Toplinska degradacija čvrstoće lijepljenja ploče od uslojenog drva jasike

The objective of this research was to study the effect of exposure time on the bonding strength of aspen plywood at elevated temperatures. The plywood samples were manufactured under laboratory conditions using two types of adhesive: urea-formaldehyde (UF) and phenol-formaldehyde (PF). The plywood samples were tested after exposure to three different temperatures (150 °C, 200 °C and 250 °C) and three exposure time levels (1, 2 and 3 hours) at each temperature. Additionally, a set of control samples was tested at room temperature. The quality of bonding was assessed by shear strength test in compliance with the requirements of the standard EN 314-1. The mass and density losses as well as colour changes of the plywood samples were also determined. The findings of this study indicated that exposure of plywood panels to elevated temperature caused significant degradation of their bonding strength. PF plywood samples lost 63.2 % of their initial strength after 3 h of exposure at 250 °C, while UF samples lost 65.9 % of their initial strength already after 3 h of exposure at the temperature of 200 °C. Statistical regression-based models were also developed for predicting the loss of plywood bonding strength as functions of mass and density losses and total colour difference. As the mass/density losses or total colour difference of panels increased, the losses in bonding strength increased too.Cilj ovog istraživanja bio je ispitati utjecaj vremena izlaganja toplini na čvrstoću lijepljenja ploča od uslojenog drva jasike. Uzorci ploča od uslojenog drva proizvedeni su u laboratorijskim uvjetima uporabom dvije vrste ljepila: urea-formaldehidnog (UF) i fenol-formaldehidnog (PF) ljepila. Uzorci ploča od uslojenog drva ispitani su nakon izlaganja različitim temperaturama (150 °C, 200 °C i 250 °C) tijekom različitog vremena izlaganja (1, 2 i 3 sata). Usto, skupina kontrolnih uzoraka ispitana je pri sobnoj temperaturi. Kvaliteta lijepljenja ocijenjena je testom smične čvrstoće u skladu sa zahtjevima norme EN 314-1. Također, određeni su gubitci mase i smanjenje gustoće, kao i promjena boje uzoraka ploča od uslojenog drva. Rezultati ove studije pokazali su da izlaganje ploča od uslojenog drva povišenoj temperaturi uzrokuje znatno smanjenje njihove čvrstoće lijepljenja. Uzorci ploča od uslojenog drva zalijepljeni PF ljepilom izgubili su 63,2 % svoje početne čvrstoće nakon tri sata izlaganja na 250 °C, dok su uzorci ploča od uslojenog drva zalijepljeni UF ljepilom izgubili 65,9 % početne čvrstoće već nakon tri sata izloženosti temperaturi 200 °C. Nadalje, razvijeni su statistički regresijski modeli za predviđanje gubitka čvrstoće lijepljenja ploča od uslojenog drva kao funkcije gubitka mase, smanjenja gustoće i ukupne razlike u boji. Kako se povećavao gubitak mase, smanjivala gustoća ili povećavala ukupna razlika u boji ploča, tako su se povećavali i gubitci čvrstoće lijepljenja

Lagane drvno-plastične kompozitne ploče: mogućnost proizvodnje i svojstva

Usually the conventional wood plastic composites (WPC) are produced with the densities of approximately 800-1000 kg/m3. The possibility of manufacture and properties of the lightweight fl at pressed WPC using expanded polystyrene was described in this study. The shredded recycled low density polyethylene (rLDPE), wood particles (WP) and expanded polystyrene (EPS) were used for making one-layer lightweight WPC boards (non-laminated and laminated). Bending strength (MOR), modulus of elasticity (MOE), tensile strength perpendicular to the plane of the board (IB) and thickness swelling after immersions in water for 2 hours (TS/2h) and 24 hours (TS/24h) of the lightweight WPC boards were evaluated. It was established that the EPS content and boards’ density as well as the lamination process have a significant impact on the properties of lightweight WPC boards. Thus, it was found that the use of expanded polystyrene enables the production of lightweight WPC within a density range of 500-700 kg/m3, which is almost twofold less than the density of the conventional WPC. The results of research have shown that the bending strength, modulus of elasticity and internal bond strength of non-laminated lightweight WPC boards meet the requirements (for lightweight particleboards) of EN 16368 (type LP1) and ANSI A208.1 (types LD-1 and LD-2) standards. The bending strength and modulus of elasticity of laminated lightweight WPC boards meet the requirements of ISO 13894-2.Konvencionalni drvno-plastični kompoziti (WPC) obično se proizvode s gustoćom od približno 800 – 1000 kg/m3. Tema ove studije jest mogućnost proizvodnje lakih WPC ploča proizvedenih dodatkom ekspandiranog polistirena i njihova svojstva. Za izradu jednoslojnih laganih WPC ploča (nelaminiranih i laminiranih) upotrijebljeni su: usitnjeni reciklirani polietilen niske gustoće (rLDPE), drvne čestice (WP) i ekspandirani polistiren (EPS). Istraživanjem su određena ova svojstva laganih WPC ploča: čvrstoća na savijanje (MOR), modul elastičnosti (MOE), vlačna čvrstoća okomito na ravninu ploče (IB) i debljinsko bubrenje nakon uranjanja ploča u vodu u trajanju 2 sata (TS/2 h) i 24 sata (TS/24 h). Utvrđeno je da udio EPS-a i gustoća ploča, kao i proces laminiranja imaju značajan utjecaj na svojstva laganih WPC ploča. Tako je utvrđeno da upotreba ekspandiranog polistirena omogućuje proizvodnju laganih WPC ploča u rasponu gustoće 500 – 700 kg/m3, što je gotovo dvostruko manje od gustoće konvencionalnih WPC ploča. Rezultati istraživanja pokazali su da čvrstoća na savijanje, modul elastičnosti i čvrstoća unutarnje veze nelaminiranih laganih WPC ploča udovoljavaju zahtjevima (za lagane ploče iverice) standarda EN 16368 (tip LP1) i ANSI A208.1 (tip LD-1 i LD-2). Čvrstoća na savijanje i modul elastičnosti laminiranih laganih WPC ploča udovoljavaju zahtjevima norme ISO 13894-2

Svojstva modificiranoga fenol-formaldehidnog ljepila za furnirske ploče proizvedene od furnira s visokim sadržajem vode

This paper presents the results of laboratory investigations of bonding high moisture content (15 %) birch veneers (Betula pubescens Ehrh.) with the use of modifi ed phenol-formaldehyde (PF) resin. Wheat starch, rye flour, resorcinol and phenol-resorcinol-formaldehyde resin were chosen as modifying agents. Dynamic viscosity, hydrogen ions concentration, solid content, curing time, pot life of developed adhesive compositions and shear strength of plywood samples were evaluated. ANOVA analysis has shown that type, mixture and content of modifying agents affect significantly the mechanical performance of plywood panels. The obtained results of shear strength values were above the standard requirements (1 N/mm2), and the properties of samples met the European standard EN 314-2 for gluing quality of class 3 and such plywood panels can be used in exterior conditions.U radu su prikazani rezultati laboratorijskih istraživanja furnirskih ploča proizvedenih od furnira od drva breze (Betula pubescens Ehrh.) s visokim sadržajem vode (15 %) i uz primjenu modifi ciranoga fenolformaldehidnog PF) ljepila. Pšenični škrob, raženo brašno, rezorcinol i fenol-rezorcinol-formaldehidna smola izabrani su kao sredstva za modifi ciranje. Analizirane su dinamička viskoznost, koncentracija vodikovih iona, sadržaj krute tvari, vrijeme otvrdnjavanja, otvoreno vrijeme smjese za lijepljenje i smicajna čvrstoća uzoraka furnirskih ploča. ANOVA analiza pokazala je da vrsta, smjesa i težinski udjel sredstava za modifi kaciju ljepila značajno utječu na mehanička svojstva furnirskih ploča. Dobivene vrijednosti čvrstoće smicanja iznad su standardnih zahtjeva (1N/mm2), a svojstva uzoraka furnirskih ploča zadovoljavaju europsku normu EN 314-2 za kvalitetu lijepljenja klase 3 koja se odnosi na furnirske ploče koje se mogu rabiti u vanjskim uvjetima

Procjena dinamičkoga dodirnog kuta površine toplinski komprimiranoga bukova furnira

Rotary-cut veneer is characterised by two sides, namely loose and tight surface, which have different properties. The information concerning dynamic contact angle behaviour of veneer sides plays an important role in efficient use of veneer. Therefore, the objective of this study was to investigate the influence of different compression temperatures and pressures on various wetting behaviour of loose and tight sides of birch veneer. Veneer sheets were compressed in a hot press at temperatures of 150 and 180 °C using seven pressure levels from 0.5 to 3.5 MPa. Wettability of loose and tight sides of thermally compressed veneer was evaluated by measuring the dynamic contact angle with distilled water. The results showed that thermal compression decreased the surface wettability of both loose and tight sides of the samples, especially for veneer samples compressed at a temperature of 180 °C. Tight side of the samples had lower wettability than loose side, even after thermal compression. Therefore, adhesive or any kind of finishing can be applied to both sides of thermally compressed veneer sheets without having any adverse influence on not only the bonding quality but also the whole finishing process.Za ljuštene je furnire karakteristično da njihove dvije površine, tzv. otvorena i zatvorena strana, imaju različita svojstva. Za učinkovitu uporabu furnira važni su podatci o ponašanju dinamičkoga dodirnog kuta površina furnira. Stoga je cilj istraživanja bio ispitati utjecaj različitih temperatura i tlakova kompresije na ponašanje površina furnira pri kvašenju. Listovi furnira komprimirani su u vrućoj preši pri temperaturi 150 i 180 °C te uz primjenu sedam različitih tlakova, od 0,5 do 3,5 MPa. Ispitana je sposobnost kvašenja površine na obje strane toplinski komprimiranog furnira mjerenjem dinamičkoga dodirnog kuta primjenom destilirane vode. Rezultati su pokazali da toplinsko komprimiranje smanjuje površinsko kvašenje na obje strane furnira, posebice na uzorcima furnira koji su komprimirani pri temperaturi 180 °C. Zatvorena strana uzoraka furnira pokazala je manju sposobnost kvašenja nego otvorena, čak i nakon toplinske kompresije. Stoga se ljepilo ili neko drugo sredstvo za završnu obradu furnira može nanositi na obje strane toplinski komprimiranog furnira bez ikakve opasnosti od nepovoljnog utjecaja na kvalitetu lijepljenja i završnu obradu furnira

The influence of short-term thermo-mechanical densification on the surface wettability of wood veneers

The study investigated the effects of short-term thermo-mechanical (STTM) densification temperature and pressure on changes in surface wettability of alder (Alnus glutinosa), beech (Fagus sylvatica), birch (Betula verrucosa) and pine (Pinus sylvestris) wood veneer. Veneer sheets were densified using pressure levels of 4 MPa, 8 MPa and 12 MPa at three temperatures: 100°C, 150°C and 200°C for a short time of 4 min. Wettability was determined by measuring contact angles with distilled water. The results were compared with those of non-densified veneers. The results showed that in arelatively short process time wettability can be changed significantly. The wettability analysis showed that STTM-densified veneer surfaces became more hydrophobic, which indicates poor wettability. However, it was found that even STTM densification of veneers provides stable properties; in particular, contact angle values were stable for 24 hours after densification, which is an important consideration for industrial applications. The effect of temperature on the contact angle was more evident than thatof pressure. Linear correlations were found between contact angle and both mass loss and compression ratio for all investigated wood species. These findings may be used to provide initial data for adhesive/ coating application processes in woodworking industry

Effects of Wood Particles from Deadwood on the Properties and Formaldehyde Emission of Particleboards

The volume of deadwood increases annually because of changes in environmental, climatic, and hydrological conditions. On the other hand, during the last decade, manufacturers of wood-based boards have been facing an acute problem of a shortage of conventional raw materials. The purpose of this study was to evaluate the possibility of using wood particles from deadwood in the production of particleboards. Three-layer particleboards with different content of deadwood particles (0%, 25%, 50%, 75%, 100%) were produced. Conventional urea-formaldehyde (UF) resin was used for gluing the particles. The physical and mechanical properties of the boards, as well as the formaldehyde content in the boards, were determined. In addition, the effect of adding melamine-urea-formaldehyde (MUF) resin to UF adhesive on the properties of the boards was investigated. Replacing conventional sound wood particles with deadwood particles leads to deterioration of the physical and mechanical properties of the boards. The boards from deadwood particles absorb more water and swell more. The bending strength (MOR), modulus of elasticity in bending (MOE), and internal bonding (IB) values for boards with 100% deadwood particles are reduced by 26.5%, 23.1%, and 72.4%, respectively, compared to reference boards from sound wood particles. Despite this, a significant advantage is that boards made from 100% deadwood particles are characterized by 34.5% less formaldehyde content than reference boards made from conventional sound wood. Moreover, adding 3% of MUF resin to UF adhesive increases MOR, MOE, and IB by 44.1%, 43.3%, and 294.4%, respectively.O

Characterization of randomly oriented strand boards manufactured from juvenile wood of underutilized wood species

The wood-based panel industry in Europe, which is dominated by the use of Norway spruce, will face new challenges due to environmental changes and the bark-beetle calamity, which started a new era of forestry. To explore the possibility of replacing spruce with other wood species, juvenile wood of nine underutilized wood species (Scots pine, European larch, poplar, willow, alder, birch, European beech, English oak and hornbeam) were used to make randomly oriented strand boards (OSBs). Single-layer OSBs were produced with 3% pMDI resin and 0.5% wax. Standard physical and mechanical properties were measured. The bending strength (MOR) values showed that there was no statistically significant difference between the values for, on the one hand, spruce (34.6 MPa) and, on the other, larch (25.9 MPa), poplar (25.2 MPa), willow (27.8 MPa), alder (34.3 MPa) or birch (27.1 MPa). A similar trend was found for the boards modulus of elasticity (MOE). The highest MOE values of 5,185 MPa and 4,472 MPa were found for spruce and alder, respectively. There was no significant difference between spruce and other wood species in internal bond strength. Boards made from high-density wood species showed better physical performance, whereas those made from low-density wood species (except pine) gave better mechanical properties. Strand-generalized characteristics, such as the slenderness ratio and specific surface, were analyzed for all investigated physical and mechanical properties. European larch, poplar, willow, and alder are potential wood species for manufacturing OSBs in future without mixing species, as they can replace spruce in the wood-based panel industry.OA-hybri

Utjecaj različitih vrsta materijala za oblaganje na svojstva ravnih prešanih drvno-plastičnih kompozitnih ploča

The effects of different kinds of coating materials on the properties of flat pressed wood plastic composite (WPC) panels were studied in this work. Rotary-cut birch veneer, sliced oak veneer, phenolic impregnated paper, polyethylene (PE) film, and recycled polyethylene (rPE) layer were used as coating materials. One or two-side coating of WPC panels was carried out simultaneously with their fl at pressing. No coupling agents were used for production of WPC. It was found that properties of fl at pressed WPC panels improved by coating with all investigated coating materials. The highest values of modulus of rupture (MOR) were observed in WPC panels coated with rotary-cut birch veneer and MOR values were higher in along direction than in across direction of veneer fibers. The highest values of water resistance were observed in WPC coated with PE fi lm or rPE layer. Coating of WPC with natural veneer leads to the decreasing of water resistance. Besides, water resistance of WPC coated with one side of natural veneer was higher in comparison with two side coated WPC panels with natural veneer. The two-side coating of WPC with phenolic impregnated paper, PE film or rPE layer leads to the decreasing of water absorption and thickness swelling.U radu su predstavljeni rezultati istraživanja utjecaja različitih vrsta materijala za oblaganje na svojstva ravnih prešanih drvno-plastičnih kompozitnih (WPC) ploča. Za oblaganje ploča primijenjeni su ljušteni brezov furnir, rezani hrastov furnir, fenolni impregnirani papir, polietilenska (PE) folija i reciklirani polietilen (RPE). Oblaganje WPC ploča s jedne ili s obje strane obavljeno je istodobno s prešanjem ploča. Za proizvodnju ploča nisu upotrebljavana sredstva za kondenzaciju. Utvrđeno je da su svojstva ravnih prešanih WPC ploča poboljšana oblaganjem bilo kojim navedenim ispitivanim materijalom. Najveće vrijednosti modula loma (MOR) zabilježene su za WPC ploče obložene ljuštenim brezovim furnirom. MOR vrijednosti bile su veće uzduž vlakanaca furnira nego okomito na njihov smjer. Najveća otpornost na vodu zabilježena je u ploča obloženih polietilenskom folijom i recikliranim polietilenskim slojem. Oblaganje WPC ploče prirodnim furnirom utječe na smanjenje otpornosti na vodu. Osim toga, otpornost na vodu WPC ploča obloženih s jedne strane prirodnim furnirom bila je veća nego WPC ploča obloženih prirodnim furnirom s obje strane. Dvostrano oblaganje WPC ploča fenolnim impregniranim papirom, polietilenskom folijom i recikliranim polietilenskim slojem pridonosi smanjenju apsorpcije vode i debljinskog bubrenja

Effects of Wood Particles from Deadwood on the Properties and Formaldehyde Emission of Particleboards

The volume of deadwood increases annually because of changes in environmental, climatic, and hydrological conditions. On the other hand, during the last decade, manufacturers of wood-based boards have been facing an acute problem of a shortage of conventional raw materials. The purpose of this study was to evaluate the possibility of using wood particles from deadwood in the production of particleboards. Three-layer particleboards with different content of deadwood particles (0%, 25%, 50%, 75%, 100%) were produced. Conventional urea-formaldehyde (UF) resin was used for gluing the particles. The physical and mechanical properties of the boards, as well as the formaldehyde content in the boards, were determined. In addition, the effect of adding melamine-urea-formaldehyde (MUF) resin to UF adhesive on the properties of the boards was investigated. Replacing conventional sound wood particles with deadwood particles leads to deterioration of the physical and mechanical properties of the boards. The boards from deadwood particles absorb more water and swell more. The bending strength (MOR), modulus of elasticity in bending (MOE), and internal bonding (IB) values for boards with 100% deadwood particles are reduced by 26.5%, 23.1%, and 72.4%, respectively, compared to reference boards from sound wood particles. Despite this, a significant advantage is that boards made from 100% deadwood particles are characterized by 34.5% less formaldehyde content than reference boards made from conventional sound wood. Moreover, adding 3% of MUF resin to UF adhesive increases MOR, MOE, and IB by 44.1%, 43.3%, and 294.4%, respectively

Environmentally-Friendly High-Density Polyethylene-Bonded Plywood Panels

Thermoplastic films exhibit good potential to be used as adhesives for the production of veneer-based composites. This work presents the first effort to develop and evaluate composites based on alder veneers and high-density polyethylene (HDPE) film. The effects of hot-pressing temperature (140, 160, and 180 °C), hot-pressing pressure (0.8, 1.2, and 1.6 MPa), hot-pressing time (1, 2, 3, and 5 min), and type of adhesives on the physical and mechanical properties of alder plywood panels were investigated. The effects of these variables on the core-layer temperature during the hot pressing of multiplywood panels using various adhesives were also studied. Three types of adhesives were used: urea–formaldehyde (UF), phenol–formaldehyde (PF), and HDPE film. UF and PF adhesives were used for the comparison. The findings of this work indicate that formaldehyde-free HDPE film adhesive gave values of mechanical properties of alder plywood panels that are comparable to those obtained with traditional UF and PF adhesives, even though the adhesive dosage and pressing pressure were lower than when UF and PF adhesives were used. The obtained bonding strength values of HDPE-bonded alder plywood panels ranged from 0.74 to 2.38 MPa and met the European Standard EN 314-2 for Class 1 plywood. The optimum conditions for the bonding of HDPE plywood were 160 °C, 0.8 MPa, and 3 min