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CANADIAN PLASTICS INDUSTRY ASSOCIATION

2TABLE OF CONTENTS

SCIENCE: MATERIALS & TECHNOLOGYPages 3-12 TEACHER’S NOTES

ACTIVITY CARDSCard Number THINKING IN TERMS OF PROPERTIES

S-1 Recognizing Plastics at HomeS-2 Recognizing Plastics in CarsS-3 Extending Your VocabularyS-4 Physical PropertiesS-5 Why Plastics?S-6 Matching Properties to ProductsS-7 Not All Products Are Perfect

GETTING TO KNOW PLASTICSS-8 What Are Plastics Made From?S-9 Major Categories of PlasticsS-10 Plastics In PackagingS-11 High-density and Low-density PolyethyleneS-12 A Model for Elastomers

TESTING PROPERTIES OF PLASTICSS-13 Mass And VolumeS-14 Relative DensityS-15 ConductivityS-16 Properties of Food WrapsS-17 Testing Some Materials for Puncture Resistance

WORKING WITH PLASTICSS-18 Changing Properties with AdditivesS-19 Engineering PlasticsS-20 Designing with PlasticsS-21 Some Environmental Aspects of Plastics:

The Automobile bumper — A Case Study

3SCIENCE: MATERIALS & TECHNOLOGY

THINKING IN TERMS OF PROPERTIES

Card S-1 — Recognizing Plastics At Home

An amazing variety of products are madefrom plastics. You may want to refer to CardMB-21 for some types of products to con-sider.

You may want to organize a scavenger hunt.Label several cards, “Things in the gymmade of plastics, “Things in a car made ofplastics” and “Things in a classroom made ofplastics”. Send students out to search ingroups. Set a time limit.

Ask students to categorize their findings andshare results with the class in the form of achart.

According to the Kirk-Othmer Encyclopedia ofChemical Technology (Wiley, New York, 1982),a standard chemical reference, a plastic isdefined as a material that:a) contains one or more organic polymeric

substances of high molecular weight asan essential ingredient,

b) is solid in its finished state, andc) can be shaped by flow at some stage in

its manufacture or processing.

However, in a court case in the United States,an expert witness for the State of New Yorkstated, “Plastics is a vague amorphous termthat does not inform the Court about theissue at hand.”

The very first plastics were made from agroup of substances called phenols, whichwere derived from coal tar. Today most plas-tics are made from oil and gas, but someplastics are now being made entirelyfrom substances of vegetable origin.

Card S-2 — Recognizing Plastics in Cars

Card S-3 — Extending Your VocabularyThe physical properties most often introducedat this level do not include many propertiesstudents encounter in their lives. Some of theseproperties have very specific technical defini-tions that are usually defined in engineeringschools. The intent of this activity is to encour-age a general understanding of terms like these,and to encourage students to use the wordswithout worrying about technical definitions.Encourage students to start thinking aboutproducts in terms of their properties, and touse a wide vocabulary.

As an alternative, you may wish to write thewords on cards and distribute them amongsmall groups of students. Have them check adictionary for definitions, or have the groupsdevelop working definitions. Each groupshould share the following information withthe whole class:a) a working definition of the property,b) a material having this property, andc) a circumstance where the property is important.Some students may wish to create a chart for awall display.

Card S-4 — Physical PropertiesFocus on properties identified in you curricu-lum. You may wish to add brief discussions ofchemical or biological properties. Such adiscussion may help students identify thedifference between a physical property andother kinds of properties.

Card S-5 — Why Plastics?You may want to design a few simple experi-ments to demonstrate some of these properties.The experiments found in Testing Properties ofPlastics (see Cards S-13 to S-17) may fit wellhere.

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Card-S-6 — Matching Properties to Products

Use this card to extend stu-dents’ understanding of proper-ties to other materials besidesplastics. You may want to askthe class to prepare a collage ofpictures of products and usethis to make the link between products andproperties.

Card S-7 — Not All Products ArePerfectCards S-6 and S-7 are intendedto make explicit the connec-tion between products andtheir properties. Use this cardto emphasize that there isalways room for improvement

and there are always business opportunitiesto make a better product.

SAFETY NOTEDo not heat plastics in anopen flame. Caution shouldbe taken to avoid accidents& injury.

GETTING TO KNOW PLASTICSCard S-8 — What Are Plastics Made

From?Plastic resins are usually derived from oiland natural gas using complex chemicalprocesses.

Although they are very important materialsand are manufactured in large quantitiestheir production uses a small fraction ofCanada’s annual consumption of oil andnatural gas.

Card S-9 — Major Categories of Plastics

ThermoplasticsThermoplastics start as resins. They meltwhen heated and harden when cooled. Theyare easily recycled because they can bemelted and remoulded repeatedly.

Many household containers are thermoplas-tics. They can be identified by a symbolstamped into the plastic.

The table on the following page lists most ofthe thermoplastics students will encounter,along with their identification symbols.

Other thermoplastics of commercial impor-tance are high cost, low volume engineeringthermoplastics, which have higher physicaland mechanical properties for very specificstructural applications.Here are some examples:

nylonspolycarbonatesthermoplastic polyurethanespolyphenylene oxidesacetalsthermoplastic polyimides

ThermosetsThermosets usually start as liquids. Whenthey are heated they form chemical bonds.This leads to very strong crosslinks. Theprocess is similar to the process of cooking anegg. The cooled product is solid. It does notsoften or melt when reheated. Scrap materialfrom thermoset products cannot be recycledusing technologies designed for therecycling of thermoplastics.

There are several common types ofthermosets:

polyestersepoxiespolyurethane foamsphenolics

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PP

CommonThermoplastics Properties and Uses

Polyethylene terephthalate Density 1.29 - 1.40g/cm3. Sinks in water.Transparent and shiny.Uses: carbonated drinks bottles.

High-density Polyethylene Density 0.94 - 0.96g/cm3. Floats on water.Relatively hard, difficult to scratch with fingernail. Film has a crinkly feel.Uses: department store bags, bottles for milk,bleach and other household chemicals, drums,crates, pails and toys, pipes and coatings forwire and cables.

Polyvinyl chloride Density 1.38 - 1.45 g/cm3. Sinks in water.Rigid PVC is hard and stiff. Fairly easy to cut.Uses: bottles for cooking oil, window cleaner,liquid detergent, house siding, sewer pipes.

Low-density Polyethylene Density 0.92 - 0.94 g/cm3. Floats on water.Flexible, softer than HDPE, easily scratchedwith fingernail. Waxy feel.Uses: grocery and garbage bags.

Polypropylene Density 0.90 g/cm3. Floats on water.High resistance to heat and chemicals.Uses: margarine tubs, yogurt containers, fastfood microwave trays.

Polystyrene Density 1.05g/cm3. Sinks in water.Rigid polystyrene is hard and stiff. It has acharacteristic ring when tapped.Uses: food containers, pen barrels.Expanded polystyrene is usually white.Crumbles when cut.Uses: meat trays, disposable cups, insulation,packing material.

PETE

HDPE

PVC

LDPE

PS

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3

4

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6

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Many polyesters are made into fibres forclothing, carpets and other fibre products.They can be reinforced to form fibreglassreinforced plastics (FRPs).

Epoxies are used in paints,adhesives, and composite orreinforced plastics.

Polyurethanes are most oftenmade into foams.

Phenolics have many uses.They are the easiestthermosets for studentsto test. Small squares ofcountertop material or electri-cal wall switch plates make convenient test-ing samples.

ElastomersNatural rubber, synthetic rubber, syntheticsponges, chewing gum — all are examples ofelastomers. Elastomers processed into foamare used for cushions, padding and insula-tion. The amount of crosslinking in anelastomer has an important effect on itsproperties. For example,rubber used for tires musthave many crosslinks to makeit more durable.

These types of plastics areboth elastomers and thermoplastics:

styrene-elastomerpolyurethane- and polyester-polyetherpolyolefine blends;thermoplastic polyolefines

Thermoplastic elastomers combinethe elastic properties of rubber withthe strength and melting propertiesof thermoplastics. They have the

SAFETY NOTE

Do not allow students toheat plastices in an openflame.Use a hot needle to testwhether a plastic melts.Remind students that a hotneedle looks like a coldneedle. Making a mistakecan cause a small burn.

crosslinks of elastomers, but the links can beundone by heat. They can be melted andremoulded repeatedly. Thermoplasticelastomers are used for footwear, adhesives,

sealants, moulded tires andbumpers, and extruded gas-kets, hoses and covers forwires and cables.

Card S-10 — Plastics in Packaging

This topic is examined from anenvironmental point of view inCards E-17 - E-23 found in thePlastics and the Environmentmodule.

Answers to Questions3. Plastic bottles weigh much less than glass

bottles with the same capacity. Plasticbottles and other plastic packaging use upless energy for manufacture anddistribution. The mass of a one-litre plasticbottle is about 6 per cent of the mass of aone-litre glass bottle.

4. In Canada the refilling of plastic foodcontainers is discouraged. Onenever knows to what use acontainer may have been putprior to reuse. For examplesomeone might have storedgasoline or pesticide in a soft

drink bottle. Plastics may absorb the sub-stance and simple washing can not re-move it.

Over the least decade Canada has devel-oped a substantial infrastructure to collectand recycle plastic containers. These con-tainers may be remoulded into “new”containers for non-food applications, forexample oil bottles.

SAFETY NOTE

Students should not testepoxies.

75. Students might identify factors such as:• environmental impact of the package

manufacturing process• cost of manufacturing the package• weight and bulk of the package. The

higher these are, the more transportationwill cost, and the greater will be theamount of fuel used in transportation andthe environmental impact of that use offuel.

• ability to protect the product• attractiveness of the package• ability of the package to present informa-

tion to the consumer• “end fate” of the package

Card S-11 — High-density and Low- density Polyethylene

Density is a difficult concept for many stu-dents. This model may help students betterunderstand density. Collect glass, metal,wooden and plastic beads of the same size.The beads can represent molecules. Put themin identical glass jars. This produces differentmasses in the same volume . The jar with thehighest mass in the same volume has thehighest density.

You might introduce this activity by display-ing a liquid bleach detergent bottle madefrom LDPE and a bleach bottle made fromHDPE. Look for these signs on the bottles:

While the difference in density may not beapparent, students should notice the differ-ence in hardness and rigidity. Challengestudents to account for these differences inproperties.

Answers to Questions1. High-density polyethylene contains few

branches. As a result, more polymer

HDPE LDPE

strands can pack together in a given vol-ume.

2. The tighter packing of unbranched poly-mer chains also accounts for HDPE beingharder and more rigid, although otherfactors such as crosslinks and additivesalso have an effect.

3. Polymer chains typically contain fromseveral hundred to a few thousand repeat-ing units. It would be impractical andunnecessary to use this many connectiblecubes. A more important problem with themodel is that unbranched chains can onlybe constructed straight, and branches canonly be made at certain angles to the mainchain.

Low-density polyethylene has a density inthe range of 0.92 - 0.94g/cm3, while the den-sity of high-density polyethylene is 0.94 - 0.96g/cm3. The densities of the models will, ofcourse, be different from these, but the modelcan be helpful in introducing the idea ofdensity.

Card S-12 — A Model for ElastomersMethodThe quantity of spaghetti and boiling watercan be varied according to the class size. Thecooking instructions are standard directionstaken from a packet of spaghetti.

Answers to Questions1. Freshly cooked spaghetti can be poured

from one container to another, much like aliquid. Also, the spaghetti takes on theshape of the container, an important prop-erty of liquids. The few crosslinks betweenstrands can easily be broken.

2. After about 30 minutes, spaghetti will nolonger pour as it did when freshly cooked.

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8It will not take on the shape of its containerbut it can be easily deformed. These areproperties of a solid rubber material, anelastomer. Students are likely to describethe spaghetti as “rubbery”. This change isthe result of spaghettistrands sticking together,forming crosslinks.

3 After several hours thespaghetti will be harderand less rubbery. Therewill be more crosslinksbetween strands and thecrosslinks will be stronger.The spaghetti will resemblea thermoset rather than anelastomer.

ExtensionsSilly Putty® behaves like a viscous liquid.When pulled gently it deforms but is notelastic. When pulled quickly it breaks, and,when dropped it bounces. The crosslinks

between polymer chains inSilly Putty are very weak. Agentle force allows the SillyPutty to flow, but a quickpull will break the crosslinks,snapping the material.

ReferenceGail Marsella, ChemMatters,1986, pages 15-17.

Students must be super-vised if they boil the waterfor this exercise. An adultshould drain the waterfrom the spaghetti. Cautionstudents that cooked spa-ghetti will stay hot forseveral minutes

TESTING PROPERTIES OF PLASTICSCard S-13 — Mass and VolumeStudents should have samples of both paperand expanded polystyrene cups. They do notneed the same number of each type of cup ifthey find the average mass for each type.

There are different ways to compare thevolume of material used to make the cups.Students might simply crush the cups andmake a pile of those that are the same, andthen compare heights. A similar, but slightlymore accurate method, is to tear the cups intotiny pieces. The pieces could be packed into agraduated cylinder, or measuring cup, andthe volumes measured.

Answers to Questions4. A landfill can handle a certain volume of

garbage, so volume is more important thanmass in landfills. Other important landfillconsiderations include the production ofmethane gas and leaching of toxic chemi-cals into the groundwater. Because poly-styrene is chemically inert, it does notbreak down and release gases or otherproblem chemicals.

Students may mention that it is important for materials to biodegrade in a landfill.

This is a common misconception.Landfills consist of layers of crushedgarbage and soil. Biodegradation requiresmoisture, bacteria, warm temperaturesand especially air. Even biodegradablematerials do not biodegrade in landfills,because they are not exposed to air. Forexample, if last night’s leftover vegetables

were dumped in a landfill instead ofbeing composted, they would still berecognizable many years later.

5. The alternatives to landfilling disposablecups are incineration, recycling, or reus-able cups. Students should be made tounderstand that each option has draw-backs: incineration must take place inspecial plants at high temperatures; papercups cannot be recycled because of theglue used on the seams; and reusablecups must be washed, creating a differentwaste and energy problem.

SAFETY NOTE

9ExtensionStudents might like to know the relative costsof different types of cups, how many therestaurant uses, and justification for usingthis type of cup, especially if the student’sinvestigations suggest a different type mightbe better.

There are several cards found in Plastics andthe Environment that could be integrated atthis point. If you wish to discuss landfillsnow, use cards E-10 to E-16.

Card S-14 — Relative DensityA variety of different plastics should be used.Some types of plastics have a range of densi-ties because of factors such as branching. Thefollowing values may be useful:

SubstanceDensity (g/cm3 )polypropylene 0.90low-density polyethylene 0.92-0.94high-density polyethylene 0.94-0.96polystyrene 1.05acrylonitrile butadiene styrene 1.1(ABS)polymethylmethacrylate 1.2rubber 1.2polyvinyl chloride 1.4polyethylene terephthalate 1.3-1.4

The density of a saturatedsalt solution is 1.2 g/cm3.

Polypropylene andpolyethylene will float onwater. As salt is added, poly-styrene will begin to float, followed by ABSand perhaps polymethylmethacrylate andrubber. Polyvinyl chloride and polyethyleneterephthalate will not float even when thesolution becomes saturated.

Answers to Questions1. The plastic strips do not have to have

either the same mass or volume. If thevolume increases, so does the mass. Thekey property is density, the ratio of mass tovolume. This is a fixed property of thematerial. Both forms of polyethylene,LDPE and HDPE, and polypropylene (PP)will float on water. Corn oil has a densityof 0.92 g/cm3 and can be used to separatepolypropylene (floats) and polyethylene(sinks). Linseed oil has a density of 0.94 g/cm3, so it could be used to separate HDPEfrom LDPE. However, it would be easier torely on other characteristics such as thewaxy feel of LDPE and harder, more rigid

properties of HDPE.

Card S-15 — ConductivityThis experiment provides experience ingraphing, and in interpreting the meaning ofthe slope of the graph. This exercise does notrequire mathematical calculations of specificheat capacities of the different cups.

Card S-16 — Properties of Food Wraps

This topic is also in cards E-18 and E-23. Ithelps establish connections between purescience topics (properties of materials) andapplications of science.

A food package must a) ensure the safety andnutritional value of food year-round; b) protect the qualityof the product, from itsmanufacture to its consump-tion; and c) meet consumerneeds and preferences.

To meet food safety requirements, the pack-age must:• meet all regulations that apply to the pack-

age materials,• provide acceptable package integrity

through final consumer usage,• provide a barrier to microorganisms and

other potential contaminants,

Students using hot watermust be supervised by anadult.

SAFETY NOTE

10• provide protection against infestation by

insects, rodents and other vermin, and• withstand distribution, storage, and any

other functions.

To maintain product quality, the food pack-age must provide:• a barrier to prevent transfer of flavours

and odours• an oxygen barrier to preserve colour, fla-

vour, and nutrients,• a barrier to prevent moisture transfer• a carbon dioxide barrier to retain internal

pressure (e.g. carbonated beverages)• a barrier to contain gases such as nitrogen

or carbon dioxide (used as preservatives incontrolled or modified atmosphere packag-ing),

• a light barrier for vitamins or colours thatbreak down in light,

• a thermal barrier for products above orbelow room temperature.

To meet consumer needs and preferences, thepackage should:• provide critical information on labels (e.g.

product brand identification, weight,ingredients list, manufacturer’s name and

Card S-18 — Changing Propertieswith Additives

Answers to Questions1. Plastics for raincoats might contain plasti-

cizers, UV stabilizers, fire retardants, bio-cides, antistatic agents, and antiblockagents.

2. Home installation (polystyrene), electricalwire insulation, electronic components allcontain fire retardants.

address, codes, date, preparation instruc-tions, nutritional profile),

• discourage and give evidence of tamper-ing,

• display contents (in some cases), and• open and reclose, be microwavable, dis-

pense or serve, resist shattering, and en-sure safe handling.

Specific package requirements will vary fromfood to food, but these lists highlight themany concerns of the packager.

ReferenceHorizons, Volume 1, Issue 2, December 1991.

Card S-17 — Testing Film forPuncture Resistance

Students should realize that this test providesinformation about how different films be-have in a very specific way. Films have otherproperties that should be considered — afterall, we do not buy films to drop weights onthem. Encourage students to think about theproperties of films, and how these propertiesrelate to how we use them. For example, wewould use only aluminium foil in an oven,but never in a microwave.

WORKING WITH PLASTICS3. Additives often remain in plastic after it’s

been recycled. These additives, for exam-ple colourants, limit the possible uses forthe recycled plastic. The recycled plastic isoften used as a middle layer in multi-layered containers.

Card S-19 — Engineering PlasticsThe ability to tailor a raw resin for a widerange of specific applications by suitableadditives is one of the great advantages thatplastics offer.

11Card S-20 — Designing with

PlasticsUse this card as a means of getting studentsto think about characteristics of careerswhich might suit them. Have them identifyreasons for their choice. Some science teach-ers may want to consider integrating aselection of cards from The PlasticsManufacturing Business section.

Card S-21 — Case Study: TheAutomobile BumperYou may want to chooseanother product and havestudents investigate its usefollowing this model.

Supplemental Card 1 -Teacher DemonstrationRecycling a PlasticThis activity card can begiven to students if youwish. Students can preparethe mould, tear up the piecesof polystyrene, and set upthe heating apparatus. Youshould actually heat thepolystyrene.

MethodThe key to a successfuldemonstration is to use very small pieces ofpolystyrene and to heatthem slowly at a low temperature.

Answers to Questions1. Thermoplastics soften when heated and

can go through many cycles of heatingand moulding. Thermosets do not softenwhen heated.

SAFETY NOTE

Wear safety glasses duringthis demonstration, both foryour own safety and to set agood example for the stu-dents.

Perform this demonstrationin a fume hood. If one is notavailable, use a well ventedarea.

If the polystyrene catchesfire, avoid breathing thegases and extinguish it withwater immediately.

2. Different thermoplastics soften at differ-ent temperatures. As a result unsortedmixtures of different plastics have limitedvalue and applications.

A major problem with recycling householdplastics has been that so little plastic has beencollected in the past. That situation ischanging. Many major collection initiativeshave been started. Recyclers can now collectsufficient raw material to ensure an economi-

cally viable operation.Students should be madeaware that plastic waste fromindustry is recycled. Onealternative to recyclinghousehold plastic waste is toincinerate it. The energyreleased through incinerationis about the same as thatreleased by an equal mass ofoil. Incinerators that burnplastics operate at hightemperatures. That keepspotentially harmful gasesand ash well below regulatedlimits.

12TEACHER DEMONSTRATION: RECYCLING A PLASTIC

Thermoplastics become soft when heatedand can be moulded into a new shape. Thisprocess can be repeated, which makesthermoplastics goodmaterials for recycling.

Problem

To melt polystyrene (athermoplastic) and mould itinto a new shape.

Materials

polystyrene coffee cupor tart cupaluminium foilwire gauzebunsen burnertripod

a. Make an aluminium mould in any shape,using either a piece of aluminum foil, ora small tart cup.

b. Tear the coffee cup intothe smallest pieces possible.Each piece should be nomore than a few squaremillimetres. Place the piecesinto the mould.

c. Use a low flame to gentlyheat the polystyrene in themould. The polystyrene willmelt and solidify in the

shape of the mould when cool.

Questions

1. Why are thermosets not recyclable in thesame way as thermoplastics.

2. A mix of different thermoplastics isdifficult to heat and remould. Why doyou think this is so?

SAFETY NOTEDo this demonstration in awell vented area. A fumehood is ideal.

Avoid overheating polysty-rene. If it catches fire, coverit with water and removefrom heat.

Supplemental Card 1