Kinetic analysis and modelling of PET macromolecular changes during its mechanical recycling by extrusion

Abstract

The rheometer cavity has been chosen to analyze, in carefully controlled exposure conditions, the PET macromolecular changes generated during its mechanical recycling by extrusion. Isothermal ageing experiments at 280 C, under constant or variable oxygen partial pressures (between 0% and 21% of the atmospheric pressure), have allowed us to establish that two types of oxidative macromolecular changes take place successively in an extruder reactor. Chain scissions predominate in the "strongly oxygenated" zones (at the feeder and die), whereas chain couplings (mainly chain branching) predominate in "poorly oxygenated" zones (in the middle of the reactor). Thus, it appears that the relative predominance of both types of modifications is closely related to the extruder geometry and size (in particular, the feeder and die sections and the screw length). A kinetic model of thermal ageing of molten PET has been built to check these assumptions. It describes satisfyingly all the rheometric results obtained in the present study.

Effect of multiple extrusions and influence of PP contamination on the thermal characteristics of bottle grade recycled PET

“…Their presence in small amounts in rPET-bg can significantly affect crystallinity during multiple extrusions. Some researchers have studied the degradation of rPET during processing and concluded that chain scission can occur and that formation of grafted copolymers and crystallization can be facilitated [4,5] and others concluded that during repetitive extrusion, chain scission predominated and no chain branching or cross-linking were observed which decreased capabilities and crystallinity [7,8], whereas others concluded that cross-linking and chain branching occur during extrusion [9,10]. This research study investigates the influence of thermo-mechanical degradation during repetitive extrusion cycles on the crystallinity of non-contaminated and contaminated rPET matrix with 5% PP.…”

Nouvelles avancées en modélisation cinétique de la thermo-oxydation des matrices époxy-diamine

“…A titre d'information, les paramètres d'Arrhenius et les ordres de grandeur de k 3à 30 • C des principaux types de liaisons méthyléniques C-H sont donnés au Tableau 2. Ces valeurs sont issues d'études antérieures menées au laboratoire [3][4][5][6][7].…”

“…Tout comme les polyesters [5] et les polyamides (PA) aliphatiques [6], les matrices EPO-DA vont donc subir une oxydation beaucoup plus sévère que le polyéthylène (PE …”

“…Le mécanisme d'oxydation dit en (( boucle fermée )), mis au point au laboratoire pour les matrices polyméthyléniques dans desétudes antérieures [3][4][5][6], aété naturellement choisi pour décrire la thermo-oxydation des matrices EPO-DA dans cetteétude. Sa généralisation aux matrices EPO-DA a nécessité un réajustement des rendements de consommation du substrat PH dans les différentes réactions bilan (i.e.…”

“…-Recombinaisons (terminantes et non-terminante) : [3][4][5][6][7]. (i)À t = 0, en tout point z de l'épaisseur de la pièce : la littérature [8,9,[11][12][13][14].…”