Morphological changes of poly(ethylene terephthalate‐co‐isophthalate) during solid state polymerization

Abstract

Poly(ethylene terephthalate-co-isophthalate) (PETI) prepolymer was submitted to solid state polymerization (SSP) at 184-230 C in a fixed bed reactor, to study the evolution of morphological changes during the process. Short reaction times were selected to investigate crystallization phenomena during nonisothermal (heating) and isothermal SSP phases. More specifically, multiple PETI melting behavior was observed and attributed to secondary crystallization, the rate of which increased significantly with SSP temperature. Reaction time was also found to exert a positive effect on solid-phase perfection of secondary crystals, leading at each temperature to melting points close to the value of bottle-grade poly(ethylene terephthalate). Finally, the mass fraction crystallinity of the SSP grades was found to comply with the crystal morphology encountered.=ðq a À qÞ, where q ¼ x v (q c À q c ) þ q a is the polymer density (g cm À3 ), q c ¼1.455 g cm À3 the density of the crystalline phase, and q a ¼1.355 g cm À3 the density of the amorphous phase. c DH 0 ¼ 135 J g À1 . 11 4458VOUYIOUKA ET AL.

Comparative Analyses of Poly(ethylene 2,5‐furandicarboxylate) − PEF − and Poly(ethylene terephthalate) − PET − Resins and Production Processes

“…The existence of two crystallization events for PEF and the absence of crystallization events during the heating process for PETc (as observed by Vouyiouka et al) and PET is an evidence that PEF presents a higher tendency to crystallize than PET, as confirmed by XRD. However, analyzing the DSC results for the polyesters, summarized in Table , it is possible to observe that the variation in the enthalpy recorded during the melting process for the PEF resin is lower than both PET and PETc, which could contradict the other experimental data and indicate that PEF is less crystalline.…”

“…The fact that PEF melts at lower temperatures than PET may constitute an intrinsic advantage of PEF, since less energy may be required for processing. However, the lower thermal stability and the higher degree of crystallinity of the furanic polyester demands a more efficient control of the processing temperature in order to avoid both degradation and nucleation during processing …”

Long‐term statistical stability of industrial plants: Performance indicators and monitoring of an industrial pet plant

“…Despite that, significant fluctuations can be observed in the t‐ charts built to monitor crystallinity in Year02 and the F‐ charts built to monitor the acetaldehyde concentration in Year03. It is interesting to observe that heated nitrogen is used simultaneously to promote the PET crystallisation and to remove volatile byproducts, which can explain why the control charts are usually similar for crystallinity and acetaldehyde concentration. As the control of crystallinity and acetaldehyde concentration are more stable than control of the IV, it seems reasonable to assume that these variables are subject to distinct perturbations at plant site.…”

“…As one can see in Figure , the distribution of measured acetaldehyde concentrations is narrow and the process is able to keep this output variable within the specification limits. It is also important to emphasise that it is well known that acetaldehyde averages and variances are reduced at PET solid state polymerisation plants because of the carrier gas effect.…”

Solid state polymerization of pet/pc extruded blend: effect of reaction temperature on thermal, morphological and viscosity properties

“…Vouyiouka et al studied the morphological changes of PET prepolymer during SSP. They concluded that secondary crystals are strongly dependent on the SSP temperature [1] . Commercial PET was exposed to ethylene diamine vapors in order to reduce its molecular weight.…”