Frost kill and kenaf fiber quality

Kenaf (Hibiscus cannabinus) grown in northern Mississippi and elsewhere often is injured by early frost and killed before harvest. Frost kill often is associated with fungal growth or rot, so its effect on fiber quality is a major concern. Fiber processing also affects the quality and chemical composition of fibers. Therefore, this study was aimed at determining the effects of frost kill on processing, fiber quality and chemical composition of kenaf fibers. Frost-damaged kenaf with fungal growth was decorticated by hand and divided into six sections (26.88 cm/each) from the base to tip of the stem and then retted chemically or bacterially in the laboratory. Fiber characteristics were compared between the two processes and the six locations on the plant. Ash, cellulose, hemicellulose, and lignin contents of the resultant fibers were measured. Bacterially retted (BR) fibers were stronger (11.8 g/tex) than the chemically retted fibers (CR), 7.5 g/tex, at all locations. The BR fibers from decorticated green ribbons were stronger than those from frost-killed ribbons. However, no significant differences occurred between the CR fibers from decorticated and frost-killed ribbons. Residual gum content was higher for the BR fibers (23.3%) than for the CR fibers (8.1%). The stretch properties were not affected significantly by the frost kill or fungus. The base of the stem had the weakest fibers in both processes, which may have been due to greater fungal disease. The CR process extracted more fiber than the BR process, with a consistent higher yield of clean fibers. In the BR process, the fiber extracted was higher at the tip than at the base of the stem. This may have been related to the presence of fungus, which inhibits the BR process. Analysis of chemical composition of the processed fibers indicated that CR is efficient in reducing hemicellulose and lignin contents. These results indicate that frost kill may not be the appropriate method for harvesting kenaf for quality fibers. However, fibers extracted by chemical retting were unaffected by the presence of fungus as a result of frost kill.