all, except 4, 11 12, 13: see the table in the book hint 18: think of the small, small amount available to you hint: see chart on page 138

Transcription

1 Fibers Chapter 6

2 all, except 4, 11 12, 13: see the table in the book hint 18: think of the small, small amount available to you hint: see chart on page 138

3 Objectives You will understand: Why fibers are class evidence. How fibers can be used as circumstantial evidence to link the victim, suspect, and crime scene.

4 You will be able to: Distinguish and identify different types of fibers. Understand polymerization. Judge the probative value of fiber evidence. first, though, let s look at some...

5 on graph paper in pen title, purpose (your words) & procedure ( Refer to page p129 ) Make sure you have both samples, correctly labelled (including fabric type), and accurately sketched in detail! In color!

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7 Fibers Good thing? *fibers they are everywhere so can easily be transferred Bad thing? They are everywhere, & are considered just class evidence But have probative value And are common trace evidence at a crime scene

8 fibers are wound up together to make a thread or yarn

9 How yarn is made

10 can be characterized based on comparison of both physical and chemical properties the more properties that are similar, the more likely the connection but get one not to match and *poof* - game over

11 Sources and Types of Fibers *fabric (again) is made of fibers fibers made of twisted *filaments that are either natural of artificial

12 fibers are everywhere... (here wool from creepy girl s creepy sheep, creepy rope & the material of creepy kids clothes and bedding and wallpaper) cloth, carpeting, cordage (rope, string, nets), brushes, filling materials (furniture, mattresses, optical fibers, structural materials)

13 Types of fibers and fabric: Natural animal, vegetable, or *inorganic Artificial synthesized or created from altered natural sources

14 Synthetic Rayon Nylon Acetate Acrylic Spandex Natural Silk Cotton Wool Mohair Cashmere Polyester

15 before we look closely at the different types of fibers, we will briefly look at fabric...

16 Fabric Production Fabrics are composed of individual threads or yarns that are made of fibers and are knitted, woven, bonded, crocheted, felted, knotted, or laminated. Most are either woven or knitted. The degree of stretch, absorbency, water repellence, softness, and durability are all individual qualities of the different fabrics.

17 Weave Terminology *yarn a continuous strand of fibers or filaments that may be twisted together *warp lengthwise yarn *weft crosswise yarn *blend a fabric made up of two or more different types of fibers

18 Simple - very, very simple - look at weaving

19 How fabric is made...

20 Plain Weave the simplest and most common weave pattern the warp and weft yarns pass under each other alternately design resembles a checkerboard

21 Twill Weave the weft yarn is passed over one or more warp yarns before going under two or more, with a step between rows. makes a diagonal weave pattern. design resembles stair steps. denim is one of the most common examples.

22 a famous twill pattern

23 Satin Weave interlacing weave floats over four or more yarns Satin itself is the most obvious example light is not scattered as much so appears silky

24 Knitted Fabric Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination. Either way, the yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric.

25 How to knit... (just get the idea)

26 back to fibers...

27 Fiber Morphology What are important characteristics that can be used to identify and compare fibers as forensic evidence???

28 The Chemical Structure of Fibers fibers are made of polymers, which are long chains of repeating chemical units. The word polymer means many (poly) units (mer). The repeating units of a polymer are called monomers. By varying the chemical structure of the monomers or by varying the way they are joined together, polymers are created that have different properties. As a result of these differences, they can be distinguished from one another forensically.

29 Classification Natural fibers are classified according to their origin: Vegetable or cellulose Animal or protein Mineral

30 Some are based on the plant polymer material, cellulose: Cotton vegetable fiber; strong, tough, flexible, moisture-absorbent, not shape-retentive Rayon chemically altered tree cellulose; soft, lustrous, versatile Cellulose acetate cellulose that is chemically altered to create an entirely new compound not found in nature...

31 cotton burns and smells like burning leaves is made up of long chains of cellulose cotton is king in fiber land (60% of clothing and home furniture made of cotton) downside: too much makes it tough to prove anything (low probative value) natural

32 How jeans are made...

33 linen is made from cellulose, too made from flax plant

34 jute, also of cellulose, much coarser used to make burlap, rope, carpets

35 rayon is cellulose that has been altered very pure cellulose burns like cotton

36 acetates = chemically treated cellulose its lustrous sheen and smooth, satiny texture make it a good synthetic alternative to silk an acetate dress and a cigarette filter are made of same stuff :)

37 Some are based on protein: Wool animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama, or vicuña Silk insect fiber that is spun by a silkworm to make its cocoon; the fiber reflects light and has insulating properties

38 source of mohair (he probably can t hold any mohair) a silk-like fabric or yarn made from the hair of the Angora goat.

39 source of cashmere fine in texture, strong, light, and soft, garments made from it provide excellent insulation.

40 angora rabbit source of angora wool

41 wool is composed of polypeptide chains, helix-shaped, called keratin one of the amino acids is cysteine cysteine contains sulfur, which means stinky when burned

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43 this structure allows it to be waterinsoluble, but also it has room for a lot of water to get stuck up in there and makes a good insulator

44 silk also a protein most is made of just two amino acids

45 How silk is made

46 Some are based on minerals: Asbestos a natural fiber that has been used in fire-resistant substances Rock wool a manufactured mineral fiber Fiberglass a manufactured inorganic fiber

47 synthetics are made from derivatives of petroleum, coal, and natural gas Nylon most durable of man-made fibers; extremely lightweight Polyester most widely used man-made fiber Acrylic provides warmth from a lightweight, soft, and resilient fiber Spandex extreme elastic properties synthetic

48 nylon = completely synthetic used e v e r y w h e r e synthetic

49 polyesters have this basic monomer structure they are everywhere (Dacron is an example of a polyester) synthetic

50 acrylics are all over the place, too (there are also Spandex and olefins and a bunch of others) natural and synthetic fibers seem to be everywhere! ;) synthetic

51 Fiber Cross Sections Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven.

52 The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross section the cross sections can help ID a particular sample Round 4-lobed Trilobal Dogbone or Dumbbell Octalobal Irregular Multi-lobed or Serrate 52

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54 work as groups use descriptive words found here #4) no #5! no blends, all 100% pure fabric just fill out handout; the handout is your lab don t use all your sample! you ll need some for the next lab! don t forget unknown!

55 the handout is your lab! don t worry about the questions within the text this time, we ll talk about it instead half a wet litmus paper on the inside top leave some sort of space for smoke to escape (prevents popping off) after burning, let it cool on the wire mesh, then chuck it work like a team!!! lead acetate = no change or grey/black red litmus = no change or turns blue blue litmus = no change or turns red residue = best description

56 Refractive Index when light travels through a medium it slows down bottom line: when a fiber is put in something of the same refractive index, the fiber vanishes Becke lines the Becke line appears as a halo if your fiber s r.i. does not match the standard...

57 if liquid r.i. > fiber r.i. Becke lines appear outside the fiber edges if liquid r.i. = fiber r.i. fiber seems to vanish!!! if liquid r.i. < fiber r.i. Becke lines appear inside

58 Refractive index: Imagine the glass stirring rod is a fiber...

59 Fluorescence some fibers fluoresce when exposed to UV some naturally, some by dyes, some by *optical brighteners these agents absorb UV, but re-emit in the blue end of the vis spectrum hence, fabrics and paper can look whiter than white

60 Other Tests of Fiber Evidence Fourier Transform Infrared analysis (FTIR) can be done on single fibers to figure out what it is

61 Pyrolysis gas chromatography-mass spectrophotometry (PGC-MS) burns a sample and analyses the waste products, but the sample is destroyed

62 Collection of Fiber Evidence Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged. Make tape lifts of exposed skin areas and any inanimate objects. Removed fibers should be folded into a small sheet of paper and stored in a paper bag.

63 We will watch a show on this, and it will be on the quiz. :)

64 EOCs all, except 4, 11 hint 18: think of the small, small amount available to you hint 20: see chart on page 138