Preparation of fibrous porous materials by chemical activation 1. ZnCl2 activation of polymer-coated fibers

Fibrous porous materials (FPMs) have been prepared by coating a glass fiber with a solution of polymer and ZnCl2, followed by stabilization in air and heat treatment in N-2. The ZnCl2 was then removed by washing with D.I. water and HCl. Four kinds of polymers, a phenolic resin, polyacrylonitrile, poly(vinyl alcohol) and cellulose, were used to prepare solutions with ZnCl2. The results showed that ZnCl2 acts as a dehydration agent to promote the thermal cross-linking of polymer at a much lower temperature, leading to FPMs having much higher char yields and very high surface areas. The porosity was created in part by dissolution of the ZnCl2 left in the charred coating. The activation temperature and ZnCl2 concentration play an important role in porosity development. In the early stage of heating, the specific surface area, micropore and mesopore volumes increased with increasing temperature. As the activation temperature increases above 450 degreesC, ZnCl2 begins to volatilize out of the coating, and further charring and aromatization of the coating results in a dimensional contraction leading to a decrease in the micropore and mesopore volumes. It was observed that the specific surface area, as well as micropore and mesopore volumes. increased with increasing ZnCl2 concentration. Pore size analysis showed that the FPMs activated with ZnCl2 were mainly microporous. For FPMs activated with concentrated ZnCl2 (66 wt.%), there is a remarkable and large mesopore size distribution in addition to the typical micropore size distribution. In addition, such FPMs have very high specific surface area, more than 1600 for PAN-based and 2500 m(2)/g of coating for cellulose-based FPMs. (C) 2002 Published by Elsevier Science Ltd.