Two-Phase Model: Crystalline and Amorphous Regions
topic
The classical two-phase model of semicrystalline PET describes fibres as a composite of crystalline lamellae (folded-chain, ~10–20 nm thick, 5–15% of volume in as-spun; 35–50% in drawn fibre) embedded in an amorphous matrix. Modified model includes 'rigid amorphous fraction' (RAF) between crystal surfaces and mobile amorphous fraction (MAF). Intermediate phase fraction determined by dynamic mechanical analysis and DSC.
Role
The two-phase (and three-phase) model is the fundamental conceptual framework for interpreting mechanical properties, Tg behaviour, dye diffusion, and moisture uptake of polyester fibres. It is the starting point for all structure–property analysis in fibre science.