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PVC Compounds for Weather Resistant Applications - 2

Moisture

Rain and humidity are the two main contributors to moisture. Humidity keeps the material constantly moist, which can cause growth of bacteria as well as plasticizer leaching. Rain has a washing and impacting effect that could be detrimental to the material.


Wind

Wind is a carrier of particles such as dust, gases and moisture that can contribute to weathering effects on the material. Similarly, the absence of wind can allow the accumulation of air contaminants which could also contribute significantly to the weathering of a material.


Gases

In industrial areas especially, gases are present, possibly causing a chemical reaction with some materials which results in color changes or degradation.


Location

The geographical location is an important environmental factor. Fewer effects are produced where there are fewer sunlight hours per year and where the radiation is less intense. For example, a specific period of exposure in Arizona is more detrimental than in the Northeast region due to the obvious extra hours of UV (ultraviolet) exposure and, less obviously, to the higher ambient temperatures encountered.


Effects of Weathering

The effects of weathering on a flexible pvc material can vary from a complete loss of tensile strength and reduction of flexibility to only minimal surface degradation that does not detract from overall performance. Generally speaking, the first effect of weathering will be a slight discoloration of the pigment resulting in a chalky surface or whitening of the coloration.


Other forms of material degradation caused by weathering include loss in surface gloss, discoloration, odor, surface erosion and increased brittleness.


Additives for Weather Resistance

Lubricants

Required in order to prevent the material from sticking to the extruder or the mold while processing and also ensures a good heat transfer during the melt. During this time the lubricant plays an important role in breaking down the PVC particle into its sub-segments, which ultimately is important for maintaining the physical properties of the final product. Commonly used lubricants for weather resistant applications include parrafin wax, stearic acid and phtalic acid esters.

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