Solid‐state polycondensation of poly(ethylene terephthalate) recycled from postconsumer soft‐drink bottles. II

Poly(ethylene terephthalate) (PET) taken from postconsumer soft‐drink bottles was subjected to solid‐state polycondensation after cutting into small pieces or after dissolution in trifluoracetic acid, trifluoracetic acid/dichloromethane mixture (50/50%, v/v), or nitrobenzene, and coagulation in methanol. The effect of various reaction parameters such as time and temperature of reaction (180, 200, 220, and 230°C) on intrinsic viscosity [η] and carboxyl and hydroxyl end‐group content have been investigated. The highest number average molecular weight, M̄ n = 61,400 was obtained from PET ( M̄ n = 20,300) dissolved in nitrobenzene and solid‐state polycondensated by heating under vacuum at 230°C for 8 h. The thermal behavior of solid‐state samples was studied by differential scanning calorimetry (DSC); all samples showed a characteristic double endothermal melting peak and no glass‐transition temperature. The PET samples taken from the bottles without dissolution were also studied by thermomechanical analysis. The heat distorsion temperatures obtained by this analysis were in very good agreement with the two endothermal melting peaks taken by DSC. This finding indicates that in these samples the crystallites form a coherent matrix and the amorphous phase is dispersed in the voids.