Fiber Evidence A fiber is the smallest unit

Fiber Evidence A fiber is the smallest unit of a textile material that has a length many times greater than its diameter. A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric. The type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers and the significance of fiber associations. This becomes very important when there is a possibility of fiber transfer between a suspect and a victim during the commission of a crime. Matching unique fibers on the clothing of a victim to fibers on a suspect’s clothing can be very helpful to an investigation, whereas the matching of common fibers such as white cotton or blue denim fibers would be less helpful. The discovery of cross transfers and multiple fiber transfers between the suspect's clothing and the victim's clothing dramatically increases the likelihood that these two individuals had physical contact. http: //www. fbi. gov/hq/lab/fsc/backissu/july 2000/deedric 3. htm#Fiber%20 Evidence

Natural Fibers Many different natural fibers that come entirely from plants and animals are used in the production of fabric. Plant fibers Cotton: Most common type of fiber used today • Hard to use as evidence due to commonality Linen: From flax plant Animal fibers: Wool: Most common type of fiber, usually from sheep Silk: Spun from the silk worm Other animals used for fibers: goats, llamas, camels Animal furs: Mink, rabbit, beaver, fox http: //www. fireflydiapers. com/articles/diaperarticle_naturalfibersabsorb. htm

Natural Fibers Plant fibers Animal fibers/furs https: //fril. osu. edu/index. cfm? fuseaction=site. get. This. Page&Site. Page. ID=124&Pag e=Browse%20 Collections http: //www. fireflydiapers. com/articles/diaperarticle_naturalfibersabsorb. htm

Manufactured Fibers Definition: Fibers derived from natural or synthetic polymers History: • 1911 – Introduction of rayon (from processed/chemically treated plant material, treatment of cellulose) • 1939 – Introduction of nylon (1 st synthetic fiber, made entirely of chemicals) Production: • Polymers are forced through spinnerets to align particles and create long strands (think Play. Dough press) Cross-section of a man-made fiber • Became possible w/ ability to produce polymers Images: http: //www. trashforteaching. org/phpstore/product_images/Yarn. WS. JPG http: //www. fbi. gov/hq/lab/fsc/backissu/july 2000/deedric 3. htm#Fiber%20 Evidence http: //www. jivepuppi. com/images/fiber_evidence. jpg

Analysis of Manufactured Fibers Microscopic: • Compare color and diameter using a comparison microscope (easy elimination of sources, but not enough to confirm matches) • Also allows comparison of pitting and striations Analytical techniques: • Visible light microspectrophotometer is a good 1 st step, more detail/comparison preferred • Thin-layer chromatography separates pigments and allows for comparison of dyes Chemical composition: • Use GCMS to match chemical composition of fibers, should determine class, better if it can determine sub-class Birefringence: • Looks at colors exhibited by crystalline materials under polarized white light Infrared absorbance: • Polymers absorb infrared light in a characteristic pattern, therefore can provide information as to class and possibly subclass of fibers. Images: http: //www. trashforteaching. org/phpstore/product_images/Yarn. WS. JPG http: //www. fbi. gov/hq/lab/fsc/backissu/july 2000/deedric 3. htm#Fiber%20 Evidence http: //www. jivepuppi. com/images/fiber_evidence. jpg

Manufactured Fibers Rayon Acetate Nylon Cross-section of a man-made fiber Images: http: //www. trashforteaching. org/phpstore/product_images/Yarn. WS. JPG http: //www. fbi. gov/hq/lab/fsc/backissu/july 2000/deedric 3. htm#Fiber%20 Evidence http: //www. jivepuppi. com/images/fiber_evidence. jpg

Fiber Evidence Significance when found at a crime scene: • No analytic technique gives a 100% positive result • No statistical database available determining the ratio of a fiber’s origin • However: • Unlikely to find 2 individuals w/ same clothing • Many different colors and dye lots, therefore a match is pretty meaningful • Weight of evidence increases dramatically if 2 or more distinctly different fibers can be linked to the same object • Helps to significantly enhance case if corroberated with other evidence Images: http: //www. trashforteaching. org/phpstore/product_images/Yarn. WS. JPG http: //www. fbi. gov/hq/lab/fsc/backissu/july 2000/deedric 3. htm#Fiber%20 Evidence http: //www. jivepuppi. com/images/fiber_evidence. jpg

It’s time to examine some hairs and fibers! http: //micro. magnet. fsu. edu/primer/techniques/polarized/gallery/images/humansmall. jpg

Can you identify the animal hairs shown? A B C D G E F H Think About It … (1)In which samples are we viewing the cuticle? How do they compare? (2) In which samples are we viewing the medulla? How do they compare? (3) What characteristics can be used to identify hair samples? I

Can you identify the types of fibers shown? A B D Think About It … (1)Which samples are natural fibers? (2) Which samples are synthetic fibers? (3) What characteristics can be used to identify fiber samples? C E F

Answer Keys http: //micro. magnet. fsu. edu/primer/techniques/polarized/gallery/images/humansmall. jpg

Types of Animal Hairs - Key A Cat B Horse C Pig D Human G E Deer F Dog Rabbit H Rat I Human

Types of Fibers - Key A Acrylic Yarn Polyester Yarn B D Cotton Yarn Rayon Rope C E Nylon Rope Wool Yarn F