3D printing has rapidly risen in popularity, with desktop 3D printers enabling low-cost, custom production of items by hobbyists and industry alike. However, this technology is also being increasingly misused to produce homemade firearms or firearm components [1]. The limited success of standard toolmark-based examination in characterising 3D printed weapons has prompted forensic interest in a chemistry-based approach [2].
We present a multi-modal study into the physicochemical variability of 3D printing polymers from the Australian retail market. 67 filaments based on polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), or polyethylene terephthalate glycol (PETG) were first analysed by ATR-FTIR spectroscopy [3]. Chemometric modelling of this data rapidly differentiated the main polymer classes and, in some cases, specific filament sub-types containing minor additives. Raman spectroscopy was successful in discriminating individual ABS or PETG filaments due to the presence of different copolymers and additives, as well as peaks shifts potentially associated with polymer tensile strain. Differential scanning calorimetry enabled further separation of PLA filaments based on variations in the thermal properties and history.
Comparisons of printing filament and printed exemplars revealed the presence of a removable outer coating on raw filaments that could affect vibrational spectroscopic measurements, although the scale of these variations was small relative to differences between different filament products. The alteration of thermal history during the printing process limited comparison of pre- and post-print material, however annealing was determined to overcome these limitations.
These findings will inform specific forensic analysis workflows for 3D printed firearms, enabling comparisons between seized firearms and materials to assist criminal investigations relating to 3D printed weapons.