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Polymer changes under UV light: Why does sunlight make plastics brittle?
When we are outdoors enjoying the sunshine, have you ever thought about how much potential damage this beautiful day may cause to our plastic items? In this modern society filled with plastic objects, the durability of plastics has always been a key consideration in their design and use. However, ultraviolet light in sunlight can cause unexpected changes to polymers, causing them to become brittle and lose their functionality. This article will examine how UV light affects polymers, causing them to deteriorate during use.
The Effect of UV Light on Polymers
Many polymers, when exposed to UV radiation, will experience degradation phenomena in their chain structure. This process is called UV degradation, and it occurs primarily at weak points in the polymer's chain structure. For example, the structure of polypropylene will crack severely if antioxidants are not added. This is because ultraviolet light promotes the generation of active oxygen, which attacks the tertiary carbon atoms in the polymer chain and eventually leads to chain breakage.
Many plastic items, including those used in everyday life such as parasols or outdoor furniture, are victims of degradation by UV light.
UV Degradation in Polyethylene
Polyethylene is also susceptible to UV degradation, especially branched polymers such as low-density polyethylene. The branching points in this polymer are also tertiary carbon atoms, so the degradation process also starts from these points, leading to chain shearing and embrittlement. The properties of the polymer gradually degrade, making it more susceptible to fracture and failure.
Effects of oxidation
In addition to UV light, polymers are also attacked by oxygen in the atmosphere. This oxidation reaction is more pronounced in the high temperature processing environment, which is necessary during the polymer molding process. For example, oxidation of polypropylene during suction mold processing can cause a supporting crutch to suddenly break, causing injury to the user. Carbon-based oxides produced by oxidation can be clearly detected by IR spectroscopy.
The strong absorption spectra of the oxidation products make the oxidation of polyolefins relatively easy to detect.
Ozone Decomposition and Polymer Strength
Ozonolysis is also an important factor in the degradation of polymers. When double bonds react with ozone, ozonides are formed, a process that directly leads to the cleavage of polymer chains. This means that the molecular weight of the polymer decreases, resulting in a significant reduction in its mechanical strength. Once the polymer chains break, the cracks may gradually expand, eventually leading to product failure.
ConclusionDifferent spectroscopic techniques provide insight into the chemical changes that occur in polymers after exposure to UV light and other environmental factors. These changes not only affect the durability of the plastic, but may also cause safety concerns in a variety of applications. Therefore, plastic items in our daily lives require appropriate protective measures to reduce the impact of these deterioration processes. As we gain a deeper understanding of the problems of plastic use, we should reflect on how these materials are used. Can future plastic products continue to meet the needs of sustainable development?
