Forensic characterisation of 3D printing polymers used for the manufacture of privately made firearms using ATR-FTIR spectroscopy and chemometrics

Abstract

Abstract3D printing polymers are becoming increasingly popular among criminal communities for the production of privately made firearms and associated components. Recent seizures have raised questions among the international forensic community about the preparedness of crime laboratories for the influx of these new materials. Conventional firearms examination based on toolmarks has shown limited effectiveness for the analysis of 3D printed firearms, leading to interest in a chemistry-based approach. However, little published research has investigated the chemical composition of 3D printing filament as forensic evidence, and no published research exists in the Australian context. We present the first study to our knowledge investigating the chemical variability among 67 polymeric 3D printing filaments available on the Australian market. ATR-FTIR spectroscopy was used with chemometric analysis to explore intrinsic dissimilarity between a range of acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polyethylene terephthalate glycol (PETG) 3D printing filaments. ATR-FTIR successfully identified filament from each polymer category and in some cases, was able to achieve separation of filament sub-groups based on the presence of minor additives, although identification of specific suppliers was not possible. We show for the first time that raw printing filaments may have an outer coating producing a different chemical profile to the inner core or printed exemplars, which has significance for the comparison of pre- and post-print material. The outcomes of this research will aid in the development of interpretation frameworks for these materials, guiding the establishment of crime-laboratory analysis workflows.