Forensic Chemistry CHS 5542

Fibers, Hairs and Related Evidence

Background Information and Terminology

Module 5- Part 1Tatiana Trejos, PhD.

Professional Science Fonsic ScienceDepartment of Chemistry and BiochemistryInternational Forensic Research Institute

Florida International University

Forensic Fiber Examinations

Fiber examinations typically involves

both identification of the fiber type

and comparison of K/Q to determine if

there is an association or not

Introduction to Textile Fibers

What is a fiber?

• Natural or man made material that is the basic element of textiles

Natural Fibers

Animal•Silk

• Fibroin

•Wool• Keratin

•Hair Fibers• Keratin

Vegetable• Seed Fibers

Cotton, kapok, coir

• Bast (Stem) Fibers Flax, hemp

• Leaf Fibers Manila, sisal

Mineral• Asbestos

Animal (Protein) Fibers

• Protein• Greek word “proteios” meaning “first”

• Chain-like molecules • Union of α-amino acids joined with peptide

linkage

H

• H2N-C-COOH

R• Acidic and basic group attached to α-carbon atom

Silk

• Composed of fibroin• Very different to keratin

• Continuous filament• Transfer during contact is unlikely

Image source: http://micro.magnet.fsu.edu/primer/techniques/dic/dicgallery/images/wildsilkfiberssmall.jp

Wool

• Keratin• Staple fiber

• Scaled surface• Readily transferred

Wool

Epicuticle

Cortex

Endocuticle

Exocuticle

Cuticular scales

Hair Fibers (animal)

• Goat Family• Mohair (Angora goat – Capra hircus

aegagrus)• Cashmere (Asiatic goat – Capra hircus

laniger)

• Camel Family• Dromedary Camel – (Camelus bactrianus) • Alpaca – (Lama Pacos)• Vicuna – Undercoat hair (similar in all

ways to cashmere)

• Fur Bearing Animals• Angora Rabbit

Vegetable Fibers

• Categorized by the section of the plant from which they are harvested• Seed• Bast (Stem)• Leaf

• Chemical composition dependent on source

Vegetable Fiber Principal Constituents

• Cellulose• Hemi-Cellulose• Lignin• Pectins

Seed Fibers

• Cotton – genus Gossypium• Produces flower, which falls off leaving

boll (pod)• Boll contains seeds with immature

fibers attached• As the fibers mature, the boll expands

and breaks open

• Kapok – Ceiba petrandra • Unsuitable for yarns, formally used as

filling

• Coir• Outer husk of coconut• Mostly used in twine

Stem (Bast) Fibers

• Flax (linen) – Linun usitatissimum• Over 6,000 years old

• Ramie – Boehermeria nivea• Tablecloths

• Hemp – Cannabis sativa• The term “hemp” is used to describe other

fibers• Jute – Corchorus capsularis

• Ropes and cordage

Leaf Fibers

• Sisal – Agave sisalana• Ropes, cordage

• Abaca (Manila Hemp) – Musa textilus• Better quality ropes and cordage

Mineral Fibers

• Asbestos (Greek for incombustible)• Chrysotile - very fine fibers (25 nm diameter)

Man-Made Fibers

• Refers to fibers that were manufactured

• Synthetic fibers are those made from synthesized polymers• Bi-products of the petroleum industry

• Regenerated fibers are those made from regenerating naturally occurring polymers and forming the fiber with that material• Cellulose

Common Man-Made fibers

• Nylon• Polyester• Acrylic• Polypropylene• Cellulosic

• Rayon• Acetate