About the whitening of PVC products

- Jun 21, 2018 -

Flooding and whitening. Many types of transparent PVC products exhibit a whitish misty appearance when exposed to water or water vapor for an extended period of time. Soft products are more powerful than hard products. Due to water soaking, plasticizers, stabilizers, etc. are precipitated from PVC, and hydration occurs. Hydrated precipitates (impacting transparency) are formed on the surface, even if moisture is not absorbed, plasticizers, stabilizers It is also impossible to return to the original sample. Only by increasing the temperature, the compatibility between the plasticizer and the stabilizer can be restored and it can become transparent. Tests have shown that stabilizers, plasticizers, lubricants, impact modifiers, and processing aids can all cause this phenomenon.


 Exposure to whitening. PVC products are exposed to the sun, and due to the effects of moisture, carbon dioxide, sulfur dioxide, and light in the air, whitening occurs. This is related to the compatibility of the stabilizer. In metal soaps, benzoates with good compatibility with PVC have less bleaching than stearates. Organic tin is not easily bleached, and sulfur-containing organic tin is the best, followed by laurate and maleate. The addition of light stabilizers, phosphites, liquid compound stabilizers, etc. can prevent or alleviate the whitening phenomenon of PVC due to exposure to a certain extent.


 Stress whitening. Stress whitening refers to the fact that PVC transparent hard products are subjected to mechanical external forces. For example, after bending and stretching, PVC products locally appear as whitening at the bend creases and stretched parts. This may be due to changes in the molecular structure caused by external forces, polymer molecular chain orientation, PVC density changes, while some voids appear between some molecules, resulting in light scattering, and make PVC products appear white.


 Other bleaching. During the processing of PVC transparent products, if an excessive amount of lubricant is used, more lubricant precipitates will also cause white turbidity in the transparent products. This phenomenon is sometimes referred to as whitening. This whitening phenomenon, the product surface will generally have more obvious waxy material. The solution is to reduce the amount of lubricant, or to use a more compatible type of lubricant, so that the formula slip into a balance between inside and outside.