Importantpolymers • Plastics • Rubbers • Proteins • Starch • Cellulose • Lignin • Fats • PAHs
Other important monomers • PVC is poly vinyl chloride. Vinyl chloride is the common name for chloroethene Note howtherepeatunitisshown!
Nylon • One of the first polymers synthesised • Made from a di-carboxylic acid and a diamine
Polyacrylamide • Poly 2 propenamide or poly(1-carbamoylethylene) • Repeating units -CH2CHCONH2
Uses of plastics • Plasticshavemany uses: • There are alsomanytypes of plastics • Why do youthinkplastics are so useful? • Whataffectswhichplasticisused, forwhichpurpose? • Do youknowwhatplasticisers are?
Differenttypes of plastics • Plastics divide intotwomaintypes: Can youthink of examples.
Whythedifference: Bonding • There are twotypes of bonds • Strongbondsbetweenthemonomerswithin a polymermolecule. • Weakerbondsbetweenthepolymermolecules: sometimescalled Van der Walsforces.
Thermosoftening • In thermosoftening plastics like poly(ethene) the bonding is like ethane except there are lots of carbon atoms linked together to form long chains. They are moderately strong materials but tend to soften on heating and are not usually very soluble in solvents. • The structure is basically a line of monomers strongly bonded. The polymer molecules are held together by weak intermolecular forces and NOT strong chemical bonds. The long polymer molecules mean the intermolecular forces are appreciable but the material is flexible and softens on heating
Thermosetting • Thermosetting plastic structures like melamine have a 3 dimensional cross-linked giant covalent structure network similar to diamond or silica in principle, but rather more complex and chaotic! Because of the strong 3D covalent bond network they do not dissolve in any solvents and do not soften and melt on heating and are much stronger than thermoplastics
Thefuture of plastics • Modern plasticsincludebioplastics. • These are madefrom and orby living organisms. • Theymay be madebyfermentation: Bacteria or other microorganisms mass-produce the biopolymers in bioreactors (fermentation tanks). The biopolymers (lactic acid, polyesters) are extracted from the bioreactors and chemically processed into plastics. • Orbygeneticengineering: genes are introducedintoplants to makeplastics: In 1997, Cargille Dow made a clear plastic (polylactide) from corn. The polylactide fibers woven into sports clothes, upholstery fabrics and bioplastic wraps.
Advantages of Bioplastics • Bioplastics have the advantage of being produced from renewable resources (bacteria, plants) rather than nonrenewable resources (oil, natural gas). Bioplasticsare biodegradable -- they can break down in the environment. • Bioplasticsis a potentially important industry.
Disadvantages of Bioplastics • With current technology, bioplastics might be more expensive to produce, but biotechnology is rapidly advancing and production may become more economical in the future
Ester plasticisers • Plasticisersused in PVC and other plastics are often based on esters of polycarboxylic acids with linear or branched aliphatic alcohols of moderate chain length. These compounds are selected on the basis of many criteria including low toxicity, compatibility with the host material, non-volatility, and expense. Phthalate esters of straight-chain and branched-chain alkyl alcohols meet these specifications and are common plasticizers. Ortho-phthalate esters have traditionally been the most dominant plasticizers, but regulatory concerns have led to pressure to change to non-phthalate plasticizers, especially in Europe.
Healthconcerns • Manyplasticisershave led to concernsabouttheirtoxicity, especially to the hormone producingorgans in thebody. • Phthalateplasticisers are nowbeingreplacedbybio-basedplasticiserswhich are thought to be lesstoxic.
Reduce, Re-use, Recycle • Why
Healtheffects • Additives to plastics to improvetheir performance ordesirabilitycarrynegativehealthimpacts. • Additivessuch as cadmiummercury and lead are directlytoxicwhentheyleachfromtheplastic • Theplasticiser DEHP iscarcinogenic • Endocrinedisruptionleading to birthdefects
Important links forrevision • Types of plastics and their uses GCSE Bitesize: • http://www.bbc.co.uk/schools/gcsebitesize/design/graphics/materialsandcomponentsrev3.shtml • The 7 mostcommontypes of plastics • http://www.reuseit.com/product-materials/the-7-most-common-plastics-and-how-they-are-typically-used.htm • Howstuffworks: plastics • http://science.howstuffworks.com/plastic4.htm • Types of plastics: http://www.wrap.org.uk/content/types-plastic • http://www.the-warren.org/GCSERevision/resistantmaterials/plastics.html