DEVELOPMENT OF A CONTINUOUS METHOD FOR PRODUCTION OF COPPER- SULPHIDE WOOD-POLYMER PLATE NANOCOMPOSITE MATERIALS

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1 Journal of the University M. Dragnevska, of Chemical P. Velev, Technology S. Nenkova, and Metallurgy, R. Garvanska 46, 4, 2011, DEVELOPMENT OF A CONTINUOUS METHOD FOR PRODUCTION OF COPPER- SULPHIDE WOOD-POLYMER PLATE NANOCOMPOSITE MATERIALS M. Dragnevska 1, P. Velev 2 S. Nenkova 2, R. Garvanska 2 1 Lesoplast AD - Troian 2 University of Chemical Technology and Metallurgy 8 Kl. Ohridski, 1756 Sofia, Bulgaria p_velev@uctm.edu Received 05 July 2011 Accepted 10 October 2011 ABSTRACT An original method for wood fiber materials modification by a two-component cupri reduction system in the presence of saturated steam is developed for production of copper sulphide lignocellulose nanocomposites. The cuprosulphide as an additive to polymers lends high electrical conductivity which, as an indirect indicator of the respective dielectric losses, leads to producing new materials with microwave absorption properties. Keywords: wood fiber, nanocomposites, cupro-sulphide. INTRODUCTION Presently metal containing nanomaterials and particularly the polymer nanocomposites are of great interest because of their unique physical and chemical properties, and possibilities for application [1]. Composites of improved characteristics strength, thermal resistance and other specific properties are produced by adding mineral fillers, metals and fibers to polymers. In the recent twenty years a great progress has been achieved in this direction by means of creating nanocomposite materials of better and novel properties with low filler percentage and many possibilities for new applications [2]. There is a large variety of new hybrid and metal polymer nanocomposite materials in which a strong interaction of the nanoparticles and the polymer chains is observed on the level of chemical bonding [3]. The nanocomposites provide a possibility to manufacture products with super conductive properties. The research in this line is very promising and could result in the development of new materials with unique properties [4-6]. The studies devoted to production, characterization and adoption of electro-conductive polymers and fiber materials with microwave absorption properties are of special interest [7]. During the past years there is an intensification of the research related to the methods for copper sulphide electrolytic deposition on polyacrylonitrile in the presence of complexing agents, such as triethanolamine and ethylenediamine tetra acetic acid [8, 9]. The investigations show the actuality, importance and necessity to carry on thorough studies on production of a new type of metal containing nano composite polymer materials with improved electrical conductivity and microwave absorption capability for application in engineering and household like products for electromagnetic wave protection. In this respect, a particular interest present the wood polymer plates as construction materials to be used in the furniture industry, building and packaging. The aim of the present research is the development of a continuous one-stage method for production of copper-sulphide wood-polymer nanocomposite materials is adoptable to the existing equipment and technology for wood fiber plates (WFP) production in LESOPLAST Inc. Troyan, Bulgaria. The researches incudes: - experiments on the development of an appropriate and optimal method for wood fiber material modification to obtain cupro-sulphide lignocellulose nanocomposites; 349

2 Journal of the University of Chemical Technology and Metallurgy, 46, 4, experiments on defining the technological stage and adequate equipment to obtain copper-sulphide wood fiber nanocomposite plate materials; - optimization of the developed method in respect of compositions, proportion of the individual components and parameters for the achievement of improved electrical conductivity (corresponding electromagnetic wave absorption) while retaining the level of the initial standardized WFP characteristics. EXPERIMENTAL The theoretical basis for the development of methods for production of cupro-sulphide wood nanocomposites is grounded on the fact that cupro-sulphide as an additive to polymers lends high electrical conductivity which, as an indirect indicator of respective dielectric losses, leads to producing new materials with microwave absorption properties. A considerable increase of the effect is achieved when the cupro-sulphide is in the nanostate and coordinately deposited as a network in the polymer lignocellulose matrix. In this sense, the development of the methods is based on performing chemical modification of the lignocellulose material by water solutions of a copper containing compound and a sulphur containing reducer in appropriate quantities and proportions at definite process parameters, temperature and duration. Under such conditions a possibility is provided for realization of the process of reducing the cupri ions to cupro ones and their subsequent coordinative deposition in the lignocellulose matrix. In the present work we use wood fibers and technological wood carpet from the current production of LESOPLAST Inc. Troyan. 1. Development of an adequate method for wood fiber material modification to obtain copper sulphide lignocellulose nanocomposites. Basic variants to carry out the process of the lignocellulose material chemical modification By means of preliminary experiments, varying the type and composition of the individual components, it has been found that two variants are suitable for experimentation: - with a three-component system (copper sulphate (CuSO 4. O); sodium thiosulfate (Na 2. O) and glyoxal (CHO) 2. - with a two-component system (copper sulphate (CuSO 4 O); sodium thiosulfate (Na 2 O). The elaboration of the method was made on the basis of the data for the modified specimen s electrical conductivity by measuring the electrical resistivity. The measurements were made in an electrode cell for powder materials under constant pressure and quantity of the examined material with the apparatus Teraom II meter (IEC Ed. 2.0 b:1980). Optimization of the methods was performed by determination of: - Waste water quantity; - Copper and sulphur contents in the waste water and - Copper and sulphur contents in the modified lignocellulose specimens. The wood fiber material modification by the threecomponent reduction system was carried out under the following preset conditions: proportion of the components CuSO 4 O:Na 2 O : (CHO) 2 = 1,6:1,4:1 in quantity 40 % in respect the lignocellulose material at module 1:12, temperature 90 o C for 30 minutes. Table 1 presents the results of the measurements. The obtained data determined the direction of our subsequent studies connected with development and optimization of the modification method with the twocomponent reduction system. The wood fiber material modification by the twocomponent reduction system was initially performed in a heat chamber with saturated steam at 110 o P for 30 minutes and proportion of the components CuSO 4. O : Na 2. O = 1:1 and 1:2 in quantity 20 % and 40 % in respect to the lignocellulose material at a constant hydromodule Ì = 1:12. The obtained results were satisfactory in respect of the electrical resistivity decrease by about 2 orders but with significant copper and sulphur contents in the waste water. Therefore, the modification process was additionally optimized at a lower hydromodule Ì = 1:6, proportion of CuSO 4 O:Na 2 O = 1:2 and variation of the components contents, in relation to the wood fiber material, in the range from 20 % to 40 %. The low modification module results in a very low waste water quantity, without disturbance of the modification process normal course. The data in Table 1 show that the electrical resistivity values decrease by approximately about two orders of magnitude for the 350

3 M. Dragnevska, P. Velev, S. Nenkova, R. Garvanska specimens modified with 20 %, 30 % and 40 %, which considerably improves the electrical conductivity of the treated wood material. At 40 % of the two-component system to the wood material an optimal proportion between the modifying components is achieved (copper:sulphur) in comparison with the specimens produced at 20 % and 30 %. 2. Experiments to define the technological stage and the adequate equipment for cooper-sulphide woodfiber nanocomposite plate materials production. Lesoplast Inc. manufactures solid wood fiber plates with equipment of the Swedish company Defibrator. The WFP production comprises the following operations: 1. A treatment in steaming chamber by saturated water vapor of pressure atmospheres and temperature o C. 2. Defibering. 3. Gluing. Paraffin emulsion of concentration % is used as an water-repelling agent, and for improvement of the plate strength properties phenolformaldehyde resin of concentration % is used. With the purpose to decrease the loss of bonding agent and fibers during pouring the wood fiber mass and its passing through the circulating water, a flocculating agent a cationic polyacrylamide was included in the scheme. 4. Dilution and dewatering. The wood fiber mass is further diluted by circulating water at concentration 1,3 1,8 %. The dewatering comprises: draining, vacuuming and pressing. After the draining the wood carpet is cut laterally and transversally by means of water jet nozzles into dimensions 5600 x 1740 mm and transported to the hot press. 5. Pressing at 185 o C. 6. Sample preparation. With the purpose to specify an appropriate technological stage, preliminary experiments were carried out by the equipment for WFP production in conditions which imitate the technological stages (gluing, dewatering and pressing). Three specimens that were characterized for electrical conductivity volume electrical resistivity by apparatus Teraom II meter (IEC Ed. 2.0 b:1980) and apparatus Agilent E 4991 ARF, Ip.edance/ Material Analyzer Germany, as well as the characteristics - thickness, bending strength and swelling in water (according to the accepted standards) were obtained. 3. Optimization of the developed method in respect of composition, proportion of the individual components and parameters for achievement of improved electrical conductivity (corresponding electromagnetic wave absorption) while retaining the level of the initial standard WFP characteristics. The laboratory tests in this section were carried out with the wood fiber carpet from the pouring machine after the nozzles for surface laying of the paraffin emulsion in quantity of 500 grams for each specimen and sizes 20x40 cm at 27 % dry content. Adequate quantities of the modifying solutions were laid on the carpet surface. The pressing was carried out at constant temperature of the press 170 o C, duration of pressing 5, 10 and 15 minutes. The specimens produced were characterized in respect of electrical conductivity (volume electrical resistivity by apparatus Teraom II meter (IEC Ed. 2.0 b:1980) and by apparatus Agilent E4991ARF, Ipedance/Material Analyzer Germany, as well as characteristics: thickness, bending strength and swelling in water (in accordance with the accepted standards). RESULTS AND DISCUSSION From the data in Table 1 the following observations and conclusions can be made: The reduction process during the wood fiber material modification by a three-component system is strongly expressed. This results in almost zero sulphur content in the modified material; There is a low content of copper and sulphur after the wood fiber modification in the waste waters. The electrical resistivity decreases by approximately half order of magnitude. In this way, the data obtained from the use of the three-component reduction system unambiguously show that if wood fibers characterized by a specific structure are used there can be produced cupro-sulphide containing lignocelluloses by only a sulphur containing reducer and thus avoid the use of additional reducing agent (glyoxal, for instance) that would be a great advantage from ecological point of view. 351

4 Journal of the University of Chemical Technology and Metallurgy, 46, 4, 2011 Table 1. Copper containing lignocelluloses produced during wood fiber material modification by three- and two-component systems. No Conditions of modification Non - modified wood fibers (WF) Modified with three component system WF F modified at module 1:6, 1:2, ratio 20 % bicomponent system WF modified at module 1:6, 1:2, ratio30 % bicomponent system WF modified at module 1:6, 1:2, ratio 40 % bicomponent system Copper in sample, % Sulfur in sample, % Copper in filtrate, mg l -1 Sulfur in filtrate, mg l -1 0, Specific electric volume resistance, Ω m 8, ,7860 >0,05 362, , , ,06 21, ,9451 3,82 35,5 67 1, ,7833 2,88 20,7 80 1, Table 2. Preliminary experiments for wood fiber plates production conditions and characteristics. No Conditions 1 4 %WFM; bonding stage; ratio 1:2; 40 % 2 4 % bonding stage; ratio 1:2; 40 % 3 12% WFM; dewatering stage; ratio 1:2; 40 %; pressing C, 10 min Physico-mechanical properties Flexural strength, MPa Thickness, mm Swelling, % 3,3 33,45 26,7 4, ,2 51,11 27,6 8, ,1 60,78 32,6 7, Specific volume electrical resistance, Ω m Table 2 presents a generalized description of the experimental conditions and the characterization results. For specimens 1 and 2 the modifying solutions were added at 4 % wood fiber mass (WFM) in the pools at the technological stage gluing while for specimen 3 to wood carpet with 12 % WFM before the stages dewatering and pressing. The data in Table 2 show that the suitable technological stage for carrying out the modification process is the one before the wood carpet pressing which is also preferable from ecological point of view because of the minimum quantity of chemicals which have to be regenerated. x - 6, Ω m is the volume electrical resistivity of unmodified wood fiber plates (WFP). 352

5 M. Dragnevska, P. Velev, S. Nenkova, R. Garvanska Fig. 1. Dependence of the electrical resistance (in Ω m) on the frequency (in MHz). Fig. 2. Dependence of the electrical resistance (in Ω m) on the frequency (in MHz). Physical and physical-mechanical characteristics Significant differences between the individual test specimens and the zero specimen in respect of the thickness characteristic in mm have not beenobserved. The values of the specimen swelling indicator (%) is close to that of the zero specimen except for the specimens pressed for shorter time (5 minutes). The following dependences are observed in the bending strength characteristic: 1. With increase of the modifying system percentage from 15 % to 45 % the bending strength decreases in comparison with that of the zero specimen. 2. When modifying the system of 30 % the highest bending strength is achieved for the 10 minutes pressing and for the one of 45 % - for 5 minutes. 3. In the cases of pressing for 5 and 15 minutes the specimens modified by greater quantity of the cuprisulphide system show a greater bending strength. 353

6 Journal of the University of Chemical Technology and Metallurgy, 46, 4, 2011 Table 3. Wood fiber plates production during dewatering and pressing stages conditions and characteristics. No Conditions Physico-mechanical properties Flexural strength, MPa Thickness, mm Swelling, % 0 Zero sample 2,7 36,31 21,9 6, % reagents to WFM; ratio1:2; 2,6 34,18 22,7 4, î Ñ, 10 min 2 30 % reagents to WFM; ratio 1:2; 2,6 31,68 22,7 2, î Ñ, 10 min 3 45 % reagents to WFM; ratio1:2; 170 î Ñ, 10 min 1 / 30 % reagents to WFM; ratio 1:2; 170 î Ñ, 5 min 2 / 45 % reagents to WFM; ratio 1:2; 170 î Ñ, 5 min 3 / 30 % reagents to WFM; ratio 1:2; 170 î Ñ, 15 min 4 / 45 % reagents to WFM; ratio 1:2; 170 î Ñ, 15 min 2,6 25,25 20,9 2, ,8 24,51 34,0 6, ,6 27,46 34,0 3, ,6 19,57 23,4 8, ,5 23,57 23,4 5, Specific volume electrical resistance, Ω m Fig. 3. Dependence of the electrical resistance (in Ω m) on the frequency in MHz. Electrical conductivity The modified specimens electrical conductivity determined by measuring the volume electrical resistivity (Table 3), does not differ significantly and behav- ior depending on the production conditions is not observed. Interesting dependences are observed for the specimens electrical resistance at different frequencies 354

7 M. Dragnevska, P. Velev, S. Nenkova, R. Garvanska Table 4. Electrical-physical characteristics of the copper-sulphide wood fiber materials. ELECTRO-PHYSICAL VALUES Sample R( Ω ) Z(k Ω ) ì' (U) ì" (ku) å' (U) å" (ku) 0 116, , , , , , , , , , , , ' 105, , , ,1668 2,7902 0, p 100, , , , , , , , , , ,9421 0, ' 93, , , , , , p 98, , , , ,085 0, , , , , , , ' 90, ,1424 4, ,2725 2,8809 0, p 105, , , , ,1117 0, ' 86, , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,1263 of the modification parameters when using the device Agilent E4991ARF, Ipedance/Material Analyzer Germany (Figs 1, 2 and 3) as follows: The electrical conductivity increases, i. e. an electrical resistance decrease is achieved only when using 45 % of the modifying system (Fig. 1). At 30 % quantity of the modifying system the lowest electrical resistance is obtained for 15 minutes pressing (Fig. 2), and at 45 % - for 10 minutes (Fig. 3). Electromagnetic absorption The dielectric and magnetic losses and the electromagnetic waves attenuation, respectively are calculated from the electrical-physical characteristics (Table 4). It is obvious from the data that the highest electromagnetic wave protection can be achieved by the wood fiber composite (specimen 2) produced with 30 % modifying cupri sulphide system and pressing at Ñ for 10 minutes and for specimen 4 with 45 % modifying cupri sulphide system and pressing at C for 15 minutes. CONCLUSIONS An original method for wood fiber materials modification by a two-component cupri reduction system in conditions of saturated steam is developed for production of copper sulphide lignocellulose nanocomposites. The optimum process parameters are defined: % of the two-component system towards the wood material; module 1:6 and proportion of copper sulfate: sodium thiosulfate = 1:2. There is determined the technological stage and adequate equipment for copper-sulphide wood fiber nanocomposite plate material production. The method developed is optimized in respect of compositions, proportion of the individual components and parameters for achievement of improved electrical conductivity (respective electromagnetic wave absorption), while retaining the level of the WFP initial standardized characteristics. The authors acknowledge a favor to Fund Researches, Ministry of Education, Science and Youth, for the financial support rendered in carrying out the present investigations. REFERENCES 1. L.Wang, P. Brazis, M. Rocci, C. Kannewurf Kanatzidis, M., α -RuCl 3 : A new host for polymer intercalation. Lamellar polymer/rucl 3 nanocomposites, Mat. Res. Soc. Sympl. Proc. 519, 1998,

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