Preparation and crosslinking of oligoesterified woods based on phthalic anhydride and glycidyl methacrylate

Summary Oligoesterification reaction of wood with phthalic anhydride and glycidyl methacrylate (GMA) was investigated. The reaction proceeded smoothly at 90°C. The products obtained consisted of acetone-insoluble and soluble parts. The insoluble parts were novel oligoesterified woods with oligoester chains having methacrylate double bonds. The soluble parts were viscous liquids consisting mainly of free oligoesters not linked with the wood matrix, and contained small amounts of GMA and oligoesterified wood components which were dissolved out. The products (the oligoesterified wood-containing mixtures), when subjected to hotpressing, gave plasticized crosslinked wood boards whose surfaces are smooth, glossy, and plasticlike. In this case, plasticization of wood components and thermal polymerization of the methacrylate double bonds in the oligoester chains occurred simultaneously even in the absence of radical initiator. The soluble parts worked as a plasticizer for the wood components. The crosslinked wood boards exhibited outstanding properties in tensile strength (ca. 700 kg/cm²), flexural strength (ca. 900–1030 kg/cm²), and Rockwell hardness (ca. 120).     

Preparation and properties of oligoesterified wood blocks based on anhydride and epoxide

Summary Preparation and properties of oligoesterified woods in the form of block are reviewed. The oligoesterified wood blocks are prepared by stepwise addition reactions of dicarboxylic acid anhydride and epichlorohydrin (EpCl), or one-step chemical treatment with reactant solution of the anhydride and EpCl. Among the preparation methods investigated, the heating-suction method is industrially advantageous. In this method, wood blocks impregnated with the reactant solution are heated and then subjected to suction under reduced pressure and heating, to remove unreacted reactant solution. The oligoesterified wood blocks thus obtained contain oligoester chains formed by the alternate additions of the anhydride and EpCl to OH groups of wood. They also contain small amounts of free oligomers not linked with the wood matrix. Their dimensional stabilities against moisture and water become greater with increase in the apparent total weight increase due to the oligoester chains and the free oligomers. The oligoesterified wood blocks based on phthalic anhydride-EpCl are industrially promising, and exhibit higher compressive and flexural strenghts, greater chemical resistance, electric insulation, and much lower water absorption than untreated wood block. Furthermore, excellent resistances are observed against weathering and biodeterioration.     

Preparation and utilization of esterified woods bearing carboxyl groups

Summary Preparation and utilization of esterified woods bearing carboxyl groups are reviewed. The esterified woods are prepared by the addition reactions of wood with dicarboxylic acid anhydrides in the presence or absence of a solvent such as dimethylformamide. The reactions without solvent are industrially advantageous and can give esterified woods with a wide range of monoester contents. The esterified woods can be molded into sheets by hot pressing. By addition reactions of the esterified woods with epoxide, or epoxide and anhydride at high temperatures, epoxide-adducted esterified woods and oligoesterified woods are obtained. These can also be molded by hot pressing. The addition of epoxide to esterified woods results in an improvement in moisture resistance of the molded sheets. When esterified woods are subjected to crosslinking reactions with bisepoxide both at high temperatures and under high pressures, the wood components plasticize to give reddish brown, yellowish brown, or blackish brown crosslinked wood boards whose surfaces are smooth, glossy, and plastic-like. Among the plastic-like crosslinked wood boards, the phthalic anhydride-based board shows the best physical properties. Especially, this board exhibits very high compressive strength and water resistance.     

Reaction wood drying kinetics: tension wood in <Emphasis Type="Italic">Fagus sylvatica</Emphasis> and compression wood in <Emphasis Type="Italic">Picea abies</Emphasis>

The drying kinetics of reaction woods in Picea abies (compression wood) and Fagus sylvatica (tension wood) in comparison with their corresponding normal woods was investigated under constant convective drying conditions. Moisture profiles along the thickness of small flat-sawn boards taken from reaction and opposite wood zones were evaluated using a polychromatic X-ray system, a non-destructive method. The results revealed substantial differences in the drying behavior between the reaction and opposite woods. Both reaction woods represented slower drying rate than their matching normal woods mainly during the period of free water loss. However, the reaction and opposite woods reached the final moisture content (MC) of about 12% at the same time due to higher initial MC in the opposite woods. In the case of reaction wood, it took a longer time for the moisture profile to become approximately uniform. Overall, a more striking difference was observed in the drying behavior of compression and opposite wood in P. abies. Some important anatomical differences like the cell and pit dimensions and their proportion give some explanations for these drying behaviors.     

PRELIMINARY STUDY ON MAKING OF WATER RESISTANCE WOOD FIBERBOARD

In the present study,described that preparation of oligoesterified wood fibre by theaddition reaction of the wood fibre with maleic anhydride(MA)and allyl glycidyl ether(AGE).Further,made of crosslinkable oligoesterified fiber board at high temperature and underhigh pressues,accompanying plasticization of the wood fibre components.The product exhibitedthe high the modulus of repture in bending(MOR),good water repellency and dimesionalstability.     

Leachability,decay, and termite resistance of wood treated with metaborates

The formation of insoluble metaborates in wood was investigated by impregnating the wood with borax and metallic salts, after which their properties (e.g., leachability in running water and biological resistance) were evaluated. The solubility of three metaborates in acidic solutions was also evaluated. Double-diffusion treatment was carried out to form the precipitates of metaborates in sapwood specimens of Japanese cedar (Cryptomeria japonica) at room temperature. Water-saturated wood specimens were first impregnated by a saturated borax solution and then diffuse-penetrated with Zn²⁺, Ca²⁺, or Pb²⁺ solution. The precipitates of the three metaborates in the wood proved to be insoluble or hardly soluble in water by the leaching test. With the decay test using a brown-rot fungus (Fomitopsis palustris) and a white-rot fungus (Trametes versicolor) and with the termite test using a virulent subterranean termite (Coptotermes formosanus), the metaborate-treated woods showed generally good decay and termite resistance with negligible mass loss of the specimens. Particularly, the lead metaborate formed in the wood provided superb biological resistance against decay and termite attacks. In addition, the precipitates of these metaborates were found to be soluble in acidic solution, suggesting a way to remove these chemicals from wood when disposing of waste materials.     

Hydrophobization of wood surfaces: covalent grafting of silicone polymers

 The hydrophilicity of Maritime pine wood surfaces was modified by silicone, an extremely hydrophobic material. A generic method for the introduction of a variety of silicones at the surface of pre-treated wood was developed. The initial treatment of wood with maleic anhydride and allyl glycidyl ether resulted in oligoesterified wood bearing terminal alkenes. The hydro- osilylation of these groups, performed with hydride-terminated silicones, led to very hydrophobic surfaces, even after extensive soxhlet extraction with good solvents for silicones. Thze presence of silicon, only at the surface of hydrosilylated wood, was confirmed by ESCA. The silicones appear to be attached to the wood by covalent bonds. Received 20 December 1998     

我国木材及林产品供需平衡研究

在分析我国森林资源与木材供求状况,以及木材需求趋势与供需缺口的基础上,就如何实现我国木材与林产品自给,达到供需平衡进行了研究。研究表明,大力发展工业人工林,定向培育、提供适用木材,高效利用木材、节约林木资源、增加林产品供给,扩大原料来源、开发利用生物质资源生产林产品,是实现我国木材与林产品供需平衡的行之有效的途径。     

Utilisation of wood biomass residues from fruit tree branches,evergreen hardwood shrubs and Greek fir wood as raw materials for particleboard production. Part A. Mechanical properties

This paper investigates the potential of utilising wood biomass from fruit tree branches and evergreen hardwood shrubs as raw materials in the production of particleboards when mixed with Greek fir wood particles. The main mechanical properties of the boards made therefrom were determined and compared with those made of typical industrial wood (IW) particles. The highest modulus of rupture and elasticity (30.0 N/mm² and 4330 N/mm², respectively) in bending and screw withdrawal (SW) resistance (127.8 N/mm) were reported for boards made of Greek fir and were downgraded when the fruit tree branches or evergreen hardwood shrub particles also participated. The participation of fruit tree branch particles in proportions higher than 50% improved the internal bond (IB) of fir produced boards, while the highest IB strength (0.95 N/mm²) was reported for boards made of fruit tree branches. Particleboards made of evergreen hardwood shrubs showed inferior mechanical properties compared with those made of IW particles. The latter also showed superior bending strength but inferior SW resistance compared with boards made of fruit tree branches. Hygroscopic and other properties are under determination and will be presented and discussed in the second part of the work.     

Forest management and carbon sequestration in wood products

Wood products are considered to contribute to the mitigation of carbon dioxide emissions. A critical gap in the life cycle of wood products is to transfer the raw timber from the forest to the processing wood industry and, thus, the primary wood products. Therefore, often rough estimates are used for this step to obtain total forestry carbon balances. The objectives of this study were (1) to examine the fate of timber harvested in Thuringian state forests (central Germany), representing a large, intensively managed forested region, and (2) to quantify carbon stocks and the lifetime of primary wood products made from this timber. The analyses were based on the amount and assortments of actually sold timber, and production parameters of the companies that bought and processed this timber. In addition, for coniferous stands of a selected Thuringian forest district, we calculated potential effects of management, as expressed by different thinning regimes on wood products and their lifetimes. Total annual timber sale of soft- and hardwoods from Thuringian state forests (195,000 ha) increased from about 136,893 t C (~0.7 t C ha⁻¹ year⁻¹) in 1996 to 280,194 t C (~1.4 t C ha⁻¹ year⁻¹) in 2005. About 47% of annual total timber harvest went into short-lived wood products with a mean residence time (MRT) < 25 years. Thirty-one per cent of the total harvest went into wood products with an MRT of 25–43 years, and only 22% was used as construction wood and glued wood, products with the longest MRT (50 years). The average MRT of carbon in harvested wood products was 20 years. Thinning from above throughout the rotation of spruce forests would lead to an average MRT in harvested wood products of about 23 years, thinning from below of about 18 years. A comparison of our calculations with estimates that resulted from the products module of the CO2FIX model (Nabuurs et al. 2001) demonstrates the influence of regional differences in forest management and wood processing industry on the lifetime of harvested wood products. To our knowledge, the present study provides for the first time real carbon inputs of a defined forest management unit to the wood product sector by linking data on raw timber production, timber sales and wood processing. With this new approach and using this data, it should be possible to substantially improve the net-carbon balance of the entire forestry sector.     

Utilization of wood biomass residues from fruit tree branches,evergreen hardwood shrubs,and Greek fir wood as raw materials for particleboard production. Part B. Hygroscopic properties and formaldehyde content

This paper investigates the basic hygroscopic properties and formaldehyde content (FC) of particleboards produced with wood biomass from fruit tree branches and evergreen hardwood shrubs as substitute raw materials for fir particles. One-layer laboratory particleboards with two distinct target densities (0.63 g/cm³ and 0.69 g/cm³) were produced using various mixtures of the above materials. Industrially produced wood particles were also used for comparison purposes. The results showed that the replacement of fir wood (FW) by evergreen hardwood material significantly upgraded board's quality in terms of thickness swelling (TS) and water absorption (WA) (except boards with density of 0.63 g/cm³) after immersion in water for 24 h and residual swelling (RS) after reconditioning. The contribution of branch-wood (BW) particles in the production of FW boards with density of 0.63 g/cm³ induced increase of TS, WA, and RS while for boards with density of 0.69 g/cm³ did not result to significant changes except for RS. In terms of FC, boards made of BW and evergreen hardwood showed significantly lower FC compared to those produced by FW and industrial particles.     

Longitudinal shrinkage behaviour of compression wood in radiata pine

The behaviour of longitudinal shrinkage was investigated in the corewood of a swept, 17-year-old New Zealand radiata pine stem. Wood categories in terms of normal wood, mild compression wood and severe compression wood were identified microscopically using autofluorescence of lignin. Average longitudinal shrinkage was collated according to corewood location and wood category within corewood in the leaning and the vertical parts of the stem, and then maximum radial difference of longitudinal shrinkage within growth ring was examined. The results show that the average longitudinal shrinkage is significant (2.4%) in the corewood of the leaning part of the stem. Among wood categories, severer compression wood displays the highest (2.9%) average longitudinal shrinkage. In the context of this study, growth rings may consist of one of three types of wood: (1) only normal wood; (2) a single compression wood type; and (3) mixed-type wood. Where multiple compression woods co-existed with normal wood, the maximum radial difference of longitudinal shrinkage within the growth ring was found to be 4.0%. A strong correlation (R ² = 0.90) between average MFA and average longitudinal shrinkage suggests a significant influence of the average MFA on average longitudinal shrinkage across the three growth ring types.     

Magnetic resonance imaging used for the evaluation of water presence in wood plastic composite boards exposed to exterior conditions

Abstract

Two wood plastic composite (WPC) boards, one experimental and one commercial, were exposed to exterior conditions and evaluated non-destructively using a clinical magnetic resonance imaging (MRI) unit for moisture content (MC) and distribution. The experimental board was exposed in Vancouver, British Columbia, for more than 8 years, and the commercial board was exposed near Hilo, Hawaii, for 2 years. Both boards were characterized in terms of wood content, density, water uptake properties and voids content. The experimental board was additionally destructively analysed for water absorption of the WPC and MC calculated based on the wood content for verification of MRI results. MRI detected the presence of free water and its distribution in both of the WPC boards. Fibre saturation in the experimental board was found to be about 22–24%, in comparison to 25–30% present in most wood species. There was good correlation between the detection of free water by MRI and by destructive testing. Magnetic resonance images showed various major points of water entry in the WPC boards such as the support area, the cut ends, the dripping edge and the sides of the boards. For the experimental board, significant water entry also occurred at the upper exposed surface.     

Development of high-performance strand boards: engineering design and experimental investigations

Strand-based engineered wood products such as oriented strand boards enjoy great popularity in structural engineering and are widely used for a variety of applications. To strengthen their competitiveness and to enlarge their range of utilization particularly in the load-bearing sector, the mechanical properties of these products need to be improved. This motivated the research efforts to use large-area, slender veneer strands for the production of strand boards with increased stiffness and strength. Target-oriented development of these products requires comprehending the effects of the relevant (micro-)characteristics, such as wood quality, strand geometry, and strand orientation and compaction during the production process, as well as layer assembly and density profile, on the mechanical properties of the finished strand boards. Comprehensive test series, in which these effects on tension, bending and shear properties of the boards have been studied individually, are presented in this paper. The obtained results provided insight into the microstructural load-carrying mechanisms and, thus, yielded valuable knowledge for product optimization and further improvement of custom-designed strand-based engineered wood products.     

The impact of former agriculture on habitat conditions and distribution patterns of ancient woodland plant species in recent black alder (Alnus glutinosa (L.) Gaertn.) woods in south-western Poland

Little is known about the influence of former agricultural use of soils on the forest recovery process in post-agricultural black alder (Alnus glutinosa) woods – the most fertile and the wettest forest habitats among the European temperate forest types. Thus, studies focusing on edaphic, hydrological and light conditions responsible for colonization mechanisms present in such woodlands adjoining ancient ones were undertaken in south-western Poland. In the 16 m² quadrats of the 33 transects laid out perpendicularly across the ancient-recent forest boundary, data were collected on herb layer composition, chemical soil properties, as well as illumination level. Additionally, groundwater level in the spring months was recorded in piezometers. The number and cover of true woodland herbs were higher in ancient woods, regardless of forest type. Soils in ancient woodlands reached higher levels of Al³⁺, K⁺, cation exchange capacity (CEC), available K, P, and organic C, whereas their pH was lower. The illumination level of the forest floor was greater in recent woods. Linear regression showed that recent wood age had a negative effect on pH and base cations, but positive on Fe²⁺, Ca²⁺, available P and Mg, CEC, and on C and N contents. CCA results showed that woodland age, pH, humus type, groundwater level, available Mg and K were always among those variables having the highest contribution in explaining the distribution pattern of woodland species in recent woods. Total N and available P contents were always higher in ancient woodland soils than in recent, and their content grew with time. Thus, they cannot be treated as indicators of former agricultural use of recent alder wood soils. Urtica dioica, Poa trivialis and Galium aparine, the three competitive herbs, avoided sites with a high level of groundwater, combined with poor illumination level. In order to create the best possible conditions allowing for effective forest recovery in habitats of such high fertility, it is essential to maintain a good water regime and shade in the forest floor. This in turn reduces the competitive exclusion of woodland flora by the aggressive herbs and facilitates the immigration of typical woodland herbs.     

Effects of UV light irradiation on colour stability of thermally modified, copper ethanolamine treated and non-modified wood: EPR and DRIFT spectroscopic studies

A series of experiments were carried out to investigate the colour stability of chemically treated and thermally modified wood compared to non-modified wood during long term artificial UV light irradiation. One set of wood samples was vacuum-pressure impregnated with alkaline (pH 9.8) copper (II) ethanolamine aqueous solution, while another set of samples from the same wood block was thermally modified at 210°C and −0.90 bar for 2 h. The treated and modified wood samples along with the non-modified ones were exposed to artificial UV light with the wave length in the region of UVA (315–400 nm) and UVB (280–315 nm) intermittently for 500 h. Colour measurements were carried out throughout the irradiation period at an interval of 100 h according to CIEL*a*b* system, where the results are presented in terms of ΔE, ΔL*, Δa* and Δb* values. Better photo-stability in terms of colour changes was recorded for both treated and modified woods compared to the non-modified one. By means of EPR and DRIFT spectroscopic study it was shown that some degree of colour stability of treated and modified woods, achieved during artificial UV light irradiation, resulted from lignin modifications and monomers of phenolic compounds.     

Chemical modification of wood by anhydrides without solvents or catalysts

Acetylated, propionylated, butyrylated, isobutyrylated, and hexanoylated woods were prepared at several temperatures. The reaction rate, dimensional stability, and changes in the ratios of specific gravity and dimensions in the tangential and radial directions were estimated. The reaction rate of propionylation was slow at temperatures under 90°C but increased with the temperature. The butyrylated, isobutyrylated, and hexanoylated woods showed little or no weight percent gain (WPG) and little or no antiswelling efficiency (ASE) below 110°C even for 24h, but they achieved significant WPG and ASE values at 140°C with a longer reaction time. The acetylated, propionylated, and butyrylated woods showed almost the same values for dimensional stabilization efficiency based on WPG (DSE). The specific gravity and dimensions ratios for acetylated, propionylated, and butyrylated woods compared to those of untreated wood increased with an increase in WPG.     

Distribution of lignin interunit bonds in the differentiating xylem of compression and normal woods of Pinus thunbergii

The lignification process and lignin distribution at different stages of cell wall differentiation in the secondary xylem of compression and normal woods of Pinus thunbergii were investigated by thioacidolysis and subsequent desulfuration. We prepared 50-µm-thick, contiguous tangential sections of pine shoots, cut from the cambial zone through to mature xylem. In compression wood, uncondensed guaiacyl (G) and p-hydroxyphenyl (H) lignins were deposited simultaneously from early to late stages of lignification. The various types of G-G, G-H, and H-H dimers were detected in compression wood, and the ratio of G-H and H-H dimers to total dimers increased as lignification proceeded. In contrast, uncondensed and condensed H units were detected in trace amounts in normal wood. Significant differences in the relative distributions of lignin interunit linkages were not observed between compression and normal woods or between differentiating and mature xylems in either compression or normal woods.Part of this report was presented at the 10th International Symposium on Wood and Pulping Chemistry, Yokohama, June, 1999     

Recent research and development work on wood composites in Japan

Summary This paper highlights a number of articles on research and development on wood composites. The coefficient of variation in the mechanical properties of wood components tends to decrease when the thickness of the wood elements decreases. This finding was utilized in the manufacture of hollow cylindrical columns of laminated veneer lumber (LVL) from Cryptomeria plantation thinnings. In the future, the marketing of wood composite boards will tend toward two types: thick boards with low density properties and thin boards with fiber orientation. For the production of thick boards, fundamental parameters and application of steam-injection pressing have been studied, and continuous steam-injection pressing has been developed. For thin board production, generation principles of aligning torque in high-voltage system and the application has been studied. A new oriented mat former with electrodes positioned only at the reverse side of a forming belt has been developed. Various synthetic resins of low-molecular weight have been applied to improve dimensional stability of laminated products, such as LVLs and particleboards. Acetylation and formalyzation of fibers and particles were investigated to provide stabilized panels. High pressure steam treatment during pressing of wood composites has been studied and the process has been found effective and promising.The authors wish to thank Mr. Dwight A. Eusebio for his help in the preparation of this paperThis paper was presented at the IUFRO All Division 5 conference in Nancy, France, on August 15, 1992