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Hydrothermal synthesis of zirconium dioxide coating on the surface of wood with improved UV resistance
Applied Surface Science 321 (2014) 38–42
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Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Hydrothermal synthesis of zirconium dioxide coating on the surface of wood with improved UV resistance Caichao Wan, Yun Lu, Qingfeng Sun, Jian Li ∗ Material Science and Engineering College, Northeast Forestry University, Harbin 150040, China
a r t i c l e
i n f o
Article history: Received 10 June 2014 Received in revised form 11 September 2014 Accepted 19 September 2014 Available online 28 September 2014 Keywords: Hydrothermal synthesis Inorganic compound Photodegradation Nanoparticle Layer-by-layer self-assembly
a b s t r a c t Nano-ZrO2 aggregations were successfully layer-by-layer deposited on the wood surface by a simple mild one-pot hydrothermal method. The resulting ZrO2 /wood nanocomposites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The results indicated that the strong hydrogen bonds between the amorphous ZrO2 and the hydroxide radicals of wood surface were formed, and the strong interaction contributed to the enhancement of the nanocomposites heat stability. Moreover, compared with the original wood, the ZrO2 /wood showed more superior UV-resistant ability through a 600-h QUV accelerated aging test. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Wood, the oldest material utilized by humans for construction after stone, has many alluring properties such as renewability, low density, low thermal expansion, easy machining, desirable mechanical strength and esthetically pleasing. As a result, wood has been intensively applied in various fields like building, shipbuilding, railway, papermaking, furniture, interior decoration, etc. However, as a complex natural biopolymer principally composed of cellulose, hemicellulose and lignin, wood has inferior resistance to degradation from environmental agencies including fire, water, light and microorganisms compared with many artificial materials [1–5]. Especially for exposure in the sun, sharp degradations in surface color and mechanical strength would occur due to strong ultraviolet (UV) light absorption ability of lignin leading to radical induced depolymerisation of wood compositions [6–9]. There is no doubt that these unfavorable declines would reduce utilization value, service life and esthetic feeling of wood adverse to the long-term development and comprehensive utilization of wood. To date, many effective approaches to protecting wood products from photodegradation or minimizing UV irradiation effect
∗ Corresponding author at: Northeast Forestry University, No. 26, Hexing Road Xiangfang District, Harbin 150040, China. Tel.: +86 451 82192399; fax: +86 451 82192399. E-mail address: [email protected] (J. Li). http://dx.doi.org/10.1016/j.apsusc.2014.09.135 0169-4332/© 2014 Elsevier B.V. All rights reserved.
have been widely reported such as finishing [10,11], treatment with dilute aqueous solutions of inorganic salts [12,13] and depositing hybrid inorganic–organic thin films on wood substrates [14,15]. Currently, chemically bonding or grafting stabilizing chemicals including UV absorbers or antioxidants is considered as one of the most effective methods of stabilizing photo-labile polymers when subjected to exterior exposure or severe environments [16–19]. Meanwhile, it is worth noting that this class of absorbers or antioxidants must be colorless or light-colored and avirulent, and do not significantly damage wood surface. According to the previous reports, some chemically stable and nontoxic inorganic nanoparticles such as TiO2 , ZnO and ZrO2 hold great prospects as photoprotective agents for wood owing to their UV irradiation absorption or scatter ability. The cases that TiO2 and ZnO serve as UV resistant agents have been extensively studied [20–22], whereas the literatures aiming at ZrO2 for UV resistance application are not abundant [23,24]. Actually, zirconia is one of the important ceramic which is widely used as structural materials, thermal barrier coating, optical coating, solid oxide fuel cell electrolytes, semiconductor materials and catalysis or catalytic supports because of its biocompatibility, high mechanical strength and fracture toughness, high melting point, high refractivity, stable photochemical properties and corrosion resistance [25]. Recently, Smirnov et al. [26] reported a new type of ZrO2 /SiO2 interference mirrors capable of efficiently protecting against UV radiation prepared by spin-coating-assisted layer-by-layer deposition of colloidal suspensions of nanoparticles of ZrO2 and SiO2 .
C. Wan et al. / Applied Surface Science 321 (2014) 38–42
Zhou et al. [27] manufactured a kind of UV-resistant nano-ZrO2 composite polyester functional fiber. Shi et al. [28] fabricated cosmetics containing ZrO2 with improved optical activity, which could better resist full-waveband UV radiation. Motivated by these studies, adopting a versatile hydrothermal method to deposit ZrO2 nanoparticles on wood surface might receive an excellent UV resistance effect. Hydrothermal method is regarded as an efficient and mild way of synthesizing inorganic/wood hybrid materials, which has been demonstrated by our previous researches [29,30]. Moreover, to the best of our knowledge, this is the first attempt to utilize ZrO2 as wood photoprotective agent by hydrothermal method. In this work, a simple mild one-pot hydrothermal method was employed to prepare ZrO2 /wood nanocomposites. SEM observation suggested that the nano-ZrO2 aggregations had been uniformly deposited on wood surface layer-by-layer, and the following characterizations including XPS, XRD, FTIR EDX and TGA demonstrated the formation of ZrO2 and the strong interaction between ZrO2 and the hydroxide radicals of wood substrate resulting in the significant enhancement of the ZrO2 /wood thermal stability compared with that of the original wood. Under prolonged strong UV irradiation, the nanocomposites showed extraordinary UV resistance with only tiny discoloration. Meanwhile, we also proposed a possible schematic diagram of the deposition of ZrO2 on wood surface according to the experimental results. 2. Experimental 2.1. Materials Polar wood slices were cut with the sizes of 20 mm (longitudinal) × 20 mm (tangential) × 10 mm (radial), and the slices were subsequently ultrasonically washed in deionized water for 30 min and dried at 80 ◦ C for 24 h in a vacuum. Zirconium oxychloride octahydrate (ZrOCl2 ·8H2 O) and ammonia solution (NH4 OH) used in this experiment were supplied by Tianjin Kermel chemical Co. Ltd., and used without further purification.
39
2.4. Accelerated aging test A QUV accelerated weathering tester (Atlas, Chicago, IL, USA) was applied to induce photo-discoloration of the nanocomposites, which could reproduce the damage caused by sunlight, rain and dew. The samples were placed under a 340 nm fluorescent UV lamps (UV-B region) and underwent continuous light irradiation at 60 ◦ C for 2.5 h and following water spray for 0.5 h as well as succedent condensation at 45 ◦ C for 24 h. The whole weathering schedule lasted for 600 h, and the surface color changes were measured about every 24 h for 0–200 h, 48 h for 200–400 h, and 96 h for 400–600 h. The color changes induced by UV irradiation were determined using a portable spectrophotometer (NF-333, Nippon Denshoku Company, Japan) with CIELAB system in accordance with the ISO2470 standard. The CIELAB system was characterized by three parameters L*, a*, and b*. The L* axis represents lightness, and L* varies from 100 (white) to 0 (black); a* and b* are the chromaticity coordinates, and +a* is for red, −a* for green, +b* for yellow, −b* for blue. The change of L*, a*, and b* are calculated using Eqs. (1)–(3). L∗ = L2 − L1
(1)
a∗ = a2 − a1
(2)
b∗ = b2 − b1
(3)
where L*, a*, and b* represent the differences of initial and final values of L*, a* and b*; L1 , a1 and b1 are the initial color parameters; L2 , a2 and b2 are the ultimate color parameters after UV irradiation, respectively. The overall color change (E*) was calculated using the Eq. (4), and lower E* value represents less significant color change. E ∗ =
(L2∗ − L1∗ )2 + (a∗2 − a∗1 )2 + (b∗2 − b∗1 )
2
(4)
The accelerated aging tests were performed in triplicate and were done at least two different times to ensure reproducibility. All parameters were measured at eight locations on each sample at least, and the average values were calculated as the final decision.
2.2. Preparation of ZrO2 /wood
3. Results and discussion
The preparation of ZrO2 /wood was implemented as follows: firstly, ZrOCl2 ·8H2 O (0.78 g) was dissolved in 100 mL of deionized water with magnetic stirring for 30 min, and then 0.6 mL NH4 OH was dropwise added into the mixed aqueous solution with continuous stirring to form an emulsion. Subsequently, the dried wood slices and the above mixed solution were transferred to a Teflonlined stainless-steel autoclave, and the autoclave was sealed and heated to 90 ◦ C for 4 h. After reaction, the wood specimens were took out and ultrasonically rinsed with deionized water for 30 min. Finally, the samples were dried at 60 ◦ C for 24 h in vacuum, and the following ZrO2 /wood nanocomposites were obtained.
XPS analysis was used to clarify the chemical states of elements on the resulting ZrO2 /wood surface. Fig. 1a showed the survey broad scan XPS spectrum of ZrO2 /wood, in which elements of Zr, C and O assigned to wood components and ZrO2 were detected on the powder surface corresponding to peaks at binding energy of about 182.4, 285.4 and 532.3, respectively. The corresponding narrow scan analysis of Zr 3d XPS spectrum, within the B.E. range of 176–194 eV, was shown in Fig. 1b. As shown, two Zr 3d peaks were observed at the binding energies of 182.5 eV and 184.9 eV, which were attributed to ZrO2 [31,32]. Fig. 1c showed the XRD patterns of the original wood and ZrO2 /wood. Apparently, the original wood displayed typical cellulose I crystalline structure, which exhibited characteristic peaks at around 15.0◦ , 16.5◦ , 22.3◦ and 34.8◦ corresponding to the (1¯ 1 0), (1 1 0), (2 0 0) and (0 4 0) planes [33,34], respectively. Similarly, the ZrO2 /wood also exhibited obvious cellulose characteristic peaks, whereas there were no other obvious diffraction peaks related to ZrO2 for the ZrO2 /wood indicating that the oxide coating on the wood surface was exclusively constituted of amorphous particles [35], which was similar to some previous reports that fabricated ZrO2 materials at such similar low temperatures [31,36,37]. For further exploring the surface chemical compositions differences before and after the hydrothermal treatment, the FTIR measurements of the original wood and ZrO2 /wood were performed, and the results were shown in Fig. 1d. Apart from some wood characteristic peaks, such as the peaks at 3315 cm−1 and 2886 cm−1
2.3. Characterization The as-prepared ZrO2 /wood samples were observed using a FEI Quanta 200 SEM attached with an EDX spectrometer unit. XRD patterns were taken with XRD technique (Rigaku, D/MAX 2200) ˚ at 40 kV and 30 mA. using Ni-filtered Cu K␣ radiation ( = 1.5406 A) Scattered radiation was detected in the range of 2 = 5 − 80◦ at a scan rate of 4◦ min−1 . FTIR spectra were recorded in the range of 400–4000 cm−1 on a Thermo Electron Corp (Nicolet Magna 560) FTIR spectrometer. XPS spectra were recorded in the range of 0–1200 eV using a Thermo Escalab 250Xi XPS spectrometer (Germany). The thermal stabilities were investigated by a TA Q600 TG analyzer from 28 to 700 ◦ C with a heating rate of 10 ◦ C min−1 under nitrogen atmosphere.
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C. Wan et al. / Applied Surface Science 321 (2014) 38–42
Fig. 1. Broad scan XPS spectrum (a) and high resolution XPS spectrum (b) of ZrO2 /wood. XRD patterns (c) and FTIR spectra (d) of ZrO2 /wood and original wood.
attributed to the O H stretching and the C H stretching [38], the peaks at 1423 cm−1 , 1029 cm−1 and 894 cm−1 related to the CH2 symmetric bending, the C(6) OH stretching and C(1) H out-ofplane bending (Glucose ring, ˇ bond) of cellulose structure [39], the peak at 1512 cm−1 belonging to aromatic phenyl C C of lignin [40], and the peak at 1737 cm−1 for C O stretching in unconjugated ketone, carbonyl and aliphatic groups (xylan) of hemicellulose [41], it was not hard to find that a new strong adsorption peak attributed to Zr O Zr band at around 486 cm−1 occurred in the FTIR spectrum of the nanocomposites [42], revealing that the ZrO2 nanoparticles were successfully deposited on the wood surface by the
hydrothermal process. In addition, the broad adsorption band of the original wood at around 3334 cm−1 was shifted to lower wavenumber (ca. 3315 cm−1 ) in the spectrum of ZrO2 /wood, indicating the strong interaction between hydroxyl groups of wood surface and ZrO2 nanoparticles [43]. The micrograph (Fig. 2a) obtained by SEM backscattering electron imaging, for the ZrO2 /wood nanohybrids, clearly showed large-scale even-distributed aggregations of the oxide particles, appearing as bright points on the wood surface. These bright points were subsequently proved to be nano-ZrO2 aggregations by EDX because of the strong Zr peaks (Fig. 2c); besides, the Cu peaks were
Fig. 2. SEM images at low magnification (a) and high magnification (b) of ZrO2 /wood.
Fig. 3. Schematic illustrations for fabricating the ZrO2 /wood using the hydrothermal method.
C. Wan et al. / Applied Surface Science 321 (2014) 38–42
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Fig. 4. TG (a) and DTG (b) curves of ZrO2 /wood and original wood, respectively.
originated from the coating layer used for electric conduction during the SEM observation, and all carbon and partial oxygen were derived from the wood matrix. Fig. 2b showed the SEM image of ZrO2 /wood nanocomposites under higher magnification. Clearly, plentiful irregularly shaped ZrO2 aggregations were layer-by-layer adhered to the wood substrate surface as indicated by the white arrow, and the driving force of layer-by-layer self-assembly behaviors of the aggregations was primarily due to the electrostatic adsorption [44]. Moreover, the increasing thickness of ZrO2 protective layer might be beneficial to resist UV radiation. Based on the above investigation of the experimental parameters for the ZrO2 /wood nanocomposites, a possible formation mechanism could be described as follows (Fig. 3): firstly, the precipitation reaction, which took place as the result of mixing ZrOCl2 ·8H2 O aqueous solution and ammonia, might refer to the Eq. (5) [45]. Then, the obtained Zr(OH)4 nanoparticles were gradually reacted to generate nano-ZrO2 with the help of hydrothermal
energy (Eq. (6)), and then the resulting nano-ZrO2 formed strong interaction with the hydroxyl groups of wood surface leading to formation of plentiful hydrogen bonds, contributing to the deposition and stabilization of ZrO2 nanoparticles on the wood substrate. Subsequently, owing to the electrostatic adsorption force, increasing ZrO2 nanoparticles were attracted and layer-by-layer combined with the previous ZrO2 resulting in multilayer ZrO2 nanoparticles on the wood surface. ZrOCl2 · 8H2 O + NH4 OH → Zr(OH)4 + NH4 Cl + H2 O Zr(OH)4
hydrothermal process
−→
ZrO2
(5) (6)
Fig. 4 represented the TG and DTG curves of the original wood and ZrO2 /wood, respectively. The small initial drops occurring before 150 ◦ C in both cases were due to the evaporation of retained moisture [46]. For the original wood, the DTG curves displayed two main regions: the first region occurred between 192 ◦ C and 315 ◦ C,
Fig. 5. Change tendencies of L*, a*, b* and E* of ZrO2 /wood and original wood, respectively.
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C. Wan et al. / Applied Surface Science 321 (2014) 38–42
and showed a pronounced shoulder related to the hemicellulose decomposition; the second region (315–391 ◦ C) was attributed to the attainment of the maximum, principally due to cellulose degradation, followed by a rapid decay and a long tail [47]. Furthermore, as the most difficult one to decompose among the three main components of wood, lignin decomposed slowly under the whole temperature ranged from ambient to 700 ◦ C leading to no obvious characteristic peaks [48]. Compared with the original wood, aside from the similar decomposition tendency, the ZrO2 /wood also exhibited more superior thermal stability. In detail, the original wood started to degrade at around 192 ◦ C, whereas the ZrO2 /wood began to decompose at 223 ◦ C, respectively. At 50% weight loss, the decomposition temperature occurred at 339 ◦ C for the native wood and 381 ◦ C for the nanocomposites. Moreover, the original wood reached maximum degradation rate at 357 ◦ C, which was 27 ◦ C earlier than the ZrO2 /wood (ca. 384 ◦ C). These results implied that the thermal stability of ZrO2 /wood was higher than that of original wood. The reason of this enhancement was probably due to the strong interaction between wood substrate and ZrO2 [49,50]. It was consistent with the shift of FTIR adsorption peak of ZrO2 /wood at 3334 cm−1 to lower wavenumber in Fig. 1b. The color stabilities of the two material classes, the original wood and ZrO2 /wood, were examined by means of the change tendencies of L*, a*, b* and E* [51]. It could be observed in Fig. 5 that all color feature parameters changes of original wood from 0 to 600 h were more significant than those of ZrO2 /wood notwithstanding the two materials both showed similar change tendencies of L*, a*, b* and E*, which suggested that the color stability of the ZrO2 /wood composite was more superior under UV light. Furthermore, the higher a* and b* and lower L* of original wood at the end of the 600-h treatment (Fig. 5a–c) represented that the light-colored sample turned deeper shade of red, dark yellow and black, respectively. In addition, the total color change (E*) of original wood was also significant (Fig. 5d), nevertheless the change in the composite E* was much less (approximately 2/3). Thus, the untreated wood with limited UV resistance suffered serious surface damage under UV light; whereas, hydrothermal treated wood exhibited stronger UV protection, which also revealed that the ZrO2 nano-coating was an effective UV protected agent. 4. Conclusions The ZrO2 /wood nanocomposites were successfully prepared by a simple mild one-pot hydrothermal method. The amorphous ZrO2 aggregations, which were layer-by-layer deposited on the surface of wood substrate with the help of hydrothermal energy and electrostatic adherence, generated plentiful hydrogen bonds with the hydroxide radicals of wood surface leading to significant improvement of thermal stability of the ZrO2 /wood nanocomposites. Through the 600-h QUV accelerated aging test, the original wood suffered serious discoloration, whereas the nanocomposites showed superior anti-UV capability. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (grant no. 31270590). References [1] E. Ncube, M. Meincken, Appl. Surf. Sci. 256 (2010) 7504–7509. [2] A. Temiz, U.C. Yildiz, I. Aydin, M. Eikenes, G. Alfredsen, G. C¸olakoglu, Appl. Surf. Sci. 250 (2005) 35–42.
[3] X. Wang, H. Ren, Appl. Surf. Sci. 254 (2008) 7029–7034. [4] R.K.W.M. Klaassen, B.S. van Overeem, J. Cult. Herit. 13 (2012) S129–S134. [5] U. Råberg, N. Terziev, G. Daniel, Int. Biodeterior. Biodegrad. 79 (2013) 20–27. [6] D. Rosu, C.-A. Teaca, R. Bodirlau, L. Rosu, J. Photochem. Photobiol. B 99 (2010) 144–149. [7] L. Tolvaj, Z. Molnar, R. Nemeth, J. Photochem. Photobiol. B 121 (2013) 32–36. [8] T.E. Madey, N.S. Faradzhev, B.V. Yakshinskiy, N.V. Edwards, Appl. Surf. Sci. 253 (2006) 1691–1708. [9] T.-C. Chang, H.-Y. Lin, S.-Y. Wang, S.-T. Chang, Polym. Degrad. Stab. 105 (2014) 42–47. [10] D.J. Pogge, S.M. Lonergan, S.L. Hansen, Meat Sci. 97 (2014) 419–427. [11] P. Nzokou, D.P. Kamdem, A. Temiz, Prog. Org. Coat. 71 (2011) 350–354. [12] A. Khelfa, A. Bensakhria, J.V. Weber, J. Anal. Appl. Pyrolysis 101 (2013) 111–121. [13] L. Liu, J. Sun, C. Cai, S. Wang, H. Pei, J. Zhang, Bioresour. Technol. 100 (2009) 5865–5871. [14] J. Van den Bulcke, J. Van Acker, H. Saveyn, M. Stevens, Prog. Org. Coat. 58 (2007) 1–12. [15] P.-L. Chou, H.-T. Chang, T.-F. Yeh, S.-T. Chang, Bioresour. Technol. 99 (2008) 1073–1079. [16] B. Forsthuber, U. Müller, A. Teischinger, G. Grüll, Polym. Degrad. Stab. 98 (2013) 1329–1338. [17] F. Aloui, A. Ahajji, Y. Irmouli, B. George, B. Charrier, A. Merlin, Appl. Surf. Sci. 253 (2007) 3737–3745. [18] M. Vlad Cristea, B. Riedl, P. Blanchet, Prog. Org. Coat. 69 (2010) 432–441. [19] M. Kiguchi, P.D. Evans, Polym. Degrad. Stab. 61 (1998) 33–45. [20] B. Forsthuber, U. Müller, A. Teischinger, G. Grüll, Polym. Degrad. Stab. 105 (2014) 206–210. [21] T. Kallio, S. Alajoki, V. Pore, M. Ritala, J. Laine, M. Leskelä, P. Stenius, Colloids Surf. A 291 (2006) 162–176. [22] J. Salla, K.K. Pandey, K. Srinivas, Polym. Degrad. Stab. 97 (2012) 592–596. [23] P. Rodiˇc, J. Iskra, I. Miloˇsev, J. Non-Cryst. Solids 396–397 (2014) 25–35. [24] K. Nallis, K.-I. Katsumata, T. Isobe, K. Okada, P. Bone, R. Othman, Appl. Clay Sci. 80–81 (2013) 147–153. [25] X. Pian, B. Fan, H. Chen, B. Zhao, X. Zhang, R. Zhang, Ceram. Int. 40 (2014) 10483–10488. [26] J.R.C. Smirnov, M.E. Calvo, H. Míguez, Adv. Funct. Mater. 23 (2013) 2805–2811. [27] X. Zhou, J. Wu, Google Patents, 2012. [28] X. Shi, C. Cui, C. Di, Y. Zou, M. Xu, Google Patents, 2011. [29] Q. Sun, Y. Lu, H. Zhang, H. Zhao, H. Yu, J. Xu, Y. Fu, D. Yang, Y. Liu, Mater. Chem. Phys. 133 (2012) 253–258. [30] J. Li, H. Yu, Q. Sun, Y. Liu, Y. Cui, Y. Lu, Appl. Surf. Sci. 256 (2010) 5046–5050. [31] S. Shukla, S. Seal, R. Vanfleet, J. Sol–Gel Sci. Technol. 27 (2003) 119–136. [32] M.A. Botzakaki, N. Xanthopoulos, E. Makarona, C. Tsamis, S. Kennou, S. Ladas, S.N. Georga, C.A. Krontiras, Microelectron. Eng. 112 (2013) 208–212. [33] J. Cai, S. Kimura, M. Wada, S. Kuga, Biomacromolecules 10 (2008) 87–94. [34] J. Cai, L. Zhang, Macromol. Biosci. 5 (2005) 539–548. [35] C. Zhao, O. Richard, H. Bender, M. Caymax, S. De Gendt, M. Heyns, E. Young, G. Roebben, O. Van der Biest, S. Haukka, Appl. Phys. Lett. 80 (2002) 2374–2376. [36] U.P.R. Filho, Y. Gushikem, F.Y. Fujiwara, S.C. de Castro, I.C.L. Torriani, L.P. Cavalcanti, Langmuir 10 (1994) 4357–4360. [37] N. Zink, F. Emmerling, T. Hager, M. Panthofer, M.N. Tahir, U. Kolb, W. Tremel, Dalton Trans. 42 (2013) 432–440. [38] W. Lan, C.-F. Liu, F.-X. Yue, R.-C. Sun, J.F. Kennedy, Carbohydr. Polym. 86 (2011) 672–677. [39] A.-M. Olsson, L. Salmén, Carbohydr. Res. 339 (2004) 813–818. [40] R. Rana, R. Langenfeld-Heyser, R. Finkeldey, A. Polle, Wood Sci. Technol. 44 (2010) 225–242. [41] M. Kacurakova, P. Capek, V. Sasinkova, N. Wellner, A. Ebringerova, Carbohydr. Polym. 43 (2000) 195–203. [42] S.B. Khan, K.A. Alamry, H.M. Marwani, A.M. Asiri, M.M. Rahman, Compos. B-Eng. 50 (2013) 253–258. [43] G. Lucovsky, G. Rayner, Appl. Phys. Lett. 77 (2000) 2912–2914. [44] H. Dun, W. Zhang, Y. Wei, S. Xiuqing, Y. Li, L. Chen, Anal. Chem. 76 (2004) 5016–5023. [45] H. Zhou, R. Tian, M. Ye, S. Xu, S. Feng, C. Pan, X. Jiang, X. Li, H. Zou, Electrophoresis 28 (2007) 2201–2215. [46] J. Li, Y. Lu, D. Yang, Q. Sun, Y. Liu, H. Zhao, Biomacromolecules 12 (2011) 1860–1867. [47] F. Shafizadeh, Y. Fu, Carbohydr. Res. 29 (1973) 113–122. [48] H. Yang, R. Yan, H. Chen, D.H. Lee, C. Zheng, Fuel 86 (2007) 1781–1788. [49] R. Valiokas, M. Östblom, S. Svedhem, S.C. Svensson, B. Liedberg, J. Phys. Chem. B 106 (2002) 10401–10409. [50] L. Haurie, A.I. Fernández, J.I. Velasco, J.M. Chimenos, J.-M. Lopez Cuesta, F. Espiell, Polym. Degrad. Stab. 92 (2007) 1082–1087. [51] Q. Sun, Y. Lu, H. Zhang, D. Yang, Y. Wang, J. Xu, J. Tu, Y. Liu, J. Li, J. Mater. Sci. 47 (2012) 4457–4462.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Hydrothermal synthesis of zirconium dioxide coating on the surface of wood with improved UV resistance Caichao Wan, Yun Lu, Qingfeng Sun, Jian Li ∗ Material Science and Engineering College, Northeast Forestry University, Harbin 150040, China
a r t i c l e
i n f o
Article history: Received 10 June 2014 Received in revised form 11 September 2014 Accepted 19 September 2014 Available online 28 September 2014 Keywords: Hydrothermal synthesis Inorganic compound Photodegradation Nanoparticle Layer-by-layer self-assembly
a b s t r a c t Nano-ZrO2 aggregations were successfully layer-by-layer deposited on the wood surface by a simple mild one-pot hydrothermal method. The resulting ZrO2 /wood nanocomposites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The results indicated that the strong hydrogen bonds between the amorphous ZrO2 and the hydroxide radicals of wood surface were formed, and the strong interaction contributed to the enhancement of the nanocomposites heat stability. Moreover, compared with the original wood, the ZrO2 /wood showed more superior UV-resistant ability through a 600-h QUV accelerated aging test. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Wood, the oldest material utilized by humans for construction after stone, has many alluring properties such as renewability, low density, low thermal expansion, easy machining, desirable mechanical strength and esthetically pleasing. As a result, wood has been intensively applied in various fields like building, shipbuilding, railway, papermaking, furniture, interior decoration, etc. However, as a complex natural biopolymer principally composed of cellulose, hemicellulose and lignin, wood has inferior resistance to degradation from environmental agencies including fire, water, light and microorganisms compared with many artificial materials [1–5]. Especially for exposure in the sun, sharp degradations in surface color and mechanical strength would occur due to strong ultraviolet (UV) light absorption ability of lignin leading to radical induced depolymerisation of wood compositions [6–9]. There is no doubt that these unfavorable declines would reduce utilization value, service life and esthetic feeling of wood adverse to the long-term development and comprehensive utilization of wood. To date, many effective approaches to protecting wood products from photodegradation or minimizing UV irradiation effect
∗ Corresponding author at: Northeast Forestry University, No. 26, Hexing Road Xiangfang District, Harbin 150040, China. Tel.: +86 451 82192399; fax: +86 451 82192399. E-mail address: [email protected] (J. Li). http://dx.doi.org/10.1016/j.apsusc.2014.09.135 0169-4332/© 2014 Elsevier B.V. All rights reserved.
have been widely reported such as finishing [10,11], treatment with dilute aqueous solutions of inorganic salts [12,13] and depositing hybrid inorganic–organic thin films on wood substrates [14,15]. Currently, chemically bonding or grafting stabilizing chemicals including UV absorbers or antioxidants is considered as one of the most effective methods of stabilizing photo-labile polymers when subjected to exterior exposure or severe environments [16–19]. Meanwhile, it is worth noting that this class of absorbers or antioxidants must be colorless or light-colored and avirulent, and do not significantly damage wood surface. According to the previous reports, some chemically stable and nontoxic inorganic nanoparticles such as TiO2 , ZnO and ZrO2 hold great prospects as photoprotective agents for wood owing to their UV irradiation absorption or scatter ability. The cases that TiO2 and ZnO serve as UV resistant agents have been extensively studied [20–22], whereas the literatures aiming at ZrO2 for UV resistance application are not abundant [23,24]. Actually, zirconia is one of the important ceramic which is widely used as structural materials, thermal barrier coating, optical coating, solid oxide fuel cell electrolytes, semiconductor materials and catalysis or catalytic supports because of its biocompatibility, high mechanical strength and fracture toughness, high melting point, high refractivity, stable photochemical properties and corrosion resistance [25]. Recently, Smirnov et al. [26] reported a new type of ZrO2 /SiO2 interference mirrors capable of efficiently protecting against UV radiation prepared by spin-coating-assisted layer-by-layer deposition of colloidal suspensions of nanoparticles of ZrO2 and SiO2 .
C. Wan et al. / Applied Surface Science 321 (2014) 38–42
Zhou et al. [27] manufactured a kind of UV-resistant nano-ZrO2 composite polyester functional fiber. Shi et al. [28] fabricated cosmetics containing ZrO2 with improved optical activity, which could better resist full-waveband UV radiation. Motivated by these studies, adopting a versatile hydrothermal method to deposit ZrO2 nanoparticles on wood surface might receive an excellent UV resistance effect. Hydrothermal method is regarded as an efficient and mild way of synthesizing inorganic/wood hybrid materials, which has been demonstrated by our previous researches [29,30]. Moreover, to the best of our knowledge, this is the first attempt to utilize ZrO2 as wood photoprotective agent by hydrothermal method. In this work, a simple mild one-pot hydrothermal method was employed to prepare ZrO2 /wood nanocomposites. SEM observation suggested that the nano-ZrO2 aggregations had been uniformly deposited on wood surface layer-by-layer, and the following characterizations including XPS, XRD, FTIR EDX and TGA demonstrated the formation of ZrO2 and the strong interaction between ZrO2 and the hydroxide radicals of wood substrate resulting in the significant enhancement of the ZrO2 /wood thermal stability compared with that of the original wood. Under prolonged strong UV irradiation, the nanocomposites showed extraordinary UV resistance with only tiny discoloration. Meanwhile, we also proposed a possible schematic diagram of the deposition of ZrO2 on wood surface according to the experimental results. 2. Experimental 2.1. Materials Polar wood slices were cut with the sizes of 20 mm (longitudinal) × 20 mm (tangential) × 10 mm (radial), and the slices were subsequently ultrasonically washed in deionized water for 30 min and dried at 80 ◦ C for 24 h in a vacuum. Zirconium oxychloride octahydrate (ZrOCl2 ·8H2 O) and ammonia solution (NH4 OH) used in this experiment were supplied by Tianjin Kermel chemical Co. Ltd., and used without further purification.
39
2.4. Accelerated aging test A QUV accelerated weathering tester (Atlas, Chicago, IL, USA) was applied to induce photo-discoloration of the nanocomposites, which could reproduce the damage caused by sunlight, rain and dew. The samples were placed under a 340 nm fluorescent UV lamps (UV-B region) and underwent continuous light irradiation at 60 ◦ C for 2.5 h and following water spray for 0.5 h as well as succedent condensation at 45 ◦ C for 24 h. The whole weathering schedule lasted for 600 h, and the surface color changes were measured about every 24 h for 0–200 h, 48 h for 200–400 h, and 96 h for 400–600 h. The color changes induced by UV irradiation were determined using a portable spectrophotometer (NF-333, Nippon Denshoku Company, Japan) with CIELAB system in accordance with the ISO2470 standard. The CIELAB system was characterized by three parameters L*, a*, and b*. The L* axis represents lightness, and L* varies from 100 (white) to 0 (black); a* and b* are the chromaticity coordinates, and +a* is for red, −a* for green, +b* for yellow, −b* for blue. The change of L*, a*, and b* are calculated using Eqs. (1)–(3). L∗ = L2 − L1
(1)
a∗ = a2 − a1
(2)
b∗ = b2 − b1
(3)
where L*, a*, and b* represent the differences of initial and final values of L*, a* and b*; L1 , a1 and b1 are the initial color parameters; L2 , a2 and b2 are the ultimate color parameters after UV irradiation, respectively. The overall color change (E*) was calculated using the Eq. (4), and lower E* value represents less significant color change. E ∗ =
(L2∗ − L1∗ )2 + (a∗2 − a∗1 )2 + (b∗2 − b∗1 )
2
(4)
The accelerated aging tests were performed in triplicate and were done at least two different times to ensure reproducibility. All parameters were measured at eight locations on each sample at least, and the average values were calculated as the final decision.
2.2. Preparation of ZrO2 /wood
3. Results and discussion
The preparation of ZrO2 /wood was implemented as follows: firstly, ZrOCl2 ·8H2 O (0.78 g) was dissolved in 100 mL of deionized water with magnetic stirring for 30 min, and then 0.6 mL NH4 OH was dropwise added into the mixed aqueous solution with continuous stirring to form an emulsion. Subsequently, the dried wood slices and the above mixed solution were transferred to a Teflonlined stainless-steel autoclave, and the autoclave was sealed and heated to 90 ◦ C for 4 h. After reaction, the wood specimens were took out and ultrasonically rinsed with deionized water for 30 min. Finally, the samples were dried at 60 ◦ C for 24 h in vacuum, and the following ZrO2 /wood nanocomposites were obtained.
XPS analysis was used to clarify the chemical states of elements on the resulting ZrO2 /wood surface. Fig. 1a showed the survey broad scan XPS spectrum of ZrO2 /wood, in which elements of Zr, C and O assigned to wood components and ZrO2 were detected on the powder surface corresponding to peaks at binding energy of about 182.4, 285.4 and 532.3, respectively. The corresponding narrow scan analysis of Zr 3d XPS spectrum, within the B.E. range of 176–194 eV, was shown in Fig. 1b. As shown, two Zr 3d peaks were observed at the binding energies of 182.5 eV and 184.9 eV, which were attributed to ZrO2 [31,32]. Fig. 1c showed the XRD patterns of the original wood and ZrO2 /wood. Apparently, the original wood displayed typical cellulose I crystalline structure, which exhibited characteristic peaks at around 15.0◦ , 16.5◦ , 22.3◦ and 34.8◦ corresponding to the (1¯ 1 0), (1 1 0), (2 0 0) and (0 4 0) planes [33,34], respectively. Similarly, the ZrO2 /wood also exhibited obvious cellulose characteristic peaks, whereas there were no other obvious diffraction peaks related to ZrO2 for the ZrO2 /wood indicating that the oxide coating on the wood surface was exclusively constituted of amorphous particles [35], which was similar to some previous reports that fabricated ZrO2 materials at such similar low temperatures [31,36,37]. For further exploring the surface chemical compositions differences before and after the hydrothermal treatment, the FTIR measurements of the original wood and ZrO2 /wood were performed, and the results were shown in Fig. 1d. Apart from some wood characteristic peaks, such as the peaks at 3315 cm−1 and 2886 cm−1
2.3. Characterization The as-prepared ZrO2 /wood samples were observed using a FEI Quanta 200 SEM attached with an EDX spectrometer unit. XRD patterns were taken with XRD technique (Rigaku, D/MAX 2200) ˚ at 40 kV and 30 mA. using Ni-filtered Cu K␣ radiation ( = 1.5406 A) Scattered radiation was detected in the range of 2 = 5 − 80◦ at a scan rate of 4◦ min−1 . FTIR spectra were recorded in the range of 400–4000 cm−1 on a Thermo Electron Corp (Nicolet Magna 560) FTIR spectrometer. XPS spectra were recorded in the range of 0–1200 eV using a Thermo Escalab 250Xi XPS spectrometer (Germany). The thermal stabilities were investigated by a TA Q600 TG analyzer from 28 to 700 ◦ C with a heating rate of 10 ◦ C min−1 under nitrogen atmosphere.
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C. Wan et al. / Applied Surface Science 321 (2014) 38–42
Fig. 1. Broad scan XPS spectrum (a) and high resolution XPS spectrum (b) of ZrO2 /wood. XRD patterns (c) and FTIR spectra (d) of ZrO2 /wood and original wood.
attributed to the O H stretching and the C H stretching [38], the peaks at 1423 cm−1 , 1029 cm−1 and 894 cm−1 related to the CH2 symmetric bending, the C(6) OH stretching and C(1) H out-ofplane bending (Glucose ring, ˇ bond) of cellulose structure [39], the peak at 1512 cm−1 belonging to aromatic phenyl C C of lignin [40], and the peak at 1737 cm−1 for C O stretching in unconjugated ketone, carbonyl and aliphatic groups (xylan) of hemicellulose [41], it was not hard to find that a new strong adsorption peak attributed to Zr O Zr band at around 486 cm−1 occurred in the FTIR spectrum of the nanocomposites [42], revealing that the ZrO2 nanoparticles were successfully deposited on the wood surface by the
hydrothermal process. In addition, the broad adsorption band of the original wood at around 3334 cm−1 was shifted to lower wavenumber (ca. 3315 cm−1 ) in the spectrum of ZrO2 /wood, indicating the strong interaction between hydroxyl groups of wood surface and ZrO2 nanoparticles [43]. The micrograph (Fig. 2a) obtained by SEM backscattering electron imaging, for the ZrO2 /wood nanohybrids, clearly showed large-scale even-distributed aggregations of the oxide particles, appearing as bright points on the wood surface. These bright points were subsequently proved to be nano-ZrO2 aggregations by EDX because of the strong Zr peaks (Fig. 2c); besides, the Cu peaks were
Fig. 2. SEM images at low magnification (a) and high magnification (b) of ZrO2 /wood.
Fig. 3. Schematic illustrations for fabricating the ZrO2 /wood using the hydrothermal method.
C. Wan et al. / Applied Surface Science 321 (2014) 38–42
41
Fig. 4. TG (a) and DTG (b) curves of ZrO2 /wood and original wood, respectively.
originated from the coating layer used for electric conduction during the SEM observation, and all carbon and partial oxygen were derived from the wood matrix. Fig. 2b showed the SEM image of ZrO2 /wood nanocomposites under higher magnification. Clearly, plentiful irregularly shaped ZrO2 aggregations were layer-by-layer adhered to the wood substrate surface as indicated by the white arrow, and the driving force of layer-by-layer self-assembly behaviors of the aggregations was primarily due to the electrostatic adsorption [44]. Moreover, the increasing thickness of ZrO2 protective layer might be beneficial to resist UV radiation. Based on the above investigation of the experimental parameters for the ZrO2 /wood nanocomposites, a possible formation mechanism could be described as follows (Fig. 3): firstly, the precipitation reaction, which took place as the result of mixing ZrOCl2 ·8H2 O aqueous solution and ammonia, might refer to the Eq. (5) [45]. Then, the obtained Zr(OH)4 nanoparticles were gradually reacted to generate nano-ZrO2 with the help of hydrothermal
energy (Eq. (6)), and then the resulting nano-ZrO2 formed strong interaction with the hydroxyl groups of wood surface leading to formation of plentiful hydrogen bonds, contributing to the deposition and stabilization of ZrO2 nanoparticles on the wood substrate. Subsequently, owing to the electrostatic adsorption force, increasing ZrO2 nanoparticles were attracted and layer-by-layer combined with the previous ZrO2 resulting in multilayer ZrO2 nanoparticles on the wood surface. ZrOCl2 · 8H2 O + NH4 OH → Zr(OH)4 + NH4 Cl + H2 O Zr(OH)4
hydrothermal process
−→
ZrO2
(5) (6)
Fig. 4 represented the TG and DTG curves of the original wood and ZrO2 /wood, respectively. The small initial drops occurring before 150 ◦ C in both cases were due to the evaporation of retained moisture [46]. For the original wood, the DTG curves displayed two main regions: the first region occurred between 192 ◦ C and 315 ◦ C,
Fig. 5. Change tendencies of L*, a*, b* and E* of ZrO2 /wood and original wood, respectively.
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and showed a pronounced shoulder related to the hemicellulose decomposition; the second region (315–391 ◦ C) was attributed to the attainment of the maximum, principally due to cellulose degradation, followed by a rapid decay and a long tail [47]. Furthermore, as the most difficult one to decompose among the three main components of wood, lignin decomposed slowly under the whole temperature ranged from ambient to 700 ◦ C leading to no obvious characteristic peaks [48]. Compared with the original wood, aside from the similar decomposition tendency, the ZrO2 /wood also exhibited more superior thermal stability. In detail, the original wood started to degrade at around 192 ◦ C, whereas the ZrO2 /wood began to decompose at 223 ◦ C, respectively. At 50% weight loss, the decomposition temperature occurred at 339 ◦ C for the native wood and 381 ◦ C for the nanocomposites. Moreover, the original wood reached maximum degradation rate at 357 ◦ C, which was 27 ◦ C earlier than the ZrO2 /wood (ca. 384 ◦ C). These results implied that the thermal stability of ZrO2 /wood was higher than that of original wood. The reason of this enhancement was probably due to the strong interaction between wood substrate and ZrO2 [49,50]. It was consistent with the shift of FTIR adsorption peak of ZrO2 /wood at 3334 cm−1 to lower wavenumber in Fig. 1b. The color stabilities of the two material classes, the original wood and ZrO2 /wood, were examined by means of the change tendencies of L*, a*, b* and E* [51]. It could be observed in Fig. 5 that all color feature parameters changes of original wood from 0 to 600 h were more significant than those of ZrO2 /wood notwithstanding the two materials both showed similar change tendencies of L*, a*, b* and E*, which suggested that the color stability of the ZrO2 /wood composite was more superior under UV light. Furthermore, the higher a* and b* and lower L* of original wood at the end of the 600-h treatment (Fig. 5a–c) represented that the light-colored sample turned deeper shade of red, dark yellow and black, respectively. In addition, the total color change (E*) of original wood was also significant (Fig. 5d), nevertheless the change in the composite E* was much less (approximately 2/3). Thus, the untreated wood with limited UV resistance suffered serious surface damage under UV light; whereas, hydrothermal treated wood exhibited stronger UV protection, which also revealed that the ZrO2 nano-coating was an effective UV protected agent. 4. Conclusions The ZrO2 /wood nanocomposites were successfully prepared by a simple mild one-pot hydrothermal method. The amorphous ZrO2 aggregations, which were layer-by-layer deposited on the surface of wood substrate with the help of hydrothermal energy and electrostatic adherence, generated plentiful hydrogen bonds with the hydroxide radicals of wood surface leading to significant improvement of thermal stability of the ZrO2 /wood nanocomposites. Through the 600-h QUV accelerated aging test, the original wood suffered serious discoloration, whereas the nanocomposites showed superior anti-UV capability. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (grant no. 31270590). References [1] E. Ncube, M. Meincken, Appl. Surf. Sci. 256 (2010) 7504–7509. [2] A. Temiz, U.C. Yildiz, I. Aydin, M. Eikenes, G. Alfredsen, G. C¸olakoglu, Appl. Surf. Sci. 250 (2005) 35–42.
[3] X. Wang, H. Ren, Appl. Surf. Sci. 254 (2008) 7029–7034. [4] R.K.W.M. Klaassen, B.S. van Overeem, J. Cult. Herit. 13 (2012) S129–S134. [5] U. Råberg, N. Terziev, G. Daniel, Int. Biodeterior. Biodegrad. 79 (2013) 20–27. [6] D. Rosu, C.-A. Teaca, R. Bodirlau, L. Rosu, J. Photochem. Photobiol. B 99 (2010) 144–149. [7] L. Tolvaj, Z. Molnar, R. Nemeth, J. Photochem. Photobiol. B 121 (2013) 32–36. [8] T.E. Madey, N.S. Faradzhev, B.V. Yakshinskiy, N.V. Edwards, Appl. Surf. Sci. 253 (2006) 1691–1708. [9] T.-C. Chang, H.-Y. Lin, S.-Y. Wang, S.-T. Chang, Polym. Degrad. Stab. 105 (2014) 42–47. [10] D.J. Pogge, S.M. Lonergan, S.L. Hansen, Meat Sci. 97 (2014) 419–427. [11] P. Nzokou, D.P. Kamdem, A. Temiz, Prog. Org. Coat. 71 (2011) 350–354. [12] A. Khelfa, A. Bensakhria, J.V. Weber, J. Anal. Appl. Pyrolysis 101 (2013) 111–121. [13] L. Liu, J. Sun, C. Cai, S. Wang, H. Pei, J. Zhang, Bioresour. Technol. 100 (2009) 5865–5871. [14] J. Van den Bulcke, J. Van Acker, H. Saveyn, M. Stevens, Prog. Org. Coat. 58 (2007) 1–12. [15] P.-L. Chou, H.-T. Chang, T.-F. Yeh, S.-T. Chang, Bioresour. Technol. 99 (2008) 1073–1079. [16] B. Forsthuber, U. Müller, A. Teischinger, G. Grüll, Polym. Degrad. Stab. 98 (2013) 1329–1338. [17] F. Aloui, A. Ahajji, Y. Irmouli, B. George, B. Charrier, A. Merlin, Appl. Surf. Sci. 253 (2007) 3737–3745. [18] M. Vlad Cristea, B. Riedl, P. Blanchet, Prog. Org. Coat. 69 (2010) 432–441. [19] M. Kiguchi, P.D. Evans, Polym. Degrad. Stab. 61 (1998) 33–45. [20] B. Forsthuber, U. Müller, A. Teischinger, G. Grüll, Polym. Degrad. Stab. 105 (2014) 206–210. [21] T. Kallio, S. Alajoki, V. Pore, M. Ritala, J. Laine, M. Leskelä, P. Stenius, Colloids Surf. A 291 (2006) 162–176. [22] J. Salla, K.K. Pandey, K. Srinivas, Polym. Degrad. Stab. 97 (2012) 592–596. [23] P. Rodiˇc, J. Iskra, I. Miloˇsev, J. Non-Cryst. Solids 396–397 (2014) 25–35. [24] K. Nallis, K.-I. Katsumata, T. Isobe, K. Okada, P. Bone, R. Othman, Appl. Clay Sci. 80–81 (2013) 147–153. [25] X. Pian, B. Fan, H. Chen, B. Zhao, X. Zhang, R. Zhang, Ceram. Int. 40 (2014) 10483–10488. [26] J.R.C. Smirnov, M.E. Calvo, H. Míguez, Adv. Funct. Mater. 23 (2013) 2805–2811. [27] X. Zhou, J. Wu, Google Patents, 2012. [28] X. Shi, C. Cui, C. Di, Y. Zou, M. Xu, Google Patents, 2011. [29] Q. Sun, Y. Lu, H. Zhang, H. Zhao, H. Yu, J. Xu, Y. Fu, D. Yang, Y. Liu, Mater. Chem. Phys. 133 (2012) 253–258. [30] J. Li, H. Yu, Q. Sun, Y. Liu, Y. Cui, Y. Lu, Appl. Surf. Sci. 256 (2010) 5046–5050. [31] S. Shukla, S. Seal, R. Vanfleet, J. Sol–Gel Sci. Technol. 27 (2003) 119–136. [32] M.A. Botzakaki, N. Xanthopoulos, E. Makarona, C. Tsamis, S. Kennou, S. Ladas, S.N. Georga, C.A. Krontiras, Microelectron. Eng. 112 (2013) 208–212. [33] J. Cai, S. Kimura, M. Wada, S. Kuga, Biomacromolecules 10 (2008) 87–94. [34] J. Cai, L. Zhang, Macromol. Biosci. 5 (2005) 539–548. [35] C. Zhao, O. Richard, H. Bender, M. Caymax, S. De Gendt, M. Heyns, E. Young, G. Roebben, O. Van der Biest, S. Haukka, Appl. Phys. Lett. 80 (2002) 2374–2376. [36] U.P.R. Filho, Y. Gushikem, F.Y. Fujiwara, S.C. de Castro, I.C.L. Torriani, L.P. Cavalcanti, Langmuir 10 (1994) 4357–4360. [37] N. Zink, F. Emmerling, T. Hager, M. Panthofer, M.N. Tahir, U. Kolb, W. Tremel, Dalton Trans. 42 (2013) 432–440. [38] W. Lan, C.-F. Liu, F.-X. Yue, R.-C. Sun, J.F. Kennedy, Carbohydr. Polym. 86 (2011) 672–677. [39] A.-M. Olsson, L. Salmén, Carbohydr. Res. 339 (2004) 813–818. [40] R. Rana, R. Langenfeld-Heyser, R. Finkeldey, A. Polle, Wood Sci. Technol. 44 (2010) 225–242. [41] M. Kacurakova, P. Capek, V. Sasinkova, N. Wellner, A. Ebringerova, Carbohydr. Polym. 43 (2000) 195–203. [42] S.B. Khan, K.A. Alamry, H.M. Marwani, A.M. Asiri, M.M. Rahman, Compos. B-Eng. 50 (2013) 253–258. [43] G. Lucovsky, G. Rayner, Appl. Phys. Lett. 77 (2000) 2912–2914. [44] H. Dun, W. Zhang, Y. Wei, S. Xiuqing, Y. Li, L. Chen, Anal. Chem. 76 (2004) 5016–5023. [45] H. Zhou, R. Tian, M. Ye, S. Xu, S. Feng, C. Pan, X. Jiang, X. Li, H. Zou, Electrophoresis 28 (2007) 2201–2215. [46] J. Li, Y. Lu, D. Yang, Q. Sun, Y. Liu, H. Zhao, Biomacromolecules 12 (2011) 1860–1867. [47] F. Shafizadeh, Y. Fu, Carbohydr. Res. 29 (1973) 113–122. [48] H. Yang, R. Yan, H. Chen, D.H. Lee, C. Zheng, Fuel 86 (2007) 1781–1788. [49] R. Valiokas, M. Östblom, S. Svedhem, S.C. Svensson, B. Liedberg, J. Phys. Chem. B 106 (2002) 10401–10409. [50] L. Haurie, A.I. Fernández, J.I. Velasco, J.M. Chimenos, J.-M. Lopez Cuesta, F. Espiell, Polym. Degrad. Stab. 92 (2007) 1082–1087. [51] Q. Sun, Y. Lu, H. Zhang, D. Yang, Y. Wang, J. Xu, J. Tu, Y. Liu, J. Li, J. Mater. Sci. 47 (2012) 4457–4462.