The Plastic Waste Problem
At the end of its life, plastic, and more specifically plastic packaging, ends up in the environment as waste. Massive amounts of plastic waste accumulates on the ground and in the sea every year contributing to the growing issues of landfill overflow and marine pollution. Bio- or photodegradable plastics are a trend that could help to address this issue by reducing the amount of time it takes for plastics to breakdown from natural processes.
Photodegradable Plastic
Photodegradable plastics can be produced in a comparable way to their conventional variants. The trick to faster photodegradability lies in special additives that when exposed to UV radiation activate a two-part oxidation process causing the plastic to degrade. In the first step, photo-oxidation takes place initiated by UV radiation, heat, and oxygen causing the polymer matrix of plastics to begin to break. Next, carbon dioxide- and water-induced degradation pathways begin to occur as encouraged by humid environments. Ultimately, biomass is created via microorganisms. Quick-degrading plastic typically takes around a year to fully breakdown in landfills. But, although they are designed to degrade faster, photodegradable plastics still must achieve a certain lifetime and properly function for their intended application—This is where weathering testing comes into play.
ASTM Standard Weathering Testing
Like with any new material, R&D teams will need to gain experience with the degradation rates of photodegradable plastics ultimately with the expectation that the target service lifetime of the material must be achieved to ensure the proper functioning of the product. International standards organizations such as ASTM have developed outdoor and laboratory weathering test methods to that end.
ASTM D5208-14 is the standard practice for exposure of photodegradable plastics in a fluorescent UV device using UVA-340 lamps. UVA-340 lamps provide a great spectral match to natural UVB radiation and the short wavelength range of UVA. It is missing, however, the long wavelength UVA, VIS, and NIR wavelength ranges. The Atlas UVTest® is the applicable instrument for ASTM D5208-14. Guidance towards three different test cycles is given in this standard:
- 20 h continuous light phase dry, followed by 4 h dark/condensation phase
- 4 h continuous light phase dry, followed by 4 h dark/condensation phase
- Continuous light phases dry
ASTM D5071-08 is the standard for testing inside xenon weathering chambers using the Daylight filter. Opposite to UVA-340 based testers, xenon chambers will provide the full solar spectrum, which can be beneficial for achieving results that are consistent with natural weathering. The Atlas SUNTEST® XXL+, Xenotest® 440, or Ci Weather-Ometer® are suitable for this test. The method gives guidance on three different test cycles:
- Continuous light phase dry
- Continuous light phases with alternating dry / wet phase
- Continuous light phases dry / wet, followed by dark humid phase
Finally, ASTM D5272-08, is the standard practice for natural outdoor exposure. It is performed by mounting samples to 5° exposure racks and leaving them to degrade naturally for a customer- or test method-defined period of time. The major benefit of outdoor testing is that the results are real-world data points that can be used as a baseline for comparison with accelerated laboratory testing results to evaluate correlation and acceleration of your laboratory test to the natural environment.
More Information
Photodegradable and biodegradable plastics are vast subjects that we just briefly touched upon today. For further useful information, download free Application Guides about
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Note: Title image courtesy of the authors of “The future of plastic”. Nat Commun 9, 2157 (2018).
https://doi.org/10.1038/s41467-018-04565-2