Why do PVC products have whitening phenomenon? Transparent PVC products are usually whitened by water immersion, outdoor exposure, bending, stretching, etc., and lose their transparency.
1 Water whitening:
When many types of transparent PVC products are in contact with water or water vapor for a long time, they show a whitish foggy appearance. Soft products are more powerful than hard products. This phenomenon is believed to be caused by the presence of easily hydrating adjuvants or adjuvant decomposition products in the formulation. Due to the penetration of water, plasticizers, stabilizers, etc. are precipitated from PVC, and hydration occurs, forming hydrated precipitates on the surface (affecting transparency). Even if the soaked water is gone, plasticizers, stabilizers, etc. The stabilizer cannot return to its original state, and it can only become transparent if the temperature is raised to restore the compatibility of the plasticizer and the stabilizer.
2 Exposure to whitening:
When PVC products are exposed to the sun outdoors, due to the effects of moisture, carbon dioxide, sulfur dioxide and light in the air, they will also appear whitening. This is related to the compatibility of the stabilizer. Among metal soaps, benzoate with better compatibility with PVC has less whitening phenomenon than stearate. Organotin is not easy to produce albinism, sulfur-containing organotin is better, followed by laurate and maleate. Adding light stabilizers, phosphites, and liquid composite stabilizers can prevent or alleviate the whitening of PVC due to exposure to the sun to a certain extent.
3. Stress whitening:
Stress whitening refers to the phenomenon of whitening of PVC products in parts such as bending creases and stretching parts after being subjected to external mechanical forces, such as bending and stretching. This may be due to the change of molecular structure due to external force, the orientation of polymer molecular chains, and the change of PVC density. At the same time, gaps appear between some molecules, forming light scattering, and making PVC products white. state.
4 Other whitening:
During the processing of PVC transparent products, if excessive lubricant is used, more lubricant precipitates will also lead to white turbidity of transparent products. This phenomenon is sometimes called whitening. In this whitening phenomenon, there is usually a more obvious waxy substance on the surface of the product. The solution is to reduce the amount of lubricant used, or use a lubricant with better compatibility to achieve a balance between the internal and external sliding of the formula.
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