2.2. Chemical degradation of PET by glycolysis
Post-consumer and virgin PET were chemically degraded by
glycolysis reactions employing DEG and Ca/Zn stearate as catalysts
(Table 1). The degradation reaction was carried out by using a
Brabender Plastograph mixer with an internal chamber of 50 cc,
applying a temperature of 250 C. The rpm profile was gradually
increased from 50 rpm (feeding) until 90 rpm within 3 m in. The
chamber was initially filled with 45 g of polymer; after 3 min,
when the polymer was completely molten, the catalyst and the
glycol were simultaneously added into the chamber.
The reaction was stopped after 20 min. and the degraded PET
product was carefully removed from the Brabender chamber; the
fraction collected was around 80–85% by wt. with respect to the
initial amount of polymer. The degraded PET was a green viscous
liquid at high temperature and a brittle solid at room temperature.
The torque behavior and the temperature profile were collected
and processed by Win Mix software. Before the degradation reac-tion experiences, all the PET samples were stored for 3 days under
controlled atmosphere (50% humidity) in order to avoid the occur-rence of hydrolysis reactions due to the presence of water traces.