WOOD RESEARCH Volume 68, Number 3, 2023
Mehmet Gunes and Mustafa Altunok

Investigation of Bending Strength of Tannin Impregnated Wooden Beams after Heat Treatment

In this study, the changes in bending strength were investigated by applying heat-treatment to laminated beams modified with acorn tannin to improve the mechanical properties of wooden load-bearing structural members. For this purpose, acorn tannin was impregnated on samples prepared from Scotch pine (Pinus sylvestris L.), oak (Quercus petraea L.), and chestnut (Castanea sativa Mill.) woods. Heat treatment was applied to the samples impregnated with acorn tannin at 150ºC for 3 hours. Untreated, heat-treated, and tannin-modified samples were conditioned until they reached constant weight at 20ºC at 65% relative humidity (RH), 40ºC at 35% RH, and 10ºC at 50% RH. Bending resistance tests were applied to the elements that are conditioned in outdoor conditions according to ISO 13061-3. The results of bilateral interaction between tree species and treatment type were compared, the highest bending strength increase was found in Scotch pine samples by 5% compared to control samples.

WOOD RESEARCH Volume 61, Number 2, 2016
Alireza Bastani, Holger Militz, Stergios Adamopoulos, and Anti Rohumaa

Development of bonding strength of modified birch veneers during adhesive curing

This study investigated the bonding strength development of furfurylated, N-methylol melamine (NMM) modified and thermally treated birch veneers glued with hot curing phenol formaldehyde (PF) adhesive in different pressing (20, 160 s) and open assembly times (20 s, 10 min). For testing, the automated bonding evaluation system ABES was used with 2 N.mm-2 applied pressure at 130°C. The bonding strength of both modified and unmodified samples increased significantly by prolongation of the pressing time from 20 to 160 s in all cases and for both open assembly times. A deviation was observed for the samples treated at 220°C and at 20 s open assembly time. With the exception of NMM modified veneers, bonding strength did not change significantly by increasing the assembly time in the case of 20 s pressing for both modified and unmodified samples. At 160 s pressing time, extension of the assembly time developed a better bonding for controls, NMM modified and thermally treated veneers at 180°C. The combination of 10 min assembly time and 160 s pressing time proved as the optimal bonding condition for controls, NMM modified and thermally treated veneers at 180°C while the highest bonding strength was noted in 20 assembly time and 160 s pressing time for furfurylated veneers. In most of the cases modification affected negatively the bonding performance of the veneers, in particular for furfurylated and NMM modified samples.

WOOD RESEARCH Volume 61, Number 1, 2016
Bodo Caspar Kielmann, Holger Militz, and Carsten Mai

The effect of combined melamine-resin-colouring agent modification on water related properties of beech wood

Beech wood (Fagus sylvatica L.) was modified with aqueous solutions of methylated N-methylol melamine (NMM) and a metal-complex dye and the water related properties were determined. Wood blocks, treated to the highest weight percent gain (WPG), attained approximately 5 % cell wall bulking and 30 % anti-swelling efficiency (ASE) after ten cycles of water saturation and drying. The metal-complex dye was stably fixed in the resin matrix and was hardly washed out. The equilibrium moisture content of the modified samples related to the dry mass of untreated beech wood (EMCR) was not considerably reduced compared to the EMC of the control. The maximum swelling of the modified samples as a result of vapour sorption was only reduced above 65 % relative humidity compared to the control. Capillary water uptake of wood was significantly reduced by the resin modification. The results indicate the potential of the combined modification to improve the water related properties of wood.

WOOD RESEARCH Volume 62, Number 3, 2017
Aytekin Onduran, S. Sadiye Yasar, and Mustafa Altunok

Investigation of the effects of some modification process to the mechanical performance and deformation of the woodwork

In this study, wood modification (thermo-processing and impregnation) and outdoor conditions of storage (natural aging) the effects on the mechanical performance of industrial woodwork was investigated. For this purpose, naturally grown in Turkey and the commercial value of high Scots pine (Pinus sylvestris L.) and chestnut (Castanea sativa Mill) wood was used. Experimental examples are specifically woodwork has been applied in actual size. Considering the previously conducted research literature only diagonal L-type samples used, not on the actual size samples of woodwork. In addition, there is no study that the combination of the heat-treatment and impregnation. This reveals the original values of this study. For preparing of samples is used the double tenon-mortise corner joint from constructions method and as glue polyurethane based Desmodur VTKA and Polyvinyl acetate based two-component D4. Diagonal woodwork test samples prepared by Thermo S class (185°C temperature with a thermo-vapor process protections) applying. After application of the heat treatment, the test samples impregnated with a solution of 95 % natural pine cone resin and %5 pine tannin by dip method (2 hours). Then, the untreated samples (control), only heat-treated samples and heat treatment + impregnated samples kept for 1 year with outdoor conditions (aging). At the end of the aging, the samples tested according to the principles stated in TS 2472 and TS 7251 EN 107 standard. As result, the performance of woodwork decreased after aging in untreated and heat treatment pieces, the other side after aging – heat treatment, impregnation materials increased the values. The deformation value of woodwork increased after aging most untreated materials, Heat treatment and heat treatment-impregnated reduced aging effectiveness.

WOOD RESEARCH Volume 62, Number 2, 2017
Xiaoshuai Han, Qinqin Zhang, Ren Li, and Junwen Pu

Grafting organic-inorganic compound modifier onto wood cell walls for enhanced mechanical strength in wood composites

The present study describes the possibility to polymerize functional composite modifier within wood cell walls to obtain functional wood composites (FWCs) with poplar wood acting as the base template. The physical and mechanical properties of the composites, including density, bending strength, compressive strength parallel to grain, surface hardness and water uptake, were evaluated. The FWCs were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD). According to the results, the functional composite modifiers were successfully in situ deposited into the wood structure by kiln drying. The chemical treatment not only significantly improved the physical and mechanical properties of wood, but also provided the wood with better hydrophobic properties. The abbreviations for substances used in this study are: N-wood (natural wood), MD-wood (methylolurea/DMDHEU copolymerization treated wood), FCM-wood (functional composite modifier treated wood).

WOOD RESEARCH Volume 63, Number 3, 2018
Mátyás Báder and RÓBERT NÉMETH

The effect of the relaxation time on the mechanical properties of longitudinally compressed wood

Longitudinal compression makes natural wood easier to bend. The relaxation after compression results in much improved bending properties. During a bending test, the maximum deflection increases with the relaxation time, while the needed force to reach the same deflection decreases, similarly to the modulus of elasticity (MoE). The modulus of rupture (MoR) of the compressed wood does not change considerably compared to the untreated wood, except at the long-time relaxed samples. The ideal relaxation time is 1 minute. After that the change of the important properties slows down. Of course with special demands, the relaxation time can be also very long. In this case the process leads to a wood sample with pronounced flexible properties. Samples were left to rest between normal circumstances for 1 day, but this resting period did not have a significant effect on its mechanical properties.

WOOD RESEARCH Volume 64, Number 5, 2019
Wenbo Che, Zefang Xiao, and Yanjun Xie

Modification of radiata pine wood with low molecular weight modifying agents and large molecular weight styrene/acrylic acid copolymer dispersion

Our previous study revealed that treatment with aqueous styrene/acrylic acid copolymer (SA) is a cell-lumen filling process, and the treated wood exhibited negative values for cell wall bulking efficiency (BE) and anti-swelling efficiency (ASE). In this study, three low-molecular-weight agents (LMWAs), 1, 3-dimethylol-4, 5-dihydroxyethyleneurea (DM, 10%), glutaraldehyde (GA, 10%), and n-methylol acrylamide (NMA, 10%), were separately combined with SA (5, 10, 15, or 20%) and used to modify radiata pine wood at the levels of cell walls and cell lumens. The combinative treatments caused positive BE and ASE values, indicating restrained wood deformation, likely due to the diffusion and reaction of LMWAs in the wood cell walls. Infrared spectroscopy and dynamic mechanical analysis showed that LMWAs exhibit little reaction with SA, and the SA copolymer retains thermoplasticity in the wood cell lumen. The combinative treatments resulted in considerable improvement in bending modulus, bending strength, and compression strength of wood of 36, 36, and 124%, respectively, but there was little effect on impact strength. These findings confirm that LMWAs can act as cell wall modifying agents to synergistically improve wood properties, especially the dimensionally stability, when used together with SA.