1 INSTYTUT TECHNOLOGII DREWNA WOOD TECHNOLOGY INSTITUTE DREWNO PRACE NAUKOWE DONIESIENIA KOMUNIKATY WOOD RESEARCH PAPERS RESEARCH REPORTS ANNOUNCEMENTS Vol. 56 POZNAŃ 2013 Nr 190
2 Wydanie publikacji dofinansowane przez Ministerstwo Nauki i Szkolnictwa Wyższego w ramach programu Index Plus. The journal is financially supported by Polish Ministry of Science and Higher Educations under the Index Plus programme. Recenzenci vol. 56 (Reviewers): Elijah Ajuong, PhD; Prof. Dr. Drs. h.c. rer. silv. habil. Albrecht Bemmann; Myrsini Christou, PhD; Grzegorz Cofta, PhD (Eng); Prof. Claudia Crestini, PhD; Dorota Dziurka, PhD; Benjamin Engler, PhD; Marek Gawor, PhD (Eng); Mark Irle, PhD; Doc. dr. sc. Jaroslav Kljak; Prof. Mgr Juraj Ladomersky, CSc; Elżbieta Mikołajczak, PhD (Eng); Martin Ohlmeyer, PhD; Bartosz Pałubicki, PhD (Eng); Prof. Ing. Ladislav Reinprecht, CSc; Jarosław Szaban, PhD (Eng); Assc. Prof. Maja Szymura-Tyc, PhD; Prof. Ing. Jozef Zajac, CSc Publikacje indeksowane są w bazach danych (Publications are indexed in the databases): Agro Science Citation Index Expanded BazTech SCOPUS DREWINF The Central European Journal of Social Sciences and Humanities Ebsco Impact Factor (2012): 0,200 Punkty MNiSW (2013): 15 Wersja pierwotna papierowa The original version paper Wydawca (Publisher): Instytut Technologii Drewna ul. Winiarska 1, Poznań, Polska (Poland) Adres Redakcji (Editor s address): Instytut Technologii Drewna ul. Winiarska 1, Poznań tel.: , , fax: , Copyright by Instytut Technologii Drewna w Poznaniu Poznań 2013 ISSN Projekt okładki (Cover design): Piotr Gołębniak Skład komputerowy (Computer typesetting) oraz druk (Print): Studio Poligrafia, ul. Bułgarska 10, Poznań, tel.: Nakład (Edition): 520 egz.
3 SPIS TREŚCI CONTENTS Prace naukowe Research papers Xue-Fei Zhou: Co(salen)-catalysed oxidation of synthetic lignin-like polymer: O 2 effects (Katalizowane Co(salen) utlenianie syntetycznego lignino-podobnego polimeru: efekt O 2 )... Dorota Dziurka, Radosław Mirski: Lightweight boards from wood and rape straw particles (Lekkie płyty z wiórów drzewnych i słomy rzepakowej)... Agata Stachowiak-Wencek, Włodzimierz Prądzyński: Concentration of volatile organic compounds in the production halls of a selected furniture manufacturing plant (Stężenie lotnych związków organicznych na terenie hal produkcyjnych w wybranym zakładzie przemysłu meblarskiego)... Emília Hroncová, Juraj Ladomerský, Christoph Adam: The use of wood from degraded land for carbon sequestration (Wykorzystanie drewna z terenów zdegradowanych do sekwestracji węgla)... Mariusz Bembenek, Dieter F. Giefing, Zbigniew Karaszewski, Agnieszka Łacka, Piotr S. Mederski: Strip road impact on selected wood defects of norway spruce (Picea Abies (L.) H. Karst) (Wpływ szlaków operacyjnych na wybrane wady drewna świerka pospolitego (Picea Abies (L.) H. Krast))... Agnieszka Jankowska, Paweł Kozakiewicz: The identification of charcoal from archaeological finds in Risan (Montenegro) (Identyfikacja węgli drzewnych ze stanowiska archeologicznego w Risan w Czarnogórze)... Aleksandra Szostak, Gabriela Bidzińska, Ewa Ratajczak, Magdalena Herbeć: Wood biomass from plantations of fast-growing trees as an alternative source of wood raw material in Poland (Biomasa drzewna z upraw drzew szybkorosnących jako alternatywne źródło surowca drzewnego w Polsce)... Milena Ratajczak-Mrozek, Magdalena Herbeć: Actors-resources-activities analysis as a basis for Polish furniture network research (Specyfika polskiego przemysłu meblarskiego w ujęciu sieciowym. Perspektywa modelu ARA (aktorzy-zasoby-działania))
4 Doniesienia naukowe Research reports Jacek Wilkowski, Piotr Borysiuk, Jarosław Górski, Paweł Czarniak: Analysis of relative machinability indexes of wood particle boards bonded with waste thermoplastics (Analiza względnych wskaźników skrawalności płyt wiórowych spajanych termoplastami poużytkowymi)... Michał Aniszewski, Piotr Witomski: The state of preservation of archaeological wood uncovered in the Grotto foundations of the retaining wall of the Palace Museum in Wilanów (Stan zachowania drewna archeologicznego odkrytego przy fundamentach Groty muru oporowego Pałacu w Wilanowie)
5 Drewno 2013, vol. 56, nr 190 DOI: /wood PRACE NAUKOWE RESEARCH PAPERS Xue-Fei Zhou 1 Co(SALEN)-CATALYSED OXIDATION OF SYNTHETIC LIGNIN-LIKE POLYMER: O 2 EFFECTS Molecular oxygen (O 2 ) is widely used as an oxidant in catalytic oxidation. This study was part of a biomimetic oxidation targeted at increasing the use of lignin in the production of chemicals through the application of salen transition metal catalysts. In this work, the catalytic performance of a cobalt-schiff base catalyst Co(salen) in the presence of an oxidant and a ligand, such as pyridine, was analysed using two polymeric lignin model compounds. Oxidation experiments were carried out in alkaline water (ph 11-12) with the use of H 2 O 2 and atmospheric oxygen (1atm) as oxidants. Co(salen) was an active catalyst, increasing the oxidation rate of the S- and G- type phenolic model polymers. In studies with FTIR, C-13 NMR, and GC-MS spectroscopy, the Co(salen)- -catalysed oxidation rate was found to be high in the presence of O 2. O 2 had effects on the activity of the Co(salen), and it was concluded that the rate of the decomposition of the polymer was increased with the addition of O 2. The structure of the lignin model polymers also had an effect on their decomposition. In the form of two CH 3 O-group polymers (S-type lignin model polymer), the depolymerisation decreased. Irrespective of the polymer (both S- and G- type lignin model polymers), the depolymerisation generated benzaldehydes as the main observed products. The model polymer studies were confirmed to be a useful way to obtain information about the reactions occurring during catalytic oxidation. Keywords: Co(salen), catalyst, catalytic oxidation, lignin model polymer, O 2 effect, FTIR, C-13 NMR, GC-MS Xue-Fei Zhou, Kunming University of Science and Technology, Kunming, China; Fudan University, Shanghai, China; Nanjing Forestry University, Nanjing, China; Huaiyin Normal University, Huaian, China; Tianjin University of Science and Technology, Tianjin, China
6 6 Xue-Fei Zhou Introduction Co(salen) is a coordination complex derived from the salen ligand and cobalt. The complex reversibly binds O 2 to give the oxygenated product, a 1:1 (Co:O 2 ) or a 2:1 (2Co:O 2 ) complex. O 2 accepts one electron from each Co 2+, forming a superoxide, O 2-, bound to Co 3+, in the 1:1 complex; O 2 accepts one electron from both Co 2+, forming a peroxide, O 2-2, bound to two Co 3+, in the 2:1 complex (fig. 1). This complex is very much like porphyrin but is relatively easy to prepare, cheap, stable in water and small in size, and a number of its derivatives have been widely used as catalysts in a wide variety of useful catalytic reactions. Besides being environmentally more benign, the catalytic oxidation of organic compounds with oxidants, such as dioxygen and hydrogen peroxide, is less economically wasteful than traditional methods and is now an important reaction in both research laboratories and industry [Cozzi 2004; Manickam, Kulandaivelu 2012; Sandaroos et al. 2012]. Fig. 1. Two possible structures for the O 2 adduct of Co(salen) Rys. 1. Dwie możliwe struktury adduktu Co(salen) z O 2 Salen-catalysed oxidations of organic compounds have been widely studied. These complexes can catalyze the oxidation of substrates that serve as models for lignin phenolic subunits. In the studies of Meguro et al. [1984a; 1984b; 1989], Co(salen) was the most active Co-complex in the oxidation of the phenolic lignin model compound guaiacol. In the O 2 -oxidation of veratryl alcohol in an alkaline solution, Kervinen et al.  compared several cobalt catalysts, namely Co(salen), Co(α-CH 3 salen), Co(4-OHsalen), Co(sulfosalen), Co(acacen) and Co(N-Me-salpr). The unsubstituted Co(salen) was the most active and the oxidation was selective at the benzylic position as veratryl aldehyde was the sole product. Reactivity increased linearly with increased O 2 pressure. In one study [Sippola 2006], the decomposition of Co(sulfosalen) catalyst was higher in the absence of oxygen. In particular it was demonstrated that they were able to oxidize high
7 Co(salen)-catalysed oxidation of synthetic lignin-like polymer: O 2 effects 7 yields of lignin model compounds. Arylglycerol-β-aryl ethers, phenylcoumarans and apocynol showed very high conversion values within 30 min [Haikarainen 2005; Rajagopalan et al. 2008; Badamali et al. 2011]. A series of biomimetic oxidations of lignin and a lignin model compound using Co(salen) were successfully studied in our laboratory [Zhou et al. 2011; Zhang, Zhou 2012; Zhou, Liu 2012]. From this and related studies, it was found that salen-type complexes of cobalt had an ability to selectively catalyse oxidation reactions in all experiments and a high catalytic activity was reached with the complex. Co(salen)-catalysed oxidations appeared to allow the creation of high-value products to extend the role of lignin for future biomass and biofuel applications [Crestini et al. 2010; Aresta et al. 2012]. On the basis of these studies, in this paper a synthetic lignin polymer was chosen as the model substrate for further studies on the reactions of lignin and the effect of O 2 (O 2 effect) because synthetic lignin polymer is more able to resemble natural lignins in their structures, even though it does not have a γ-hydroxymethyl group. Model polymer studies in lignin are important as they can clarify the mechanism occurring during catalytic reaction [Kishimoto et al. 2005; Katahira et al. 2006; Megiatto et al. 2009]. Materials and methods Reagents Co(salen), and 4-hydroxy-3-methoxy-acetophenone, 4-hydroxy-3,5-dimethoxyaceto phenone were obtained from Sigma-Aldrich. 1,4-dioxane, diethyl ether, bromine, K 2 CO 3, DMF, NaBH 4, DMSO, NaOH, H 2 O 2, pyridine, O 2, CH 2 Cl 2, HCl, and Na 2 SO 4 were purchased from Sinopharm Chemical Reagent Co. Shanghai, China. The chemicals were used as received, without further purification. Synthesis of lignin model polymer Referring to the methods of Kishimoto et al. (2005), the lignin model polymer composed of only the β-o-4 structure was prepared using simple aromatic compounds as starting materials (fig. 2). The commercially available 4-hydroxy-3-methoxy-acetophenone, 4-hydroxy-3, 5-dimethoxyacetophenone was dissolved in anhydrous 1,4-dioxane-diethyl ether (3:4, v/v), adding bromine to the mixture, then kept at 0ºC for 1 hour to prepare the bromide. Adding K 2 CO 3 as the catalyst, the bromide was dissolved in anhydrous DMF, stirred under nitrogen at 50ºC for 3 hours, and polymerized to obtain the given polymer. The given polymer was reduced with NaBH 4 in DMSO to obtain the G- and S-type lignin model polymers composed of the β-o-4 structure. The molecular weight (Mw) was determined by gel permeation chromatography (GPC). The Mw of the guaiacyl type polymer (G-type polymer) was 5753, where the value for the syringyl type (S-type poly-
8 8 Xue-Fei Zhou mer) was The Mw of the polymers was comparable to that of technical lignin. The chemical structure of the lignin model polymers was characterized by FTIR and 13 C-NMR. Fig. 2. Synthesis of S- and G-type lignin model polymers Rys. 2. Synteza modelowych polimerów ligniny typu S- i G- Catalytic experiments treatment in H 2 O 2 pyridine NaOH Co(salen) + with O 2 filtration residue ( S with O 2 Gwith O ) 2 FTIR, 13 C -NMR G, S filtrate ( S with O, G ) 2 with O 2 GC-MS treatment in H 2 O 2 + pyridine + NaOH Co(salen) + + without O 2 filtration residue ( Swithout O 2, G without O ) 2 FTIR, 13 C -NMR, Fig. 3. Programmable route of experiment Rys. 3. Programowalna ścieżka doświadczenia filtrate ( S without O2, G without O ) 2 GC-MS The reactions and reaction conditions of biological systems were mimicked by carrying out oxidation experiments in aqueous solutions. In these experiments, in which the effect of O 2 was evaluated in the oxidation of the S- and G-type lignin model polymers in the presence/absence of O 2, the standard procedure was to dissolve the lignin model polymers (30 mg), hydrogen peroxide (0.6 ml, 30%) and pyridine (0.96 ml, 0.5 g L -1 ) in water (10 ml) and adjust the ph with 0.9 mg NaOH (ph ~12). Following this, the Co(salen) (4.0 ml, 0.5 g L -1 ) was added, the reaction flask was evacuated and the ambient oxygen pressure ( 99.5%) was bubbled constantly through the solution at a rate (2.5 cm 3 /min) low enough to avoid evaporation of the solvent. The mixture was then stirred at 90ºC for 1 hour. The reaction was stopped by cooling the solution to the ambient temperature, after which the reaction mixture was filtered using a fritted glass filter. The final residue (S with O2, G with O2 ) was collected for FTIR and 13 C-NMR analysis. The ph of the filtrate was adjusted to 12 with 2M NaOH and the soluble organic products were extracted with methylene dichloride. The organic phase was separated. The residual filtrate was adjusted to ph 2 with 2M HCl and the soluble organic products were
9 Co(salen)-catalysed oxidation of synthetic lignin-like polymer: O 2 effects 9 similarily extracted. The two organic phases were merged and dried with sodium sulphate, filtered and finally concentrated to 1mL for reaction product analysis with GC-MS (S with O2, G with O2 ) (fig. 3). FTIR The FTIR spectra of the lignin model polymers (S, G) and residual lignin model polymers (S with O2, G with O2 ) obtained from the catalytic experiments were made on a Bruker Tensor 27 spectrophotometer between KBr plates with a 0.1 mm thick layer in wavelength bands from 4000 to 400 cm -1. C-13 NMR spectrometry All 13 C-NMR spectra were recorded under quantitative conditions, which were accomplished by using a pulse sequence (inverse-gated) that eliminated the Nuclear Overhauser Effect (NOE) and had a sufficiently long pulse delay, allowing for all nuclei to be fully relaxed before the next pulse. The pulse delay, commonly used for lignin, was 10 seconds. The samples were dissolved in d 6 -DMSO and the spectra were recorded on Bruker DRX 500 apparatus at 318 K with TMS as the internal reference (δ 0.00) in a 5-mm diameter tube. Some of the acquisition parameters used during the recording of the spectra included 9 15 k number of acquisitions, 90 pulse width (pl = 8 usec, pl 1 = 1.00 db), 222 ppm sweep width, and a 10-second pulse delay. The total acquisition time for recording each spectrum was typically quite long, ranging from 24 to 36 hours. During the processing, a line broadening of 10.0 Hz was used to obtain acceptable line widths. GC-MS The separation and identification of the oxidation products were performed using gas chromatography-mass spectrometry (GC-MS) with an Agilent Technologies HP 6890/5973 system fitted with a fused silica column (HP-INNOWAX, 30 m 0.25 mm i.d., 0.25 μm film thickness). Each sample was injected into a deactivated glass liner inserted into the GC injection port, using He as the carrier gas (~1.0 ml min -1 ). The GC oven was programmed from 80ºC (with a 5 min initial delay) to 290ºC (held 40 min) using a 4ºC min -1 temperature ramp. The GC injector and GC-MS interface were maintained at 290ºC. The mass spectrometer was operated in electron ionization mode (EI, 50 ev). Compound identification was performed using GC retention times and by Mainlib database.
10 10 Xue-Fei Zhou Results and discussion Two types of lignin model polymers were synthesised: a G-type with one electron-donating CH 3 O-group and S-type with two electron-donating CH 3 O-groups. The reactions and reaction conditions of biological systems were mimicked by carrying out the oxidation experiments in aqueous solutions. The capability of the Co(salen) complex was tested in the catalytic oxidations of the lignin model polymers, G- and S-type lignin model polymers. In addition, a study was made of the O 2 effect of the catalyst at the rate of the oxidation of the lignin model polymers. Polymeric β-o-4 lignin model compounds G- and S-type were the first model compounds to be tested. The oxidation of lignin model polymers lead to the formation of degradation products by the superoxocobalt complex initially formed [Nishinaga, Tomita 1980; Lyons, Stack 2013]. The species formed under these conditions have been spectrally observed in the lignin oxidations [Zhang, Zhou 2012]. The oxidation products consisted of mixtures of benzaldehyde, phenol, and quinone compounds (fig. 6: 7.2 min, 13.9 min, min; fig. 7: I, II, III). The main oxidation products were benzaldehydes with good selectivities. Identification was based on the NMR and mass spectra, as well as comparison with authentic samples [Schmidt 2010]. Compounds were formed by a rapid oxidation of α-c alcohol of the polymers. Some minor structural components (compounds II and III) in the oxidation mixtures were formed by other oxidative cleavage, but the amount was usually very low [Zhou et al. 2011]. The results obtained in the oxidations of the lignin model polymers with the use of the Co(salen) complex as a catalyst depended on the oxidant O 2 and the structure of the polymer, such as the CH 3 O-group. The different results obtained in the reactions were compared in the spectra from fig. 4 to fig. 6. The effect of O 2 was tested by conducting the oxidations in the presence/absence of O 2. According to the results, the catalytic oxidations with the Co(salen) catalyst benefitted from the addition of O 2 ; adding O 2 to the reaction mixture in most cases markedly increased the reaction rate. This was because, by adding O 2, more of the superoxo complex was formed to more easily oxidise the lignin model polymers. In addition, the degree of degradation in the experiments varied with the CH 3 O-group of lignin model polymers in the Co(salen)-catalysed oxidations. The G-lignin model polymer gave products with a high degree of degradation, whereas this was low with the S-lignin model polymer, suggesting that the CH 3 O-group of the polymer has a significant effect on the oxidations. This is probably because the polymer was more stable towards destruction when the second electron-donating CH 3 O-group was introduced into the ring [Lebo Jr. et al. 2001]. Kervinen et al.  investigated oxidations of 3,4-dimethoxybenzyl alcohol to 3,4-dimethoxybenzaldehyde in aqueous alkaline media using Co(salen) and its derivatives as catalysts, and dioxygen as the terminal oxidant, when the catalyst substrate ratio dropped to 1:5950, a TON (turnover number) as huge as 330 was obtained at ambient dioxygen pressure, the
11 Co(salen)-catalysed oxidation of synthetic lignin-like polymer: O 2 effects 11 mechanism involved the initial formation of a superoxo complex, which performed a two-electron oxidation of the substrate [Kervinen et al. 2003; Kervinen et al. 2005]. Sippola  found that the best conversion of the substrate to the corresponding aldehyde was 15.1% at atmospheric pressure of dioxygen in the oxidation of 3,4-dimethoxybenzyl alcohol using Co(sulfosalen) as the catalyst. Das and Punniyamurthy , Velusamy and Punniyamurthy  used cobalt and copper complexes of tetrahydrosalen ligand to oxidize benzylic alcohols with H 2 O 2, as dioxygen was found to be an ineffective oxidant with these tetrahydrosalen catalysts. Fig. 4. FTIR spectra of lignin model polymers Rys. 4. Widma FTIR modelowych polimerów ligniny
12 12 Xue-Fei Zhou For the above oxidations of phenolic lignin model polymers, a reaction mechanism is postulated (fig. 8) [Becker 1980]. First, the catalytically active species removes a hydride ion from the benzylic position. The resulting cation loses a proton, and after tautomerization the oxidised product is obtained. Since the main observed products were aldehydes, the reaction appears to be a two-electron oxidation. Fig. 5. C-13 NMR spectra of lignin model polymers Rys. 5. Widma C-13 NMR modelowych polimerów ligniny
13 Co(salen)-catalysed oxidation of synthetic lignin-like polymer: O 2 effects 13 G with O2 S with O2 G without O2 S without O2 G with O2 S with O2 G without O2 S without O2 Fig. 6. Total ion chromatograms of S and G samples for GC-MS detection Rys. 6. Chromatogramy całkowitej zawartości jonów próbek S i G przy zastosowaniu detekcji GC-MS Fig. 7. Formation of products I-III by the oxidative cleavage of lignin model polymers Rys. 7. Tworzenie się produktów I-III podczas oksydacyjnego rozkładu modelowych polimerów ligniny
14 14 Xue-Fei Zhou Fig. 8. Postulated mechanism for the oxidation of lignin model polymers Rys 8. Postulowany mechanizm oksydacji modelowych polimerów ligniny Conclusions A system of Rusing Co(salen) oxidant for oxidation was investigated. The presented system allowed the oxidation of lignin model polymers, analysing their viability and promoting the production of chemicals. Synthetic lignin-like polymers were synthesized from simple aromatic compounds which offered an additional advantage of enabling the lignin model compounds to resemble natural lignins in their structures. The Co(salen) as the catalyst was capable of catalysing the oxidative degradation of the lignin model polymers. The oxidation of the benzylic positions of both the G- and S-lignin model polymers catalysed by the Co(salen) was studied, and the corresponding aldehydes were identified as the main products with fair yields, especially in the presence of O 2. The effects of O 2 were to make the reaction smooth and increase the catalytic ability of the Co(salen) within the oxidation. There were some influences of the CH 3 O-group of the lignin model polymers on the reactions: the presence of the electron-donating CH 3 O- -group in the lignin model polymers was found to decrease the reaction rate. High yields were obtained with the G-type substrate, whereas low yields were obtained with the S-type substrate. The Co(salen) complexes therefore appear to be promising oxidation catalysts for selective transformations of monomeric, dimeric and polymeric lignin model compounds with H 2 O 2 or O 2 as terminal oxidants. To confirm the use of a Co(salen) oxidant system for lignin transformations, further studies on lignin model compounds followed by lignins are needed.
15 Co(salen)-catalysed oxidation of synthetic lignin-like polymer: O 2 effects 15 References Aresta M., Dibenedetto A., Dumeignil F. : Biorefinery: From Biomass To Chemicals and Fuels. Water de Gruyter Gmbh & Co. KG, Berlin/Boston Badamali S.K., Luque R., Clark J.H., Breeden S.W. : Co(salen)/SBA-15 catalysed oxidation of a β-o-4 phenolic dimer under microwave irradiation. Catalysis Communications 12 : Becker H.D., Bjork A., Adler E. : Quinone dehydrogenation: oxidation of benzylic alcohols with 2,3-dichloro-5,6-dicyanobenzoquinone. Journal of Organic Chemistry 45 : Cozzi P.G. : Metal Salen Schiff base complexes in catalysis: practical aspects. Chemical Society Reviews 33 : Crestini C., Crucianelli M., Orlandi M., Saladino R. : Oxidative strategies in lignin chemistry: A new environmentally-friendly approach for the functionalisation of lignin and lignocellulosic fibers. Catalysis Today 156: 8 22 Das S., Punniyamurthy T. : Cobalt(II)-catalyzed oxidation of alcohols into carboxylic acids and ketones with hydrogen peroxide. Tetrahedron Letters 44 : Haikarainen A. : Metal-Salen Catalysts in the Oxidation of Lignin Model Compounds. Unpublished doctoral dissertation, University of Helsinki, Finland Katahira R., Kamitakahara H., Takano T., Nakatsubo F. : Synthesis of β-o-4 type oligomeric lignin model compound by the nucleophilic addition of carbanion to the aldehyde group. Journal of Wood Science 52 : 1 6 Kervinen K., Korpi H., Leskelä M., Repo T. : Oxidation of veratryl alcohol by molecular oxygen in aqueous solution catalyzed by cobalt salen-type complexes: the effect of reaction conditions. Journal of Molecular Catalysis A: Chemical 203 [1-2]: 9 19 Kervinen K., Korpi H., Mesu J.G., Soulimani F., Repo T., Rieger B., Leskelä M., Weckhuysen B.M. : Mechanistic insights into the oxidation of veratryl alcohol with Co(salen) and oxygen in aqueous media: an in-situ spectroscopic study. European Journal of Inorganic Chemistry : Kishimoto T., Uraki Y., Ubukata M. : Easy synthesis of β-o-4 type lignin related polymers. Organic & Biomolecular Chemistry 3 : Lebo Jr. S.E., Gargulak J.D., McNally T.J. : Lignin. In: Kirk Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. Lyons C.T., Stack T.D.P. : Recent advances in phenoxyl radical complexes of salentype ligands as mixed-valent galactose oxidase models. Coordination Chemistry Reviews 257 : Manickam R., Kulandaivelu K. : Meso-tetraphenylporphyriniron (iii) chloride catalyzed oxidation of aniline and its substituents by magnesium monoperoxyphthalate in aqueous acetic acid medium. Polish Journal of Chemical Technology 14 : Megiatto J.D. Jr., Cazeils E., Grelier S., Gardrat C., Ham-Pichavant F., Castellan A. : Synthesis of a lignin polymer model consisting of only phenolic β-o-4 linkages and testing its reactivity under alkaline conditions. Holzforschung 63 : Meguro S., Sakai K. [1984a]: Factors affecting oxygen-alkali pulping IV. The effects of oxygencarrying cobalt complexes on guaiacol oxidation. Mokuzai Gakkaishi 30 : Meguro S., Sakai K., Imamura H. [1984b]: Factors affecting oxygen-alkali pulping VI. The effect of alkali on the catalytic activity of Co-salen [cobalt(ii) bis(salicylidene)ethylenediamine]. Mokuzai Gakkaishi 30 : Meguro S., Imamura H. : Factors affecting oxygen-alkali pulping X. Method of estimating the catalytic activity of cobalt complexes in delignification. Mokuzai Gakkaishi 35 : Nishinaga A., Tomita H. : Model catalytic oxygenations with Co(II) schiff base complexes and the role of cobalt-oxygen complexes in the oxygenation process. Journal of Molecular Catalysis 7 :
16 16 Xue-Fei Zhou Rajagopalan B., Cai H., Busch D.H., Subramaniam B. : The catalytic efficacy of Co(salen) (AL) in O 2 oxidation reactions in CO 2 -expanded solvent media: Axial ligand dependence and substrate selectivity. Catalysis Letters 123 [1-2]: Sandaroos R., Goldani M.T., Damavandi S., Mohammadi A. : Efficient asymmetric Baeyer Villiger oxidation of prochiral cyclobutanones using new polymer-supported and unsupported chiral Co(salen) complexes. Journal of Chemical Sciences 124 : Schmidt J.A. : Electronic spectroscopy of lignins. In: Lignin and Lignans Advances in Chemistry. Heitner C., Dimmel D. R., Schmidt J. A., Eds.; CRC Press, Sippola V. : Transition Metal-Catalysed Oxidation of Lignin Model Compounds for Oxygen Delignification of Pulp. Unpublished doctoral dissertation, Helsinki University of Technology, Espoo, Finland Velusamy S., Punniyamurthy T. : Copper(ii)-catalyzed oxidation of alcohols to carbonyl compounds with hydrogen peroxide. European Journal of Organic Chemistry : Zhang N., Zhou X.-F. : Salen copper (ii) complex encapsulated in Y zeolite: An effective heterogeneous catalyst for tcf pulp bleaching using peracetic acid. Journal of Molecular Catalysis A: Chemical 365: Zhou X.-F., Liu J. : Co(salen)-catalysed oxidation of synthetic lignin-like polymer: Co(salen) effects. Hemijska Industrija 66 : Zhou X.-F., Qin J.-X., Wang S.-R. : Oxidation of a lignin model compound of benzyl-ether type linkage in water with H 2 O 2 under an oxygen atmosphere catalyzed by Co(salen). Drewno 54 : KATALIZOWANE Co(salen) UTLENIANIE SYNTETYCZNEGO LIGNINO-PODOBNEGO POLIMERU: EFEKT O 2 Streszczenie Co(salen) to kompleks koordynacyjny stanowiący pochodną ligandu salenowego (disalicylaloetylenodiaminy) i kobaltu. Jego pochodne znajdują zastosowanie jako katalizatory. Przeprowadzono badania nad biomimetycznym utlenianiem ligniny i modelowych związków lignin z wykorzystaniem kompleksu Co(salen). Stwierdzono, że reakcje utleniania katalizowane kompleksu Co(salen) pozwalają na powstania wartościowych produktów, które umożliwią wykorzystanie ligniny w aspekcie przyszłych zastosowań jako biomasa i biopaliwa. W pracy zastosowano dwa syntetyczne polimery ligninowe typu S i G, jako modelowe substraty do dalszych badań nad zachowaniem ligniny w reakcjach utleniania katalizowanych kompleksem Co(salen). Jego katalityczną skuteczność i wpływ O 2 analizowano za pomocą spektroskopii FTIR, C-13 NMR i chromatografii GC-MS. Odkryto, że Co(salen) zwiększa stopień utlenienia polimerów typu S i G. Natomiast O 2 wpływa na jego aktywność. Stopień rozkładu omawianych dwóch polimerów zwiększa się wraz z dodaniem O 2. Struktura polimerów wpływa na ich rozkład. W przypadku polimeru z dwiema grupami CH 3 O- (typ S) depolimeryzacja zmniejszała się. Niezależnie of typu polimeru (S lub G) w procesie depolimeryzacji tworzyły się znaczne ilości benzaldehydów, jako głównych produktów reakcji, zwłaszcza w obecności O 2.
17 Co(salen)-catalysed oxidation of synthetic lignin-like polymer: O 2 effects 17 Kompleksy Co(salen) wydają się być obiecującymi katalizatorami utleniania dla selektywnych transformacji syntetycznych lignino-podobnych polimerów z wykorzystaniem O 2, jako końcowego (ostatecznego) utleniacza. Efekt O 2 zwiększają zdolność katalityczną Co(salen)u w reakcji utleniania. Słowa kluczowe: Co(salen), katalizator, utlenianie katalityczne, model polimeru ligninowego, efekt O 2, FTIR, C-13 NMR, GC-MS Acknowledgements This work was financed by the National Natural Science Foundation of P. R. China (No , ), the Open Project of State Key Laboratory of Molecular Engineering of Polymers at Fudan University (K ), the Open Project of Jiangsu Provincial Key Lab of Pulp and Paper Science and Technology at Nanjing Forestry University (201320), the Open Project of Jiangsu Key Laboratory for Biomass-based Energy and Enzyme Technology at Huaiyin Normal University (JSBEET1318) and the Open Project of Tianjin Key Laboratory of Pulp and Paper at Tianjin University of Science and Technology (201314).
19 Drewno 2013, vol. 56, nr 190 DOI: /wood Dorota Dziurka, Radosław Mirski 2 LIGHTWEIGHT BOARDS FROM WOOD AND RAPE STRAW PARTICLES The study investigates the properties of lightweight ( kg/m 3 ) particleboards made using wood or rape particles and with veneers applied to their surfaces. Their suitability for the production of furniture and elements of interior design is discussed. Panels with veneer on their faces were made using a one shot pressing cycle. It was found that rape particles may be used for the production of lightweight particleboards, and that they are a good alternative to wood chips. Particleboards made of rape straw, covered with beech veneer during the pressing cycle in order to strengthen their subsurface layers, have better properties than the corresponding wood-chip-based particleboards. However, all the boards, throughout the whole density range, meet the requirements for P2 boards, i.e. boards intended for interior decoration and furniture production (MOR 11 N/mm 2, MOE 1600 N/mm 2, IB 0.35 N/mm 2 according to EN 312). Keywords: particleboard, lightweight boards, rape straw, veneer, mechanical properties Introduction Constant growth in the production and consumption of wood-based boards, used mainly in the construction and furniture industry, has been observed for many years at a global and European level. The development of the furniture industry depends on easy access to timber, the global resources of which are limited. The continuing shortage of wood, its increasing price and the growing competition for this material between manufacturers of boards, the pulp and paper industry, and the energy sector using biomass, means that the demand of the wood-based boards industry for lignocellulosic materials can only be met in the coming years by recourse to the existing potential reserves, such as agriculture, especially the plantations of fast-growing or annual crops. Dorota Dziurka, Poznań University of Life Sciences, Poznań, Poland Radosław Mirski, Poznań University of Life Sciences, Poznań, Poland
20 20 Dorota Dziurka, Radosław Mirski Activities concerning the potential use of annual plants in the production of particleboards and fibreboards have been undertaken for many years. It is estimated that the resources of these plants significantly exceed the demand of the wood-based boards industry for lignocellulosic materials. Although the seasonality of supply, the need for storage, the low bulk density, and other negative aspects should be taken into account when using such materials, they should be considered an additional, but still high quality, resource. In recent years a lot of research projects have been conducted investigating the possibilities of using the waste of such plants as flax [Tröger, Ullrich 1994; Tröger et al. 1998], hemp [Girgoriou et al. 2000], sugar cane, rice straw [Yang et al. 2003], jute, grasses (Miscantus) [Tröger et al. 1998], cotton fibers [Guler, Ozen 2004], sunflower stalks [Khristova et al. 1998], vine prunings [Ntalos, Grigoriou 2002], eucalyptus [Pan et al. 2007], evening primrose [Dukarska et al. 2010, 2012], mustard [Dukarska et al. 2011], Pennsylvanian mallow [Czarnecki et al. 2010], cereal straw [Sampathrajan et al. 1992; Hague 1997; Girgoriou 2000; Bowyer, Stockmann 2001; Pawlicki et al. 2001; Mo et al. 2003; Zhang et al. 2003; Boquillon et al. 2004; Zheng et al. 2007] and even rubberwood [Tongboon et al. 2002], bamboo [Papadopoulos et al. 2004], Scots pine needles [Nemli et al. 2008], and shells of coconuts [Papadopoulos et al. 2002], peanuts [Guler et al. 2008] and almonds [Gürü et al. 2006; Pirayesh, Khazaeian 2012]. The most interesting raw material, from among the wide range of above possibilities, which can be used for the production of particleboards, seems to be the straws of major cereal species, mainly because of their prevalence in any climate. The particular suitability of isocyanate adhesives for the manufacturing of this type of boards is due to the extremely good wettability of the straw surface facilitating the creation of a sufficient number of bonds between the individual particles [Mo et al. 2001; Boquillon et al. 2004]. Studies in this area have shown that straw or straw-chip particleboards produced according to the developed technologies and resinated with pmdi, exhibited higher static bending strength, better hydrostatic properties, and a smoother surface than boards produced from wood chips alone. In the 1960s, the Polish Flaxboard Production Plant Lenwit in Witaszyce made its first attempts at manufacturing particleboards using rape straw. It was found that rape straw particles combined with wood chips were good quality materials for the production of particleboards, intended for insulation purposes. They were characterized by higher thermal insulating power, lower hygroscopicity and specific gravity. However, the high costs of material preparation and the lack of appropriate binding agents (with high adhesion forces) prevented the implementation of their regular production. The chemical composition of rape straw is slightly different to wood [Dziurka et al. 2005]. Rape straw contains less cellulose and lignin, but more hemicelluloses and mineral compounds. Cellulose positively affects the mechanical pro-
21 Lightweight boards from wood and rape straw particles 21 perties of the boards, but the content of extraction substances is also important, as they determine the adhesion quality. The content of extraction substances in rape straw is slightly higher than the contents of such substances in wood, although similarly to wood they are dispersed throughout its mass. Therefore, in contrast to cereal straws, in which olefin substances are mostly accumulated on the surface and thus hinder resination, they should not have a disadvantageous effect on the gluability of rape straw particles, even if typical polar wood adhesives are applied. Considering the literature data discussed above, it seems that the appropriate legal regulations and promotion of the idea among farmers could make rape straw a relatively easy and quick wood substitute. Traditional particleboards with a mean density ranging from 650 to 720 kg/m 3, have been used in the furniture industry for many years. However, in the light of new regulations and tendencies, the high density becomes an unquestionable disadvantage. The EU is expected to shortly introduce regulations, according to which the weight of a package containing elements designed for self-assembly cannot exceed 15 kg. Lightweight wood-based boards have been produced for a long time, and they are commonly used mainly in the construction industry, as insulating and soundproof material. However, due to poor mechanical properties, they have not been widely used for furniture production. The furniture industry is, to a large extent, based on honeycomb boards. Their layered structure with a honeycomb core provides a maximal reduction in weight without diminishing the load capacity, stiffness and other structural features. They are not, however, universal materials, and one of their most significant drawbacks is the need to use specialized machinery and equipment, special hardware and significant expenditure of labor. Given the above, it was decided to investigate the possibility of the production of lightweight particleboards, that were refined by overpressing beech veneer in order to strengthen their subsurface layers. Additionally, in view of the wood deficit persisting over the last few years, it was also decided to assess the suitability of rape particles as an alternative raw material for manufacturing particleboards used for the production of furniture and interior design elements. Materials and methods In the board manufacture, commercial pine chips and rape straw particles obtained as a result of double shredding in a knife shredder were used together with peeled beech veneer with a thickness of 1.7 mm. The moisture content in the raw materials used in the tests was 2.5, 3 and 5.1%. Table 1 presents their basic parameters.
22 22 Dorota Dziurka, Radosław Mirski Table 1. The basic parameters of the raw materials used for the production of lignocellulosic boards Tabela 1. Podstawowe parametry surowców stosowanych do wytwarzania płyt lignocelulozowych Parameter Parametr Average dimensions Średnie wymiary l, b, a [mm] Slenderness ratio Smukłość Flatness Płaskość Specific surface Powierzchnia właściwa [m 2 /kg] l, b, a length, width, thickness l, b, a długość, szerokość, grubość Formula Wzór Rape straw Słoma rzepakowa Wood chips Wióry drzewne l = a λ b ψ = a F = w l b a ρ Two versions of lightweight wood and rape straw particleboards of densities 550, 500, 450, 400 and 350 kg/m 3 were produced: single-layer particleboards and those with improved surfaces by the inclusion of decorative veneers (1.7 mm thick) in the surface layers. The 3-layer sandwich structure was hot-pressed together without applying a separate layer of adhesive to the veneers. The thickness of all the boards was 19 mm. The raw and veneered boards were manufactured under laboratory conditions in 3 replications, applying the following pressing parameters: pressing time 300 s, unit pressure 2.5 N/mm 2, temperature 200 ºC, resination rate for both wood and rape particle pmdi 10 %. The properties of the manufactured boards were tested following the respective standards: modulus of rigidity (MOR) and modulus of elasticity (MOE) according to EN 310 (parallel and perpendicular to the grain), internal bond (IB) according to EN 319, swelling in thickness (TS) after 24 h of soaking in water according to EN 317 and water absorption (WA). In order to evaluate the mean value and standard deviation, 12 samples of each board were tested (the total number of samples being 36).
23 Lightweight boards from wood and rape straw particles 23 Additionally, for the veneered boards (550 kg/m 3 ), the density profiles were analyzed (laboratory density profile measuring system GreCon DA-X, measurement resolution 0.02 mm at a rate of 0.05 mm/s). Results and discussion The properties of the wood and rape straw particleboards with reduced density are shown in tables 2 and 3. As might be expected, the reduced density of the particleboards resulted in a lower bending strength and modulus of elasticity. Nevertheless, significantly better results were observed for rape straw particleboards. The strength of the particleboards with a density reduced to 350 kg/m 3 as compared to those with a density of 550 kg/m 3, was only 18% for the wood chip boards and 32% for the rape straw boards. The modulus of elasticity tests yielded similar results. Adding veneer to the particleboard surfaces greatly improved their properties, and some tests even showed a four-fold increase in strength compared to the raw particleboards (table 3). The veneered boards of either wood or rape particles met the requirements of EN 312 standard for P5 particleboards when the density was 450 kg/m 3 or greater (only parallel to the grain). This standard assumes that the bending strength and modulus of elasticity for load-bearing particleboards used in humid conditions should not be lower than 2400 N/mm 2 and 16 N/mm 2. It should be additionally emphasized, that in respect of these properties, the requirements of this standard were even met by the rape straw particleboards with a reduced density of 350 kg/m 3. As could be expected, the bending strength perpendicular to the grain in the surface layers was low due to a very weak natural wood strength in this direction (table 3). As shown by the study results, the manufactured boards displayed good strength perpendicular to the plane of the board. Reducing the density was in fact accompanied by a decrease in strength, but the changes were not as sudden as in the case of the bending strength. It was further observed that the strength of the boards with the lowest density amounted to an average 38% of the strength of the highest density boards for both types of particles. Finishing the board surface with veneer did not improve this property and the strength of those boards was in fact similar to that of the raw boards.
24 24 Dorota Dziurka, Radosław Mirski Table 2. Mechanical and physical properties of raw particleboard and rape straw boards Tabela 2. Mechaniczne i fizyczne właściwości surowych płyt z wiórów drzewnych i cząstek rzepaku Target Założona Density Gęstość MOR MOE IB TS WA Measured f m E m f t G t Nasiąkliwość Zmierzona kg/m 3 N/mm 2 % Raw particleboard Płyta wiórowa (21 * ) 14.4 (2.1) 2370 (370) 1.00 (0.11) 11 (3.5) 96 (4.8) (20) 8.51 (1.7) 1570 (110) 0.90 (0.09) 9.6 (1.9) 101 (5.2) (12) 6.65 (0.8) 1270 (90) 0.62 (0.08) 9.3 (1.2) 115 (6.2) (25) 3.77 (0.6) 710 (80) 0.48 (0.09) 8.1 (1.4) 132 (7.6) (16) 2.56 (0.4) 360 (80) 0.35 (0.08) 7.0 (1.3) 139 (8.2) Raw rape straw board Płyta z cząstek rzepaku (23) 12.7 (2.3 * ) 2330 (390) 0.82 (0.10) 14 (3.6) 49 (8.9) (22) 9.38 (1.3) 1970 (70) 0.69 (0.09) 14 (2.1) 50 (9.7) (20) 8.37 (0.7) 1630 (290) 0.64 (0.09) 14 (1.3) 55 (8.2) (12) 5.47 (0.5) 1180 (180) 0.45 (0.10) 13 (1.6) 68 (9.2) (14) 4.09 (0.6) 900 (110) 0.35 (0.04) 12 (1.1) 72 (11.3) * standard deviation, * odchylenie standardowe MOR modulus of rigidity, f m wytrzymałość na zginanie MOE modulus of elasticity, E m moduł elastyczności IB internal bond, f t wytrzymałość na rozciąganie prostopadłe do płaszczyzn płyty TS thickness swelling, G t spęcznienie WA water absorption, nasiąkliwość
25 Lightweight boards from wood and rape straw particles 25 Table 3. Mechanical and physical properties of veneered particle- and rape straw boards Tabela 3. Mechaniczne i fizyczne właściwości fornirowanych płyt z wiórów drzewnych i cząstek słomy rzepakowej Target Założona Density Gęstość Measured Zmierzona MOR MOE MOR MOE f m E m f m E m IB TS WA f t G t Nasiąkliwość kg/m 3 N/mm 2 % Veneered particleboard Fornirowana płyta wiórowa (21 * ) 49.2 (2.7) 7050 (440) 12.2 (1.6) 1620 (280) 0.96 (0.11) 12 (3.6) 86 (5.3) (20) 40.5 (1.5) 6600 (180) 8.85 (1.1) 1210 (170) 0.84 (0.10) 12 (2.9) 921(5.9) (12) 32.4 (1.8) 6010 (250) 6.52 (0.7) 970 (90) 0.66 (0.08) 11 (1.7) 98 (5.8) (25) 24.4 (1.1) 4840 (190) 5.05 (0.5) 810 (90) 0.48 (0.09) 9 (1.3) 111 (6.3) (16) 14.5 (0.8) 4390 (140) 4.93 (0.3) 480 (60) 0.37 (0.07) 9 (1.4) 120 (5.6) Veneered rape straw board Fornirowana płyta z cząstek rzepaku (15 * ) 51.0 (1.9) 7910 (410) 13.5 (1.2) 1860 (180) 0.85 (0.11) 13 (3.4) 66 (6.0) (19) 47.4 (1.7) 6960 (390) 11.3 (0.9) 1660 (230) 0. 76(0.10) 11 (2.0) 69 (8.2) (17) 42.5 (1.2) 7120 (210) 8.17 (1.1) 1340 (190) 0.64 (0.09) 10 (1.3) 82 (8.6) (18) 36.5(1.1) 6090 (410) 6.63 (0.8) 1050 (70) 0.49 (0.07) 9(1.0) 88 (8.3) (12) 30.8 (0.9) 5620 (340) 5.64 (0.6) 840 (60) 0.38 (0.06) 9 (1.2) 95 (6.8) * standard deviation, * odchylenie standardowe, MOR modulus of rigidity, f m wytrzymałość na zginanie, MOE modulus of elasticity, E m moduł elastyczności, II parallel, ^ perpendicular to grain, II równolegle, ^ prostopadle do przebiegu włókien IB internal bond, f t wytrzymałość na rozciąganie prostopadłe do płaszczyzn płyty TS thickness swelling, G t spęcznienie, WA water absorption, nasiąkliwość
26 26 Dorota Dziurka, Radosław Mirski Summing up, the study results revealed that the manufactured particleboards met the IB strength requirements for P5 boards, regardless of the type of particles and method of surface finishing, with the exception of the lowest density boards (350 kg/m 3 ). As shown in tables 2 and 3, the tensile strength perpendicular to the plane of those boards was higher than 0.45 N/mm 2. The tests concerning swelling and water absorption showed that even though the swelling fell with decreasing density, it was accompanied by a significant increase in water absorption. This was due to the more porous structure of the lower density boards, which on the one hand reduced its tendency to swelling, and on the other hand improved its ability to absorb water. As could be expected, applying the veneer to the faces moderated water penetration into the boards, resulting in a reduced water absorption of the refined boards by an average of 12%, compared to the corresponding raw boards. It was found that the rape particles may be used for the production of lightweight particleboards, and that they are a good alternative for wood chips. Particleboards made of rape straw and covered with beech veneer during the pressing cycle in order to strengthen their subsurface layers, had better properties than the corresponding wood-chip-based particleboards. While the rape straw particleboards met the requirements for P5 boards (16 N/mm 2 and 2400 N/mm 2 ) concerning their mechanical properties (MOR and MOE parallel to grain) even at the lowest density, the wood chip particleboards met those requirements only down to the density of 450 kg/m 3. However, both types of boards with a density of 350 kg/m 3 met the requirements for the boards used for interior decoration and furniture production (type P2 11 N/mm 2 according to EN 312). In the case of the boards intended for furniture production, another important factor was the peeling resistance of the subsurface layers. This feature was particularly important for boards with a surface covered with a veneer during the board manufacturing cycle, without using an additional adhesive layer. Again, better results were obtained for the rape straw boards. The density profiles of the veneered boards presented in fig. 1 showed a clearly visible zone of reduced density at the veneer-board interface in the wood chip particleboards, which would result in a lower peeling resistance of this layer. The density profiles of the rape straw particleboards were quite different. The data presented in fig. 1 clearly showed a significant increase in density at the veneer-board border. It was therefore highly probable that this interface would not be the weakest point of the board. These different density profiles may be due to the fact that the presence of waxes in straws of different origins hinders pmdi penetration, thus allowing for better coverage of their surface with resin [Liu et al. 2004]. This way the surface of the straw particles is covered by a uniform adhesive layer which determines the formation of effective bonds. This fact, combined with the higher plasticity of the rape particles and lower bulk density as compared to the wood chips, resulted in a much higher density of rape straw boards after compression to the same thi-
27 Lightweight boards from wood and rape straw particles 27 ckness. In rape straw boards the contact area of straw particles and veneer significantly increased, which undoubtedly improved their bonds. The situation was different in the case of wood chips. Their structure is dissimilar, more porous as compared to rape straw and they are not covered with waxes [Roll et al. 1990; Roll, Roll 1994; Shi, Gardner 2001]. pmdi penetrated into them, thereby weakening the adhesive-bonded joint between the chips and the veneer, which was reflected in the density profiles. a) b) thickness, grubość [mm] thickness, grubość [mm] Fig. 1. Density profiles of veneered particleboard (a) and rape straw board (b) with density 550 kg/m 3 Rys. 1. Profile gęstości fornirowanych płyt z wiórów drzewnych (a) i cząstek rzepaku (b) o gęstości 550 kg/m 3