Lecture 4: Polymers and fibres Flashcards
Introduction to polymers
- Large molecules
- Linked molecule units
Some examples of monomer units: vinyl chloride, styrene and glucose
- Linked molecule units
Interconnection/interaction between chain polymers
- Branched
- Polyethylene (LDPE and HDPE)
- Cross linked
- Poly(isoprene) rubber
- Epoxy resin (glue)
- Linear
- PVC, polystyrene, and nylon
- Dendrimer
- Specialised polymers
Types of polymers
- Natural (biopolymers)
-Natural fibres, proteins
and DNA - Semi-synthetic polymers
-Rayon fibres and
cellophane - Synthetic polymers
-PVC, polystyrene, PTFE,
and nylon - Co-polymers
-different linker monomers
-styrene (25%) and 1,3-
butadiene
Synthesis and classification of synthetic polymers
- Chain growth polymerisation- thermoplastic
- Cationic polymerisation- Thermosetting
- Anionic polymerisation- Thermosetting
Step growth polymerisation- Elastomer
Classification of synthetic polymers
- Thermoplastics
- Hard at room temperature
- Soft and viscpus at higher
temperature- shaped and
moulded - Polystrene, polyethylene,
acrylonitrile butadiene
styrene (lego) and PET
- Thermosetting polymers
- On heating: become highly
cross-linked and solidify - Cannot be reshaped or
remoulded - Bakelite and automobile
and
- On heating: become highly
- Elastomers
- Ability to stretch and
return to their original
shape - Rubber Tyres
- Ability to stretch and
What are fibers?
- Thin threads
- Spinneret
- Cooled and drawn
out - Tension strength
Why are fibers important?
-Transfer and trace evidence
-Largest category of polymer evidence analysed
-Homicide, assault, sexual offences and hit and run
Classification of fibers
-Natural
* Animal source
* Plant Source
* Mineral
-Semi-Synthetic
-Synthetic
Cellulose
-Cellulose Fibres
-Cotton Fibres
-Other Natural fibres
Cellulose- Dicot fibers
-Transparent, colourless, curved twisted fibres
-Circular Cross Section and Surface Striations
Kapok- Seed fiber
- Smooth, hollow, thin walled cylinders
- 2-3 cm/10-35 µm, Twisting and sharp bending and surface irregularities
- Silky cotton like substance
- Tiny cellulose tubes air sealed inside
- Removed by hand, dried, separated and exported
- Brittle and inelastic
Buoyancy aids
Flax (linen)- Dicot fiber
-Skin Fibre
-Vegetable Fibre
-Cellulose
-Stronger than cotton
-Transverse Nodes shapes I, X, V and Y
Hemp- Dicot fibers
- Colourless, transparent cylinders
- Surface irregularities
Polygonal in cross section - Cannabis plant
- Primary Bast Fibres (70%)
-Long, high cellulose, low lignin
-One of the strongest natural fibre - Secondary Bast Fibres (30%)
-Medium, high lignin, low cellulose
Ramie- Dicot
- Nodelike ridges
- Longitudinal striations
- Smooth Surface
- Raised Nodes
- Long, Glossy, Naturally white and silky appearance
- Composed of Cellulose
- Extremely porous
- Strongest natural fibres
Greater strength when wet
Jute
- Straight, smooth cylinders
- Bundles of individual fibres
- 1-4 m long, soft and shiny fibres
- White to brown
- Spun
Cellulose and Lignin
Coir- fruit fibre
-Cordage and brushes
-Fibre Bundles
-Floor Mats and Ropes
Sisal- monocot fibre
-Transparent colourless to light yellowish tan
-cylinders.
Manilla- monocot fibers
-Bundles of individual fibres
-High magnification 0.2-0.4 μm protuberances
Silk- animal fibres
-Pale yellow to brown/yellow fibres
-Broad Continuous Ribbons
-Longitudinal Striations
Silk
-Protein fibre
-Silk worm
-Shiny fibre
-Strongest Fibres
-Decreases when wet
Cellulose- cotton fibres
-90% Cellulose
-Seed fibre
-Seed Pods “boll”
-Cotton Fibres: yellow-white colour length around 2 inches
-Microscopic analysis
Semi synthetic fibres: Rayon fibres
- Extraction from wood pulp or cotton
- Reaction with a strong base and carbon disulphide
- Cellulose Xanthate (viscose)
- Spinneret into a bath of acid
- Rayon filaments drawn out to form rayon fibres
- Long, Smooth, highly reflective and shiny fibre
Synthetic fibres: characteristics
No surface Characteristics, Regular and Uniform in shape
Synthetic fibres: nylon
- Step-Growth Polymer
- 6-aminohexanoic acid
- Uses:
-Nylon Stockings
-Carpets
-Seat Belts