A METHOD TO OBTAIN A WELL-DEFINED FRACTION OF RESPIRABLE PARA-ARAMID FIBERS

We developed a preparation method to obtain respirable-sized fractions of para-aramid fibers. The procedure, based on floatability, consists of stirring and subsequent settling of p-aramid pulp in distilled wat er. Two distinct phases are obtained, with small fibers in the upper p art of the suspension, which represents about 33% of the total volume. Optimal results were obtained when 2.0 g pulp was stirred for 15 hr i n 800 ml distilled water containing 0.125% ethanol and settled for 5 h r. The mass yield ranged between 0.4 and 0.6%, more than 90% of the pa rticles had an aspect ratio greater-than-or-equal-to 3:1. The mean fib er length was about 6 mum, and the mean fiber diameter was about 0.4 m um as determined by transmission and scanning electron microscopy. The number of fibers obtained was 4 x 10(6) fibers/mug under our standard conditions.