Solid-State Polymerisation (SSP)
topic
SSP increases IV of PET chips from 0.60 to 0.80–0.95 dL/g by heating crystallised chips at 200–230°C under N₂ flow or vacuum, allowing further polycondensation in solid phase while removing glycol and water by-products. Prevents degradation that would occur in melt phase at high IV. Used for high-tenacity industrial yarns and bottle-grade PET.
Role
SSP is essential for producing high-MW PET required for high-tenacity tyre cord, geotextile yarns, and seatbelt yarns where melt-phase polymerisation alone cannot achieve sufficient IV without thermal degradation.