Other methods
As it was already pointed out any technique capable of identification of plastic may be also of used for the description of degradation progress over a large time interval.
There are some of the possible candidates which were used for identification of plastics such as Fourier Transform Infrared spectroscopy, Solid Phase Micro Extraction (SPME) coupled to GCMS etc. Such non-invasive analytical techniques proved to be suitable not only for identifying plastics but also for the estimation of the degradation extent.