The Chemistry of Plastics: Its Formation, Properties, & Decomposition

1. The Chemistry of Plastics:Its Formation, Properties, & Decomposition Dr. Stacey j. smith

2. Plastic: What is it? • A “Polymer” • Chain of identical molecules called monomers • Monomer = one unit • Polymer = many units (several thousand) • Carbon backbone + side chains • (N, O, S, Cl, F sometimes mixed in – these are called ‘heteroatoms’) • Change the monomer, change the properties a polyester

3. Plastics are classified by the chemical structure of their backbone & side chains

4. Plastic: What is it?Polyvinyl chloride (PVC) and Polytetrafluoroethylene (Teflon) Polyvinyl chloride(PVC) Polytetrafluoroethylene(Teflon) Properties: Hydrophobic: Water & water-containing substances do not stick! Strong, tough Flexible at higher temps Non-stick surfaces for frying pans, plumbers’ tape, water slides, lubricant Properties: • Lightweight • Strong • Can be made soft/flexible or hard/rigid Plumbing pipes, window frames, flooring, shower curtains, electrical cable insulation, inflatable products polymer monomer monomer polymer Change the monomer, change the properties!

5. Plastic: What is it?Polypropylene (PP – the 2nd most produced plastic) and Polystyrene (PS) polypropylene(Pp) polystyrene(PS) Properties: Lightweight Hard & brittle Poor barrier to air & moisture Can be rigid or foamed Packaging foam/”peanuts”, food containers, disposable cups/plates/cutlery, CD and cassette boxes, trays Properties: • Lightweight • Strong & impact-resistant • Good air & moisture barrier • Intrinsic viscosity (ability to flow & be molded) Bottle caps, drinking straws, yogurt containers, car bumpers, appliances monomer monomer polymer polymer Change the functional group(s) on the monomer, change the properties!

6. Plastic: What is it?Polyethylene: the #1 plastic produced High Density polyethylene(HDPE) Low density polyethylene(LDPE) Properties: Flexible Transparent or opaque Tough but breakable Grocery bags, six-pack rings, hard disk drives, playground slides, plastic wrap Properties: • Strong, hard, dense • Opaque • Can withstand higher temps Detergent bottles, milk jugs, shampoo bottles, folding chairs, food storage containers, hard hats, gas pipelines monomer monomer polymer polymer HDPE Sometimes how the polymer chains are cross-linked is most important!

7. Plastic: How is it made? • Start with a source of carbon • Petrochemicals: compounds derived from petroleum • most plastics are made from these • Renewable plant materials: cellulose, starch.. • plastics made from these are called ‘bioplastics’ Cellulose from wood Starch from corn HDPE PVC

8. Plastic: How is it made? • Make the monomer or monomers • Plastics that have 1 type of monomer in the chain = Homopolymers • Example: the vinyl chloride for polyvinyl chloride (PVC)  pipes • Plastics that have more than one type of monomer in the chain = Co-polymers • Example: acrylonitrile butadiene styrene (ABS)  computer monitors

9. Plastic: How is it made? • Perform the Polymerization Reactionthe reaction to connect the monomers.. • Condensationrxn: monomer+ monomer = polymer+ byproduct(e.g.H2O, HCl, etc.) • Additionrxn: monomer + monomer = polymer + = + + = Examples: Polyamide (Nylon), silk, polyester, proteinsDEMO!! Examples: Polyethylene (PETE, HDPE, LDPE), polypropylene (PP), polyvinyl chloride (PVC), Teflon, polystyrene (PS)

10. Plastic: How is it made? • Mix in “additives” • Fillers (cheap minerals like chalk to reduce cost) • Stabilizers (materials like fire retardants to enhance performance & stability) • Plasticizers (oily compounds that improve flexibility) – largest group of additives • Reinforcing agents • Colorants The average content of additives in plastics is 20% by weight, ranging from 0% for polymers used to wrap foods up to 50% for polymers used in electronic applications.

11. Plastic: Why do we use it? • Generally non-toxic • Cheap, easy to make • Alternatives are wood, metal, glass, stone, clay, natural cloths (cotton, linen, silk), etc., which are: • Limited resources with much more limited properties/uses • More difficult & expensive to process (gather, shape, control, etc.) • Customizable properties(Change the monomer & additives, change the properties) • Soft/hard (packing foam vs. car bumpers) • Flexible/rigid (garbage bagsvs. garbage cans) • Conductive/insulating (solar cells vs. house insulation) • Colors • Moldable shape • Thermosetting plastic: irreversibly cures (changes chemically) after being heated, generally > 200°C • Thermosoftening plastic: heat makes it pliable but does not change it chemically, so it can be molded again & again • Examples: PE (PETE, HDPE, LDPE), PVC, PP, PS • Durable (yet Disposable) • Recyclable HDPE PVC

12. Plastic: How long does it last?(when we don’t recycle it) • PETE/PET 5-10 years • HDPE just under 100 years • LDPE 500-1,000 years if exposed to UV light, indefinite otherwise • PVC indefinite(gives off toxic materials when it is degraded) • PP indefinite, possibly millennia • PS less than 50 years (less time with more exposure to sunlight) • Others indefinite Plastics take a long time to decompose naturally – remember to Recycle! http://www.brighthub.com/environment/green-living/articles/107380.aspx

13. Plastic • “…modern plastics have revolutionized our lifestyle…“ • “…Since 1976, plastic materials have become the most widely used materials in the world…” • Today polymers are products of high technology capable of unmatched prowess in all areas of health, automobiles, construction, aerospace, decoration, packaging, sports… • “…plastic is now listed as one of the 100 most significant events of the last century…” • “…It took less than 100 years for plastics to fit so well in our daily lives, and it is difficult to imagine life without them…” • Quotes from “History of Plastics: The Best Is Yet To Come For The Plastics Industry,” by MaximeGoualin, April 12, 2011. http://www.cereplast.com/history-of-plastics-the-best-is-yet-to-come-for-the-plastics-industry/Pictures & information throughout the presentation were acquired from various websites including Wikipedia