Differential Scanning Calorimetry of Fibres

Differential scanning calorimetry (DSC, ISO 11357-3 melting, ISO 11357-2 Tg) measures heat flow into or from a fibre sample as temperature is scanned at 10–20°C/min, recording thermal transitions as peaks (exothermic crystallisation, endothermic melting) or step changes (glass transition Tg) that characterise polymer molecular structure and processing history. Sample preparation: 5–10 mg fibre cut into 1–2 mm fragments, hermetically sealed in 40–100 µL aluminium pan — proper sample contact with pan base critical for reproducible heat flow measurement. PET fibre DSC signature: cold crystallisation exotherm at 130–160°C (amorphous fraction crystallising on heating — cold crystallisation area ΔHcc J/g indicates poorly drawn or undrawn fibre content); melting endotherm at 252–258°C (ΔHm J/g); crystallinity = (ΔHm − ΔHcc) / 140 × 100 — well-drawn PET fibre shows no cold crystallisation peak (crystallinity already achieved during drawing). Draw ratio effect: low-draw (DR 3.0) PET ΔHcc = 25 J/g, ΔHm = 50 J/g, crystallinity = (50−25)/140 = 18%; high-draw (DR 5.5) PET ΔHcc = 0 J/g, ΔHm = 52 J/g, crystallinity = 37%. Heat setting adequacy verification: heat-set polyester fabric shows no shrinkage peak (secondary endotherm below Tm = memory of previous heat treatment temperature) when re-scanned — absence of secondary endotherm at 190°C confirms adequate 190°C heat setting treatment. PA6 fibre Tg: ~50°C (affected by moisture — moisture plasticises nylon, reducing Tg to 15–25°C at standard 65% RH — must condition samples to reproducible moisture level before DSC testing per ISO 11357 protocol).