Testing Plastics for Photodegradability

Weatherability of plastic materials can be investigated under natural or accelerated laboratory exposure. Typically, standard ASTM (dog-bone shaped) test pieces of the plastic of interest are exposed outdoors in natural weathering exposure sites. Ideally, locations of high insolation (such as AZ and FL) are selected to ensure fast degradation. The samples exposed outdoors, usually on South-facing racks, are periodically removed and tested to determine their extent of degradation. 

Tensile extensibility is a particularly sensitive measure of the extent of weathering. Alternatively, the development of carbonyl functionalities ( C=0) or other spectral changes in samples determined in Fourier Transform Infra-Red Spectroscopy, FTIR, might be used to assess degradation, hi PE (Andrady et al., 1993b), the development of the carbonyl functionalities correlates well with the decrease in extensibility. Plastics such as PVC, PC, or PS (Ghaffar et al., 1976) turn yellow on photodegradation. Surface 

Most plastic products, such as plastic building prodncts, ontdoor furniture, and artificial turf used outdoors, are stabilized against solar UV-indnced damage to ensure full service life outdoors. A discussion of the different stabilization mechanisms and the interesting chemistry associated with stabilization are beyond the scope of this chapter. The reader is directed to other works that discuss the topic comprehensively (Wypych, 2010). 

Stabilizers generally protect the polymer against solar UV damage via three strategies  

Absorbing incident UV radiation using organic (e.g., with benzophenones and benzotriazoles) or inorganic (e.g., rutile titanium dioxide) additives. 

---