木质素改性酚醛树脂胶的研究

利用价廉、可再生的木质素代替不可再生且有毒的苯酚、甲醛制取木质素改性酚醛树脂胶。结果表明该胶的性能均达到国家标准，且当胶粘剂的粘度在70～80S、固含量在40％～50％、木质素的用量在30％～40％时，胶粘剂具有较高的剪切强度。     

Artificial weathering of wood surfaces modified by melamine formaldehyde resins

Spruce and poplar samples were treated with different melamine formaldehyde resins. A long term artificial weathering experiment was performed in order to clarify the resistance to weathering regarding wood colour and surface hardness. The increase in hardness due to melamine treatment was well preserved after simulated long term weathering. The treated samples also showed advantages compared to untreated reference samples regarding discolouration and crack formation. Low molar mass and low degree of methylolation of the melamine resin used was found to be favourable for a successful treatment.     

Modification of beech veneers with lignin phenol formaldehyde resins in the production of laminated veneer lumber (LVL)

Rotary cut beech (Fagus sylvatica L.) veneers were treated with four different lignin phenol formaldehyde (LPF) solutions using dimethyl sulfoxide (DMSO) as a solvent. Four of these veneers were bonded with PF adhesive to produce four-layer laminated veneer lumber (LVL). To synthesize the LPF solutions, a commercial phenol formaldehyde resin (PF resin) was individually mixed with three different technical lignins (Indulin AT, BioChoice lignin, organosolv lignin) and lignin cleavage products (LCP) at a ratio of 3:2 (60%:40%). Differential scanning calorimetry showed an increased curing temperature for the LPF resins in comparison to the PF resin. The mechanical and water-related properties of the LPF-modified LVL were shown to be similar or slightly improved compared to PF-modified LVL. Fungal degradation experiments with white-rot fungus (Trametes versicolor) and brown-rot fungus (Coniophora puteana) exhibited no significant differences in the mass loss of the LPF-modified and PF-modified samples except in one case: LVL made from veneers treated with Indulin AT exposed to the white-rot fungus. The resistance to weathering of LVL samples made from veneers treated with technical lignins was low; however, specimens treated with LCP and the reference PF resin displayed a higher resistance to weathering. It is concluded that technical lignins or LCP can, to a certain extent, be used as a substitute for crude-oil based PF resin.     

Bonding of densified beech wood using adhesives based on thermally modified soy proteins

The bondability/glueability of aged and sanded thermo-hydro-mechanically (THM) densified beech wood (Fagus sylvatica L.) was tested and compared with undensified sanded beech wood as a control. THM and control specimens were bonded with five different soy protein isolate (SPI) based adhesives. Commercial SPI powder was thermally modified in the vacuum chamber at 50 or 100?°C and pH adjusted (to pH 10.0) dispersions in water prepared at 24, 50 or 90?°C. Wettability was determined with measuring the sessile drop contact angles of water. Effective penetrations (EPs) and tensile shear strengths of THM and control specimens were determined. THM and control wood had similar wettability. Although THM wood had lower moisture content than control wood, it absorbed the water more slowly than control wood. THM specimens showed lower EPs than control specimens when comparing individual adhesives due to increased density of THM wood. Adhesives prepared with SPI thermally modified at 50?°C showed statistically significantly lower tensile shear strength of bonded THM specimens than that of bonded control specimens. THM densification had no significant effect on the bonding strengths of adhesives prepared with non-modified SPI and SPI thermally modified at 100?°C.     

Characterization of novolac type liquefied wood/phenol/formaldehyde (LWPF) resin

Novolac type liquefied wood/phenol/formaldehyde (LWPF) resins were synthesized from liquefied wood and formaldehyde. The average molecular weight of the LWPF resin made from the liquefied wood reacted in an atmospheric three neck flask increased with increasing P/W ratio. However, it decreased with increasing phenol/wood ratio when using a sealed Parr reactor. On average, the LWPF resin made from the liquefied wood reacted in the Parr reactor had lower molecular weight than those from the atmospheric three neck flask. The infrared spectra of the LWPF resins were similar to that of the conventional novolac resin but showed a major difference at the 1800–1600 cm^-1 region. These results indicate that liquefied wood could partially substitute phenol in the novolac resin synthesis. The composites with the liquefied wood resin from the sealed Parr reactor yielded higher thickness swelling than those with the liquefied wood resin from the three neck flask likely due to the hydrophilic wood components incorporated in it and the lower cross-link density than the liquefied wood resin from the three neck flask during the resin cure process.     

Interactions of a waterborne coating with plasma pre-treated densified beech wood

European Journal of Wood and Wood Products - Densification is a modification technique usually applied to low-density wood species to improve the mechanical properties of the wood. However,...     

Radial variation of total phenol content in beech (Fagus sylvatica L.) wood with and without red heartwood

A comparative study of the radial distribution of the total phenol contents has been carried out on two Beech (Fagus sylvatica L.) discs, one with red heartwood and the other without red heartwood. The wood disc samples were investigated immediately after felling and at the different stages of room-drying. In the disc without red heartwood the concentrations increased from the bark towards the pith. In the disc with red heartwood the total phenol concentration rose steeply in front of the colour boundary, but this could only be measured in the fresh tissues. This suggests, that in these tissues either the formation of phenols (accumulation) is more intense or that special phenols are also formed. Beyond the boundary the concentration decreased dramatically. After drying of the wood samples the concentration decreased in all wood parts of the discs, but the amount of this is the highest in the white tissues next to the red heartwood. The results prove that the transformation of the phenols in the white tissues next to the colour boundary takes place faster.     

Investigation on bonding quality of beech wood (Fagus orientalis L.) veneer during high temperature drying and aging

In the present study, the effects of high drying temperature and UV light induced aging on bonding quality of plywood manufactured from untreated and treated veneer layers were investigated. Rotary cut veneers with dimensions of 500 mm×500 mm×2 mm produced from beech (Fagus orientalis Lipsky) log were selected for topochemical, chemical and mechanical analyses. The veneer sheets were oven-dried at 100°C and 180°C after the peeling process. Afterwards, the surfaces were exposed to artificial UV irradiation in an UV chamber for 24 h, 48 h and 72 h representing natural sun irradiation of 2, 4 and 6 months, respectively. Topochemical distribution of lignin and phenolic extractives of the treated and untreated veneers was investigated on a cellular level using UV microspectrophotometry (UMSP). For the chemical characterization of accessory compounds high performance liquid chromatography (HPLC) was used. Furthermore, the shear and bending strengths of plywood manufactured from the treated samples are determined in order to study the bonding quality. The UV microscopic detection shows that after high drying temperature and aging treatment, lignin condensation occurs. With increasing drying temperature and aging duration, more phenolic extractives are situated in parenchyma cells and vessel lumens which can be proved by increased absorbance at 278 nm. The HPLC analysis of the treated tissue showed distinct signals of polymerized compounds such as catechin and 2,6-dimethoxybenzoquinone which are chromophoric compounds in discolored beech wood. The mechanical properties of plywood showed that with increasing drying temperature up to 180°C does not negatively affect shear and bending strengths of samples. After exposure of the veneers to UV irradiation (especially 6 months), decreasing shear and bending strengths of plywood samples can be observed.     

Modification of sawdust from pine and beech wood with the succinic anhydride

The aim of this study was to compare the reactivity of the succinic anhydride with the comminuted softwood (Pinus sylvestris L.) and hardwood (Fagus sylvatica L.). By extending the time of reaction (from 4 to 8 hours), products with different degrees of modification were obtained. It was demonstrated that in comparison with beech wood, the wood of Scots pine enters the reaction with the succinic anhydride easier. The results of the thermogravimetric analysis showed that the esterification of softwood and hardwood reduced the initial temperature of their thermal degradation. Wood modified with the succinic anhydride is characterised by poorer thermostability in comparison with natural wood.     

On the formaldehyde release of wood particles

The emission of formaldehyde from softwood particles, as measured by the flask method (EN 717-3), depends highly on the particle size. Therefore, no definite value for the formaldehyde release from wood can be given.     

Rheology of tannin-added phenol formaldehyde adhesives for plywood

2 adhesive consumption in double glue line, which is significantly lower than the aprox. 400 g/m² allowed by commercially available phenol-formaldehyde adhesives. The adhesives prepared with resols containing 36% reactive solids, the tannins representing aprox. 20%, has permitted the preparation of eucalyptus plywood boards exceeding the requirements of the European norm for exterior grade plywood.

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2 je doppelter Klebeline erlaubt. Dies ist bedeutend niedriger als die etwa 400 g/m², die bei kommerziell erh?ltlichen Harzen n?tig sind. Die hier hergestellten Harze enthalten etwa 36% reaktive Harze, wovon ca. 20% Tannine darstellen. Mit diesen Harzen konnten Eukalyptus-Sperrh?lzer hergestellt werden, welche die Anforderungen der europ?ischen Normen für Au?enverwendung übersteigen.

     

Rheology of tannin-added phenol formaldehyde adhesives for plywood

adhesive consumption in double glue line, which is significantly lower than the aprox. 400 g/m² allowed by commercially available phenol-formaldehyde adhesives. The adhesives prepared with resols containing 36% reactive solids, the tannins representing aprox. 20%, has permitted the preparation of eucalyptus plywood boards exceeding the requirements of the European norm for exterior grade plywood.     

Influence of ageing on mechanical properties of wood to wood bonding with wheat flour glue

Earlier research into native wheat flour for wood to wood bonding showed excellent bonding properties comparable to synthetic adhesives, but no data about ageing behaviour is available. Short and long term effects on mechanical properties were analysed by lap joint testing and modified DCB-specimens. Results showed no significant reduction in bonding properties, but a trend to lower adhesive strength after 12 months of storage was noticeable. Changes in wheat polymers were observed by means of DSC and FTIR-ATR. Soluble degradation products of starch were analysed by GC-FID after methanolysis and derivatisation. FTIR measurements indicated changes in the structure of starch, but no appreciable alteration of proteins. Investigations by DSC showed increasing crystallinity during 3 months of storage. After 6 months more degradation products were detected. Results indicated that hydrolysis of starch is responsible for a moderate decrease of bonding performance; wheat proteins seem to be less affected.     

Macroscopic and microscopic monitoring of swelling of beech wood after impregnation with furfuryl alcohol

Wood furfurylation is a modification method that improves several wood properties. Thereby wood is impregnated with a solution of furfuryl alcohol, catalysts and water, in general. The objective of this study was to understand the penetration of furfuryl alcohol into wood. Furthermore, a possible relationship between the substance amount and the swelling behaviour should be determined. To this end microscopic investigations were conducted to describe the temporal process of penetration and swelling. It was found that the swelling coefficients differ at the microscopic and macroscopic level. The microscopic swelling can reach twice the values of macroscopic swelling.     

Influence of drying temperature upon some mechanical properties of beech wood

The paper presents the results obtained in an experimental study concerning the influence of drying temperature upon the mechanical properties of beech wood (Fagus sylvatica L.). Sound wood samples without red heart were cut from white (unsteamed) beech timber parts, dried at different temperatures: 20 °C, 80 °C, 90 °C, 100 °C, 115 °C and same relative air humidity: 50%. After performing classical tests for evaluation of some selected mechanical properties, the following conclusions could be drawn: all bending properties (static bending strength, modulus of elasticity and impact bending strength) increased with increasing temperature, confirming thus the benefiting effect of heat upon wood plasticity. The tensile strengths, both parallel and perpendicular to grain, increased with increasing temperature, but only in the range below 100 °C; as soon as the temperature exceeded this value, the tensile strengths began decreasing. As far as compression strength parallel to grain, shearing strength and splitting resistance is concerned, no significant influence of temperature could be established. However, it seems that these properties are negatively affected by kiln-drying, as even with low kiln-drying temperatures these strengths are much lower than in case of air-drying.     

Moisture-dependent, viscoelastic creep of European beech wood in longitudinal direction

In the present study, the pure viscoelastic behaviour of European beech wood is analysed in the longitudinal direction at three different moisture contents. The moisture-dependent creep compliance is identified using a four-point bending test device. The viscoelastic behaviour is ascertained to be linear with moisture content and quantified by means of a Kelvin-Voigt model approach.     

Weathering of chemically modified wood

Acctylation of radiata pine vencer was shown to improve the colour stability and weathering resistance of material exposed to accelerated weathering conditions. Two exterior finishes, an opaque acrylic stain and a semi-transparent alkyd stain, as well as unfinished veneer, were studied. Significantly less checking was observed for unfinished, acetylated samples or acetylated vencers finished with the alkyd stain when compared with untreated controls. Examination of unifinished samples by scanning electron microscopy (SEM) showed that, although checking was not completely prevented by acetylation of the vencer, it gave significant protection from the effects of weathering.