Solid-state Polycondensation of Polyester Resins Fundamentals and Industrial Production

Modem Polyesters Chemistry and Technology of Polyesters and Copolyesters. Edited by J. Scheirs and T. E. Long 2003 John Wiley Sons, Ltd ISBN 0-471-49856-4 

Polycondensation of highly viscous polyesters in the melt phase is limited. The removal of the volatile by-products becomes more difficult due to diffusion inhibited by the increased viscosity of higher-IV polyesters. In addition, undesirable side reactions due to thermal degradation impede the growth of the molecular chains. As a consequence, the reaction rate decreases and decomposition reactions dominate, thus resulting in a decrease in the melt viscosity [2], As it is able to address these limitations, SSP has become the method of choice and is therefore so popular. 

SSP can be carried out batchwise or continuously, either in vacuo or supported by an inert gas flow. Another variation of SSP is the so-called suspension process in the swollen state, which allows for the production of extremely high-molecular-weight polyesters [3], This technology is more of academic interest than for commercial application since it requires complete removal of the high-boiling suspending oils. 

The continuous process is appropriate for the large-scale production of polyesters used in bottle manufacture. Currently, reactors with capacities of more than 600 t/d have been employed. The discontinuous technology based on tumble dryers allows for the successful production of specialities on a smaller scale, particularly for engineering plastics and with respect to the fiber industry. This route is preferred due to its flexibility, simple process control and the excellent quality of the final product. It is, however, restricted by the volume of the reactors, which is generally limited to 44 m3. 

The SSP process allows polycondensation under gentle conditions to obtain the desired high molecular weights and excellent polymer quality for various applications. It can be successfully introduced for the production of sensitive co-polyesters as well as for the recovery of polyester waste. 

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Solid-State Polycondensation of Polyester Resins Fundamentals and Industrial Production... 

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