Forensic Fiber Analysis

It includes the definition of fiber, types of fiber, characteristics, collection and analysis of fiber as a evidence.

1. Fibers Forensic Physics Presented By Shreyaskumar Jitendra Patel

2. Content What is Fiber ? Different types of fibers The significance of fibers as trace evidence Methods of collecting fiber samples from the crime scene Different methods for the analysis of fibers

3. Introduction ( Fibers ) Fibers are thread like structures from fabric and other materials which are easily identifiable under a microscope or smallest unit of a textile material that has a length many times greater than its diameter. Its source can be determined by comparing it with fiber of a controlled sample. Just as hair left at a crime scene can serve as identification, the same logic can reasonably be extended to the fibers that compose our fabrics and garments. Fig.1 Photomicrograph of cotton Fiber (450×)

4. Polymer The word ‘polymer’ is coined from two Greek words: poly means many and mer means unit or part . The term polymer is defined as very large molecules having high molecular mass (10 3 -10 7 u). These are also referred to as macromolecules , which are formed by joining of repeating structural units on a large scale. The repeating structural units are derived from some simple and reactive molecules known as monomers. linked to each other by covalent bonds. This process of formation of polymers from respective monomers is called Polymerisation. Classification Based on Source 1. Natural polymers e.g cellulose, starch, resins 2. Semi-synthetic polymers e.g Cellulose derivatives 3. Synthetic polymers e.g synthetic fibers

5. Classification of fibers Fibers Natural Fibers Manmade/ Artificial Fibers Animal Fibers E.g Silk, wool, Hair of Animal,etc . Plant Fibers E.g Cotton, Leaf, etc. Synthetic Polymer E.g Polyester, Nylon, Dacron, Polyvinyl derivatives, etc. Natural Polymer E.g Rayon, Cellulose ester, etc. Mineral Fibers E.g Asbestos

6. Natural Fibers The oldest fibers known to us. Since these are made up of cells, they have better ability to absorb moisture and are thus, considered to be very comfortable. So, the clothing that directly touches our skin is mostly made up of natural fibers. Natural fibers are further divided into two categories: Fibers from plant source Examples are cotton, jute, linen etc. Cotton fibers are commonly used in textile material. The type of cotton, fiber length, the degree of twist contributes to the diversity of these fibers. The processing techniques and color application also influence the value of cotton fiber identification.

7. Natural Fibers Fibers from Animal source Animal fibers which are mostly used in textile materials is wool and the most common wool fibers come from sheep. The end use of sheep’s wool indicates the fineness of woolen fibers. The finer wool fibers are used in making clothing while coarser wool fibers are used to make carpets. Thus, the diameter of the wool fibers holds importance in the analysis of the fiber from the crime scene. Wool from Angora goat, camel are also found. Other example for animal fibers is silk.

8. Wool Fiber Cotton Fiber Wood Fiber Cotton Dacron Fiber Nylon Fiber Polyester Fiber Nylon Fig.2 Natural Fibers Fig.3 Manmade Fibers

9. Manmade/ Artificial Fibers These fibres are alternative to the natural fibres . More than 50 percent of the fibres are man-made. The most common examples of man-made fibres are nylon, Dacron followed by acrylic etc. These are mostly used in garments, foam padding and sound proofing etc. Today, such fibers are marketed under hundreds of different trade names . To reduce confusion there are Generic/ family names for the grouping of all manufactured fibers. E.g. Acetate, Acrylic, Rayon, Nylon, Polyester, etc (Generic Group)

10. Significance of fibers as trace evidence They are easily transferred from the clothing of a suspect to that of the victim. They are capable of multiple transfers. For example from carpet, bed etc to the suspect’s clothing These transfers can be direct or indirect. By direct transfers, we mean that the fiber is transferred directly from a fabric onto a victim’s body. While by indirect transfer, we mean that the already transferred fibres on the clothing of a suspect are transferred to a victim’s body. Fibers vary according to their end use. Another important consideration is the time delay between the actual physical contact and the collection of clothing items from the suspect or victim. If the victim is immobile, very little fibre loss will be there whereas the suspect’s clothing will lose the transferred fibres quickly. The possibility of finding transferred fibres on the clothing of the suspect a day after the actual contact had been made will be very remote depending upon the use and the handling of the of that clothing.

11. Collection and Packaging Photographs of all the evidence should be taken prior to collecting them Same procedure as used for Hair. Collected with Handpicking Methods. (Hand should be covered with gloves) Collected with the help of Plastic Tweezers or Forceps. Other Methods for Collection: 1. Tap lifting 2. Vacumming Method Packed into Paper bag or Druggist Fold

12. Analysis of fibers Primary Examination Chemical Examination Microscopic Examination

13. 1. Primary Examination Fiber colour Fiber location Birefringence Fig. 4 Birefringence

14. 2. Chemical Examination The chemical analysis will involve the extraction of the dye from the fibre sample and then characterizing and identifying its chemical structure. It is actually difficult to extract a dye from the fibre sample as these samples are typically small and it is also made sure by the textile dyers that the dye stays in the fibre . This method of dye analysis is a destructive method which leaves the fibre useless for further color examination. But, still since some fibres have similar colors that chemical analysis becomes a necessity.

15. 3. Microscopic Examination Fiber diameter The fibers vary in size from 10 to 50 micrometers. The softer materials will have smallest fibres while the most durable materials will have the largest fibers Also, for example, the finer woolen fibers are used for making clothing while the coarser ones for using carpets. So again the size of the fibers can tell its origin. Fiber cross section Basically, it is the cross section of the fibre that varies according to the type of the fiber. The natural fiber have their origin from plants and animals and thus look rough at the edges. This feature on the examination can actually reveal whether the fibre is natural or man-made. Microtome is used to make cross-section

16. Fig.5 microscopic view of various cross Section of Fibers

17. Fig.6 Analytical Processing Chart for Fiber Analysis

18. 3. Microscopic Examination Atomic force microscopy Atomic force microscopy is a method which is carried out using an atomic force microscope. It is an instrument to analyze and characterize samples at the microscopic level. The instrument will allow an analyst to look at the surface characteristics with very accurate resolution ranging from 100 micrometers to even less than 1 micrometer.

19. 3. Microscopic Examination Other Microscopes which used for Fiber Examination : Scanning Electron Microscope Polarized Light Microscope Comparison Microscope Other Methods Used For Examination: Raman Spectroscopy IR Spectroscopy UV-Visible Spectroscopy A photomicrograph of a nylon fiber displaying interference colors when observed between the crossed polars of a polarizing microscope (100×). Fig .7

20. Any Questions ? Reference : Forensic Science -An Introduction to Scientific and Investigative Techniques, 2 nd edition, CRC Press Epg Pathshala (Module: FSC_P7_M25 ) Encyclopedia of Forensic Science Criminalistics : An introduction to forensic science by R. Saferstein

21. Thank You !!!