## 5 PET Bottle Degradation Management Strategies
### Preventing PET Bottle Degradation  
The use of various coatings and films on PET bottles is one of the most effective ways to increase their durability and reduce degradation. This is particularly important from both an environmental and human health perspective. Figure 5: Strategies for managing PET bottled water degradation. The degradation of PET during the storage of water in PET bottles can lead to the migration of microplastics and various chemical substances, such as formaldehyde and acetaldehyde, as well as antimony, which is used as a catalyst in PET production [19; 111]. Therefore, it is crucial to monitor the presence of microplastics and harmful chemical substances in bottled water, as well as to develop more advanced methods for their detection, which are discussed in Section 4. This approach will allow for more effective monitoring and quicker identification of potential health risks for consumers. It is worth noting that exposing PET water bottles to sunlight during transport and storage can cause the breaking of polymer bonds in the chemical structure, which promotes the migration of microplastics into the water [33]. Studies indicate that the main source of microplastics in bottled water is the degradation of PET bottles, which occurs at every stage--from production, through transport, to consumption [33]. Additionally, UV radiation and high temperatures can lead to the release of volatile organic compounds (VOCs) from PET bottles, which affects the quality and safety of the water [112]. To minimize these risks, it is necessary to ensure proper storage and transport conditions for PET bottles, particularly avoiding exposure to high temperatures and direct sunlight. Additional protection can be provided by coatings on PET bottles, which limit the contact of PET with water, thereby reducing the risk of harmful substance migration. Moreover, appropriate coatings on PET bottles improve their barrier properties, increase thermal and mechanical resistance, and effectively protect against UV radiation. Surface modifications of PET to increase their resistance to degradation involve various materials and techniques. A popular approach is the use of polymer coatings. Poly(vinyl alcohol) (PVOH) is one of the materials that significantly improves the durability and barrier properties of PET, particularly in terms of oxygen permeability [113]. Reducing oxygen permeability not only prevents the oxidation of the contents but also reduces the risk of PET degradation caused by contact with oxygen. Similarly, polyacrylates, such as methyl methacrylate-methyl acrylate-diallyl maleate-maleic acid (MMA-MAc-DAM-MA), improve these properties, although too thick a layer can paradoxically worsen them [114]. Another solution is hybrid coatings, modified with OVPOSS (octavinyl-polyhedral oligomeric silsesquioxane), UV-curable [115]. These types of coatings significantly improve the surface properties of PET, making them more durable and resistant to mechanical and chemical damage. These coatings also exhibit good thermal stability. One of the most effective materials used to provide a gas barrier for PET bottles is silicon-based coatings. Studies have shown that a thin protective layer of silicon oxide (SiO\({}_{\mathrm{x}}\)), applied to the inner side of the PET bottle using the plasma impulse chemical vapor deposition (PICVD) process, effectively reduces the permeability of gases such as oxygen and carbon dioxide [36]. The effectiveness of SiO\({}_{\mathrm{x}}\) coatings in reducing the migration of substances from PET material into food simulants has been quantitatively assessed in studies conducted under realistic storage and transport conditions, such as elevated temperatures (40 \({}^{\circ}\)C). Although these studies did not directly cover prolonged UV exposure or variable temperatures, they evaluate the effectiveness of the coating under conditions simulating contact with food.