods: reed length, bundle breaking tenacity, elongation at break, color, luster, and residual gum content. Comparisons were also made to determine if varietal differences affected fiber characteristics.

Reed length is the total length from base to tip of the decorticated kenaf stalk before and after processing. This criteria may be important for fiber yield, and when intended use is for products such as ropes and cordage.

Bundle breaking tenacity is defined as the load required to break a fiber bundle of fixed length and weight. The flat bundle method is believed to be a good indicator of yarn strength and has a high correlation to yarn quality index.

Elongation at break is the amount of stretch of a fiber bundle at break and it is an important measure to indicate the ability to stretch.

Color and luster are important properties depending on the fiber end use; luster has a positive correlation with strength.

Gum content refers to the total wax, oil, lignin, and other hemicellulosic material. Residual gum content, the amount of gum left after processing, affects the fineness of fibers, which ultimately determines the success of using these fibers in a fine, woven textile structure.

The fiber processing and characterization research has significant implications. It establishes criteria for selection and improvement of kenaf varieties for breeders and growers because breeders usually need to establish quality with a single plant.

Bundle breaking tenacity as a measure of fiber quality would provide quick, accurate results depending on linear density of the bundle. It establishes the possibility of extracting fibers for large scale production of fibers.

Modified bacterial retting is recommended as it produces fibers with better characteristics; time required for bacterial retting can be reduced by natural and synthetic activators.

The fiber characteristics indicate the feasibility of incorporating the retted fibers into nonwoven structures that have multiple end uses, such as in erosion mats, tea bags, pillow covers, mattress liners, etc. The trials with fiber processing are being done to reduce the residual gum content, which will enable extraction of finer quality fibers that may be incorporated into blended woven fabrics for apparel use.

Studies were also undertaken to evaluate the effect of residual gum on the quality of fibers extracted from the base to the tip of the plant. Fiber uniformity was studied using fiber characteristics and scanning electron microscopy (SEM). Since fiber quality also depends on the molecular structure, the effect of gum on crystallinity of fibers, extracted by the two methods was also evaluated.

The three textile product lines of interest to the researchers are (1) nonwovens for uses such as medical and chemical protection, furniture underlays, linings, and interlinings' (2) wovens for apparel, domestic, and medical uses wound dressings); and (3) hand spun and woven yarns for use in rugs, placemats, and decorative items.

To achieve the goals, fibers were processed, degummed, combed, and sometimes softened. The fibers for nonwoven products were taken to TANDEC (Textiles and Nonwoven Development Center) Knoxville, Tennessee where preliminary trials were done to make a meltblown laminate (polypropylene, kenaf). The nonwoven laminate made resulted in uniform distribution of kenaf, which made up 70% of the laminate by weight. The laminate will be point­bonded and finished to obtain nonwoven fabric that will be tested for barrier effectiveness against blood, body fluids, and pesticide formulations; moisture absorbency; abrasion, tear and tensile strength. Kenaf laminates will be compared with cotton laminates for the same characteristics. Trials with 100% kenaf webs laminated by either meltblown polypropylene (MB PP) or spunbonded polypropylene (SB PP) have also been done. These nonwovens are also being characterized and tested for barrier effectiveness. Kenaf webs were also needle punched to make nonwovens suitable for automobile and air conditioning filters.

Nonwovens were also made at SRRC, USDA, New Orleans, Louisiana, where kenaf was blended with polypropylene and calendared. This product may be used in furniture underlays and wallpaper backings.

Fibers processed in four different ways to obtain pliable fibers were used for making yarns and fabrics. The different kinds of chemical processes were aimed at preserving strength while reducing the residual gum content, thus increasing pliability. Fibers from all four processes were stapled (1 inch) and blended (80 cotton/20 kenaf) with cotton and spun and knitted at SRRC, USDA, New Orleans, Louisiana.

Fibers were opened, hand­blended with cotton and carded to obtain the card lap. The card lap was put on a drawing machine to form the drawing sliver and then sent for spinning. Spinning resulted in 900 yards of yarn of 16s size, z­twist and 15.5 twists per inch. These yarns were then knitted into fabric tubes. Of the four processes, fibers processed bacterially and then chemically treated resulted in the best characteristics; fibers were the strongest, had the least residual gum content, and exhibited the best stretch property. The same experiment will be repeated to confirm the findings and also to make more yarns so tests on yarn quality index can be determined.

Hand spun/woven

Plain and softened fibers were hand­spun and woven for experimentation. Results of this work are very encouraging and resulted in:

(1) A rug made of cotton warp and kenaf weft (or filling). Kenaf yarns were dyed in black and red using natural dyes;

(2) Fine hand­woven placemats made of cotton linen in warp and kenaf in weft;

(3) Jacket weight fabric made of cotton in warp and carded kenaf in weft;

(4) Yarns ­­ single and plied yarns were spun.

These preliminary trials with nonwoven and woven textile product lines illustrate the possibility of kenaf being used as a textile fiber similar to jute, ramie, and/or linen. Major obstacles may be the process to soften and processing costs. Preliminary experiments with fabric finishes may take care of the softening problem. So far, tests have been made only with cotton blends for the wovens and polypropylene for the nonwovens. In the future, trials may be conducted to blend kenaf with other manmade or natural fibers to enhance the natural luster and texture.

Gita N. Ramaswamy is Associate Professor and Catherine R. Boyd is Professor, Department of Home Economics, Mississippi State University.