Structural Evolution of Phenolic Fibers during the Forming Process

This article focused on preparing high-ortho phenolic resin using phenol and formaldehyde as precursors and using zinc acetate as catalysts. High ortho-phenolic fibers were produced through wet spinning, solution thermal curing (STC), microwave thermal curing (MTC), and heat treatment techniques. The structural and mechanical properties of the fibers were evaluated using gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), micro-infrared imaging (Micro-FTIR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TG), mechanical testing and scanning electron microscopy (SEM). The high-ortho phenolic fibers experienced a reduction in hydroxymethyl groups and an augmentation in methylene groups upon microwave curing, which enhanced cross-linking. Through the escalation of solution cross-linking bath and heat treatment, the hydroxymethyl groups within the phenolic molecules underwent a reaction to form methylene groups. Methylene groups facilitated the increase of intramolecular crosslinking degree, thereby enhancing the stability of the fibers structure. As a result, the mechanical properties of the fibers were improved and reached an optimal level under microwave heat curing, with an elongation of 3.1% and a tensile strength of 107 MPa.