Introduction. Fibers are used in forensic science to create a link between crime and suspect. Through normal activities

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Lionel Underwood
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1 Intrductin 2 Fibers are used in frensic science t create a link between crime and suspect When fibers are transferred directly frm victim t suspect r suspect t victim, this is called: direct transfer. Thrugh nrmal activities We shed fibers We picked up fibers Very small fibers are classified as trace evidence Cllecting fibers within 24 hurs is critical Frensic Science: Fundamentals & Investigatins, Chapter 4

2 Fiber Evidence A fiber is the smallest unit f a textile material that has a length many times greater than its diameter. A fiber can be spun with ther fibers t frm a yarn that can be wven r knitted t frm a fabric. The type and length f fiber used, the type f spinning methd, and the type f fabric cnstructin all affect the transfer f fibers and the significance f fiber assciatins. This becmes very imprtant when there is a pssibility f fiber transfer between a suspect and a victim during the cmmissin f a crime. Matching unique fibers n the clthing f a victim t fibers n a suspect s clthing can be very helpful t an investigatin, whereas the matching f cmmn fibers such as white cttn r blue denim fibers wuld be less helpful. The discvery f crss transfers and multiple fiber transfers between the suspect's clthing and the victim's clthing dramatically increases the likelihd that these tw individuals had physical cntact.

Cttn fibers are the plant fibers mst cmmnly used in textile materials Cmmn plymer is cellulse. Cttn has nly ne (1) seed.

3 Natural Fibers Many different natural fibers that cme frm plants and animals are used in the prductin f fabric. Natural plant fibers are prduced by stems, leaves seeds and fruits. Cttn fibers are the plant fibers mst cmmnly used in textile materials Cmmn plymer is cellulse. Cttn has nly ne (1) seed. The animal fiber mst frequently used in the prductin f textile materials is wl, and the mst cmmn wl fibers riginate frm sheep.

Crss-sectin f a man-made fiber Fibers under a micrscpe Images: http://www.trashfrteaching.

4 Synthetic Fibers Mre than half f all fibers used in the prductin f textile materials are synthetic r man-made. Categrized as regenerated fibers and plymers. Nyln, rayn, and plyester are all examples f synthetic fibers. Crss-sectin f a man-made fiber Fibers under a micrscpe Images:

5 Hw Frensic Scientists Use Fibers Fiber evaluatin can shw Type f fiber Number f fibers Clr Pssibility f vilence Lcatin f suspects Pint f rigin 6 Frensic Science: Fundamentals & Investigatins, Chapter 4

6 Hw Fibers are cllected by CSI team. tweezers special vacuums sticky tape 7 Frensic Science: Fundamentals & Investigatins, Chapter 4

7 Sampling and Testing Shedding cmmn frm f fiber transfer Micrscpes reveal characteristic shapes and markings Infrared spectrscpy reveals chemical structures t differentiate similar fibers Destructive Testing Methds Burning fibers Disslving fibers in varius liquids 8 Frensic Science: Fundamentals & Investigatins, Chapter 4

8 Sampling and Testing Cmpare fibers fund n different suspects with thse fund at the crime scene 9 Frensic Science: Fundamentals & Investigatins, Chapter 4

9 Fiber Type Burn Rate/Type Smell Smke Prduct Left Wl Fiber Identificatin by Burning Test Will nt burn n it's wn, burns briefly and Chars, shrinks away frm flame Smells like burnt hair Little smke Black ash that crumbles when pked Cttn Flares int bright flame and burns rapidly Smells like burnt paper Little smke Fine gray ash Nyln Burns ut shrtly after remving frm flame, melts and burns away Smells like celery Gray smke Cream clred bead, bead darkens if Plyester Burns ut shrtly after remving frm flame Mild burnt plastic smell Black smke Melts and beads int black mass 10 Linen Silk Flares int bright flame and burns rapidly Desn't burn n wn fr extended time Smells like burnt paper Mild smell, burnt r charred meat Little smke Little smke Black ash that crumbles when pked Black ash that crumbles when pked

10 Fiber Classificatin Natural Fibers Animal fibers (made f prteins): Wl and cashmere frm sheep Mhair frm gats Angra frm rabbits Hair frm alpacas, llamas, and camels Silk frm caterpillar ccns (lnger fiber des nt shed easily) wven wl textile 11 Frensic Science: Fundamentals & Investigatins, Chapter 4

11 Fiber Classificatin Natural Fibers Plant fibers (made f the plymer cellulse): Absrb water Insluble in water Very resistant t damage frm harsh chemicals Disslvable nly by strng acids Becmes brittle ver time 12 Frensic Science: Fundamentals & Investigatins, Chapter 4

and flax frm stems grw in bundles Manila and sisal frm leaves

12 Fiber Classificatin Natural Fibers Plant fibers: Cttn mst cmmn textile plant fiber (picture) ne (1) seed Cir frm ccnuts is durable Hemp, jute, and flax frm stems grw in bundles Manila and sisal frm leaves deterirate mre quickly 13 Frensic Science: Fundamentals & Investigatins, Chapter 4

13 Fiber Classificatin Natural Fibers Mineral Fibers: Fiberglass a fibrus frm f glass Asbests a crystalline structure 14 Frensic Science: Fundamentals & Investigatins, Chapter 4

14 Fiber Classificatin Synthetic Fibers 50% f fabrics are artificially prduced Examples: Rayn Acetate Nyln Acrylic Plyester 15 Frensic Science: Fundamentals & Investigatins, Chapter 4

15 Fiber Classificatin Synthetic Cellulse Fibers 16 Regenerated Fibers (derived frm cellulse r mdified natural fibers) Add t ntes Rayn Mst cmmn in this grup Imitates natural fibers, but strnger Celenese Cellulse chemically cmbined with acetate Fund in many carpets Plyamide nyln Cellulse cmbined with three acetate units Breathable and lightweight Used in perfrmance clthing Frensic Science: Fundamentals & Investigatins, Chapter 4

16 Fiber Classificatin Synthetic Plymer Fibers Synthetic Plymer Fibers Petrleum base Very different frm ther fibers Mnmers jin t frm plymers Fibers are spun tgether int yarns N internal structures Unifrm diameters 17 Frensic Science: Fundamentals & Investigatins, Chapter 4

17 Fiber Classificatin Synthetic Plymer Fibers Plyester Plar fleece Wrinkle-resistant spandex nyln Nt easily brken dwn by light r cncentrated acid Added t natural fibers fr strength Nyln Easily brken dwn by light and cncentrated acid Otherwise similar t plyester 18 Frensic Science: Fundamentals & Investigatins, Chapter 4

18 Fiber Classificatin Synthetic Plymer Fibers Acrylic Inexpensive Tends t ball easily Substitute fr artificial wl r fur Olefins High perfrmance Quick drying Resistant t wear 19 Frensic Science: Fundamentals & Investigatins, Chapter 4

19 Cmparisn f Natural and Synthetic Fibers Visual Diagnstics f Sme Cmmn Textile Fibers under Magnificatin 20 Frensic Science: Fundamentals & Investigatins, Chapter 4

20 Yarns, fabrics, and textiles Yarns fibers (f any length, thick r thin, lse r tight) twisted r spun tgether Blending fibers meets different needs (e.g., resistance t wrinkling) Fibers are wven int fabrics r textiles Threads are arranged side by side (the warp) Mre threads (the weft) are wven back and frth crsswise thrugh the warp 21 Frensic Science: Fundamentals & Investigatins, Chapter 4

21 Weave Patterns 22 Frensic Science: Fundamentals & Investigatins, Chapter 4

22 Summary.... Fibers are a frm f class evidence. Fibers are a frm f trace evidence. Fibers are spun int yarns having specific characteristics. Yarns are wven, with different patterns, int clthing r textiles. Fiber evidence is gathered using different techniques. 23 Frensic Science: Fundamentals & Investigatins, Chapter 4

23 Summary Fibers are analyzed using burn tests, tests fr slubility in different slutins, plarized light micrscpy, r infrared spectrscpy. Fibers are classified as natural r synthetic. Natural fiber surces include: Animal hair Plant seeds, fruit, stems, r leaves Minerals. 24 Frensic Science: Fundamentals & Investigatins, Chapter 4

Chapter 4 A Study of Fibers and Textiles By the end of this chapter you will be able to:

Chapter 4 A Study of Fibers and Textiles By the end of this chapter you will be able to: Chapter 4 A Study f Fibers and Textiles By the end f this chapter yu will be able t: 1 Identify and describe cmmn weave patterns f textile samples Cmpare and cntrast varius types f fibers thrugh physical