POLYMERS“Plastics”

Third GenerationCAPT Science Preparation for

Strand II: Chemical Structures and Properties

What is a Polymer?Any of numerous natural and synthetic

compounds of usually high molecular weight consisting of up to millions of repeated linked units (monomers), each a relatively light and simple molecule.

Polymerization

Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain.

Natural Polymers(Biopolymers)

Examples:

Cellulose Shellac Amber Proteins Nucleic

Acids

Synthetic Polymers

Examples: Nylon Neoprene PVC

Polystyrene Silicone Silly Putty

®

Fractional Distillation

Plastics (synthetic polymers) can come from crude oil. Within crude oil are many different substances such as gasoline, jet fuel, heating fuel etc. To separate these the fractions or parts the mixture is heated. When each part or fraction’s boiling point is reached, that part comes off as a vapor and is separated from the mixture.

Cracking

We do not obtain enough gasoline from fractional distillation but the yield can be increased by cracking. In cracking, longer-chain hydrocarbons like lubricants (16+ carbon atoms) are broken into shorter chained fractions like gasoline with 5 to 12 carbons (ex. Octane = C8H18)

Some Common Synthetic PolymersName(s) Formula Monomer Properties Uses

Polyethylenelow density (LDPE)

–(CH2-CH2)n–ethyleneCH2=CH2

soft, waxy solid film wrap, plastic bags

Polyethylenehigh density (HDPE)

–(CH2-CH2)n–ethyleneCH2=CH2

rigid, translucent solid electrical insulationbottles, toys

Polypropylene(PP) different grades

–[CH2-CH(CH3)]n–propyleneCH2=CHCH3

atactic: soft, elastic solidisotactic: hard, strong solid

similar to LDPEcarpet, upholstery

Poly(vinyl chloride)(PVC)

–(CH2-CHCl)n–vinyl chlorideCH2=CHCl strong rigid solid pipes, siding, flooring

Poly(vinylidene chloride)(Saran A)

–(CH2-CCl2)n–vinylidene chlorideCH2=CCl2

dense, high-melting solid seat covers, films

Polystyrene(PS)

–[CH2-CH(C6H5)]n–styreneCH2=CHC6H5

hard, rigid, clear solidsoluble in organic solvents

toys, cabinetspackaging (foamed)

Polyacrylonitrile(PAN, Orlon, Acrilan)

–(CH2-CHCN)n–acrylonitrileCH2=CHCN

high-melting solidsoluble in organic solvents

rugs, blanketsclothing

Polytetrafluoroethylene(PTFE, Teflon)

–(CF2-CF2)n–tetrafluoroethyleneCF2=CF2

resistant, smooth solid non-stick surfaceselectrical insulation

Poly(methyl methacrylate)(PMMA, Lucite, Plexiglas)

–[CH2-C(CH3)CO2CH3]n–methyl methacrylateCH2=C(CH3)CO2CH3

hard, transparent solid lighting covers, signsskylights

Poly(vinyl acetate)(PVAc)

–(CH2-CHOCOCH3)n–vinyl acetateCH2=CHOCOCH3

soft, sticky solid latex paints, adhesives

cis-Polyisoprenenatural rubber

–[CH2-CH=C(CH3)-CH2]n–isopreneCH2=CH-C(CH3)=CH2

soft, sticky solid requires vulcanizationfor practical use

Polychloroprene (cis + trans)(Neoprene)

–[CH2-CH=CCl-CH2]n–chloropreneCH2=CH-CCl=CH2

tough, rubbery solid synthetic rubberoil resistant

Resin Identification CodeSymbol Abbreviation Polymer Type

PET or PETE Polyethylene Terephthalate

HDPE High Density Polyethylene

PVC Polyvinyl Chloride or Vinyl

LDPE Low Density Polyethylene

PP Polypropylene

PS Polystyrene

Other Polymers or blends of polymers that do not fall into

the other 6 classifications.

Properties of Polymers

Polymers can be very resistant to chemicals.

Polymers can be both thermal and electrical insulators.

Generally, polymers are very light in weight with significant degrees of strength.

Testing Plastics

tensile strength - the amount of pulling force placed upon a material before it breaks

abrasion resistance - toughness of material against scraping, scuffing or scarring

puncture resistance - ability of a material to keep moving objects from perforating the surface

Properties of Polymers cont.

Polymers can be processed in various ways. 

Polymers are materials with a seemingly limitless range of characteristics and colors.

Polymers are usually made of petroleum, but not always. 

Polymers can be used to make items that have no alternatives from other materials.

• Chain length

• Chain branching

• Interchain bonding

Three factors that influence the degree of crystallinity (or “stiffness”) are:

The importance of the first two factors is nicely illustrated by the differences between HDPE and LDPE.

HDPE: High Density Polyethyleneand LDPE: Low Density

Polyethylene POLYETHYLENE produced in greater quantity than any other

synthetic polymer  resistant to chemical attack, cheap to produce

HDPE vs LDPE HDPE is composed of very long

unbranched hydrocarbon chains. These pack together easily in crystalline domains that alternate with amorphous segments, and the resulting material, while relatively strong and stiff, retains a degree of flexibility.

In contrast, LDPE is composed of smaller and more highly branched chains which do not easily adopt crystalline structures. This material is therefore softer, weaker, less dense and more easily deformed than HDPE. As a rule, mechanical properties such as ductility, tensile strength, and hardness rise and eventually level off with increasing chain length.

Cross-linking

Cross-linked Polymers have a web-like pattern as in a net or hammock

Properties: extremely strong and difficult to tear

Ex’s like Threaded bottle caps, and Rubber tires are Thermoset Polymers

Rubber Tires: Example of Cross-linking

Vulcaniztion involves cross-linking rubber. By adding sulfur, rubber becomes more durable and prevents the polymer from moving independently so that when a stress is applied the rubber deforms but reverts back to its original shape when the stress is released.

Thermoset Polymers

A Thermoset is a polymer that solidifies or “sets” irreversibly when heated or cured. A thermoset polymer can’t be softened once “set”. Thermosets are valued for their durability and strength and are used extensively in automobiles and construction including applications such as adhesives, inks, and coatings.

The most common thermoset is the rubber truck and automobile tire.

Thermoplastic PolymersA Thermoplastic is a polymer in which the molecules are

held together by weak secondary bonding forces that soften when exposed to heat and return to its original condition when cooled back down to room temperature. When a thermoplastic is softened by heat, it can then be shaped by extrusion, molding, or pressing.

Examples include milk jugs and carbonated soft drink bottles.

The End Life of PolymersDurables vs. Non-Durables

Products with a useful life of three years or more are referred to as durables. They include appliances, furniture, consumer electronics, automobiles, and building and construction materials.

Products with a useful life of less than three years are generally referred to as non-durables. Common applications include packaging, trash bags, cups, eating utensils, sporting and recreational equipment, toys, medical devices and disposable diapers.

What do we do with Polymers when they are no longer

useful?Three Options

and their consequences

1. Disposal in a landfill

2. Incinerate3. Recycle

Disposal in a landfill

Polymers are fairly resistant to chemicals and therefore would take a very long time to decompose if just buried in a landfill.

In the meantime, the waste polymers take up a lot of space and could possibly decompose or react with other materials that might eventually result in compounds that could be potentially harmful to the environment.

IncinerateThe burning (combustion) of polymers produces

harmful gases that are toxic to the environment.

Recycle - The best choice! Mechanical

Recycling Feedstock

Recycling Source Reduction

Mechanical RecyclingOnce collected, reclamation is the next step

where the plastics are chopped into flakes, washed to remove contaminants and sold to end users to manufacture new products such as bottles, containers, clothing, carpet, plastic lumber, etc.

Feedstock RecyclingPyrolysis (heating without oxygen) and

other chemical recycling is a special case where condensation polymers such as PET or nylon are chemically reacted to form starting materials.

Source Reduction Use less! Redesign products and packaging that uses less

polymer material.

Reduce the amount the amount of polymer products that are purchased.

Clean and Reuse the polymer products that have been purchased.

What is the first question you are asked at the grocery store checkout:

paper or plastic?

Paper bags can be recycled. Plastic bags are being recycled in many places, with about 50% of supermarkets now having recycling programs for plastic bags.

However, a stack of 1,000 paper bags is 46 inches high and weigh 140 pounds. A stack of 1,000 plastic bags is only 4 inches tall and weighs 16 pounds. That is a 124 pound savings.

When you translate these weight and volume differences into transportation efficiencies, it takes seven trucks to haul the same number of paper bags as can be hauled by only one truck carrying plastic ones.

Convinced you should stick with plastic bags ?

Extra credit points to attend the 5:30 pm showing of the movie “Bag-It” at the Darien Library, this Sunday March 5.

There will be a sign-in sheet.