The fibers were washed with a 2% detergent solution at 60 8C for 1 h and then with distilled water, and finally dried in a vacuum oven at 80 8C. The washed fibers were treated with 4% NaOH solution for 45 min, washed in running tap water and then with distilled water until the pH value reached 7.0, followed by drying in an oven to obtain the alkali-treated fibers.