Molecular Weight and Intrinsic Viscosity
topic
Intrinsic viscosity (IV) of PET, measured in phenol/tetrachloroethane (60:40) at 25°C, correlates with viscosity-average molecular weight via Mark–Houwink equation [η] = KMᵃ (K=2.1×10⁻⁴, a=0.82 for PET). Fibre-grade PET requires IV 0.60–0.68 dL/g; bottle-grade 0.72–0.86 dL/g. Polydispersity index (PDI) typically 1.8–2.2.
Role
IV is the primary industrial quality parameter for PET polymer. It governs melt viscosity, spinnability, fibre tenacity, and elongation-at-break. Precise control is essential for consistent spinning performance.