Forensic Examination of Adhesives PDF

FORENSIC EXAMINATION OF ADHESIVES Ms. Manisha Panda Assistant Professor, SoFS, CUTM BBSR Introduction 1. Sample description The initial evaluation begins with a critical review of each sample’s chain of custody, package sealing, and identification markings. In additi...

FORENSIC EXAMINATION OF ADHESIVES Ms. Manisha Panda Assistant Professor, SoFS, CUTM BBSR Introduction 1. Sample description The initial evaluation begins with a critical review of each sample’s chain of custody, package sealing, and identification markings. In addition, any potential for cross-contamination between samples is evaluated. The next step in forensic tape analysis is the visual evaluation, description, and documentation of the original condition of the sample(s). This step involves describing the general condition, weathering characteristics, size, shape, color, and classification of the tape. This evaluation can be performed macroscopically both with the naked eye and using a stereomicroscope. If necessary, separate tape from an item or from itself to complete a full examination on the tape. Written descriptions, sketches, photographs, or other images are used to document each sample’s characteristics. The resulting notes shall be sufficient to document the conclusions reached in the examiner’s report. Introduction 2. Physical Fit The most conclusive type of examination that can be performed on tape samples is a physical end match. This involves the comparison of edges, surface striae, and other surface irregularities between samples in which corresponding features possess individualizing characteristics. Physical fits shall be documented with descriptive notes to include images or videography. Images should contain a scale when possible. During the course of a physical fit examination, the tape classification is determined, and some of the physical characteristics are examined and documented. Introduction 3. Physical characterization of the tape Macroscopic and stereo microscopic observations provide initial, and often discriminating, information for tape comparisons. Separate comparison of each major component (backing, adhesive, reinforcing material) Color, surface texture, thickness, width, and layer structure can be determined. Cross-sections of the tape sample can be utilized to determine layer structure. The comparison of backings and adhesives shall include the use of at least two instrumental techniques (one for organic and one for inorganic analysis) Characterization of reinforcing materials utilizing appropriate methods (e.g., PLM and FTIR for fabric reinforcement; PLM and elemental analysis for glass). The analysis can be concluded at any point during a comparison if an exclusionary difference is found. Introduction 4. Polarized Light Microscopy Characterization of inorganic materials and other tape additives are accomplished with the use of Polarized Light Microscopy. Clear and semi-opaque film backings are examined for the optical properties of oriented polymers. By examining the sample under polarized light, different materials can exhibit distinct optical behaviors, which can help differentiate between various components. Inorganic fillers, such as silica, calcium carbonate, or talc, are often added to adhesives to enhance properties like strength, viscosity, and thermal stability. Under PLM, the size, shape, and distribution of these fillers can be observed, providing insights into how they might influence the adhesive's performance. Introduction The cross-section of the adhesive and its backing material (like a tape or film) can be examined under PLM. This helps in understanding the adhesive's adhesion properties, layer thicknesses, and any interface issues. Observations can reveal how well the adhesive penetrates or bonds to the backing, which is crucial for ensuring effective performance. In tape applications, reinforcement fibers (such as glass, aramid, or carbon fibers) are added to enhance strength and durability. PLM can be used to analyze these fibers’ arrangement, orientation, and interaction with the adhesive. Introduction 5. Fourier Transform Infrared Spectroscopy (FTIR) The base material of the tape, often made of polymers like polyethylene, polypropylene, or vinyl. FTIR helps identify the type of polymer and any specific characteristics that may influence the tape’s performance. FTIR can distinguish between different types of adhesive elastomers and assess their chemical structure, which is crucial for understanding bonding performance. Plasticizers are additives that increase flexibility and workability of the adhesive and backing. FTIR can identify various plasticizers and their concentrations, which affect the tape's physical properties. Adhesives are different compounds that may be included in the tape formulation, such as stabilizers, fillers, or colorants. FTIR can detect these additives, providing insight into their potential effects on the tape’s durability and performance. Introduction 5. Fourier Transform Infrared Spectroscopy (FTIR) Reinforcement Fibers includes fibers for added strength (like glass or carbon fibers), FTIR can help identify these materials and assess their interaction with the adhesive and backing. Introduction 6. Raman Spectroscopy Raman spectroscopy can also be used to obtain compositional information about the backings, adhesives, and additives used in tapes. While both Raman spectroscopy and FTIR (Fourier Transform Infrared Spectroscopy) are used to analyze materials, they provide different types of information. For instance, Raman is often better for analyzing non-polar molecules and can provide insights into molecular structure and interactions. Limitations of this technique include strong interfering fluorescence produced by some tape components and thermal damage to some materials. Introduction 7. Pyrolysis gas chromatography Pyrolysis Gas Chromatography (PGC) is a technique used to analyze organic materials by breaking them down through heating (pyrolysis). The high temperatures cause the organic compounds in the tape to decompose into smaller molecules. PGC helps identify and compare the different structural elements of the tape, like the adhesive and the backing material. The combination of flame ionization detection and mass spectrometry provides both quantitative and qualitative information about the adhesive and backing materials, helping to understand their composition and properties better. Introduction 8. Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy SEM-EDS can be used to characterize the texture and elemental composition of tape samples. Emitted X-rays provide information regarding the presence of specific elements Comparison of the composition of tape backings or tape adhesives is generally performed by a direct spectral comparison or evaluation of relative peak intensities. Introduction 9. X-ray Fluorescence Spectrometry XRF is another elemental analysis technique that can be used to characterize the elemental composition of tape samples. Like SEM-EDS, emitted X-rays provide information about the presence of specific elements based upon the emission of characteristic X-rays following excitation of the sample by an X-ray source.