The Chemistry of Plastics: Its Formation, Properties, & Decomposition DR. STACEY J. SMITH

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

PolymerUses PESPolyesterTextiles, synthetic fibers, Resin, films PETEPolyethylene terephthalateDrink bottles, chip bags, Textiles, fibers, PB jars, microwavable packaging (#3) PEPolyethyleneShopping bags, plastic bottles (#1 plastic produced) HDPEHigh density polyethylene Detergent bottles, milk jugs, shampoo bottles, folding chairs, food storage containers, hard hats, natural gas pipelines LDPELow density polyethyleneGrocery bags, six-pack rings, hard disk drives, playground slides, plastic wrap PVCPolyvinyl chloridePlumbing pipes, shower curtains, window frames, flooring PVDCPolyvinylidene chlorideOriginal Saran wrap PPPolypropyleneBottle caps, drinking straws, yogurt containers, car bumpers, appliances (#2) PSPolystyrene Packaging foam/”peanuts”, food containers, plastic tableware, disposable cups, plates, cutlery, CD and cassette boxes PMMAPolymethyl MethacrylateHard contact lenses, acrylic paints, Plexiglass, rear light covers for vehicles PTFEPolytetrafluoroethylene (Teflon)Non-stick surfaces for frying pans, plumbers’ tape, water slides, lubricant PAPolyamidesNylon ropes, toothbrush bristles, fishing lie, machine parts, gun frames ABSAcrylonitrile butadiene styreneComputer monitors, printers, keyboards, drainage pipes PCPolycarbonateCD cases, eye glasses, security windows, traffic lights PC/ABSPolycarbonate/ABSCar interior & exterior parts, mobile phone bodies PUPolyurethaneThermal insulation, cushioning foams, surface coatings EpoxyPolyepoxideAdhesive, potting agent for electrical components, matrix for composites Plastics are classified by the chemical structure of their backbone & side chains

Plastic: What is it? Polyvinyl chloride (PVC) and Polytetrafluoroethylene (Teflon) POLYVINYL CHLORIDE (PVC) Properties: ◦Lightweight ◦Strong ◦Can be made soft/flexible or hard/rigid Plumbing pipes, window frames, flooring, shower curtains, electrical cable insulation, inflatable products 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 Change the monomer, change the properties! monomer polymer monomer polymer

Plastic: What is it? Polypropylene (PP – the 2 nd most produced plastic) and Polystyrene (PS) POLYPROPYLENE (PP) 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 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 Change the functional group(s) on the monomer, change the properties! monomer polymer monomer polymer

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

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’ Plastic: How is it made? HDPEPVC Cellulose from woodStarch from corn

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 Plastic: How is it made?

Perform the Polymerization Reaction the reaction to connect the monomers.. ◦Condensation rxn: monomer + monomer = polymer + byproduct (e.g. H 2 O, HCl, etc.) ◦Addition rxn: monomer + monomer = polymer Plastic: How is it made? + = Examples: Polyamide (Nylon), silk, polyester, proteins DEMO!! Examples: Polyethylene (PETE, HDPE, LDPE), polypropylene (PP), polyvinyl chloride (PVC), Teflon, polystyrene (PS) + = +

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.

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 bags vs. 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 HDPEPVC

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!

“…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…” Plastic Quotes from “History of Plastics: The Best Is Yet To Come For The Plastics Industry,” by Maxime Goualin, April 12, Pictures & information throughout the presentation were acquired from various websites including Wikipedia