Morphological and Spectroscopic Measurements of Plastic Bags for the Purpose of Discrimination

Abstract

The discrimination of noncolored transparent polyethylene bags was studied by several nondestructive and semidestructive analytical methods. X-ray diffraction, infrared spectroscopy, and optical microscopy (differential interference contrast microscopy and phase contrast microscopy) were applied to polyethylene films. X-ray diffraction was used to distinguish variations in the crystalline phase, infrared spectroscopy was used to distinguish variations in the molecular components, and optical microscopy was used to distinguish the different surface morphologies. The results show that X-ray diffraction classifies the crystalline phase of the film depending on whether it is made from low-density polyethylene, linear low-density polyethylene, or high-density polyethylene; that infrared spectroscopy is useful to distinguish the molecular components and it is the most discriminating technique; and that optical microscopy discriminate films easily by their morphological differences.

Polymers on the crime scene: How can analytical chemistry help to exploit the information from these mute witnesses?

“…XRD has found application in forensic science mainly for the analysis of inorganic species and minerals in soils or metals, 102,103 whereas just a very few examples exist of its use for polymeric items. 69,[104][105][106] Both regions of the semicrystalline framework contribute to the XRD pattern of a polymeric sample: crystalline domains originate sharp reflections, whereas the amorphous zones produce a wide and diffused halo. A fitting procedure of the experimental patterns can be performed, by which the contributions of the crystalline and amorphous domains are deconvoluted 107 (Fig.…”

Forensic examination of plastic drinking straws based on their physical characteristics and manufacturing marks

“…To the best of our knowledge, while the forensic examinations of other drug packaging materialssuch as plastic bags [11][12][13][14][15][16][17], packaging films [17,18], newspapers [19,20], and adhesive tapes [21][22][23][24][25][26][27]had been reported, corresponding studies of drinking straws have not been done. We thus compared the physical characteristics and manufacturing marks of drinking straws from various commercial sources available in Singapore to evaluate their discriminatory values, as well as to gain a better understanding of typical internal variations that might be encountered.…”

Discrimination of Transparent Polyethylene Films Based on Identification of Inorganic Antiblocking Agents

“…Vibrational spectroscopy methods such as infrared absorption and Raman scattering are useful for classifying various types of polymer samples. However, because particles of the antiblocking agents are scattered and buried in the films, it is difficult to apply infrared spectrometry with attachments such as attenuated total reflectance and microscopic Fourier transform infrared spectroscopy instruments (4). On the other hand, microscopic Raman (micro-Raman) spectroscopy might be applicable to the analysis of antiblocking agents in transparent and thin films because of its small focusing area.…”