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Penetration of urea-formaldehyde adhesives in wood tissue, part I: Radial penetration of UF adhesives into beech
Gavrilovi?-Grmu?a Ivana,Miljkovi? Jovan,?iporovi?-Mom?ilovi? Milanka,Rado?evi? Gordana
Glasnik ?umarskog Fakulteta , 2008, DOI: 10.2298/gsf0898039g
Abstract: Adhesive penetration plays an important role in wood adhesion, since wood is a porous material. The degree of penetration mostly depends on the wood factors, resin type and formulation and processing parameters. Tangentially cut 5 mm thick beech wood (Fagus moesiaca) plies, 100 mm long (parallel to grain) and 30 mm wide, were prepared for this study. The urea-formaldehyde (UF) adhesive was applied to the surface of one ply. Two plies were assembled into sample so that the grains of two plies were parallel. Samples were pressed in a hydraulic press at 120°C and 0,7 MPa for 15 min. Microtome test-specimens were cut of each sample. 20 μm thick microtomes were cut by sliding microtome apparatus, exposing a bondline with a cross-sectional surface. The lack of more exhausting research on the penetration of urea-formaldehyde adhesives in wood is evident. Since ureaformaldehyde (UF) glue resins were the most important type of adhesives in the wood industry in the last 60 years (Dunky, 2000), the objective of this research was microscopic detection of UF adhesive penetration in wood tissue. Four types of UF resins with different levels of polycondensation were used in this research. Safranin was added in resins, since epi-fluorescence microscope was used in this research for measuring the adhesive penetration.
WHEY PROTEIN-BASED WATER RESISTANT AND ENVIRONMENTALLY SAFE ADHESIVES FOR PLYWOOD  [PDF]
Wenbo Wang,Zongyan Zhao,Zhenhua Gao,Mingruo Guo
BioResources , 2011,
Abstract: Whey protein is a renewable and environmentally safe biomaterial, a by-product of cheese production. It can be utilized for non-food applications for value-added products. The substances glyoxal (GO), glutaraldehyde (GA), polymeric methylene biphenyl diisocyanate (p-MDI), urea-formaldehyde (UF) resin, and phenol-formaldehyde oligomer (PFO) that contain reactive groups were applied together with whey protein as modifier in order to increase crosslinking density and molecular weight for improving the bond strength and water resistance of whey protein. A water-resistant and environmentally safe whey protein-based wood adhesive for plywood was developed by evaluating the effects of these modifiers on the bond strength, bond durability, and free formaldehyde emission of the resulting plywood panels. Results of FTIR and SEM analyses and bond evaluation indicated that GO, GA, and p-MDI were not suitable to modify whey proteins due to their high reactivity with whey proteins, causing phase separation. UF resin was not a good modifier for whey proteins because of either its poor water-resistance or higher emission of hazardous formaldehyde. Whey protein adhesives modified with PFO had a dry shear bond strength of 1.98 MPa and a 28h-boiling-dry-boiling wet shear strength of 1.73 MPa, which were both much higher than the required values for structural use according to standard JIS K6806-2003, while its formaldehyde emission was 0.067mg/L, much lower than the required value for green plywood according to standard JIS A5908.
Penetration of urea formaldehyde adhesives in wood tissue, Part II: Radial penetration of UF adhesives into silver fir  [PDF]
Gavrilovi?-Grmu?a Ivana,Miljkovi? Jovan,?iporovi?-Mom?ilovi? Milanka,Rado?evi? Gordana
Glasnik ?umarskog Fakulteta , 2009, DOI: 10.2298/gsf0999033g
Abstract: Penetration is the ability of the adhesive to move into the voids on the substrate surface or into the substrate itself. Wood's cellular nature allows significant penetration of the adhesive into the substrate. Objective of this work was the evaluation of the penetration and hence the distribution of urea-formaldehyde (UF) resins by means of microscopic detection of the penetration of such UF adhesives into the wood tissue. Tangentially cut 5 mm thick silver fir (Abies alba Mill.) plies, 100 mm long (parallel to the grain) and 30 mm width, were prepared for this study. Four types of UF resins with different degree of condensation were investigated in this research. Safranin was added to the resins and epi-fluorescence microscope was used for measuring the adhesive penetration. The UF adhesive mixes, consisting of the various resins, extender and hardener were applied to the surface of one ply. Two plies, one with applied adhesive mix and one without adhesive mix, were assembled with parallel grain direction. Samples were pressed in a hydraulic press at 120°C and 1.0 MPa for 15 minutes. Test-specimens of 20 μm thickness were cut of each sample using a sliding microtome apparatus, exposing a bondline on a cross-sectional surface. The results show a significant correlation between the penetration behaviour and the degree of condensation (molecular sizes, viscosity) of the resins. The higher the degree of condensation, the lower the possibility for penetration, expresses as average penetration (AP) and as portion of filled tracheids on the whole cross section of interphase (filled interphase region FIR).
Some characteristics of urea-formaldehyde powder adhesives  [PDF]
Miljkovi? Jovan,Gavrilovi?-Grmu?a Ivana,?iporovi?-Mom?ilovi? Milanka,Popovi? Mla?an
Glasnik ?umarskog Fakulteta , 2006, DOI: 10.2298/gsf0694223m
Abstract: Urea-formaldehyde (UF) glue resins were the most important type of adhesives in the wood industry last 60 years, especially for the production of wood based panels. More convenient spray dried UF powders went into use last two decades. Small and medium private wood processing plants in Serbia prefer to use such powder adhesives, since they are more convenient for small capacity production. There is no production of UF powder resin in Serbia so necessary quantities are imported from abroad including producers from Asia. However, their characteristics are variable, dependent on syntheses steps and not well known among users. Objective of this research was to determine conveniences and lacks in application of two imported UF powder resins in comparison to domestic UF emulsion.
"Low mole ratio UF and UMF resins entailing uron-type methylene-ether groups and their low formaldehyde emission potentials,"  [PDF]
BioResources , 2015,
Abstract:
Factor Affecting Gel Time/Process-Ability of Urea Formaldehyde Resin Based Wood Adhesives  [PDF]
Ravindra V. Gadhave, Prakash A. Mahanwar, Pradeep T. Gadekar
Open Journal of Polymer Chemistry (OJPChem) , 2017, DOI: 10.4236/ojpchem.2017.72003
Abstract: Urea-formaldehyde (UF) resin presents the most utilized adhesive system in the manufacture of plywood, particleboard and fiberboard. At the temperatures above 100°C in the presence of hardener, this resin undergoes cross-linking reaction and the formation of three dimensional cross linked structures takes place and bonding of wood particles in a hot press [1]. UF powder resins show high reactivity and good performance in the production and by their low price; however they lack in water resistance of the hardened resin [2]. Urea-formaldehyde (UF) resins are the most important type of adhesive resins for the production of wood based panels but process-ability and curing behavior of urea formaldehyde resin depended on various factors related to resin properties, types of wood and their properties, amount & type of catalyst, types and amount of polymers addition and environmental conditions [3]. This factor decides the process-ability of UF resin based composite during manufacturing of plywood, particle board and fiberboard. In this review paper, various factors affecting gel time and process-ability of UF resin based wood composite are reviewed.
改性超支化聚合物对脲醛树脂性能的影响  [PDF]
王辉,杜官本,李涛洪,周晓剑
- , 2018, DOI: 10.13360/j.Issn.2096-1359.2018.03.012
Abstract: 采用“碱-酸-碱”合成工艺,在树脂合成反应末期加入不同比例的尿素及改性超支化聚合物,合成了2种脲醛树脂(UF0和UF1),测试了2种脲醛树脂的基本性能及其所制胶合板的力学性能,并借助差示扫描量热仪(DSC)和热重分析仪(TG)对树脂的固化性能及耐热性能进行了表征和分析。试验结果表明:加入改性超支化聚合物的UF1树脂具有较低的固化温度,有利于提升树脂的固化速度,且树脂具有较好的热稳定性; 胶合板的2 h耐冷水胶合强度可以提升近50%,树脂中游离甲醛含量明显下降,而对树脂的固体含量及黏度影响不大。13C NMR 结构分析表明,改性超支化聚合物的加入可以有效提升树脂中亚甲基桥键(―CH2―)和尤戎环(Uron)的比例,对树脂耐冷水性能的提升具有重要作用。
With the “alkali-acid-alkali” technology, two kinds of urea-formaldehyde resins(UF0 and UF1)were synthesized in laboratory by adjusting the mass ratio of urea and modified hyperbranched polymer at the end of resin synthesis, and the properties of the two urea-formaldehyde resins were tested according to the standard of GB/T 14074-2006. At the same time, the curing characteristics and thermal resistance performance of the two resins were analyzed by the differential scanning calorimeter(DSC)and thermogravimetric analysis(TG), respectively. The results showed that the resin with modified hyperbranched polymer(UF1)had lower curing peak temperature with or without curing agent, being beneficial to improve the resin curing rate, increase productive efficiency, and enhance the thermal resistance performance because of the higher carbon content and thermal decomposition temperature. It was found that the urea-formaldehyde resin with modified hyperbranched polymer had better performance compared with the unmodified urea-formaldehyde resin did under the same conditions. Moreover, the three-layer poplar plywood was made in the laboratory, and the bonding strength was evaluated after 24 h stress-release and equilibrium at room temperature. In this study, the wet bonding strength was determined after the specimens were immersed into cold water for 2 h at room temperature. The results showed that the wet bonding strength of modified urea-formaldehyde resin was improved by nearly 50%, and the free formaldehyde content in resin(UF1)decreased markedly. The structures of the two resins were analyzed by using the 13C nuclear magnetic resonance(13C NMR), and the results further indicated that the contents of the methylene(―CH2―)and uron in the modified resin with hyperbranched polymer was much higher than those in the unmodified resin. The methylene played an important role in bonding, while uron was beneficial to waterproof performance of urea-formaldehyde resin
PREPARATION AND MECHANICAL CHARACTERIZATION OF PARTICLEBOARD MADE FROM MARITIME PINE AND GLUED WITH BIO-ADHESIVES BASED ON CORNSTARCH AND TANNINS
Moubarik,Amine; Allal,Ahmed; Pizzi,Antonio; Charrier,Fatima; Charrier,Bertrand;
Maderas. Ciencia y tecnología , 2010, DOI: 10.4067/S0718-221X2010000300004
Abstract: in this presented work, we describe the development and characterization of a new, environmentally friendly adhesive derived from cornstarch and tannins. the production of wood composites mainly relies on the petrochemical-based and formaldehyde-based adhesives such as urea formaldehyde (uf), phenol formaldehyde (pf) and melamine urea formaldehyde (muf), which can generate under certain conditions, problems for health and environment. the aim of our work is to replace totally these synthetic resins. in order to evaluate the quality of cornstarch-tannin adhesives, particleboards were produced and physical and mechanical properties were investigated. these physical properties included rheological, thermogravimetric analysis and solid phase 13c nmr analysis of resins. internal bond, surface soundness, modulus of rupture and modulus of elasticity mechanical properties of particleboards bonded with cornstarch-tannin adhesives were also determined. particleboards bonded with formaldehyde-free cornstarch-tannin adhesive showed comparable mechanical properties to the panels made with the commercial uf resins and satisfied the exigencies of panels for interior fittings used in dry medium (p2) according to european norms en 312 (2004). beyond 4 hours, rheological characterization show excellent structural stability of cornstarch-tannin adhesive.
PREPARATION AND MECHANICAL CHARACTERIZATION OF PARTICLEBOARD MADE FROM MARITIME PINE AND GLUED WITH BIO-ADHESIVES BASED ON CORNSTARCH AND TANNINS  [cached]
Amine Moubarik,Ahmed Allal,Antonio Pizzi,Fatima Charrier
MADERAS : Ciencia y Tecnología , 2010,
Abstract: In this presented work, we describe the development and characterization of a new, environmentally friendly adhesive derived from cornstarch and tannins. The production of wood composites mainly relies on the petrochemical-based and formaldehyde-based adhesives such as urea formaldehyde (UF), phenol formaldehyde (PF) and melamine urea formaldehyde (MUF), which can generate under certain conditions, problems for health and environment. The aim of our work is to replace totally these synthetic resins. In order to evaluate the quality of cornstarch-tannin adhesives, particleboards were produced and physical and mechanical properties were investigated. These physical properties included rheological, thermogravimetric analysis and solid phase 13C NMR analysis of resins. Internal bond, surface soundness, modulus of rupture and modulus of elasticity mechanical properties of particleboards bonded with cornstarch-tannin adhesives were also determined. Particleboards bonded with formaldehyde-free cornstarch-tannin adhesive showed comparable mechanical properties to the panels made with the commercial UF resins and satisfied the exigencies of panels for interior fittings used in dry medium (P2) according to European norms EN 312 (2004). Beyond 4 hours, rheological characterization show excellent structural stability of cornstarch-tannin adhesive.
Formaldehyde Emission from Wood-Based Panels Bonded with Different Formaldehyde-Based Resins  [PDF]
Mohamed Salem,Martin B?hm,?tefan Barcík,Jitka Beránková
Drvna Industrija , 2011,
Abstract: In this study, the formaldehyde emission (FE) from different types of particleboard, medium density fiberboard (MDF), and plywood products supplied from a commercial plant in the Czech Republic were evaluated by gas analysis (EN 717-2) and European small chamber (EN 717-1) methods. The significant effects of manufacturing variables (board type and thickness) as well as different types of formaldehyde-based resins on FE measured by gas analysis were obtained. When the E1 type adhesives were employed, a wide variation in the quantity of free formaldehyde was observed among the three product types. The FE values of plywood samples measured by gas analysis were lower than those of the particleboard and MDF samples. The correlation between the two methods for the particleboard and MDF were good (R2 = 0.82 and 0.76, respectively) and however for plywood (R2 = 0.52) it was not convincing. FE specifi ed in EN 717-2 was comparable with the EN 717-1 values for the same board type and thickness as well as the resin type and below the E1-emission class.
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