MARINA BICCHIERI. FERRIC AND CUPRIC IONS: INTERACTIONS WITH CELLULOSE AS A FUNCTION OF ph.

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1 Interntionl onference on onservtion nd Restortion of Archive nd Lirry Mterils (Erice, April 22nd-29th 1996) ed. y rlo Federici, Pol F. Munfò. Plermo, Biliotec entrle dell Regione Sicilin, 1998, II, p MARINA BIHIERI FERRI AND UPRI IONS: INTERATIONS WITH ELLULOSE AS A FUNTION OF ph. INTRODUTION: DEGRADATION OF ELLULOSE The cellulose polymer chin cn e chiefly degrded y hydrolytic or y oxidtive mechnisms. Hydrolysis occurs oth in cid nd in lkline environments (1) (2) (3), ttcking the β-glucosidic ond nd thus cusing depolymeriztion of the cellulose chin. Alkline hydrolysis plys very importnt role only if cellulose contins oxidized groups. In this cse β-lkoxyelimintion (see generl scheme in Fig.1) tkes plce, leding to cellulose chin depolymeriztion. O OR OH - - O O OR H + - OR Fig.1. ß-lkoxyelimintion mechnism Following this mechnism, lkline hydrolysis occurs even with diluted lklis nd it cn ecome the min degrdtion process, especilly if cellulose is sumitted to strong decidifiction. Metl ctions too ply n importnt role in cellulose degrdtion (4) (5): some uthors (6) consider tht metl cts s ctlyst in the homolytic scission of the cellulose peroxide, which is formed y free rdicl mechnism; other uthors (7) postulte donor-cceptor Lewis mechnism involving either the semicetlic oxygen on the nhydroglucose unit or the β-glucosidic oxygen : in the first cse clevge of glucopyrnose unit occurs; in the second depolymeriztion of the chin immeditely tkes plce. The gol of this experimentl work is to quntify the degrdtion effects induced y iron nd copper ions t different ph vlues nd to test, s function of the ph of the smples, the ehviour of reducing gent, the orne tert-utylmine complex, lredy studied in the I..P.L. hemistry lortory (8). EXPERIMENTAL SET-UP Mterils : - Whtmn pper no. 1 for chromtogrphy. - Aqueous solution of iron III chloride M. - Aqueous solution of copper II chloride M. - Aqueous solution of iron III chloride M + hydrochloric cid 1-3 M to otin ph=2 solution. - Aqueous solution of copper II chloride M + hydrochloric cid 1-2 M to otin ph=2 solution. - Aqueous solution of sodium cronte M. - Aqueous solution of orne tert-utylmine complex M. Ageing : Untreted nd treted smples were ged following : method ISO 563/ (9): 8 65% R.H. ; totl time 28 dys; drwing t, 7, 14, 21, 28 dys. The ppers treted t ph =2 were only ged for 7 dys, drwing smples t,3,7 dys, ecuse the reduction in their chemicl properties ws so effective tht ny further geing would hve een pointless. Exclusively for mesurements of croxyl content of cellulose, smples were drwn lso fter 3 nd 1 dys.

2 Mesurements : For ech geing time on untreted nd treted smples mesurements were crried out of: ph of queous extrct, hot extrction method (TAPPI T435 om-88) (1). Blue reflectnce fctor (ISO 247/77) (11). Intrinsic viscosity of cellulose (ASTM ) (12). roxyl content of cellulose (ASTM ) (13). Moisture content of cellulose (ASTM ) (14). All vlues of experimentl dt re corrected for the moisture content (ASTM D ). Mesurements were crried out on smples, fter conditioning t 23 nd 5% R.H. (ASTM D685-87) (15). Preprtion of smples ) To prepre the "cid" nd the "low-cid" specimens, smples of Whtmn pper were immersed in the metls solutions (rtio: ml 1 solution/g 1 pper) for 15 min, then sumitted to ccelerted geing. ) The "low-lkline" smples were otined from "low-cid" smples, y further immersion for 1 hour in sodium cronte solution 1-2 M (rtio: ml 1 solution/g 1 pper). After immersion the smples were wshed twice with distilled wter (5 minutes the first time nd 15 minutes the second time). Mesurements of metl concentrtion on pper, crried out with Atomic Asorption, showed tht the "cid", "low cid" nd "low lkline" smples hd the sme ctions content, i.e. g of iron for g 1 of pper nd g of copper for g 1 of pper. c) For the reduction, unged nd ged smples (treted with metl ctions nd left untreted) were immersed in the reducing solution (rtio: ml 1 solution/g 1 pper) for 5 hours. RESULTS ) ph ph mesurements were crried out in ccordnce with TAPPI T435 om-88, using freshly oiled, twice-distilled, cron dioxide-free wter. Results, listed in Tle 1 nd presented in Fig.2, show tht oth ctions led to cidifiction of the pper. ) rightness of pper Diffuse lue reflectnce fctor (IRB%) mesurements re listed in Tle 2 nd presented in Fig.3. Results show tht iron ions immeditely induce yellowing of pper, of deeper intensity thn copper ions. Tle 1. ph s function of geing time (TQ=untreted, Fe=treted with Fel 3, u= treted with ul 2; : low cid medium; : low lkline medium; c: ph=2 solution) Time dys 3 dys 7 dys 14 dys 21 dys 28 dys Δ ph -28 dys Smple TQ 6.58 ± ± ± ± ±.2.56 Fe u c c 5.99 ± ± ± ± ± ± ± ± ± ±.2 3. ± ± ±.2 3. ± ± ± ± ± ± ± ± ± ± ± ± ±

3 ph TQ Fe low-cid Fe low-lkline Fe cid u low-cid u low-lkline u cid geing dys Fig. 2. ph s function of geing time Tle 2. Diffuse lue reflectnce fctor (IRB%) s function of geing time (TQ=untreted, Fe=treted with Fel 3, u=treted with ul 2; : low cid medium; : low lkline medium; c: ph=2 solution) Time Smple dys 3 dys 7 dys 14 dys 21 dys 28 dys TQ 88.2 ± ± ± ± ±.93 Fe ± ± ± ± ± ± ± ± ± ±.98 c ± ± ± 1.5 u 9.34 ± ± ± ± ± ± ± ± ± ± 1.54 c ± ± ± IRB % TQ Fe low-cid Fe low-lkline Fe cid u low-cid u low-lkline u cid geing dys Fig. 3. Diffuse lue reflectnce fctor (IRB%) s function of geing time c) intrinsic viscosity The intrinsic viscosity [η] of ll the smples ws not otined from listed tles (ASTM Method) ut y extrpolting t zero concentrtion the vlues of Log [(η rel -1)/c] s function of c (η rel is the reltive viscosity of the solution of pper in cupriethylenedimine hydroxide nd c is the concentrtion of the cellulose solution expressed in g/dl). The stright line prmeters were otined using lest-squrefit method, tking into ccount the proper error for ech mesurement.

4 The verge viscosity degrees of polymeriztion, listed in Tle 3 nd presented in Fig.4, re otined from Mrk- Houwnik equtions : (1) [!] " = KMv (2) [!] " = K' DPv Tle 3. Averge degree of polymeriztion s function of geing time (TQ=untreted, Fe=treted with Fel 3, u=treted with ul 2; : low cid medium; : low lkline medium; c: ph=2 solution) Time dys 3 dys 7 dys 14 dys 21 dys 28 dys Smple TQ 1521 ± ± ± 6 19 ± ± 2 Fe u c c 596 ± ± ± 8 4 ± 1 68 ± ± 1 52 ± ± 9 57 ± 7 76 ± 1 34 ± ± 8 85 ± ± ± ± ± 8 52 ± ± ± ± ± ± 2 36 ± 4 2 ± ± DP TQ Fe low-cid Fe low-lkline Fe cid u low-cid u low-lkline u cid geing dys Fig. 4. Averge degrees of polymeriztion d) reduction mount mesurement The soluiliztion of the pper in cupriethylenedimmine hydroxide, for intrinsic viscosity mesurements, tkes plce in n lkline medium. If the cellulose polymeric chin contins oxidized sites, dissolution in the solvent fcilittes the β- lkoxyelimintion nd cuses n pprent reduction in the verge degree of polymeriztion. It is to e stressed tht this reduction is due to the mesurement method itself nd not to the geing period. The pprent lowering of the degree of polymeriztion is less evident for untreted pper, where geing minly leds to hydrolysis, ut is visile when metl ctions re present, ctlyzing oxidtive reductions. In order to reduce this effect, which cuses systemtic errors, mesurements of the verge degree of polymeriztion were crried out, fter reduction with orne tert-utylmine complex.

5 This compound, like other orohydrides, rects specificlly with cronyls (oth ldehyde nd ketone) groups, reducing them ck to lcohol (Fig.5). Its rectivity is similr to sodium orohydride ut it is lso ctive in reltion to cron-cron doule onds (which re not reduced y sodium orohydride). H R =O or R R =O orohydride OH Fig. 5. Scheme of specific reduction with orohydride The fluctution in the weight of the smples ws mesured efore nd fter immersion in orne tertutylmine complex. Firstly the dry weight of the smples ws mesured. These were then ech immersed in orne tertutylmine complex for 5 hours nd susequently wshed twice y immersion in distilled wter for 5 minutes. After drying nd conditioning t 23, 5%R.H. the dry weight fter reduction ws evluted. The results, set out in Tle 4 (where the vrition in weight (W) is expressed s: [( W fter reduction - W efore reduction) / W efore reduction]. 1), show tht there is no systemtic vrition in weight which could interfere with the intrinsic viscosity mesurements of reduced smples. The vlues of the degree of polymeriztion otined fter reduction re not ffected y systemtic errors due to the reduction method itself or to the β-lkoxyelimintion nd re closer to the true vlue of the degree of polymeriztion of pper. Results, listed in Tle 5, re presented in Fig.6. Tle 4. Weight vrition fter the reduction tretment: dry weight efore reduction nd fter reduction tretment. (TQ=untreted, Fe=treted with Fel 3, u=treted with ul 2; : low cid medium; : low lkline medium) Time Smple efore dys weight fter efore 7 dys weight fter efore 14 dys weight fter efore 21 dys weight fter efore 28 dys weight TQ Fe u Smple vrition vrition vrition vrition vrition TQ Fe u fter Tle 5. Averge degree of polymeriztion fter reduction s function of geing time (TQ=untreted, Fe=treted with Fel3, u=treted with ul2; : low cid medium; : low lkline medium;) Time Smple dys 7 dys 14 dys 21 dys 28 dys TQ 1573 ± ± ± ± ± 9 Fe u 732 ± ± 5 12 ± ± ± ± ± ± 7 48 ± ± ± 3 58 ± ± 4 47 ± ± ± ± 3 4 ± ± ± 9

6 DP 8 6 TQ Fe low-cid Fe low-lkline u low-cid u low-lkline geing dys Fig. 6. Averge degrees of polymeriztion fter reduction Figures 7 nd 8 present comprison etween the verge degrees of polymeriztion efore nd fter reduction, s function of ph of metl slts. 16 untreted untreted reduced Fe low-cid Fe low-cid reduced u low-cid u low-cid reduced DP dys Fig. 7. Averge degrees of polymeriztion of low-cid smples efore nd fter reduction

7 14 12 Fe low-lkline Fe low-lkline reduced u low-lkline u low-lkline reduced 1 8 DP dys Fig. 8. Averge degrees of polymeriztion of low-lkline smples efore nd fter reduction e) croxyl content of pper Evlution of croxyl content of cellulose ws crried out in ccordnce with ASTM (13), y mesuring sornce t 62 nm of methylene lue solution. The increse of oxidized groups in cellulose molecules cuses reduction in methylene lue concentrtion, mesured photometriclly. Results of mesurements, reported s millimoles of croxyl groups per g 1 of cellulose, re listed in Tle 6 nd presented in Fig.9. Tle 6. Millimoles of croxyl s function of geing time. (TQ=untreted, Fe=treted with Fel 3, u=treted with ul 2) Time [dys] TQ [millimoles] Fe low-cid [millimoles] Fe low-lkline [millimoles] u low-cid [millimoles] u low-lkline [millimoles].331 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± After crrying out mesurements t, 7, 14, 21 nd 28 dys, it ws decided to clculte the croxyl content t intermedite times for ll the tretments, in order to clrify the progression of the curve. Another set of smples ws then ged for 3 nd 1 dys nd their croxyl content ws mesured. Tle 6 contins these results. DISUSSION OF RESULTS AND ONLUSIONS Experimentl dt show tht iron nd copper ct differently in cellulose degrdtion. From nlysis of dt, it ws possile to come up with more generl eqution, llowing us to descrie the ehviour of croxyl groups formtion s function of geing time. All the smples re descried y Boltzmnn distriution function:

8 A1! A2 (3) y = A2 + ( + e x! 1 x )/ dt where: x = time; y = m.moles OOH/g 1 pper; A1 = initil vlue (lower symptote); A2 = finl vlue (upper symptote); x = vlue of x (time) t the flex point; dx = width The prmeters, found experimentlly, for the croxyl formtion in ll the ppers re reported elow. Prmeters Smple A1 A2 x dx hi^2 R correltion TQ.324± ± ± ± Fe low-cid.376± ± ± ± Fe low lkline.464± ± ± ± u low-cid.435± ± ± ± u low lkline.377 ± ± ± ± For low-cid smples, Fig.9 shows tht the formtion of croxyl groups in the untreted ppers (TQ) nd in the ppers treted with iron (Fe) follows the sme mechnism, unlike tht which descries the ehviour of the ppers treted with copper solution (u). In low-lkline environments, s fr s u-ppers re concerned, there is no pprecile vrition in croxyl content during the first 6-7 geing dys. The numer of croxyl groups increses rpidly fter 1 dys nd reches sturtion level fter 14 dys. For the iron treted ppers, in low lkline environments, the increse of croxyl groups is prcticlly constnt over the entire period studied. Deriving from the eqution (3) it is possile to clculte the rte of croxyl groups formtion for ll the ppers (Fig.1) In low-cid environments, if neither the glucosidic ond nor the pyrnosic ring reks, croxyl groups cn e formed only on 6 nd the rte is constnt (-4 dys for u ppers); if the oxidtion of the primry lcohol group is coupled with the β-glucosidic ond clevge nd susequent oxidtion, the rte of croxyl formtion (-15 dys for TQ nd -13 dys for Fe ppers) is liner function of the time nd then, when ll possile sites hve een oxidized, the rte of croxyl formtion decreses for ll the smples, following n exponentil lw. 1, u low-lkline u low-cid Fe low-lkline Fe low-cid untreted m.moles OOH/g1 pper,9,8,7,6,5,4, geing time (dys) Fig. 9. roxyl groups formtion s function of tretment nd geing

9 ,12 u low-lkline u low-cid Fe low-lkline Fe low-cid untreted,1 dooh/dt,8,6,4,2, time Fig. 1. Rte of croxyl groups formtion s function of tretment nd geing As reported in previous work (8) the iron in low-cid medium seems to ctlyze the clevge of the 1-4-β-glucosidic ond, ccelerting the rte of hydrolysis, while the copper cts especilly on the glucopyrnosic ring, opening it, without chnging the rte of hydrolysis. This interprettion is confirmed y the dt of verge degrees of polymeriztion efore nd fter reduction. The polymeriztion degrees of the ppers treted with copper fter reduction re twice s high s efore the tretment. This mens tht oxidized groups re present in the pyrnosic ring, llowing β- lkoxyelimintion mechnisms, which cuse n pprent reduction in the chin length, efore reduction. After tretment with orne tert-utylmine complex, the cronyl groups re reduced ck to lcohol nd the vlue of the degree of polymeriztion is higher thn efore ecuse the mesurement is not ffected y the presence of oxidized groups. For the ppers treted with iron, reduction does not cuse gret increse in the degree of polymeriztion. The decrese in the cellulose chin length, cn indeed e explined s minly due to the clevge of the 1-4-β-glucosidic ond nd not to the presence of oxidized groups in the ring. In low-lkline smples results show tht reduction does not gretly increse the degree of polymeriztion of the ppers treted with oth the ctions exmined. The decrese in the cellulose chin length seems to e due to the clevge of the 1-4-β-glucosidic ond nd not to the presence of oxidized groups in the ring. In conclusion, ll experimentl results highlight tht : in low cid medium iron, ions ct s ctlyst for the clevge of cellulose 1-4-β-glucosidic ond, wheres copper ions ctlyze the oxidtion on the nhydroglucose ring. This ehviour verifies experimentlly the donor-cceptor Lewis mechnism for metl ctlysis; in low lkline medium oth ion seems to ct in the sme wy, ctlyzing the clevge of the cellulose 1-4-β-glucosidic ond. Moreover, copper seems to e prticulrly ctive in the clevge of the cellulose 1-4-β-glucosidic ond, in oxidizing the 6 nd lso, presumly, the ldehyde ending groups. (This, coupled with the reking of the 1-4-β-glucosidic ond, would explin the higher numer of croxyl groups in the pper treted with copper in low lkline medium compred to the other smples nlyzed.) in ph=2 medium ll degrdtion processes occur so fst tht it is impossile to evlute if the two metl ctions present different ehviourl ptterns. It is to e noted tht, during reduction with orne tert-utylmine complex, lck mrks pper on the smples treted with copper ions.

10 These re proly cused y reduction u2+ + e- u+. The mrks dispper fter the pper is exposed to the ir. An exmple of the effect of the reducing gent on the colours is shown in Fig.11 nd 12. The orne th tert-utylmine complex ws used for the restortion of privtely-owned qutint (y R. Lorrin, 19 century). As reported in previous work (16) the qutint ws seriously dmged: the colours were severely yellowed nd the unprinted edges hd ecome rown, due to the oxidtion of the cellulose (Fig.11). PR Fig. 11. The qutint y R. Lorrin efore the tretment with orne tert-utylmine complex EP T IN R For restortion the print ws wshed in cold wter nd, supported y non-woven tissue, susequently immersed for 48 hours in the reducing solution. The most noticele results were the increse of the degree of polymeriztion (from 171 to 386), the increse of the ph vlue of the pper (from 4.5 to 8.5), the recovery of the intensity of the colours1 nd the leching of the pper (Fig.12). Fig. 12. The qutint y R. Lorrin fter the tretment with orne tert-utylmine complex 1 The chromticity co-ordintes in L*** spce were mesured, efore nd fter the tretment with orne tert-utylmine complex, in severl coloured res of the print. The reduction gve rise to n increse in luminosity (L* co-ordinte) nd in decrese of the yellow content (* co-ordinte). The * co-ordinte lwys shifted to n intensifiction of the colour.

11 REFERENES (1) P.M. Whitmore, J. Bogrd, Determintion of the cellulose scission route in the hydrolytic nd oxidtive degrdtion of pper, «Resturtor», 15 (1994), n.1, p (2) R.L. Feller, S.B. Lee, J. Bogrd, The kinetics of cellulose deteriortion, in Historic textile nd pper mterils, conservtion nd chrcteriztion (Advnces in hemistry Series, n. 212), ed. y H. Needles nd S. H. Zeronin, Wshington D , p (3) L. Sntucci, Il ruolo dell chimic nell conservzione del ptrimonio lirrio, «Boll. IPL», 38, ( ), p (4).J. Shhni, F.H. Hengemihle, The influence of copper nd iron on the permnence of pper, in Historic textile nd pper mterils, conservtion nd chrcteriztion (Advnces in hemistry Series, n. 212), ed. y H. Needles nd S. H. Zeronin, Wshington D , p (5) H. Frrh, W.F. Pickering, The effect of ph nd lignds on the sorption of hevy metl ions y cellulose, «Aust. J. hem.», 31 (1978), p (6) J.. Arthur, O. Hinojos, Oxidtive rection of cellulose initited y free rdicls, «J. Polymer Sci.», 36 (1971), p (7) R.I. Sryev, A.S. Sultnkulov, T.V. Vsilikov, V.A. Afnsiev, Degrdtion of cellulose in the presence of Lewis cids, «ell. hem. Tecnol.», 25 (1991), p (8) M. Bicchieri, S. Pep, The degrdtion of cellulose with ferric nd cupric ions in low cid medium, «Resturtor», 17 (1996), n.3, p (9) ISO/563/3: Pper nd ord. Accelerted ging. 3. Moist tretment t 8 nd 65% Reltive Humidity, I.S.O., Genev, 1981 (1) TAPPI T435 om-88: Hydrogen ion concentrtion (ph) of pper extrcts - Hot extrction method. New York: Technicl Assocition of Pulp nd Pper Industry, (11) ISO 247/77: Pper nd ord. Mesurement of diffuse lue reflectnce fctor (ISO rightness), I.S.O., Genev, 1981 (12) ASTM D1795-9: Stndrd method of test for intrinsic viscosity of cellulose. Phildelphi: Americn Society for Testing nd Mterils, 199. (13) ASTM D : Stndrd test method for croxyl content of cellulose. Phildelphi: Americn Society for Testing nd Mterils, 1989 (14) ASTM D : Stndrd method for moisture in cellulose. Phildelphi: Americn Society for Testing nd Mterils, 199 (15) ASTM D685-87: Stndrd method of conditioning pper nd pper products for testing. Phildelphi: Americn Society for Testing nd Mterils, 199 (16) M. Bicchieri, P. Brus, The leching of pper y reduction with the orne tert-utylmine complex, to e pulished in «Resturtor». ABSTRAT - Acids, strong lklis nd mny oxidizing gents cuse degrdtion of cellulose, leding to the loss of pper resistnce. Metl ctions lso ply n importnt role. For the cellulose-metl interction different mechnisms hve een proposed: free rdicl mechnism in which the metl cts s ctlyst in the homolytic scission of the cellulose peroxide nd Lewis mechnism involving either the semicetlic oxygen on the nhydroglucose unit or the β-glucosidic oxygen, with formtion of donor-cceptor onds. The first im of our experimentl work is to quntify the degrdtion induced y iron nd copper ions s function of ph of metl solutions nd to verify whether experimentl dt re in greement with one of the mechnisms proposed in the literture. All experimentl dt show tht in low cid medium iron, ions ct s ctlyst for the clevge of cellulose 1-4-β-glucosidic ond, wheres copper ions ctlyze the oxidtion on the nhydroglucose ring. Results re in greement with the Lewis mechnism. In low-lkline medium oth metl ions seem to e ctive on the clevge of the glucosidic ond. The very cid mient led to such rpid depolymeriztion of the cellulose chin tht it is impossile to differentite the ction of the two metl ctions. The second gol is to check if the use of reducing compound cn impede oxidtion ctlyzed y metls, producing t the sme time opticl leching of pper. The orne tert-utylmine complex gve prticulrly good results in reducing ldehydes nd ketones nd it is lso le to produce opticl leching of pper.