Same polymer, different story: DSC analysis of commercial PLA 3D-printing filaments for forensic comparisons

The proliferation of 3D-printed firearms has raised interest worldwide into the forensic capacity for the source determination of items seized in relation to the manufacture, trade, firing and concealment of these weapons. Given the limited success achieved from conventional firearms toolmarks analysis, recent interest has focussed on the physiochemical characterisation of the polymers used. This study demonstrates the first research, to our knowledge, exploring the thermal properties of 3D-printing polymers used for the manufacture of privately made firearms in a forensic context. Twenty-eight polylactic acid (PLA) 3D-printing filament samples, sourced from the Australian market, were analysed via differential scanning calorimetry (DSC) and chemometric analysis to investigate the degree of variability in their thermal properties. DSC proved successful in discerning twenty-six PLA filament samples, including same-colour filaments of different brands, using characteristic features in their thermograms. This methodology was also applied to acrylonitrile butadiene styrene (ABS) and polyethylene terephthalate glycol (PETG) 3D-printing filament samples, however, limited useful information was provided due to their amorphous nature. The impact of thermal history on the thermal properties of PLA initially limited the ability to establish links between filament and printed samples. However, heat treatment was subsequently used to control the thermal history of the PLA samples, allowing printed samples to be correctly associated with the corresponding filament material. The outcomes of this research will help to inform a material-specific approach for the analysis of semicrystalline 3D-printing polymers when seized in relation to a criminal investigation.