Amorphous Orientation and Sonic Modulus
topic
Amorphous orientation (fa) is distinguished from crystalline orientation (fc) by comparing birefringence (total orientation) with WAXD crystalline orientation: fa = (Δn − fcΔnc)/Δna°. Sonic modulus (from pulse propagation velocity, Ec = ρv²) provides overall chain orientation. Dynamic mechanical analysis (DMA) storage modulus E' vs. temperature reveals amorphous phase mobility. Amorphous orientation critically affects Tg, dye diffusion, and shrinkage.
Role
Amorphous orientation is the structural parameter most directly related to polyester's thermal shrinkage and dye uptake rate — properties critical for fabric processing. Distinguishing its contribution from crystalline orientation is fundamental to complete fibre structure characterisation.
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