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)
a polyester
◦ Carbon backbone + side chains
◦ (N, O, S, Cl, F sometimes mixed in – these are called ‘heteroatoms’)
◦ Change the monomer, change the properties
Polymer
Uses
PES
Polyester
Textiles, synthetic fibers, Resin, films
PETE
Polyethylene terephthalate
Drink bottles, chip bags, Textiles, fibers, PB jars, microwavable packaging (#3)
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
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
Polymethyl Methacrylate
Hard contact lenses, acrylic paints, Plexiglass, rear light covers for vehicles
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
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
PE
PVDC
PMMA
PTFE
PC/ABS
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)
monomer
polymer
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)
monomer
polymer
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!
Plastic: What is it?
Polypropylene (PP – the 2nd most produced plastic) and Polystyrene (PS)
POLYPROPYLENE
(PP)
monomer
polymer
POLYSTYRENE
(PS)
monomer
polymer
Properties:
◦ Lightweight
◦ Strong & impact-resistant
◦ Good air & moisture barrier
◦ Intrinsic viscosity
(ability to flow & be molded)
Properties:
◦ Lightweight
◦ Hard & brittle
◦ Poor barrier to air & moisture
◦ Can be rigid or foamed
Bottle caps, drinking straws, yogurt
containers, car bumpers, appliances
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!
Plastic: What is it?
Polyethylene: the #1 plastic produced
HIGH DENSITY POLYETHYLENE
(HDPE)
LOW DENSITY POLYETHYLENE
(LDPE)
HDPE
monomer
monomer
polymer
polymer
Properties:
◦ Strong, hard, dense
◦ Opaque
◦ Can withstand higher temps
Properties:
◦ Flexible
◦ Transparent or opaque
◦ Tough but breakable
Detergent bottles, milk jugs, shampoo
bottles, folding chairs, food storage
containers, hard hats, gas pipelines
Grocery bags, six-pack rings, hard disk
drives, playground slides, plastic wrap
Sometimes how the polymer chains are cross-linked is most important!
Plastic: How is it made?
Start with a source of carbon
◦ Petrochemicals: compounds derived from petroleum
◦ most plastics are made from these
HDPE
PVC
◦ Renewable plant materials: cellulose, starch..
◦ plastics made from these are called ‘bioplastics’
Cellulose from wood
Starch from corn
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
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.)
+
=
Examples: Polyamide (Nylon), silk, polyester, proteins
DEMO!!
◦ Addition rxn:
monomer + monomer = polymer
+
=
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
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 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