The Solid State Postcondensation of PET, 3

Abstract

Summary: It was demonstrated that it is possible to produce prepolymers with a number‐average degree of polymerisation on the order of 5–40 directly in a liquid‐liquid dispersion in less than three hours. It was also shown that prepolymers made via this route and rapidly crystallised by the addition of a dispersant at ambient temperature are more porous than prepolymers made in an industrial liquid melt process.SEM micrograph of prepolymers pLL‐PTA with \overline {DP} _{\rm n} = 28, dp ∈ 63–125 μm.magnified imageSEM micrograph of prepolymers pLL‐PTA with \overline {DP} _{\rm n} = 28, dp ∈ 63–125 μm.

The Solid State Postcondensation of PET, 4

“…In addition to the particle size, it is possible that particle porosity can influence the rate of mass transfer inside the particles in much the same way as occurs in olefin polymerisation 5,6. It was shown in Part 34 that the prepolymers made by the liquid‐liquid dispersion route are more porous than those from the industrial site, which means that it is important to understand any differences that might occur due to this factor. A kinetic study was carried out on different samples to investigate this, and the results are shown in Figure 6.…”

“…However, as we can see in this Table, the structure of the crystals seems to be important. In the unmilled sample of pIND‐DMT3, the WAXS analysis revealed no crystal structure at all (this contrasts with the results in Part 3,4 where very small crystals of 4 nm were seen, so it is possible that there are similar structures here, but that we missed them with the analysis. This is not unreasonable since we are at the limit of detection of WAXS.…”

“…The prepolymers and precursor molecules used in this study are summarised in Table 1. In the event that the prepolymers were synthesized in the laboratory, the process and kinetics are discussed in Gantillon et al4 Industrial products were taken directly from the production lines of our industrial partners (Tergal Fibres, Gauchy, France).…”

“…This is important since the condensation reaction is reversible, and high molecular weights are possible only if the forward reaction is favoured by evacuating this by‐product; and (2) “chemical” diffusion, or the diffusion of the reactive chain ends toward each other in the reaction mass. It was shown in Part 2 and 33,4 that analysing the polycondensation reaction in this manner allowed us to demonstrate that it was indeed possible to envisage a new process for the production of PET in which the product of the prepolymerisation reaction was crystallised in a particular manner and then treated directly in a solid state postcondensation (SSP) step, with no need to increase the molecular weight in an expensive and time consuming liquid phase process (typically done in specially designed disk‐ring reactors).…”

“…The prepolymerisation can be done either in a liquid‐liquid dispersion in our laboratory (pLL), or in the melt at the industrial site (pIND). The prepolymer is crystallised, and if it is pIND, it is milled to reduce the size of the particles, other wise the particles issued from pLL can be used ‘as‐is’ 3,4. The particles are then polycondensed in the solid state in a gas phase reactor (SSP(g)), or in a solid‐liquid slurry (SSP(s)).…”