Open-air fires or forest fires are becoming a key factor in reducing the forest surface areas and they are one of the major factors of devastation and degradation of forests and forest land and their ...ecosystems in the Mediterranean, mainly in coastal karst. They cause extreme material and economic damage, and they negatively affect biological and landscape diversity. After the forest fire, significant quantities of fired trees are left behind, representing a significant amount of lignocellulosic biomass available for conversion into a variety of biobased products. The question arises as to what degree they are chemically degraded, or whether they still have the properties required for further application in mechanical or chemical processing. The main aim of this paper was to study the group chemical composition as a biomass chemical property of the Aleppo pine (Pinus halepensis Mill.) sapwood before and after the impact of low ground fire and high fire of the treetops at tree height of 0, 2 and 4 m. Therefore, the impact of forest fires on the Allepo pine sapwood group chemical composition was studied in terms of quality for further application in production of biorefinery products. In addition, research results on group chemical composition of the same unfired and fired Aleppo pine wood bark from previous study were used for comparison with sapwood from this study. The obtained results show that the distribution of the main chemical components of Aleppo pine unfired wood bark and sapwood is similar to the results of previous studies for different wood species. That means that the bark contains a significantly higher content of ash, accessory materials (extractives) and lignins, and a significantly lower content of polysaccharides cellulose and polyoses (hemicellulose) than sapwood. The bark results from previous studies show a significant difference in reduced ash, cellulose and lignin content, and in the increased accessory materials and wood polyoses (hemicellulose) content between the unfired and fired wood. Furthermore, the content of individual chemical components of fired bark at different forest fires heights of 0,2 and 4 m for each sample did not differ significantly. Contrary to fired bark, no significant differences have been observed in the chemical composition of sapwood between unfired and fired wood, not even resulting from different forest fires heights. It can be concluded that the forest fire did not have any effect on Aleppo pine sapwood, where the fired wood bark took over all the damage caused by high temperature during the forest fire. In addition, the fired sapwood still retains the chemical properties required for further application in biorefinery biobased products. Keywords: Aleppo pine (Pinus halepensis Mill.), sapwood group chemical composition, forest fires, fired wood
This paper presents the results of research on carbon fiber angle orientation and quantity of carbon fi bers in yarn on bending properties of plywood. For that purpose the specimens have been defined ...as multilayer composites made from carbon fibers and veneer. Carbon fibers were inserted in the second and third glue line of the composite with angle variation of 15°. Stresses and strain were analyzed in significant layers together with displacement of the whole composite plate. The influence of carbon fiber angle orientation on properties of the composite (amount of stresses and related strains) was significant. The best results have been achieved with carbon fiber angle of 0°, and bidirectional carbon fiber type (BCF) with the orientation angle of 90°. The lowest values have been achieved with carbon fiber angle of 65° (unidirectional carbon fibers-UCF), and bidirectional carbon fiber type (BCF) with the orientation angle of 45°. Greater quantity of carbon fibers per one yarn has positive influence on decrease of stresses and strains in veneer layers and provides better stiffness of plywood.
After reaching its independence, Croatia’s (CRO) main economic goal was to enter the international market and join the European Union (EU). As foreign trade relations developed, it was necessary ...toestablish a quality control system for wood-based panels. The development of the quality system started at the State Offi ce for Standardization and Metrology (SOSM). The Faculty of Forestry was intensively involved in all activities related to the establishment of the quality system, such as the establishment of testing laboratories, education, certifi cation, quality control, work in technical committees, and special activities were directed towards the implementation of technical regulations in wood technology practice. The system was fi rst introduced by the Order of obligatory certifi cation of particleboard panels for general use and construction (Offi cial Gazette “Sl. list” 61/83), based on laws of the former state. In accordance with the Order, in 1995 SOSM authorized the Faculty of Forestry for conducting the certifi cation of particleboards. The Ministry of Economy was also included in the development of the system in areas not covered by the Order and regulations under SOSM’s jurisdiction. In the field of wood-based panels, a respectable system was built by the end of 1998. The next step was the preparation of technical regulations with the implementation of harmonized European standards. However, for reasons beyond understanding, the system completely collapsed, and in early 2004 it practically ceased to exist. The Ministry of Economy and the Croatian Government abolished all decisions on quality control of wood-based panels, except the obligatorily certifi cation of particleboards performed by SOSM, and it stopped its activities in 2003. The Ministry of Environmental Protection, Physical Planning and Construction (MEPPPC), as the competent institution, took over the certifi cation of particleboards after a whole year of lack of any quality control of wood-based panels, and implemented the European standards for particleboards into technical regulations for construction. However, the certification of particleboards is still performed in accordance with standards of the former state. In the attempt to enact the Technical Regulation for wood-based panels, initiated by the Ministry of Regional Development, Forestry and Water Management (MRDFWM), no consensus was reached, due to the application of wood-based panels both in the area of general use and in the fi eld of construction.
The use of resins, whose curing reaction takes place by high temperature and hardener addition, is inevitably involved in particleboard manufacturing process. In addition to commercial hardeners, ...such as ammonium sulphate, with the aim of optimizing the production process and reducing the production costs, a certain percentage of hardener can, among other things, be replaced with price affordable bio-based materials. Tartaric acid, that is its salts (tartrates), which are commercially produced for the needs of wine and food industries, are a part of the aforementioned group of products. Since tartaric acid is a relatively inexpensive, readily available, weak diprotic and aldaric acid, the question arises whether it can be used as a component of the hardener system for curing urea-formaldehyde resins that are commercially used in particleboard production. For that reason, in this paper, the influence of partial replacement of ammonium sulphate hardener with tartaric acid on the mechanical properties (bending strength, modulus of elasticity and internal bond) and free formaldehyde content of experimentally produced particleboards was examined. Boards thickness, density and moisture content were also determined. The test results suggest that tartaric acid has a beneficial effect on the above particleboard properties, but they also indicate that the extent of that effect is strongly dependent on panel press time. Key words: particleboards; hardener; tartaric acid; mechanical properties; free formaldehyde content Proces proizvodnje ploca iverica neminovno podrazumijeva upotrebu smola cija se reakcija otvrdnjavanja ostvaruje uz pomoc povisene temperature i katalizatora. Uz komercijalne katalizatore poput amonijeva sulfata, radi optimizacije procesa i racionalizacije troskova proizvodnje ploca, katalizatore je u odredenom postotku moguce zamijeniti, medu ostalim, i cijenom prihvatljivim proizvodima na biobazi. U navedenu se skupinu proizvoda svrstava i vinska kiselina, tocnije njezine soli (tartarati), komercijalno proizvedene za potrebe vinske i prehrambene industrije. S obzirom na to da je vinska kiselina relativno jeftina, lako dostupna, slaba diprotonska, aldarna kiselina, postavlja se pitanje potencijala njezine primjene u sustavima katalizatora za otvrdnjavanje urea-formaldehidne smole koja se upotrebljava u proizvodnji ploca iverica. Upravo je zato u ovom radu ispitano kako se zamjena dijela amonijeva sulfata tartaratnom kiselinom odrazava na mehanicka svojstva (savojnu cvrstocu, modul elasticnosti, vlacnu cvrstocu) i na koncentraciju slobodnog formaldehida eksperimentalno proizvedenih ploca iverica. Usto, u eksperimentu su odredene debljina i gustoca ploca te sadrzaj vode u njima. Rezultati ispitivanja upucuju na to da dodatak vinske kiseline povoljno utjece na navedena svojstva ploca, ali i na cinjenicu kako taj ucinak iznimno ovisi o vremenu presanja ploca. Kljucne rijeci: ploce iverice; katalizator; vinska kiselina; mehanicka svojstva; koncentracija slobodnog formaldehida
This paper shows the results of finite element (FE) models of three-layer particle boards. Two particle board FE models were made with differently defined structures. In the first model, the ...structure of commercial three-layer particle board is defined as single-layer with isotropic (PB-1L) properties, while in the second model, it is defined as three-layer with orthotropic properties (PB-3L). The results of FE models were compared with values obtained by testing the commercial particle board. Dimensions of FE models and applied loads were prepared according to bending strength testing mode defined according to EN 310:1993. Model comparison is based on comparison of sample deflection and von Mises stress in the middle of the sample. The analysis was done only in linear elastic region. The obtained results show that models with homogenous material (PB-1L) achieved greater agreement with measured results (deviation app. 2%), while models with three-layer material (PB-3L) displayed deviation of app. 7%. Lower agreement of results obtained for PB-3L model and measured values of commercial particle board is due to a greater number of approximations (elastic characteristics) involved in the simulation model. Despite the greater deviation, the preparation of a three-layer model would be more acceptable for the analysis of strain distribution across the cross-section of the particle board. Key words: particle board, structure, finite element (FE) model, bending properties U radu su prikazani rezultati ispitivanja simulacijskih modela troslojne ploce iverice. Izradena su dva simulacijska modela iverice razlicito definirane strukturne grade. U prvom je modelu strukturna grada komercijalne troslojne ploce iverice definirana kao jednoslojna, s izotropnim (PB-1L) svojstvima, a u drugom je modelu definirana kao troslojna ploca ortotropnih svojstava (PB-3L). Vrijednosti simulacijskih modela usporedene su s komercijalnom plocom ivericom. Dimenzije i opterecenja simulacijskih modela izradeni su prema nacinu ispitivanja savojnog opterecenja definiranoga normom EN 310:1993. Usporedba modela temelji se na usporedbi velicine progiba te von Misesovih naprezanja na sredini duzine uzorka. Analiza je provedena samo u linearno elasticnom podrucju. Dobiveni rezultati pokazuju da je za model homogene grade (PB-1L) zabiljezena veca podudarnost s mjernim rezultatima (odstupanje je iznosilo priblizno 2%), dok je za modela troslojne grade (PB-3L) odstupanje bilo nesto vece (priblizno 7%). Manja podudarnost rezultata dobivenih za model PB-3L nego za mjerne rezultate komercijalne ploce posljedica je veceg broja aproksimacija pri definiranju elasticnih svojstava ploce. Unatoc vecem odstupanju, izrada troslojnih modela bila bi prihvatljivija za analizu raspodjele naprezanja po poprecnom presjeku ploce iverice. Kljucne rijeci: ploca iverica, strukturna grada, simulacijski model, savojna svojstva
This paper investigates the influence of plywood grain direction on bending properties of a sandwich panel, as well as on stress distribution in each layer. Experimental sandwich panels (tnom= 29 mm) ...were made of two three-ply plywood panels and a rigid PVC core between them. Grain directions of plywood panels were between 0° and 90°, continuously raised by 15°. Seven models of sandwich panels were made. Bending properties of a sandwich panel was determined by three point bending method and stress in each layer was determined by using finite element method. Simulation models were developed with equal load conditions as applied during empirical measurement of bending properties of the sandwich panel. The research results show that grain direction has a great influence on bending properties of the sandwich panel, as well as on stress values in each layer. Results also indicate the importance of analyzing stress in each layer of plywood for the purpose of avoiding stress concentration in respective layers and for optimizing structural construction of the sandwich panel. Such stress analyses are not covered by standardized empirical methods for determining bending properties of sandwich panels.
The use of resins, whose curing reaction takes place by high temperature and hardener addition, is inevitably involved in particleboard manufacturing process. In addition to commercial hardeners, ...such as ammonium sulphate, with the aim of optimizing the production process and reducing the production costs, a certain percentage of hardener can, among other things, be replaced with price affordable bio-based materials. Tartaric acid, that is its salts (tartrates), which are commercially produced for the needs of wine and food industries, are a part of the aforementioned group of products. Since tartaric acid is a relatively inexpensive, readily available, weak diprotic and aldaric acid, the question arises whether it can be used as a component of the hardener system for curing urea-formaldehyde resins that are commercially used in particleboard production. For that reason, in this paper, the influence of partial replacement of ammonium sulphate hardener with tartaric acid on the mechanical properties (bending strength, modulus of elasticity and internal bond) and free formaldehyde content of experimentally produced particleboards was examined. Boards thickness, density and moisture content were also determined. The test results suggest that tartaric acid has a beneficial effect on the above particleboard properties, but they also indicate that the extent of that effect is strongly dependent on panel press time.
Proces proizvodnje ploča iverica neminovno podrazumijeva upotrebu smola čija se reakcija otvrdnjavanja ostvaruje uz pomoć povišene temperature i
katalizatora. Uz komercijalne katalizatore poput amonijeva sulfata, radi optimizacije procesa i racionalizacije troškova proizvodnje ploča, katalizatore je u određenom postotku moguće zamijeniti, među ostalim, i cijenom prihvatljivim proizvodima na biobazi. U navedenu se skupinu proizvoda svrstava i vinska kiselina, točnije njezine soli (tartarati), komercijalno proizvedene za potrebe vinske i prehrambene industrije. S obzirom na to da je vinska kiselina relativno jeftina, lako dostupna, slaba diprotonska, aldarna kiselina, postavlja se pitanje potencijala njezine primjene u sustavima katalizatora za otvrdnjavanje ureaformaldehidne smole koja se upotrebljava u proizvodnji ploča iverica. Upravo je zato u ovom radu ispitano kako se zamjena dijela amonijeva sulfata tartaratnom kiselinom odražava na mehanička svojstva (savojnu čvrstoću, modul elastičnosti, vlačnu čvrstoću) i na koncentraciju slobodnog formaldehida eksperimentalno proizvedenih ploča iverica. Usto, u eksperimentu su određene debljina i gustoća ploča te sadržaj vode u njima. Rezultati ispitivanja upućuju na to da dodatak vinske kiseline povoljno utječe na navedena svojstva ploča, ali i na činjenicu kako taj učinak iznimno ovisi o vremenu prešanja ploča.
This paper analyses individual stress components that appear in plywood panels subjected to tensile load. The analysis was conducted on a seven-layer beech plywood panel, 10.52 mm in thickness. ...Tensile load was applied on the plywood panel according to the guidelines of the European Norm HRN EN 789. Measurement results obtained by empirical measurement methods were used as the basis for developing a simulation model using the finite elements method (FEM). The study results show that there are substantial differences in the distribution of stress between the parallel- and perpendicular-oriented veneer layers. In parallel layers, the highest values of the s vm (Von Mises) stress were distributed along the narrow or central region of the test piece, which also represents the desired stress distribution. Contrary to this, in perpendicular layers, the stress distribution is concentrated at the transition between the narrow and wider areas, which indicates the presence of a significant problem in determining the tensile properties of plywood panels. The study results also indicate that the shear component t xy accounts for a significant share of the total stress and that its influence on the overall stress is significantly more pronounced in perpendicular layers. The values of the remaining two shear components t xz and t yz are virtually negligible, which is reasonable considering that the numerical model was subjected to in-plane load.
This paper presents an optimization of plywood construction aimed at achieving the desired relationship between the bending and tensile properties of plywood. The optimization is based on the ...analysis of stress and strain distribution, the values of which were computed using the finite element method. The control panel was seven-ply okoume plywood. The control plywood had approximately the same bending properties parallel and perpendicular to the face grain direction, however, the tensile strength parallel to the face grain direction was substantially lower than that perpendicular to the face grain direction. Consequently, the objective of the research was to change the values of tensile stress without changing the values of bending stress, nominal plywood thickness or total number of layers. The research results show that by changing the thickness of only three layers located closest to the middle surface of the panel, full optimization of tensile stress was achieved, while retaining the three said parameters.
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