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

Polymer Uses

PES Polyester Textiles, synthetic fibers, Resin, films

PETE Polyethylene terephthalate Drink bottles, chip bags, Textiles, fibers, PB jars, microwavable packaging (#3)

PE Polyethylene Shopping bags, plastic bottles (#1 plastic produced)

HDPE High density polyethylene Detergent bottles, milk jugs, shampoo bottles, folding chairs, food storage containers, hard hats, natural gas pipelines

LDPE Low density polyethylene Grocery bags, six-pack rings, hard disk drives, playground slides, plastic wrap

PVC Polyvinyl chloride Plumbing pipes, shower curtains, window frames, flooring

PVDC Polyvinylidene chloride Original Saran wrap

PP Polypropylene Bottle caps, drinking straws, yogurt containers, car bumpers, appliances (#2)

PS Polystyrene Packaging foam/”peanuts”, food containers, plastic tableware, disposable cups, plates, cutlery, CD and cassette boxes

PMMA Polymethyl Methacrylate Hard contact lenses, acrylic paints, Plexiglass, rear light covers for vehicles

PTFE Polytetrafluoroethylene (Teflon) Non-stick surfaces for frying pans, plumbers’ tape, water slides, lubricant

PA Polyamides Nylon ropes, toothbrush bristles, fishing lie, machine parts, gun frames

ABS Acrylonitrile butadiene styrene Computer monitors, printers, keyboards, drainage pipes

PC Polycarbonate CD cases, eye glasses, security windows, traffic lights

PC/ABS Polycarbonate/ABS Car interior & exterior parts, mobile phone bodies

PU Polyurethane Thermal insulation, cushioning foams, surface coatings

Epoxy Polyepoxide Adhesive, 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!

monomerpolymer

monomerpolymer

Plastic: What is it?Polypropylene (PP – the 2nd 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 monomerpolymer

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?

HDPE PVC

Cellulose from wood Starch 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. H2O, HCl, etc.)

◦ Addition rxn: monomer + monomer = polymer

Plastic: How is it made?

+ =

Examples: Polyamide (Nylon), silk, polyester, proteinsDEMO!!

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

HDPE PVC

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

“…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, 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