rope made of cellulose fibers , the polymeric chemical structure of which fibers has not been modified , are subjected to intense electron beam irradiation insufficient to degrade their chemical structure but sufficient to modify their physical structure so as to allow them to be comminuted into fragments having a length no more than 6 . 35 mm , preferably less than 3 . 175 mm , and preferably 50 % by weight of the fibers have a length less than 70 μm . such fragments of fibers are found to be particularly susceptible to being micronized in a micronizer into elongated granular fragments smaller than about 20 μm at an economical production rate in excess of 22 . 7 kg / hr which was not possible when the micronizer was fed with naturally occurring fibers .