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Advanced Forensic Science > Fibres > Flashcards

Fibres Flashcards

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Biology 101 flashcards
1
Q

Where can fibres transfer to

A
  • Contact between persons = transfer from one individual to another
  • Left at a scene of a crime
  • Left on a weapon or car
  • Secondary transfer
  • Tertiary transfer
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2
Q

Give an example of a crime where person to person fibre transfer can occur

A

Sexual Assault
GBH
Manslaughter
Murder

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3
Q

Give an example of a where person to scene fibre transfer can occur

A

Point of entry
Deceased
property

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4
Q

What are the 2 broad groups fibres can be classified into

A

Natural and Man-made

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5
Q

What are the most common natural fibres and where do they come from

A

Animal:

  • Wool
  • Cashmere
  • Animal skin

Plant:

  • Cotton
  • Hemp
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6
Q

Define Man-made/synthetic fibres

A

Produced solely from synthetic chemicals.
Synthesised long-chained molecules
(polymers).

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7
Q

What are common synthetic fibres

A

Nylon
Polyester
Acrylics

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8
Q

Describe cotton fibres

A

Very Fine
Regular
Twisted Ribbon or collapsed twisted tube shape

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9
Q

Describe wool fibres

A

Thick fibre
Regular
Distinctive scale pattern

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10
Q

How can you differentiate between natural and synthetic fibres

A

Synthetic fibres are all created to look the same
Delusterant - Titanium oxide particles added
during manufacturing to reduce
shine.
Seen as particles within the fibre.
Striations along fibre length
Dye pigment
Cross-section - Created by manufacturing process

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11
Q

When will transferred fibres begin to be lost from an item

A

Immediately after contact therefore the items will need to be recovered ASAP

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12
Q

What factors effect the rate of loss of fibres

A
  • Degree of activity after fibre transfer
  • Packaging
  • Location on the person of contact e.g. exposed areas = increase chance of loss
  • Washing
  • Clothing worn over areas of contact
  • Physical properties e.g. burning
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13
Q

Describe tape searching (fibres)

A
  • Fabric garments are taped using adhesive clear tape to recover extraneous fibres anywhere on the surface of the item.
  • Amount of tape depends on the garment and how it readily sheds
  • systematic approach is used
  • Looked at under a LPM (light polarizing microscope)
  • The relevant fibres are circled with permanent pen
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14
Q

Name the ways fibres can be analysed

A
  • Comparison Microscopy
  • TLC - Thin layer chromatography
  • FT-IR
  • MSP - Microspectrophotometry
  • PLM - Polarized light microscope
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15
Q

What information can you gain from analysing fibres

A 
Type
Colour
Number of fibres
Presence of multiple fibres
What textile the fibre came from
Uniqueness of the fibre
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16
Q

Describe Comparison Microscopy (fibres)

A

-Compare control fibres with unknown fibres
recovered from tapes side-by-side under the
comparator.
-Can compare under different wavelengths of light:
white (visible)
blue
UV

17
Q

Describe Thin Layer Chromatography (TLC) (fibres)

A

-The analysis of fibre dyes to determine their colour
comparison.
-At this stage can exclude some fibres as matches.
-Technique incorporates a solid stationary phase
and a moving liquid phase to effect the separation
of dyes.
-Solid phase – thin layer plate coated in silica gel.
-Moving liquid phase – suitable solvent
-Rf values are calculated after liquid moves past 10cm

18
Q

How are Rf values calculated

A

Rf value = Distance travelled by component/Distance travelled by moving phase

19
Q

How are Refractive Indexes measured (RI)

A

RI = Velocity of light through vacuum/ Velocity of light through medium

20
Q

Describe Microspectrophotometry (fibres)

A
  • The instrumental analysis of the colour characteristics of a fibre.
  • Microscope combined with a spectrophotometer.
  • Obtains an electromagnetic spectrum of any dyes or pigments present.
  • Can be compared to that of control fibres.
21
Q

Describe Fourier Transform Infra-red Spectroscopy (FT-IR) (fibres)

A
  • The instrumental analysis of the chemical composition of the fibre itself (man-made fibres only).
  • Concerned with the energy changes involved in the stretching and bending of covalent bonds in molecules.
  • Each peak corresponds to a specific chemical bond
  • Used as a qualitive tool only

Advanced Forensic Science (2 decks)

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