Usporedba simulacijskih modela za ploče iverice homogene i troslojne strukturne građe

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.U radu su prikazani rezultati ispitivanja simulacijskih modela troslojne ploče iverice. Izrađena su dva simulacijska modela iverice različito definirane strukturne građe. U prvom je modelu strukturna građa komercijalne troslojne ploče iverice definirana kao jednoslojna, s izotropnim (PB-1L) svojstvima, a u drugom je modelu definirana kao troslojna ploča ortotropnih svojstava (PB-3L). Vrijednosti simulacijskih modela uspoređene su s komercijalnom pločom ivericom. Dimenzije i opterećenja simulacijskih modela izrađeni su prema načinu ispitivanja savojnog opterećenja definiranoga normom EN 310:1993. Usporedba modela temelji se na usporedbi veličine progiba te von Misesovih naprezanja na sredini dužine uzorka. Analiza je provedena samo u linearno elastičnom području. Dobiveni rezultati pokazuju da je za model homogene građe (PB-1L) zabilježena veća podudarnost s mjernim rezultatima (odstupanje je iznosilo približno 2 %), dok je za modela troslojne građe (PB-3L) odstupanje bilo nešto veće (približno 7 %). Manja podudarnost rezultata dobivenih za model PB-3L nego za mjerne rezultate komercijalne ploče posljedica je većeg broja aproksimacija pri definiranju elastičnih svojstava ploče. Unatoč većem odstupanju, izrada troslojnih modela bila bi prihvatljivija za analizu raspodjele naprezanja po poprečnom presjeku ploče iverice

Effect of shear components on stress values in plywood panel subjected to tensile load

U radu su analizirane pojedine komponente naprezanja koje se pojavljuju pri vlačnom opterećenju furnirske ploče. Analiza je provedena na sedmeroslojnoj bukovoj furnirskoj ploči debljine 10,52 mm. Vlačno opterećenje furnirske ploče izvedeno je prema smjernicama europske norme HRN EN 789. Mjerni rezultati dobiveni empirijskim metodama mjerenja upotrijebljeni su kao osnova za postavljanje simulacijskog modela metodom konačnih elemenata (FEM). Rezultati istraživanja pokazuju da postoji velika razlika u distribuciji naprezanja izme|u paralelno i okomito orijentiranih listova furnira. U paralelnih slojeva najveći su iznosi s vm (Von Mises) naprezanja distribuirani po užem, tj. središnjem djelu epruvete, što je ujedno poželjna raspodjela naprezanja. Za razliku od toga, u okomitih slojeva koncentracija naprezanja nalazi se upravo na prijelazu između širega i užeg dijela, što upućuje na postojanje specifičnog problema pri određivanju vlačnih svojstava furnirske ploče. Rezultati istraživanja također pokazuju da smicajna komponenta t xy ima znatan udio u analizi ukupnih naprezanja te da je njezin utjecaj na ukupna naprezanja znatno izraženiji u okomito orijentiranih listova furnira. Ostale dvije komponente smicajnih naprezanja, t xz i t yz, imaju praktički zanemarive iznose, što je i posve razumljivo jer se pri analizi djelovalo opterećenjem u ravnini.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, 10.52mmin 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

Mehanička svojstva i sadržaj slobodnog formaldehida ploča iverica izrađenih primjenom katalizatora na bazi amonijeva sulfata djelomično zamijenjenoga vinskom kiselinom

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

Influence of plywood grain direction on sandwich panel bending properties

U radu je istraživan utjecaj varijacije kuta vlakanaca u furnirskoj ploči na savojna svojstva sendvič-ploče te na naprezanja u pojedinim slojevima. Eksperimentalne sendvič-ploče (tnom= 29 mm) izrađene su od dvije troslojne furnirske ploče i krute PVC srednjice između njih. Kutovi vlakanaca vanjskih slojeva furnirskih ploča kretali su se u rasponu od 0 do 90° kontinuirano rastući po 15°. Ukupno je izrađeno sedam modela sendvič-ploča. Savojna svojstva sendvič ploče određena su metodom s tri uporišne točke, a naprezanja u njihovim pojedinim slojevima dobivena su uporabom računalnoga simulacijskog programa, tj. metodom konačnih elemenata. Simulacijski modeli kreirani su prema jednakim uvjetima opterećenja kao i pri empirijskom mjerenju savojnih svojstava eksperimentalne sendvič-ploče. Rezultati istraživanja pokazuju da varijacija kuta vlakanaca ima velik utjecaj na promjenu savojnih svojstava sendvič-ploče, kao i na veličinu naprezanja u pojedinim njezinim slojevima. Rezultati također upućuju na važnost analiziranja naprezanja u svakom sloju furnirske ploče, radi izbjegavanja koncentracije naprezanja u pojedinim slojevima, s ciljem optimizacije strukturne konstrukcije sendvič-ploče. Takve vrste analize naprezanja ne obuhvaćaju se standardiziranim empirijskim metodama određivanja savojnih svojstava sendvič- ploče.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

Utjecaj modifikacije karbamid-formaldehidne smole s utekućenim drvom na svojstva ploča iverica

In the group of wood composite materials from fragmented wood, “valueless” biomass and residues are converted to valuable material. The problem of application of other necessary synthetic chemical components, particularly adhesives, which are essential non-wooden components in wood composite production (mainly oil derivatives), has been the subject of many scientific researches that gave positive results. Further to the above, many researches are focused on wood liquefaction and liquefied wood (LW) application as potential adhesives, related to gluing solid particles with liquid wood. Based on previous studies, maximum attention was given to LW applications in modification of phenol-formaldehyde (PF) resins, polyurethanes, saturated and unsaturated polyesters, isocyanates and epoxy resins, and their further application in novel material types. It is evident that because of their “inferior” properties, researches on urea-formaldehyde (UF) resins failed, as well as researches on preparations of UF base adhesives modified with LW. Therefore, the subject of this study was to research the influence of specific experimental parameters on liquefied wood compatibility with UF resins, its influence on polymer structure and adhesion-cohesion properties of modified UF adhesives, and particleboard physical mechanical properties and formaldehyde emission. The results showed that in all cases of UF resin replacement with LW, there was a significant reduction of formaldehyde emission in particleboards, which is one of the aims of this study. Furthermore, it was shown that LW does not show any polymer or adhesion properties, and in this regard laboratory synthesis was conducted of designed liquefied wood-formaldehyde (LWF) resin and LW was synthesized with formalin. With the LWF resin modification of particleboards, results showed increased mechanical properties and free formaldehyde emission as a direct influence of added formalin. To reduce the increased free formaldehyde emission, LWF resin was synthesized analogously to the production of PF resin novolak type, and prepared based on the percentage of lignin content (because of polyphenol properties) in investigated wood species (black poplar), which was applied in further researches.U drvnim kompozitnim materijalima od usitnjenog drva „bezvrijedna“ se biomasa i ostaci nakon uporabe pretvaraju u vrijedan materijal. Problem primjene ostalih nužnih sintetičkih kemijskih komponenata, osobito ljepila koja su esencijalne nedrvne komponente u proizvodnji drvnih kompozita (uglavnom naftni derivati), već je odavno predmetom znanstvenih istraživanja koja daju pozitivne rezultate. Vezano za navedenu problematiku, brojna su istraživanja usmjerena na utekućenje drva i primjenu utekućenog drva kao ljepila, odnosno na lijepljenje krutih drvnih čestica tekućim drvom. Na temelju dosadašnjih istraživanja, najviše je pozornosti pridano primjeni utekućenog drva u modifikaciji fenol-formaldehidnih (FF) smola, poliuretana, zasićenih i nezasićenih poliestera, izocijanata i epoksidnih smola te njihovoj daljnjoj primjeni u novim vrstama materijala. Evidentno je da su zbog njihovih „lošijih“ svojstava, istraživanja karbamid-formaldehidnih (KF) smola modificiranih utekućenim drvom izostala. Stoga je predmet istraživanja ovog rada utjecaj eksperimentalnih parametara na kompatibilnost utekućenog drva s KF smolama, utjecaj na polimernu strukturu i adhezijsko-kohezijska svojstva modificiranih KF ljepila te na fizikalno-mehanička svojstva i emisiju formaldehida ploča iverica. Rezultati su pokazali da je u svim primjerima zamjene KF smole UD-om znatno smanjena emisija formaldehida u pločama ivericama, što je i jedan od ciljeva ovog rada. Nadalje, pokazalo se da UD ne pokazuje polimerna ni vezivna svojstva, te je u tom smislu provedena laboratorijska sinteza projektirane utekućeno drvo-formaldehidne (UDF) smole, odnosno UD je sintetiziran formalinom. Modifikacijom ploča iverica UDF smolom, rezultati su pokazali povećana mehanička svojstva i emisiju slobodnog formaldehida kao izravan utjecaj dodanog formalina. Da bi se smanjila povećana emisija slobodnog formaldehida, UDF smola sintetizirana je analogno proizvodnji FF smola novolačnog tipa, te je pripravljena na temelju postotka sadržaja lignina (zbog polifenolnih svojstava) u istraživanoj vrsti drva (topolovini), te je upotrijebljena u daljnjim istraživanjima

The Quality of Fired Aleppo Pine Wood (Pinus Halepensis Mill.) Biomass for Biorefinery Products

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

Development options of composite materials from wood particles in the Republic of Croatia

Republika Hrvatska je gotovo u potpunosti zanemarila vrlo važan segment razvoja drvnog gospodarstva, a to su drvni kompoziti od usitnjenog drva. S obzirom na izrazito veliku sirovinsku bazu za takvu proizvodnju (oko 3,76 milijuna m3 godi{nje), nedopustivo je da se u Hrvatskoj proizvode samo troslojne ploče iverice volumena oko 73 000 m3 u 2004. godini, a da proizvodnja MDF-a, OSB-a i ostalih vlaknatica uopće ne postoji. Na europskoj razini bilježi se stalan porast proizvodnje kompozita od usitnjenog drva. Države maksimalno iskorištavaju komparativne prednosti vlastitoga šumskog potencijala u proizvodnji kompozitnih materijala od usitnjenog drva. Tako Irska maksimizacijom iskorištenja šumske biomase postiže izrazito veliku proizvodnju usprkos relativno malom šumskom potencijalu. Hrvatska proizvodnja iznosi samo 0,16 % europske, a hrvatski izvoz samo 0,22 % europskoga. Prema površini šuma po stanovniku, Hrvatska pripada u sam europski vrh, a prema proizvodnji kompozita od usitnjenog drva po stanovniku i po opsegu proizvodnje ubraja se među najzaostalije zemlje Europe. Potrošnja je 3,4 puta veća od proizvodnje, pa se uvozi čak 213 000 m3 drvnih kompozita od usitnjenog drva. Prema prognozama FAO-a, u Hrvatskoj se ne očekuju gospodarske mjere za razvoj drvnih materijala koji se proizvode primjenom suvremenih sofisticiranih tehnologija. Na Hrvatsku se u budućnosti gleda kao na zemlju koja će biti isključivo izvoznik drvne sirovine.The Republic of Croatia had almost entirely neglected an important development segment of wood economy, and namely wood composites made from wood particles. In respect to distinctively large feedstock base for the above production (about 3.76 million m3 per year), it is inadmissible that particleboards production in Croatia amounted to about 73 000m3 in 2004, while MDF, OSB and other fibreboards production overall does not exist at all. In the European framework, an increasing trend has been recorded of production of composites from wood particles, and countries make maximum use of comparative advantages of their own forest potential in the production of composite materials from wood particles. Thus, Ireland achieves extremely large production by maximum utilisation of forest biomass despite its rather small forest potential. Croatian production is only 0.16%of European production, and Croatian export is only 0.22%of European export. According to forest area per capita, Croatia is highly ranked in Europe, but according to production of composites from wood particles and production volume per capita it is ranked among the most underdeveloped European countries. Consumption is 3.4 times higher than production, so our import of wood composites made from wood particles amounts to as much as 213 000 m3. According to FAO forecasts, no economy measures are expected in Croatia for the development of wood material, which could be produced with the application of modern sophisticated technologies. In future, Croatia is seen as a country that will exclusively export wood as raw material

The Quality of Fired Aleppo Pine Wood (Pinus Halepensis Mill.) Biomass for Biorefinery Products

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

Establishment and Development of Croatian Quality Control System for Wood-Based Panels in Accordance with European Technical Regulations

Nakon osamostaljenja Republike Hrvatske (RH) osnovni gospodarski cilj bio je uključenje na međunarodno tržište i ulazak u Europsku uniju (EU). S razvojem vanjskotrgovinskih odnosa bilo je nužno uspostaviti sustav kontrole kvalitete drvnih ploča, a taj proces počinje u sklopu Državnog zavoda za normizaciju i mjeriteljstvo (DZNM). Pod ingerencijom DZNM-a provodi se edukacija, ovlašćivanje, osnivanje i rad tehničkih odbora (TO), donose se novi propisi te obavlja implementacija europskoga tehničkog zakonodavstva. Prema Naredbi o obaveznom certificiranju ploča iverica za opću uporabu i graditeljstvo (Sl. list 61/83), DZNM ovlastio je godine 1995. Šumarski fakultet za obavljanje poslova certifi ciranja ploča iverica. Ministarstvo gospodarstva također se uključilo u izgradnju sustava, pa je krajem 1998. godine na području drvnih ploča izgrađen respektabilan sustav kontrole kvalitete. Sljedeći korak bila je izrada tehničkih propisa i implementacija europskih normi. No tada slijede potezi zbog kojih dolazi do potpunog raspada sustava, koji početkom 2004. godine više praktički ne postoji. Ministarstvo gospodarstva i Vlada Republike Hrvatske ukidaju sve odluke o kontroli kvalitete drvnih ploča, osim obveznog certifi ciranja ploča iverica, koje je pod ingerencijom DZNM-a, a on prestaje raditi tijekom 2003. godine. Ministarstvo zaštite okoliša, prostornog uređenja i graditeljstva (MZOPUG) kao nadležna institucija preuzima 2005. godine potvrđivanje ploča iverica, a potom u tehničku regulativu za graditeljstvo uvodi europske norme za drvne ploče. No potvrđivanje ploča iverica i dalje se obavlja prema normama bivše države. U pokušaju donošenja Tehničkog propisa za drvne ploče, koji je iniciralo Ministarstvo regionalnog razvoja, šumarstva i vodnoga gospodarstva (MRRŠVG), nije postignut konsenzus zbog primjene drvnih ploča i za opće uporabe i na području graditeljstva.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 to establish 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

Influence of Synthetic Fibers Angle Orientation on Bending Properties of Composite Plywood

U radu je istraživan utjecaj varijacije kuta orijentacije karbonskih vlakana i količine karbonskih vlakana po snopu pletiva na savojna svojstva furnirske ploče. Za tu su namjenu izrađeni modeli epruveta defi nirani kao višeslojni kompoziti sastavljeni od karbonskih vlakana i furnira, pri čemu su slojevi vlakana umetnuti u drugu i treću sljubnicu, s varijacijama kuta po 15°. Od dobivenih rezultata analizirana su naprezanja i pripadajuće deformacije u relevantnim slojevima te progib kompozitnih furnirskih ploča. Nakon analize rezultata vidljiv je izrazit utjecaj varijacije kuta orijentacije karbonskih vlakana na svojstva kompozitnih furnirskih ploča pri savijanju odnosno na iznose naprezanja i deformacija, te je on najpovoljniji kada su karbonska vlakna orijentirana pod kutom od 0°, a u dvosmjernih karbonskih vlakana (BCF) i pri kutu orijentacije od 90°. Najnepovoljniji kut orijentacije karbonskih vlakana jest kada su dvosmjerna karbonska vlakna (BCF) orijentirana pod kutom od 45°, dok za jednosmjerna karbonska vlakna (UCF) taj kut orijentacije iznosi 65°. Veća količina karbonskih vlakana po snopu pletiva pozitivno djeluje na smanjenje naprezanja i pripadajućih deformacija u slojevima furnira te povećava krutost furnirske ploče.This paper presents the results of research on carbon fiber angle orientation and quantity of carbon fibers 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