Microwave promoted rapid curing reaction of phenolic fibers

Curing reaction of the as-spun fiber derived from melt-spinning of a novolac resin in a solution of formaldehyde and hydrochloric acid was carried out under microwave irradiation by controlling the reaction time. IR spectroscopy, scanning electron microscopy, and dynamic mechanical analysis were employed to characterize the change of structure and mechanical performance of these phenolic fibers. At the heating rate of 1.2 degrees C min(-1) or in a period of 86 min the homogeneous highly crosslinked phenolic fiber was obtained with the maximum tensile strength being similar with that of the fiber cured under conventional heating reflux (8 h), suggesting that microwave irradiation promotes not only the diffusion of +CH2OH from the skin into the inner layer of the fiber but also the reaction of +CH2OH with the phenolic ring in a suitable extent. During pyrolysis the increase of crosslinking degree in the phenolic fibers diminishes the formation of low molecular weight compounds and promotes the formation of graphite layers. (c) 2007 Elsevier Ltd. All rights reserved.