## 5 PET Bottle Degradation Management Strategies
### Preventing PET Bottle Degradation
The Plasmax technology [116], used in the coating process of PET bottles, known as FreshSafe and offered by the German PET machinery manufacturer KHS Coroplast, allows for the creation of micro-thin, glass-like SiO\({}_{\mathrm{x}}\) coatings on PET bottles. FreshSafe PET bottles can be fully recycled. During the recycling process, the coating is hydrolyzed using hot caustic lye, which allows for its removal from the inner wall of the bottle. It is worth noting that the FreshSafe PET protective technology is also suitable for coating PET bottles made from recycled PET (rPET). Another method is coating PET bottles with a thin layer of hydrocarbon silicate (SiOC) using the hot wire CVD (chemical vapor deposition) technique assisted by plasma [117]. SiOC coatings are characterized by high gas barrier properties against oxygen, carbon dioxide, and water vapor, and unlike SiO\({}_{\rm x}\) coatings, they exhibit stability in contact with various liquids, including neutral pH beverages. Another group of materials used to modify the surface of PET is carbon coatings. Among them, hydrogenated amorphous carbon coatings (a-C:H) [35] and diamond-like carbon (DLC) coatings [118] are of particular importance. The deposition of carbon films on PET bottles is carried out using plasma technologies, which allow for the creation of thin, uniform layers. Carbon coatings on PET bottles significantly enhance their gas barrier properties, as well as improve their resistance to mechanical and chemical damage, increasing their durability. Moreover, the use of carbon coatings does not hinder the recycling process of PET bottles. Stabilizers, used as additives in plastics, aim to increase the material's resistance to degradation. UV stabilizers are added to improve the durability of the plastic under UV radiation. This effect has been confirmed in studies by [PERSON] et al. [27]. This study focused on comparing the effects of UV radiation on the degradation of plastic with and without the addition of a stabilizer commercially known as Tinuvin 1577w. The presence of Tinuvin 1577w stabilizer results in a reduction in the formation of carboxyl groups. Data obtained from fluorescence measurements showed the formation of monohydroxyterephthalate derivatives on the surface of PET with the addition of Tinuvin 1577w. This stabilizer primarily acts at the surface level by absorbing UV radiation, thereby delaying the photochemical degradation of the material's outer layers. In the context of UV protection, PET surfaces are coated with titanium dioxide (TiO\({}_{2}\)) nanoparticles [119]. TiO\({}_{2}\) in its non-photocatalytic form serves as a physical barrier to UV radiation, while also improving the material's thermal stability and mechanical properties, such as crack resistance. However, it is worth noting that the impact of TiO\({}_{2}\) on the recyclability of PET composites has not yet been clearly determined. Another way to reduce UV permeability through PET and improve the mechanical properties of PET bottles is to produce composite PET bottles using borates such as takedaite (Ca\({}_{3}\)B\({}_{2}\)O\({}_{6}\)) [120] or calcium metaborate (CaB\({}_{2}\)O\({}_{4}\)) [121]. These compounds act as barriers to UV/visible light, significantly reducing radiation permeability and increasing the material's resistance to environmental stress cracking. Composites of PET with other polymers can also delay the degradation process. [PERSON] et al. [83] conducted a study that compared the photodegradation of pure PET and PET composite with polyurethane (PET-U). The results indicated that the addition of polyurethane (PU) significantly delays the degradation rate of the material. Despite the lower degradation rate, the PU and PET mixture still generates significant amounts of micro- and nanoplastics. Furthermore, this study demonstrated a decrease in the average molecular weight for both pure PET and PET-U composite.