Water dispersed polymers for textile conservation: a molecular, thermal, structural, mechanical and optical characterisation

Journal of Cultural Heritage 7 (2006) 236–243 http://france.elsevier.com/direct/CULHER/

Original article

Water dispersed polymers for textile conservation: a molecular, thermal, structural, mechanical and optical characterisation Mariacristina Coccaa, Lucia D’Arienzoa, Loredana D’Oraziob, Gennaro Gentileb, Carlo Mancarellab, Ezio Martuscellia,*, Carmen Polcaroa b

a CAMPEC s.c.r.l, P. le E. Fermi, c/o CRIF, 80055 Portici, Italy Istituto di Chimica e Tecnologia dei Polimeri del CNR, Via Campi Flegrei, 34, Fabbricato 70, 80078 Pozzuoli, Napoli, Italy

Received 28 November 2005; accepted 15 May 2005

Abstract With the aim of identifying new water dispersed polymers for textile conservation, the structure and properties of three commercial polyacrylates and one commercial polyvinylacetate were analysed. The characteristics of these materials, not previously used in the conservation and restoration fields, were compared with that shown by Primal AC33 and Mowilith DMC2 and SDM5, widely used as consolidating or adhesive agents of ancient textiles. To achieve a thorough characterisation of each polymer, molecular, thermal, structural and mechanical investigation techniques were applied on film samples, obtained from polymer water dispersions through water casting at room temperature and/or compression moulding. The photo-oxidative resistance of these materials was also assessed by artificial weathering of water cast films and by measuring the Yellowing Index (YI) as a function of the exposure time under xenon-arc lamp. Collected data were used to appropriately compare the performances shown by these polymers when applied on artefacts consisting of natural fibres. In particular it was found that, among the products not previously used in the conservation and restoration fields, a high potential for carrying out treatments on textiles is shown by the samples commercialised with the trade names of Acrilem RP6005 and Acrilem 30WA. These products, in fact, exhibit properties that make them suitable as substitutes for Primal AC33 and Mowilith DMC2 and SDM5, respectively, depending upon conservation needs. It was very interesting to note that Acrilem 30WA, also after aging, shows YI values lower than that shown by Mowilith DMC2 and SDM5. © 2006 Published by Elsevier Masson SAS. Keywords: Polyacrylates; Polyvinylacetates; Textile conservation; Adhesive; Durability

1. Research aims Synthetic polymers have been widely used as consolidating agents or adhesives in the conservation and restoration of Cultural Heritage consisting of natural fibres, such as textiles, books, papyri and parchment. Depending upon conservation needs, polymeric material should be characterised by physicochemical properties suitable for binding damaged fibres and yarns, imparting physical strength to the artefact or improving the adhesion between the artefact and a support fabric [1–3]. The ideal properties should be flexibility, transparency, adhesion, cohesion, lack of colour, long-term durability, reversibility, possibility of reactivation for adhesives, ease and rapid * Corresponding

author. Tel.: +39 081 750 2621; fax: +39 081 750 2618. E-mail address: [email protected] (E. Martuscelli).

1296-2074/$ - see front matter © 2006 Published by Elsevier Masson SAS. doi:10.1016/j.culher.2005.11.002

application with no risks for the operators. Currently there are no commercial polymers that simultaneously fulfil all of the above-mentioned requirements and often products largely used by conservators and restorers are discontinued. The performances shown by different materials cannot be appropriately compared owing to the fact there are few scientific data on their chemical constitution, composition, structure and properties. Thus it would be very useful to identify new polymer formulations with improved properties, and to set up characterisation methods to assess suitability and efficiency of polymeric materials for conservation and restoration of textile items. In this paper we report on results of investigations carried out to compare physico-chemical properties and aging resistance shown by polymers widely used for conservation purposes (such as Primal AC33, Mowilith DMC2 and SDM5)

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[1–6], with those exhibited by selected commercial acrylate and vinylacetate polymers. In fact Primal AC33 and Mowilith products have been applied on artworks [4–8] for their physico-chemical properties (good transparency and glass transition temperature close to the environmental temperature), although they show some limitations. In particular Primal AC33 has been discontinued by Rohm and Haas and research works are still in progress [9] to find the best substitute; furthermore Mowiliths are products not easily available and their photo-oxidative aging behaviour is not well understood. Films of each polymer, cast from the commercial water dispersions at room temperature, have been investigated applying Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Wide Angle X-ray Scattering (WAXS) and Colorimetric techniques. Mechanical properties of these materials at room temperature has been investigated by means of a tensile testing machine. Finally photo-oxidative resistance of each polymer has been determined by artificial weathering of water cast films and by measuring their Yellowing Index (YI) [10,11] as a function of the exposure time under xenon-arc lamp. 2. Experimental 2.1. Materials and sample preparation The following commercial polymers have been characterised: ● AC1: a polyethylacrylate used in fabric finishing, commercialised with the trade name Acrilem RP6005; ● AC2: an ethylacrylate-co-methylmethacrylate polymer used as coating for stiff curtains, commercialised with the trade name Acrilem 674; ● VA1: a vinylacetate-co-vinylversatate polymer used as binder for water-based paints and wall coatings, commercialised with the trade name Acrilem 30WA; ● AC3: a copolymer styrene-acrylonitrile-buthylacrylate used as binder for non-woven textiles, commercialised with the trade name Acrilem ST1997; ● AC4: Primal AC33: an ethylacrylate-co-methylmethacrylate polymer; ● VA2: Mowilith DMC2: a vinylacetate-co-di-n-butylmaleate polymer; ● VA3: Mowilith SDM5: a vinylacetate-co-n-butylacrylate polymer. The products coded as Acrilem are synthesised as water dispersions and sold by ICAP SIRA, Parabiago (MI, Italy); they have been never used for conservation purposes previously. Primal AC33 is made and sold as a water dispersion by Rohm and Haas, whereas Mowilith DMC2 and SDM5 are made by Hoechst and sold by Kremer Pigment. Films of each polymer were prepared from the water dispersions by casting at room temperature. Dumbbell-shaped sam-

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ples for mechanical analysis (UNI 882) were also obtained from the water cast films. For Acrilem ST1997, homogeneous films cannot be obtained either by water casting or by compression moulding, while for Acrilem 674 homogeneous films can be obtained by compression moulding at 70 °C. Moreover the films cast from the dispersion of Mowilith SDM5 were too soft for performing mechanical analysis. 2.2. Techniques 2.2.1. Fourier Transform Infrared Analysis (FTIR) FTIR spectra were obtained with a Perkin Elmer spectrometer (model Paragon 500) using 16 scans summation and a nominal resolution of 4 cm−1. The analysis was carried out on thin films obtained by dissolving Acrilem 30WA, 674, RP6005, Primal AC33, Mowilith DMC2 and SDM5 samples in chloroform and then casting these solutions directly on NaCl or KBr disks. FTIR analysis of Acrilem ST1997 sample was performed on dry polymer powder mixed with anhydrous KBr. 2.2.2. Differential Scanning Calorimetry (DSC) The thermal behaviour of the investigated polymers was analysed by means of a Differential Scanning Calorimeter Mettler DSC 30 equipped with a control and programming unit Mettler TC 11. Film samples were heated under nitrogen flow from –50 °C to a temperature below the temperature corresponding to the starting of degradation processes (run I), cooled with a scanning rate of 50 °C min–1 and finally heated again from – 50 to 400 °C with a scanning rate of 10 °C min–1 (run II). 2.2.3. Thermogravimetric Analysis (TGA) TGA was carried out on film samples, using a Mettler microbalance equipped with a Mettler Thermogravimetric Analyser model TG 50. The measurements were performed with a heating rate of 10 °C min–1 from 50 to 600 °C in air and nitrogen atmosphere in order to determine the decomposition temperature. 2.2.4. Wide Angle X-ray Scattering (WAXS) WAXS investigations were carried out on film samples by means of a PW 3020/00 Philips diffractometer (Cukα Nifiltered radiation) equipped with a sample holder for sample spinning. The high voltage was 40 kV and the tube current was 30 mA. A standard sample was employed to determine the instrumental broadening. 2.2.5. Mechanical analysis Uniaxial tensile tests were carried out in agreement with UNI 8422, by means of an Instron 5564 tensile testing machine operating with a crosshead speed of 10 mm min–1 at the temperature of 25 °C and 50% of relative humidity.

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2.2.6. Colorimetric analysis Colorimetric analysis of films of all the investigated materials was carried out by means of a Minolta 3600d spectrophotometer. Colour data were calculated using illuminant D65 (daylight 6500°K), 10 standard observer, sphere geometry, specular component included, UV energy included. 2.2.7. Artificial aging of the polymeric film Polymeric films obtained as reported in Section 2.1 were weathered in an Angelantoni SB3000E solarbox equipped with a xenon-arc lamp. Aging treatments were carried out with an irradiation of 1000 W m–2, dry bulb temperature (DBT) of 50 °C, without filters, and with exposure times ranging from 0 to 500 hours [12].

Table 1 Characteristics of the water dispersions: pH, viscosity and dry content Code

Commercial name

pH

AC1 AC2 VA1 AC3 AC4 VA2 VA3

Acrilem RP6005 Acrilem 674 Acrilem 30WA Acrilem ST1997 Primal AC33 Mowilith DMC2 Mowilith SDM5

7.5 4.5 5 4 9 4–5 4–5

Viscosity at 25 °C (mPA*s) 180 125 3000 100 max 500 5000–12,000 5000–12,000

Dry content (130 °C – 1 h) (% wt./wt.) 59 50 50 40 46 55 50

that shown by Primal; Mowiliths being characterised by higher viscosity value. It is to be remarked that, depending on the conservation needs, viscosity could be lowered by dilution or increased by adding a thickening agent.

3. Results and discussion 3.2. FTIR analysis

3.1. Physico-chemical properties The main characteristics of the commercial water dispersions, such as pH, viscosity at 25 °C and material dry content are reported in Table 1. It should be noted that Primal AC33 and Acrilem RP6005 are basic whereas Mowiliths, Acrilem 674, Acrilem 30WA and Acrilem ST1997 are acidic, thus indicating that basic dispersions could be useful for application on cellulose substrata and acidic dispersions on protein substrata. As far as the viscosity values are concerned, such values fall in a wide range. In particular Acrilem RP6005, 674 and ST1997 exhibit viscosity values more or less comparable to

In Table 2 the main frequencies of the absorption bands, relative intensities and main assignments are reported for each investigated polymer and corresponding FTIR spectra are shown in Fig. 1. For all the investigated materials the presence of the C=O groups is confirmed by a strong absorption band in the range 1740–1735 cm−1 (stretching), while the bands in the range 1260–1237 cm−1 confirms the presence of the C–O bonds (stretching). The absorption bands at 1372 cm−1 and in 1432 ± 2 cm−1 are diagnostic of the acetate group.

Table 2 Frequencies of absorption bands, relative intensity and tentative assignments for the investigated polymers Frequency (cm−1) 2985–2981 2963–2961 2951 2935–2926 2875–2870 2240 1740–1735 1544 1496 1465–1445 1433–1430 1385–1379 1372 1240–1237 1260–1238 1176–1160 1118 1124–1111 1099–1020 950–940 855–846 760–754 762 702

Polymera AC1, AC2, AC4 VA1, VA2, VA3 AC2, AC4 AC1, VA1, VA2, VA3 AC1, VA1, VA2, VA3 AC3 AC1, AC2, VA1, AC3, AC4, AC3 AC3 AC1, AC2, VA1, AC3, AC4, VA1, VA2, VA3 AC1, AC2, AC3, AC4 VA1, VA2, VA3 VA1, VA2, VA3 AC1, AC2, AC3, AC4 AC1, AC2, AC3, AC4, VA2, AC3 VA1, VA2, VA3 AC1, AC2, VA1, AC3, AC4, VA1, AC3, VA2, VA3 AC1, AC2, AC4 AC1, AC2, AC4 AC3 AC3

VA2, VA3

VA2, VA3

VA3

VA2, VA3

Relative intensityb S S S S M S S M M S M M M S S M–W W W M W W M–W S S

Tentative assignmentsc n (CH aliphatic) n (CH aliphatic) n (CH aliphatic) n (CH aliphatic) n (CH aliphatic) nitrile group n (C=O ester) aromatic ring aromatic ring β (CH2 aliphatic) β (CH in –OCOCH3) β (CH2 aliphatic) β (CH in –OCOCH3) n (C–O) n (C–O) δ (CH aliphatic) aromatic ring β (CH2 aliphatic) n (C–C) n (C–C) n (C–C) η (C–H) aromatic ring aromatic ring

a AC1: Acrilem RP6005; AC2: Acrilem 674; VA1: Acrilem 30WA; AC3: Acrilem ST1997; AC4: Primal AC33; VA2: Mowilith DMC2; VA3: Mowilith SDM5. b Relative intensity is based on the whole infrared spectrum of a sample at room temperature: S = strong, W = weak, M = medium. c Main assignments are: n = stretching, β = bending, δ = bending out-of-plane; η = rocking.

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[13], while this ratio decreases for Acrilem 674, thus indicating of a comparatively higher amount in the co-monomer MMA. For Acrilem ST1997 (Fig. 1d) the absorption band at 2240 cm−1 confirms the presence of the acrylonitrile monomeric unit; the presence of styrene groups being shown by the absorption bands at 702, 762, 1496 and 1544 cm−1. 3.3. Thermal analysis

Fig. 1. FTIR spectra of: (a) AC1: Acrilem RP6005; (b) AC2: Acrilem 674; (c) VA1: Acrilem 30WA; (d) AC3: Acrilem ST1997; (e) AC4: Primal AC33; (f) VA2: Mowilith DMC2: (g) VA3: Mowilith SDM5.

The presence of versatate group for Acrilem 30WA cannot be evidenced by FTIR analysis. FTIR spectrum of Acrilem RP6005 (Fig. 1a) matches the spectrum of a polyethylacrylate. It can be also noted that FTIR spectra of Acrilem 674 (Fig. 1b) and Primal AC33 (Fig. 1e) match spectra of commercial ethylacrylate-co-methylmethacrylate polymers reported in literature. For Primal AC33 the ratio between co-monomers EA/MMA seems to be 2/1

For all the materials the results of thermal analysis obtained by DSC are summarised in Table 3. DSC analysis does not reveal melting phenomena, thus suggesting that all the materials are in amorphous structure. All the investigated materials show glass transition temperatures (Tg), detected through DSC, between –13 and 42 °C. In particular Acrilem RP6005 shows a clear Tg located at –11 °C; such a value is close, within the experimental error, to the Tg value reported in literature for PEA [14i], thus confirming the results of FTIR analysis. Tg values of Acrilem 674 and Acrilem ST1997 are higher than 40 °C, so that they seem to be unsuitable for textile conservation because they can induce stiffness on the treated substrata. Moreover it is to be noted that such a Tg value for Acrilem 674, a poly(ethylacrylate-co-methylmethacrylate), suggests that the ratio between the co-monomers EA/MMA is lower than 2; this result confirming what has been evidenced by FTIR analysis. From the DSC trace (I run) obtained for Acrilem 30WA it can be noted that this material exhibits a single Tg at 12 °C. Taking into account that literature [3] gives a Tg value for PVAc at about 30 °C, it can be deduced that the presence of vinylversatate units results in a lowering of the Tg. This result agrees with the trend generally expected for the Tg values of vinyl polymers, which decrease with increasing length of the aliphatic side chains [1]. Primal AC33 shows a clear Tg at 14 °C with run II practically confirming this Tg value. Such a value is close to the Tg value reported [14] for poly(ethylacrylate-co-methyl-

Table 3 Thermal properties of the investigated polymers Transition

AC1: AC2: VA1: AC3: AC4: VA2: VA3: a b

Sample Acrilem RP6005 Acrilem 674 Acrilem 30WA Acrilem ST1997 Primal AC33 Mowilith DMC2 Mowilith SDM5

Glass transition (°C) (DSC–run I)

Glass transition (°C) (DSC–run II)

Thermal degradation in nitrogen flowa(°C) (TGA)

Thermal degradation in air flowa(°C) (TGA)

–11

–13

365

364

b

41

332

321

12

21

b

42

14

16

318 477 356 530 371

326 459 356 535 375

18

15

8

4

311 511 305

314 505 307

Temperature values corresponding to maximum rates in weight loss. Not clearly detectable.

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methacrylate) with a ratio between co-monomers EA/MMA = 2/1. Finally DSC traces (run II) of Mowilith DMC2 and SDM5 show Tg values of 15 and 4 °C, respectively. In Table 3 and Fig. 2 decomposition temperatures and TGA traces under nitrogen flow are respectively reported for all the investigated polymers. It can be inferred that all the materials show a thermal resistance appropriate for use in conservation and restoration of Cultural Heritage consisting of natural fibrous polymers. Furthermore the thermal degradation processes of all the materials are unaffected by oxygen presence: the temperatures corresponding to the maximum weight loss rates by heating the materials in air flow is, in fact, very close to that measured in nitrogen flow. In conclusion, in order to evaluate the potential of the investigated materials for conservation and restoration purposes, Tg values must be carefully considered. In fact, a polymer coating with a Tg value considerably higher than room temperature (which is the use temperature) is unable to respond to changes in the dimensions of the item and could thus damage it. In contrast, a polymer coating showing a Tg value noticeably lower than room temperature can be too soft to act as consolidating agent, tending also to pick up dirt. Similar restrictions can be applied for the use of these materials as adhesives.

Fig. 2. TGA traces of the investigated polymers. Weight residual (WR) and weight loss rate (WLR): (a) AC1: Acrilem RP6005; (b) AC2: Acrilem 674; (c) VA1: Acrilem 30WA; (d) AC3: Acrilem ST1997; (e) AC4: Primal AC33; (f) VA2: Mowilith DMC2: (g) VA3: Mowilith SDM5.

3.4. WAXS investigation In Fig. 3 WAXS intensity profiles shown by Acrilem RP6005 and Acrilem 674 are compared with WAXS intensity profile exhibited by Primal AC33, whereas Acrilem 30WA WAXS intensity profile is compared with those shown by Mowilith DMC2 and Mowilith SDM5. In Table 4 the reflection maxima with the corresponding angles (2θ), spacings (d) and relative intensities are listed for all the investigated polymers. The materials are characterised by an amorphous structure, even though certain local regularity is observed. To be noted is that a comparatively higher local regularity is shown by Mowilith DMC2 among the polyvinylacetates and by Acrilem RP6005 among the polyacrylates. As shown by the WAXS intensity profile, Acrilem 674 sample exhibits four reflections highly convoluted each other, whereas Primal AC33 displays three diffuse scattering reflections. Fig. 3c,f,g show WAXS intensity profile of Acrilem 30WA, Mowilith DMC2 and SDM5, respectively. As shown by data reported in Table 4, three diffuse scattering reflections are observed both for Acrilem 30WA and Mowiliths. The first two, convoluted each other, are in the range between 5° and 35° of 2θ. The last one, very broad and weak in intensity, is between 35° and 60° of 2θ. By comparing the WAXS intensity profiles and the related data, and considering that Acrilem

Fig. 3. WAXS intensity profiles of: (a) AC1: Acrilem RP6005; (b) AC2: Acrilem 674; (c) VA1: Acrilem 30WA; (e) AC4: Primal AC33; (f) VA2: Mowilith DMC2: (g) VA3: Mowilith SDM5.

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Table 4 X-ray reflection maxima with corresponding angle (2θ), spacing (d) and relative intensity Material 2θ (°) AC1: Acrilem RP6005 AC2: Acrilem 674 VA1: Acrilem 30WA AC2: Acrilem ST1997 AC3: Primal AC33 VA2: Mowilith DMC2 VA3: Mowilith SDM5 a

11.7 12.5 15.1 8.2 13.1 9.3 11.9

Reflection 1 d (Å) Relative intensitya 7.6 s 7.1 vvs 5.9 vs 10.8 w 6.8 vw 9.5 s 7.4 vw

2θ (°) 21.5 16.4 20.8 19.9 20.4 20.2 21.6

Reflection 2 d (Å) Relative intensitya 4.1 vs 5.4 s 4.3 vs 4.5 vs 4.3 vw 4.4 s 4.1 vw

2θ (°) 37.1 29.8 40.0 40.0 40.5 44.7 43.8

Reflection 3 d (Å) Relative intensitya 2.4 vvw 3.0 w 2.3 w 2.3 vw 2.2 vvw 2.0 vw 2.1 vvw

s = strong, w = weak, v = very.

30WA, Mowilith DMC2 and SDM5 materials are polyvinylacetates, it is confirmed that the local regularity decreases with increasing steric hindrance along the copolymer chain. As far as the potential of the investigated polymers for conservation and restoration is concerned, it is important to note that the local regularity decreases the rubber-like elasticity and affects the mechanical behaviour of the material. 3.5. Tensile behaviour Typical stress–strain curves obtained at room temperature for Acrilem RP6005 (a), 674 (b), 30WA (c), Primal AC33 (e) and Mowilith DMC2 (f) dumbbell-shaped specimens are shown in Fig. 4; the tensile properties for each investigated material are summarised in Table 5. As shown in Fig. 4 and from the data reported in Table 5, very different uniaxial tensile behaviours are observed. In particular Acrilem RP6005 and 30WA together with Primal AC33 exhibit stress–strain curves typical of uncrosslinked elastomers. Note that better properties are shown by Primal AC33, whereas Acrilem RP6005 shows the lowest values of elastic modulus and stress at maximum load, the value of the strain at break being slightly higher than that found for Acrilem 30WA. Taking into account that Acrilem RP6005 and Primal AC33 are both acrylic polymers, the different mechanical behaviour can be related to the different Tg values: at room temperature Primal AC33 is considerably closer to its Tg (14 °C) than Acrilem 6005 (Tg –11 °C). Mowilith DMC2 shows a stress–strain curve whose shape is similar to that shown by cross-linked elastomers. In fact this material is characterised by a modulus value twice as high as that shown by Primal AC33, lower stress at maximum load and strain at break. By comparing the mechanical behaviour of vinyl polymers (Acrilem 30WA and Mowilith DMC2) it is observed that Mowilith DMC2 shows a

Young’s Modulus and a stress at maximum load higher than that shown by the Acrilem 30WA, whereas the strain at break value is slightly lower. Considering that these materials at room temperature are both close to their Tg, the different mechanical responses could be related to the different local regularity already evidenced by WAXS analysis. Finally to be noted is that Acrilem 674 shows a stress–strain curve typical for a ductile material (Fig. 4b). During deformation, in fact, the material undergoes yielding and cold-drawing phenomena before breaking. Thus, considerably higher elastic modulus, stress at maximum load as well as lower deformation at break are found (see Table 5). Such a tensile behaviour is to be related to the higher amount of MMA co-monomer in respect to Primal AC33.

Table 5 Tensile properties shown by Acrilem RP6005, 674, 30WA, Primal AC33 and Mowilith DMC2 Sample

AC1: Acrilem RP6005 AC2: Acrilem 674 VA1: Acrilem 30WA AC4: Primal AC33 VA3: Mowilith DMC2

Young's Modulus (MPa) 0.54 ± 0.07 540 ± 80 5.5 ± 1.1 15.4 ± 2.0 31.6 ± 2.3

Stress at maximum load (MPa) 0.51 ± 0.05 20 ± 1 1.1 ± 0.1 5.8 ± 0.6 3.3 ± 0.9

Strain at break (%) 780 ± 90 310 ± 30 670 ± 60 2500 ± 300 640 ± 80

Fig. 4. Typical stress–strain curves for: (a) AC1: Acrilem RP6005; (b) AC2: Acrilem 674; (c) VA1: Acrilem 30WA; (e) AC4: Primal AC33; (f) VA2: Mowilith DMC2.

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On the basis of these results, higher potential for conservation purposes is shown by Acrilem RP6005 and 30WA, i.e. ethylacrylate and vinylversatate products, even though they exhibit poorer mechanical properties in comparison with those shown by the corresponding polyacrylate (Primal AC33) or polyvinylacetate (Mowilith DMC2) already used in conservation. 3.6. Colorimetric analysis For the measure of the optical properties we used the Yellowing Index (YI). YI is a measure of the yellowing phenomena of the film normalised with respect to the thickness of the film. YI is calculated using the formula YI ¼ ðA380
A600 Þ  0:1mm=T where: T = thickness of the film in mm; A380 = Absorbance of the film at 380 nm; A600 = Absorbance of the film at 600 nm. For each polymeric film YI values calculated before xenonarc lamp exposure are reported in Table 6. To be noted is that the only material showing a relevant yellowing is Acrilem ST1997 (Table 6). All the remaining materials show conversely excellent optical properties of colourlessness and transparency, thus indicating that the aesthetic of objects should be minimally affected by using such polymers as coating. Moreover films of each polymer, except for Acrilem ST1997, artificially aged in solarbox as described in Section 2.2, were undergone to colorimetric analysis. In Fig. 5 the curves of YI as a function of the exposure time (hours) are reported for each material. As expected, after the aging treatment, acrylate polymers show more relevant yellowing phenomena, while vinyl based materials show lower yellowing. It is interesting to observe that, among acrylic polymers, the YI shown by the ethylacrylate material Acrilem RP6005 is comparable to the one shown by Primal AC33 through the whole exposure period. Concerning vinyl polymers, it is to be noted that the best performing is the vinylversatate polymer Acrilem 30WA; in fact this material shows YI values constant throughout the whole exposure period, thus suggesting that this material offers a satisfactory durability. Table 6 YI of the films obtained by compression moulding (Acrilem 674 and ST1997) and by water casting (Acrilem RP6005, 30WA, Primal AC33, Mowilith DMC2 and SDM5) before exposure treatments under xenon-arc lamp Code AC1 AC2 VA1 AC3 AC4 VA2 VA3

Sample Acrilem RP6005 Acrilem 674 Acrilem 30WA Acrilem ST1997 Primal AC33 Mowilith DMC2 Mowilith SDM5

YI 0.0052 ± 0.0004 0.0021 ± 0.0003 0.0029 ± 0.0003 0.0506 ± 0.0018 0.0018 ± 0.0003 0.0108 ± 0.0012 0.0051 ± 0.0009

Fig. 5. YI of polymeric films versus exposure time (hours) under xenon-arc lamp: (a) AC1: Acrilem RP6005; (b) AC2: Acrilem 674; (c) VA1: Acrilem 30WA; (e) AC4: Primal AC33; (f) VA2: Mowilith DMC2: (g) VA3: Mowilith SDM5.

4. Conclusion With the aim of identifying new water dispersed polymers with consolidating and/or adhesive properties for textile artefacts, seven different commercial polymers have been selected and characterised by applying molecular, thermal, structural and mechanical investigation techniques on polymeric films. In particular the properties of polyacrylates and polyvinylacetate not previously used in conservation have been compared with those shown by polyacrylates and polyvinylacetates used as consolidating or adhesive agents for ancient textiles, such as the discontinued Primal AC33 and the not easily available Mowilith DMC2 and SDM5. The photo-oxidative resistance of such products has also been investigated through artificial weathering of water cast films and measuring the YI as a function of the exposure time under a xenon-arc lamp. To be remarked is what follows: ● through water casting at room temperature, transparent and homogeneous films are formed from the commercial polymer dispersions, thus indicating that polymers, when used

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● ●

●

●

●

●

as coatings, would minimally affect the aesthetics of the artefacts; the chemical constitution of each polymer has been confirmed by means of FTIR, showing moreover the extent of same molecular similarity among investigated products; as far as the thermally induced degradation is concerned, it has been shown by TGA that all the materials, irrespective of chemical composition, are appropriate for use in conservation and restoration of Cultural Heritage consisting of natural fibres; DSC analysis revealed that, among polymers not previously used in conservation, ethylacrylate and vinylversatate based polymers, i.e. Acrilem RP6005 and 30WA, exhibit glass transition temperatures close to room temperature and, thus, suitable for conservation and restoration purposes; wAXS investigation showed that both polyacrylates and polyvinylacetates investigated are characterised by amorphous structure, even tough different local regularity is observed; at room temperature the investigated materials exhibit very different uniaxial tensile behaviours; Acrilem RP6005, 30WA and Primal AC33 exhibiting stress–strain curves typical of uncrosslinked elastomers, whereas Mowilith DMC2 and Acrilem 674 show stress–strain curves typical of ductile materials. Taking into account that Acrilem RP6005 and Primal AC33 are both acrylic polymers, the different behaviour has been related to the different Tg, which determines the state of the amorphous structure at room temperature. For Acrilem 30WA and Mowilith DMC2, both classified as vinyl polymers, the different mechanical response has been related to different local regularity, since both the copolymers are close to their Tg at room temperature; after aging Acrilem RP6005 shows YI values comparable to those exhibited by Primal AC33, while Acrilem 30WA exhibits the lowest YI values throughout the whole aging period.

From all the above it may be concluded that, among the products not previously used in conservation, ethylacrylate and vinylversatate based polymers like the commercial products Acrilem RP6005 and 30WA, show suitability for use in the conservation and restoration field. Depending upon the needs, these materials could substitute polyacrylates such as Primal AC33 and polyvinylacetates such as Mowilith DMC2 and SDM5. It is important to stress that vinylversatate based

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product, Acrilem 30WA, also after aging, shows YI lower than that shown by Mowilith DMC2 and SDM5. Acknowledgements The authors would like to thank Dr. Marco Cerra (ICAP SIRA) for the materials supplied and the scientific support offered. References [1] C.V. Horie, Materials for Conservation: Organic Consolidants, Adhesives and Coatings, Butterworth-Heinemann, London, 1987. [2] S. Landi, The Textile’s Conservator Manual, Butterworth-Heinemann, Oxford, 1992. [3] A. Timàr-Balàszy, D. Eastop, Chemical Principles of Textile Conservation, Butterworth-Heinemann, Oxford, 1998. [4] V. Hartman, ‘Il restauro del sipario del teatro Verdi di Salerno dipinto da Domenico Morelli’, I beni culturali 4 (5) (1996) 17–21. [5] G. Lewis, N. Muir, N.S. Yates, The link between the treatments for paintings and the treatments for painted textiles, in: Conservation and Restoration of Church Textiles and Painted Flags; Investigation of Museum Objects and Materials Used in Conservation and Restoration, Fourth International Restorer Seminar, Veszprém, Hungary, July 1983, pp. 2–10. [6] J.A. Logan, Red Bay 1982—Textile discovery’, in: Textile conservation newsletter Canada, 1983, pp. 2–9. [7] K. Trampedach, ‘IIntroduction to Danish Wall Paintings—Conservation Ethics and Methods of Treatment’, National Museum of Denmark—Conservation Department, July 2001. [8] P. Plummer, Conservator Team of St., Alban, ‘Conservation of the Presbytery Vault, St. Albams Cathedral’, Conservator News 77 (2002) 44– 47. [9] L. M. Cocca, L. D’Arienzo, G. D’Orazio, E. Gentile, Martuscelli, Polyacrylates for conservation: chemico-physical properties and durability of different commercial products, Polymer Testing 23 (2004) 333–342. [10] J.L. Down, M.A. MacDonald, J. Tetreault, R.S. Williams, ‘Adhesive testing at the Canadian Conservation Institute—an evaluation of selected poly(vinylacetate) and acrylic adhesives’, Studies in Conservation 41 (1996) 19–44. [11] E. Martuscelli, Le fibre di polimeri naturali nell’evoluzione della civiltà. Le fibre di seta, Consiglio Nazionale delle Ricerche, Monografie scientifiche, Serie Scienze Chimiche, Rome, 1999. [12] V. Massa, E. Cozzi, A. Trovati, ‘Purbinder PA711: un adesivo di nuova concezione per il restauro tessile’, in: Il restauro dei dipinti contemporanei. Soluzioni per evitare la foderatura e per limitare le alterazioni che essa comporta. Corso di aggiornamento, 22–26 Maggio 1989, Botticino, ENAIP, Brescia, 1990. [13] D.O. Hummel, F. Scholl, Atlas of Polymer and Plastic Analysis, Second Edition, Carl Hanser Verlag, Verlag Chemie, Munich, 1984. [14] J. Bandrup, E.H. Immergut, E.A. Grulke, Polymer Handbook, Fourth Edition, John Wiley and Sons Inc., Wiley Interscience Pubblication, New York, 1999.