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 and chemical analysis Describe principle characteristics used t identify cmmn fibers Apply frensic science techniques t analyze fibers All Rights Reserved Suth-Western / Cengage Learning 2012, 2009 Frensic Science: Fundamentals & Investigatins, Chapter 4
Intrductin 2 Fibers are used in frensic science t create a link between crime and suspect Thrugh nrmal activities We shed fibers We picked up fibers Direct transfer fibers transferred frm victim t suspect, r vice versa Secndary transfer victim has fibers n his clthes already, then transfers them t the suspect. Very small fibers are classified as trace evidence Cllecting fibers within 24 hurs is critical Frensic Science: Fundamentals & Investigatins, Chapter 4
Hw Frensic Scientists Use Fibers 3 Fiber evaluatin can shw Type f fiber Clr Pssibility f vilence mre fibers transferred means lnger cntact, mre likely vilent Lcatin f suspects Pint f rigin The mre unique the fiber, the mre valuable it is as evidence. Frensic Science: Fundamentals & Investigatins, Chapter 4
Cllecting/analyzing fiber evidence Special vacuums, tape, frceps Accurately recrd lcatin f fibers Identify type f fiber and characteristics Match it t fibers frm a suspect surce (car hme) 4 Frensic Science: Fundamentals & Investigatins, Chapter 4
Sampling and Testing Plarizing light micrscpy Micrscpes with special filters reveal characteristic shapes and markings Infrared spectrscpy -- uses a beam f light t reveal chemical structure t differentiate similar fibers 5 Frensic Science: Fundamentals & Investigatins, Chapter 4
Testing fibers Destructive Testing Methds (nly used when there are a lt f fibers available) Burning fibers Disslving fibers in varius liquids 6 Frensic Science: Fundamentals & Investigatins, Chapter 4
Sampling and Testing Cmpare fibers fund n different suspects with thse fund at the crime scene 7 Frensic Science: Fundamentals & Investigatins, Chapter 4
Textiles Clthing, carpets, uphlstery Cnstructed by weaving yarns Yarns are made f fibers spun tgether 8 Frensic Science: Fundamentals & Investigatins, Chapter 4
Fiber Classificatin Natural Fibers 9 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) Used in clthing, carpets, hangings, bedding Frensic Science: Fundamentals & Investigatins, Chapter 4 wven wl textile
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, small pieces break ff 10 Frensic Science: Fundamentals & Investigatins, Chapter 4
Fiber Classificatin Natural Fibers Plant fibers: Cttn mst cmmn textile plant fiber (picture) cmes frm the seedpd Cir frm ccnuts is durable, used in drmats and baskets 11 Frensic Science: Fundamentals & Investigatins, Chapter 4
Plant fibers Hemp, jute, and flax frm stems grw in bundles Flax is used t make linen, an expensive, durable material Jute is used fr rpe, mats, handbags Manila and sisal frm leaves deterirate mre quickly Used t make rpes, twine, netting 12 Frensic Science: Fundamentals & Investigatins, Chapter 4
Fiber Classificatin Natural Fibers Mineral Fibers: 13 Fiberglass a fibrus frm f glass Fibers are shrt, weak, brittle Used in insulatin Can cause a rash Asbests a crystalline structure Lng, thin fibers Durable Pipe cverings, brake linings, tiles, insulatin Frensic Science: Fundamentals & Investigatins, Chapter 4
Fiber Classificatin Synthetic Fibers 50% f fabrics are artificially prduced Examples: Rayn Acetate Nyln Acrylic Plyester 14 Frensic Science: Fundamentals & Investigatins, Chapter 4
Synthetic fiber prductin Mnmers are jined int plymers Plymer sup made in a large vat Made int fibers as it is drained thrugh tiny hles called spinnerets Quality f the textile can be changed by changing the shape f the spinnerets. http://yutu.be/y479oxbzcbq 15 Frensic Science: Fundamentals & Investigatins, Chapter 4
Synthetic Cellulse Fibers 16 Regenerated Fibers (derived frm cellulse): Rayn http://yutu.be/f_avqnmtjjg Mst cmmn in this grup Smth and silky 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
Fiber Classificatin Synthetic Plymer Fibers 17 Synthetic Plymer Fibers Petrleum based Many different characteristics Easily distinguished using plarizing light micrscpy r infrared spectrmetry Mnmers jin t frm plymers Fibers are spun tgether int yarns N internal structures Unifrm diameters Frensic Science: Fundamentals & Investigatins, Chapter 4
Fiber Classificatin Synthetic Plymer Fibers Plyester Plar fleece Wrinkle-resistant 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 Artificial silk 18 Frensic Science: Fundamentals & Investigatins, Chapter 4
Fiber Classificatin Synthetic Plymer Fibers Acrylic Inexpensive Tends t ball easily Used fr artificial wl r fur Olefins High perfrmance Quick drying Resistant t wear 19 Frensic Science: Fundamentals & Investigatins, Chapter 4
Cmparisn f fibers Synthetic fibers are strnger than natural fibers Synthetic fibers are nt damaged by micrrganisms Synthetic fibers deterirate in bright sunlight Synthetic fibers melt at a lwer temperature than natural fibers 20 Frensic Science: Fundamentals & Investigatins, Chapter 4
Cmparisn f Natural and Synthetic Fibers Visual Diagnstics f Sme Cmmn Textile Fibers under Magnificatin 21 Frensic Science: Fundamentals & Investigatins, Chapter 4
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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) Yarns 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 24 Frensic Science: Fundamentals & Investigatins, Chapter 4
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Weave Patterns 26 Frensic Science: Fundamentals & Investigatins, Chapter 4
............. 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. 27 Frensic Science: Fundamentals & Investigatins, Chapter 4
................. 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. 28 Frensic Science: Fundamentals & Investigatins, Chapter 4