- Email: [email protected]
Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper
G Model CULHER-2820; No. of Pages 7
ARTICLE IN PRESS Journal of Cultural Heritage xxx (2013) xxx–xxx
Available online at
ScienceDirect www.sciencedirect.com
Original article
Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper Saira Arif a,1 , Sergey Bushuk b , Andrei Kouzmouk b , Hennady Tatur b , Sergei Batishche b , Wolfgang Kautek a,∗ a b
University of Vienna, Department of Physical Chemistry, Währinger Strasse 42, 1090 Wien, Austria Institute of Physics, National Academy of Sciences of the Republic of Belarus, F. Scorina Avenue 68, 220012 Minsk, Belarus
a r t i c l e
i n f o
Article history: Received 24 October 2012 Accepted 18 November 2013 Available online xxx Keywords: Laser cleaning ;·Cellulose Paper
a b s t r a c t Ground wood cellulose paper exhibits a practicable cleaning laser fluence window during middle-UV radiation processing. In this case, a minimum dose volume density should be applied. However, cleaning of bleached cellulose paper is accompanied by strong yellowing and destruction. The presence of charcoal graphite particulates shows substantial influence on the yellowing with increasing coverage. © 2013 Elsevier Masson SAS. All rights reserved.
1. Introduction
2. Experimental
Laser cleaning has been of great attention in cultural heritage recently [1–5]. The cleaning of organic materials such as paper or polymers is characterized by the limitation of photochemical and photothermal destruction [6–17]. This is minimized when visible laser wavelengths are chosen such as the second harmonic (532 nm) of a Nd:YAG lasers [7,18]. Ultraviolet laser radiation, on the other hand, provides minimized light penetration depth and can serve as a quasi ultra-precise non-contact scalpel [19,20]. Moreover, wavelength mixing of infrared (1064 nm) and ultraviolet radiation (213 nm) can provide further options for laser cleaning of organic materials [21]. Yellowing is often a side effect of laser cleaning [7,9,22–24]. Paper cleaning studies showed that yellowing could be minimized choosing 532 nm [13,14,25,26]. The present investigation is a complementary study of laser cleaning of ground wood cellulose paper in contrast to pure cellulose [20] and ancient thoroughly aged papers [27]. The application of 213 nm on originally yellowish acid mechanical ground wood cellulose paper with alum-rosin sizing in comparison to bleached sulphite softwood cellulose paper without fillers and sizing is presented with charcoal as contaminant model.
Acid mechanical ground wood cellulose paper with alumrosin sizing served as model for lignin containing yellowish paper (Fig. 1b). This is compared with a widely pure cellulose sample, i.e. bleached sulphite softwood cellulose paper with no filler and no sizing (Fig. 2b). Sample morphologies were investigated by electron microscopy (Zeiss Supra 55 VP). The extent of the charcoal model contamination coating was varied by a deposition procedure described before [20]. A “low” contamination density was realized by graphite particulates in the range between 0.3 and 2 m with a coverage of < 20%. The “high” coverage of > 80% represented a size distribution of 0.3–10 m. A prototype Nd:YAG laser system with an output at the fifth harmonic (213 nm) with up to 100 mJ, a repetition rate of 1–7 Hz and a pulse duration of 16 ns, served as the mid-ultraviolet source [20]. The determination of the beam diameter and cross section was realized by the progressive shading of the beam during energy measurements in the x and y direction and the transmission energy measurements [28]. The evaluation of cleaning, modification or ablation (destruction) zones were performed by microscopical diameter measurements [20,28], where the square of the diameter of the modified zones, D2 , was plotted versus the logarithm of the pulse energy E0 yielding the Gauss radius w0 and the threshold energy Eth :
∗ Corresponding author. Tel.: +43 1 4277 52470; fax: +43 1 4277 52449. E-mail address: [email protected] (W. Kautek). 1 Present address: COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan.
D2 = 2w02 ln
E 0
Eth
(1)
1296-2074/$ – see front matter © 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.culher.2013.11.011
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7 2
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
Fig. 2. Scanning electron micrographs of bleached sulphite softwood cellulose paper. a: contaminated with charcoal (high coverage); b: original; c: laser-cleaned, N = 2, F = 1.78 J/cm2 .
Fig. 1. Scanning electron micrographs of alum-rosin sized ground wood cellulose paper. a: contaminated with charcoal (high coverage); b: original; c: laser-cleaned, N = 2, F = 2.1 J/cm2 .
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model
ARTICLE IN PRESS
CULHER-2820; No. of Pages 7
S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
3
Table 1 Destruction and cleaning thresholds (J/cm2 ). Paper type
Ground wood cellulose paper
Bleached cellulose paper
N
Uncontaminated
Coverage < 20%
0
Fp,th
Fp,th
1 2 5 9 20 50 80 100
0.44 0.25 0.22 0.18 0.16 0.11
1 2 5 9 20 50 80 100
1.04 0.99 0.93 0.74 0.69 0.66 0.50 0.39
0.77 0.40 0.31 0.22 0.16
3.52 1.98 1.54 1.34 1.19
Coverage > 80% Fc,th
Fp,th
Fc,th
0.61 0.39 0.28 0.22 0.14
0.20 0.14 0.12
0.06 0.04 0.03 0.02 0.02 0.02 0.01 0.01
0.75 0.45 0.38 0.34 0.32
1.25 0.99 0.82 0.67 0.57 0.51 0.43
0.47 0.30 0.16 0.13 0.11 0.09 0.09 0.08
Maximum fluence values in the Gaussian profile, F0 , could be calculated from E0 : F0 =
2E0 w02
(2)
Area values from this approach were in good agreement with the above-described progressive shading method. D-data were averaged from at least three independently irradiated substrate areas. Colorimetry with a spectrophotometer (SpectroEye, X-Rite Europe AG) allowed a relative colour comparison in respect to both lightness changes, L, representing the cleaning status and saturation and hue changes given by the chromaticity coordinates a and b according to the CIE-L*a*b* colour space. The yellowing can be represented by b. 3. Results and discussion 3.1. Morphological evaluation Laser cleaning action on alum-rosin sized ground wood cellulose paper (shortly “wood cellulose paper”) was successful without observable fibre destruction at low N (Fig. 1c). However, laser cleaning could not generate a clean surface comparable with the original (Fig. 1b). Laser processing of bleached sulphite softwood cellulose paper (shortly “bleached cellulose paper”) with the wavelengths of 213 nm above the destruction threshold resulted in deeply torn fibres (Fig. 2c). 3.2. Threshold determination The threshold fluence evaluation according to the D2 -lnE relationship (Eq. (1)) are shown for wood cellulose paper and bleached cellulose paper (Fig. 3, Table 1). The destruction thresholds of the originals, 0 Fp,th , is practically the same as in the case of the contaminated paper, Fp,th , (insert on Fig. 3a). Extremely strong shielding with UV radiation due to low penetrations depths can be assumed. Thus the particles are evaporated or combusted only in very thin slices in the irradiated region, whereas the part attached to the substrates stays rather unaffected. Surprisingly week thermal interaction with the substrate fibres may result in contrast to the visible case where the removals of the particles accelerate the destruction. The cleaning threshold results, Fc,th , appreciated by the extrapolation of the D2 /lnF-data exhibit comparatively high uncertainties (Fig. 3a and 3b). Fig. 4a/b summarizes the incubation dependence of the Fc,th and Fp,th values, i.e. the cleaning window (compare insert
Fig. 3. Squared modified spot diameter versus logarithm of pulse fluence (D2 vs. log F). “High” contamination coverage. a: alum-rosin sized ground wood cellulose paper; b: bleached sulphite softwood cellulose paper. The slope of the straight N = 1; N = 2; N = 5; dashed lines represents the 1/e2 radius (w0 ). Cleaning: N = 9; N = 20; N = 50; N = 80; N = 100. Insert (a): destruction of contaminated paper: N = 50; N = 80; N = 100. Insert (b): cleaning window for N = 5.
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
4
Fig. 4. Threshold fluences, Fth , versus pulse number, N. a: alum-rosin sized ground wood cellulose paper; b: bleached sulphite wood cellulose paper. Destruction (Fp,th ): “high” contamination coverage, “low” contamination coverage, no con“high” contamination coverage, “low” tamination (0 Fp,th ). Cleaning (Fc,th ): contamination coverage.
in Fig. 3b). In the case of the dark yellow wood cellulose paper sample it practically is not existent (Fig. 4a). That of bleached cellulose paper is comparatively narrow and decreases with N and incubation (Fig. 4b). 3.3. Colorimetric evaluation Uncontaminated papers exhibited practically negligible L and b values under middle-UV radiation irradiation (Figs. 5a, 6a, 7a and 8a) indicating no photochemical or photophysical changes. The lightness results, L, represent the cleaning status of the “low” and “high” contamination coverage cases (Figs. 5 and 6). The yellowing data b (Figs. 7 and 8) represent irreversible chemical and/or photochemical changes. Cleaning results without irreversible modifications can be represented by L and b values approaching zero. Wood cellulose paper cleaning thresholds (L ∼ 0) were found to be Fc,th ≈ 0.4 J/cm2 at N = 1, 2 and 5 with “low” contamination coverage, and Fc,th ≈ 0.1 J/cm2 at N = 9 (Fig. 5b). The cleaning threshold (L ∼ 0) for “high” contamination coverage were found to be Fc,th ≈ 1.8 J/cm2 at N = 1, 2 and 5 and at lower fluence values for higher N (Fig. 5c).
Fig. 5. Colorimetric lightness, L. Alum-rosin sized ground wood cellulose paper. a: no contamination; b: “low” contamination; c: “high” contamination. White columns: above destruction threshold fluence, Fth . Grey columns: below Fth .
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
Fig. 6. Colorimetric lightness, L. Bleached sulphite wood cellulose paper. a: no contamination; b: “low” contamination; c: “high” contamination. White columns: above destruction threshold fluence, Fth . Grey columns: below Fth .
5
Fig. 7. Colorimetric yellowing, b. Alum-rosin sized ground wood cellulose paper. a: no contamination; b: “low” contamination; c: “high” contamination. White columns: above destruction threshold fluence, Fth . Grey columns: below Fth .
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7 6
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
Cleaning thresholds (L ∼ 0) of bleached cellulose paper were found to be Fc,th ≈ 0.4 J/cm2 at N = 1 and 2 with “low” contamination coverage and Fc,th ≈ 0.24 J/cm2 at N = 5 and 9 (Fig. 6b). At all N values, Fc,th is separated from the destruction threshold of the contaminated sample Fp,th . In the case of “high” contamination coverage the cleaning thresholds (L ∼ 0) were Fc,th ≈ 1.78 J/cm2 at N = 1, 2 and 5 (Fig. 6c). The reason for higher cleaning thresholds in this case of high contamination is the dense coverage and the filling of the inter-fibre spaces with particulates, so that higher energies are required for their complete removal. Again, Fc,th is separated from the destruction threshold of the contaminated sample, Fp,th , in analogy to the “low” contamination case. The presence of the particulates, however, shows some influence on the yellowing with increasing coverage. The wood cellulose paper with high contamination exhibits low yellowing below the destruction threshold in the region of high F and low N (Fig. 7c). That is a finding in analogy to the historical papers [27]: a lower dose volume density is more advantageous than high values accompanied by high N. Yellowing of wood cellulose paper is caused by higher dose volume density values. This suggests that photochemical changes are produced by repetitive irradiation (incubation). Strong yellowing occurred below and above Fp,th (Fig. 8c) as in the case of the pure cellulose [20] in contrast to the ground wood cellulose paper type where this was only observed at high dose parameters [27]. The bleached cellulose paper underwent more yellowing in the entire cleaning fluence window (Fig. 8b, c) than the ground wood cellulose paper. This suggests that particles in the status of removal affect the neighbouring fibres. A thermomechanical removal by expansion of the strongly absorbing particle are not expected to heat or affect the substrate fibres. A vaporisation and/or a plasma formation, on the other hand, heat the fibres in next proximity during a short but sufficient time period. 4. Conclusions Ground wood cellulose paper exhibits a limited cleaning window between Fc,th which is just the beginning of particulate removal, and Fp,th . Therefore ground wood cellulose paper can be cleaned by middle-UV radiation when the minimum dose volume density strategy is applied [27]. However full cleaning of bleached cellulose paper is only reached at Fp,th accompanied by strong yellowing. That means that a practicable window is non-existent for this paper type. Cleaning and destruction thresholds of both substrates decrease with increasing N, which is a direct indication of strong incubation processes. The presence of the particulates shows substantial influence on the yellowing with increasing coverage. The coloured ground wood cellulose paper type shows low yellowing below the destruction threshold in the region of high F and low N. Yellowing is caused by higher dose volume density values. Acknowledgements We acknowledge partial financial support by the International Science and Technology Center, ISTC project B-1397. One of the authors (S. A.) has generously been supported by a scholarship from the Higher Education Commission (HEC), Pakistan. References Fig. 8. Colorimetric yellowing, b. Bleached sulphite wood cellulose paper. a: no contamination; b: “low” contamination; c: “high” contamination. White columns: above destruction threshold fluence, Fth . Grey columns: below Fth .
[1] Lasers in the conservation of artwork I, in: W. Kautek, E. König (Eds.), Restauratorenblätter, Special Issue, Verlag Mayer, Wien, 1997. [2] M. Cooper, Laser Cleaning in Conservation, Butterworth-Heinemann, Oxford, 1998. [3] C. Fotakis, W. Kautek, M. Castillejo (Eds.), Laser Chemistry, Special Issue. Lasers in the preservation of cultural heritage, Hindawi, New York, 2006. [4] D.M. Kane (Ed.), Laser Cleaning II, World Scientific, Singapore, 2006.
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
[5] M. Schreiner, M. Strlic, R. Salimbeni (Eds.), Handbook on the Use of Lasers in Conservation and Conservation Science, COST office, Brussels, Belgium, 2008 (http://www.science4heritage.org/COSTG7/booklet/). [6] W. Kautek, S. Pentzien, P. Rudolph, J. Kruger, E. König, Laser interaction with coated collagen and cellulose fibre composites: fundamentals of laser cleaning of ancient parchment manuscripts and paper, Appl. Surf. Sci. 127–129 (1998) 746–754. [7] J. Kolar, M. Strlic, S. Pentzien, W. Kautek, Near-UV, visible and IR pulsed laser light interaction with cellulose, Appl. Phys. A 71 (2000) 87–90. [8] J. Kolar, M. Strlic, M. Marincek, IR pulsed laser light interaction with soiled cellulose and paper, Appl. Phys. A 75 (2002) 673–676. [9] M. Strlic, J. Kolar, V.S. Selih, M. Marincek, Surface modification during Nd:YAG (1064 nm) pulsed laser cleaning of organic fibrous materials, Appl. Surf. Sci. 207 (2003) 236–245. [10] J. Kolar, M. Strlic, D. Muller-Hess, A. Gruber, K. Troschke, S. Pentzien, W. Kautek, Laser cleaning of paper using Nd:YAG laser running at 532 nm, J. Cult. Herit. 4 (2003) 185–187. [11] F. Bloisi, L. Vicari, A.C. Barone, E. Martuscelli, G. Gentile, C. Polcaro, Effects of Nd:YAG (532 nm) laser radiation on “clean” cotton, Appl. Phys. A 79 (2003) 331–333. [12] S. Georgiou, Laser cleaning methodologies of polymer substrates, in: T. Lippert (Ed.), Polymers and Light, Springer-Verlag, Berlin Heidelberg Germany, 2004, pp. 1–49. [13] A. Kaminska, M. Sawczak, M. Cieplinski, G. Sliwinski, B. Kosmowski, Colorimetric study of the post-processing effect due to pulsed laser cleaning of paper, Opt. Appl. 34 (2004) 121–132. [14] P. Rudolph, F.J. Ligterink, J.L. Pedersoli, M. Van Bommel, J. Bos, H.A. Aziz, J.B.G.A. Havermans, H. Scholten, D. Schipper, W. Kautek, Characterization of lasertreated paper, Appl. Phys. A 79 (2004) 181–186. [15] S. Pentzien, A. Conradi, J. Krüger, The influence of paper type and state of degradation on laser cleaning of artificially soiled paper, in: R. Radvan, J.F. Asmus, M. Castillejo, P. Pouli, A. Nevin (Eds.), Lasers in the Conservation of Artworks VIII, Taylor & Francis Group, London, 2011, pp. 59–65. [16] S. Arif, O. Armbruster, W. Kautek, Pulse laser particulate separation from polycarbonate: surface acoustic wave and thermomechanical mechanisms, Appl. Phys. A 111 (2013) 539–548.
7
[17] S. Arif, O. Armbruster, W. Kautek, Pulse laser induced particle separation from polymethyl methacrylate: a mechanistic study, Appl. Phys. A 111 (2013) 309–317. [18] W. Kautek, Lasers in cultural heritage: the non-contact intervention, Springer Ser. Mater. Sci. 130 (2010) 313. [19] E. Sarantopoulou, Z. Samardzija, S. Kobe, Z. Kollia, A.C. Cefalas, Removing foxing stains from old paper at 157 nm, Appl. Surf. Sci. 208 (2003) 311–316. [20] S. Arif, M. Forster, S. Bushuk, A. Kouzmouk, H. Tatur, S. Batishche, W. Kautek, Mechanistic comparison of pulse laser induced phase separation of particulates from cellulose paper at 213 nm and 532 nm, Appl. Phys. A 110 (2012) 501–509. [21] S. Batishche, A. Kouzmouk, H. Tatur, T. Gorovets, U. Pilipenka, V. Ukhau, W. Kautek, Simultaneous UV-IR Nd:YAG laser cleaning of leather artifacts, Springer Proc. Phys. 116 (2007) 221–227. [22] M. Strlic, V.S. Selih, J. Kolar, D. Kocar, B. Pihlar, R. Ostrowski, J. Marczak, M. Strzelec, M. Marincek, T. Vuorinen, L.S. Johansson, Optimisation and on-line acoustic monitoring of laser cleaning of soiled paper, Appl. Phys. A 81 (2005) 943–951. [23] J. Krüger, S. Pentzien, A. Conradi, Cleaning of artificially soiled paper with 532nm nanosecond laser radiation, Appl. Phys. A 92 (2008) 179–183. [24] S. Pentzien, A. Conradi, R. Koter, J. Krüger, Cleaning of artificially soiled paper using nanosecond, picosecond and femtosecond laser pulses, Appl. Phys. A 101 (2010) 441–446. [25] A. Kaminska, A. Sawczak, K. Komar, G. Sliwinski, Application of the laser ablation for conservation of historical paper documents, Appl. Surf. Sci. 253 (2007) 7860–7864. [26] W. Kautek, Laser cleaning of paper and other organic materials, in: M. Schreiner, M. Strlic, R. Salimbeni (Eds.), Handbook on the Use of Lasers in Conservation and Conservation Science, COST office, Brussels, Belgium, 2008 (http://www.science4heritage.org/COSTG7/booklet/). [27] S. Arif, S. Bushuk, A. Kouzmouk, H. Tatur, S. Batishche, W. Kautek, Microparticle separation mechanism from ancient cellulose papers by middle-ultraviolet (213 nm) and visible (532 nm) pulsed laser radiation, in: R. Radvan, S. Akyüz, M. Simileanu (Eds.), The Unknown Face of the Artwork, Istanbul Kültür University, Istanbul, 2012, pp. 43–60. [28] J. Krüger, W. Kautek, in: T.K. Lippert (Ed.), Advances in Polymer Science, Springer-Verlag, Berlin/Heidelberg, 2004, pp. 247–289.
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
ARTICLE IN PRESS Journal of Cultural Heritage xxx (2013) xxx–xxx
Available online at
ScienceDirect www.sciencedirect.com
Original article
Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper Saira Arif a,1 , Sergey Bushuk b , Andrei Kouzmouk b , Hennady Tatur b , Sergei Batishche b , Wolfgang Kautek a,∗ a b
University of Vienna, Department of Physical Chemistry, Währinger Strasse 42, 1090 Wien, Austria Institute of Physics, National Academy of Sciences of the Republic of Belarus, F. Scorina Avenue 68, 220012 Minsk, Belarus
a r t i c l e
i n f o
Article history: Received 24 October 2012 Accepted 18 November 2013 Available online xxx Keywords: Laser cleaning ;·Cellulose Paper
a b s t r a c t Ground wood cellulose paper exhibits a practicable cleaning laser fluence window during middle-UV radiation processing. In this case, a minimum dose volume density should be applied. However, cleaning of bleached cellulose paper is accompanied by strong yellowing and destruction. The presence of charcoal graphite particulates shows substantial influence on the yellowing with increasing coverage. © 2013 Elsevier Masson SAS. All rights reserved.
1. Introduction
2. Experimental
Laser cleaning has been of great attention in cultural heritage recently [1–5]. The cleaning of organic materials such as paper or polymers is characterized by the limitation of photochemical and photothermal destruction [6–17]. This is minimized when visible laser wavelengths are chosen such as the second harmonic (532 nm) of a Nd:YAG lasers [7,18]. Ultraviolet laser radiation, on the other hand, provides minimized light penetration depth and can serve as a quasi ultra-precise non-contact scalpel [19,20]. Moreover, wavelength mixing of infrared (1064 nm) and ultraviolet radiation (213 nm) can provide further options for laser cleaning of organic materials [21]. Yellowing is often a side effect of laser cleaning [7,9,22–24]. Paper cleaning studies showed that yellowing could be minimized choosing 532 nm [13,14,25,26]. The present investigation is a complementary study of laser cleaning of ground wood cellulose paper in contrast to pure cellulose [20] and ancient thoroughly aged papers [27]. The application of 213 nm on originally yellowish acid mechanical ground wood cellulose paper with alum-rosin sizing in comparison to bleached sulphite softwood cellulose paper without fillers and sizing is presented with charcoal as contaminant model.
Acid mechanical ground wood cellulose paper with alumrosin sizing served as model for lignin containing yellowish paper (Fig. 1b). This is compared with a widely pure cellulose sample, i.e. bleached sulphite softwood cellulose paper with no filler and no sizing (Fig. 2b). Sample morphologies were investigated by electron microscopy (Zeiss Supra 55 VP). The extent of the charcoal model contamination coating was varied by a deposition procedure described before [20]. A “low” contamination density was realized by graphite particulates in the range between 0.3 and 2 m with a coverage of < 20%. The “high” coverage of > 80% represented a size distribution of 0.3–10 m. A prototype Nd:YAG laser system with an output at the fifth harmonic (213 nm) with up to 100 mJ, a repetition rate of 1–7 Hz and a pulse duration of 16 ns, served as the mid-ultraviolet source [20]. The determination of the beam diameter and cross section was realized by the progressive shading of the beam during energy measurements in the x and y direction and the transmission energy measurements [28]. The evaluation of cleaning, modification or ablation (destruction) zones were performed by microscopical diameter measurements [20,28], where the square of the diameter of the modified zones, D2 , was plotted versus the logarithm of the pulse energy E0 yielding the Gauss radius w0 and the threshold energy Eth :
∗ Corresponding author. Tel.: +43 1 4277 52470; fax: +43 1 4277 52449. E-mail address: [email protected] (W. Kautek). 1 Present address: COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan.
D2 = 2w02 ln
E 0
Eth
(1)
1296-2074/$ – see front matter © 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.culher.2013.11.011
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7 2
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
Fig. 2. Scanning electron micrographs of bleached sulphite softwood cellulose paper. a: contaminated with charcoal (high coverage); b: original; c: laser-cleaned, N = 2, F = 1.78 J/cm2 .
Fig. 1. Scanning electron micrographs of alum-rosin sized ground wood cellulose paper. a: contaminated with charcoal (high coverage); b: original; c: laser-cleaned, N = 2, F = 2.1 J/cm2 .
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model
ARTICLE IN PRESS
CULHER-2820; No. of Pages 7
S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
3
Table 1 Destruction and cleaning thresholds (J/cm2 ). Paper type
Ground wood cellulose paper
Bleached cellulose paper
N
Uncontaminated
Coverage < 20%
0
Fp,th
Fp,th
1 2 5 9 20 50 80 100
0.44 0.25 0.22 0.18 0.16 0.11
1 2 5 9 20 50 80 100
1.04 0.99 0.93 0.74 0.69 0.66 0.50 0.39
0.77 0.40 0.31 0.22 0.16
3.52 1.98 1.54 1.34 1.19
Coverage > 80% Fc,th
Fp,th
Fc,th
0.61 0.39 0.28 0.22 0.14
0.20 0.14 0.12
0.06 0.04 0.03 0.02 0.02 0.02 0.01 0.01
0.75 0.45 0.38 0.34 0.32
1.25 0.99 0.82 0.67 0.57 0.51 0.43
0.47 0.30 0.16 0.13 0.11 0.09 0.09 0.08
Maximum fluence values in the Gaussian profile, F0 , could be calculated from E0 : F0 =
2E0 w02
(2)
Area values from this approach were in good agreement with the above-described progressive shading method. D-data were averaged from at least three independently irradiated substrate areas. Colorimetry with a spectrophotometer (SpectroEye, X-Rite Europe AG) allowed a relative colour comparison in respect to both lightness changes, L, representing the cleaning status and saturation and hue changes given by the chromaticity coordinates a and b according to the CIE-L*a*b* colour space. The yellowing can be represented by b. 3. Results and discussion 3.1. Morphological evaluation Laser cleaning action on alum-rosin sized ground wood cellulose paper (shortly “wood cellulose paper”) was successful without observable fibre destruction at low N (Fig. 1c). However, laser cleaning could not generate a clean surface comparable with the original (Fig. 1b). Laser processing of bleached sulphite softwood cellulose paper (shortly “bleached cellulose paper”) with the wavelengths of 213 nm above the destruction threshold resulted in deeply torn fibres (Fig. 2c). 3.2. Threshold determination The threshold fluence evaluation according to the D2 -lnE relationship (Eq. (1)) are shown for wood cellulose paper and bleached cellulose paper (Fig. 3, Table 1). The destruction thresholds of the originals, 0 Fp,th , is practically the same as in the case of the contaminated paper, Fp,th , (insert on Fig. 3a). Extremely strong shielding with UV radiation due to low penetrations depths can be assumed. Thus the particles are evaporated or combusted only in very thin slices in the irradiated region, whereas the part attached to the substrates stays rather unaffected. Surprisingly week thermal interaction with the substrate fibres may result in contrast to the visible case where the removals of the particles accelerate the destruction. The cleaning threshold results, Fc,th , appreciated by the extrapolation of the D2 /lnF-data exhibit comparatively high uncertainties (Fig. 3a and 3b). Fig. 4a/b summarizes the incubation dependence of the Fc,th and Fp,th values, i.e. the cleaning window (compare insert
Fig. 3. Squared modified spot diameter versus logarithm of pulse fluence (D2 vs. log F). “High” contamination coverage. a: alum-rosin sized ground wood cellulose paper; b: bleached sulphite softwood cellulose paper. The slope of the straight N = 1; N = 2; N = 5; dashed lines represents the 1/e2 radius (w0 ). Cleaning: N = 9; N = 20; N = 50; N = 80; N = 100. Insert (a): destruction of contaminated paper: N = 50; N = 80; N = 100. Insert (b): cleaning window for N = 5.
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
4
Fig. 4. Threshold fluences, Fth , versus pulse number, N. a: alum-rosin sized ground wood cellulose paper; b: bleached sulphite wood cellulose paper. Destruction (Fp,th ): “high” contamination coverage, “low” contamination coverage, no con“high” contamination coverage, “low” tamination (0 Fp,th ). Cleaning (Fc,th ): contamination coverage.
in Fig. 3b). In the case of the dark yellow wood cellulose paper sample it practically is not existent (Fig. 4a). That of bleached cellulose paper is comparatively narrow and decreases with N and incubation (Fig. 4b). 3.3. Colorimetric evaluation Uncontaminated papers exhibited practically negligible L and b values under middle-UV radiation irradiation (Figs. 5a, 6a, 7a and 8a) indicating no photochemical or photophysical changes. The lightness results, L, represent the cleaning status of the “low” and “high” contamination coverage cases (Figs. 5 and 6). The yellowing data b (Figs. 7 and 8) represent irreversible chemical and/or photochemical changes. Cleaning results without irreversible modifications can be represented by L and b values approaching zero. Wood cellulose paper cleaning thresholds (L ∼ 0) were found to be Fc,th ≈ 0.4 J/cm2 at N = 1, 2 and 5 with “low” contamination coverage, and Fc,th ≈ 0.1 J/cm2 at N = 9 (Fig. 5b). The cleaning threshold (L ∼ 0) for “high” contamination coverage were found to be Fc,th ≈ 1.8 J/cm2 at N = 1, 2 and 5 and at lower fluence values for higher N (Fig. 5c).
Fig. 5. Colorimetric lightness, L. Alum-rosin sized ground wood cellulose paper. a: no contamination; b: “low” contamination; c: “high” contamination. White columns: above destruction threshold fluence, Fth . Grey columns: below Fth .
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
Fig. 6. Colorimetric lightness, L. Bleached sulphite wood cellulose paper. a: no contamination; b: “low” contamination; c: “high” contamination. White columns: above destruction threshold fluence, Fth . Grey columns: below Fth .
5
Fig. 7. Colorimetric yellowing, b. Alum-rosin sized ground wood cellulose paper. a: no contamination; b: “low” contamination; c: “high” contamination. White columns: above destruction threshold fluence, Fth . Grey columns: below Fth .
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7 6
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
Cleaning thresholds (L ∼ 0) of bleached cellulose paper were found to be Fc,th ≈ 0.4 J/cm2 at N = 1 and 2 with “low” contamination coverage and Fc,th ≈ 0.24 J/cm2 at N = 5 and 9 (Fig. 6b). At all N values, Fc,th is separated from the destruction threshold of the contaminated sample Fp,th . In the case of “high” contamination coverage the cleaning thresholds (L ∼ 0) were Fc,th ≈ 1.78 J/cm2 at N = 1, 2 and 5 (Fig. 6c). The reason for higher cleaning thresholds in this case of high contamination is the dense coverage and the filling of the inter-fibre spaces with particulates, so that higher energies are required for their complete removal. Again, Fc,th is separated from the destruction threshold of the contaminated sample, Fp,th , in analogy to the “low” contamination case. The presence of the particulates, however, shows some influence on the yellowing with increasing coverage. The wood cellulose paper with high contamination exhibits low yellowing below the destruction threshold in the region of high F and low N (Fig. 7c). That is a finding in analogy to the historical papers [27]: a lower dose volume density is more advantageous than high values accompanied by high N. Yellowing of wood cellulose paper is caused by higher dose volume density values. This suggests that photochemical changes are produced by repetitive irradiation (incubation). Strong yellowing occurred below and above Fp,th (Fig. 8c) as in the case of the pure cellulose [20] in contrast to the ground wood cellulose paper type where this was only observed at high dose parameters [27]. The bleached cellulose paper underwent more yellowing in the entire cleaning fluence window (Fig. 8b, c) than the ground wood cellulose paper. This suggests that particles in the status of removal affect the neighbouring fibres. A thermomechanical removal by expansion of the strongly absorbing particle are not expected to heat or affect the substrate fibres. A vaporisation and/or a plasma formation, on the other hand, heat the fibres in next proximity during a short but sufficient time period. 4. Conclusions Ground wood cellulose paper exhibits a limited cleaning window between Fc,th which is just the beginning of particulate removal, and Fp,th . Therefore ground wood cellulose paper can be cleaned by middle-UV radiation when the minimum dose volume density strategy is applied [27]. However full cleaning of bleached cellulose paper is only reached at Fp,th accompanied by strong yellowing. That means that a practicable window is non-existent for this paper type. Cleaning and destruction thresholds of both substrates decrease with increasing N, which is a direct indication of strong incubation processes. The presence of the particulates shows substantial influence on the yellowing with increasing coverage. The coloured ground wood cellulose paper type shows low yellowing below the destruction threshold in the region of high F and low N. Yellowing is caused by higher dose volume density values. Acknowledgements We acknowledge partial financial support by the International Science and Technology Center, ISTC project B-1397. One of the authors (S. A.) has generously been supported by a scholarship from the Higher Education Commission (HEC), Pakistan. References Fig. 8. Colorimetric yellowing, b. Bleached sulphite wood cellulose paper. a: no contamination; b: “low” contamination; c: “high” contamination. White columns: above destruction threshold fluence, Fth . Grey columns: below Fth .
[1] Lasers in the conservation of artwork I, in: W. Kautek, E. König (Eds.), Restauratorenblätter, Special Issue, Verlag Mayer, Wien, 1997. [2] M. Cooper, Laser Cleaning in Conservation, Butterworth-Heinemann, Oxford, 1998. [3] C. Fotakis, W. Kautek, M. Castillejo (Eds.), Laser Chemistry, Special Issue. Lasers in the preservation of cultural heritage, Hindawi, New York, 2006. [4] D.M. Kane (Ed.), Laser Cleaning II, World Scientific, Singapore, 2006.
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011
G Model CULHER-2820; No. of Pages 7
ARTICLE IN PRESS S. Arif et al. / Journal of Cultural Heritage xxx (2013) xxx–xxx
[5] M. Schreiner, M. Strlic, R. Salimbeni (Eds.), Handbook on the Use of Lasers in Conservation and Conservation Science, COST office, Brussels, Belgium, 2008 (http://www.science4heritage.org/COSTG7/booklet/). [6] W. Kautek, S. Pentzien, P. Rudolph, J. Kruger, E. König, Laser interaction with coated collagen and cellulose fibre composites: fundamentals of laser cleaning of ancient parchment manuscripts and paper, Appl. Surf. Sci. 127–129 (1998) 746–754. [7] J. Kolar, M. Strlic, S. Pentzien, W. Kautek, Near-UV, visible and IR pulsed laser light interaction with cellulose, Appl. Phys. A 71 (2000) 87–90. [8] J. Kolar, M. Strlic, M. Marincek, IR pulsed laser light interaction with soiled cellulose and paper, Appl. Phys. A 75 (2002) 673–676. [9] M. Strlic, J. Kolar, V.S. Selih, M. Marincek, Surface modification during Nd:YAG (1064 nm) pulsed laser cleaning of organic fibrous materials, Appl. Surf. Sci. 207 (2003) 236–245. [10] J. Kolar, M. Strlic, D. Muller-Hess, A. Gruber, K. Troschke, S. Pentzien, W. Kautek, Laser cleaning of paper using Nd:YAG laser running at 532 nm, J. Cult. Herit. 4 (2003) 185–187. [11] F. Bloisi, L. Vicari, A.C. Barone, E. Martuscelli, G. Gentile, C. Polcaro, Effects of Nd:YAG (532 nm) laser radiation on “clean” cotton, Appl. Phys. A 79 (2003) 331–333. [12] S. Georgiou, Laser cleaning methodologies of polymer substrates, in: T. Lippert (Ed.), Polymers and Light, Springer-Verlag, Berlin Heidelberg Germany, 2004, pp. 1–49. [13] A. Kaminska, M. Sawczak, M. Cieplinski, G. Sliwinski, B. Kosmowski, Colorimetric study of the post-processing effect due to pulsed laser cleaning of paper, Opt. Appl. 34 (2004) 121–132. [14] P. Rudolph, F.J. Ligterink, J.L. Pedersoli, M. Van Bommel, J. Bos, H.A. Aziz, J.B.G.A. Havermans, H. Scholten, D. Schipper, W. Kautek, Characterization of lasertreated paper, Appl. Phys. A 79 (2004) 181–186. [15] S. Pentzien, A. Conradi, J. Krüger, The influence of paper type and state of degradation on laser cleaning of artificially soiled paper, in: R. Radvan, J.F. Asmus, M. Castillejo, P. Pouli, A. Nevin (Eds.), Lasers in the Conservation of Artworks VIII, Taylor & Francis Group, London, 2011, pp. 59–65. [16] S. Arif, O. Armbruster, W. Kautek, Pulse laser particulate separation from polycarbonate: surface acoustic wave and thermomechanical mechanisms, Appl. Phys. A 111 (2013) 539–548.
7
[17] S. Arif, O. Armbruster, W. Kautek, Pulse laser induced particle separation from polymethyl methacrylate: a mechanistic study, Appl. Phys. A 111 (2013) 309–317. [18] W. Kautek, Lasers in cultural heritage: the non-contact intervention, Springer Ser. Mater. Sci. 130 (2010) 313. [19] E. Sarantopoulou, Z. Samardzija, S. Kobe, Z. Kollia, A.C. Cefalas, Removing foxing stains from old paper at 157 nm, Appl. Surf. Sci. 208 (2003) 311–316. [20] S. Arif, M. Forster, S. Bushuk, A. Kouzmouk, H. Tatur, S. Batishche, W. Kautek, Mechanistic comparison of pulse laser induced phase separation of particulates from cellulose paper at 213 nm and 532 nm, Appl. Phys. A 110 (2012) 501–509. [21] S. Batishche, A. Kouzmouk, H. Tatur, T. Gorovets, U. Pilipenka, V. Ukhau, W. Kautek, Simultaneous UV-IR Nd:YAG laser cleaning of leather artifacts, Springer Proc. Phys. 116 (2007) 221–227. [22] M. Strlic, V.S. Selih, J. Kolar, D. Kocar, B. Pihlar, R. Ostrowski, J. Marczak, M. Strzelec, M. Marincek, T. Vuorinen, L.S. Johansson, Optimisation and on-line acoustic monitoring of laser cleaning of soiled paper, Appl. Phys. A 81 (2005) 943–951. [23] J. Krüger, S. Pentzien, A. Conradi, Cleaning of artificially soiled paper with 532nm nanosecond laser radiation, Appl. Phys. A 92 (2008) 179–183. [24] S. Pentzien, A. Conradi, R. Koter, J. Krüger, Cleaning of artificially soiled paper using nanosecond, picosecond and femtosecond laser pulses, Appl. Phys. A 101 (2010) 441–446. [25] A. Kaminska, A. Sawczak, K. Komar, G. Sliwinski, Application of the laser ablation for conservation of historical paper documents, Appl. Surf. Sci. 253 (2007) 7860–7864. [26] W. Kautek, Laser cleaning of paper and other organic materials, in: M. Schreiner, M. Strlic, R. Salimbeni (Eds.), Handbook on the Use of Lasers in Conservation and Conservation Science, COST office, Brussels, Belgium, 2008 (http://www.science4heritage.org/COSTG7/booklet/). [27] S. Arif, S. Bushuk, A. Kouzmouk, H. Tatur, S. Batishche, W. Kautek, Microparticle separation mechanism from ancient cellulose papers by middle-ultraviolet (213 nm) and visible (532 nm) pulsed laser radiation, in: R. Radvan, S. Akyüz, M. Simileanu (Eds.), The Unknown Face of the Artwork, Istanbul Kültür University, Istanbul, 2012, pp. 43–60. [28] J. Krüger, W. Kautek, in: T.K. Lippert (Ed.), Advances in Polymer Science, Springer-Verlag, Berlin/Heidelberg, 2004, pp. 247–289.
Please cite this article in press as: S. Arif, et al., Middle-ultraviolet laser cleaning of particulates from sized ground wood cellulose and pure cellulose paper, Journal of Cultural Heritage (2013), http://dx.doi.org/10.1016/j.culher.2013.11.011