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PVC Compounds for Weather Resistant Applications

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
  • Temperature
  • Moisture
  • Wind
  • Gases
  • Location

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

  1. UV Stabilizers:
    • UV stabilizers are crucial additives in PVC formulations for outdoor use. They protect the polymer from the damaging effects of ultraviolet (UV) radiation, preventing degradation, discoloration, and loss of mechanical properties over time.
  2. Impact Modifiers:
    • PVC inherently tends to be rigid, and in outdoor applications where impact resistance is important (such as in construction and fencing), impact modifiers are often added. These modifiers improve the material’s ability to withstand impact forces and reduce brittleness.
  3. Heat Stabilizers:
    • Heat stabilizers are included to protect PVC compounds from thermal degradation during processing and exposure to high temperatures. This is particularly important in regions with hot climates.
  4. Weathering Resistant Pigments:
    • Pigments are added to PVC compounds not only for coloration but also for their impact on weather resistance. Weathering resistant pigments can contribute to the long-term color stability of the PVC material.
  5. Acrylic Impact Modifiers:
    • Acrylic impact modifiers are often used in PVC formulations to improve impact resistance, weatherability, and processing performance. They are effective in maintaining impact strength under prolonged exposure to sunlight.
  6. Tin Stabilizers (for Lead-Free Formulations):
    • Traditionally, lead-based stabilizers were used in PVC formulations, but due to environmental concerns, there has been a shift towards lead-free stabilizers. Tin stabilizers are commonly used as alternatives to provide heat and UV stabilization in lead-free PVC compounds.
  7. Antioxidants:
    • Antioxidants are added to PVC formulations to prevent oxidative degradation, which can occur due to exposure to oxygen and other environmental factors. They help maintain the material’s integrity and prevent embrittlement.
  8. Processing Aids:
    • Processing aids can be included to improve the processing characteristics of PVC compounds, ensuring uniformity and consistency during manufacturing. This contributes to the overall quality and performance of the final product.
  9. Biocides (for Applications Susceptible to Biological Growth):
    • In outdoor applications where PVC may be exposed to moisture and organic matter, biocides can be added to prevent the growth of mold, mildew, and other microorganisms.

Weather Testing

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.

Examples of weather-resistant applications for PVC compounds include:

  • Window Profiles: PVC window frames and profiles require weather resistance to withstand exposure to sunlight, rain, and temperature variations.
  • Outdoor Furniture: PVC is used in the production of durable and weather-resistant outdoor furniture.
  • Vinyl Siding: PVC compounds are utilized in the production of weather-resistant vinyl siding for buildings.
  • Fencing and Decking: PVC compounds are employed in the manufacture of weather-resistant fences and decking materials.

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