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    • Ageing
    resistance

     

    As defined by DIN 50035, ageing refers to all the chemical and physical processes that irreversibly occur to a material over time. Polymeric materials can age for a variety of reasons, such as heat, UV radiation and media, and ageing is highly dependent on operating and environmental conditions, e.g. the service temperature.

    Representative products

    WEVOPUR 1222

    • UV-resistant
    • Operating temperature range: -40 °C to +100 °C
    • Transparent/clear
    • Scratch-resistant in the upper Shore D range

     

    WEVOPUR 7210 FL

    • Hydrolysis-resistant, 85/85 damp heat test
    • High heat-distortion resistance
    • Good flow properties, low mix viscosity
    • Low water absorption

     

    WEVOPOX 6501 / WEVODUR HC 3001

    • High dielectric strength
    • Low shrinkage
    • Outdoor applications or weathering; UV-stable
    • Hot curing

    The ageing of polymeric materials largely depends on the operating and ambient conditions.

    Permanent storage diagram over the time at different temperatures

    Types of ageing

    Chemical ageing (Post-polymerisation)

    Degradation by molecular cleavage caused by:

    • High temperatures (thermal)
    • Radiation, e.g. UV
    • Oxygen and ozone (oxidation)
    • Agglomeration, e.g. exudation (plasticisers)
    • Water (hydrolysis)
    •  Microorganisms (microbial)

    Physical ageing

    • Relaxation, stress relief
    • Post-crystallization
    • Separation (phase separation)
    • Plasticiser diffusion

    Symptoms of ageing

    • Deformation of the object, cracking:
      • Stress cracking, e.g. migration of small molecules, corrosion
      • Cracks caused by oxygen or ozone, surface
      • Fatigue cracks due to structural changes
      • Fractures caused by embrittlement
    • Discolouration from oxidation or UV
    • Measurable changes – mechanical, optical or electrical
    • Changes in chemical behaviour, e.g. chemical resistance and diffusion behaviour
    • Deposition, e.g. exudation of the plasticiser

    Suitable accelerated tests must be carried out to accurately predict the expected service life.

    Determination of the temperature index TI according to IEC 60216:

    • Changes in material properties, such as tensile strength at different temperatures, until 50 % of the initial value is reached
    • Time and temperature transferred to a long-term Arrhenius diagram and extrapolated to 20,000 hours

    Arrhenius diagram of time against temperature to determine the temperature index