In the field of environmentally friendly packaging, biodegradable bags are gradually replacing traditional plastic bags due to their natural degradability. Transparency, as an important appearance indicator, directly affects consumers’ usage experience and the display effect of goods. Many users have noticed that the transparency of biodegradable bags changes over time. This phenomenon is not only related to the material properties but also significantly influenced by storage and usage environments.
- Material Composition
The root cause of transparency changes in biodegradable bags lies in the evolution of the molecular structure of their core components. Currently, mainstream biodegradable bags are mainly made from base materials such as polylactic acid (PLA) and polybutylene adipate – terephthalate (PBAT). Some products may add fillers like starch and calcium carbonate to reduce costs or improve performance. In newly produced biodegradable bags, PLA and PBAT molecules are arranged in an orderly manner, resulting in less refraction and scattering when light passes through, thus presenting good transparency. However, over time, the material undergoes a slow hydrolysis reaction: moisture in the air penetrates into the gaps between molecular chains, causing the breakage of ester bonds, and macromolecules gradually decompose into small molecular fragments. This process destroys the originally regular molecular structure, enhances the scattering of light inside the material, and consequently leads to a decrease in transparency. A slight “hazy feeling” may appear on the surface of the bags.
2. Storage Environment
The storage environment is a key variable that accelerates or delays transparency changes. In high – temperature and high – humidity environments, the rate of transparency attenuation of biodegradable bags increases significantly. For example, when placed in an unventilated warehouse in summer, where the temperature exceeds 30℃ and the relative humidity is higher than 60%, the hydrolysis reaction rate of the material will increase by 2 – 3 times, and a significant decrease in transparency may occur within 3 – 6 months. In contrast, in a low – temperature and dry environment (with a temperature of 5 – 15℃ and a relative humidity of 30% – 40%), molecular activity slows down, the hydrolysis reaction is inhibited, and the transparency can remain basically stable for more than 12 months. In addition, light exposure, especially ultraviolet (UV) radiation, triggers photo – oxidation reactions in the material, damaging the molecular chain structure. This not only causes a decrease in transparency but may also lead to yellowing of the bags, further affecting their appearance.
3. Usage Process
External stimuli during the usage process can also exacerbate transparency changes. When biodegradable bags come into contact with oils, acidic or alkaline substances, the chemical media accelerate the degradation process of the material. For instance, when used to hold cooking oil, oil molecules penetrate into the interior of the material, accelerating the breakage of ester bonds. A significant decrease in transparency and brittleness of the material may occur within 1 – 2 weeks. On the other hand, biodegradable bags used to hold dry items (such as flour and coarse grains) avoid direct contact with chemical media, so the rate of transparency change is relatively slow.
It is worth noting that the change in transparency of biodegradable bags is not entirely negative; instead, it is an indirect manifestation of their degradable properties. As the material gradually degrades, while the transparency decreases, the material also becomes increasingly brittle and eventually decomposes completely in the natural environment. Therefore, in practical use, consumers can judge the degradation process of biodegradable bags by observing changes in transparency, avoiding the impact of excessive material degradation on usage effectiveness. At the same time, manufacturers can delay the rate of transparency change and extend the service life of products by optimizing formulas (such as adjusting the ratio of PLA to PBAT and adding anti – hydrolysis additives) and improving packaging methods (such as using light – proof and moisture – proof outer packaging).
In conclusion, the transparency of biodegradable bags gradually decreases over time, and this process is jointly influenced by material properties, storage environment, and usage methods. Understanding this change rule not only helps consumers use biodegradable bags more effectively but also provides directions for manufacturers to optimize product performance, promoting the sustainable development of the environmentally friendly packaging industry.
