Róbert Németh

Photodegradation of wood at elevated temperature: Infrared spectroscopic study

The purpose of this investigation was to evaluate the effect of elevated temperature on the photodegradation of solid wood. The work presented here, deals with the changes of infrared spectrum generated by the photodegradation process. Wood samples were irradiated with a mercury vapour lamp. The photodegradation behaviours of conifers and deciduous species were studied at elevated (80 °C) and at ambient (30 °C) temperatures. The infrared data were analysed using the difference spectrum method. The properly calculated difference spectrum gave much more information about the chemical changes than the visual comparison of the absorption spectra measured before and after the irradiation. The results showed considerably greater degradation at 80 °C than at 30 °C. The difference spectra revealed the absorption increase of tree different types of carbonyl groups. Remarkable differences were found between the photodegradation behaviours of softwoods and hardwoods. Poplar belongs anatomically to the hardwoods but its photodegradation properties were between that of hardwoods and softwoods.

Effect of acetylation on the chemical composition of hornbeam (Carpinus betulus L.) in relation with the physical and mechanical properties

ABSTRACT Common hornbeam (Carpinus betulus L.) is a highly underused wood species despite its great hardness, strength, wear-resistance and toughness. It is mainly used as firewood in Hungary because of its wood defects, irregular shape and low-dimensional stability. These wood defects and small breast height diameter result in a low yield. It is non-durable outdoors as it tends to turn grey, crack and be attacked by wood-decaying organisms. Indoors it lasts for hundreds of years. One technology that could improve the stability and durability properties is acetylation. Hornbeam was acetylated with the Accoya® method under industrial conditions. The aim of this research was the assessment of acetylation affecting the chemical properties of hornbeam wood and how these are related to the change in physical and mechanical properties. Main wood constituents (cellulose, hemicellulose, Klason lignin, extractives and ash content) were determined and compared. Chemical parameters related to the degradation of structural polymers were also evaluated (total phenolic and soluble carbohydrate contents, pH and buffering capacity, furfural, levulinic acid, formic acid, acetic acid). Structural changes in acetylated wood and in the Klason lignin fraction were also assessed using FTIR spectroscopy.

Chemical changes of wood during steaming measured by IR spectroscopy

Abstract Black locust, poplar and spruce samples were steamed at 80°C and 120°C for 48 hours. IR difference spectra and the CIE Lab colour coordinates were measured for determining the chemical changes caused by the steaming. Steaming at 80°C caused only small changes in both IR spectra and colour. But steaming at 120°C produced intensive colour change and well-visible changes in IR spectra. The guaiacyl lignin in hardwoods underwent slight degradation but in spruce suffered substantial degradation during steaming at 120°C. The syringyl lignin absorbing around 1600 cm−1 did not show any changes, indicating that it is more stable to steaming than guaiacyl lignin. The absorption decrease at 1175 cm−1 indicated the cleavage of ether linkage in cellulose and hemicelluloses at both steaming temperatures.

Biological resistance of pine wood treated with nano-sized zinc oxide and zinc borate against brown-rot fungi

In this work, the biological resistance of Scots pine (Pinus sylvestris L.) wood impregnated with nano-sized zinc oxide and zinc borate against the fungi Daedalea quercina, Poria placenta and Serpula lacrymans was evaluated. It can be concluded that nano-sized zinc oxide inhibited the biological degradation of pine wood against Serpula lacrymans, while it was ineffective against the brown-rot fungus Poria placenta. Pine wood treated with nano-sized zinc borate exhibited higher biological resistance against the fungi Serpula lacrymans and Poria placenta.

Improvement of dimensional stability of wood by silica nanoparticles

ABSTRACT The improving effect of nanoparticles on wood dimensional stability is barely known nowadays. The expected result of the research was the improvement of the dimensional stability through bulk hydrophobization, as a result of impregnation with hydrophobic SiO2 nanoparticles. Two different wood species, beech (Fagus sylvatica) and scots pine (Pinus sylvestris) were investigated. Two different treatments with silica nanoparticles were used. One treatment was a pure emulsion of modified (hydrophobized) silica nanoparticles (carrier material: ethanol), and another one was modified (hydrophobized) silica nanoparticles in tetrahydrofuran carrier material in combination with polydimethylsiloxane (PDMS) as a bonding agent. PDMS was used to improve the bonding of the silica nanoparticles to the wood structure. The impregnation with nanoparticles was successful. Shrinking and swelling properties decreased by 17–33%, depending on wood species and treatment. Water uptake and equilibrium moisture content decreased significantly as a result of the treatments (40–58%). Application of PDMS did not provide better dimensional stability compared to the treatment without it, however, it resulted in lower equilibrium moisture content and water uptake compared to the basic nano-SiO2 treatment.The improving effect of nanoparticles on wood dimensional stability is barely known nowadays. The expected result of the research was the improvement of the dimensional stability through bulk hydro...

Hygroscopicity of Longitudinally Compressed Wood

Abstract Knowledge of hygroscopicity is extremely important both in the use of native wood and modified wood. In this study, the modification method was steaming at 100 °C, then longitudinal compression at a rate of 20%. The moisture content (MC) of treated and untreated green beech wood (Fagus sylvatica L.) was reduced in a climate chamber with gradual reduction of air humidity at 20 °C. The difference of calculated fibre saturation points between control samples and samples compressed for a long time was 6% (MC%). In the course of desorption, this difference decreased, and finally disappeared at 10% moisture content (40% relative humidity). In the second step of the research work, the speed of vapour adsorption was checked. The absolute dry samples were placed in air with 95% relative humidity. The highest deviation in the moisture content was 1% (MC%) between the control and the compressed samples. The compressed wood dries faster than the control samples under the same conditions. Furthermore, during adsorption, the moisture content of the compressed samples at room conditions is lower.

Testing the Photostability of Acetylated and Boiled Linseed Oil-coated Common Hornbeam (Carpinus betulus L.) Wood

Abstract In this study, the effect of acetylation and coating with boiled linseed oil was evaluated concerning the photodegradation of common hornbeam wood (Carpinus betulus L.). To measure colour stability, a 10-month-long outdoor weather resistance test without soil contact was performed as well as artificial aging using a 200 hour mercury-vapour lamp irradiation test. The measurements were done on hornbeam, acetylated hornbeam, boiled linseed oil-treated hornbeam, and acetylated and boiled linseed oil-treated hornbeam samples. The control and treated samples’ colour change was determined by comparing them to the original colour in all cases. The photodegradation process was examined with Fourier Transform Infrared (FTIR) spectra. Acetylated hornbeam was less prone to crack, but the modification did not hinder the fading and greying caused by UV irradiation. Coating the samples with boiled linseed oil decreased the rate of colour change and cracking. The photodegradation of lignin was confirmed by the FTIR spectra.

Fokozott fahozamú új akácfajták, illetve fajtajelöltek faanyaga színének törzsön belüli változatossága

Kutatasunk celja a fokozott fahozamu, uj akac fajtajeloltek szinvizsgalata volt. Munkank soran kulonboző kelet-magyarorszagi termőhelyről szarmazo uj akac fajtajeloltek faanyagat vizsgaltunk meg. A szinkoordinatak meghatarozasa a nemzetkozileg elfogadott CIELab rendszerben tortent. Kimutattuk, hogy a fajtajeloltek faanyagat nagy szinbeli valtozekonysag jellemezi. A voros szinezet erteke a kontroll mintakhoz kepest tobbnyire novekedett. Az irodalmi ertekekhez kepest eredmenyeink valamennyi szinkoordinata eseteben nagyobb szorast mutattak.

Faanyag rostirányú tömörítésével kapcsolatos elméleti és gyakorlati kérdések áttekintése - 2. rész: történelem és szabadalmak, a tömörítési folyamat tulajdonságai és a tömörítést követő eljárások

A fa longitudinalis tomoritesenek celja annak hajlekonyabba, alakithatova tetele. A megfelelő minősegű tomoritett faanyag előallitasanak meghatarozo tenyezői a fafaj, alapanyag minősege, nedvessegtartalom, hőmerseklet, tomoritesi arany, stb. A legtobb 20% feletti kezdeti nedvessegtartalommal rendelkező jo minősegű kemenylombos fafaj tomorithető. Az altalaban gőzolessel plasztifikalt faanyag rostiranyu tomoritese soran a faanyagot meg kell tamasztani az oldaliranyu kihajlas megakadalyozasara, csokkentve ekozben a fellepő surlodasi erőknek az egyenletes tomoritest hossziranyban gatlo hatasat. A rostiranyu preseles hatasara a fa hidrotermikus kezelessel meglagyitott es folyamatosan legalabb 80 °C hőmersekleten tartott sejtszerkezeteben a nagyreszt lignin es hemicelluloz alkotta kozeplemez engedi elcsuszni egymashoz kepest a magas celluloztartalmu, szilarditast biztosito farostokat es egyeb szoveteket, mikozben ezeknek a longitudinalis iranyultsagu hosszukas szoveti elemeknek a sejtfala meggyűrődik. Az eljarassal a fa rugalmassagi modulusa lecsokken, igy a kezeletlen faanyaghoz kepest lenyegesen konnyebben hajlithatova valik, egyes modszerek szerint akar szaritott es szobahőmersekletű allapotban is. The purpose of the longitudinal compression of wood is to make it bendable. Several factors influence the outcome of compression (wood species and quality, moisture content, temperature, compression rate, etc.). Most hardwood species with initial moisture contents above 20% can be compressed. The wood is normally softened by steaming and, during the process, kept at a temperature above 80 °C. While compressed in fibre direction it needs to be restricted within the compression chamber to prevent the wood from suckling. Frictional forces need to be minimized so that the transformation is performed at even rate. The middle lamellae, mostly consisting of lignin and hemicelluloses, are softened by thermo-hydro wood processing, allowing of the wood fibres with high cellulose content to slip during compression, and the longitudinal cell walls crinkle. Consequently, the elasticity of the wood decreases, thus it will be much easier to bend, even when dry and at room temperature.

ENERGY CONSUMPTION IN DRYING OF FROZEN SPRUCE WOOD

Drying wood requires a significant amount of energy. This includes both thermal energy, necessary to heat-up wood, evaporate the water inside it and cover the insulation and vent losses, as well as electric energy consumed to force air circulation through the stacks. When wood is frozen, both energy consumptions increase; on one hand because frozen water requires a supplementary heat for transformation into liquid and then into gaseous state, and on the other hand, because of the low initial temperature of wood that also increases the drying time. Frozen spruce samples, as well as unfrozen control samples were kilndried in a conventional kiln within the same batch. The moisture content and temperature inside the samples was monitored throughout the process. Based on the measured drying time, the energy consumption was estimated to be up to 40% higher in the case of drying wood from frozen state. The paper concludes with some recommendations of interest for the industrial practice regarding which situation should be preferred and adopted when planning timber storage & drying in wintertime.