Evaluating Chemically Retted Kenaf Using Chemical, Histochemical, and Microspectrophotometric Analyses

Abstract

Bast ribbons from Guatemala 45 (G-45) and Tainung 1(T-1) cultivars of kenaf ( Hibiscus cannabinus ) were chemically retted for 1 hour in boiling 7% NAOH + 0.5% NaHSO₄, after which they were neutralized, washed, and air dried. Gas-liquid chro matographic analysis of extracts from unretted and chemically retted ribbon showed a decrease in syringyl and guaiacyl groups (indicative of lignin ) and xylose, arabinose, and uronic acids (indicative of hemicellulose and pectin). Glucose residues, indicative of cellulose, did not decrease in amount. Sections histochemically stained for lignin and unstained sections examined by ultraviolet absorption microspectrophotometry indicated that syringyl lignin predominated, but guaiacyl lignin was higher in the middle lamellae than in the secondary wall. Tip and base sections showed clear dif ferences in phenolics and carbohydrate content, which could be related to maturity. However, it appeared that syringyl groups were removed to a greater extent from the base sections and pectin was removed to a greater extent from the tips. Breaking strength was significantly greater for the tip than for the base, with no difference in percent elongation between regions.