Fibres and forensics Text and images by the Centre for Microscopy & Microanalysis, University of Queensland, Australia, August 2007 Slide 1

Fibres: Natural [animal & mineral] Synthetic [human –made] What we will cover: 1) Scanning Electron Microscopy (SEM). 2) How to identify fibres using the SEM. 3) The identification of a mystery fibre. Slide 2

Scanning Electron Microscope What is scale all about? Slide 3

Resolution (not magnification!) is the ability to separate two objects optically Unresolved Partially resolved Resolved Slide 4

With enough resolution we can magnify an object many millions of times and still see new detail This is why we use electron microscopes If you magnified your thumb nail just 10,000 times it would be about the size of a football pitch. Slide 5 For example think of the size of Suncorp Stadium in Brisbane

Beam passes down the microscope column Electron beam now tends to diverge But is converged by electromagnetic lenses Cross section of electromagnetic lenses Electron beam produced here Sample Diagram of Scanning Electron Microscope or SEM in cross section - the electrons are in green Slide 6

+ - Electron falls back again to inner ring [lower energy state or valence] & burst of X-ray energy given off that equals this = Characteristic packet of energy Using X-rays and the scanning electron microscope e Slide 7

Characteristic chlorine peak Characteristic carbon peak Energy of packets in thousands of electron volts come off atoms Quantity of packets Characteristic oxygen peak What the X-rays tell us Slide 8

Some definitions of fibre Any slender, elongated, threadlike object or structure. A natural (e.g. plant, animal or mineral) or synthetic filament, capable of being spun into yarn. Commonly also used in: Botany: One of the elongated, thick-walled cells that give strength and support to plant tissue. Anatomy: Any of the filaments constituting the extracellular matrix of connective tissue. Any of various elongated cells or threadlike structures, especially a muscle fiber or a nerve fiber. Slide 9

Sample preparation for SEM Fibre samples are dried then mounted on 12mm metal stubs and coated with platinum. Slide 10 Sample mount 12mm wide Adhesive tape Sample

CharacterPlant (e.g. paper) AnimalSyntheticMineral (including glass) Cross-section General appearance Surface features Uniformity [features and size] Composition Slide 11

The following images are of various natural (plant and animal) fibres and synthetic fibres imaged using a scanning electron microscope Note: electrons provide monochrome images. Slide 12

Natural Fibres (Plant) (A) Tissue paper at low magnification. (B) Same tissue paper at higher magnification showing individual fibres. How wide are these fibres? A B Slide 13

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Paper Slide 15

CharacterPlant (e.g. paper) AnimalSyntheticMineral (including glass) Cross-sectionFlat or rounded General appearance Bent Twisted Surface features Pores, Stomata Uniformity [features and size] Irregular CompositionC, O, [+Ca, Al, Si] Slide 16

Not all hair is the same! Rabbit hair (A) looks different from human hair (B) under the SEM. What are the differences? AB Slide 17

Natural fibres (Animal) (A) Human hair strands at low magnification. (B) & (C) At higher magnifications showing surface detail (scales). Slide 18

Human hair Slide 19

Wool Slide 20

CharacterPlant (e.g. paper) AnimalSyntheticMineral (including glass) Cross-sectionFlat or rounded Round [usually] General appearance Bent Twisted Curves Surface features Pores, Stomata Scales, Ridges, Pointed ends Uniformity [features and size] IrregularRegular CompositionC, O, [+Ca, Al, Si] C, O, S [Cl] Slide 21

Fibres can be natural or synthetic. But how can we tell them apart quickly and easily? We can use an SEM to examine the size, shape, surface detail and elemental composition Coconut fibres (coir) Shade cloth woven plastic fibres Slide 22

A B Synthetic fibres (A) Plastic shade cloth at low magnification. (B) Plastic shade cloth at higher magnification showing smooth individual fibres and extrusion grooves. Slide 23

Shade cloth Slide 24

Synthetic fibre: velcro Slide 25

Velcro Slide 26

CharacterPlant (e.g. paper) AnimalSyntheticMineral (including glass) Cross-sectionFlat or rounded Round [usually] Round General appearance Bent Twisted CurvesStraight Surface features Pores, Stomata Scales, Ridges, Pointed ends Grooves, Extrusion marks, Blunt ends Uniformity [features and size] IrregularRegular CompositionC, O, [+Ca, Al, Si] C, O, S [Cl]C, O, [Cl] Slide 27

AB C Synthetic fibres (A) Fibre glass at low magnification. (B) & (C) Fibre glass at progressively higher magnifications showing individual fibres. B Note smooth fibre surfaces Slide 28

Asbestos – why is it dangerous to health? A How many fibres this wide would fit across 1 mm ? B C Slide 29

Asbestos Slide 30

CharacterPlant (e.g. paper) AnimalSyntheticMineral (including glass) Cross-sectionFlat or rounded Round [usually] Round General appearance Bent Twisted CurvesStraight Surface features Pores, Stomata Scales, Ridges, Pointed ends Grooves, Extrusion marks, Blunt ends Smooth Tapered ends Uniformity [features and size] IrregularRegular Dividing CompositionC, O, [+Ca, Al, Si] C, O, S [Cl]C, O, [Cl]Mg, Si, [Fe, Ca, Al, Na] Slide 31

Mystery fibre Slide 32

CharacterPlant (e.g. paper) AnimalSyntheticMineral (including glass) Cross-sectionFlat or rounded Round [usually] Round General appearance Bent Twisted CurvesStraight Surface features Pores, Stomata Scales, Ridges, Pointed ends Grooves, Extrusion marks, Blunt ends Smooth Tapered ends Uniformity [features and size] IrregularRegular Dividing CompositionC, O, [+Ca, Al, Si] C, O, S [Cl]C, O, [Cl]Mg, Si, [Fe, Ca, Al, Na] Slide 33

Mystery fibre Slide 34

CharacterPlant (e.g. paper) AnimalSyntheticMineral (including glass) Cross-sectionFlat or rounded Round [usually] Round General appearance Bent Twisted CurvesStraight Surface features Pores, Stomata Scales, Ridges, Pointed ends Grooves, Extrusion marks, Blunt ends Smooth Tapered ends Uniformity [features and size] IrregularRegular Dividing CompositionC, O, [+Ca, Al, Si] C, O, S [Cl]C, O, [Cl]Mg, Si, [Fe, Ca, Al, Na] Slide 35

6 mm As seen by a light microscope As seen by an SEM ! Some fibres have very characteristic features that are seen easily with the SEM. Slide 36