SHORT COIR FIBER-REINFORCED NATURAL-RUBBER COMPOSITES - EFFECTS OF FIBER LENGTH, ORIENTATION, AND ALKALI TREATMENT

Natural rubber is reinforced with untreated coir fiber chopped to diff erent lengths, viz., 6, 10, and 14 mm. Mixes were also prepared using 10 mm-long coir fibers treated with 5% sodium hydroxide solution for d ifferent time intervals, viz., 4, 24, 48, and 72 h. These composites w ere vulcanized at 150 degrees C. The vulcanization parameters, process ability characteristics, and stress-strain properties of these composi tes were analyzed. The rubber-coir interface bonding was improved by t he addition of a resorcinol-hexamethylenetetramine dry-bonding system. The reinforcing property of the alkali-treated fiber was compared wit h that of the untreated one. The extent of fiber orientation in the co mposite was determined from green strength measurements. From anisotro pic swelling studies, the extent of fiber alignment and the strength o f fiber-rubber interface adhesion were analyzed. Scanning electron mic roscopic studies were carried out to investigate the fiber surface mor phology, fiber pullout, and fiber-rubber interface. (C) 1995 John Wile y and Sons, Inc.