Chapter 9: The World of Polymers and Plastics Rayon Nylon Lycra polyurethane Teflon Styrofoam 1

Polymers are large molecules made up of long chains of monomers bonded together. Monomers (from mono meaning “one” and meros meaning “unit”) are the small molecules used to synthesize the polymer chain, like a strand of paper clips. Plastics are Polymers What is a polymer? Plastics are found everywhere 2

All plastics are polymers formed from chains of smaller molecules 3

Polymers can be classified based on the structures of their monomers Homopolymers Homopolymers consist of chains in which every monomer is identical Copolymers Copolymers (or heteropolymers) are composed of chains with two or more different types of monomers A representation of a polymer made of one type of monomer A representation of a polymer made of two different types of monomers 4

Polymers are called addition polymers when each monomer is added sequentially to the growing chain without any losses Condensation polymers are formed when each monomer combines with the loss of a small molecule (such as water) Polymers can also be classified based on the type of reaction that is used to create them 5

© 2003 John Wiley and Sons Publishers Addition polymerization is the process of linking small molecules together to form chains ethylene polyethylene 6

© 2003 John Wiley and Sons Publishers Cellulose is a natural condensation polymer Cellulose is formed by condensing glucose molecules and releasing molecules of water Cellulose is the major component of wood, paper and cotton 7

Today there are over 60,000 synthetic polymers Three of the most common polymers are: 8

What makes one polymer different from another? The other three of the “Big Six” are: 9

Separating plastics of different densities with a mixture of isopropyl alcohol (rubbing alcohol) and water. The more dense plastics sink; the less dense plastics float. © 2003 John Wiley and Sons Publishers Plastics have a wide range of properties The properties of plastics depend on their molecular structures 10

Polymer Properties Thermoplastics Thermoplastics – polymers that soften when heated but become firm when cooled (examples: water bottles, compact discs) Thermosetting plastics Thermosetting plastics – soft enough to be molded but become firm when heated (examples: plastic pipes, car parts) Elastomers Elastomers – polymers that stretch easily but return to their original shape (example: rubber) 11

© 2003 John Wiley and Sons Publishers Rubber is a natural elastomer Rubber forms by addition polymerization of isoprene 12

© 2003 John Wiley and Sons Publishers Untreated natural rubber becomes soft and sticky when it is warm When you heat rubber with sulfur it becomes modified to allow it to stay elastic when it is warm Vulcanized Rubber The elastomers neoprene and styrene-butadiene rubber make up the bulk of auto and truck tires 13

© 2003 John Wiley and Sons Publishers A synthetic copolymer is now used in place of most natural rubber This is an addition copolymer formed between two different monomers, styrene and butadiene 14

© 2003 John Wiley and Sons Publishers Another synthetic elastomer is also used because of its resistance to heat and solvents This is an addition homopolymer called neoprene 15

Some applications of different types of plastics 16

© 2003 John Wiley and Sons Publishers Nylon is another synthetic condensation copolymer It consists of alternative monomers of diaminohexane and adipic acid 17

 Nylon refers to a whole class of polyamides, the most common of which in the U.S. is nylon 6,6, developed by DuPont chemist Wallace Carothers in the 1930s by polymerizing diaminohexane and adipic acid.  Nylon is most familiar as the fiber used in stockings and carpets, but much of it also goes to making engineering polymers.  In 2008, these polymers made up about 44%, or about 4.5 billion lb, of global nylon demand.  The polymer is uses in applications that get a lot of wear and tear, such as power-tool housings, door handles, brackets, and structural components found under car hoods or in baby carriages.  The basic advantage of nylon is that it combines classic thermoplastic properties—low weight and high capability of integrating different functions into one component—with its specific material properties, namely high thermal and chemical stability.  This enables nylon to substitute for many metal or other material applications in terms of weight, cost, and performance. Uses for Nylon 18

Stretching or “necking” a plastic bag The molecular rearrangement that occurs as PE is stretched Pulling on a piece of PE Why does the plastic stay distorted after it is pulled? Because the molecular structure is changed ! 19

Branching alters the physical properties of PE Low density PE (LDPE) soft, stretchy, not very strong High density PE (HDPE) greater rigidity and strength linear PEbranched PE 20

The conditions under which a polymer is formed can change its properties, even if the molecular formula is the same 21

Different properties dictate different uses 22

© 2003 John Wiley and Sons Publishers PET PET ( poly(ethylene terephthalate) a polyester copolymer a polyester copolymer PET consists of alternative monomers of ethylene glycol and terephthalic acid 23

© 2003 John Wiley and Sons Publishers Polystyrene – an addition homopolymer polystyrene sheetspolystyrene rodspolystyrene foam 24

© 2003 John Wiley and Sons Publishers PVC – a highly versatile homopolymer safety glass containing a PVC film 25

Polyurethane – another highly versatile homopolymer Polyurethane is an incredibly resilient, flexible, and durable manufactured material that can take the place of paint, cotton, rubber, metal, and wood in thousands of applications across all fields. Polyurethane might be hard, like fiberglass, squishy like upholstery foam, protective like varnish, bouncy like rubber wheels, or sticky like glue. Latex paints are based on water soluble polymers 26

Changing the properties of plastics Plasticizers Plasticizers – makes polymers more flexible Pigments Pigments – add colors to polymers Fillers Fillers – change the bulk properties of plastics (increased strength) Stabilizers Stabilizers – improve polymer properties ( antioxidants, UV stabilizers, heat stabilizers) 27

Plastics – problems with disposal Unlike many natural materials, synthetic polymers are not biodegradable Polymers are also resistant to breakdown by water and sunlight Most polymers cannot be incinerated because they produce toxic gases when burned So how do we dispose of plastics ? 28

Plastics – disposal solutions Short term solution – recycling Long term solution – modifying plastics to make them degradable Incorporate a biodegradable polymer, such as starch or cellulose Introduce chemical activators to make polymers susceptible to sunlight and moisture Biodegradable Plastics plastics that will naturally decompose made from corn-derived sugar polymers production is expected to reach 50 billion pounds within 5 years this would be a 10% market share 29

The heaviest hitter in the beverage industry is taking a swing at biobased materials. This year, Coca-Cola has introduced bottles for its Dasani-brand water with up to 30% biobased content. Beverage bottles are typically created from polyethylene terephthalate (PET), made, in turn, by reacting ethylene glycol and terephthalic acid. The ethylene glycol in the new Dasani bottles will be derived from sugar and molasses, rather than its usual origin in petroleum and natural gas. Coca-Cola's goal is to introduce bottles made with materials that are 100% recyclable and renewable. Biobased Plastic Bottles Alex Tullo, Chemical & Engineering News 30