Recyclability of PET from virgin resin

Abstract

Bottle grade virgin PET (polyethylene terephthalate) resin was investigated through five consecutive injection molding steps to simulate recycling cycles. Tests were carried out after each recycling to evaluate degradation, crystallinity (by density and Differential Scanning Calorimetry-DSC measurements), hardness, and tensile and flexural properties. Consecutive recycling resulted in cumulative chain breaks caused by the material's contact with degrading agents such as temperature, oxygen, mechanical stresses, light, and water. In the fifth recycling step, for example, the number of carboxylic end groups, an indicator of the extent of chain-break, tripled in comparison to the initial molecule. The smaller chains that were formed fit more easily among the larger ones, thus increasing the percentage of crystalline phase in the structure. These two changes in the polymer's structure explained the recycled products' final properties, i.e., the injected samples became progressively harder and more fragile in each recycling step

Morphology and properties of poly(ethylene terephthalate) and thermoplastic polyester elastomer blends modified in the melt by a diisocyanate chain extender and filled with a short glass fiber

“… When the degree of PET phase crystallinity was calculated, we assumed that the specific heat of crystallization for the completely crystalline PET amounted to 140.1 J/g …”

Despolimerização do poli (tereftalato de etileno) - PET: efeitos de tensoativos e excesso de solução alcalina

“…Os autores também mostraram que a velocidade é maior em amostras de polímero saturadas com água, ou seja, a água age como catalisador da reação. Outros pesquisadores tem estudado a reciclagem do PET [16][17][18][19][20][21][22][23][24] e encontrado resultados semelhantes usando solução aquosa de NaOH em proporções equimolares com PET em temperaturas e ou pressões menores mas, em maiores tempos de reação [16][17][18][19][20] . Existem poucos trabalhos usando catalisadores [9] para aumentar o rendimento da reação de despolimerização do PET.…”

Un modèle cinétique pour prédire les modifications de structure macromoléculaire du PET pendant son recyclage mécanique

“…Il est maintenant bien établi que la thermo-oxydation du polymère est la principale source de problèmes [24,[31][32][33][34][35][36][37][38]. Dans le cas de l'injection, bien que la durée de séjour du polymère à l'état fondu soit nettement plus brève (de l'ordre de quelques secondes), il semblerait que la thermo-oxydation joue aussi un rôle important [39][40][41]. Aux températures de mise en oeuvre (typiquement entre 210 et 280 • C), la thermo-oxydation est un mécanisme radicalaire en chaîne, essentiellement amorcé par la décomposition du principal produit de propagation : le groupe hydroperoxyde POOH [3,4,6,9,21,24,26,27,35,36].…”

“…des modifications des groupes latéraux, c'est-à-dire principalement la formation de groupes hydroxyle et carbonyle [5,6,9,11,12,15,16,21,23,24,[26][27][28], mais aussi de diverses structures conjuguées [3,5,6,8,9,15,16,20,23,26] ; -des modifications de la structure macromoléculaire, c'est-à-dire des coupures [31][32][33][34][35][36][37][38][39][40][41][42][43] et des soudures de chaînes [3, 5, 6, 8-10, 14, 16, 20, 22-24, 26, 35, 36].…”

“…Les modifications macromoléculaires affectent aussi bien le comportement rhéologique du polymère en solution ou à l'état fondu (variations de viscosité) [3, 5-7, 9, 18, 24, 31-38, 40-42], que le comportement mécanique du polymère à l'état solide (chute catastrophique des propriétés à la rupture) [27,31,33,34,[38][39][40][41]44], et ceci même aux très faibles conversions. Il est maintenant bien établi que les coupures de chaînes conduisent à la formation de nouvelles extrémités de chaînes aldéhyde [5,6,9,16,18,21,43], formate [23,27], acide carboxylique [3-12, 14, 16, 18-24, 26, 27, 33, 34, 39-42] et vinylester [3][4][5][6][7][8][9][10]12,[14][15][16]18,[20][21][22][23][24]26].…”