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  U.V Weathering Tester
The Matrusree Accelerated Weathering Tester (MWT) is used in more labs throughout the world than any other accelerated weathering tester. In just a few days or weeks, the MWT can reproduce damage that may occur over months or even years outdoors.

Long term exposure to sunlight leads to the degradation of plastic materials. In particular, the non-visible UV radiation characterized by short wavelengths is responsible for photo-degradation, a process that generally results in breaking down the polymer chains. This frequently results in a deterioration of the physical properties, changes in color or chalking of the part surface. As an example, films lose their flexibility and disintegrate, garden furniture becomes brittle or stadium seats become chalky. In order to limit or postpone the onset of degradation, several types of UV light stabilizers can be added to the polymer. The most important stabilizer types work by screening out the harmful ultraviolet light - for instance UV absorbers such as benzophenones or small dispersed particles such as carbon black or inorganic pigments.

One important factor, when the light stability of a given material or the performance of a UV stabilizer needs to be assessed, is the selection of a suitable test method. Besides outdoor exposure that closely reflects natural weathering conditions but requires long exposure times, artificial weathering tests have been developed using lightsources such as Xenon arcs or fluorescent lamps under controlled temperature and humidity conditions
Description:
This apparatus uses fluorescent UV lamps to reproduce the damaging effects of sunlight. Although ultra violet (UV) light makes up only about 5% of sunlight , its responsible for most of the sunlight damage to the polymer / Rubber/ Non Metallic materials exposed outdoors. Therefore, if it is only necessary to reproduce the short wavelength UV for testing polymer rubber degradation.

An apparatus for accelerated weathering testing specimens including discharge lamps as a concentrated light source for accelerating the deterioration of color, composition and/or structure of test specimens. Improved control calibration structures and methods of operation are also included. The test module to monitor the weathering test process from an improved location, detecting irradiance in the manner in which the specimens are exposed to such irradiance. The test modules are mounted in a pocket formed within the door for the test chamber such that the sensitive electronics of the modules are not exposed to the harsh environment within the test chamber, resulting in an exceptionally stable signal.

Light stabilizers for plastic materials:
  • UV light absorbers:

  • Absorbers convert harmful ultraviolet radiation to harmless infrared radiation or thermal energy, which is dissipated through the polymer matrix. They can be either transparent as hydroxybenzophenone or opaque like carbon black.
  • Carbon black:

  • Carbon black is one the most efficient and widespread light absorbers. Its efficiency as a UV absorber depends primarily on the primary particle size and structure. At the same loading, carbon black aggregates based on fine prime particles will present more surface to incident light - and hence a larger ultraviolet light absorbing efficiency - than a coarser grade.

    The appropriate loading level depends on the part thickness, exposure conditions and type of carbon black. Usual loadings to impart optimum UV protection vary between 2 and 3% (it should be noted that these carbon black levels correspond to 4 to 7% master batch, depending on their loading).
Titanium dioxide:
Certain pigments such as rutile titanium dioxide absorb in the 300 to 400 nm range. Hence, they contribute to the protection of the polymer, provided that the pigment has a suitable coating to prevent the photo-degradation processes usually observed with TiO2.
Weathering Test Methods:
Besides natural weathering, several test methods have been developed using artificial light sources to provide accelerated test procedures. All methods are based on the regular observation of characteristics reflecting an ageing process such as mechanical properties (elongation at break, tensile properties or impact strength) or visible characteristics, such as crack formation, chalking, changes in color or gloss.
Artificial weathering chambers:
  • UV fluorescent light source:
    Weathering chambers have been developed to provide a UV weathering. The UV simulates the effect of sunlight with fluorescent ultraviolet (UV) lamps, while rain and dew are simulated by the condensation of humidity. As stated previously, the UV light only represents roughly 5% of the sunlight but it is responsible for most of the polymer degradation. Also, materials are often tested with equipment, which simulate only the shortest wavelengths (UV). The UV-B range includes the shortest wavelengths found in sunlight. Therefore, for many applications, it is a fast and efficient method. UV equipment uses two main types of lamps: UVA-340 and UVB- 313. While these lamps have different light emission spectrum, they are both characterized by a maximum of emission in the UV range. UVA provides a reasonable match of the UV region of the solar spectrum, but this match is no longer valid for the long wavelengths (visible, IR). UVB lamps also emit UV light, but the maximum of the emission spectrum is shifted towards short wavelengths compared to the UVA lamps. The UVB-313 lamp is a widely used type of fluorescent UV lamp that provides fast test results. However, the spectrum contains short wavelengths, which are not present in the solar radiation.

    For customer support, Cabot typically uses UVB lamps characterized by their short wavelength spectrum in order to provide fast test results. Although these data might not always perfectly correlate with outdoor exposure results, QUV-B is very useful for preliminary or comparative testing, as well as for very durable applications.
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