How to solve the problem of albino PVC products

Transparent PVC products, if immersed in water, or outdoor exposure, or by bending, stretching, etc. will produce albino phenomenon, and lose transparency.

1 white water

Many types of clear PVC articles exhibit a hazy haze-like cloudy appearance when exposed to water or water vapor for prolonged periods of time. Soft products more than hard products.

In most cases, this phenomenon can be reversed, and when it is completely dry, the cloudy product regains its original transparency. However, in some transparent hard products, this phenomenon is irreversible. It is thought that this phenomenon is caused by the presence of hydration aids or auxiliary decomposition products in the formulation. Due to the penetration of water, plasticizers, stabilizers and the like are precipitated from the PVC and hydrate to form hydrated precipitates on the surface (affecting the transparency). Even if there is no saturated moisture, the plasticizer and stabilizer Can not be returned to the original sample, only to increase the temperature, the plasticizer and stabilizer compatibility has been restored, can become transparent.

Test proved that stabilizers, plasticizers, lubricants, impact modifiers, processing aids can cause this phenomenon. Stabilizers almost contain alkaline earth metal salt formulations, especially barium and calcium, are prone to varying degrees of this problem. Only cadmium or zinc salt containing materials, occasionally appear this phenomenon. Organotin generally does not appear this water white phenomenon.

2 exposure whitening

PVC products in the outdoor exposure, due to air moisture, carbon dioxide, sulfur dioxide and light effects, will also appear whitening phenomenon.

This is related to the compatibility of the stabilizer. Among metal soaps, benzoates with good compatibility with PVC show less whitening than stearates. Organotin is not easy to produce bleaching, sulfur is best organic tin, followed by laurates, maleates. The addition of light stabilizer, phosphite, liquid composite stabilizer to a certain extent, to prevent or alleviate the whiteness of PVC due to exposure.

An interesting phenomenon is that rigid PVC products become white when exposed to Florida or other humid places, and do not whiten when exposed to Arizona. So, wet is to promote the PVC exposure of a condition of albino.

3 stress whitening

Stress whitening refers to the hard transparent PVC products under mechanical external force, such as bending, stretching, PVC products, such as bending creases at the local, whitening phenomenon occurs at the stretch. This may be due to changes in the molecular structure due to external forces, the orientation of the polymer chains, the change in the density of the PVC, and voids in some of the molecules to form light scattering, leaving the PVC product white.

Broutmann believes that adding a high surface energy stabilizer to make up for voids created by molecular orientation is effective. The use of organic tin stabilizers can reduce the bleaching phenomenon, especially with the use of maleic acid organic tin better.

4 other whitening

PVC transparent products processing, if you use excessive lubricant, more lubricant precipitated transparent products can also cause white muddy phenomenon, a phenomenon sometimes called albino.

This whitening phenomenon, the product surface generally have more obvious waxy substance. The solution is to reduce the amount of lubricant, or change the lubricant with better compatibility varieties, the formula inside and outside the slide to reach a balance.

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