14
2020
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09
Why do hollow-core cardboard boxes become brittle more easily when exposed to sunlight for a long time?
If a hollow-core cardboard box is exposed to sunlight for an extended period, it may become brittle and easily break. What’s the reason behind this?
In the weaker areas of hollow board packaging boxes, under the influence of heat, light, or oxygen, fractures are likely to occur, generating reactive free radicals and hydroperoxides. These substances trigger a chain reaction that can break molecular chains or induce cross-linking, thereby reducing the plastic's strength, making it brittle, and ultimately diminishing its practical value.
The chemicals added during processing to inhibit or slow down these deteriorative degradation processes are collectively referred to as “stabilizers.” Although they cannot permanently prevent the effects of light, heat, and oxidation on polymers, they can effectively halt or slow down the extent of deterioration, ensuring that the products meet commercial requirements.
“Chemical aging” is an irreversible chemical reaction that results in changes to molecular structures, such as the embrittlement of plastics, cracking of rubber, and yellowing of fibers. Chemical aging can be categorized into two types: “degradation” and “crosslinking.” Degradation refers to the breaking of polymer chains caused by factors such as ultraviolet radiation, heat, and mechanical forces. Crosslinking, on the other hand, involves the rupture of carbon-hydrogen bonds in polymers, leading to the combination of polymer radicals and the formation of a network-like structure. Both degradation and crosslinking significantly affect the properties of polymers. Degradation reduces the molecular weight of the polymer, making the material softer and stickier, and lowering its tensile strength and modulus. Crosslinking, by contrast, makes polymeric materials harder and more brittle, reducing their elongation at break.
“Plastic aging” occurs because ultraviolet (UV) radiation accelerates the breakage of “double bonds” in plastic molecules. The UV rays in sunlight are readily absorbed by polymers containing aldehydes, ketones, and carbonyl groups, triggering photochemical reactions. Infrared radiation in sunlight is absorbed by materials and converted into heat; as temperature rises, both thermal aging and thermo-oxidative aging of polymers intensify. Oxygen is a highly reactive gas that can cause oxidation in many substances.
The chemical aging of polymers is primarily an oxidation reaction that occurs under the influence of light, heat, or other factors. During processing, storage, and use, polymers inevitably come into contact with oxygen; thus, oxygen is one of the major factors driving the chemical aging of polymers. Studies have shown that radiation in the near-ultraviolet region (300–400 nm) of sunlight is the primary factor causing the aging and degradation of plastics. Generally, as the intensity of ultraviolet radiation increases, the rate of material aging accelerates.
For more information on Ningbo hollow boards and related content, please stay tuned to the updated website of Zhejiang YORO Packaging Technology Co., Ltd.: www.nbyrbz.cn; Service hotline: 18958381786.
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