Crystallinity, Crystal Structure and Measurement

PET crystallises in triclinic unit cell (a=4.56, b=5.94, c=10.75 Å, α=98.5°, β=118°, γ=112°). Crystallinity measured by: WAXD (wide-angle X-ray diffraction, characteristic peaks at 2θ=17.5°, 22.5°, 25.6°), density gradient column (ρc=1.455 g/cm³, ρa=1.335 g/cm³), DSC (heat of fusion ΔHf, crystallinity = ΔHf/ΔHf° where ΔHf°=135 J/g). As-spun POY: 0–5%; FDY after drawing: 35–50%.