4104FSBMOL - Lecture 1c - Fibres & Polymers. Flashcards
1
Q
What are Polymers?
A
Extremely large molecules of monomer units which are linked together.
2
Q
What are some examples of Monomer Units?
A
Vinyl Chloride, Styrene and Glucose.
3
Q
What is the most common type of evidence at Crime Scenes?
A
Fibres - which are made up of Polymers.
4
Q
What is the Monomer Unit for PVC?
A
Vinyl Chloride.
5
Q
How many monomer units does Cellulose have?
A
Around 100,000.
6
Q
What are the 4 different Types of Polymer?
A
- Natural (Biopolymers).
- Semi-Synthetic.
- Synthetic.
- Co-Polymers.
7
Q
What is the Strongest Polymer in the world?
A
Kevlar.
8
Q
Give Examples of some Natural Polymers.
A
Natural Fibres, Proteins, DNA.
9
Q
Give Examples of some Semi-Synthetic Polymers.
A
Rayon Fibres and Cellophane.
10
Q
Give Examples of some Synthetic Polymers.
A
PVC, Polystyrene, PTFE, Nylon and Kevlar.
11
Q
Give Examples of some Co-Polymers.
A
- Different linked monomers.
- Styrene (25%) and 1,3-butadiene.
12
Q
What are the 4 different Types of Co-Polymer?
A
- Random.
- Alternating.
- Block.
- Graft.
13
Q
Explain a Random Co-Polymer.
A
Monomer (B) are randomly spread throughout the other monomer (A).
14
Q
Explain an Alternating Co-Polymer.
A
Monomer B alternates every other one with Monomer A.
15
Q
Explain a Block Co-Polymer.
A
There is a block of Monomer A and then a Block of Monomer B and so forth.
16
Q
Explain a Graft Co-Polymer.
A
Small chains of Monomer B act as branches to the normal chain of Monomer A.
17
Q
What are some examples of Co-Polymers?
- What is their Trade Name?
- What are they used for?
A
- Vinyl Chloride (20%) and Vinylidene Chloride (80%) - Saran - Food Wrapping and Fibres.
- Styrene (25%) and 1,3-butadiene - Styrene butadiene rubber (SBR) - Tyres and Rubber articles.
- Acrylonitrile 1,3-Butadiene - Nitrile Rubber - Adhesives and Petrol Hoses.
- Isobutylene Isoprene - Butyl Rubber - Inner Tubes (Bike).
18
Q
What are the different Interconnection/ Interaction Types between Polymer Chains?
(ways to connect monomer chains).
A
- Branched.
- Cross-linked.
- Linear (most common).
- Dendrimer.
19
Q
What does a Branched Polymer look like?
Give an example.
A
A single chain with monomer chains coming off it (like co-polymers).
Polyethylene - LDPE and HDPE.
20
Q
What does a Cross-Linked Polymer look like?
Give an example.
A
Where several single chains are joined together by branches.
Poly(isoprene), Rubber and Epoxy Resin - Glue.
21
Q
What does a Linear Polymer look like?
Give an example.
A
A single chain made up of monomers.
PVC, Polystyrene and Nylon.
22
Q
What does a Dendrimer Polymer look like?
Give an example.
A
Where every monomer is branched to another, normally forming a circle shape.
Specialised Polymers where every unit is branched.
23
Q
What different types of Polymerisation are there for Synthetic Polymers?
A
- Chain Growth Polymerisation.
- Cationic Polymerisation.
- Anionic Polymerisation.
- Step Growth Polymerisation.
24
Q
What are the 3 Classifications of Synthetic Polymers?
A
- Thermoplastic Polymers.
- Thermosetting Polymers.
- Elastomer Polymers.
25
What are the *features* of **Thermoplastics**?
## Footnote
Give examples of them.
* Hard at RTP.
* Soft and Viscous at High Temperatures (allows to be shaped and moulded).
## Footnote
Polystyrene, Polyethylene, Acrylonitrile butadiene styrene (LEGO) and PET.
26
What are the *features* of **Thermosetting Polymers**?
## Footnote
Give examples of them.
* Become highly cross-linked and solidify when heated.
* Can't be reshaped or remoulded.
## Footnote
Bakelite and automobile top coats.
27
What are the *features* of **Elastomers**?
## Footnote
Give examples of them.
* Ability to Stretch and return to their original shape.
## Footnote
Rubber and Tyres.
28
How does **Chain Growth Polymerisation** work?
1. Formation of Free Radicals.
2. Reaction of Monomer with radicals.
3. Chain propagating step (repeated).
4. Termination Step - Chain Combination **OR** Impurity.
29
Give *examples* of Polymers formed by **Chain Growth Polymerisation**.
PVC and Polyethylene.
30
How does **Cationic Polymerisation** work?
1. An electrophilic (electron poor) initiator attacks a nucleophilic (electron rich) monomer.
2. Chain Propagating Step (repeated).
3. Termination Step - Loss of a Proton **OR** Chain-transfer reaction with solvent.
31
Give *examples* of Polymers formed by **Cationic Polymerisation**.
Polyisobutylene, Bicycle Inner Tubes and Bicycle Tyres.
32
How does **Anionic Polymerisation** work?
1. A nucleophilic (electron rich) initiator attacks an electrophilic (electron poor) group.
2. Chain Propagating Step (repeated).
3. Termination Step - Reaction with Water **OR** Carbon Dioxide.
33
Give *examples* of Polymers formed by **Anionic Polymerisation**.
Superglue Fuming Process, Polystyrene, Cyanocrylate Glue.
34
How does **Step-Growth Polymerisation** work?
Formed by a **repeated condensation reaction** (reacting 2 of the same monomer together and reacting with water).
35
Give *examples* of Polymers formed by **Step-Chain Polymerisation**.
**Nylon, Kevlar**, Formaldehyde Polymers, **Proteins**, Polyesters, Polycarbonates and Polyurethanes.
36
What are **Fibres** and how are they made?
They are Thin Threads which are made by Spinnerets - cooled down and drawn out.
37
What *sort of crimes* can **Fibres** be found in?
Homicides, Assaults, Sexual Offences, Hit & Run crimes.
38
How can **Fibres** be *Classified*?
* Natural - animal and plant source.
* Semi-Synthetic.
* Synthetic.
39
Give *Examples* of **Natural Fibres**.
* **Cellulose**.
* **Kapok** - Seed Fibre.
* **Flax (Linen)** - Dicot Fibre.
* **Hemp** - Dicot Fibre.
* **Ramie** - Dicot Fibre.
* **Jute**.
* **Coir** - Fruit from a coconute.
* **Sisal** - Monocot Fibre.
* **Manilla** - Monocot Fibre.
* **Silk** - Animal Fibre.
* **Cotton** - Seed Fibre.
40
Give *Examples* of **Semi-Synthetic Fibres**.
* Regenerated forms of Cellulose.
* **Rayon** Fibres.
41
Give *Examples* of **Synthetic Fibres**.
* **Bicomponent** Fibres (2 polymer types).
* **Nylon**.
* **Kevlar**.
42
*Explain* about **Cellulose Fibres**.
* Makes up 90% of Cotton Fibres.
* Cellulose -Dicot Fibres - plant with 2 leaves.
* Fibres are transparent, **colourless**, curved twisted fibres.
* Circular Cross Section.
43
*Explain* about **Kapok - Seed Fibres**.
* Smooth, hollow, thin-walled cylinders 2-3cm/ 10-35µm, Twisting and sharp bending and surface irregularities.
* Silky cotton like substance.
* Tiny Cellulose tubes air-sealed inside.
* Brittle and Inelastic.
* 30% of weight in water.
* Non-Allergenic, Non-Toxic.
44
*Explain* about **Flax (Linen) - Dicot Fibres**.
* Skin Fibre.
* Vegetable Fibre.
* Stronger than Cotton.
* Transverse Nodes shaped I, X, V and Y.
45
*Explain* about **Hemp - Dicot Fibres**.
* Comes from a **Cannabis Plant**.
* **Colourless**, Transparent cylinders.
* Polygonal Cross Section.
* Primary Bast Fibres (70%) - Long, high cellulose, low lignin, one of the strongest natural fibres.
* Secondary Bast Fibres (30%) - medium, high lignin, low cellulose.
46
*Explain* about **Ramie - Dicot Fibres**.
* Node-like ridges.
* Longitudinal striations.
* Smooth.
* Long, Glossy, Naturally **White** and Silky.
* Extremely pourous.
* Stronger when Wet.
47
*Explain* about **Jute Fibres**.
* Straight Fibres.
* Smooth Cylinders.
* Bundles of Fibres.
* 1-4 metres long.
* Soft, Shiny Fibres.
* **White to Brown** colours.
48
*Explain* about **Coir - Fruit Fibres**.
* From the outside of a coconut.
* Cordage and Brushes.
* Fibre Bundles.
* Used to make Floor Mats and Ropes.
49
*Explain* about **Sisal - Monocot Fibres**.
* Transparent.
* **Colourless to light yellowish/ tan** coloured cylinder.
50
*Explain* about **Manilla - Monocot Fibres**.
* Bundles of Indivdual Fibres.
* **Need a high magnification** to see.
* 0.2-0.4µm protuberances.
* Used in envelopes.
51
*Explain* about **Silk - Animal Fibres**.
* **Pale Yellow to Brown** Fibres.
* Broad ribbons.
* Protein Fibre.
* Made from Silk Worms.
* Shiny Fibre.
* *One of the strongest fibres.*
* *Strength decreases when wet.*
* Used in making Parachutes.
52
*Explain* about **Cotton - Seed Fibres**.
* Made of 90% cellulose.
* **Yellow-white** in colour.
* Length is usually 2 inches.
* Microscopy.
53
*Explain* about **Rayon Fibres**.
* Extracted from wood pulp or cotton.
* Reacted with a strong base and carbon disulphate.
* Spinneret into a bath of acid.
* Rayon filaments drawn out to form rayon fibres.
* Long, Smooth, Highly reflective and shiny fibres.
54
*Explain* about **Bicomponent Fibres**.
* Made up of 2 different polymer types.
* Sheath and Core Design.
* Side by Side Design.
* Regular and Uniform in shape.
55
*Explain* about **Nylon Fibres**.
* Made in Step-Growth Polymerisation.
* e.g. 6-aminohexanoic acid.
* Used for Nylon Stockings, Carpets and Seat Belts.
56
*Explain* about **Kevlar**.
* **Strongest material** in the world!
* Stephanie Kwolek made it.
* Used in many things such as Bullet-proof vests.
* Chemical Chains are Parallel to each other and are bonded together by Hydrogen Bonds which are extremely strong.
* Kevlar has 8-9 times the strength of steel of comparative weight.
57
What are the 8 different things you need to look out with Microscopic Analysis of Fibres?
1. General Morphology.
2. Cross Section and Diameter.
3. Shape - Modification Ratio (MR).
4. Dichroism and Pleochroism.
5. Refractive Index (RI) and Birefringence.
6. Signs of Elongation.
7. Isotropy and Anisotropy.
8. Interference Colours/ Double Refraction.
58
What does **General Morphology** mean in the *Microscopic Analysis of Fibres*?
Shape (e.g. cylinders/ ribbons, twisted or not).
59
What does **Cross Section and Diameter** mean in the *Microscopic Analysis of Fibres*?
What the shape is at the end of the fibre (e.g. cylinder/ oval/ square) and the length of the diameter.
60
What does **Modification Ratio (MR)** mean in the *Microscopic Analysis of Fibres*?
It assesses *how round a fibre is* (cross-section), the **lower the MR, the rounder the fibre**. It uses this and assesses how this impacts the strength/ durability.
61
What does **Dichroism** mean in the *Microscopic Analysis of Fibres*?
Exhibits 2 different colours (e.g. Nylon 66).
62
What does **Pleochroism** mean in the *Microscopic Analysis of Fibres*?
Exhibits **more** than 2 different colours (e.g. Asbestos Fibre).
63
What does **PLM** stand for in Microscopy?
**P**olarised **L**ight **M**icroscopy - used in seeing colours of things.
64
What does **Refractive Index (RI)** mean in the *Microscopic Analysis of Fibres*?
When light hits the interface between air and the fibre, some light is **reflected** back and the other part is **refracted** into the fibre. The light ray that is refracted becomes '**bent**' and will travel at a **different velocity** through the fibre. RI notes the differences between things.
65
What does **Birefringence** mean in the *Microscopic Analysis of Fibres*?
* Parrallel RI - Perpendicular RI.
* Indicates the Absolute difference in the 2 Refractive Indicies.
66
How do you determine the Ri of a Fibre?
1. A fibre placed onto glass slide.
2. Immersed in a drop of oil of specific RI (**Immersion Oil**)
3. Place the Cover slip and observe.
4. If the oil and fibre have the **same RI** = Light travels in a **straight, parallel line.**
5. If the oil and the fibre have **different RI** = Light will **bend** (refract).
6. Test using a series of oils of known Refractive indices.
67
What does **Sign of Elongation** mean in the *Microscopic Analysis of Fibres*?
* Sign of Elongation **(+)** = Crystals elongated *parallel* to the **slow direction** have a positive sign of elongation or are said to be **length slow.**
* Sign of elongation **(-)** = Crystals that are elongated *parallel* to their **fast direction** have a negative sign of elongation or are said to be **length fast.**
68
What does **Isotropy** mean in the *Microscopic Analysis of Fibres*?
* Amorphous (shapeless).
* Rays of Light travel **same velocity in all directions.**
* **Same** RI.
69
What does **Anisotropy** mean in the *Microscopic Analysis of Fibres*?
* Crystalline or pseudo-crystalline nature.
* Light transmitted at **different velocities in different directions.**
* **Different** RI.
* Interference colours produced.
70
What does **Interference Colours** mean in the *Microscopic Analysis of Fibres*?
* Colours produced by Double Refraction.
* Different degrees of retardation = different interference colours.
71
What does **Double Refraction** mean in the *Microscopic Analysis of Fibres*?
* As light passes into an anisotropic substance the single light ray is broken into 2 polarised rays, which travel at different velocities.
* Different RI's.
## Footnote
* Perpendicualr = **High** RI + **Slower** Velocity.
* Parallel = **Low** RI + **Faster** Velocity.
72
What happens to the *Interference Colour* at **0°**?
Extinction (nothing).
73
What happens to the *Interference Colour* at **45°**?
Maximum Brightness.
74
What happens to the *Interference Colour* at **90°**?
Extinction (nothing).
75
What happens to the *Interference Colour* at **135°**?
Maximum Brightness.
76
What happens to the *Interference Colour* at **180°**?
Extinction (nothing).
77
What *colour light* does **Nylon** show?
Pink.
78
What are the different ways to Analyse Fibres?
* Raman.
* FTIR.
* Visible Micro-spectroscopy.
* duPont Fibre Identification Stain No.4.
79
What happen in the Herzog Test for Vegetable Fibres?
* Hydration and Dehydration - causes different twist directions.
## Footnote
(Flax and Hemp look similar under the microscope).
80
What are the 2 different **Twist directions** of Vegetable Fibres in the Herzog Test?
* S-Twist.
* Z-Twist.
