There are mainly three methods to produce high IV PET chips.

1 Direct Polymerisation Method

This method uses continuous polycondensation and direct esterification to produce an oligomer with a high degree of esterification. As the critical ratio of the carboxyl group increases, the reaction speed accelerates and the vacuum requirement decreases, making it easier to produce high-viscosity polyester chips. However, the polymerisation process takes a long time.

High carboxyl content in high-temperature spinning causes more serious degradation, resulting in a decline in the molecular weight and ultimately affecting the tensile strength of polyester fibres.

Therefore, this method is not commonly used, but it can be used for coarse denier requirements.

2 Catalyst Addition Method

In Japan and other countries, many patents document the addition of a special catalyst to the melt polycondensation process, thereby reducing the polymerization time. When the molecular weight goes up a lot, the intrinsic viscosity generally reaches 0.8~1.1 dl/g.

3 Solid-state Polycondensation Method

The regular PET chips (IV: 0.60 ~ 0.68 dl/g) are heated to 200 – 240℃ in a vacuum or inert gas protection. At the same time, the intrinsic viscosity is increased to 0.9–1.2 dl/g. The drying of PET chips is completed during the condensation polymerization process.
This low-cost, stable quality, and easy to reach a certain production is the most widely used production method of high-strength polyester.
Solid-state polycondensation is used to produce high-viscosity PET by heating the lower-viscosity PET polymer to a temperature above Tg and below the melting point.

Under vacuum or inert gas protection, the end groups of the polymer chain have enough activity

to carry out the polycondensation reaction, increasing the relative molecular mass.