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Science For Conservators-Book 4

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Science For Conservators-Book 4

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ClaudiaBaciuEmanuela
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‘SCIENCE FOR CONSERVATORS ADHESIVES COATINGS THE CONSERVATION UNIT Ss ston ven ‘mtn Atiyseth Ghee Sanne Kepecncrene erst stern "Slee aberian Roipetatg ice senatioratstay Serine ‘ecu Gea one ate ance = Pieomcome Sctnaiooe Smt rai esas oetarey kwon omy Rococo ‘puma emi tiheniyefcage tino Foie by The Cnr it ‘senate Conon Sater Sue Lond I¥0U msn eran Des egy abs pdt Gln Cy ld ‘nein gy Whar Toe ae Contents Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Introduction Sticking things together The chemistry of polymers Making joints with different types of adhesive The strength and stiffness of materials How long will it last? Coatings Consolidants Answers to exercises Index 10 22 46 64 90 108 120 U3 134 Preface to the 1987 Edition a eee nT eT ‘Theirs thre books in the serie Scien for Conseratrs vere produced bythe Cate Councland have teen widely acknowledged as exentl primer forthe traning of conservators who do nt areas Rave 8 scietfc background. ven those wth some since ave found tha they wefllyencapsulte te base ‘theoretical background to conservation processes and materials Having taken over the Cans ‘esponsiiiesin this eld, The Conservation Units pleased to be reprinting these dre tilesand tobe planning others nthe sri David Leigh July 1987 Introduction “Win are you” sid the Cater. ‘his was not an encouraingopenitg for a convertion. Alice pled, rather shyly, "t= I hardly knows just a present ~ at Test now who | wae when got up thie mening but think t mus have been changed several ine inet." “what do you mean by that” sid the Caterpillar sternly Explain youre” “Tear expan yf leis," si Ale, "becuse 1m got mysel, you see.” "tdont se,” said the Caerp “Cm ala can't pt mote cleary,” Alice replied very pole, "for Tcant understand itmyselt begin wth and Fring So many difeent sis in 2 day very confusing” "ont" ad the Caterple “well perhaps you havent found it oye." Ae "but when youhave w turn inte achrysai~ you wl ome day, you Know ~ and then afer that into a buts, Tshoulé tink you fea ta ie quer wont you?” “Not a bi sid the Caterpillar “Well perhaps you felings may be dere ‘nowt ould fee very gue om." “out” sid the atrplecontemptusly. "Who are yu” ‘lce's Advenures in Wonderland esis Cael, 1865, sad Alice “a ace with the enormous variety of molecular sractures whieh create the ferent properties in materials, you might be forgiven for feeling as confused a Alice Polymer chemistry is central understanding the materiales often sed in adcsives aad Coating and, cones othe unsympatstic atituce of the srerersicnas rears cena cee {ual deterration ad so on. Ther ze bound o be compromises he stones adhesive may be the mt ailicultreverse: the surac contig least permeable to pollsant ses may give 00 much los tale abject. But, aun, appecaig the Unde jing since the process involved shold ep you in ur deison-making Using This Book Tis bak I dv nto three pats joling coating, aa Consciation, and they are consdered sn thst order A numberof {sli topics are relevant al tee processes, bt mint ‘None and coberent development ofthe ebeman science topes uch asthe chemistry of polymers andthe mechanical behaviour of sls they ae allstedaced i the context of Janing aed del with thee a ally 386 neded for consideration both fining ad coating Structuring the bon a hi way means thatthe fs port by far the lngest, bu this ds not mean that joining as een given tore compechensiv or deeper tenet However docs fncan ti you ae aot ail with te sles covered in the frst chapters, you ae unlit understand Capers 6 and 7 ‘Newt the oer books ntsc, he best way owe the ‘ istostireat he beyoning and work slowly through ak 3 ht saben writen onthe assumption that You ate furl withthe scent ens and wary already covered In Book 1, Au etn Matra. and Book 2, Clea rice, you wil eed tobe Calor with the allowing jet: soliiy solutes and sent (Bok 2, Sston 3B) polar and no plar molecles (Bok 2, Sections 1C and 4) ssconday bonds betweun molecules: pole dipole: Van dee Waals hydrogen bord Bok 1 Seton 41 sd A,B 2 Séetons1C and 33) the ype an formal of commes eran compounds, [irl alae, alkene, loko ett a Ketones (Book ection 56 Rook 2 Seton) sure tension of hauls how detergents work: the wetting of futfces hydrophilic ad hydropblse walculs (Bok 2, Stone 342 an 5D) oxkltion ad reduction (Bok 2 Seton 78) Sipe denonstaions have hee ince tills clan certain pn the tex, Ne sientic wands and ems tepid in Eel type ad repeat nthe outer mangle ‘ay tlerene Cros eferences te given wee my help you (ote bask won prevens pests (ote ener hes Ete Seve) and ful decd at he cd he ask a Sticking things together In this chapter the question “What makes things stick ogee?” tackled. The requlrements of» good adhesive anda pod jin are also considered, and, aly, the characteristics, advantages aid “dnadvanagesftbe vanourtyper of adhesives used in conservation, A How do things stick together? “Te obec you del with are nepal eties, thas, they stay in cue pls, bss they are hd fgethr bythe song coheree torets ht sem fom ether ele cove or meta pay bonds fetes tr costuent sos oo 1 Chapter) ors secondary bonds beween thr oleae (Bok 2 Chapter) Ae ou know fom cmon experience ofa broken jet sup op Eeniyou tthe pcs bak together very early they wo Sick, and you cn stlsee the ne of he break alioug the ‘Reka of th ne can be extenely sal a freee os miler iti sl very re compared th ibe dnt vet sich the aes ice at ‘ne veavan why the Boke srtices connote put bk ino innate that onawieroncp wa hey ae nck vey ego: Eventbe actrees pe afghan whi ne withthe aaked eye av beg extemclysnooth reveled tore powell misop to bea any sen of rage and aioe bee Ege Li) 1s mt supring therefore date soe coe, ‘not be prety mated as tey wll oly mle oe Smicrocopicslestrare pnts and ote mat che cane wal bei between the pce =e ‘cohesive forces contaminated surfaces power mceoscope.shawing des and vas Further, mediately an objects broken, the newly created fre ture surfaces become contaminated by oxygen, water or oer ‘hema nthe envionnent. Those atoms or molecules tthe su {ace ofthe object that, prior to facture, contributed to thecobesive fonees in the material are now free to make bonds with the omminant atoms or moles. I this way mal onie By pr ‘mary bonds being formed between metal and ox)gen atoms water roles fom th atmosphere hydrogen-bond to mates sch Paper and wood leading toa thin yer of moire on the sure, ind soon.Procestes ke there are the one that have to be reversed ‘hen sm bjet is eeanedSurac contaminais adhere, i primary br secondary bonds, toa facut surface, and 0 they sobibi e r joining ofthe broken pce. Since the broken surfaces will not Join themselves together, another way most Be found. Basal, there ar tivo ways by which ied mater can be joined tgeber bite of 1 sing some srt of device that mechanically lacks the pices together (Mecham in this context mean non-chemical) 2 Usingamadbesive tht a material whic, dally ls the gaps Fckny strong and rigid interface eticen the plc. Sewing torn pieces of fabric together is an obvious example of, ‘mechani locking and sis the us of Screws. rivets and dowels The jong mechanism does pt depend onany primary o Sean Ary tending between the locking device and the pieces of the ject, Of ours, chemical reactions may occur with tine; te rest ing of screws, and the oting of heen are examples which may Tea to reakdoven of the joint ‘Adbesves have been the subject of considerable scientific research, but exactly how they bond to sais s sill nt clearly Understood is thought that adhesions due to secondary bonding between the molecules i the adhesive andthe atoms o¢ molecules atthe surface ofthe pices tobe oined (the adherend or substrate). Gly, the magntide of these forces i an osportne ctr 0 ‘termining the strength ofthe resulting jot Nowadays, ollng the development of a wide variety of syathetic polymers, a mul titade of new adbesves ofthis type Is avaiable tn addition to the teaditonl narral polymeric adhesives made from animal hide and bone starch, cellulose nd 2 on ‘Some adhesives are formed by chemical rections inst between diferent ingredients, This happens, for instance, with epony resins and cyanoacrylate adhesives OF cours, in 9 chemical reaction, ‘Primary bonds inthe starting materials are broken and new ones ae ‘ade form the products of Ue reaction. Even with there adhesives, it thought that no new primary bonde a formed acess the Interface between the adhesive and the sold surface, but tht sabeson i esentlly by means of secondary bonds Insome particular ese the joining process does reduce riary Banding eight eros the interac 29 much ao thi the orginal Imterfce disappears. This happens, for instance, when joint i tmade by lnclly meting the two pees and haling them together ‘ntl they resol examples ae rasing and welding. Figure 2 Isanilusvationofhow the interac destroyed by welding. om Figure 1.2 A hoxonizegaph oa woied ot showing adherend mechanical interlocking "conservation viewpoint sucha technique bas sme obwows desirable fetes 2s ‘The dlference between the two way of joining ~ by mechanical locking ot by an adhesive ~ Becomes rather lured when you on sider how an adhesive works at microrcopicleve. Ta oti any ‘aes, mechanical interlocking may contribute sigafcaiy tothe lMfectiveness of an adhesive, yo Tok apna he gla factare surface lusteated in igre 11, you wil appreciate that a suitable ‘uheriv could penetrate the nooks and cries onthe surface, nd so the surface to which itis o be joined, and thus produce an interlocking af the agments Simi, pieces of ape fabric an be joined by an adesive that penetrates between the bres. The Plccer are eld together by the veins adbesve, which acta books [round th paper texte fibres, an Velo. Tn the cote ofthis book thet ena need to pursue the details of theories of adhesion any furthe, however the base mecanisns ff secndary bonding and microscopic imerlcking jst derrbed ‘wll enlighten ner discussions Inthe net section the carats ‘es that a adhesive and the surfces tobe Joined should have in order to produce a aitacory oit ae explored. B What is needed to make a good joint? ‘What is meant by 2 god joint relly depends onthe meaning of "good" involves a Dalaae eten judgementeaboat the quahty of the joint on technical, aestheie and etal rounds the equted properties of the adhesive and theecency with whi the june Eade. IRt this pint eis important to appt hat in discussing t= ferent types of adhesive and the scence eating them, there 4 very Frc definition of “good” when considering adbesves for conservation work Most-madern adhesives have been sry afters themselves y the OO, y ee ieatyoeetysen fering em Th some re i L ‘exc’ user ‘named after part, ox all, oftheir chemical constituents (as are all of sme CN thowe in Bure 23) acbers have uninformative and inaccorate Ch hie se ahah el other rope exes pote 8) oo {hat have entered our vocabulary for example celulokdand aylon ‘Asysematc method of amin needed ad In ecent yeas stp tas ben made othe ght dection withthe adoption of tandrd seat Abbrevitons.Thowe given in Figure 2.5 and oters you wil cet et Pv Iter in the text are used, for instance, by the British Standards Bialimase eo Insiution (RS, the American Solty fot Testing and Materials from Pac (ASTM). andthe international Union of Pure and Applied Chemistry {WoPAc), You sbould get ino the habit of using these standard beevatons wil el, for example, to clear up the confusion NA A Se ras ees pre oe Feira pe bo ig ene ee Se oa ‘many types ofsynthetle polymeric materials, but one of the most ee ee ea sino) [ropertesia the bulk materia, One ofthe technological aims oftheir fm ee eee funds, o that do them beter than alternative material Imagine forexample, amas poynermade up of polyeylene Koy (@) molecales and. another made of polymetbylmetharylate hs PMMA) molecules, ath materials will tetain large numbers of J ae long-bainmolesles, but the types molecule ate very different Woy molecules bave only hydrogen sie groups attached to the cit Sppane bom Backbone, and as you kaow, these are non ola groups apd Cena ain) nly very weak secondary fore te setup between neighbouring ‘molecules. Ata direct consequence the molecules ean be drawn ‘pare quiteready which means that PE asa low melting pint and Cee re S 3 ‘is relatively soft and flexible (see Book 2 Section 4B). On the other ain ee ees eee bl eC tenons teen Tre Fete rip eect lar ps cere ie ie et noe et ete) sna methane canmereat ute at alse ond adresves Te chemisy of pens Ades on Cogs Tyee Example ——_‘Sructure oR oH Cita at rtarice Nl EME EE Ee tate i voter paviemne ‘sepia —© rons iio O00 Figure 26 fvarpitcofpolye with carton atoms substi i the hab tar some rogen origen and icon pect pee een cet ere cnet eed Uinmare ioetoeeroan tS eae a a ar as cant ae ee eas eet seah e mce (egy art nylon 1hded to achieve specie modifications ofthe properties of the plain ‘polymer. The ubiguitous adhesive often known as PVA Is 4 co polymer of vinyl acetate with esters of maleic aid sich as dibuty tone ‘The repeated units ina copolymer canbe arranged in diferent ways again lading to changes in properties. thee ate three main types the alternating cospolyeme, the random copolymer, and alternating. random and the block co-polymer; they ae ilustated schematically in igure block co-polymers 2.7. o-polymers wih at leas three base units ae made sythetic- Aly and of couse, in Natur potest co-plyers of pt 2, 4 sternaing besndom cebiock Figure 2.7 Schematrepresentvon of aerating. ano ard black co polymer We have now discussed the basic types of longchai polymers Most are mae spntheral: Nair peers neiork lye However. sme ncn yes distin Nature ft water dees ont ngs addition polymerisation condensation polymerisation ‘bitumen a complex mnsare of hydrocarbons) and cellulose @ major steacturlcoesponent of pans). ‘Before looking at work polymers wil ep f you fist con sider the mechanisns cf making longchain polymers, that of palmer B Polymerisation Molecules ike ethylene and methyl methaeryat can be persuaded by chemical mean to jn together consecutively using Ove of he bone inthe double carton bond, C=C In pine any mozomee nth a double bond between carbon atoms can be polymeried 3 this way is called addition polymerisation. Note thatthe polymer isthe sole product of thi sort of resetion (pat ofcourse, Rom a great deal of het). Soms long-chain payers, and network polymers, ae produced boy sehen teacton called condensation polymerisation. The {Hemition of he pepe lnk i types example fa condensation reaction sce Book 2 Chapter 7} Iasuchaveachon wo different sors ‘of molocle rect to form the desired product aswell as small toc asa by-product which is wualy but nor alway, water. ‘The long-chain polymers called ylon and polyester and abo Cellos and roti, ate polymerized by successive condensation actions Asan examples analyte oration ofthe polyester ‘Shown in Figure 25 i avaible commercially a Bbres (or ex- Spl, Teryene 0d fms (Melinex and Myla) Teis made fom wo monomers, ttephtaic aid which has the structural formu: and tas two acd ide groups: ° 7 on and thane ethylene glycol —wsed in antiicezs which has wo Inydroxyl (OM) side groups. let Ho-¢-£-on ial Ae ‘Aidan hydroxy side groups are strongly polar and they are the ‘ones involved nthe reaction between the wo aponomers. The ist ‘ondeneation reaction i then given By [A ydropen atom from the hydroxy group combines with an OH fromm an acid sidegroup 10 form a molecule of water (40) which selene, "The molecule thats the produc f the eacton sil as reactive groups at each end which am react farther wth the monomers: the o cehanedio (glycol) reacts ith the nd, andthe terephthalic aid reacts with the —OH end, Cnccatatng on the righthand (OH) side of the molecule ifthe aid monomer reacts with it fllowed by the diel monomer, the falloog It proued oe | Pail Se OHo-cnciro LO) le ovcinonmo w “These condensation reactions continu, releasing a poke of HO cach time to pve logetan polymer, eee oF ‘Amongst thers, nylons and elle ae produce inthe sume say. Since cellule based adhesives ae afte used in comervation sot he oman af else wl be cred in some dea Its molecular structure and polymerisition are rather complica and the description given ete isch simplified. PE ‘The cella structure of plants bik up fem cellos, andthe amount of cellulose varies fom one typeof plant to ante, the cellulose Tintern cotton plans ar weal al cellulose whereas weds are only about 40 percent cellos (tbe other mujor component tring lignin, a network polymer Cellule polymer of glucose, sugar sehich has the chemical forma CHO, and structural formu: lignin on te a on \Zh NSA aa Aan the reatve OH (hytony side groups ace iovelved in confention extn: youll meth eB of he ine oc masts The pre wane rn ect fr 2 ‘age sent poles © sch, frie, cos two Felner fluc eafled amylopectin spd amylose. The st isa Inca polymer Tesco wha the mj component Ras unt Seats te many vestve sites o he ens of he rts ht make arch sha ese sen ie therepet nits two glcoe makes which re bonded ogee stat De wit trndhupte dwn th eget to he oer, 3 Tite For simpy tee cbn sd sngle by ogen ates ae boc left ut): HoH 0 H = ie HO. on 5 ‘on ar mn aon i con on Ho oe, y No’ ‘on chow “This process continued by Further condensation reactions cach releasing ameiecule af 1,0, Atypical ellos molecule conta as ‘any a5 10,000 glucose unis 11s the OH (hydroxyl on heli nd ighthandsides ofthe glucose molecule nthe diagram that take tin the polymerisation Faction. In the cellulose polymer, each licose ring sll hae three —-OH groups. The hydrogen-bonding etiveen these groups, which are highly pols, provides strong bonding between neighbouring polymer molecule. ‘The hydroxyl gros canbe attacked by rc aid (HNOS) con veri ther a nitete group (NO). Being bulkier than —O1 {groups the nitrate groupe force the polymer cans further apart, If ithe hydroxyl groups ae eplaced inthis way, the results gua ‘cotton ~an explosive. Controling the mitration so that on average, to of the OM groups om each glucose ring are replaced by NO, yields cellule trate incorrectly known 38 ntrocelvlose) whic hae bess used at am adhesive for many years (solved In Ketones eters) and was the material sed erignaly athe base for photographic ir buts highly unstable should be emphasised again that using tbe stuctural formula ofa polymer it adeguate forthe present purpose of depicting the Covalentbonds inthe chain, but that real polymers actual lok very Aiflerent. They ae three dimensional, ot two-dimensional, the ¢hains re wal ot straight: and depending on the sie ofthe side _roups they canbe “Lnobbly”. Extensive studies of cellulose have Shown that it saJong-caln molecule and Figure 2.8 isa close {ppeoximation oa very smal part of Figure 28 Schone eresenoion of acaliose mlecule shown ts feng chan fom a C Network polymers In conrast oa long-chain polymer, a network polymer can fort bulk material that s composed of a continuous three dimension molecule the whole of which s bound togetber by primary bonds network polymer crosetinking “Tiel, network polymeric materials ave very diferent proper ties from those consiting of many long chain molecules. The roc ture cannot be disrupted 0 ready by heat, solvents or mechanical Torces,Thereare many Kinds ofthe typeof mater, both syothetic ‘nc atral, frm Bakelite to proteins, Such networks on be created In owo basi ways: 1 The linking of long chains by atoms or small molecules, 2 teraction becca sesso produce branched chine that join wget ‘an important example of the fist method isthe vuleanising of ‘ber Natural rubber, poly oprene, sa hydrocarbon consisting ‘long cham molecules (ee Figure 25) These chains canbe Hike. together by sulphur atoms sna to the inks between cysteine [groups in proteins ce Book 2, Chapter 7) 113 Ny ' teeth dt. UL Pero rit te superar Figure29 One may in whch poysopene natu! bbe) eas 30 ne contend Bonded ogee es tnking SP BS ach sulphur atom forms 2 croselink Beoween two cai by forming scant bond wt exch nT cam wing the dbl ‘ed aoe he oprene unt. The avaably of «double ‘Sin thechaisnecesary rset of buiig Petar. ‘tua robber soft and sy, but 9 ype rubber wed I thes cutains abut per et sulphur, which proce» network nab 30 arom tn Rete ol, 0 vr pees many ote eorlinks and fsa in td, Ft une ante and Fonte. You cane os Fe depecet cot linking hss dramae eft on he ROP test te per ‘Shu Be'plyser mode of plete tepals conde san evampl along chances prouce by co {eation plymersaon, in lng molecules con ao Be ros iehed we odece network polyester nde t do bis te lang ‘im polyester molecules mus be wnatratd, Wat i, contain ‘dsble ons. This means tht the manemer fam which the long ‘ln formed must contain a carbon to carbon double bond. One ‘ofthe bonds in the davble-bond fn the lng cain can be wsed ‘este 3 cromlink with an Kents ste om 2 neighbouring chain 5ust sulphur toms provide the ean inks i vulcased rubber, ‘monomer sucha styrene 2 \, can provide cw ks betwee the unsurted lng chal poles ter molecles Te rer hr glny materi td 8 ange and ge quae tn” guar enoreed pasts” (GRD tap. he egal poles aerials dseled in Syrene 1 form vo yup, etre eth harder (2 Clhlys) wh ner sd alts he ros king proves Stel mot The epny resin frm actor pyri mat Syl of est example, vlanicd rubber poet ad {pory rite the eralatng occurs by addon polymers Ato. an 0 9 byproduct gered Sar Goto Taman molecu an ocutsn many poe, fr cxampl in collgen fe ain conponent cf bone inden, sin sod bence Tea an in Krai ester, non) The rood way of producing nett plyer tat bythe “interaction of small molecules that generate branched chains that lnk up, toler storie condeoation renee, Example ore ena ormalachyae (Pandas feealdehyde (UF) bah of ‘ich ad applzaonssaUbsives arta iledunty, Fhe 1 lneresng appenion to "wctatengt” paper tes and touch The rent ncorporatedsppe up arog marca and rmes cating round ech be Tis prevents weer seating the tolow bres bt tl lows abortion by elastin, “the polymritonof pena armed cn be tered as fale Phenol CHO har the sacar formal ss Formaldehyde, HCHO, represented by dition polymerisation collagen Keratin condensation polymerisation —_— LED EER RR BSB ee se -— - “These two monomers an eat i he ellowing way it San OH OH $ ‘Waters again piven off daring the condensation reaction. Sin reactions con osror between the fommldehye mole and other hydrogen atoms i the pheno molec opve 3 thre dimensional setrk. The netwuri can be depicted 3 om, foo chy wb a. te TH gt : hb AG eH i, Wo “he bsc types plymer andthe way they eer as been cubis You ca no code som ofthe characteris hat “cermin how they are ued, pray In comnreaton wotk, D Some important characteristics of polymeric materials DI Terminology tthe at numbers of hemi compounds that ex rest many sree an yang fh ree Sui a Elle pleas pn ett) aod aly sage ‘Sd mr mater sh eto he le nsf protein DNAsnd beyond Alolynersenbecons perma e wo typesitedacedinthcaper To. and sence peyars, Hoeven rest el of rear abd devp- ‘Menton polymers hallowed the conser production of the Ti pli pocs round te tar ofthc, hi ak Iedethe nortan cms ith wich you eed be aia {npc heroplasti sod temesting pls spy, thems ‘sista imple» thermoplate matil hat becones pls capsbl fing mule i bested. When tae steal ste mirmed thy Bone st ad ca be formed into 3 dese shape Om cosing hey Become ig hut shen gn o0 teen Phrmopait const of longehain polymers com bined wt vans eter woes tt ost thee proper, tara longhair lcs ld geo only By ‘ney ek sendy Bona etecnnebring maces Consquty, be mkv cn fem tlie oe eae ‘ela esti presi wih esig tempest. yu wile he wk tanding teen moe ncn nny of the import popes of heap ‘Athermoseting pati when uly polymer, o ca on sis of continua network in wc siding bree mace {Soot oc es the nil race oe Inge meee sith sons ined by rina cova bods. The leno estar plmerason Sn pede perma s of he sat ene to thermo tn gen, then, temopis are ted on lnpchain toler anthems on het eles tn comets eras cme a athe enna an dona welsh ply aso you ay itl conse ths semen te se youn mars ceing ef hg. pyr have the Chasers themupsis anf stor pen beave he hese oe hone aly ced te eet an eo betes usd deste oso, ahs Seed may er bar orc ow thera hee infeed, fine mld wish Te ase tht when sg ened hr sl thermos tht conse ong can maces ae tetpet nn tpt honey tere necacey aang tooling, trashing resign S00} ce es tec ts il me ts ne themmctingseiversichas nated faye this cin be ranged very consent ees the mono tht ‘tes thee naan appr el eed Nea ae ‘wo-pck bner in whch naa a wna ee ne ‘onthe peed leg ayer ae tatdener (ang gen tt dics tcc ne yn he nn is nay tl yy sh led i scp oxen fms te cee a Se ei eles frm the ed pa ln AS EE the Avis its aoropeieoteempbaie the action seo eer been je ad es ee echo afpmes thermoplastic long-chain polymers thermosetting plastic hardener curing agent cystine solids crystallinity amorphous solids Tage molecules made up bythe successive Kakingwgeter of one fr tore small melecues (nome) plastics are yeti lend bose on ene cr re types of polymer, usually with addons of ‘ther materia designed to produce dered changes in peoperis to amprove clr flow preportes,reastance to exiaton, ese of andl colour and soon. Commer adhesives, pains, equers fad comliant, ae all examples of pti. How some ofthese {Aktion work wl Be dacused sm he next section D2 Relating properties to structure ‘Asachass, polymers provide marvellous demonstration of how the Properties of amattul are determined by ther intermalstrctue [Rr all combinations of toms of only two lemens, carbon and hydrogen produce materials diferentas methane, natural robber wipliyewrene: add another ement oxygen, andthe varity of ‘rodcts scems endless, fom the sple rnecal of formaldehyde BS paymethyimethacryite polyesters, celllose fats and many ‘edmins Ths enommos range aries bese the constituent atoms Ton be arranged in so many diferent ways. The inceral structure ‘tpolymers ean be conventedy ese at thee diferent levels orale 1 The types of atm and the way they are held ogetber inthe cece. 2 The size and shape of the molecule 4 How the molecule ate aranged retiv to one anober fore explving nse eves and dhe inter elton, fo Tesi proper, wo em need to be defied: caine Seanad When the star or moles io soi Ferm 3 Weir gee dimensional ray, that said sald ro be crystalline anth an svangement the afoms or molecules are in thee most TEAS poutins So eotaliity the normal onde of sad Meicandaloysarc ogee of mal crystal, Saw fakes cry nd sare asmonds, hires and rubies, When lowed TETea athoat poy const (or instance, stowiake) the sero ntdr as eysaline sold manifested eteroally By 85 ee al plane ove These repagomei superar a RI snk fas ests. However the ele seal rare et dens ryan ot the outa appearance. eer hand sli in wiih e aangenent of SES IS eo eplor rder ove any appecaie ance ikamorphous he wae verity of gs and ges ae Sample 2 ymesarecomplteysoephous, some at ily er phat sfa ew cystine pions and oes hea sion Feet a ery. la some forms of polythene insane, et oh lth vlume hexane The degre testi ae ye an important torn determining ts OPE ‘oir isusefl obama btmaredetailat why cyst cn vary Sommch Conse, for stance, what happens to a termopastic (2 tussofknghain molecules a itis cooked fom the mol guid) ’As you sil rember fom Book I, the liquid state fs charac tered by an actangement ofimalecules eich Is highly disordered Sa therfore seaively less clasely packed. As a consequence a Tid hase lower density tha the eguvaent sali and aoa lower Whey, tt iy the molecules oceupy more space a, because They rele stongly Bound, se over one aether more essily [Baer and ce are exceptions ~ thee might be Iss rose damage I Ice were denser than water) “AS the thermoplastic cons below ss melting point, at oehich temperature the 2d form becomes more stable than the Iq form, the molecules attempt to atain the odered arrangement of {ysl AS you know from Boks ard 2, the aon or molecules in ‘Mineral at na constant state of moton dae othe thecal (Kit ch)eneray thy posts, a the higher the emperatre the greater Is the thermal nergy, The gue aeangement ofa cysal eset ‘cer instantaneously on cooling Beene taken me forthe atoms Grnolecalesto move toan appropriate plac nthe ordered range mene In practice crystallin eps begin o grow a various pois (Called nce, but tot to be confused with tore nucle) In the Tiguan they grow loo the guid a further atoms molecu ‘ve toon the regler area. The final esl of this process would trea wld consisting of 3 muss small cysts: a polyerystalline aggregate sv itiscalet. Theis what happens amet boa he lngle tome involved are suificendy mile to ft into a epula tray, In polymers, however, the sae coatguration i rarely, treated. There ae to reasons fr this. Fst, long molecules fave avery led mobs sn the quel compared ith single ‘sors, Second, even they could move ely, the sie and shape the mlecleclten miltatepsnetalofthemeleulesliningup ike sickeina bundle bulky side groupsareatachedatsrepulr points slong the molecule, they are woicly to pack together vai For ‘example random epolymers res key to ryt tha lock. ‘copolymers On the ether hind strong secondary bonding between pgmer nnlecles encourages the development of erystalnity. Pjgure 210 liste some of the crnmon polymers that are ether amcephows of ignieanty crystal Crystatine polyethylene (PE) Extra polyesters cellulose calulose acetate (CA) polyamides (or example Amorphous pega rtacae RFA‘ co: plers PVRC-PE co: poner poistnane (29) rtons) Figwe2:10 Cyatieandanorpnauspohers (Tat nocangntcte polycrystalline aggregate ‘Asie nd sins las ranition temperature, (glass point) "Nice thatthe lists rar out the general points made above about solecule shape, Those tht give rise to strong secondary forces, between molecules due to pola side groups, especially C =0, often take par in hydrogen-bonding (lo ~OH groups, for instance) and tend to havea degre of exystalnty: those wih small regulary spaced sideroups behave silly, but those with age side- {foupoure sual) smurphous, Where her an ep stratus that no polar side groups the polymers tend to be “rubbery” (fr cxample, natural rubber. TO belp you visualise the molecule arrangements In long-chain polymers, igure 2.11 ilastrates the type of model that hae been used to describe an amorphous and 3 igh crystalline material, ens eion —anoghous region bhigiy ensatine Figure241 Anophove senate nome sts Drawings plyme cutie ineesesits crys jut antec pce oct. vot ses my ofthe ier the SStocepul astpure2 1 Meare, evens hgly yraline me oan sores repos. "rfea the sve dacosoon of te pote of yslisaton ii estat sorphosplys ave sok awh lcs sees gh vacouty ta they do not erie al When (ied they exittehe popes ssl seks becoming me Sita deme vite eral ners they donot show « Ee Making point astheychnge ond oh on heing Werbereay they ae lke loses shih ater gradually foe beng Metin kes overa cage oftenperture see eat of i emperor Tie’ mpertre (0 sel, am point), The convertion si sete) Eo, ath temperte he tral gyms cmd ih ore ting anne erage tower tapes, ey he maeca an pi, cer wars the molec Str Ser empl, be iy is onion ogee “fore pos lye ype hard and lesbo Ty na Ter snd mre ruber moe readily perme ty on ean be doled more easy. ‘aly the glass transition temperature ofa polymer extremely relevant to the uses ofthe polymer. The values of 7 for many ofthe pulyers referred toin this text are given in Figure 212. Notice that thermoplastic that are clase as crystaline also have a 7; because they, inevitably, contan amorphous regions "You cam se that in thee ea state materials such as ellulose atte, polymethylnetacryate and PV arehard, brite and las like at ordinary temperatures. However, long-chain polymers ike these can be mixed with other chemical which effectively decrease Tg that is, they induce rubberlke properties, sch as enhanced Aor 3 lower temperatures, Polymer paleo (PE) unto sien fal conde (P¥C) botavane (8) almmetiymenacte (MMA) ‘ae setae (08) 105, Figure 212 The appoumat las anston tempera forse ‘cornon pyre (oun th owt 8) Such substances are called plasticlsers and are relatively invlatile solvents of the polymer. By being incorporated between the molecules of individual polymers and weakening the infer molecular bonds, they separate the long chains and facilitate thei movement relave 10 ne another, Plaeticets need to behave lke» solvent in fonder to carey out thee fuetin and they alsa need to ave slot Figure 2.13 The atcha co om ts 1920 handbag mbotemert ove 188 of camphor piace tom cela ches of pers plasticisers Abs od Conigs ‘vapeur pres ~ so thal They do not evaporate o do 9 only Slowly. (they sormally havea molest macs greater than 300) Cay he evaporation of a plsiiser lads to britenes ~ a2 cing problem often met im adhesives, costings ad consaidans ‘Ree pectic examples shoul help to emphasie the importance a pstiser, Cellulose nitrate ia bard bile thermoplastic at trary temperatures is Ty ser to that of cellulose acetate, Shout 100" Mining a with camphor athe pater led to Ckvlopments of the Grst pak tamcly Pakesie and, ltr, Ghd PC nits pur fra one ofthe hard, ig plasies you come across inthe clear pase bates used contain rit dak. When [steed tesomer soft and plibl, ands sed in “letherlth forkockbinding, ct seat, loves and soon. Conmon pastciers for PVC ate estes forme between crtho-pialie ac: coon and alcool containing about eight carbon atin. ‘Nunpulating the frmuston a pas can each high degree cf sabley, For istance, a yo wl se i Chap 6, the hss tration temperature fr an emulsion pnt shoud hi ntl she dees below ovdiary temperatures whes the punts being pln that continvowe paint Bl is obtained. Uiately, ome the i ay need tobe bard and laske thats, ave rpahve ndinry temperatre, This eacieved by incorporating | atl amount of fue (volatile) plaster inthe thermoplastic oly ps base Dating the nal ges of drying this psiser Raowy lost by evaporation, ehus producing 2m in Ty Thalys tte eee of the strctare- property ration snip gechin polymers iis important to appreciate thatthe fle of eystllngy has 2 marked effect on properties. This is tly bec in 4 erysalline region the maces are packed ary eleely together compared with the arrangement it 30 01~ Tinks repio. Which eats tht the spees between molecule te rater and the binding forces sronger. AS a consequence, in fine 2 erystline polymer expected to have, for example 2 goer svengdh and gry than the egulalent amorphous ppljmc, ado bela enol dissolved and less realy pment by ase. Scouse, network polymer (thermoset) ae very iferent 10 long-chain polymer (ermoplastis)By the very nature, they ate inkpbourand since they consi fone comtinuousmolesl, they ‘Tooundergo glass tanston inthe sme way 35 thermos ‘Tk mechan stength,sgidity and hardnes ate determined Ccoemally. by the spacing between the crosslinks along the Mules’ the more frequent the cros inks, the more eg the ner ad the more asluble i eens. Neleiraonteamimenicrsa bjdogcle Pri eee en inet ee) Erion Po ter te Reet ether Making joints ‘Now tat some ofthe chemistry of polymers as been explained i is posible took in are deta tthe range of adhesives webich re ‘lable for jint-making, Since this ook is not am adhesives ‘anal, by no mean all he individual adhesves wil be covered Thu the thre lise of abesoes hich embrace sl he mteria ‘edn conservation - willbe dlacured, They ar solvent eiton nd ree reer adbesves A Solvent adhesives ‘Noone shoul use a solvent-based adhesive and nbedy should rake ane. They contain only one-quarter to one hid of sel aes; they ae lnlommabl owe ful seling and expensive ‘Snee you are ging throw overall he bulk aay by evaporstion Salvent adhesives ae legislated against, one by one solvents are banned [J (KW. Hamrson, Aso, Va. 3, Applied Sense Publishers, 193) In spite of these very appropeate thought solvent adhesives are widely used in conervauon and threlore waerant serious com Sideratin this ext “The principle on which salvent adhesives te see simple: the deste is dsaved in a sultable solvent so tat can be split toa surlce a haul form, The slvent then evaporates oleae the ‘old joint, The adhesive bones formed ae mainly de to sscon dary forces between molecules in the adhesive and thow of the surface. The considerable advantages of solvent adhesives In om Secvation work are tat unlike meefreze adhesives they eam he with different types of adhesive 7 1 1 1 | | solvent adhesives Sycant 17 cre al 383.97 Niro 55 Mt 1-8 acre 3 Tetereking mechan 161 ee al ee os a. meres Machi tae teing 79 go etn ogc 25 Myla” 32 Cpe aad ath ee =a" AS an pat Te ease mn Peano a Picasa ae a fic doen eng Popes a ene 23.36 ryan 36-2.38 rae) apn tee alyoprene 28.36 Siem 8 riya 1-38 Mita doe ia wee PSC mas 8 Inga 2535.38.46 Foe SS nS itty na aces ere Taj ti mci tiara pH eae spine on Ht safer mr 2 6. 981 Tatparny 11-116 Tanchoryntyiane 19 - ive 2 ‘Scatter ight 109 ia ‘hg ee 30,1) 14 Sines Sitar 0-44 Shang 9 tn at “fans sacs BL aes a ne | ee ane TT ene he fray 3.1 Welding sion 60-83 Making joints with different types of adhesive [Nor tat sme of the chemistry of polymers bas been explained t ‘spose lok in more dea at the range of adhesives which are tvallable fir Jolatmakng. Since thi book is not an adhesives ‘cara byt meal tnvidladesives wil be vere Dut the three clases af adhesives ~ which embrace ll the msterils usedlin conservation wil be dicurted. They ar solvent, rection and mel fcee sabes. A Solvent adhesives ‘Noone should sea solvent-based adhesive and nobody should make one, They contain only one-quarter to one thie of sel Adhesive; they ar inflammable, tox oul-sneling and expensive Since you ar going to throw over bal the blk away by evaporation, Solvenadhesves ae leisted against. one by one solvents are bunned "(KW Haein, adhesion, Vl, 3, Applied Science Pblichers, 1979) Tn spite ofthese very appropriate thoughts, solvent adhesives solvent adhesives, are widely used in conservation and theelore warrant serowe con "eration in this text ‘The principle on which solvent adhesives are hase is simple: the sahesive i disolved in a suiabe solvent so that t can be applied toa surface i qu form, The solvent then evaporates to lee the sold ot, The adbesive bonds so forme are mainly due to sesom ary forces between molecules in thease and those of the surface. Te considerable advantages of salvent aesives i cn ‘servation work are that unlike meteeze adhesives they ea be Se Ne se io spread very ely (eae of very low von and sie reaction adhesives, the joa are more edly eversed. On ‘he oer hand in addition tthe dsadvanages ced the above sol sole do0000000000 000000000000, 000000000000 000000000000 emogomaneAgg 00 © 000908000800 900000000000 ‘sadn (otc) ele metal Figure 33 Ta shows th saga i he ae sale scot Pesala suc fhe oie Isaealy reset onsver gh tempest wills al sa tet) or decanting, cate ad soo) “eazingisasinar ross soldering nde he two terse ‘ot matly excuse. A convention at could be ted at Selering i performed at temperatures blow 300 bean at teperatrs stove #50 Talons, Being aye eons monly spite two clases, hightenptaure Basing an es temperature Dracng Lowtcpeaturrang oem ed shee sclicng er bnd widening. The bain lysate be on te Silver copersystem ith vos oter adams snd hve necking rosin ag 0° Tey ae cen ed res Eade of aver. ightcmperturebacng is arts jainig metod for base alos of cope and Zine} and ees (alos a appr anti) sd cans be ned x caine ea ‘wrouptron The run lysed aed entice se ‘sem wa meting range fou 880-90 Tet ing an ening sey eked a 2 point onthe jolt an dra noth ja by capa ine of whats bes sn Caper Lou ll sprees thao epiiny acto o work eltetnly. anthony the sures ofthe objet to heed. Sac beth the nthe (pole rb atoy) and te sates fo bene are me Senay be sopposel tat tere null feo prleminthe eate ‘oy weg the objet Tas ast the case howene ees fen mth tis ob je i Bc te Sully tbe sme way. psa, esac hey oe Parc sale cheat ect ah chem ae ome. The eedomiantracn thatmemione ogee which produces save eCordeon the sara te seal Sig eat ppl the ate oh cheval ecm inecne ont ae fox welding hhammer-forging ‘resultant surface Ol stops the molten adhesive weiting the meta and therefore causes weak joint be formed the molten adhesive ‘does not penetrate the ont, and the surface film inhibits the forma tion of an adhesive bond. For tis reason, the oides and ether ‘ontaminantshave tobe retoved, and thsi done by using a speci substance called a lax, tn conjunction with the adhesive ‘flux isa material which, when molten, wes the rsisbed meal and resets chemialy withthe oxide or other contaminant toy bare the clean underlying metal surfce The hax aa he prods ‘of ts reactions donot remain in the oie once the olen deste Is introduced becmse they are much les dense and therfore fat ‘onthe molten adhesive. larly, these fates, plas the need fore ‘ux tobe molten at the soldering or brazing temperature, puttin gent requirements onthe choice of materia for ux. ‘raved joints are several tins stronger thn soldered joints an, when used on silver ee copper alloys, of rength comparable with that ofthe orgial met “The relative strenghs of diferent metajoining techniques cn Aictate which isused na particular ete in conservation For exam ple, the handles of pewter and sve jupe and cups tend to come Seay fromthe main body ofthe abject ates many years of constant Use. These may be reattached by an orgie dbesve, but the adhesive bond achieved may nt be ule or he abject to be lined cepeatedy by the handles alone, andthe ait wil probably fal. However, a lesd-slder Joint on 8 pewter objet, or 3 sivee-sldr (bated) oint ona ver objet, shuld be suliently strong sotha the handles will ot come say from the objet whe supporting the whol ofits weight Forstrogjnts in objects made of ro loys, or higher melting-point met an even higher es perature proces, welding, must be use, 2 Weldag ee eins on nereeentae ee ee See Siar martes tis a er ome Se ee ao gett ume my son ee aes been bert onbeberenenr 4 ere Soc innkencmeraienar eae ora Se iste ceaieatinine tte Leow a: immertorglg preset by Bucsnts Fonseca ey sng tc ae See et compaeeie coer ae cere nga te can pe a al reer mnied riley asl ll opts

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