If PVC profile products are immersed in water, exposed to outdoor exposure, or bent, stretched, etc., whitening will occur and lose transparency. Next, let’s analyze the three major whitening problems of water immersion whitening, exposure whitening and stress whitening from the perspective of PVC stabilizers.
1. Water immersion whitening: When many types of transparent PVC profile products are in contact with water or water vapor for a long time, they will show a whitish misty appearance. Soft products are more powerful than hard products.
It is believed that this phenomenon is caused by the presence of additives or decomposition products of additives that are easy to hydrate in the formulation. If it is only analyzed from the perspective of PVC stabilizers, it is due to the infiltration of water that the stabilizers are separated from the PVC, and hydration occurs, forming hydrated precipitates on the surface (influencing transparency).
In this case, even if the soaked water is gone, the stabilizer cannot return to its original form. Only when the temperature is raised to restore the compatibility of the stabilizer can it become transparent.
2. Exposure to bleaching: PVC profile products will also show bleaching when exposed to outdoor sunlight.
This is related to the compatibility of PVC stabilizers. Among metal soap PVC stabilizers, benzoate with good compatibility with PVC has less whitening phenomenon than stearate.
3. Stress bleaching: Stress bleaching refers to the phenomenon of bleaching in parts of PVC products such as bending creases and stretched parts under the action of mechanical external force, such as bending and stretching. This may be due to changes in the molecular structure caused by external forces, the orientation of polymer molecular chains, the change in PVC density, and the appearance of gaps between some molecules, resulting in light scattering, which makes the PVC products appear white.
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Post time: Apr-22-2021