This study explores the potential of using condensate generated during beech wood steaming (BSC) as an eco-friendly additive in urea-formaldehyde (UF) adhesives for wood-based panel (WBP) production. The research aimed to assess the hardening behavior of pure commercial UF resin and UF with added condensate (UF-BSC), investigating the potential catalytic effect of BSC on the hardening characteristics of UF adhesives. Changes in chemical structure after the curing process were observed with Fourier transform infrared spectroscopy (FTIR). The curing kinetics was studied by differential scanning calorimetry (DSC) under a dynamic scanning regime with heating rates of 5, 10, and 20 °C/min. Obtained data were analyzed using Kissinger-Akahira-Sunose (KAS) and Friedman (FR) kinetic iso-conversional methods to estimate the activation energy (Ea) of the curing reaction in the investigated UF adhesive systems. The results of DSC analysis imply that BSC lowers the temperature of the curing reaction of UF adhesive along with the prolongation of the curing reaction. The obtained kinetic data supported by FTIR and chemical analysis suggest that phenolic compounds present in BSC interfere with the main curing reactions leading to lower peak temperatures but higher activation energy. Тhis suggests that BSC increased the number of active sites involved in the reaction and, consequently, the number of collisions. BSC, as wastewater of the wood processing industry, can be efficiently utilized as an environmentally friendly, inexpensive substitute for deionized water in UF adhesive formulations for WBP manufacturing.

Addition of poly(diallyldimethylammonium chloride) (PDDA) on the performances of urea-formaldehyde (UF) adhesives was evaluated in this work. Three types of UF adhesives were prepared, one without PDDA addition, and two types with PDDA addition of 1 and 3 wt.% per dry UF adhesive mass. These UF adhesive systems were used for producing experimental particleboard panels. The addition of PDDA decreased the thickness swelling of the panel samples, while the internal bond of the particleboards increased significantly only at the highest PDDA content (3 wt.%). Differential scanning calorimetry (DSC) was applied to address the influence of PDDA on UF adhesive curing kinetics. DSC scans were performed in non-isothermal regimes using different heating rates (5, 10, and 20 ?C?min?1). The activation energy (Ea) of the curing reaction showed slightly lower values for the UF adhesive systems containing PDDA. However, the peak temperatures and enthalpy of reaction did not change significantly. The Kissinger-Akahira-Sunose and Friedman iso-conversional methods were applied to investigate the effects of PDDA addition on the UF adhesive curing process.

The goal of this paper is to analyze the chemical composition of untreated and treated wooden chips from the native narrow-leaved ash (Fraxinus angustifolia Vahl. ssp. Pannonica Soó & Simon). In order to determine the effect of pretreatment with liquid hot water (LHW) on changes in chemical composition, the content of moisture, cellulose, lignin, minerals (ash), extractives soluble in hot water, extractives soluble in organic solvents, for treated and for untreated wooden chips was determined. This was done in accordance with TAPPI and ASTM standard methods. The properties of wooden chips, treated for 30 min and 60 min at a temperature of 100 °C, are compared to untreated wooden chips and changes in the chemical composition that occurred are defined as a result of the applied treatments. The research was performed under controlled conditions in a laboratory, and the results of treatments were the subject of comparative analysis. Applied treatments had a statistically significant effect on decreasing the content of extractives. The content of cellulose and hemicellulose increased in the treated wooden chips compared to untreated wooden chips, while the lignin content did not significantly change.

There is an increased research interest in methods for transparent wood production and its use. Wood transparency could be achieved by its delignification followed by an impregnation process with polymers having proper optical properties. However, delignification processes are mainly time consuming and not environmentally friendly. The possibility of treating mahogany wood (Swietenia macrophylla King) with 20% hydrogen peroxide for 70, 100, 135, and 170 min at 103 °C is presented in this research. According to the treatment duration, lignin content decreased 40 to 94% relative to its initial content in the control samples, whilst the cell structure remained intact. Due to the light scatter effect, caused mainly by wood tissue structure, the direct optical transmittance of treated samples in the visible light spectrum (400 to 800 nm) was less than 40%. Simultaneously, the total optical transmittance of samples treated for 100 and 135 min reached values between 70 to 80% with high values of the haze at approximately 30 and 60%. Optical transmittance in the visible spectrum area of the samples treated for 170 min was from 45 to 80% and the haze from 25 to 45%.

Particles of beech wood were treated with hot water at the temperature of 150 oC, during 60 min, prior to the pelleting process. The applied hot water pretreatment affected the chemical composition and heating value of particles. Two groups of pellets, designated as PT 10 and PT 20, were produced from treated beech particles, with the moisture content of particles being 10.5 and 20.5 %, respectively. Pellets from nontreated beech particles (PNT) served as controls to assess the hot water pretreatment effects on the pellet properties. Both, the applied pretreatment, and the particle moisture content, affected properties of the obtained pellets. The heating value of PT 10 ad PT 20 pellets has increased for ~6 and 1 %, respectively. The mineral (ash) content in treated pellets decreased for about 24 % in comparison to that in PNT pellets. In addition, the bulk (apparent) density of pellets has increased for 21 % (PT 10) and 10 % (PT 20), as a consequence of the hot water pretreatment of particles. The specific density of PT 10 pellets was for 16 % higher, while the equilibrium moisture content (after conditioning at RH 68 % and 20.1?C) was for about 32 % lower in comparison to the respective properties of PNT pellets.

The urea-formaldehyde (UF) adhesive is still most important adhesive system in the production of interior grade particleboards and medium density fibreboards (MDF). However, the furniture and interior fitments, incorporating these products, present one of the sources of formaldehyde emission into the indoor air. The recognition of formaldehyde as a substance that presents the risk for a human health had a strong impact on wood-based panels industry, as it came under constrains by the number of national and international regulations. Hence, this paper presents the overview of standards and regulations that define formaldehyde emission limits for wood-based panels today, and of a special interest for a wood-based panels market in the Republic of Serbia. The paper also gives an overview on a possible methods and procedures for the production of wood-based panels with low or no formaldehyde emission.

The formaldehyde potential of particleboards imported on Serbian market was evaluated in this research. The sampling and testing of particleboards were conducted in two discrete periods: first was during 2011 and the second was in the period of 2015-2016. For both periods, the samples of raw particleboards originated from three different producers. The perforator method (EN 120) was used to test the formaldehyde content in the particleboard samples. In general, the results have showed that the majority of the samples belong to the E1 class of particleboards. In addition, 19 % of the particleboards sampled in 2011 and 31 % of the boards sampled in 2015-2016 were found to have formaldehyde content below 50 % of E1 class requirements.

This paper evaluates two methods for ultrasonic mixing of nano-SiO2 into urea-formaldehyde (UF) adhesives. Nano-silica (SiO2) was used in the form of 30% colloidal suspension, with the nanoparticles having a diameter of 7 nm. Its addition into the UF adhesive was 15%, based on the dry weight. The mixing of these components was performed with a probe-type ultrasonic homogenizer and with an ultrasonic bath, during 25 minutes of mixing time. The effects of each method were evaluated by SEM microscopy, and the results showed that the ultrasonic probe achieved much higher and almost complete homogenization of the UF / nano-SiO2 mixture, in contrast to the ultrasonic bath method. Therefore, the ultrasonic probe was subsequently used to test the influence of the mixing time on the homogenization level and on the curing kinetics of the UF adhesive with nano-SiO2. The homogenization level was not significantly altered when decreasing the mixing time from 25 to 5 minutes. For the same time range, the differential scanning calorimetry analysis also showed no significant influence of the mixing time on the curing behavior of the UF adhesive with nano-SiO2. The results of this research provide the basis for a more effective and efficient mixing procedure when using similar nanomaterials with UF adhesives, without significantly decreasing its performances.

Wood composite panels produced with formaldehyde-based resins present one of the major sources of formaldehyde emissions in the interior. This problem has become publicly recognized during 1970ies, and since then the significant efforts were addressed to control the formaldehyde emission from wood-based panels. The European and USA regulations on this subject have led to further improvements in the resin development, and to the technology of wood based panels in a broader aspect. Today, the regulations in Serbia concerning the formaldehyde emission standards are based on the accepted European standards, and the same applies to the testing methods. The capacities for testing the wood based panels on the free formaldehyde were developed in Serbia during the 1980ies, firstly at the Faculty of Forestry of the Belgrade University. The analysis of existing capacities for formaldehyde testing in Serbia is given in this paper, as well as the possibilities for further improvements in this field.

The formaldehyde release and the formaldehyde content from the commercial particleboards were determined using the flask and perforator methods. Since the melamine faced boards were used in this research, the flask method was applied to evaluate how much the decorative surface (melamine impregnated paper) affects the test results in terms of reducing the formaldehyde emission from the samples. Hence, the flask method tests were performed simultaneously with one test series presenting the melamine faced samples, and the other one presenting the samples with sanded surface. Also, the decorative surface was sanded off from all of the test samples intended for formaldehyde content measurements using perforator method. During this research, it was found that by removing the decorative surface, the formaldehyde emission increased in the range from 12.6% to 16.6%, suggesting that the decorative surface acts as a barrier to formaldehyde emission even for the samples of such a small size used in the flask method. In addition, very high correlation, of 0,989 and 0,959, was found between the formaldehyde content values (perforator method) and the values of formaldehyde release from sanded and melamine faced samples, respectively.

We report a new educational approach for teaching students about contemporary Materials Science and Engineering (MSE) research. It describes how MSE can be introduced to high school students as examples for analysis in mathematical classes. We discuss, in this example, how such students are introduced to MSE materials preparation experiments by scientists from the Faculty of Technology at the University of Novi Sad. This kind of educational approach accomplishes at least two important objectives. First, students have an opportunity to learn about connections between Mathematics and MSE. Second, this educational approach raises chances of MSE being a possible choice of future profession for students. This is very important since most high school students are not acquainted with MSE as a profession.

This work deals with the influence of specific pressure during the press process on the radial and tangential penetration of urea-formaldehyde (UF) adhesive into poplar, as well as on the shear strength of lap joints prepared at these different pressures. An epi-fluorescence microscope was used for measuring the adhesive penetration when investigating microtome slides (20-µm thick) cut from the joint samples. The average penetration depth (dap) and the size of the interphase region (I) increased with the increase of pressure from 0.5 to 1.0 N/mm2. Further increase in the pressure to 1.5 N/mm2 did not produce a significant change in dap or I. On the contrary, the area of filled lumens and rays (A) showed a steady decrease as the specific pressure increased. Such behavior influenced the filled interphase region (If), which also decreased with increased pressure. Tangential samples (radial penetration) obtained higher values of lap shear strength and showed less dependence on the specific pressure than the radial samples (tangential penetration). Higher shear strength based on radial penetration corresponded to the thicker interphase region of these samples. The highest shear strength for both directions of penetration was obtained for the specific pressure of 1.0 N/mm2.

The acidity of wood has an important role in many areas of wood applications. Hence, this paper presents a study on the acidity of beech, fir and poplar, as the representatives of the most industrially utilized wood species in Serbia. The contents of both the soluble and insoluble acids were determined through the extraction methods with cold distilled water and sodium acetate solution, respectively, followed by the titration with sodium hydroxide solution. The acidity strongly differs among the three wood species used in this research. The amount of insoluble acids was the highest in fir, almost twice as much than in poplar, and about 68 % higher than in fir wood species. Such differences also showed a strong correlation with the gel times of UF adhesive mixes with hot water extracts. [Projekat Ministarstva nauke Republike Srbije, br. TP 31041: Establishment of Wood Plantations Intended for Afforestation of Serbia]

We discuss a new educational approach for teaching Materials Science and Engineering (MSE). MSE can be introduced to high school students via classes of Mathematics. We describe how such students are introduced to MSE experiments by scientists from the Faculty of Technology of the University of Novi Sad. Subsequently, students share their experiences with their peers. Application of our approach accomplishes at least two objectives. First, students see Applied Mathematics via demonstrated connections between Mathematics and MSE. Second, MSE appears on their radar when they reach the stage of choosing their major at the college level and thus their future professions. This is important since most high school students do not get in contact with exhibitions of the Materials Research Society or with other MSE related activities of professional societies.

The effect of chemical treatment on wood tissue leads to changes in the chemical composition of wood, thereby changing its wetability and its chemical reactivity with adhesive. In this study, wood samples of narrow-leaved ash (Fraxinus angustifolia Vahl. ssp. Pannonica Soo & Simon) were treated with water and with the aqueous solutions of acetic acid and sodium carbonate at the temperatures of 100 and 120 degrees C, and for a period of 60 min. The addition of acetic acid and sodium carbonate was 0.03, 0.06 and 0.09 g.g(-1) dry matter of wood. The effects of the applied treatments on the lap shear strength were evaluated by the standard test method using urea-formaldehyde adhesive. The entire sample series treated with the sodium carbonate have shown the significant increase of the shear strength when compared to the control sample series (17.5 to 49.6 %). In addition, the increase of the shear strength corresponded to the increase in the concentration of the sodium carbonate solution. On the other side, the acetic acid and the water treatments have not caused any significant changes to the shear strength of the samples. The increase in the concentration of the acetic acid solution has showed a tendency to decrease the shear strength, but this effect could not be confirmed statistically. Finally, the results of the shear strength for all the treated sample series have not been significantly affected by the applied temperature.

The objective of this work was to evaluate the influence of the molar mass of the urea-formaldehyde (UF) resins on the wetting properties of beech, fir and poplar. It was achieved by monitoring the contact angle formation between the small resin drops and the radial and tangential surfaces of the selected wood species. Three UF resins samples were used, having different degree of condensation, and thus having different molar mass distribution. The results have showed relatively high contact angle at the zero position for all three UF resins, which could be observed by the formation of the so-called "sitting drops". Subsequent measurements at the selected time intervals (5, 10 and 15 seconds after the initial contact) have showed that the increase in the UF resins molar mass also increases the contact angle, resulting in the lower wetting of substrates from all three wood species. Comparing the effects of the wood species, the results showed that the fir wood has the highest wettability in regard to both beech and poplar. This was noticed with all of the UF resin samples and for all of the measuring intervals. Contrary, the beech substrate has resulted in the highest contact angle, under the same test conditions. The effects of wood substrate on the wettability can be addressed to the anatomical structure of the selected wood species and the percentage ratio of the early wood versus late wood.

Rheological analysis was used to evalute the influence of the wood species of beech, fir and poplar on the gelation time of commercial urea-formaldehyde (UF). The UF adhesive samples were mixed with hot water extracts of selected wood species. Two series of samples were prepared, one without the catalyst addition and the other with the addition 0,2% of amonium chloride, per dry adhesive mass. Both series included the control UF adhesive samples, without the addition of wood extracts. Measurements of the viscoelastic properties of UF adhesive samples during cure were conducted at the temperature of 80C, and at the constant frequency of 1Hz. The addition of wood extracts had a positive catalytic influence in the case of the UF adhesive samples without the catalyst addition. Contrary, wood extracts have retarded the curing of the UF adhesive samples with catalyst.

The influence of wood species on the curing kinetics of commercial urea-formaldehyde (UF) adhesive was investigated with differential scanning calorimetry (DSC) by mixing the prepared adhesive with the hot water extracts of beech, fir and poplar. DSC measurements were done in dynamic scanning regime with heating rates of 5, 10, 15 and 20°C/min in order to determine the activation energy for each adhesive/extract mix and the adhesive alone. The addition of extracts showed a general retarding effect on the curing reaction of UF adhesive, in such a way that the higher acid buffer capacity of extracts have increased the peak temperature and activation energy for the relevant adhesive mixes, and in regard to UF adhesive alone. Obtained data were additionally analysed using isoconversional methods with application of Ozawa – Flynn – Wall and Kissinger – Akahira – Sunose kinetic models. The results showed a different behaviour of adhesive/extract mixes during cure. The appearance of diffusion controlled curing reaction, at the higher reaction rates (α>75%), were noticed for the UF adhesive mixes with poplar extracts, having the lowest pH values and the highest acid buffer capacity.

Urea-formaldehyde (UF) resin presents, by far, the most utilized adhesive system in the manufacture of particleboard and fiberboard. At the temperatures above 100 degrees C in the presence of catalyst, this resin undergoes cross-linking reaction and bonding of wood particles in a hot press. In this work the cross-linking of the new type of commercial UF adhesive for E1 type of wood based panels was studied using infra red (IR) spectroscopy and differential scanning calorimetry (DSC). IR spectra of examined UF adhesive showed distinctive characteristics in comparison to the older types of UF adhesives. The influence of different industrial wood species (obtained from beech, fir and poplar) on the curing behavior of wood-flour/adhesive mixtures has been evaluated using DSC method. The peak temperature and enthalpy of the curing reaction were evaluated from scans obtained with different heating rates. The activation energy for the curing reaction of pure adhesive and for wood-flour/adhesive mixtures was calculated using the Kissinger method.

Differential scanning calorimetry (DSC) was used to evaluate the curing kinetics of two commercial urea-formaldehyde (UF) adhesives having different formaldehyde to urea (F/U) ratio of 1.112 (UF1) and 1.086 (UF2). DSC measurements were done in dynamic scanning regime with heating rates of 5, 10, 15 and 20?C?min-1 in order to determine the activation energy for each adhesive. Obtained data were analyzed using isoconversional methods with application of Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose kinetic models. In addition, different catalyst levels were tested at the heating rate of 10?C/min. Results showed that the adhesive with higher F/U ratio achieved higher activation energy, while having lower peak temperature of curing reaction. It was also noticed that the increase of catalyst level influenced the increase of reaction enthalpy of the adhesive with lower F/U ratio.