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

Reading experimental literature : unreadability, discomfort and reading strategies

Peer reviewe

‘We’ and the Language of War : On the Poetry of Serhiy Zhadan

Non peer reviewe

Comparative study of the rheological and thermal properties of the formol phenol novolac epoxy and those of the model resin diglycidylether of bisphenol A (DGEBA).

The objective of this work is to study the thermal and rheological properties of thermoset polymers, epoxy polymers cases, such as novolac and bisphenol A diglycidylether (BADGE). The macroscopic characterization epoxy resins Diglycidyl ether of bisphenol A and phenol formaldehyde epoxy novolac was made by the method of analysis of the rheological behavior of standard matrices before their cross-linking in order to determine their storage conditions. Both thermosetting matrices showed high mechanical stability in view of temperature, time and constraints. This leads us to assume that they can be stored to standard thermodynamic conditions without fear of cross-linking. The viscosimetric study shows that a good storage of the resin (non-self-cross-linkable) leads to a homogeneous mixture of the composite after the addition of the hardener. Subsequently, these two resins have been an objective of two cross-linking reactive systems in the presence of an aromatic diamine (MDA) Epoxy / Amine (DGEBA / MDA) and epoxy novolac / MDA). Subsequently, we compared their thermal stability. Thermo-gravimetric study shows firstly, that standard resins are thermodynamically stable, and then epoxy novolac systems / MDA and DGEBA / MDA. Furthermore, the thermal behavior of novolac / MDA system is better than the DGEBA / MDA system

Synthesis and Microscopic Characterization Of The Urea Macromolecule Tetraglycidyl Ether Of Bisphenol A (TGEUBA) : Optimizating The Parameters By The Experimental Design And The Formulation of A Nanocomposite By Trisodium Phosphate And TGEMDA.

The main objective of our work is to synthesize the standard matrix and formulate it by the tri-sodium phosphate: Urea tetraglycidyl ether of Bisphenol A (TGEUBA). We obtained the precursor molecule of the epoxy matrix Urea tetrabisphénol A (Utba) and then we tended towards the functionalization of the latter with epichlorohydrin. Microscopic characterization of the TGEUBA resin was obtained by using the Fourier Transform Infrared (FTIR) and was confirmed by the nuclear magnetic resonance (NMR). The dispersion power of the tri-sodium phosphate in the presence of an adjuvant in the TGEMDA TGEUBA prepolymer crosslinked and formulated at different percentages (0%, 10% PTS TGEMDA 10% and 10% TSP + 10% TGEMDA) was followed up by using the Scanning Electron Microscope (SEM). Moreover, we have optimized the synthesis with the erection of the TGEUBA by the method of experimental design (Nimrod W)

The optimization of experimental parameters of the synthetic polymer containment in the conditioning of solid radioactive wastes used in the purification of the circuits of TIGA Mark II reactor

In this study, we treated the conditioning of radioactive wastes by the method of management [1] using the ion exchange resin (IER) as radioactive waste [1, 2, 3]. From the values ​​obtained by experimental studies [2], we were able to optimize the conditioning process by the experiments plan approach using the NEMRODW software.The objective of this article is an in-depth theoretical study of the conditioning of radioactive wastes with the introduction of an adjuvant which is the synthesized polymer. The optimization of parameters by this software has enabled us to determine the optimal conditions for a better packaging.The influenced theoretical parameters results in the most adopted parameter to optimize the number of experiences used for the conditioning of ion exchange resins to obtain a better formulation to reduce the number of the realized tests on the one hand, and to increase the resistance to the compression of matrices in polymer on the other.

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

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

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