The effect of adhesive concentration, reactivation time, and pressure on the peel strength of heat
and solvent-reactivated
Lascaux 360/498 HV bonds to silk
Irene F Karsten*
302 Human Ecology Building
University of Alberta
Edmonton
Alberta T6G 2N1
Canada
Fax: +1 780 492 4821
E-mail: ikarsten@ualberta.net
Jane Down
Canadian Conservation Institute
1030 Innes Road
Ottawa
Ontario K1A 0M5
Canada
Fax: +1 613 998 4721
E-mail: jane_down@pch.gc.ca
*Author to whom correspondence should be addressed
Abstract
The peel strength of fabric specimens adhered with Lascaux 360/498 HV and prepared using
acetone, IMS, and heat reactivation under varying conditions of adhesive concentration,
reactivation time, pressure, and temperature was compared. Acetone reactivation gave stronger
bonds than IMS or heat at constant time and pressure. IMS produced stronger bonds than heat at
times over 5 min. Increasing reactivation time, pressure or temperature increased peel strength. If
levels were too high, the bond was very strong and adhesive was transferred to the artifact fabric
on peeling. Tests using a continuous film of adhesive are recommended for determining optimum
reactivation time, pressure and temperature. Clipon weights can be used to classify the peel
strength of mock-up specimens.
Keywords
adhesive, textiles, solvent reactivation, heat reactivation, peel strength
Introduction
When considering the use of an adhesive support treatment for textile artifacts, conservators can
be easily overwhelmed by the number of choices the treatment involves and by difficulties in
comparing different approaches. Choices have become more complex with the recent
introduction of solvent reactivation techniques. Although precise techniques vary, solvent
reactivation usually involves methods similar to humidification but with solvent-soaked paper
separated from the coated support by a membrane (Krueger-Willson 2002, Squire 2002, Takami
and Eastop 2002). Glass weights or vacuum provide the pressure that secures the bond. This
study was stimulated by claims that Lascaux 360/498 HV bonds formed by solvent reactivation
were stronger than those produced using conventional heat-sealing (Squire 2002). In solvent
reactivation, solvent and pressure are usually applied for a much longer time, however, than heat
and pressure are applied in heat reactivation. Differences in bond strength, therefore, might be
due to differences in technique other than the switch from heat to solvent. This research
examined the effects of four key treatment variables on the peel strength of silk habutae adhered
to Tetex with Lascaux 360/498 HV: concentration of the adhesive solution, mode of reactivation
(solvent/heat/temperature), time exposed to the reactivating agent, and pressure applied during
reactivation. A simple method to quantify the bond strength of mock-up test specimens was also
tested for its ability to accurately estimate relative peel strength.
Experimental procedures
Preparation of fabric specimens
To model textile artifacts treated with adhered supports, specimens were prepared from silk
habutae (artifact) and polyester crepeline (Tetex, support). Both fabrics were washed in a 0.3 per
cent (w/w) sodium lauryl sulphate detergent solution, rinsed, and air dried before cutting into
strips measuring 200 mm × 30 mm (warp × weft) and ravelled to 25 mm in width. Strips were
randomly assigned to treatment groups. The adhesive used to produce the specimens was a
mixture of two acrylic dispersions, Lascaux 360 HV and Lascaux 498 HV. These adhesives, both
poly(butyl acrylate)/poly(methyl methacrylate) copolymers thickened with acrylic butylester,
were combined in a 1:2 (360:498) mass ratio. One part adhesive mixture was diluted with either
one or ten parts water to give coatings that produced, respectively, a continuous film over the
fabric or a coating over only the yarns. Tetex strips were clamped to a sheet of Teflon®-coated
glass cloth attached to a glass plate and brushed with adhesive solution. The adhesive was
allowed to air dry in ambient lab conditions. One week after drying, the coated support fabric was
adhered to silk habutae through either solvent or heat reactivation. Alignment of the coated
support and artifact fabric strips was maintained during reactivation by taping the strips to a
matboard support, with the silk habutae next to the board. To facilitate peel testing, silicone
release paper prevented adhesion of the upper 50 mm of each specimen.
Adhesive reactivation
Solvent reactivation was performed using a strip of chromatography paper moistened with 2 ml
of either acetone or industrial methylated spirits (IMS). Because IMS is not available in Canada,
a solution of 95 parts absolute ethanol to 4 parts methanol and 1 part water (by volume) was
prepared before each reactivation session in accordance with the composition of IMS commonly
used by textile conservators in the UK (Wyeth 2003). The moistened paper was covered with a
barrier layer of Sympatex®, a polyester/polyether block copolymer membrane attached to a thin
layer of polyester batting. The batting side was positioned next to the solvent-moistened paper.
Although Sympatex®, like Goretex®, is impermeable to liquid water, these membranes permit
solvents like acetone and IMS to pass through in both liquid and vapour form. The Sympatex®
layer provided very controlled solvent penetration to the adhesive coating. The membrane side of
the Sympatex® never felt wet. Preliminary tests showed that Sympatex® provided more control in
this regard than Goretex® (nonwoven-supported) or filter paper. The sandwich was completed by
laying the specimen on top of the Sympatex®, support fabric side down, covering the whole
assembly with polyethylene sheeting and providing pressure by placing a weight over the
specimen (Figure 1). Custom-cut weights all measured 25 mm × 150 mm but were of varying
thickness to provide a range of pressures. Most solvent-reactivated specimens were pressed under
6 mm glass (1.4 g/cm2) or 12.7 mm steel bar (10 g/cm2). To demonstrate the effects of greater
pressure, 25.4 mm steel bar (21 g/cm2), 50.8 mm steel bar (42 g/cm2), or two 50.8 mm steel bars
(84 g/cm2) were used on specimens reactivated with IMS for 5 min. Weights were left in place
for reactivation times of 0.5 to 20 min. The times chosen for each solvent reflected the range of
bond strengths possible from weak to strong as determined through pre-testing. Times that
produced overly weak or strong bonds were not included.
Figure 1. Solvent and heat reactivation methods
Heat reactivation was performed using a DigiPrep HP hot plate to model a hand-held tacking
iron. The heated surface of this hotplate is a Teflon®-coated graphite block. Temperatures varied
over time by less than 1 ºC and over the surface of the hotplate by ±1 °C. Specimens attached to a
matboard support were laid specimen-side down onto a silicone release paper barrier set on the
hotplate surface (Figure 1). Temperatures from 75 °C to 155 °C were used to demonstrate the
effect of temperature on peel strength. Steel bars supplied pressures from 10 to 84 g/cm2. The
reactivation time for most specimens was 1 min. The effect of reactivation times from 0.5 to 20
min was demonstrated at 115 °C. A summary of all treatment variables is given in Table 1.
Table 1. Levels of reactivation variables
Figure 2. Clip peel test
Measurement of peel strength
The peel strength of each specimen was determined by a T-peel test conducted on an Instron
Universal Testing Instrument, Model 4201, using a 2.5 N load cell and 6 mm spring-loaded fibre
grips set at a gauge length of 25 mm. The separated ends of the silk habutae and coated Tetex
were placed in the upper and lower grips respectively. Specimens were peeled over 100 mm at a
crosshead speed of 50 mm/min. Tests were conducted in a controlled environment of 23 ± 1 °C
and 50 ± 3 per cent RH after one week of conditioning. Peel strength was estimated using the raw
data recorded by the Instron’s Series IX software. Load values corresponding to every peak in the
peel graph were extracted using Microsoft Excel and averaged. The average load was divided by
the width of the adhesive coating to give the peel strength for each specimen. Six specimens were
tested for each treatment group. Peel strength was also categorized according to failure threshold
when weighted with small, clip-on weights. The clip peel classification was determined on 50
mm of each specimen not peeled during Instron tests. The specimen was suspended from a clip
attached to the artifact fabric. Clip-on weights, constructed from fold-back binder clips and
unbleached cotton bags filled with lead shot to give masses of 10, 25, 50, 75, 100 and 150 g, were
attached to the support fabric end of the specimen (Figure 2). The support fabric was gently
lowered until it hung free. If the specimen supported the mass of the weight without peeling, the
next weight was tested, until the mass that caused the bond to fail immediately was determined.
Masses were chosen to give categories that corresponded to bond strengths ranging from very
weak to very strong. Results from clip peel tests were compared to those of Instron tests to see if
this simple test could give reliable results.
Results
The peel strength results for all treatment groups are given in Table 2 (solvent reactivation) and
Table 3 (heat reactivation). Peel strength values ranged from 0.8 to 56.3 N/m. By manipulating
reactivation time, pressure, and temperature, specimens with peel strengths across this range
could be produced with acetone, IMS, and heat reactivation (Table 4). For example, equally
strong peel strengths (40–45 N/m) were produced with acetone reactivation for 1 min under 10
g/cm2 pressure, with IMS reactivation for 10 min under 10 g/cm2 or with heat reactivation at 115
°C for 10 min under 42 g/cm2. Clip peel results exhibited good correspondence with peel strength
values (Table 4). Bond failure occurred at the adhesive/artifact fabric interface in most cases.
Some stripping of the edges of yarns-only coatings from the support fabric was observed for
acetone reactivations longer than 2 min and IMS reactivations longer than 10 min. Tiny pockets
of delamination were observed on one quarter of the specimens. Most occurred along the edges
of heat-reactivated specimens, both those with continuous films and yarn coatings. The
specimens had been
Table 2. Peel test results for solvent-reactivated specimens (mean and standard deviation for six
specimens)
*Adhesive forms either a continuous film or a coating over only the yarns
Table 3. Peel test results for heat-reactivated specimens (mean and standard deviation for six
specimens)
*Adhesive forms either a continuous film or a coating over only the yarns
reactivated using lower temperatures (75–115 °C) and lighter weight (10 g/cm2). Delamination
was observed immediately after heat reactivation. In a few cases, pockets of delamination were
observed just before peeling solvent-reactivated specimens, mostly IMS-reactivated at short times
and low pressure. Adhesive concentration and reactivation mode significantly affected peel
strength results. The peel strength of specimens adhered with a continuous film was
approximately four to eight times higher than equivalent specimens adhered with adhesive
coating only the yarns. Acetone-reactivated bonds were almost three times stronger than
equivalent IMS-reactivated bonds and four times stronger than equivalent 115 °C-reactivated
bonds. IMS and heat reactivation results were less clearly distinguished. Heat reactivation of a
continuous film of adhesive for one minute at 75 ºC resulted in peel strengths that were slightly
higher (6.0 N/m) than those of equivalent specimens reactivated with IMS for 2 min (4.5 N/m).
IMS reactivation and heat reactivation at 115 °C for 5 min at 42 g/m2 gave identical peel strength
results (36 N/m). Increasing the heat reactivation temperature from 75 to 155 °C resulted in
increased peel strength (Figure 3). No scorching of the habutae was observed at any temperature,
nor after long heat reactivation periods at 115 °C. Specimens did exhibit cupped distortion
towards the support for reactivations at 115 °C longer than 2 min and at 135 and 155 °C.
Increasing reactivation time (Figure 4) and pressure (Figure 5) resulted in increases in peel
strength for all modes of reactivation, other variables being equal. At longer reactivation times,
the rate of peel strength increase diminished, particularly for heat reactivation and acetone
reactivation of yarn coatings. The pressure effect was most noticeable on specimens adhered with
a continuous film of adhesive. The increase in peel strength diminished at very high pressure (84
g/cm2). The effect of increasing reactivation time was greater at higher pressures and vice versa.
Table 4. Comparison of Instron peel and clip peel results. Dual clip peel categories indicate
treatments characterized by more than one clip peel classification
Discussion
The results of this study indicate that general comparisons of bond strength produced by solvent
vs. heat reactivation of Lascaux 360/498 HV adhesive coatings may be misleading if the
temperature, pressure, and reactivation time of the treatments are not specified. The results also
provide evidence of the relative efficacy of solvent reactivation techniques. Acetone reactivation
created very strong bonds at short times with little pressure. This is not surprising since acetone is
a good solvent for these Lascaux adhesives (Lascaux 2004). One minute was sufficient to
reactivate a continuous film and produce moderate to strong bonds. Even 30 s produced a
reasonable bond. Preliminary peel tests of 2 and 5 min reactivations resulted in peel strengths that
exceeded the capacity of the Instron load cell. Considerable adhesive transferred to the artifact
fabric in both cases. Visible staining of the silk habutae was observed in the 5 min test.
Reactivation times over one minute resulted in little increase in peel strength of specimens
adhered with adhesive coating only the yarns. The small increases recorded are probably due to
the force required to strip the edges of the adhesive
Figure 3. Effect of temperature on peel strength (continuous film, 42 g/m2 pressure)
Figure 4. Effect of reactivation time on peel strength
coating from the support fabric. Such stripping, the extent of which was only visible under high
magnification (Figure 6), suggests that longer times produce very strong localized bonding.
Acetone reactivation times over 1 min should, therefore, be used with caution. IMS reactivation
required longer reactivation times or higher pressure to equal the results of acetone. A 2 min
reactivation with IMS on a continuous film produced hardly any bond strength at all, whereas it
gave too strong a bond with acetone. Ten minutes with IMS produced bonds as strong as one
minute with acetone. Stripping of the edges of yarns-only coatings from specimen supports
suggests that 20 min is too long for IMS reactivation. Twenty-minute reactivation with IMS on a
continuous film was cut from the study when the peel strength exceeded the capacity of the
Instron load cell. Five to ten minute reactivations are, therefore, recommended for IMS. If
lengthy solvent exposure is safe for the artifact, conservators might choose IMS over acetone for
health and safety reasons. Heat reactivation gave relatively weak bonds under conditions that
conservators would consider using in treatments. Heat reactivation resulted in much lower peel
strengths than acetone reactivation under identical conditions of time and pressure. Trends
suggest that heat reactivation at 115 °C for 10 min or longer would give lower peel strengths than
equivalent IMS reactivation as well, although IMS was less effective at times less than 5 min.
The poor results for lower temperature bonds are in part due to the prevalence of delaminated
pockets. Further study to elicit the cause of these pockets, which may be related to less effective
pressure at the edges of the weights, might help explain similar delamination observed on treated
artifacts (Karsten and Kerr 2003). Production of moderately strong to strong bonds with heat,
given the equipment used to
Figure 5. Effect of pressure on peel strength
model heat reactivation in this study, required temperatures, reactivation times, and pressures that
textile conservators would not use. The planar distortion of specimens exposed to high
temperatures or long periods of heat is further evidence that such exposure is inappropriate for
artifacts. The results of this study suggest that conservators should use continuous films of
adhesives in mock-up testing to determine appropriate reactivation times, pressure levels or
temperatures for reactivation techniques. The degree to which the artifact fabric is embedded into
the coating (Figure 7), which corresponds to peel strength, is visible to the naked eye on
continuous films and can be easily seen with magnification. Increases in peel strength due to
changes in reactivation time or pressure can be readily identified by manually peeling specimens.
Conditions that create overly strong or weak bonds can be quickly ruled out. In contrast,
embedding into or adhesive transfer from adhesive coating only the yarns is not easily visible due
to the transparency of the coating and the presence of the underlying yarns. As well, peel strength
remains low and changes little when reactivation techniques are modified because the artifact
fabric has little adhesive into which to embed. Increasing reactivation time, pressure or
temperature to increase peel strength, may simply create tiny points of very strong bonding –
even localized penetration of adhesive into the artifact fabric – without substantially increasing
overall peel strength. Determining optimal reactivation conditions is thus easier on a continuous
film of adhesive. Moreover, reactivation conditions that provide sufficient embedding into a
continuous film will do likewise for a thinner coating over only the yarns. Once determined,
conservators could use the reactivation conditions to test the bond adequacy of more dilute
adhesive solutions that coat only the yarns, because continuous adhesive films might be
considered unsuitable for treating historic textiles. The good correspondence with Instronmeasured peel strength suggests that the clip peel test is an appropriate tool for classifying the
bond strength of adhered specimens. This test would permit conservators to compare their
techniques with those used in other labs, provided specimen width remains constant. Because the
bond strength of specimens can vary over their length, determining the clip peel category at
several points is recommended. The results of this study suggest that failure of a 25 mm wide
specimen to hold a 10 g weight indicates a very weak bond. On the other hand, the ability to hold
a 150 g weight probably denotes a bond too strong for most purposes. Moderate bond strength is
characterized by failure at 50–100 g.
Conclusions
By comparing the peel strength of specimens reactivated using acetone, IMS, and heat under
varying conditions of adhesive concentration, reactivation time, pressure,
Figure 6. SEM image of Tetex yarns partly stripped of adhesive (20 min reactivation). Reprinted
with permission from the Canadian Conservation Institute (photo: Jane Sirois)
Figure 7. SEM images of weave imprints in adhesive coatings after peeling that correspond to
weak (left) and strong (right) bonds. Reprinted with permission from the Canadian Conservation
Institute (photo: Jane Sirois)
and temperature, this study has shown that conservators can manipulate these variables to achieve
bonds with Lascaux 360/498 HV that range from very weak to very strong. Increasing adhesive
solution concentration to form a continuous film of adhesive as opposed to a coating over the
yarns increased the peel strength substantially owing to greater bonding area. With increased
reactivation time, bonds became so strong that adhesive was stripped from the support fabric
when specimens were peeled. The time at which this occurs was specific to the reactivation agent
and technique, occurring in a few minutes with acetone, as compared to 20 min with IMS or heat
(115 °C). Increasing the pressure applied during reactivation also increased peel strength. Very
strong bonds were achieved more rapidly at higher pressures. Increasing the temperature of heat
reactivation increased peel strength, although some of the difference was due to pockets of
delamination in specimens heat-sealed at lower temperatures and pressures. Because bond
strength depends on fabric weave and stiffness, adhesive type and thickness, and specimen size,
as well as the materials and techniques used for reactivation, which often vary from studio to
studio, this research does not replace the need for mock-up tests. These results suggest that tests
using continuous films of adhesive would facilitate determination of the appropriate reactivation
times, pressures, and temperatures for specific reactivation materials and techniques. The
resulting reactivation techniques could then be used to determine the appropriate adhesive
solution concentration. This study also illustrates the usefulness of a simple method, the clip peel
test, for quantifying the results of mock-up peel tests. Such quantification would better permit
comparison of treatment techniques from project to project and studio to studio.
Acknowledgements
This project was completed while the principal author was a visiting postdoctoral fellow in
Canadian Government Laboratories at the Canadian Conservation Institute. We thank Paul Bégin,
Jane Sirois, Maureen MacDonald, Jan Vuori, Renée Dancause, Janet Wagner and Season Tse of
the CCI for their assistance.
References
Karsten, I F and Kerr, N, 2003, ‘The effectiveness of adhesive support treatments for flags
and banners: condition of treated artifacts surveyed in Canada and the UK’ in Vuori,
J (comp.), Tales in the Textile: The Conservation of Flags and Other Symbolic Textiles,
Albany, North American Textile Conservation Conference, 155–166.
Krueger-Willson, M, 2002, personal communication, Textile Conservator, Victoria &
Albert Museum, South Kensington, London, UK.
Lascaux, 2004, Lascaux water-soluble acrylic adhesives 360 HV, 498 HV, 498-20X
www.lascaux.ch/english/restauro/pdf/7050.02und7051.02.pdf (accessed 14 October
2004).
Squire, L, 2002, personal communication, Textile Conservator, private practice, London,
UK.
Takami, M and Eastop, D, 2002, ‘The conservation of a Korean painted silk banner, c
1800: paint analysis and support via solvent-reactivated acrylic adhesive’ in Vontobel,
R (ed.), Preprints of the 13th Triennial Meeting of the ICOM Committee for Conservation,
London, James and James, 747–754.
Wyeth, P, 2003, personal communication, Conservation Scientist, Textile Conservation
Centre, University of Southampton, Winchester, UK.
Materials
Lascaux 360HV, Lascaux 498HV, Tetex
Talas
20 West 20th Street, 5th Floor
New York
NY 10011, USA
Tel.: +1 212 219 0770
Fax: +1 212 219 0735
E-mail: info@talasonline.com
Silk Habutae
Testfabrics
PO Box 26
West Pittston
PA 18643, USA
Tel.: +1 570 603 0432
Fax: +1 570 603 0433
E mail: info@testfabrics.com
Sympatex®
Preservation Equipment Ltd.
Vinces Road
Diss
Norfolk IP22 4HQ
United Kingdom
Tel.: +44 (0)1379 647400
Fax: +44 (0)1379 650582
E mail: info@preservationequipment.com
DigiPREP HP Hotplate
SCP Science
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Quebec H9X 4B6
Canada
Tel.: +1 800 361 6820
Fax: +1 800 253 5549
E-mail: sales@scpscience.com