Pretreatment of polyethylene terephthalate (PET) using physicochemical methods and their effects on biodegradation

Abstract Recently, biodegradation has gained importance as a potential solution to alleviate pollution. This study dives into the physicochemical transformations of polyethylene terephthalate (PET) to enhance biodegradation efficiency. PET films were subjected to pretreatments, including UV irradiation, thermal oxidation, size reduction, and a combination of thermal oxidation and size-reduction pretreatments. These pretreated samples were then biodegraded using either an immobilized enzyme or the whole-cell Thermobifida fusca YX. The physicochemical effects of these treatments were evaluated through techniques such as attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), and weight-loss analysis. The findings revealed that UV irradiation caused repetitive cycles of photo-oxidation over 3 h, which impaired biodegradation due to increased crystallinity. Conversely, thermal oxidation improved biodegradation up to an optimal temperature of 80 °C. Higher temperatures were favorable for whole-cell biodegradation, while slightly lower temperatures (70–80 °C) were optimal for enzyme-mediated processes. A similar trend was observed for thermally oxidized size-reduced particles, with the smallest particle size exhibiting the highest biodegradation rates, 21.25 ± 0.24% with the immobilized enzyme and 16.61 ± 0.63% with whole cells. The study further demonstrated that all pretreatments primarily targeted the ester linkage, specifically the C = O and C–H bonds. Additionally, the effects of pretreatments were tested on chemical hydrolysis. Due to its inherently caustic nature, chemical hydrolysis did not require any pretreatment. These findings shed light on the interplay of physical and chemical factors influencing biodegradation, offering valuable insights into the importance of pretreatments for the biological hydrolysis of such polymers. Graphical Abstract