Textiles are used in:
Clothing, home furnishings, upholstery, carpets, auto seats and end products.
- Natural or artificial origin
- Wide variety of methods used to turn fibers into fabrics
Fiber is:
- The most fundamental unit of a fabric.
- Grouped according to origin (natural or artificial)
- Elongated structure whose length exceeds its breath
Natural fibers are:
- Animal
- Mineral
- Vegetable
Animal fiber is:
Keratin based, (sheep, wool, any fur type)
Non-keratin based (cultivated silk and wild silk)
Mineral fiber is:
Asbestos fibers
Vegetable fiber is:
Seed, cotton, coconut; leaf, bast (flax and hemp);
Artificial fiber is:
- Originate from natural substances and are truly synthetic.
- Polymers of long chains of basic chemical units.
Ex: rayon regenerated from natural substance; basic
building block is cellulose.
Fibers encountered in forensics:
Most common is Polyester (1/3 of global production).
Cotton is second most common.
Fiber transfer types:
- Primary and Secondary
Case management questions:
What is alleged to have taken place?
Who is involved and how?
Where it took place? House? Car? Who was occupant? Owner?
When did incident happen? Delay in scene examination?
Persons having access to scene?
Description of perpetrator’s clothing?
Factors that effect transfer:
- Fiber type
- Fiber morphology and thickness
- Fiber texture and construction
- Area of contact
- Number of contacts
- Force or pressure of contact
Within one fiber type, __________will transfer in greater numbers than coarser fibers.
Finer Fibers
Ex: wool, acrylic, cotton, polyester, nylon and viscose
Fiber transfer:
Area of contact -more fibers will transfer from a coarse than a smooth fabric.
Number of contacts-transfer increases with number of contacts.
Force of pressure and contact-transfer increases with force or pressure of contact until plateau is reached. Greater exchange of short fibers.
Fiber transfer types:
Primary-direct transfer from a donor item to a recipient item.
Secondary-indirect fiber transfer (subject B pickup fibers from a car seat left by subject A).
Fiber persistence:
Whether or not fibers will be found after a transfer. Factors include: force of pressure of contact, location of contact, wearing of recipient garment and placement of recipient garment.
Effect of fiber size and morphology:
Persistence of short fibers under 2.5mm in length is greater than longer fibers. Micro fibers have greater persistence compared with natural fibers.
Target fibers are:
- sheddable and of color that is suitable for searching.
- recover with tape and searched for with low power microscopy
- fibers in color range as that of known target are marked for examination
- what happens next: microscopic examination, color analysis and ID
Microscopy can determine fiber:
Color
Relative diameter
Crimp
Man made or natural
Retardation is:
Synthetic fibers has different RI between parallel axis and perpendicular axis of the fiber. The difference is known as “Retardation Factor”.
Retardation Factor (synthetic fibers):
If parallel RI>than perpendicular RI= “fiber has positive elongation”
If parallel RI
Fiber damage:
Mechanical damage- cutting by sharp edged object.
Environmental damage- normal use.
Influence of high temperature-(and pressure).
Microorganisms- bacteria and fungi.
“Mechanical” damage of fiber:
Normal wear and tear; takes the form of a thinning of the fabric prior to hole forming, pilling and unraveling of hems/seams,
tear, etc. In violent interactions, fabric maybe torn, seams fail and structure of fabric distorted.
“Mechanical” damage of fabric include:
Cutting, slashing, puncturing, abrasion, tensile failure (seat belt);
insects, moths and microorganisms. By animals (pets).
Information from fiber damage:
“Blade type and size;” more distinctive the weapon, the more unique characteristics. General observations include blunt tip, more fabric distortion around penetration point; sharp blade, cut
through without much distortion. Condition of blade, imperfections,
serrations, etc., will increase fabric distortion.
