Fecha de publicación: -- Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE In mimicking continuous industrial pre-oxidation for preparing pre-oxidized PAN-based fibers (OPFs), the non-uniform distribution of oxygen content results in the formation of the skin-core structure. When the cross-sectional area fraction of the core regions is below 30%, the elongation at break of OPFs decreases markedly. A correlation is established between the skin-core structure and the mechanical properties.

ABSTRACT
Pre-oxidized PAN-based fibers (OPFs) are prepared by continuous mimicking industrial line. A correlation is established between the skin-core structure and mechanical properties of OPFs. SEM and OM reveal that the skin-core structure of OPFs stems from radial oxygen content heterogeneity. EA and FTIR indicate that cyclization dominates in the early stage of pre-oxidation, with the surface O/C ratio remaining essentially constant. At a residence time of 30 min, the bulk O/C ratio increases by 75%, and the degree of cyclization increases by about 28%. The abundant cyclic structures formed provide ample reactive sites for subsequent oxidation and crosslinking reactions. During pre-oxidation, the crystalline damage in OPFs originates from the edges of crystallites and gradually extends to the whole crystal. Meanwhile, the radial heterogeneity of OPFs causes uneven stress distribution and microcrack formation at the skin-core interface, ultimately deteriorating the mechanical properties of OPFs. A quantitative analysis of the relationship between the core area fraction and mechanical properties reveals that the elongation at break decreases when the core area fraction falls below 30%. This study provides a reference for understanding the correlation between the skin-core structure and the mechanical properties of pre-oxidized fibers.