Ultraviolet Degradation of Plastic Materials

JEF-TEC can provide the analysis service of a root cause of failure in the plastic materials by ultraviolet irradiation and offers its solution.

Ultraviolet degradation of plastics—importance of the analysis and its outline—

Plastic products are degraded by heating and ultraviolet irradiation, but degradation mechanism depends on the type of the materials and the irradiation conditions. Proper selection of the test conditions is very important to identify the root cause of failure.

Below is a typical example to demonstrate the ultraviolet degradation of polyamide and polycarbonate.

Evaluation Example of Polyamide

Fig. Accelerated weathering test*1) of nylon 6 and differential scanning calorimetry (DSC) thermogram of exposed nylon 6 Fig. Accelerated weathering test*1) of nylon 6 and differential scanning calorimetry (DSC) thermogram of exposed nylon 6
*1)
Test conditions
Ultraviolet light intensity: 81 mW/㎠ (wavelength 295 – 780 nm) Humidity: 50% RH Black panel temperature: 63℃ Rain shower: Once every 120 min for 120 sec
*2)
DSC(Differential scanning calorimetry)
Fig. Melting point and crystallinity *3) of nylon 6 after the accelerated weathering test Fig. Melting point and crystallinity *3) of nylon 6 after the accelerated weathering test
*3)
Degree of crystallinity = ΔHm/ΔHm100% x 100 ΔHm100% = 188 J/g (Reference: M. Dole, B. Wunderlich, Makro. Chem., (1959), 29-49)
Fig. Analysis of rubber components by the thermogravimetry under nitrogen and air atmospheres

Evaluation Example of Polycarbonate

Fig.  Gel permeation chromatography (GPC) of polycarbonate after the accelerated weathering test*1) Fig. Gel permeation chromatography (GPC) of polycarbonate after the accelerated weathering test*1)
*1)
Same conditions as the one used in weathering test of nylon 6
*2)
GPC(Gel Permeation Chromatography)
Fig. Measurement of the 10% weight-loss temperature of resin by thermogravimetry Fig. Measurement of the 10% weight-loss temperature of resin by thermogravimetry
*3)
TG(Thermo Gravimetry)

An increase of the low molecular weight fraction substantially lowers the 10% weight-loss temperature.

Fig. Polycarbonate after the ultraviolet accelerated weathering test

Importance of analysis of the surface properties in polymer materials

  • Polymers such as rubbers, resins, and their films are likely to degrade at the surface on ultraviolet light exposure and heating. This degradation is reflected with a change in color and the molecular structure which can be generally determined by colorimetry and Fourier transform infrared spectroscopy (FT-IR).
    Colorimetry and FT-IR spectroscopy, however, cannot quantify the surface properties of polymers such as scratch resistance and fiction coefficients which are very important to understand the mechanism of polymer degradation and to find its remediation method.
  • Polymer materials are irradiated with a light source such as the sunshine weather meter and the xenon weather meter for the accelerated weathering test and the data obtained from the accelerated weathering test are used to predict the durability of the polymer materials with some accuracy.

Outline of nanoindentation testing

  • A load may be continuously applied to the polymer specimen until the maximum load is reached, or as a series of small increment with a Vickers probe in depth sensing indentation for measuring the mechanical properties of materials at the surface such as hardness at a certain depth, Young′s modulus, and elastic modulus.
  • An optical microscope can be used to select the position for the nanoindentation test or the specimen can be heated on a heating stage (ambient temperature to 200℃) in combination with the nanoindentation measurement for evaluating the temperature dependency of the mechanical properties of polymer materials.
Fig. Nanoindentation tester

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