Determination of the photo-degradation level of high impact polystyrene (HIPS) using pyrolysis–gas chromatography–mass spectrometry

High impact polystyrene (HIPS), together with other materials, such as polyethylene, polypropylene and polyvinyl chloride, is one of the most commonly used polymers. This fact and their use in the packaging sector results in the generation of significant amounts of wastes, which need to be recycled. During this process, polystyrene undergoes different processes in which it is exposed to different temperatures. Additionally, during these processes it often suffers from a certain degree of exposure to sunlight. These two effects are responsible of the two types of degradation which can generally affect polymeric materials; thermal degradation and photo-degradation. Several thermal analysis techniques have been used to quantify the degree of degradation, although the variations occurring in the material are so slight that these techniques make the observation of differences impossible. The use of much more sensitive techniques, such as Fourier transformed-infrared spectroscopy and pyrolysis coupled to gas chromatography–mass spectrometry have permitted the observation of structural differences among the different samples in function of the exposure time. In addition, some changes are produced at a physical level. Here, the use of atomic force microscopy facilitates the observation of differences regarding the roughness of the surface exposed to solar radiation.