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Materials Revolution

Materials Revolution. MR1 Designing Materials. For thousands of years man has used naturally occurring materials such as wood, flint, leather and wool As our understanding of making things improved we became able to make things from iron and bronze

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Materials Revolution

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  1. Materials Revolution

  2. MR1 Designing Materials • For thousands of years man has used naturally occurring materials such as wood, flint, leather and wool • As our understanding of making things improved we became able to make things from iron and bronze • Nowadays our understanding of “materials science” means that chemistry plays a key role in many other science and engineering disciplines • In this topic we will build on the work done in PR and look at a number of designed polymers • These were developed to copy and improve on the properties of certain naturally occurring substances

  3. MR2 Making and Breaking Polymers • In 1928 Wallace Carothers began working for the US company Du Pont • He led a team trying to develop polymer fibres which would behave like silk • Chemists knew that many fibres were made of long thin molecules (like the fibres themselves) • Silk was know to have a protein structure containing –CONH- groups… • …called peptides or amides

  4. Carothers worked in a very systematic way and tried to recreate these linkages using amines (‑NH2) and carboxylic acids (‑COOH) • CI13.3 and 13.4 (carboxylic acids and derivatives) • CI13.8 (amines and amides) • The –NH2 in the amine reacts with the ‑COOH in the carboxylic acid… • …when it does this, the two molecules join together to form the amide/peptide group (–CONH-) and… • …a water molecule is eliminated • This is called a CONDENSATION REACTION H2O COOH H2N NH CO

  5. NH2 COOH H2N HOOC • Carothers used diamines and dicarboxylic acids • These have the reactive groups at either end • This means they can link together to form long chains… • …POLYMERS • …made by condensation reactions… • …CONDENSATION polymers • Made of amide groups… • …POLYAMIDES • Or more commonly… • …NYLONS

  6. For example; H2NCH2CH2CH2CH2CH2CH2NH2 1,6-diaminohexane + HOOCCH2CH2CH2COOH pentanedioic acid -NHCH2CH2CH2CH2CH2CH2NHCOCH2CH2CH2CO- or -NH(CH2)6NHCO(CH2)3CO- Naming: C-atoms in diamine chain first, C atoms in diacidsecond (don’t forget C atoms of COOH groups)… Nylon-6,5

  7. NH2 COOH H2N HOOC n n • More generally… ) ) NH CO CO NH n 2n H2O

  8. This reaction is very slow. It is much more effective if an acyl chloride is used… • …in this case the small molecule released will be HCl • In 1938 “Dr.West’s miracle Toothbrush” was the first nylon product to go on sale • Nylon stockings followed in 1939 • Assignment 1 • MR2.1 • MR2.2 • MR2.3

  9. Nylon machine parts • Nylon is also used in engineering. • It combines strength, toughness, rigidity and abrasion resistance • It is far superior to poly(ethene) and poly(propene) due to its more powerful intermolecular forces • poly(ethene) and poly(propene) have weak instantaneous dipole-induced dipole attractions between the chains. • In nylon there are hydrogen bonds between adjacent polymer chains • CI5.3 (Temporary and Permanent Dipoles) • CI5.4 (Hydrogen bonding)

  10. In and out of fashion • By the end of 1970s nylon clothes were becoming less popular • One problem was that they are hydrophobic - repel water • This made them very sweaty and uncomfortable • However, companies had spent millions of pounds on development and machinery for making nylon fabrics • The solution was to redevelop nylon with a thinner filament and a different shape and texture of yarn (so it feels similar to cotton) • Further development has led to breathable fabrics with such fine yarns that water vapour can get out but water liquid can’t get in • MR2.4

  11. Polyester • In the 1940s, Rex Whinfield used 1,4-benzenedicarboxylic acid and ethane-1,2-diol to produce a polyester… • CI13.5 (Esters) • This has the ‘old’ name of polyethylene terephthalate (PET) • This is made as small granules which can then be spun to make a fibre (Terylene) or heated to make a plastic used for drinks bottles • Assignment 2

  12. Breaking Polymers - Disappearing in the body • Special polyester threads are used by surgeons to stitch wounds together. • These have been developed to ‘disappear’ as the wound heals. • The monomers that make these polyesters are 2-hydroxypropanoic acid or 2-hydroxyethanoic acid • These contain an -OH group and a -COOH group so only one monomer is needed • The polymers formed form strong threads, but the water in the body slowly hydrolyses the ester bonds in the polymer chains. • The products of this hydrolysis are non‑toxic and are passed out by the body. • 2-hydroxypropanoic acid is lactic acid • The same idea means these polyesters can be used to coat tablets to control its rate of delivery

  13. Liquid Crystals • When heated, liquid crystals can have a physical state somewhere between solid and liquid • This gives them some unusual properties • One important one is that they can have their orientation affected by an electric field • This principle is used in LCD televisions • MR2.5 • MR2.6

  14. MR3 Reuse or Refuse? • 2 billion tonnes of waste produced in Europe each year • 7% plastic • These don’t easily decompose and take up a large volume for their mass • There are three main options… Recycling… • Melt and remould - have to be sorted which is very expensive • Convert back to monomers – still needs sorting (done for some polyesters and polyamides) • Crack into smaller molecules and use as feedstocks in industry – small plants being trialled • CI15.10

  15. Burning… • Simply burning plastics is environmentally unacceptable • Incinerators that trap harmful emissions and use the energy can be effective Degradable polymers… • Most polymers can’t biodegrade because decomposer organisms don’t have the necessary enzymes however… • Biopolymers • made by organisms and broken down by bacteria • Synthetic biodegradable plastics • also be broken down by bacteria • Photodegradable plastics • broken down by sunlight

  16. Biopolymers • Poly(hydroxybutanoate), PHB, is a natural polyester made by certain bacteria • The bacteria can also digest this polymer • It has superior properties to poly(propene)… • …but costs 10 times as much • Work is ongoing to produce a range of biopolymers made by plants

  17. Synthetic biodegradable plastics • Made of poly(ethene) with starch granules in it • Microbes digest the starch • This leaves very small pieces of polythene which can then biodegrade more quickly Photodegradable plastics • Carbonyl groups absorb uv radiation • These groups can be incorporated into polymer chains to act as ‘energy traps’ • This leads to bond fission and so the chain breaks into small fragments • MR3

  18. MR4 Materials with Unusual Properties The First Aramids • After the invention of nylon, chemists began to look at the relationship between a polymer’s structure and its properties • Aromatic polyamides were studied • The first polymeric aromatic amide (aramid) was made from 3-aminobenzoic acid • This polymer had straight chains and so could be made into fibres • It has a high C:H ratio this means it needs high concentrations of oxygen and so is relatively fire resistant; • However, the polymer had a zig-zag structure • This means the chains can’t align well… • …and so the polymer is not very strong

  19. Using benzene-1,4-dicarboxylic acid and 1,4 diaminobenzene, a different aramid was made… • ...Kevlar • The only problem is that it is only soluble in conc. H2SO4 ! • Kevlar is a fibre that is; • Fire resistant • Flexible • Extremely strong • Low density • Weight for weight, five times stronger than steel

  20. Kevlar chains line up parallel to one another… • …these chain then hydrogen bond to one another… • …this leads to sheets… • By developing the way the polymer is then spun DuPont managed to get these sheets to then stack together to form a very crystalline structure • Ass4

  21. DuPont needed $400 million to build a plant for making Kevlar commercially • To make this cost effective, these properties needed to be turned into marketable uses… • Replacement for steel cords in tyres • Ropes (20x stronger than steel ropes and longer lasting) • Aircraft wings • Fencers jackets • Bulletproof vests • Motorbike clothing

  22. PEEK • Poly (ether-ether-ketone) • Very expensive but has a wide range of uses from medical implants to aerospace components • CI5.7 Mixing it • These days it is often cheaper to modify existing polymers; • Copolymers and plasticisers have been used for a long time • Sheets of polymers can be stacked together to form laminates • Some can also be mixed at a molecular level to make polymer “alloys”

  23. Shape memory polymers • Shape memory polymers are copolymers • They have two main sections; a hard segment and a soft segment • Weaker imf • Lower thermal transition temp Ttrans • Above this, these segments of the chains are flexible, below it they aren’t • Strong imf • Determine the material’s permanent shape • Shape memory polymers can be used to stitch wounds • The stitches would change shape as heated by body warmth • This would cause them to tighten and hold the wound together • MR4.1 • MR4.2

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