The problem of whitening pvc products

Update:05-05-2019
Summary:

1, PVC pipe fittings manufacturers explain its water im […]

1, PVC pipe fittings manufacturers explain its water immersion whitening

Many types of transparent PVC articles exhibit a whitish, hazy, cloudy appearance when exposed to water or water vapor for extended periods of time. Soft products are more powerful than hard products.

This phenomenon is thought to be caused by the presence of auxiliaries or auxiliaries which are easily hydration in the formulation. If it is only analyzed from the viewpoint of PVC stabilizer, it is due to the penetration of water, the stabilizer is precipitated from the PVC, and hydration occurs, and hydrated precipitates are formed on the surface (influencing transparency).

In this case, even if the water that has been saturated is not present, the stabilizer cannot be returned to the sample, and only when the temperature is raised, the compatibility of the stabilizer is restored to become transparent.

Tests have shown that formulations containing almost alkaline earth metal salts in stabilizers, especially barium and calcium, are prone to varying degrees of this problem. Occasionally, this phenomenon occurs in materials containing cadmium or zinc salts. Organotin stabilizers generally do not exhibit this phenomenon of water whitening.

2, PVC pipe fittings manufacturers explain their exposure to whitening

PVC products will be whitened when exposed to the outdoors.

This is related to the compatibility of the PVC stabilizer. Among the metal soap PVC stabilizers, benzoate having good compatibility with PVC has less whitening phenomenon than stearate.

Organotin stabilizers are less prone to whitening, and sulfur-containing organotins are preferred, followed by laurates and maleates. The addition of light stabilizers, phosphites, liquid composite stabilizers, etc., can prevent or alleviate the whitening phenomenon of PVC due to exposure to a certain extent.

3, PVC pipe fittings manufacturers explain its stress whitening

Stress whitening refers to the phenomenon of whitening of PVC hard products under the action of mechanical external force, such as bending and stretching, such as bending creases and stretched parts of PVC products. This may be due to the change of molecular structure caused by external force, the orientation of the polymer molecular chain, the change of PVC density, and the occurrence of voids between some molecules to form light scattering, which makes the PVC product appear white.