Degradation of wood surfaces by water

Weight losses and ultrastructural and chemical changes in pine and lime following exposure to deionised water in the temperature range 60° C-90° C are examined. Similar weight losses of 10% occur in pine and lime strips after 100 days exposure to water at 60 and 70° C but at 80 and 90° C lime shows greater weight losses (30%) than pine (15%). Observations of transverse surfaces exposed to water at 90° C for 50 days revealed separation of the secondary wall from the compound middle lamella region and some separation of individual cells. Chemical analysis of pine and lime wood flour exposed to deionised water at 65° C for 50 days revealed losses of hemicelluloses and lignin with little loss in cellulose. Changes in hemicellulose composition are thought to result primarily from degradation of pectinacious polysaccharides. Losses in lignin and hemicelIulose were higher and lower respectively in lime than in pine. Viscometry measurements on cuprammonium dispersions of holocellulose isolated from hot water exposed pine strips indicate that little depolymerisation of cellulose occurs. It is suggested that the chemical and ultrastructural changes noted here accord with the losses m wet tensile strength and toughness of hot water exposed thin wood strips and failure of these particularly in lime by inter-fibre shear.     

Degradation of wood surfaces by water Changes in mechanical properties of thin wood strips

European Journal of Wood and Wood Products - Thin strips of pine and lime were exposed to deionised water in the temperature range 50–90°C. Losses in wet tested tensile strength and...     

Measuring active wood fracture surfaces

This report describes a measurement method, based on image processing, for calculating the proportion of active wood fractures in a sheet of particle board that has been pulled apart. This method gives an indirect measurement of the effectiveness of the glue in a particle board. The basic procedure is to separate different surfaces on both sides of the tensile fracture. The separation of the glue covered surfaces from wood surfaces has been enhanced by a development process. The separated surfaces for each side, represented in the form of a binary image, are added, and a proportion of the surface with coinciding wood surfaces represents the proportion of wood fractures. The error analysis covers the randomly obtained coinciding surfaces.     

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.     

Processing roughness of sanded wood surfaces

Any quantitative evaluation of a sanded surface requires that the data be filtered to remove form errors and waviness. Wood surfaces contain irregularities due to both the sanding process and the anatomy, so the anatomical roughness must be excluded from any measurement of the surface if the processing roughness is to be properly evaluated. The efficacy of a number of standard filters was examined to see if they were suitable for oak, beech and spruce surfaces sanded with P1000 grit. Filters in current standards introduced distortions, but a robust Gaussian filter, contained in a draft standard, appeared to give roughness profiles free of distortions. The processing roughness and anatomical roughness, contained in the filtered profile, were separated with an algorithm based on a threshold defined in the material ratio curve. Work is continuing to compare the properties of different grit size and species combinations.     

Linear welding of grooved wood surfaces

Linear wood welding of grooved surfaces to ease the elimination of water vapour and to increase the welding surface was performed in this study.     

聚乙烯醇在超临界水氧化体系中的降解

用超临界水氧化法对聚乙烯醇(PVA)废水进行降解研究,分别考察了反应温度、反应压力、氧化剂过氧倍数以及反应时间对PVA废水降解效率的影响,并用GC/MS对液相降解产物进行表征,推测其可能降解途径.结果表明:超临界水氧化法能有效降解PVA废水,随反应温度的升高、压力的增大、反应时间的延长,COD去除率也随之提高.PVA在超临界水氧化体系中降解为烯烃、烯酮、醇和羧酸类中间产物,最终降解为小分子的饱和直链烷烃类液相产物.     

Form error removal of sanded wood surfaces

According to ISO 3274 form errors can be removed by fitting a polynomial regression through the original measured data called the total profile to obtain the primary profile. For wood surfaces it was found that the regression was affected by the presence of deep and grouped pores. To obtain a primary profile free of distortion, the deep pores can be removed from the total profile prior to applying the regression. A method was developed that eliminated the pores entirely. The efficacy of this method was tested visually and by comparing coefficients of determination r² between the polynomial regression according to ISO 3274 (1996) and the total profile and the modified regression line when the effect of deep pores was removed and the modified profile that had no pores. The influence of the shape of the primary profile obtained by the standard method in ISO 3274 (1996) on further digital processing was tested on roughness profiles filtered with a Robust Gaussian Regression Filter. The undistorted primary profile was taken as a reference.     

采用端面铣削装置加工木材表面

本文阐述木材加工商务中常用的刨加工方法与称为Rotoles System的端面铣削装置的新方法相比较。该方法代表木材加工的一种创新，对于低质量的木材和胶合梁的表面加工具有许多优点。     

Evaluation of the sensory roughness of some coated wood surfaces by image analysis

Sensory roughness is one of the most important factors that determines the quality and/or value of various wood products. The aim of the present study was to confirm whether the sensory roughness of coated wood surfaces could be estimated by the here proposed image analysis. Twelve white oak (Quercus alba) fancy veneer overlaid plywood samples were prepared with two types of grains and six coating specifications. Forty participants subjectively evaluated the sensory roughness of the samples by rubbing their surfaces without being able to see them. Sample surface images were acquired with a goniophotometric method and were submitted to an image analysis to calculate lightness differences (contrast) between relatively small areas as image characteristics. Three surface profile parameters were also measured based on the conventional stylus method. Three-way analyses of variance for the evaluation of sensory roughness revealed significant main effects of the coating specification and the rubbing direction. Although contrast and surface profile parameters were hard to estimate in terms of sensory roughness for spiny surfaces, both measures were well correlated to sensory roughness for porous surfaces. In particular, the linearity between the sensory roughness of the porous surfaces and contrast was equal to or greater than that of the surface profile parameters.     

Enthalpy-entropy compensation in water sorption by various wood species

Tsuga heterophylla ), Douglas fir (Pseudotsuga menziesii), western red cedar (Thuja plicata), sitka spruce (Picea sitchensis), and lodgepole pine (Pinus contorta). Enthalpy and entropy show a strong negative relation to the moisture content, the absolute desorption values always being higher than the adsorption ones, but with no clear trend between and within the species. Furthermore, it is shown that the linear plot of compensation between enthalpy and entropy correlates well for water sorption in wood; that water adsorption or desorption are irreversible, and that both are enthalpy-driven mechanisms.

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Tsuga heterophyll , Pseudotsuga menziesi, Thuja plicata, Picea sitchensis), und Pinus contorta. Enthalpie und Entropie steigen mit fallender Feuchte. Die Desorptionswerte sind immer etwas h?her als die Adsorptionswerte. Zwischen den Holzarten gab es keine signifikanten Unterschiede. Die lineare Kompensation zwischen Enhalpie und Entropie korrelliert gut mit der Sorption. Absorption und Desorption sind irreversible, Enthalpie-getriebene Prozesse.

     

On the modelling of colour changes of wood surfaces

Colour has an influence on the aesthetic properties of wood surfaces, and changes in colour have an impact on each individual’s perception of wood construction materials. This study examines an approach to model the discolouration of wood during natural weathering. A novel mathematical model was used to estimate colour changes of two softwoods during natural weathering. The surface colour of fir and larch samples was determined according to the CIEL*a*b* system during natural weathering over a period of one year. In order to demonstrate the value of the model, two different weathering sites were chosen. The data collected from each site was smoothed using a local regression method, and the corresponding parameters were used to generate the confidence intervals around the smoothed curves. The results show that all three colour parameters exhibit varying differences during the weathering trial. The locally weighted regression method seems to be an appropriate approach for modelling weathering effects and could be used to simulate colour change in wood in exterior applications in the future.     

Efficient recovery of superhydrophobic wax surfaces on solid wood

European Journal of Wood and Wood Products - Superhydrophobic surface coatings have enormous potential to protect wood from excessive water uptake. Unfortunately, such coatings often require toxic...     

Analysis of water adsorption by wood using the Guggenheim-Anderson-de Boer equation

The Guggenheim-Anderson-de Boer (GAB) three-parameter sorption equation has been used to interpret the adsorption and desorption isotherms of water vapour measured for 21 important cultural heritage wood species used in the past for panel paintings and woodcarving. The equation is capable of describing the full shape of the isotherms and yields meaningful physical parameters, especially the monolayer capacity from which the water accessible specific surface area can be obtained. It is demonstrated that average sorption isotherms can be derived using the GAB equation for the sorption data available for sets of specimens and that moisture properties of various wood specimens or chemically modified wood can be more easily compared.     

Analysis of wood surfaces and ground wood by diffuse reflectance (DRIFT) and photoacoustic (PAS) Fourier transform infrared spectroscopic techniques

Infrared diffuse reflectance and photoacoustle spectra were measured from wood powder and solid wood blocks and compared with the corresponding transmission spectra measured from thin wood sections. Studies indicated that high quality spectra could be obtained from either solid wood blocks or powder by diffuse reflectance (DRIFT) and photoacoustic (PAS) techniques. Positions of IR bands measured from different hardwood species by DRIFT and PAS technique are approximately same. However, the relative intensities of IR bands vary among species. For obtaining reproducible DRIFT spectra from the solid wood surfaces, roughness and structure of the cut (tangential, radial or transverse) must be identical. Whereas, for wood powder, smallest particle size results in best resolved spectrum. Specular reflection causes distortions in the intensities of the bands in the range 1150-950 cm^?1, which can be minimised either by diluting sample powder in KBr (concentration <2%) or by increasing the surface roughness of the solid block. FTIR-PAS spectra measured from wood powder are quite similar to spectra obtained by transmission and/or DRIFT techniques. Relative intensity and position of various IR bands measured by photoacoustic technique are independent of size of the particle and its concentration. These results indicate the usefulness of PAS technique over other solid sampling techniques.