Forensic characterization of polyurethane foam as a form of trace evidence Caratterizzazione a scopo forense di schiume poliuretaniche come forma di traccia di contatto

The aim of this work was to determine whether polyurethane (PU) foam fragments from different sources could be discriminated from each other. Three principal techniques were used to characterize a population of 49 samples: optical microscope, IR spectroscopy and thermal analysis. Few important features were observed with optical microscope to allow a preliminary discrimination between same samples in appearance (PD=90%). IR spectroscopy allow to distinguish samples on their chemical content (PD=74%). These techniques are non destructive and require little quantity of sample. Thermal analysis, finally, gives complementary information about morphology and structure of the samples but it is destructive so it could be used only when sample quantity is enough (PD=89%). The discrimination power (PD) of these methods grow up to 99.4% using these techniques all together. Also low resolution NMR technique could be used for the scope to evaluate chain mobility and hydrogen content. This technique and thermal analysis also could be used in failure analysis, where the quantity of sample required is bigger. Principal component analysis (PCA) allows to represent in a two dimensions space the foams and we can find the formation of clusters for final use. It would be interesting to develop these analysis on known samples to find markers and evaluate if with PCA we could find clusters for different production methods. In this case it would be possible to create a database. Some samples were also treated to simulate what could happen in the crime scene. This work is an help for forensic analysis, but also a remind to pay attention to these type of items that, if correctly utilized, could help the reconstruction of criminal events. On the other hand it would be possible to exploit this information as parameters for quality control in polyurethanes production. It is very interesting the low resolution NMR technique because it offers a quali-quantitive evaluation of the optimal polymerization process degree.