PVC Compounds for Weather Resistant Applications
6/22/2016 6:55:59 PM
|Flexible PVC is an inherently weather resistant material. Like all thermoplastics, however, it can be affected by weathering - a general term used to cover a wide range of outdoor environmental conditions.
Various additives are available to improve a compound's weather resistance. Before selecting a compound and additives, it is important to fully consider the environment that will be surrounding the end product and the other desired physical properties of your application.
Factors Influencing Weathering of Flexible PVC
The following environmental factors should be considered when selecting a flexible PVC compound for your weather resistant application.
- Sunlight - The suns rays contain a significant amount of ultraviolet radiation. When the material absorbs ultraviolet, a degrading chemical reaction occurs as well as the formation of heat.
- Temperature - Daily ranges in temperature can vary drastically between seasons and from location to location. Heat resulting from solar radiation can increase the temperature of the material by up to 60° depending on the color. Such extremes of temperature over an extended period can cause physical damage to the polymer. Therefore, heat stabilizers must be incorporated into the compounding ingredients in order to offset the negative effects of high temperatures. In addition, it should be remembered that chemical reaction rates increase exponentially as the temperature increases.
- 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.
- Fillers - Flexible pvc compounds have excellent impact resistance. However, when the end use application will be used under extreme outdoor conditions, fillers are added to perfect surface gloss, mechanical profile properties, color, weathering properties, etc. Filler types include carbon black, aluminum hydroxide, talcum and calcium carbonate.
- UV Stabilizers - UV stabilizers slow or stop the degradation process by reacting with radicals. The formulation of the stabilizer is specifically designed upon data about geographic location, weathering conditions, application type and expected life time. A well balanced incorporation into the compound is essential because the stabilizers can impair the flame resistant properties of a product.
- UV Light Absorbents - Absorbents convert UV radiation into thermal energy which then disperses throughout the material. The performance of light absorbents alone is generally not sufficient for applications with extreme weathering conditions. Common types of UV light absorbents include:
Carbon black is one of the most efficient and cost effective light absorbents and is a standard additive to grey and black formulations. Hence black compounds already offer good resistance against UV radiation in moderate climate zones. On the other hand, carbon black is not suitable for intense weather exposures or in cases when colors other than black are required.
Titanium dioxide (TiO2 ) is a widely accepted light absorbent especially for PVC products and offers very good protection against UV radiation. It is mainly used for conduit systems in other colors than black.
- Antimicrobials - These agents are added during the compounding process to prevent the growth of bacteria and fungus on products used in moist environments. Microbial growth can shorten the product life of plastic parts and can manifest itself as odor, discoloration, loss of properties, or loss of function.
Weather testing helps ensure that materials and products meet their expected functionality and lifetime even in extreme weather conditions.
The three main types of weather testing include:
- Natural Outdoor Testing - This form exposes the material to sun and weather directly. Two benchmark climates are typically used for products sold in the US: Arizona (hot and dry) and Florida (hot and moist). Other sites can be used to simulate other climates. Natural outdoor testing usually isn't the most effective method due to time and logistics.
- Accelerated Outdoor Testing - Uses natural sunlight plus the use of mirrors and other devices to intensify the natural environmental effects. These methods can obtain useful results at least eight times faster than with real-time weathering.
- Laboratory QUV Testing - Uses a QUV weathering testing machine with specialized environmental chambers and artificial light sources that simulate outdoor weather conditions including rain, sunlight and heat. In a few days or weeks, this form of testing can reproduce the damage that occurs over months or years outdoors.
Technical experts strongly advise a combination of lab testing that is validated by real-time outdoor exposures. This helps achieve both goals of good correlation to service performance and short test times.
Weather Resistant Applications
|Architectural Window Trim
||Pool Liner Bead
- UV Resistant and non-yellowing after 1000 hours of QUV aging.
- Formulated for extrusion applications that require outdoor weatherability.
- Sylvin Compound Solution: 8270-82
- Resistant to sunlight, UV and pool chemicals.
- Withstands high temperatures
- Antimicrobial additive
- Sylvin Compound Solution: 8707-84
If you would like more information about weather resistant PVC products or if your material requires weather resistance, please contact us. Our technical team is here as a resource and will work with you to find the right PVC compound solution for your application.
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