Materials Testing - Adhesives: Part A. Understanding glues and … · 1 Blu Tack is the commercial name of a "reusable" adhesive made by Bostik. Other similar products can be used

Page|1 MaterialsTesting:Adhesives(PartA)—ASELLandReMSTEP(DeakinUniversity)

L A B O R A T O R Y L E A R N I N G A C T I V I T Y

MaterialsTesting-Adhesives:PartA.Understandinggluesandadhesives

IntroductionGluesandadhesivesareacommonpartofeverydaylife.Weusethemtostickthingsinabook,onawall,ortorepairabrokenitem.

Thedeskyouaresittingatprobablyhasaplasticlaminatesurfacegluedtoaparticleboardplank.Ifyouareinaroomwithplasterwalls,theplasterboardhasprobablybeengluedtothebuildingframe.

Animportantcomponentofcompositematerialssuchascarbonfibreandfibreglassuseglue,usuallycalledaresin.Whentheresindries(cures),thefibressticktogethermakingaveryhardandstrongmaterial.Evenparticleboardisacompositematerialmadeofwoodchipsandagluecalledformaldehyderesin.


Carbonfibreisapotentialreplacementformetalpartsinmanyproducts.Itisstrongandlightbutcurrentlyitisexpensiveandslowtomanufacture.Materialsscientistsaretryingtomakecarbonfibrecheaper,strongerandfastertomake.Oneofthekeystoimprovingcarbonfibreproductionisunderstandinghowadhesiveswork.

Inthisactivity,youaregoingtoinvestigatehowadhesivesstickthingstogether.Youwillbeabletogiveascientificexplanationoftheproblemsthatthematerialsscientistsaretryingtosolveintheirresearchoncarbonfibremanufacture.

KeyideasAdhesion(force)–adhesionisthenamegiventothetendencyofonesubstancetosticktoanothersubstancesuchasgluetopaperorwatertoglass.Araindropletstickstoawindowbyadhesiveforces.


Cohesion(force)–cohesionisthetendencyofamaterialtoholdtogetherandnotfallapart.Cohesiveforcesarethepullingforcesbetweentheparticlesofthematerialthatholdittogether.Cohesionbetweenwatermoleculesholdsadropofwatertogether.

Surface–inthisactivitythewordsurfaceisusedtorefertothepartoftheobjectormaterialtowhichtheglueisapplied.

Surfacearea–isthetotalareaofthesurfaceofanobject.Whenthinkingaboutgluesweareinterestedinthetotalsurfacetowhichtheglueisattached.Ifasurfaceisroughenedupitssurfaceareaincreases.

Force–weknowthatforcesarepushesorpulls.Forcescanbeseenatthelevelofpeople’sactionssuchaswhenapersonpushesatrolley.Butforcesalsooperateattheleveloftheparticlesinsidematerials.Forcesbetweentheparticlesattractthemtooneanother.Thestrongertheforcesthestrongerandharderthematerial.

Load–theforceappliedtoanobject.

Shear–twoadjacentpushingorpullingforces,actingclosetogetherbutinopposingdirections,causeashearingload.


Basedon

Shearstrength–theshearloadrequiredtobreakanobjectorjoint.

Failure–thebreakingofamaterialexposedtoexternalforcesuchaswhenaropebeingusedtotowacarbreaks,orwhenyoubendasticktillitbreaks.

PartA1StrengthofadhesiontodifferentsurfacesInthisactivity,youwillinvestigatethequestion:“TowhichsurfacedoesBluTackstickbest,woodorplastic?”

Materials• AsmallpieceofBluTackabout6mmindiameter.[Footnote1]

• 2icypolesticks(onewithaholeinoneend)[Footnote2]

• 2plasticstrips(onewithaholeintheend)

• Slottedbrassweights–about500g

• Sandpaper

ProcedureTheinstructionsgivenherecontainsomeofthethingsyouneedtodoforthetest.Readtheinstructionsandtrythetestoutbeforeyoustartrecordingresults.Identifyandrecordwhatyouneedtodotomakethetestafairtest.

1 BluTackisthecommercialnameofa"reusable"adhesivemadebyBostik.Othersimilarproductscanbeused.

2 Icypolestick,paddlepopstick,andpopsiclestickarealternatenamesforflatpiecesofwoodabout12cmlong,1cmwide,and2mmthick.Anysimilarproductcanbeused.


1. Sticktwoicypolestickstogetherasshownsothattheyoverlapbyadistanceequaltothewidthofthestick.

2. Hanggluedicypolesticksfromclamponastandasshown

3. Hanga50-grambrassweightthroughholeinicypolestick.Progressivelyaddweightuntilthejointbreaks.RecordintheResultstabletheloadatwhichthejointfails.

4. CloselyobservethefracturedBluTacksurface.DescribeordrawtheresultintheObservationssectionbelow.

5. Repeatthetestswiththeicypolesticksandrecordyourresults.

6. Repeatthetestsusingtheplasticstrips.Recordyourresultsandobservations.

7. Usingthesandpaperroughenthesurfaceontheendofonepieceofplasticandrepeatthetests.Recordyourresultsandnoteyourobservations.

Hint:ItisimportantthatyouuseonlyaVERYsmallpieceofBluTackotherwiseitwillspreadaroundthesidesgrippingtheedges.Asphereofabout2-3mmindiameterisenough.


FairtestWriteherewhatyouneedtodotomakethetestfair.

ResultsTest Suspendedmass(g)

Wood Smoothplastic Roughplastic

1

2

3


ObservationsYourdrawingordescriptionofthebrokenBluTackjoint.

ConclusionsWhatconclusioncanyoudrawaboutthetensilestrengthofBluTackcomparedwithitsshearstrength.


RepresentationsUselabelleddiagramstorepresentwhathappenedinthisexperiment.

DrawalabelleddiagramtoshowhowtheparticlesinsidetheBluTackstuckthetwoicypolestickstogether.Usethetermsadhesiveforcesandcohesiveforces.

Hint:InyourdrawingsrepresentthewaytheBluTackstucktothewood?ShowhowtheBluTackstickstoitself?


Drawalabelleddiagramtoexplaintheeffectofrougheningthesurfaceoftheplastic.

PartA2ComparingBluTackwithTuffTacksAnofficesupplieschainhasaproducedacheaperformofBluTack.Deviseandcarryoutatesttodeterminewhetherthenewandcheaperproductisasgoodastheoriginaladhesive.

Whatvariablesareimportantinyourtest?


Whatwillyoumeasure?Whatwillyoukeepthesame?

DescribeyourProcedure.

Recordyourresults


Whatisyourconclusion?

CopyrightandCreativeCommonsExceptinglogos,trademarksorotherthird-partycontentasindicated,thisresourceisdistributedunderaCreativeCommons‘Attribution-NonCommercial-ShareAlike’4.0InternationalLicense.PixabayimagesareusedunderaCC0PublicDomainLicense.Themoralrightsoftheauthor,IanBentley,havebeenassertedundertheAustralianCopyrightAct1968(Cth).

Page|13 MaterialsTesting:Adhesives(PartB)—ASELLandReMSTEP(DeakinUniversity)

L A B O R A T O R Y L E A R N I N G A C T I V I T Y

MaterialsTesting-Adhesives:PartB.Makingandtestingglues

IntroductionTherearemanytypesofgluesfordifferenttypesofjobs.Gluesdiffer:

• inthedegreetowhichtheyadherewhen‘dried’todifferentsurfaces

• intheirflexibility,theirstrength(i.e.thestrengthofthecohesiveforceswithinthe‘dried’glue)and

• intheirsolubilityindifferentliquids.

KeyideasGluesareusuallyliquidwhentheyareappliedbutbecomesolidwhentheydryorcure.Theprocessofbecomingsolidormoresolidcanoccurinseveraldifferentways.Thegluedriesorsetswhen:

1. thesolventorliquidpartoftheglueevaporates.Thishappenswiththetraditionalgluecalledclagthatismadeofstarchandwater.Modellinggluesalsoworkinthiswaybutthesolventisusuallysomethingotherthanwaterthatevaporatesveryquickly.

2. achemicalreaction(polymerisation)occurs.Themoleculesoftheglueformchemicalbondswithoneanother.Thisiswhathappensin‘twopart’glues.Theseglueshaveonepartcalledtheresinandanothercalledthehardener.

3. thegluecools,suchaswhenthehotgluefromahotglueguncools.


Differentgluesworkbetterondifferentsurfaces,sointhisactivitywewillcomparehowwellthegluesworkonwood,plasticandpaper.

Curing–thenamegiventothehardeningofagluewhereachemicalreactioncausesbonds(strongattractiveforces)toformbetweentheparticles

Drying–someglueshardenbecausethesolvent(liquidpart)evaporates.

HazardsWearglovesandeyeprotection.

Temperaturehazard–Whenmakinggluestheywillbehotandsticky.

Droppingweights–becarefulwhentestingyourgluesthatweightsdon’tdroponyourhandsorfeet

ActivityB1MakingGluesRecipesforfourdifferentgluesyoucanmakeathomeorinthelaboratory.

Materials• Stripsofpaperandcardboard.

• Icypolesticks.

• Ingredientsformakingtheglues.

• Heatsource.

• Stirringrodsorspoons.

• Beakersorglassjarsorcups.

Yourgroupwillbeassignedoneofthefollowinggluestomake.Usetheingredientsprovidedandfollowtheinstructions

Cornsyrupglue• Cornsyrup

• Whitevinegar


• Corn-starch

1. Inasmallsaucepan,mix180mLwaterwith35mLcornsyrupand15mLtablespoonwhitevinegar.

2. Bringthemixturetoarollingboil.

3. Inbowl,mix20gcorn-starchwith180mLcoldwater.

4. Slowlyaddthecoldmixtureintothehotmixture.Stirconstantlyforoneminute.

5. Removefromheat.

Onceithascooled,pourthemixtureintoalabelledglassjarorbeakerorcup.

(Letitstandovernightatroomtemperaturebeforeusing.)

Caseinglue• gelatine[Footnote3]

• skimmilk

• cloveoil(optional)

Thisgluecanstickglasstogether,useitinitsgelled(roomtemperature)state.

1. Pourtwotablespoonsofcoldwaterintoasmallbowl.

2. Sprinkle2packetsofunflavouredgelatineoverthewaterandsetasideforaboutanhour.

3. Heat40gskimmilktojustbelowboilingandpouritintothegelatineandwater.

4. Stirthemixtureuntilthegelatineiscompletelydissolved.

Optionally,addafewdropsofcloveoilaspreservativeifyou’renotgoingtousealltheglueimmediately.(Withcloveoil,thegluewillkeepforadayorso–whenitstartssmellinglikespoiledmilk,throwitout.)

3 Gelatineandgelatinarealternatespellingsforthesamesubstance.


GumArabicglue• 45mLgumarabic

• 15mLglycerol[Footnote4]

• 8mLwater

1. Mix45mLgumarabic,15mLglyceroland8mLwaterthoroughlyinabowlorbeaker.

2. Tousethisglue,applyathincoattoeachsurfaceandholdthepiecesfirmlytogetheruntilthegluedries.(uptoanhour)

Gelatineglue• 1packetgelatine(10g)

• 15mLglycerol

• 15mLwhitevinegar

• 60mLwater

1. Addthegelatineto15mLcoldwaterinabeaker,stirgently,letstanduntilit‘blooms’

2. Mix45mLboilingwater,thewhitevinegar,andglyceroltothegelatineandstiruntilitalldissolves.

Theresultantgluemaybecomesolidandwillneedtobewarmedtosoftenbeforeeachuse.

4 Glycerol,glycerin,glycerine,1,2,3-propanetriol,propan-1,2,3-triolandpropane-1,2,3-triolareallalternatenamesandspellingsforthesamechemicalsubstance.GlycerolistheofficialIUPAC(InternationalUnionofPureandAppliedChemistry)name.Propan-1,2,3-triolisthesystematicIUPACname.Glycerinisacommonlyusedcommercialname.


ActivityB2TestingGluesWhichisthebestforgluingwood,plastic?

Indesigningyourfairtest,youneedtoidentifytheimportantvariables.

Whatvariablewillyouchange?(independentvariable)

It is expected that students will use essentially the same procedures,variables,etcasPart1.Theremaybeminormodifications.

Whatvariableswillyoukeepconstant?(controlledvariables)

Whatvariablewillyoumeasure?

Recordtheloadneededtobreakthegluejointandrecorditinyourtable

Examinethesurfaceofthebreak.Hastheglueseparatedfromitselforhasitcomeawayfromthesurfaceofthegluedobject?

Repeatthisprocedureusingstripsofrigidplastic.


Results Failureload(g)

Gluename Wood Plastic

AnalysisDrawagraphorchartusingthedatafromyourresultstable


DiscussionandConclusionsWhichofthegluesisbestforgluingeachofthematerials,woodandplastic?

Whatevidenceareyouhaveforyourclaim?

Howconfidentareyouinyourconclusions?Isthereanydoubtinyourmind?Why?


Howcouldyouimproveyourtestingproceduretoachievemorereliableresults?

ExtensionDeviseatesttomeasuretheeffectivesofthedifferentgluesonpaper.

Designaninvestigationtotestwhetherthegluesarewaterproof.

CopyrightandCreativeCommonsExceptinglogos,trademarksorotherthird-partycontentasindicated,thisresourceisdistributedunderaCreativeCommons‘Attribution-NonCommercial-ShareAlike’4.0InternationalLicense.PixabayimagesareusedunderaCC0PublicDomainLicense.Themoralrightsoftheauthor,IanBentley,havebeenassertedundertheAustralianCopyrightAct1968(Cth).

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Materials Testing - Adhesives: Part A. Understanding glues and … · 1 Blu Tack is the commercial name of a "reusable" adhesive made by Bostik. Other similar products can be used