the Whitening of PVC Products
Water immersion whitening. Many types of transparent PVC products show a white haze turbid appearance when they are in contact with water or steam for a long time. Soft goods are more powerful than hard ones. Due to water permeation, plasticizers, stabilizers, etc., are precipitated from PVC, and water is co-used to form hydrated precipitates on the surface (affecting transparency, even if the soaking water is gone, plasticizers and stabilizers cannot be returned to the original form. Only by increasing the temperature, the compatibility of plasticizer and stabilizer can be restored and become transparent. Tests show that stabilizers, plasticizers, lubricants, impact modifiers, processing aids and so on can cause this phenomenon.
The effect of air moisture, carbon dioxide, sulfur dioxide and light on the exposure of PVC products to the outside also appears albinism. This is related to the compatibility of stabilizers. In metal soap, benzoate with good compatibility with PVC has less whitening than stearate. Organotin is not easy to produce albinism, sulfur-containing organotin is the best, followed by lauric acid salts, maleate salts. The addition of light stabilizer, phosphite and liquid compound stabilizer can prevent or alleviate the albinism caused by PVC exposure to some extent.Wa
Stress whitening. Stress whitening refers to the phenomenon of whitening of PVC transparent hard products under the action of mechanical forces such as bending and bending. This may be due to the change of molecular structure caused by external force, the change of density of polymer chain orientation and the formation of light scattering between some molecules, and the white appearance on PVC products.