Adhesive Testing at the Canadian Conservation

Maney Publishing and International Institute for Conservation of Historic and Artistic Works are collaborating with JSTOR to digitize, preserve and extend access to Studies in Conservation.

http://www.jstor.org

Maney Publishing

Adhesive Testing at the Canadian Conservation Institute: An Evaluation of Selected Poly(VinylAcetate) and Acrylic Adhesives Author(s): Jane L. Down, Maureen A. MacDonald, Jean Ttreault and R. Scott Williams Source: Studies in Conservation, Vol. 41, No. 1 (1996), pp. 19-44Published by: on behalf of the Maney Publishing International Institute for Conservation of

Historic and Artistic WorksStable URL: http://www.jstor.org/stable/1506550Accessed: 18-08-2014 08:40 UTC

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of contentin a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship.For more information about JSTOR, please contact [email protected].

This content downloaded from 84.205.227.38 on Mon, 18 Aug 2014 08:40:11 UTCAll use subject to JSTOR Terms and Conditions

ADHESIVE TESTING AT THE CANADIAN CONSERVATION INSTI' I' UTE AN EVALUATION OF SELECTED POLY(VINYL ACETATE) AND ACRYLIC ADHESIVES Jane L. Down, Maureen A. MacDonald, Jean Tetreault and R. Scott Williams

Summary-In 1983 the Canadian Conservation Institute (CCI) initiated a project to evaluate 27 poly(vinyl acetate) (PVAC) and 25 acrylic adhesives on the basis of pH, emission of harmful volatiles, flexibility/ strength and yellowing upon dark aging at room temperature and fluorescent light aging. Measurement of the pH of extracts showed that the PVAC adhesives were more acidic than the acrylic adhesives and that light aging tended to decrease the pH of both classes. The PVAC homopolymers generally were more acidic than the PVAC copolymers and many acrylic adhesives containing butyl acrylate were found to be neutral. The analysis of volatile compounds from the PVAC and acrylic adhesives showed that they emitted various ester and residual solvent compounds but only the PVAC adhesives released appreciable quantities of acetic acid. The results indicated that, after an initial curing period of several weeks, the evolution of acetic acidfrom the PVAC adhesives should not pose an acute hazard. In general, both PVAC and acrylic adhesives became less flexible after dark aging and the PVAC adhesives possessed more strength and less flexibility than the acrylics. PVAC copolymers displayed and retained more flexibility than PVAC homopolymers. The PVAC adhesives yellowed approximately twice as quickly as the acrylic adhesives and light aging tended to make all the adhesives yellow more quickly than dark aging. The results of each test for each adhesive are tabulated for an overall view and assessment of the data.

Introduction

In 1983 the Canadian Conservation Institute (CCI) initiated a project to evaluate various poly(vinyl acetate) (PVAC) and acrylic adhesives. The project was outlined in a paper given at the IIC Paris Congress in 1984 [1]. The purpose of the project was to test certain properties of selected PVAC and acrylic adhesives upon aging. The properties monitored were pH, emission of harmful volatiles, flexibility, strength and yellowing. Some of the results (pH and volatiles) have been published elsewhere [2] and all of the results have been made available in an internal report [3]. The pH and volatile emission results are repeated here with more recent data, along with new information on flexibility, strength and yellowing. All of the results are examined together and, based on this, the most stable adhesives were identified.

Selecting PVAC and acrylic adhesives for testing

One hundred and seven PVAC and 49 acrylic adhesives were proposed by conservators, conservation supply houses and manufacturers for inclusion in

Received 20 December 1994 Received in revised form November 1995

this study. Since it was impossible to test all 156 adhesives, a screening procedure [2] based on chemical composition of the major components was introduced to reduce the numbers while keeping a representative sample.

Simple, quick, batch methods of analysis were used to sort the adhesives into chemical groups. Fourier transform infrared (FTIR) spectroscopy was the primary technique employed. Some addi- tional information was obtained from colour spot tests (presence of dextrin, cellulose nitrate, etc.), the Beilstein test for chlorine (presence of poly(vinyl chloride)) and X-ray microanalysis (presence of inorganic fillers such as talc, china clay, etc.). These methods were sufficient for the purpose of screening according to the composition of major components. Minor components and molecular weights were not determined.

FTIR spectra were obtained from thin films cast on silver chloride plates. The casts were made from the solutions or dispersions as received, or from tetrahydrofuran, ethanol or toluene (methylbenzene) solutions of solid products.

Spectra of the samples cast as received were useful for determining the general nature of the adhesive. However, especially for PVACs, little discrimination between products could be made from these spectra because they were dominated by

Studies in Conservation 41 (1996) 19-44 19


J.L. Down, M.A. MacDonald, J. Tetreault and R.S. Williams

Table 1 Summary of the results of the analyses of the poly(vinyl acetate) adhesivesfor adhesive selection

Vinyl acetate homopolymers

No additives

VAL/VAC Cellulose nitrate Multiwax #445 VAL/VAC + soap

VAL/VAC + PH VAL/VAC + TS Soap + dextrin PVP + PH VAL/VAC + soap + polyamide VAL/VAC + soap + PEGD VAL/VAC + soap + PH

VAL/AC + soap + UN1 VAL/VAC + soap + UN2 VAL/VAC + dye + polyamide VAL/VAC + NaCMC + PEGD VAL/VAC + NaCMC + PH Soap + PH + PVP VAL/VAC + soap + china clay + PH VAL/VAC + soap + NaCMC + PEGD VAL/VAC + soap + NaCMC + UN1 VAL/VAC + soap + PH + UN1 VAL/VAC + dye + polyamide + PH VAL/VAC + NaCMC + PEGD + UN1 Soap + China Clay + PH + PVAL

AYAA (CR;SD), AYAC (CR;SD), AYAF (CR;SD), AYAT (CR;SD), Vinac B-15 (CR;SD): Aldrich PVAC 124800 (SD), Aldrich PVAC 194800 (SD), Aldrich PVAC 237100 (SD), BDH PVAC (CR;SD), Lametec (UF), Mowilith 30 (CR;SD), Vinac ASB-516, Vinac B-25 (CR;SD), Vinac B-100 (CR;SD), Vinavil K60 (CR;SD) Sure-Grip Carpenter's (CR;E): Archival Aids Tape AFT1 (SF), Tufskin 4405 (E) UHU Al Purpose Clear (CR;SN) Rabin's Mixture (CR;SN) CM Bond M-2 (CR;E), CM Bond M-3 (CR;E): Baystix #502 Wood Glue (E), Cascorez CV-815 (E), CM Bond M-1 (CR;E), CM Bond W-5 (CR;E), Lepage's Children's Glue (E), Magna Tac 1792 (E), Nu Glu (E), PVA 2500 (E), PVA 2900 (E), PVA 5000 (E), R0065 (E), R9329(E), Rakoll-Express 25 (E), Reichold ID-066 (E), Swift's 2552 Resin (CR;E), Tanbond Assembly (E), Weldwood Presto Set (CR;E), Wood Repair Glue WRG-2 (E) 3M Superbond White Resin Glue (E) CM Bond W-4 (CR;E) Gelva S-98 (E) Promacto A-1023 (CR;E;B2;B3;B4) Canada Standard PW2A (E) Euco Weld (E), Neutral pH White Adhesive (CR;E), Swift's 2928 (E) Elmer's Glue-All (CR;E;B2), Weldbond (CR;E): Adsol 604 (E), BC #536 (E), BC #4448 (E), Bulldog Grip 500 (CR;E), C 847 (E), C 852 (E), Mastercraft All-Purpose (CR;E), Planatol BB Superior (E), R0530 (E), Ultraflex #4056 (E), Vinamul 9910 (E), White Glue (CR;E) Bondfast (CR;E): Canada Standard PW625 (E), Gelva S-52 (E), Gelva S-55R (E), Gelva S-77 (E), Gelva TS-85 (E) Ponal (CR;E), Resin 'W' (E), Tufskin J5006 (E) Titebond (CR;E) Gaylord Magic Mend (CR;E) Elmer's Glue-All (CR;E;BO;B1), Slomon's Velverette (E) Promacto A-1023 (CR;E;B1) Bulldog Grip 2311 (CR;E) Slomon's Sobo Glue (E) CM Bond W-3 (CR;E), Gelva TS-30 (E) Bulldog Grip 20 Min (CR;E): Aquadhere 501 (CR;E) Elmer's Carpenter's Glue (CR;E) CM Bond W-2 (CR;E) Vinyl Adhesive No. 6488 (E)

Additives Vinyl acetate / ethylene copolymers

No additives Fusion 4000 (UF)* VAL/VAC Vinamul 3254 (E) Terpene phenolic resin Kodak Drymount Tissue Type 2 (SF) VAL/VAC + soap Beva D-8 (CR;E), C-808 (E) VAL/VAC + NaCMC Vinamul 3252 (E) Soap + dextrin Jade No. 454 (CR;E) VAL/VAC + soap + polyacrylamide Jade No. 403 (CR;E) VAL/VAC + soap + PEGD R-2258 (CR;E) VAL/VAC + soap + PH BC #4449 (E), Dopocol21 (E), Magna Tac 1902 (E) VAL/VAC + soap + UN1 Elvace No. 1874 (CR;E), Vinnapas EP1 (CR;E) KRN + paraffin + PH Beva 371 (CR;SN)* VAL/VAC + soap + NaCMC + PEGD Slomon's Quik Glue (E) VAL/VAC + soap + PH + UN1 CM Bond W-l (CR;E) Additives Vinyl acetate / acrylic copolymers

VAL/VAC EC9722 (E) PH Document Repair Tape (SF) Soap + NaCMC Vinamul 6815 (E) VAL/VAC + soap + UN1 Mowilith DM5 (CR;E): CM Bond M-4 (CR;E) Additives Vinyl acetate / maleate copolymer

Soap + methyl cellulose Mowilith DMC2 (CR;E)

Selected adhesives are listed first in bold; BO, Bi, B2, B3, B4 = first, second, third, and fourth batches analyzed; CR = conservation referenced (sold by a conservation supply house or in use in conservation); E = emulsion; KRN = ketone resin N; NaCMC = sodium carboxy methyl cellulose; PEGD = poly(ethylene glycol) dibenzoate; PH = phthalate; PVAL = poly(vinyl alcohol); PVP = poly(vinyl pyrrolidone); SD = solid; SF = supported film; SN = solution; TS = o,p-toluene sulfonamide plasticizer; UN1 = unidentified peak at 1125 cm4'; UN2 = unidentified peak at 875 cm-'; UF = unsupported film; VAL/VAC = vinyl alcohol/vinyl acetate; * ethylene predominates in copolymer

absorptions of PVAC and poly(vinyl alcohol) which water were centrifuged at 3000rpm to separate the mask absorptions due to other components. products into centrifugates containing the water- Therefore, emulsions diluted with 10 volumes of insoluble resin components and supernatants con-

Studies in Conservation 41 (1996) 19-44

Additives

20


Adhesive testing at the Canadian Conservation Institute

Table 2 Summary of the results of the analyses of the acrylic adhesives for adhesive selection

Acrylic type Homopolymers

MA Acryloid C-O1LV (SN) EA Rhoplex LC-40 (CR;E): Primal CA 12 (CR;E), BA Rhoplex N-580 (CR;E): Rhoplex PS-83-D (CR;E) EMA Elvacite 2028 (SD): Elvacite 2043 (SD)

BMA Acryloid F-10 (CR;SN): Acrysol WS-24 (CR;E), Bedacryl 122X (CR;SN), Elvacite 2044 (CR;SD), Formstar Clear (CR;SN), Lascaux P550-40 TB (CR;SN), Plexisol P550 (CR;SN)

iBMA Acryloid B-67 (CR;SD): Elvacite 2045 (SD), Elvacite 2046 (CR;SD) Acrylic type Copolymers

MA/EMA Acryloid B-72 (CR;SD)

EA/MMA > 66% EA Pliantex (CR;SN) 66% EA Rhoplex AC-33 (CR;E), Rhoplex AC-234 (CR;E), Unsupported Texicryl

(CR;UF): Plextol B-500 (CR;E), Rhoplex AC-22 (E), Rhoplex AC-634 (CR;E), Rhoplex B-60A (E), Rhoplex MV-1 (E)

50% EA Acryloid B-82 (CR;SD), Rhoplex AC-73 (CR;E) < 50% BA Lascaux 360HV (CR;E) > >50% BA Rhoplex N-560 (CR;E)

MMA/BMA 40% BMA Elvacite 2013 (CR;SD) 50% BMA Acryloid B-66 (SD)

BA/acrylonitrile Rhoplex N-1031 (CR;E): Rhoplex LC-67 (E) EA/MMA/EMA Texicryl 13-002 (E) MMA/BMA/EMA Plextol D360 (CR;E) MMA/BMA/styrene Acryloid B-99 (SN) MA/iBMA/? Acryloid NAD-10 (SN)

Selected adhesives are listed first in bold; BA = butylacrylate; BMA = butylmethacrylate; CR conservation referenced (sold by a conservation supply house or in use in conservation); E = emulsion; EA = ethyl acrylate; EMA = ethyl methacrylate; iBA = iso-butyl acrylate; iBMA = iso-butylmethacrylate; MA = methyl acrylate; MMA = methyl methacrylate; SD = solid; SN = solution; UF = unsupported film

taining the water-soluble components. The dried residues from these fractions were analyzed by FTIR using a diamond cell microsampling acces- sory.

Most acrylic polymers did not separate into fractions when centrifuged. Therefore, no water-soluble components were detected by FTIR. Only the composition of the resin component is reported for the

acrylic polymers. The results of the PVAC and acrylic analyses are

summarized in Tables 1 and 2 respectively. Selection of adhesives for testing was based on these tables (one adhesive from each chemically similar group) and restricted to adhesives known to the conservation community. Table 3 lists all the adhesives selected. In total, 27 PVAC and 25 acrylic




Table 3 List of acrylic and poly(vinyl acetate) adhesives selected for testing Acrylic Poly(vinyl acetate) Acryloid B-44S (2) AYAA (4) Acryloid B-48S (3) AYAC (3) Acryloid B-66 (2) AYAF (2) Acryloid B-67 (2) AYAT (2) Acryloid B-72 (2) Beva 371 (2) Acryloid B-82 (2) Bondfast (2) Acryloid B-99 (2) Bulldog Grip 20 Minute Resin (3) Acryloid C-10-LV (2) Bulldog Grip R-2311 (3) Acryloid F-10 (2) CM Bond M-2 (2) Acryloid NAD-10 (2) CM Bond M-3 (2) Elvacite 2013 (4) Elmer's Carpenter's Glue (2) Elvacite 2028 (3) Elmer's Glue-All (3) Lascaux 360 HV (3) Elvace No. 1874 (2) Pliantex (2) Gaylord Magic Mend (3) Rhoplex AC-33 (3) Jade No. 403 (2) Rhoplex AC-73 (4) Jade No. 454 (2) Rhoplex AC-234 (4) Mowilith DM5 (4) Rhoplex AC-234 + Rhoplex AC-73 Mowilith DM5 + Mowilith DMC2 Rhoplex AC-235 (2) Mowilith DMC2 (4) Rhoplex LC-40 (2) Promacto A-1023 (4) Rhoplex N-560 (2) R-2258 (3) Rhoplex N-580 (2) Rabin's Mixture Rhoplex N-619 (3) Sure-Grip Carpenter's Glue (2) Rhoplex N-1031 (2) UHU All-Purpose Clear Adhesive (2) Unsupported Texicryl (4) Vinac B-15 (1)

Vinnapas Dispersion EP1 (2) Weldbond (2)

Numbers in brackets indicate number of batches ordered

products were chosen, which included a few mix- tures of products used by conservators, some solid PVAC resins with different molecular weights, and products with different forms (i.e., solid, emulsion, etc.).

There is always concern that formulators could change products and thus invalidate the results of tests conducted. To evaluate the extent of this problem, samples from separate batches ordered over a period of six years were analyzed for 24 acrylics and 24 PVACs. The number of batches analyzed ranged from two to four (two batches for 29 adhesives, three batches for 11 adhesives, and four batches for eight adhesives). Of these 48 adhesives, only two PVACs, Elmer's Glue-All (one of three different) and Promacto A-1023 (one of four different), showed minor batch-to-batch differences (see Table 1). No differences between batches were detected by this analytical procedure for the other 46 adhesives. Notwithstanding this good track record, it is always possible for formulators to change their products without notice and the reader is warned of this possibility.

Aging conditions

Dark aging at 22?C and 45% relative humidity (RH) was carried out in enclosed, melamine-lami- nated, particle-board cupboards. The samples were laid on screen shelving, with box fans venting the air to prevent unwanted volatile chemicals from

accumulating. Light aging was carried out under 40watt Duro Test Vita-Lite fluorescent lights at 700-8001ux, 190jWlm-1 (proportion of UV radia- tion in the 300-400nm range), 22?C and 45% RH. The light-aging racks were constructed of Dexion adjustable metal framing from which the fluorescent lights and melamine shelving were suspended. The fluorescent lights were suspended about 50cm above the sample shelves, and screening was used to reduce the intensity and non-uniformity of the light distribution. Box fans ran continuously to remove heat from the fluorescent lamps.

The samples were exposed continuously to the lamps. In real museum conditions, lights are not on continuously and may be at lower intensity. Based on a typical museum exposure of 3000 hours per year (six days a week, 10 hours a day), five years of continuous exposure under these experimental conditions is equivalent to about:

15 years in a museum at 700-8001ux, 190uWlm-1 or 50 years in a museum at 2001ux, 190Wlm-' or 200 years in a museum at 501ux, l90uWlm- .

Acidity or alkalinity

If an adhesive in contact with an artifact is too acidic or too alkaline it may accelerate deterioration. The most suitable adhesives for conservation (for most applications) are those with neutral pH and those that remain so upon aging. Since pH gives a measure of acidity and alkalinity, this property was included in the testing.

pH procedures Two methods for measuring pH were adopted, one for measuring the pH of extracts of the dry adhesive film and one for measuring the pH of the wet emulsion. The first method gave an indication of the long-term acidity/alkalinity of a dried adhesive in direct contact with an object. The second method focused on the effect of shelf-life on emulsion pH.

pH of extracts of dry adhesive films After assessing several procedures, a modified [2] ASTM test method [4] was adopted. The procedure was chosen for its lengthy extraction period which was found necessary to extract all the acidic and basic components, especially from the hydrophobic acrylic adhesives. The extent of acid migration from an adhesive into an artifact could depend on a host of circumstances including the nature of the adhesive and the substrate (artifact), and ambient conditions. The method chosen took into account




10

9

8

7

I- CL

6 ?

i t i ' i 2 Xas o CN 0 o.

r

0-10 1 3 0 I I I Unacceptable I

NO ADDITIVES WITH ADDITIVES WITH ADDITIVES

HOMOPOLYMERS COPOLYMERS

Figure 1 pH of extracts of dried P VA C adhesive films after two, three and four years of dark aging, and one, two and three years of light aging (see Table 4 for data). Also pH of P VAC emulsions (where applicable) after three and five years of dark storage. Each cluster of points represents an adhesive. Adhesive clusters are grouped according to chemical composition (see Table 1).

situations where the adhesive might be held in moist conditions for prolonged periods. A method using a short extraction time would only identify adhesives with acid components that migrate quickly.

The chosen method involved pouring films of each adhesive onto Teflon release paper and allowing them to dry for one month. The initial pH measurement was taken at this time. The films that remained were divided in two and placed in the two aging environments; pH measurements were taken on water extracts of these films annually thereafter. pH was monitored for about four years of dark aging and for about three years of light aging.

The procedure for measuring pH involved cutting or grinding enough dry adhesive for triplicate samples and weighing 2g into each vial. Glass-distilled Nanopure filtered water (10ml, pH between 6-5 and 7-3) was pipetted into each vial. The samples were shaken and allowed to extract for 72 hours before the pH of each sample was measured. pH measure-

ments were then taken at 24 hour intervals until the difference between consecutive readings was not greater than 0.05 pH units. The last reading was recorded as the equilibrium film pH value of that sample.

pH of wet emulsions The pH of the wet emulsion was measured shortly after receiving the product. A quantity (about 100ml) of each emulsion product was sealed in an opaque vial and stored in the dark at room temperature. The pH of the emulsion was re-measured after three and five years.

pH results Tables 4 and 5 along with Figures 1 and 2 present the updated results of the pH measurements on the PVAC and acrylic adhesives.

An acceptable adhesive was defined as one whose



4v Table 4 Results of the pH measurements on the emulsions and on dry film extracts of the poly (vinyl acetate) adhesives Adhesive pH

Emulsions Dry film extracts

Control Dark aging Control Dark aging Light aging -0 year -3 years -5 years -0 year -2 years -3 years -4 years -1 year -2 years -3 years

5.71 5.96 4.22 6.09 5.06 6.14

a5.48 6.23 7.57 7.15

6.89 A6.45 4.58 6.86 6.56 4.49 6.76 6.26 4.98 6.56 6.09 4.99 7.64 a7.61 a6.20

Bondfast Bulldog Grip 20 Minute Resin Bulldog Grip R-2311 CM Bond M-2 CM Bond M-3

Elmer's Carpenter's Glue Elmer's Glue-All Elvace No.1874 Gaylord Magic Mend Jade No.403

3.75 4.65 4.64 4.31 4.51

4.31 4.49 4.01 4.47 5.80

Jade No.454 3.84 ca Mowilith DM5 4.48 H Mowilith DM5 + Mowilith DMC2 4.02

Mowilith DMC2 4.01 Promacto A-1023 4.23

o R-2258 m Rabin's Mixture

Sure-Grip UHU All Purpose Clear Adhesive

x Vinac B-15 .1&

6.58

3.81

3.65 3.56 4.01 4.04 4.47 4.82 4.55 4.24 6.84 mouldy 4.87 4.84 4.73 4.90 4.38 4.40 6.99 too thick 4.04 3.84

4.47 4.49 4.60 4.62 4.12 4.04 4.53 4.32 5.43 5.62

4.35 4.28 4.69 4.73 4.39 4.38 4.13 4.70 7.04 7.09

3.49 3.32 4.14 4.32 3.78 3.73 a3.91 4.43 4.03 too thick 5.71 6.92 3.80 too thick 6.62 6.67 6.12 too thick 4.51 5.18

6.44 too thick 6.55 a6.30 - - a6.52 6.27

3.72 3.61 4.28 4.14 - - 4.89 4.89

-4.05 6.26

4.10 4.52 4.90 4.51 3.88

- 4.01 4.43 4.83 4.37 3.74

4.36 - 4.21 4.97 - 4.75 4.57 - 4.20 4.87 - 4.58 7.29 7.05 5.96

4.58 - 4.22 a7.06 b6.81 4.10 6.89 6.89 6.34 6.68 6.59 6.46 5.81 - 4.10

6.47 6.81 4.30 4.86

6.21 5.38 6.41 3.86

- 4.03 - 4.04 - 4.03

Vinnapas Dispersion EP1 3.81 3.37 3.23 5.08 6.32 7.28 a7.29 4.74 4.89 6.29 > Weldbond 4.74 4.77 4.64 5.46 5.02 5.24 - 4.81 4.84 -

o Values for emulsions indicate a single measurement; Values for dry film extracts indicate the mean of triplicate samples; Standard deviations for dry film extracts are o 1 % except where indicated; a Indicates standard deviation of 2-3 %; b Indicates standard deviation >3 %

-PI~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

AYAA AYAC AYAF AYAT Beva 371

b5.80 a4.76 a6.64 5.24 6.39

4.45 4.38 4.67 4.63

4.07 4.26 4.89 4.41 3.75

4.28 4.80 4.21 4.70 6.26

4.30 4.01 6.52 6.43 3.85

4.72 3.97 4.34 3.74

o

I

6.36 .

-

I 5.61 6.25 ? -

~F~ -

4.36 l 3.77 -

- I-

- z IZ


7Cl Table 5 Results of the pH measurements on the emulsions and on dry film extracts of the acrylic adhesives

M' Adhesive

A

Acryloid B4 Acryloid B-44S Acryloid B-668S Acryloid B-66 Acryloid B-67

_ 1Acryloid B-72

Acryloid B-82 Acryloid C-10-LV Acryloid C-10- Acryloid P-10 Acryloid NAD-10

Elvacite 2013 Elvacite 2028 Lascaux 360 HV Pliantex Rhoplex AC-33

pH

Emulsions Dry film extracts

Control Dark aging Control Dark aging Light aging

-O0 year -3 years -5 years -O0 year -2 years -3 years -4 years -2 years -3

6.72 3.84

a5.96 6.68 6.41

6.41 b5.77 b5.45 6.73 4.61

7.79

9.35

7.35 7.30

8.27 8.25

6.63 6.51 7.01 5.93 5.88

6.64 4.22

a6.37 6.42 6.42

6.61 6.28

a6.16 6.57 4.75

6.60 6.56 6.82 5.56 5.17

6.70 4.07 6.47 6.77 6.63

6.54 6.31 6.17 6.71 5.01

7.01 6.51 6.89 5.87 5.15

a6.59 4.22 4.87 6.33 6.23

a5.63 b6.10 5.15 6.60 4.37

6.75 5.93 6.68 5.04 5.54

6.72 3.69 4.49 7.41

b5.93

6.65 a6.40 6.42 6.01 4.44

6.56 6.42 6.54 4.36 4.40

years


1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

* Dark Aged Films 0 Light Aged Films v Dark Aged

9 _ Emulsions 7 ? % 7v o 7 Unacceptable 4- o ^o 1V

I0 CO Oi o, + x o z o

0 -1 0

00 m ^

+ 0 m p 8 'B ?0 v, o, ? . ._ 2 ? S |P SC z 0 v ,

a I Iu I I m I i I I I

": g ? s *. 6o-p I ucodn < c o - Acceptable

11 I- - '

I ^ L i .^ ^T^ '*I T nI .2

7- '5 ? rf a I r I .- < .tio r u c

070 0 ID

O 6o 0 o o >'

4 Oh I I I

L) r 0

5- ?0 0 -10

xCRY ACHTESPEA/PMMA PBA/PMMA

-'grouped a r Unacceptable

AGING TIME (years) (D 0 -10

MIETH_


Figure 2 pH of extracts of dried acrylic adhesive films after two, three and four years of dark aging, and two and three years of light aging (see Table 5 for data). Also pH of acrylic emulsions (where applicable) after

grouped according to chemical composition (see Table 2). extract pH was in a range that could be tolerated without damage by most artifacts. Since artifacts are composed of many different materials which possess varying tolerances to acid and alkali, it is difficult to set universal pH ranges. However, a pH range that can be tolerated without significant damage by most materials was chosen based on the following information.

Textiles with extract pH in the range 5.5 to 8.5 have been accepted for use with organic artifacts in permanent exhibitions [5, 6]. Research on paper and cellulosic material [7-10] has shown that cellu- losics degrade and become brittle when extract pH is below 5.5, are only slightly unstable when pH is between 5.5 and 6.0, and are stable when pH is neutral or alkaline up to pH 10. This alkali toler- ance is reflected in the ANSI standard [11] which specifies that permanent paper should have a mini- mum pH of 7-5 and alkaline reserve of 2% calcium carbonate. Steel corrodes slowly in water between

pH 43 and 10 but rapidly below this pH range [12]. Woods with cold aqueous extracts above pH 5-0-5-5 are moderately corrosive to metals, while those with pH less than 5.5 are highly corrosive [13]. For storage of black-and-white gelatin emulsion photographs, paper with a pH between 7.2 and 9.5 and an alkali reserve equivalent to 2% calcium carbonate is recommended; for colour photographs, however, non-buffered paper products with a pH of 7-0-7-5 are specified, due to the alkaline sensitivity of colour image dyes [14]. There are some argu- ments that this latter, neutral pH range is more appropriate for albumen prints than the former more alkaline recommendations [15]. At their isoelectric point, proteins are most tightly coiled, least soluble in water and most stable. The isoelectric points of collagen and its aqueous extracts vary from about pH 5, for lime-processed gelatin from which photograph emulsions are made [9], to about pH 9 for native collagen [16].




Based on these observations, the acceptable pH range was set at 5 5-8-0 and can be seen to the right in the figures. In the authors' opinion, most artifacts will not be affected significantly by contact with adhesives having an extract pH in this range. Since some artifacts are more stable in acid or alkaline conditions, these so-called acceptable adhesives are not always the most suitable for particular applications. Furthermore, it must be remembered that extract pH measures only the acidity of material extracted from the solid mass of the adhesive. Any volatile acids and alkalis that are produced by the adhesive as it degrades evaporate from the adhesive and are therefore not dissolved in the water during extraction and do not contribute to the measured pH. The possibility that these volatile acids and alkalis might cause damage to artifacts must be considered when assessing adhesive suitability and is examined in the 'Volatile emissions' section of this paper.

pH discussion

The following general trends are evident from the results:

(1) Extracts of dry PVAC adhesive films are generally more acidic than those of acrylic adhesive films. Figures 1 and 2 show that more acrylic than PVAC adhesives fall into the acceptable pH range.

(2) In most cases, light aging tends to decrease the extract pH of the adhesive.

Within the PVAC class, the following general observations were made:

(1) The majority of the PVAC dry adhesives were acidic.

(2) Homopolymers with additives showed a ten- dency to be more acidic than copolymers.

(3) Additives tended to lower the pH of the PVAC adhesives.

(4) The PVAC emulsions (i.e., in the wet form) were acidic (pH8). Most emulsions initially measured between 9 and 10. After three to five years of storage, the pH fell to between 8 and 9.

(4) The Rhoplex emulsions AC-33, AC-73, AC-234 and AC-235 were alkaline (about pH 9), while their dry film extracts were neutral. After these Rhoplex films were light aged, their pH fell into the acidic range (pH

Table 6 Summary of the emission of volatiles from the poly(vinyl acetate) adhesives Adhesives Dark aging Light aging

pig acetic acid emitted/ g adhesive Other volatiles emitted ,g acetic acid emitted / g adhesive Other volatiles emitted

-3 mos -1 year -2 year -3 year -3 mos -I year -2 year -3 year

AYAA a0.4


of the adhesives poses dangers. To determine the amount of volatile compounds emitted from dried adhesive films, a new test was designed, one that would help to evaluate the suitability of adhesives used in the vicinity of artifacts (for instance, in display or storage situations) as opposed to adhesives used directly in contact with an artifact.

Volatile emission procedure Since the original experiments for volatile emissions, which were conducted from 1986 to 1988 [2], did not involve light aging of samples and only one measurement after dark aging was taken, the procedure was repeated to include light aging and more measurements. The experimental procedure followed was similar to the original experiment except that vials with screw-top septa replaced ampoules so that repeated sampling could be performed. It was found, much later, that these vials leaked slowly but consistently. Thus, although the measured quantities were not absolute, they did indicate the adhesives that released high amounts of volatile compounds. In reality, these vials model the actual situation of adhesives in enclosed environments.

The volatile emissions procedure involved pouring adhesive products onto Teflon release paper and allowing them to dry for one month in the dark to eliminate any volatiles due to the film curing. The dry films (5g) were shredded or ground, enclosed in glass vials with septum and allowed to age. Four samples for each adhesive were prepared, two for dark aging and two for light aging. After timed aging intervals, the airspace in the vials was sampled using a gas-tight syringe. Each sample was injected into a Hewlett-Packard Model 5890A gas chromatograph with a mass-selective detector (GC- MSD) (DB wax fused silica capillary column; helium carrier gas; temperature programmed from 35 to 200?C). The amounts of acetic acid were determined quantitatively; other compounds were identified but only qualitatively.

The PVAC adhesives were sampled at three months, one and two years, while the acrylic adhesives were sampled at one and two years only. After sampling, the vials were aired for 24 hours before being resealed.

PVAC volatile emission results Two possible sources of emanation of acetic acid vapour from the PVAC adhesives are free acetic acid in the formulation or hydrolysis of the acetate side-group on the polymer upon aging.

The PVAC emission results are summarized in Table 6. During the first year of aging, over half the PVAC adhesives released measurable quantities of acetic acid. The highest amount measured was

45- 1ig acetic acid per gram of dried adhesive. Adhesives released the highest amounts of acetic acid within the first year, with the amounts decreas- ing significantly for each successive year of aging. In general, the adhesives emitted the most acetic acid when light aged for the first three months. PVAC homopolymers and copolymers released similar amounts of acetic acid. Solid PVAC adhesives tended to release less acetic acid than did emulsion products. Elmer's Glue-All released formic acid (methanoic acid), the only other acid emitted from the PVAC adhesives.

The presence of aldehydes could pose a problem for artifacts. AYAA, AYAT, Bulldog Grip 20 Minute Resin, CM Bond M-3, Elmer's Glue-All, Jade No. 403, Mowilith DMC2, Promacto A-1023, R-2258, Vinac B-15 and Weldbond all released acetaldehyde (ethanal).

The PVAC adhesives emitted various esters- butyl acetate, ethyl acetate, methyl acetate and methyl formate. The threat posed by these compounds has not been clearly established. These esters, like PVAC itself, should not pose a problem unless hydrolyzed to acids. Since water alone does not hydrolyze most esters [17], hydrolysis could occur only if an acid is already present, as with the adhesives that release high quantities of acetic acid (e.g., CM Bond M-2 or Mowilith DM5 + DMC2).

The PVAC adhesives also released alcohols, aro- matic hydrocarbons, water, ethers and chlorinated hydrocarbons. These are considered relatively harmless to artifacts in the amounts found.

Several compounds, such as ethanediol diacetate, ethanediol monoacetate, 2-ethoxyethanol, 2-ethoxy- ethyl acetate and 2-methoxyethyl acetate, were identified in the emission products of some of the PVAC products. These are thought to be degradation products from the GC-MSD column [18].

Acrylic volatile emission results

The acrylic emission results are summarized in Table 7. The only acrylic adhesive that released any acid was Lascaux 360 HV, which emitted low quantities of acetic acid. Elvacite 2028 emitted acetaldehyde.

The esters released by the acrylic adhesives included butyl crotonate, ethyl acetate, isobutyl acrylate, methyl acetate and methyl methacrylate. The acrylic adhesives also released alcohols, aro- matic hydrocarbons, water and ethers. As with the PVACs, these should be relatively harmless.

Volatile emission discussion

For many artifacts, the level at which acetic acid vapour causes damage is not known. Therefore, it




Table 7 Summary of the emission of volatiles from the acrylic adhesives

Adhesives Volatiles emitted

Dark aging Light aging

Acryloid B-44S 7, 9, 14, 15, 16, 18 5, 7, 9, 14, 15, 16, 18 Acryloid B-48S 3, 5, 7, 14, 15 3, 5, 7, 14, 15, 16 Acryloid B-66 14, 16, 18 14, 16 Acryloid B-67 7, 12, 13, 14, 16, 18 14, 15, 16, 18 Acryloid B-72 14 14, 16

Acryloid B-82 14 14, 16 Acryloid B-99 3, 5, 10, 11, 14, 15, 16 3, 7, 11, 14, 15, 16, 18 Acryloid C-10-LV 3, 11, 14, 15, 16 11 , 14, 15, 16, 18 Acryloid F-10 7, 14, 16, 18 6, 14, 16, 18 Acryloid NAD-10 14, 15, 16, 18 14, 15, 16, 18

Elvacite 2013 14 14, 16 Elvacite 2028 2, 14, 15, 16 14, 15, 16, 18 Lascaux 360 HV 8, 16 1, 8, 11, 14, 15, 16 Pliantex 14, 16 10, 14, 15, 16, 18 Rhoplex AC-33 10, 16 6, 9, 10, 14, 16

Rhoplex AC-73 14, 16, 18 6, 10, 14, 16 Rhoplex AC-234 14, 16 10, 14, 15, 16 Rhoplex AC-234 + AC-73 14, 16 6, 10, 16 Rhoplex AC-235 8, 16, 17 6, 15, 16, 17 Rhoplex LC-40 10, 16 10, 15, 16, 18

Rhoplex N-560 8, 14, 16 8, 14, 16 Rhoplex N-580 14, 15, 16, 18 6, 8, 14, 15, 16 Rhoplex N-619 5, 8, 14, 15, 16, 18 5, 6, 8, 14, 15, 16 Rhoplex N-1031 14, 15, 16 3, 8, 14, 15, 16 Unsupported Texicryl 10, 14, 15, 16 3, 14, 15, 16

1 = acetic acid; 2 = acetaldehyde; 3 = butyl crotonate; 4 = ethyl acetate; 5 = isobutyl acrylate; 6 = methyl acetate; 7 = methyl methacrylate; 8 = n-butanol; 9 = t-butanol; 10 = ethanol; 11 = methanol; 12 = 1,2,3,4-tetra methyl benzene; 13 = 2-ethyl, 1,3-dimethylbenzene; 14 = toluene; 15 = xylene; 16 = water; 17 = dibutyl ether; 18 = unknown

is not possible to determine with certainty the hazard posed by any of the PVAC adhesives. The hazard posed by organic acids to various metals is documented [19, 20]. Acetic acid will cause corrosion of lead at levels around 0.5ppm at 22?C and 54% RH [20]. To obtain such a concentration in a 0.0283m3 (one cubic foot) hermetically sealed display case, lg of dried adhesive would have to release 35pig of acetic acid. Several of the PVAC adhesives approached this level in the first three months of light aging: Sure-Grip (45-lugg-'), Bondfast (33.lpgg-), Jade No. 454 (25-llgg1), Mowilith DMC2 + DM5 (22-3,gg-'), Vinnapas Dispersion EP1 (19-0,ygg-); and in the first three months of dark aging: Mowilith DMC2 + DM5 (14-9ygg-), CM Bond M-2 (ll-lgg-1). Since even the best-sealed display case leaks, doubt exists as to whether the quantities emitted by even these PVAC adhesives should pose a problem to lead.

In a separate experiment, it was shown that increasing levels of volatile acetic acid in a closed environment resulted in a corresponding decrease in paper pH. Even though the level at which this would result in actual damage to the paper was not determined, it is more likely to take place at the higher levels. There are many situations where paper or other acid-sensitive artifacts are held in close proximity to an adhesive for prolonged periods (for example, in a book or in a closed box). In

such cases, the levels of volatile acetic acid detected in some of the PVAC adhesives may be sufficiently high to affect the paper or artifact adversely.

Although this risk assessment requires more study, it does seem that, after the initial curing period of one month [21], the evolution of acetic acid from most PVAC adhesives will not pose an acute hazard to most substrates under normal circumstances. However, it would seem prudent to avoid the adhesives that give the higher emissions of acetic acid, especially when there may be prolonged exposure in an enclosed space. Air drying the adhesive for one month prior to enclosure is strongly recommended.

Volatile acetic acid data were examined in rela- tion to the pH data for the PVAC adhesives. Despite the large variability, the general trend is that the lower the pH, the higher the emission of acetic acid.

The following adhesives released the lowest levels of acids and would be the most suitable in terms of volatile emission: all acrylic adhesives, AYAA, AYAC, AYAF, AYAT, Beva 371, Jade No. 403, Rabin's Mixture, UHU All-Purpose Clear Adhesive and Vinac B-15.

Flexibility and strength

Adhesives display varying degrees of flexibility. It can generally be stated that (1) there is an inverse relationship between flexibility and film strength of the adhesive-the higher the strength, the lower the flexibility, and (2) in most cases-except, perhaps, for rigid substrates-it is appropriate for the adhesive to mimic the flexibility and strength of the substrate. For example, applications in textile conservation benefit from very flexible adhesives and the concurrent lower strength is not an issue given the typical loads associated with textiles. Semi-rigid substrates such as wood benefit from stronger adhesives that are semi-flexible. Rigid substrates such as ceramics also benefit from semi-flexible adhesives because glassy adhesives dry with large residual stresses and are prone to fail by peel or fracture. Thus most conservation applications benefit from flexible or semi-flexible adhesives. Flexibility was studied by monitoring the stress/ strain curve of the adhesive as it aged. These curves gave information on the modulus of elasticity, elongation at break and cohesive (film) tensile strength. Stress/strain procedure The flexibility of the adhesives was measured using a modified ASTM test method for tensile properties of organic coatings [22]. The film preparation procedure involved pouring each adhesive onto Teflon




I . i i. I i i i i i

...;O.. .....*.i.......... . ... . .

s I I I I I I I I i

, p

7 'I -

I I i?i~' ?

, ?

.

, ,.

, . I ~ ~ ~

, ! i I t

* Dark Aging 0 Light Aging

T Value higher * than indicated I

I o ' a

- * 0

c E ?

?

' ZL"

-

I ' I t n

.....o.. . . . . . . . . . . . . ? . . ^ . . ,' .XSS

? I > a 6 to . . o 0

< P Lo o)U Xf m O a Z ?

a o a a I O > n -.O* 1-"

HOMt)Li.OLY Re CO QLMR

i n- W \om

a I I C ! I >

I I " I

AGING TIME (yearU ) - - a -

...... ...... ............ .................... . .... ....................... . ................. ......... ................... .

I I I I I I I I I I i

HDMPOLYMERS COPOLYMERS m m :

0 - 10 U] D C.) LLJ m --

HOO OLYER3 C3 -M

O

i ~

-- ]1 I I

III I 1 i ! I! tI I I I I iIII ( I

N4 ADIIE WITH ADIIE IT DIIE HOOPLYER C O O YMR

Figure 3 Results of the stress/strain measurements for the P VA C adhesives after two, three and four years of dark aging and one year of light aging (see Table 8 for data). Tensile strength data are represented on the upper graph, elongation at break data on the middle graph, and modulus of elasticity data on the lower graph. Each cluster of points represents an adhesive. Adhesive clusters are grouped according to chemical composition (see Table 1). Small arrows indicate that values were higher than indicated, since the samples extended beyond the limits of the Instron Tensile Tester.

release paper and allowing it to dry. To ensure uni- form thickness, the Teflon release paper was secured to flat, level, glass plates and the films were laid using a Gardner Film Applicator. The initial stress/strain curves of these films were taken after one month of drying in the dark. The films were divided into two groups for each of the two aging environments. Stress/strain curves were taken after two and four years of dark aging and after one year of light aging (no light-aging data exist for the acrylic adhesives).

For stress/strain testing, films were cut into dumb-bell shapes with a NAEF Punch-Press Model B No. 8364. This precision cutter (ASTM D 412, Die C) avoids nicking or cracking the films. The use of dumb-bell-shaped test samples avoids neck- ing problems during the extension. To facilitate cutting, brittle films were relaxed for a brief period with heat or with heat and high humidity (30?C,

80% RH). Tacky or pliable films were frozen and cut immediately. These cutting conditions were assessed to be too brief to have any effect overall. About 10 samples per adhesive were cut. Film thickness was measured at five points along the gage length, using a Federal Thickness Gage. Films that varied in thickness by more than 10% of the average were discarded. The samples were then pulled in an Instron Tensile Strength Tester (gage length 33mm, cross-head speed for brittle samples 10mmmin-1, cross-head speed for extensible samples 50mmmin-1' 50N and 5KN load cells used). This test gave modulus of elasticity, elongation at break and cohesive tensile film strength.

Stress/strain results Table 8 and Figure 3 summarize the results for the PVAC adhesives, while Table 9 and Figure 4 pre-


......... ...........

o

a.

Cv u)

C_ l

a

m

:n

c

1

m

o c

0

oC 0-

LiJ

a 0- 2

C) 3 3

-a o 2

10

1

0.1

000

100

10

1

1000

100

10

1

0.1

Strong

Medium

Weak

Extensible

Inextensible

Glassy Semi- Flexible

Flexible

I I I I _ I I I I I I I I I I I I I I I I I

rII I I I I I I I I I I I I I

31

*.. .. ..... . . ... . ..t


Table 8 Results of the stress/strain measurements (tensile strength, elongation at break and modulus of elasticity) on the poly (vinyl acetate) adhesives Adhesives Tensile strength (MPa) Elongation at break (%) Modulus of elasticity (MPa)

Control Dark aging Light Control Dark aging Light Control Dark aging Light aging aging

- 0 year - 2 year - 3 year - 4 year -I year - 0 year - 2 year ~3 year - 4 year -1 year - 0 year - 2 year - 3 year -4 year -1 year

AYAA 27.5 '28.9 - 30.4 '23.7 2.47 2.40 - 2.37 2.36 3059 3202 - *3435 2664 AYAC '8.8 - - - - '1.19 - - .2165 - - AYAF 27.5 *22.7 - 29.1 "*19.2 2.15 2.23 2.69 2.69 3674 *2776 - *3333 *2430 AYAT 34.3 29.1 - *26.1 *17.3 3.03 2.57 - *2.16 2.69 3774 *3171 - *3545 *2006 Beva 371 3.78 4.28 - 3.82 *4.45 841 902 - 607 b*251 58.1 *90.3 - *91.6 *157

Bondfast 13.3 *29.6 - *23.8 *24.6 448 b*20.9 - *5.38 *4.97 1354 *2703 - *3504 *3225 Bulldog Grip 20 Min 14.1 a15.5 - *17.8 *19.4 416 *354 - 394 "*193 1127 '1519 - *1977 *2074 Bulldog Grip R-2311 23.4 *14.8 - *21.5 *26.1 '6.40 *43.1 - *13.9 '10.2 4359 *2507 *3463 4077 CM BondM-2 7.86 - - *20.6 - 1098 - - *3.68 - 114 - - *3251 - CMBondM-3 '20.7 '21.8 - 19.8 20.2 '1.82 '3.08 - *3.35 *3.88 3025 2656 - 3400 3149

Elmer's Carpenter's 35.7 34.5 - *24.8 *24.6 b137 b64.0 - '*4.92 *4.84 2626 2886 - *3009 *3292 Elmer's Glue-All 13.9 12.8 - *23.2 *18.2 423 *328 - b*97.9 b*144 984 *1428 - *2462 *2010 Elvace No. 1874 '9.9 12.4 - *13.9 *13.6 957 1050 - 890 932 104 162 - *225 *242 Gaylord Magic Mend 14.3 *19.7 - *20.1 *18.7 833 *518 - *488 *688 305 *1056 - *1528 *869 Jade No. 403 6.80 5.98 7.34 6.42 7.94 899 824 *712 756 756 '35.1 *51.7 *121 *72.4 *160

Jade No. 454 2.12 2.05 2.16 *2.33 *3.23 50.6 53.6 *21.2 *37.1 *28.6 181 *265 *330 *295 *564 Mowilith DM5 >0.704 > >0.296 >0.578 >0.678 - >1597 > >475 >2063 >2092 - '22.8 34.2 b17.6 b22.7 -

>3 Mowilith DM5 + DMC2 '2.12 2.81 - 2.85 1.51 '1330 1608 - 1430 753 b41.1 '83.3 - '75.1 *96.2 t Mowilith DMC2 7.30 *5.67 *5.73 6.81 7.73 664 *851 708 712 614 b305 '*199 "229 *127 *468 ~" Promacto A-1023 7.45 6.94 - *5.43 7.45 1083 *761 - *969 *731 123 *180 - *92.2 *218

X' R-2258 3.74 3.32 3.34 3.38 3.18 1071 1098 974 976 894 '41.3 46.2 *62.1 *30.4 *68.7 Rabin's Mixture '0.92 *2.37 - *6.10 - '890 *155 - b*144 - b60.6 "*371 - '*717 -

z Sure-Grip Carpenter's 10.9 *30.6 - *26.9 *28.3 274 *3.93 - *4.63 *4.10 b1140 *2712 - *3305 *3796 Sl I UHU All-Purpose Clear '21.1 - - 23.6 - '172 - - 152 - '1893 - - 2175 "s Vinac B-15 35.1 '*21.8 - 34.2 *43.2 3.44 '3.08 - 3.15 3.22 '3147 2536 - 3562 *4072

~. Vinnapas Dispersion EP1 1.94 >2.31 '1.84 1.99 1.92 889 - b1014 *1392 b948 b16.8 b10.0 *9.07 *7.32 *12.1

z Weldbond 9.4 9.9 - 10.9 11.4 614 *455 - 619 *431 b488 *852 - '*248 *974

Values indicate the mean of 3-10 samples; Standard errors are < 10% except where indicated; ' Indicates standard error of 11-15 %; b Indicates standard error > 15 %;' Indicates a single measurement only; * Indicates significant difference from control



Table 9 Results of the stress/strain measurements (tensile strength, elongation at break and modulus of elasticity) on the acrylic adhesives Adhesives Tensile strength (MPa) Elongation at break (%) Modulus of elasticity (MPa)

Control Dark aging Control Dark aging Control Dark aging -0 year -2 year -4 year -0 year -2 year -4 year -0 year -2 year -4 year

Acryloid B44S 6.99 *21.7 *16.2 261 b*28.8 *2.76 670 *1795 *1683 Acryloid B-48S 27.1 *28.1 *25.6 b65.7 38.8 b39.0 1584 *1861 1629 Acryloid B-66 - - 1.49 - b.594 - - b098 Acryloid B-67 too brittle - -- - - -- Acryloid B-72 6.25 *11.9 *18.1 351 *221 b*133 501 *962 *1246

Acryloid B-82 4.82 *9.15 *12.7 332 *219 *211 450 b884 *914 Acryloid B-99 too brittle - Acryloid C-10-LV b0.130 - 0a.227 b461 - >914 b17.2- b10.8 Acryloid F-10 5.08 *4.52 *8.68 511 499 *344 204 *532 *354 Acryloid NAD-10 8.03 - *5.98 b151 - *291 601 - *352

Elvacite 2013 too brittle -- - - -- - Elvacite 2028 .96- - - 2.40 - - 1204 Lascaux 360 HV - - >0.202 - - >768 - - bl.90 Pliantex b22.1 18.2 24.6 b136 177 215 185 145 *85.1 Rhoplex AC-33 - 7.63 - - 1168 - - 28.3

Rhoplex AC-73 too brittle - -- - - - Rhoplex AC-234 - - 5.18 - - 1437 - - 10.0 Rhoplex AC-234+AC-73 8.07 - 6.46 a538 - 698 190- a*92.9 Rhoplex AC-235 - - 5.54 - - 1040 - - 24.2 Rhoplex LC-40 "0.574 - >0.411 >2899 - >1018 t2.23 - 1.31

Rhoplex N-560 - >0.0769 - - > >524 - '0.70 Rhoplex N-580 - - >0.0811 - - > >601 - 0.40 Rhoplex N-619 0.153 - >0.0656 1193 - > >492 b27.8 b*0.210 Rhoplex N-1031 0.707 - >0.174 1871 - > >514 b0.878 - a1.10 Unsupported Texicryl a4.51 a0.514 >1.05 1595 b*393 > >494 b2.61 *12.7 a*7.07

Values indicate the mean of 2-10 samples; Standard errors are 15%; * Indicates significant difference from control

sent the equivalent summary for the acrylic adhesives. In order to interpret the results to make choices of flexible adhesives, it was first necessary to determine ranges of flexibility and extensibility for conservation applications. Polymers exhibit three regimes of useful mechanical behaviour: glassy, rubbery, and the transition between the two. For purposes of classification into more general terms such as 'flexible', 'extensible', etc., the following boundaries were drawn.

Modulus of elasticity For all amorphous polymers, fully glassy behaviour gives a modulus of 3000MPa [23, p. 48] and the transition to rubbery begins at about 2000MPa [23, figures 3.2, 3.4] so 2000MPa was set as the boundary to semi-flexible behaviour. The boundary for so-called flexible behaviour was based on a percep- tible benchmark. Common plastics such as poly(vinyl chloride) and low density polyethene fall just below 400MPa (150-350MPa), so this was set as the boundary for flexible behaviour.

Elongation at break

Extensibility could arise either from rubbery behaviour or from ductile plastic behaviour. Rubbery behaviour easily gives elongations of 100% or more and plastic behaviour, which may reach well over 100%, gives about 20% elongation [23, figure 3.5] at its onset. Therefore 20% was set as the boundary between 'extensible' and 'inextensible'.

Cohesive tensile strength

'Strong' was set to include not only glassy adhesives showing their intrinsic brittle strength of 60MPa [23, p. 54] but also some ductile adhesives down to 15MPa strength. 'Weak' was reserved for those materials below the strength of a typical elastomer, polyisobutylene, 2MPa [23, figure 3.8]. 'Weak' would thus include only polymers already entering viscous flow behaviour over the course of a few minutes. These ranges can be seen on the right in Figures 3 and 4.



I I I I I I I I I I I I I I-

. . .... . .............. .......... ... ..

. ... . .... .. ........................ -....... ................. ..........

: /t * t -

r i i i L I i i I i I [ e I i ? I 1

; ..................... a~ .............~ ...................................?. .

< .........

- T o l I1 N" " I, I -oz 1 0^ Z , . 0

z

-o -e x> x -o X ? X m - _0 o

t -_

-> x L

o:~, 0 o 0 0

;* ,ve <

* i T

: _C

:j 41 Pr 0 0= o P I))

- 0 LI 0o I o-

O AGING TIME **j u ?I UoC ? J(year?) ~J < < C z


'6 -& o a

o I I Ee E

0-1o

ES METACRLATES PEA/PMMA P HOMOPOLYMERS COPOLYMERS

Strong ..............I. Medium

Weak

Extensible

Inextensible

Glassy Semi- Flexible

Flexible

I Value higher than indicated

Figure 4 Results of the stress/strain measurements for the acrylic adhesives after two and four years of dark aging (see Table 9 for data). (Note that no light aging data are available.) Single points represent aging data after four years of dark aging (i.e., only one measurement taken). Tensile strength data are represented on the upper graph, elongation at break data on the middle graph, and modulus of elasticity data on the lower graph. Each cluster of points (or a single point) represents an adhesive. Adhesive clusters are grouped according to chemical composition (see Table 2). Small arrows indicate that values were higher than indicated, since the samples extended beyond the limits of the Instron Tensile Tester.

Stress/strain discussion The results of the stress/strain experiments suggest several interesting trends and features in the flexibility and strength of the PVAC and acrylic adhesives. In general, the adhesives become less flexible upon dark aging. The PVAC adhesives generally possess more strength and less flexibility than the acrylics.

The stress/strain results of the PVAC adhesives suggest the following general trends: (1) Predictably, the PVAC copolymers displayed

and retained more flexibility than the homopolymers.

(2) PVAC copolymers, although weaker than homopolymers, displayed sufficient strength for most conservation applications.

(3) Also predictably, additives tended to increase

flexibility and decrease strength, especially phthalate plasticizer.

The most flexible PVAC adhesives were Beva 371, Elvace No. 1874, Gaylord Magic Mend, Jade No. 403, Mowilith DM5, Mowilith DMC2, Mowilith DMC2 + DM5, Promacto A-1023, R-2258, Rabin's Mixture, Weldbond and Vinnapas Dispersion EP1.

The results of the acrylic stress/strain curves con- firmed the following general predictable trends:

(1) The acrylates tended to be more flexible and weaker than the methacrylates.

(2) For the butyl acrylate/methyl methacrylate copolymers, the greater the amount of butyl acrylate, the more flexible and the weaker the adhesive.

The majority of the acrylic adhesives displayed Studies in Conservation 41 (1996) 19-44


0

Q- , 10

Mu 1 C0v 0 c

1 0.1 (f

1000

100

0

m

._

1000

CT 0 1

1000

o

0

0) :3

-0 0

2

100

10

1

0.1

* Dark Aging

34



0?~~~~.o -~~~~~~~~~~~~~~25 1 1 1 1 1 1 1 1 1 1 1 1 1 iDiscoloration Perceived

* Dark Aged Films Perceived

0 Light Aged Films

e< :s o E ? : i , ,o i

0.05~1$iLA; -s?S'X'>kS; i''.' CD 0 iS

AGING TiME (ye rs)

'

-

0 . 10

| i? r ii 11

NO ADDITIVES WITH ADDITIVES WITH ADDITIVES


Figure 5 Degree o yeong P C hived years of

dark and light aging (see Table 10 for data). Each cluster of points represents an adhesive. Adhesive clusters are grouped according to chemical composition (see Table 1).

( E I 0.05 I . . . I L

good flexibility, with the exception of Acryloid B- 67, Acryloid B-99, Elvacite 2013 and Rhoplex AC- 73, which were too brittle to measure.

Yellowing

The yellowing of clear or colourless adhesives can be an undesirable property for conservation applications, especially for transparent or light-coloured substrates. As well, yellowing may indicate instabil- ity or degradation of an adhesive. An adhesive that remains clear and colourless or that yellows little upon aging is more suitable for some conservation purposes. To determine the resistance to yellowing, a procedure was followed similar to that designed for epoxy resin adhesive testing. The method is described in detail elsewhere [24, 25] and is only briefly outlined here.

Yellowing procedure and results Adhesives were applied with microscope slides as

thin films in taped wells to acetone-degreased glass slides. Five replicate samples were prepared for each aging condition. Film absorption was measured initially at 380 and at 600nm on a Varian 2390 UV-VIS-NIR spectrophotmeter equipped with an integrating sphere to capture all scattered light. Films were then aged in the two aging environments. Samples were removed at intervals (six months, one, two, three and five years) and were measured for absorbance, again at 380 and 600nm.

Degree of yellowing (A) at time (t) was calculated using the following formula, which subtracts the baseline, absorbance at 600nm [A(600)], from the ultraviolet absorption at 380nm [A(380)] and standardizes the film thickness (F) to 0-lmm:

0 lmm A = [A(380)t - A(600),] x F

Tables 10 and 11 present the calculated yellowing data for the PVAC and acrylic adhesives, respectively. Figures 5 and 6 show the yellowing curves



Table 10 Results of the yellowing measurements on the poly(vinyl acetate) adhesives Adhesives Degree of yellowing [A, = (absorbance @ 380 nm - absorbance @ 600 nm) * (0.1 mm /film thickness)]

Dark aging Light aging 0 year 0.50 year 1.05 year 2.18 year 3.01 year 5.13 year 0 year 0.50 year 1.01 year 1.96 year 3.14 year 4.53 year

AYAA a0.0541 b0.0326 a0.0773 a0.0504 a0.0849 a.0610 b0.1015 b0.1071 bO.1257 bO.1334 b0.1975 b0.1331 AYAC b0.0493 a0.0499 aO.0688 b0.0441 aO.0728 aO.0501 0.0496 b0.0581 0.0583 0.0659 0.0927 0.0653 AYAF 0.0622 0.0603 0.0902 0.0582 0.0970 0.0627 0.0685 aO.0817 a0.0934 0.0932 ao. 1342 0.0880 AYAT b0.0592 b0.0605 b0.0878 b0.0582 b0.0953 b0.0659 0.0414 b0.0582 a0.0593 b0.0600 a0.0826 b0.0548 Beva 371 0.0434 a0.0463 0.0632 0.0649 ao.0733 0.0919 0.0425 0.1033 0.1329 0.1719 0.1760 0.1796

Bondfast 0.0338 0.0326 0.0429 0.0440 0.0479 0.0624 0.0333 0.0463 0.0472 0.0533 0.0456 0.0501 Bulldog Grip 20 Min 0.0713 0.0447 0.0556 0.0475 0.0516 0.0564 0.0739 0.0495 0.0558 0.0576 0.0568 0.0544 Bulldog Grip R-2311 0.7136 0.6581 0.6792 0.6773 0.6848 0.6962 b0.6528 b0.6229 b0.6587 b0.6956 b0.7015 b0.6969 CM Bond M-2 0.0569 0.0557 0.0607 0.0521 0.0492 0.0562 0.0594 0.0552 0.0466 0.0520 0.0564 0.0507 CM Bond M-3 b0.1212 "0.0831 b0.1013 b0.0863 b0.0749 "0.0866 0.0959 0.0685 0.0668 0.0670 0.0640 0.0579

Elmer's Carpenter's 0.1333 0.0804 0.0941 0.0823 0.0715 0.0938 0.1317 0.0908 0.0897 0.0943 0.0830 0.0890 Elmer's Glue-All 0.0608 0.0652 0.0830 0.0722 0.0763 0.0850 "0.0544 0.0521 0.0521 0.0626 0.0626 0.0583 Elvace No. 1874 0.0252 0.0270 0.0353 0.0314 0.0364 0.0336 0.0257 0.0290 0.0284 0.0327 0.0389 0.0344 Gaylord Magic Mend 0.0433 0.0349 0.0497 0.0402 0.0433 0.0537 0.0491 0.0459 0.0474 0.0549 0.0620 0.0606 Jade No. 403 0.0381 0.0481 0.0544 0.0517 0.0539 0.0557 0.0342 0.0402 0.0418 0.0453 0.0509 0.0448

Jade No. 454 0.0911 0.0888 0.0925 0.0872 0.0910 0.1056 0.0809 0.0943 0.1046 0.1185 0.1231 0.1211 Mowilith DM5 0.0447 0.0612 0.0719 0.0683 0.0779 0.0834 0.0389 0.0448 0.0458 0.0541 0.0598 0.0539 Mowilith DM5 + DMC2 0.0309 0.0458 0.0540 0.0491 0.0557 0.0605 0.0253 0.0361 0.0376 0.0411 0.0510 0.0417 Mowilith DMC2 0.0317 a0.0404 0.0452 0.0365 0.0479 0.0476 0.0336 0.0425 0.0426 0.0444 0.0569 0.0444 Promacto A-1023 "0.0648 0.0677 0.0736 0.0582 0.0515 ao.0645 0.0680 b0.0826 "0.0884 a0.0992 0.0978 0.1142

R-2258 0.0235 0.0300 0.0351 0.0295 0.0348 0.0374 0.0245 0.0286 0.0333 0.0417 0.0498 0.0456 Rabin's Mixture 0.0217 0.0302 a0.0376 aO.0217 a0.0277 0.0331 b0.0229 b0.0330 b0.0412 b0.0429 b0.0573 b0.0402 Sure-Grip Carpenter's 0.0947 0.0883 0.1024 0.0938 0.0956 0.1153 0.1001 0.0974 0.0935 0.1037 0.0923 0.0939 UHU All-Purpose Clear 0.0187 0.0190 0.0279 0.0157 0.0193 0.0205 a0.0252 a0.0264 80.0306 80.0340 80.0487 0.0318 Vinac B-15* 0.0560 0.0777 - 0.0385 0.0494 0.0518 b0.0604 b0.0873 b0.0855 b0.1255 - b0.0825

Vinnapas Dispersion EP1 0.0313 0.0397 0.0493 0.0428 0.0486 0.0576 0.0309 0.0373 0.0392 0.0484 0.0585 0.0512 Weldbond 0.0324 0.0289 0.0332 0.0280 0.0301 0.0355 0.0285 0.0294 0.0323 0.0397 0.0396 0.0314

Values indicate the mean of 3-5 samples; Standard deviations are < 15% except where indicated; a Indicates standard deviation of 16-20%; " Indicates standard deviation >20%; * aging times for this adhesive were: dark aging - 0, 0.55, 1.68, 2.52, 4.63 years; light aging - 0, 0.50, 1.55, 2.73, 4.12 years

ZI

Zs

H.

-

t-- ti- tz

Is

.

4c1

cpz

Q


Table 11 Results of the yellowing measurements on the acrylic adhesives

I. Adhesives Degree of yellowing [A, = (absorbance @ 380 nm - absorbance @ 600 nm) * (0.1 mm /film thickness)] Dark aging Light aging

0 year 0.50 year 1.05 year 2.18 year 3.01 year 4.64 year 0 year 0.50 year 1.01 year 1.96 year 3.13 year 4.53 year

z Acryloid B-44S 0.0390 0.0614 0.0754 0.0143 0.0263 0.0240 a0.0269 0.0375 80.0385 20.0230 0.0512 0.0325 0 Acryloid B-48S 0.0169 bO.0170 a0.0244 0.0147 0.0176 0.0230 0.0188 0.0239 0.0221 0.0197 0.0386 0.0286

,-, Acryloid B-66 b0.0299 b0.0396 b0.0598 a0.0296 bo.0504 b0.0478 0.0387 a0.0619 0.0690 0.0505 0.1011 0.0769 ' Acryloid B-67 b0.0091 "0.0128 a0.0187 a0.0122 a0.0189 a0.0178 0.0114 0.0184 0.0209 0.0162 0.0254 0.0172

,~ Acryloid B-72 0.0286 a0.0343 0.0485 0.0238 0.0451 0.0380 '0.0330 0.0424 b0.0430 80.0482 '0.0728 '0.0538

L Acryloid B-82 0.0231 b0.0286 0.0410 0.0173 0.0359 0.0319 0.0343 0.0464 0.0427 0.0492 0.0786 0.0538 4 Acryloid B-99 0.0200 0a.0288 - 0.0297 0.0315 0.0328 cracked films - - - -

Acryloid C-10-LV b0.0247 b0.0409 b0.0550 bO.0376 b0.0470 b0.0536 bO0.0410 b0.0506 b0.0745 b0.0998 b0.1185 b0.1053 Acryloid F-10 0.0254 0.0404 0.0543 0.0377 0.0491 0.0507 0.0344 b0.0562 0.0559 0.0538 0.0940 0.0783 Acryloid NAD10 b0.0494 80.0479 bo.0747 b0.0471 b0.0571 b0.0606 0.0352 a0.0415 0.0496 a0.0551 0.0664 0.0482

Elvacite 2013 b0.0367 b0.0608 b0.0814 b0.0554 b0.0718 b0.0712 cracked films - - - - Elvacite 2028 0.0290 a0.0351 0.0503 0.0280 0.0348 0.0376 0.0251 0.0354 0.0398 0.0261 0.0540 0.0361 Lascaux 360 HV 0.0164 0.0252 0.0311 0.0261 b0.0326 0.0336 0.0180 0.0266 0.0263 0.0294 0.0361 0.0326 Pliantex b0.0336 a0.0555 a0.0734 a0.0464 a0.0593 a0.0593 0.0208 0.0341 0.0322 0.0419 0.0508 0.0379 Rhoplex AC-33 0.0183 b0.0365 0.0462 0.0388 0.0411 0.0495 0.0207 0.0381 0.0382 0.0341 0.0484 0.0390

Rhoplex AC-73 too brittle - - - - - - - - - -

Rhoplex AC-234 0.0316 0.0472 0.0622 0.0482 0.0525 0.0643 0.0318 a0.0474 0.0475 0.0500 0.0627 0.0484 Rhoplex AC-234+AC-73 0.0256 0.0484 0.0580 0.0457 0.0570 0.0646 0.0254 0.0445 0.0493 0.0413 0.0594 0.0461 Rhoplex AC-235 0.0184 0.0382 0.0487 0.0374 0.0431 0.0492 0.0215 a0.0458 0.0493 0.0410 0.0627 0.0526 Rhoplex LC-40 0.0216 a0.0324 0.0405 0.0294 0.0334 0.0411 0.0246 0.0341 0.0394 0.0363 0.0551 0.0490

Rhoplex N-560 0.0276 0.0439 0.0542 0.0409 0.0465 0.0547 0.0256 0.0361 0.0403 0.0524 0.0610 0.0541 Rhoplex N-580 b0.0386 a0.0508 b0.0632 0.0484 0.0543 0.0683 0.0381 0.0473 0.0503 0.0663 0.0812 0.0703 Rhoplex N-619 0.0179 a0.0294 0.0407 0.0293 0.0397 0.0447 0.0181 0.0350 0.0393 0.0497 0.0577 0.0534 Rhoplex N-1031 0.0435 0.0564 0.0679 0.0566 0.0631 0.0647 0.0461 0.0527 0.0557 0.0503 0.0678 0.0597 Unsupported Texicryl "0.0630 b0.1040 b0.1205 b"0.0790 b0.0977 b"0.0987 0.0910 0.1262 0.1257 0.1272 0.1871 0.1688 (film) Unsupported Texicryl 0.0813 0.1222 - b"0.0861 a0.0947 b0.1167 a0.1094 a0.1357 0.1110 - - a0.1856 (toluene cast)*

Values indicate the mean of 3-5 samples; Standard deviations are 20%; * aging times for this adhesive were: dark aging - 0, 0.55, 1.68, 2.52, 4.08 years; light aging - 0, 0.50, 1.46, 4 years



Strong Discoloration

Perceived

Visible Discoloration Perceived

Figure 6 Degree of yellowing (A,) for the acrylic adhesives after six months, one, two, three andfive years of dark and light aging (see Table 11 for data). Each cluster of points represents an adhesive. Adhesive clusters are grouped according to chemical composition (see Table 2).

for each adhesive, and plot average At with time (t). Lines are marked on the figures at A, = 0.1, the degree of yellowing where a 0-1mm film would be perceived to be visibly yellow, and at At - 0.25, the point at which the film would be perceived to be strongly yellow [24].

Yellowing discussion

Normally, the yellowing curves would be extrapo- lated to At = 0-1 and 0-25 to determine how long it would take a film to reach these degrees of yellowing. However, to date, the yellowing curves have not yet fully developed to the point that this can be done with any certainty. Nonetheless, some trends can be identified. In general, the PVAC adhesives yellowed approximately twice as quickly as the acrylic adhesives. Light aging tended to make all the adhesives yellow more quickly than dark aging. As yet, no obvious differences in yellowing between homopolymers and copolymers have emerged.

The following PVAC adhesives displayed the best

resistance to yellowing (all A, values


General discussion

In order to compare one adhesive to another easily, the results from the pH, volatiles, strength, flexibility and yellowing tests were tabulated together. Tables 12 and 13 list these results for the PVAC and acrylic adhesives, respectively. The worst value for each of the aging conditions, for each adhesive, for each test, is shown on these tables. According to these tables, the best PVAC adhesives were Jade No. 403, Beva 371, Mowilith DMC2 and R-2258. Also performing well were Rabin's Mixture and Elvace No. 1874. The best acrylic adhesives were Acryloid B-82, Acryloid F-10, Rhoplex AC-33, Rhoplex AC-235, Acryloid B- 72, Rhoplex AC-234 and Rhoplex AC-234 + AC-73. Also performing well were Lascaux 360 HV, Acryloid B-48S, Acryloid B-67, Acryloid B-99, Acryloid B-44S, Acryloid NAD-10, Elvacite 2028, Rhoplex N-560, Rhoplex N-580, Rhoplex N-1031 and Rhoplex N-619.

This study has helped to identify several adhesives with good pH, volatile emission, flexibility, strength and yellowing properties. However, only five years-in some cases less-of aging under mod- erate conditions were studied. The results must be viewed with this limitation in mind.

Some valuable lessons were learned that could benefit others attempting a project of similar nature. Testing fewer products would have expe- dited the project. Perhaps if fewer products were tested then more properties (i.e., removability, shrinkage, gloss, etc.) could be examined. Therefore, in future, it would seem prudent to use a pH screening test to reduce still further the number of products tested.

Conclusions

Tests carried out on PVAC and acrylic adhesives have identified several adhesives with good pH, volatile emission, flexibility, strength and yellowing properties. From this study, the following general conclusions can be drawn:

(1) The pH results showed that the PVAC adhesives were more acidic than the acrylic adhesives and that light aging tended to decrease pH of both classes. The PVAC homopolymers were generally more acidic than the PVAC copolymers, and many acrylic adhesives containing butyl acrylate were found to be neutral.

(2) The analysis of volatile compounds from the PVAC and acrylic adhesives showed that they emitted various ester and residual solvent compounds. Only the PVAC adhesives released appreciable quantities of acetic acid but any

risk associated with these emissions decreases rapidly after the initial curing period of several weeks.

(3) In general, both the PVAC and acrylic adhesives became less flexible upon dark aging, and the PVAC adhesives were stronger and less flexible than the acrylic adhesives. PVAC copolymers displayed and retained more flexibility than the PVAC homopolymers.

(4) The PVAC adhesives yellowed approximately twice as quickly as the acrylic adhesives and light aging tended to make all the adhesives yellow more quickly than dark aging.

(5) This research has identified groups within the PVAC and acrylic classes (e.g., vinyl/acetate ethylene copolymers and butyl acrylate copolymers) with good properties. This suggests that a more in-depth look at these groups is war- ranted.

Although it is hoped that this study will assist conservators in making appropriate adhesive choices, it must be emphasized that each conservation applica- tion is unique and other concerns such as removability, shrinkage, gloss, bond strength, adhesive/ substrate interactions, etc., which were not examined in this study, may also be important. Each individual case must be carefully assessed before an adhesive is selected.

Acknowledgements

The authors sincerely thank and acknowledge each of the following people for their valued efforts: France Bertrand, Mona Gudgurgis and Deb Bisaillion for their technical assistance with the pH and yellowing measurements; Mark Boyle and David Miller for their technical assistance and advice on the volatile emission measurements; Helen Burgess for her advice concerning pH and the acceptability ranges for paper; Stefan Michalski for his advice on the stress/strain experiments; Dr David McLean for his expertise in the statistical analysis of the stress/strain data; Paul Marcon for his assistance with the data aquisition control mod- ule for measuring film thickness for yellowing; Tom Strang for computer assistance and programming; and Charles Costain, David Grattan, Ela Keyserlingk and Ray Lafontaine for their advice and constant support on all aspects of the project.

Materials and suppliers

Acryloid B-44S, B-48S, B-66, B-67, B-72, B-82, B- 99, C-O1LV, F-10, NAD-10: Rohm & Haas




Table 12 Overall performance of the poly(vinyl acetate) adhesives Adhesive pH Volatiles Tensile strength Flexibility Yellowing

0 D L D L 0 D L 0 D L 0 D L

Vinyl acetate homopolymers

AYAA ..............S S B B B P f P

AYAC A . A -B -f'......f......... ..

AYAF A N A I I S S S B B B f f P

AYAT A lsi s A Ig S S S B B B f f f

.......................... ::::::::::::::::

Vinac B-15 A N A I I S S S B B B f f P Sure-Grip Carpenter's A A A m h M S S R B B P P P UHU All-Purpose Clear A A A iiiiiiii i ..S S - is.: B

-

i

Rabin's Mixture A -

I W M. f CMBondM-2 A A A h h M S F B f f f CM Bond M-3 A A A m m S S S B B B P P f

Promacto A-1023 A A A I m M : F F F f f P

Elmer's Glue-All A A A m m M S S F. B B f f f Weldbond A A A m m M M F P G Bondfast A A A m

h S S B B f f

Gaylord Magic Mend A A Ai iii m S S PiiU~ii? f f

Bulldog Grip 2311 A A A I m S S S B B B P P P :.....ii.:iiiiii.iiiiiiii......

Bulldog Grip 20 Min A A A m m S S .......... B f f f Elmer's Carpenter's A A A m m S S S B B B P f f

Vinyl acetate / ethylene copolymers

Jade No.454 A A A m f P P

Elvace No. 1874m

Vinnapas Dispersion EP1 A A m I W W W .

f f Beva 37l ~ N 1N I M M F F..

.

. f P

.. . .. . . . .. . . .. . . . .

. . .. . .. .

..

.

.. . . .. . .. . .. . i:i:::::::::j::j::::j:::jj:::i:::j::::: ??:?:?:?:.5:?:'.:t.i:.. ::j:i.~::::::::~:~~: .................: :::i:s;~s;~;~;::~::~~3:::W :~:: . .......... ~ :. .....

.......:~:~: .1?: ;:f.:?:.:.:?f: ?~~~~~~~~?:.:.: ?~~~~?:?:?:.:-:?15:~~~~~~~~: ?.?.?rr: :: ~ ~ ~ ....... W eldbond ....... .. ....... ............ ...i~ ~ ~~.~:~:d c~~:;:::~;?i :~~ii~~~~ii~~j ?~~??,:? m ~ ~ ~ ~iiiii. . . . . ......... .. ............. :i~~:~~::::~~~::~~:~:l~~?:.... ................................. .... . ...................

Elmer's Capenter's A A A m m s S B B B f f Vinyl acetate ethylene copolymers~~~~~~~?:?:~:~:~:~:~:~~:~::::::~ ?~?~::::'f::~:~~: ?~?:::~~:: ? ~ :~~:~~::~:~::~~:~:~:::::i::.:i::~.:.:. .. . ..:~j~;: Jade N o.454 A A A m h ..... . ..... . ..... ........ . ......:~~:~:~::~~::~:::~::~' ~ ~ ~ i ~ i: ; ? Beva 371 :~:?:~s:~:i~:~:~::::iii~i~i~i~t?Ej~i j:c :?:~::~::;::! ~?:?~s?~st :;I:.......... ... .. ............ ? iiiiiii~~~i~~.T:~:~~.:4~:~~~ii::;;?1??r?:??:?:r;??t?I????c?I?:r; .: :::~:,, i:::~1?~:11)1:2.: ....:::: ... ..... ......... . 77. t0:.~?~5 r-?~?~?X?:?~;::R;:;:; ? ?f~5s ;. . . . .... . . ...... .... .

......?~i

Vinyl acetate / acrylic copolymer Mowilith DM5 A A A m m W W - - ii f f

Vinyl acetate / maleate copolymer Mowilith DMC2, m m ji..j.G f

Vinyl acetate / acrylic / maleate copolymer MowilithDM5 + DMC2 : .::...:: h h i iiii:i W i if f

0 = 0 years; D = dark aging; L = light aging; For each of the above, the worst value of the entire aging period was taken; pH (dry film extracts only) - A = acidic (pHpH=8.0); Volatiles - 1 = < 1IAg acetic acid / g adhesive; m = 1-10 .tg/g; h = > 10 tg/g; Tensile strength - M = medium strength (2-15 MPa); W = weak (15 MPa); Flexibility - B = brittle (elongation 2000 MPa); F = flexible (elongation >20% or modulus 0.10; Shading indicates desirable properties.




Table 13 Overall performance of the acrylic adhesives

Adhesive pH Volatiles Tensile strength Flexibility Yellowing

0 D L D L 0 D 0 D 0 D L

Homopolymers

Acryloid C-10-LV A A aa Wi

Rhoplex LC-40 A A A D R:&.f&L W W

Rhoplex N-580 Xafamaaa a {Ni 2 > W - a f f *:'. , ---. ... R.RR... -,R '.. ....... 'R'R'-'

~~~~~~~~~~..Elvaci...-"te 2028 '.fi-- .R '' ' 2- - tR*ji~i~~jiS~ '>'-',Q ::I::'--'1::::~:I::. . .. ..._ f

Acryloid F- 10 * -@- - X -- Re-0-6>-e se. i R R R R R R.R

.........,..., .....r ...:........... ...,.. ..........................

Acryloid B-67 "w? R*. -"RR-R i ...:-' .

..

nr': . ....:....... . .:R:-::-::-:.:..:- ::: : . .

CODOIVMerS. .. . ...... .... ......

?:?:?:?5?:?:?:?::?:?:?:?f......... . ... .. .... . .i:?.l.??l.??.?.................. ii~i~i tj~i~ E~ii~'"'' ~ ?'::"'::::::"':::::";' """ .:. ...... .. ....... Elvacite 2028 ""' ...~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0....... ............... .... ... .. ...........Jr.: ....

? ;V: ? ;?? . ??.....................?.?. ??.??.?..?..?..?.??. .........???? ................ ......... ...... .....??....,.,?:::.r ??????.::::. cs:s

............ ??????????. ?????? ....... :??I?::?.?.::.?.3.?:i': ....... ..

..............~~~iijii ...... X::5 ?II:: ???::~: ????: ? .......

............. ................ ~ i~~.~'..'~~.~ .......~~~...s.~ ~ ;~:. ~ ;s..~ s ,.s;~;; ~i; ~5;si . ...........................r ?.. ., '? ? ?? ??" .....

... ....... . .. .......:c??I??II???:?:::??:::??:.... . .. ,, .

..... .

. .... ..

....?'. ??. ... :. A cryloid F -10 ii~Siiiiiiji'' iiiiiii~iiiiiii~iiji~jijiii~t~iitiE tiMiiiSi:tiiiB B iii jS~.......... f fi~~iiiii ?????. ??:??? ;::.?::?::??::??? ?::? .............?? ?????i??)??

Conol~vmers9

Acryloid B-72 N.....il A i MS f. . :::::::~~~~~~~~:~~~S~~::-:il~~~~~~~~~: i?R:?:s?: ? ?.?.?.?.?.?.?.?u ? :?:5 L ~ ~ ~ ~ ~ ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ..... ...........

............ ........ . ..?.?.s?.?.?.?.?.?.?.?;:?.?.?.?;?.?.?;?.................is:!i:::?ii:::?is:i:i }

R.hoplexAC-234 Nlii~-~ iii A A i!iii?i?iil}~i~i:i!i~ii: A n! n M! F G: fiii f!i ~iiii?:.~iii!iiiii:!i~.i~:iii~:i!~~.i!!i!Mi:j:i~ii:

.:?:?:?: .......??:?: 1 '::'":::'?:: ':::......:':'......:....ii:

~~~~~~~...... ....::....... .- ... . . . . f f i::i::j:3?::i:~i::i:: ii A I: ???? ?' A~ il}iiii!?::?:.:: :??? RhoplexNAC-..3 N?:.." A A i!:i:

... ..B

......B. ............. v. . ...... ;.:-..v.....v.

Acrupported8 T e NiNr yN - A AMiMiF FiU::i!G!!ifif::::::!iii!ii!! W P P

?~:?:?u;+I::............... .::: : : : :::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::

RhoplexNA-234 N NC7 Nii?-i:~i? A Ai W W:: F::::: F Giii?i ?$?::!!f:

.......:.......:.... . ..:::j.. f

RhoplexAC-235 Niii?i::i A A !iii-iFiiGii!if: fi!iii!iiiiiii!iiiii:~~5~

RhoplexN-560~~~~~~~:5:::?:??:I N?????:::??:: ???????? N N .??.?i - W F ..?.. ? f f?

Elvaite2l3 N N n - - B B - f

AcryloidB6 i

!i'iiiiiiiiii'iiiii:ii. . .. ..... .............. . . . . ..

RhoplexNC-033 N.......... .....Ni ....

R hoplex A C -23 5 :::~:~~i:::::: :.?:.::?:1. s? ??:?::?:?::?:.?:.:.Ij~~ ? .. ............. ....'i: : : . :. : .:.:.v....v...

..

Acryloid B-99 N N N ~ ~ ~ ~~~ ~~ ~~~~~~~~- - B B U}~liii~iiii f~ -

:: : ...... '

..........'

.... . ......

Unsupported Texicryl A A ........:}:!:l f

.::: : : .:::::::::::: :

............. .......

.....

............... .............::;:i:5::;::i:;~::5;:si9. . ::...

Rhoplex AC-234s AC-73 aii:c .)A A nA:.....50 W a :i::H: .0) f f Acryloid - 99 iiiii~!iii'iii!!?~iii}liiii'i$ii"?~}iiiiii!i!iiil}!?~i!!:'~'iii!} ...............................B..........

... ........ .. . . .....................

............ ........

Rhoplex AC-73 idic ( pH 20% or modulus 0.10; Shading indicates desirable properties.

:::::~~~~~t:15:~~~~~C:. ?:?s~~~~~~~:tI: ? u ??. ?? . ... .. :?:;:?. ?.... . ... . .i A cryloid B -44S B f f~5:?:1%:::??????::::: ??:::.?:??????:"'' ??:?????~ I??O::

..........tS...... ... :::i::::::j:::i:1~::: :.?:.?:i?:~~~~~~?: .?.~~~~r?.~ ~? ..... ........... . ..........::::? S:?;?';? .::: Rhoplex N-619 W f~~~~~~~~ ????????..?.. ??.??-..???

Acryloid B-48S A A A ::s : ????:s~?~?:???????:???~.?:s?::: :? ::::l??? .;?:::: ::???~ ? :~?::::;~.::~:~:::::~.:::::::::: ~ ""'" """" '?'' ,:?:'':. . . ............. ?.?. ? ..

.. ?? ???,. ??....... ..... ... ..

..

?:??.'.:;f%::i~~i : ? ? Rhoplex AC-235 A A~.:ii?S?:i:;i:;?$: ::C:;.:). ....................~~~~~~~~~~~~~~~~~.::~~~. ;?'.

. ..................... .........

~ ~ ~ ~ ~ ~ ~ ~ ~ ?c:.?..::2.:.?:.r.:::~~::: Rhoplex N-560 f f~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~i:;::::::::;::;-::?:::::x:?::?:::

A cryloid B-66S A A iB f p?:? SS?:::';?? ;:::.???? .........?: ?.. ??...?.?.. ...... .. ... . .........''''''''

Rhoplex N-131W ........... . f ...... .... .~~???l?.? ..;?'.- ??:::::::: ?:??? Acryloid B-99 B B:.:::::: ::X.?O::X:L5?\??.. C:1:??:::~?;?f3~::I

Acryloid NAD-10 A A f f~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~?:Z:::???.\;~:.???:::: 0 =0 yars D= drk gig; = igt aing Fo ech f te bov, te ors vaue f he ntie gin peio wa taen

pH (dy fim exract only - A= acdic pH 8.0); olatles n = no dangerous volatiles released; I = < lAg acetic acid/ g adhesive; Tensile strength - M = medium strength (2-1

MN); W = weak (< 2 MN); S = strong (> 15 MN); Flexibffity - B = brittle (elongation < 20 % or modulus > 2000ss:.:t?:?:?:C?: MPa); F = flexible (elongation > 20 % or modulus < 2000 MPa) Yellowing - G = good, At < 0. 05; f = fair, A. = 0. 05~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:??::?::?::??:??f:: ??:??:??: to 0. 1 0; P = poor, At > 0. 1 0; Shading indicates de::?~?:?:sirabl prpertes


......

41


J.L. Down. M.A. MacDonald. J. Tetreault and R.S. Williams

Canada Inc., 2 Manse Road, West Hill, Ontario, Canada M1E 3T9.

AYAA, AYAC, AYAF, AYAT: Union Carbide Canada Ltd, 1000 Finch Avenue West, Downsview, Ontario, Canada M3J 2E7.

Beva 371: Sigmund Haller, Bank of Nova Scotia Chambers, 79 Queen Street, Toronto, Ontario, Canada M5C 1R8.

Bondfast: Lepage's Ltd, 50 West Drive, Bramalea, Ontario, Canada L6T 2J4, Canada.

Bulldog Grip 20 Minute Resin, Bulldog Grip Resin 2311: Canadian Adhesives Ltd, 81 Kelfield Street, Unit 7, Rexdale, Ontario, Canada M9W 5A3.

CM Bond M-2, CM Bond M-3: Conservation Materials Ltd, Box 2884, 340 Freeport Boulevard, Sparks, NV 89431, USA.

Elmer's Glue-All, Elmer's Carpenter's Glue: Borden Chemical Canada, 595 Coronation Drive, West Hill, Ontario, Canada M1E 4R9.

Elvace No. 1874: Talas, Technical Library Services Inc., 213 West 35th Street, New York, NY 10001-1996, USA.

Elvacite 2013, Elvacite 2028: Du Pont Canada Inc., PO Box 26, Toronto Dominion Centre, Toronto, Ontario, Canada M5K 1B6.

Gaylord Magic-Mend: Gaylord Library Supplies & Equipment, PO Box 4901, Syracuse, NY 13221-4901, USA.

Jade No. 403, Jade No. 454: Talas, as above. Lascaux 360 HV: Lascaux Farbenfabrik,

Riedmuhlestrasse 19, 8306 Briittisellen, Switzerland.

Mowilith DMC2, Mowilith DM5: Hoechst Canada Inc., 4045 Cote Vertue Boulevard, Montreal, Quebec, Canada H4R 1R6.

Pliantex: Originally obtained from Frank W. Joel Ltd, but no longer available.

Promacto A-1023: Talas, as above. R-2258: Talas, as above. Rabin's Mixture: 50g AYAA and 50g AYAC dis-

solved in 154ml toluene (methylbenzene) to which 12ml of Multiwax solution (2g Multiwax No. 445 melted in 25ml toluene) is added.

Rhoplex AC-33, AC-73, AC-234, AC-235, LC-40, .N-560, N-580, N-619, N-1031: Rohm & Haas Canada Inc., as above.

Sure-Grip Carpenter's Glue: Lepage's Ltd, as above.

UHU All-Purpose Clear Adhesive: Talas, as above. Unsupported Texicryl: Lisle Kelco Ltd, 6799 Steeles

Avenue West, Rexdale, Ontario, Canada M9V 4R9.

Vinac B-15: St Lawrence Chemical Inc., 5405 Pare Street, Montreal, Quebec, Canada H4P 1P7.

Vinnapas Dispersion EP1: Henley Chemicals Ltd, 1735 Bayly Street, Pickering, Canada L1W 3G7.

Weldbond: Frank T. Ross & Sons (1962) Ltd, PO Box 248, West Hill, Ontario, Canada M1E 4R5.

References

1 DOWN, J.L., 'Adhesive testing at the Canadian Conservation Institute, past and future' in Adhesives and Consolidants, IIC, London (1984) 18-21.

2 DOWN, J.L., and WILLIAMS, R.S., 'A report on the evaluation of selected poly(vinyl acetate) and acrylic adhesives for use in paper conservation' in Conservation of Historic and Artistic Works on Paper, Proceedings of Symposium 88, Ottawa (1994) 163-180.

3 DOWN, J.L., MACDONALD, M.A., TITREAULT, J., and WILLIAMS, R.S., 'Adhesive testing at the Canadian Conservation Institute-an evaluation of selected poly(vinyl acetate) and acrylic adhesives', Environment and Deterio- ration Research Report No. 1603, Canadian Conservation Institute, Ottawa (1992).

4 'Standard test method for hydrogen ion concentration of dry adhesive films, D 1583-61', Annual Book of ASTM Standards 22 (1982) 477-478.

5 BLACKSHAW, S.M., and DANIELS, V.D., 'The testing of materials for use in storage and display in museums', The Conservator 3 (1979) 16-19.

6 BRADLEY, S.M., 'Safe fabrics for permanent exhibitions', Conservation News 23 (1984) 16-18.

7 BARROW, W.J., Manuscripts and Documents. Their Deterioration and Restoration, 2nd edn, University of Virginia Press, Charlottesville, VA (1972) 45-47.

8 BARROW, W.J., The Manufacture and Testing of Durable Book Papers, Virginia State Library, Richmond, VA (1960) 14.

9 WILHELM, H., and BROWER, C., The Permanence and Care of Color Photographs: Traditional and Digital Color Prints, Color Negatives, Slides, and Motion Pictures, Preservation Publishing Company, Grinell, IA (1993) 470-472.

10 BURGESS, H.D., 'Other cellulosic materials' in Storage of Natural History Collections: A Preventive Conservation Approach, ed. C. ROSE and C. HAWKS, Society for the Preservation of Natural History Collections (1995) 291-302.

11 American National Standard for Information Sciences-Permanence of Paper for Printed Library Materials, ANSI Z39.48-1984,




American National Standards Institute, Inc., New York (1984).

12 FARMER, R.H., 'Corrosion of metals in associa- tion with wood. Part 2. Corrosion of metals in contact with wood', Wood (November 1962) 443-446.

13 'Corrosion of metals by wood', Guides to Practical Corrosion Control, Department of Industry, London (1980).

14 American National Standard for Imaging Media-Photographic Processed Films, Plates, and Papers-Filing Enclosures and Storage Containers, ANSI IT9.2-1991, American National Standards Institute, Inc., New York (1991).

15 REILLY, J.M., 'Role of the Maillard, or "pro- tein-sugar" reaction in highlight yellowing of albumen photographic prints' in Preprints of Papers Presented at the Tenth Annual Meeting, Milwaukee, Wisconsin, American Institute for Conservation, Washington, DC (1992) 160-168.

16 EASTOE, J.E., 'Composition of collagen and allied proteins' in Treatise on Collagen, Vol. 1, Chemistry of Collagen, ed. G.N. RAMACHADRAN, Academic Press, London (1967).

17 MARCH, J., Advanced Organic Chemistry, Reactions, Mechanisms, and Structure, John Wiley & Sons, New York (1968) 334.

18 MIDDLEDITCH, B.S., Analytical Artifacts, GC, MS, HPLC, TLC and PC, Elsevier Science Publishers, Amsterdam (1989) 343.

19 CLARKE, S.G., and LONGHURST, E.E., 'The corrosion of metals by acid vapours from wood', Journal of Applied Chemistry 11 (1961) 435-443.

20 TETREAULT, J., 'Corrosion of copper, zinc and lead in acetic acid vapour', unpublished work, Canadian Conservation Institute (1992).

21 TITREAULT, J., 'Evolution des produits volatils liberes par des adhesifs PVAC at acrylique', Environment and Deterioration Research Report No. 1874, Canadian Conservation Institute (1990).

22 'Standard test method for tensile properties of organic coatings, D 2370-82', Annual Book of ASTM Standards 06.01 (1988) 331-334.

23 GIBSON, L.J., and ASHBY, M.F., Cellular Solids Structure and Properties, Pergamon Press, Oxford (1989) 47-55.

24 DOWN, J.L., 'The yellowing of epoxy resin adhesives: report on natural dark aging', Studies in Conservation 29 (1984) 63-76.

25 DOWN, J.L., 'The yellowing of epoxy resin adhesives: report on high-intensity light aging', Studies in Conservation 31 (1986) 159-170.

Authors

JANE L. DOWN graduated from Queen's University, Kingston, Ontario in 1973 with an Honours BSc in chemistry and mathematics. From 1973 to 1978, she worked in various ar

Adhesive Testing at the Canadian Conservation

Documents

Transcript of Adhesive Testing at the Canadian Conservation