Solid state polymerisation

Solid State Polymerisation (SSP) is a post-polymerisation technique carried out in the solid phase at temperatures between the glass transition temperature (Tg, ~70-80°C) and the melting temperature (Tm, ~250-260°C) of PET. In this temperature range, the polymer remains in a solid, semi-crystalline state, preventing degradation and allowing a controlled increase in molecular weight through further polycondensation.

Solid State Polymerisation significantly increases the intrinsic viscosity (IV) of PET. This makes the polymer suitable for more demanding applications or increases the processability of recycled PET fractions.