Feasibility of particle board production using bone glue

This feasibility study describes a new procedure for bonding particle boards using animal protein glue produced from bone. Making use of the thermoplastic properties of bone glue, particle boards with mechanical properties partly comparable to a MUF-bonded reference board were obtained at laboratory scale.     

Improved water resistance of particleboards bonded with glutaraldehyde-blended UF resin

One-layer particleboards were bonded with a UF-glutaraldehyde adhesive system. It was shown that 5 wt % of the glutaric aldehyde in the glue mix can reduce swelling and absorptivity of the boards without deterioration of their mechanical parameters below the requirements of the respective standards.     

Gas pressure measurements during continuous hot pressing of particleboard

Knowledge about the development of the internal gas pressure during hot pressing of wood-based composites is important for the optimization of panel properties and production speed. The gas pressure heavily affects the thermodynamic conditions inside the wood furnish mat, and a too high maximum value at press opening might cause an impairment of the panel properties. In this paper, gas pressure and temperature measurements inside a particle mat while passing through a continuous hot press are presented for the first time. The measurements were performed with a transportable system, consisting of a steel tube attached to a miniature pressure transducer and a data logger. The particleboards had a target thickness of mainly 16 mm, but also of 28 mm and 38 mm, respectively.     

Chemische Eigenschaften von TMP und CTMP, hergestellt aus Kiefernholz und UF-Harz-gebundenen mitteldichten Faserplatten (MDF)

Thermo-mechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) were prepared from pine wood and from UF-bonded MDF made from pine wood. For preparing TMP pine chips as well as UF-bonded MDF were digested under pressure at 170 °C. Thereafter, the digested chips and MDF were defibrated at 170 °C using a single disc refiner. CTMP was prepared from pine wood with 0.25% NaOH (based on dry wood) under the conditions set forth above. CTMP was also made from MDF under two conditions using 0.15% sodium hydroxide (% based on dry MDF) and a mixture of sodium sulphite (1%) and sodium hydroxide (0.25%). The pulps show distinct differences in their properties: TMP from UF-bonded MDF shows lower extractive content in cold and hot water, lower pH-value and higher buffering capacity towards alkali of the cold water extractives than the CTMP counterpart. Moreover, CTMP prepared by using sodium hydroxide alone as a pulping agent increases the content of formate and acetate ions in the cold water extractives. The use of a mixture of sodium sulfite and sodium hydroxide as a pulping agent decreases, however, significantly the content of formate and acetate ions in the cold water extractives. This may be due to the buffering action of sodium sulfite. In general, CTMP decreases the formaldehyde release of the fibres, as measured by the flask method. In presence of sodium sulfite as a pulping agent for recycled MDF, the formaldehyde release is slashed to almost 30% of its original value. The formaldehyde release of CTMP from UF-bonded boards seems to be in the same range as that of TMP from virgin wood.      

Laboratory-made cement-bonded OSB with negligible swelling: fact or fantasy?

The purpose of this paper was to evaluate the dimensional stability of cement-bonded oriented strand boards produced from fir strands, which have previously been chemically modified at a weight gain of 10.4%, after 30 min reaction with acetic anhydride. The strands were used to form laboratory boards, which were tested in accordance with EN standards. Boards made from these acetylated strands exhibited negligible thickness swelling even after one month of immersion in water.     

The measurement of wood density by microwave sensor

This paper presents the first results of wood density measurement using a microwave sensor. The information given by the sensor are amplitude variations and phase variations of the transmitted wave. This work concerns the calibration of the sensor. To eliminate the problem of wood anisotropy we used boards made from glued and pressed sawdust. There are 5 kinds of sawdust and from each five different board densities were prepared. The first measurements concerned the geometry and the realibility of the sensor. The results show that the sensor does not present defect geometry and that its readings are reliable. Then we looked for a relationship between board density and the variations of the microwave parameters. An accurate linear relationship was found, but it appears to be necessary to consider each sawdust type separately. Based on these results we prepared other samples with different glue contents to control the influence of glue on microwave parameters. The results show that in our ranges of densities (0.55–0.75 g/cm³) and glue contents (6–12%) the influence of glue is negligible. Furtheron, it appears that measuring the amplitude variation may be a means for controlling the granulometry of particle boards.     

Zeitstandversuche mit Spanplatten

Tests regarding fatigue behavior of particle boards bonded with different glue types, the characteristics of which are given, have been carried out with a loading period of 588 days. The periodically measured deflections were compared with the initial deflection and the deflection ratiof _t/f₀ was determined. After a loading period of one year the best of the tested boards had doubled their initial deflection showing no essential increase of deflection until determination of tests. The worst boards reached, already after 150 days, a deflection 5 times higher than the initial one and increased it up to more than 7 times until determination of tests. The course of the deflection ratio and the respective moisture content of the boards in dependence on the surrounding climate is demonstrated.     

Zeitstandversuche mit Spanplatten

Tests regarding fatigue behavior of particle boards bonded with different glue types, the characteristics of which are given, have been carried out with a loading period of 588 days. The periodically measured deflections were compared with the initial deflection and the deflection ratiof _t/f₀ was determined. After a loading period of one year the best of the tested boards had doubled their initial deflection showing no essential increase of deflection until determination of tests. The worst boards reached, already after 150 days, a deflection 5 times higher than the initial one and increased it up to more than 7 times until determination of tests. The course of the deflection ratio and the respective moisture content of the boards in dependence on the surrounding climate is demonstrated.     

Reduction of glue consumption in the plywood production by using previously compressed veneer

The production of plywood from previously compressed veneer allows to save up to 25% of glue, to halve the roughness of veneer and plywood and to press the plywood at a 22% lower pressure. However, the thickness of plywood reduces from 8.3 mm for uncompressed veneer to 6.4–8.0 mm for compressed veneer, and the density increases from 793 kg/m³ to 807–1005 kg/m³ accordingly.     

Untersuchungen über die Festigkeiten von Verklebungen mit reaktiven PUR-Schmelzklebstoffen

Reactive PUR-hotmelts grow hard rapidly by cooling. The glueline properties can be enhanced in connection with a chemical reaction. Shear strength, resistance to heat and cold as well as the resistance to moisture can be improved. The specific properties of different PUR-hotmelts were tested on a large scale. Shear, strength of the gluelines increases with elapsed time. As expected, strength is reduced by higher storing temperature. Foamed PUR-hotmelts have nearly the same strength and approximately the same temperature resistance compared to compaet PUR-hotmelts. For glueing together wood with plastics and metall by using PUR-hotmelts individual test have to be carried out in order to find correct primer and appropriate glue. Shear tests on solid wood edge banded particle boards show nearly the same results as the laboratory tests.     

Thermal properties of wood-gypsum boards

Transient simultaneous measurements of thermal conductivity, volume heat capacity and thermal diffusivity of laboratory wood-gypsum boards have been performed with ISOMET 2104 at room temperature. The influences of wood particle content, density and moisture content on thermal properties were investigated. The measurements were performed in a direction perpendicular to the board plane. The effect of density and wood particle content on the thermal properties may be related to the presence of voids both between and inside particles. It seems, that the dominant mechanism of heat transfer across the board is the heat conduction through the voids. Wood-gypsum boards with a density of 850–1300 kg/m³, a moisture content of 2–11% and a wood particle content of 0–35% have the following thermal conductivity of 0.189–0.753 W m^-1 K^-1, volume heat capacity of 0.683–1.43×10⁶ J m^-3 K^-1 and thermal diffusivity of 0.171–0.367×10^-6 m² s^-1; their magnitudes are higher than those ones of OSB, MDF, particleboard and plywood.     

A?novel method for the quantitative analysis of the water content in lignocellulosic material

A novel method for the determination of the water content in wood has been developed and experimentally tested. Based on the reaction of trimethylchlorosilane with various wood constituents and water, the generation of a by-product (hexamethyldisiloxane) was pursued and quantified via gas-chromatography and the water content was subsequently calculated back. The experiments were carried out with preconditioned spruce wood meal (particle sizes ranging between 60 and 140 microns) using water free solvents and reagents in a water free reaction atmosphere. The results showed that the investigated samples incorporated around 10 wt. % of water after preconditioning for 48 h.     

Influence of the adhesive layer on the mechanical properties of thin veneer-based composite materials

For the production of spliced veneers the veneers are coated with thin cellulose fleece or special paper layers, and thereby thin composites are generated. This article describes the mechanical properties of such a composite material consisting of 0.35 mm beech (Fagus sylvatica  L.) veneer and a 0.12 mm cellulose fleece bonded with a PVAc adhesive.     

Formaldehydarme Flächenverleimung mit Aminoplastharzen

Aminoplast-bonded plywood, coreboard, and venecred or faced particle board may also release formaldehyde. This report deals with the factors that have an influence on the quantity of formaldehyde released during the production of boards. The quantity of formaldehyde subsequently released by the panels is determined not only by the carrier material, but also by the working and pressing conditions in laminating and veneering. The formaldehyde content of the glue for veneering apparently also plays an important role.     

Bark extractives fromPinus halepensis Mill. fortified with polymeric diisocyanate for exterior grade particleboards

Extractives taken with hot water from bark ofPinus halepensis Mill. were used as basic adhesive components for exterior grade particleboards. In order to make the extract solutions sprayable onto the wood chips their viscosity was reduced by adding 15% ethanol (on extracts solids) to 40% concentration extract and by supplementary stirring and heating. The pH increase of extract solutions (38%) in the area from 4 to 9 was followed by viscosity increase while gelation times decreased. At initial pH 4.15 the viscosity of extract solution slightly increased with storage time, whereas it increased rapidly at pH 7. Commercial polymeric diisocyanate (PMDI) was used as fortifier for the extract adhesive. Glue formulations consisting of seven extract/PMDI combinations were chosen for preparing one-layer particleboards. Fine powder of paraformaldehyde was used as hardener for bark extract. The three components extract-PMDI-paraformaldehyde were sprayed onto the wood chips separately of each other. The results of the tested particleboards showed that the addition of PMDI to extractives improved both strength and swelling properties of the boards. Particularly, glue formulations containing PMDI in amounts of 20% and 30% (based on solid resin) provided wet bonding strengths (V100 and V313), which satisfied the requirements of the related standard for board use in humid conditions (EN 312 part 5). The same glue formulation improved the thickness swelling of the boards in levels considerably lower than those of boards bonded with pure bark extract or pure PMDI adhesive. Furthermore, wet bonding strength and swelling properties of PMDI-bonded boards were improved by adding relatively high amounts of extracts (70 and 80%). From the mixed formulations studied, the bark extract: PMDI, 70∶30 was by far the most promising for weather resistant boards. The results indicated that theP. halepensis bark extractive/PMDI adhesive system is capable of producing exterior grade particleboards.     

Thermal modification of consolidated oriented strandboards: effects on dimensional stability, mechanical properties, chemical composition and surface color

The objective of this paper was to propose a thermal post-treatment to improve the dimensional stability of oriented strandboard (OSB). Commercial OSB panels were obtained from an industrial batch and thermally treated in a single opening hot-press at two temperature levels (190 and 220 °C) and three duration times (12, 16 and 20 min). Dimensional stability, mechanical properties, chemical composition and surface color were studied. The results pointed-out that the proposed treatment can be applied to significantly improve the OSB dimensional stability by reducing thickness swelling, water absorption, and equilibrium moisture content in comparison to the untreated board. The mechanical properties were partially affected with reduction in modulus of rupture and without any adverse effect on the other properties. Chemical degradation occurred, mainly in relation to hemicelluloses contents, reducing equilibrium moisture content. The board surface became darker and this characteristic was correlated with the observed properties improvement. Dimensional stability properties were affected by both temperature and duration of the treatment, while the others mainly by temperature. The proposed thermal treatment can be recommended as a post-treatment to improve the OSB performance.     

Beitrag zur Herstellung PMDI-verleimter Spanplatten mit verschiedenen Strohanteilen

Wheat straw was milled in different types of laboratory mills using a variety of screens. Two from six different particle mixtures for the core layer were selected, one of which was produced in a cutting mill and the others in a hammer mill. These two core layer mixtures were turned into surface layer material by putting them through a wing beater mill. Later, industrial surface layer and core layer flakes were added. A PMDI glue was used for blending with the surface and core layer material. Five different combinations, two containing straw only, two various portions of straw and wood flakes and one containing only wood flakes were pressed to three-layer boards. Testing the tensile strength perpendicular to the surface, bending strength, internal bond, screw withdrawal strength, thickness swelling and surface roughness, the 100% straw-boards usually had the lowest values. The combination with wood flakes led to a marked improvement of strength properties but never reached the level of those in wood based particleboards. Straw boards partly comply with minimum standard values (e.g. bending strength) or fail to reach them by only a narrow margin.     

About the possibility of producing wood particle boards with extremely low formaldehyde content

Laboratory investigations have been conducted with the aim of producing wood particle boards with formaldehyd content less than that of initial wood particles. Wood particle boards have been produced on the basis of low-mole urea-formaldehyde resins using mole ratios of urea to formaldehyde 1∶1.2 and 1∶1.15. Physical-mechanical properties of the boards are similar to those made on the basis of commercial-grade resins.     

Der Einfluß des Trocknungsgrades der Holzspäne auf die Festigkeit zementgebundener Spanplatten

Cement bonded particle boards were made of undried, air dried and kiln dried particles of spruce and poplar wood and the bending strengths of the boards were measured after 3, 10 and 28 days. Air dried particles of both wood species gave boards with better strength properties than undried particles. Kiln drying of the particles was found to have a substantially improving effect on the bending strength of cement bonded particle boards made of poplar particles whereas the same procedure did not produce any effect with spruce particles.     

Beitrag zur Kurzzeitfestigkeit und zum Dauerstandverhalten von MDF der ersten Generation

Characteristic features of MDF of the first generation are: manufacture of MDF from inferior wood assortments with bark, multilayer structure of the boards on fibrous materials of different fineness, gluing of the fibrous material in mixers, lower middle density. Typical properties of these MDF: density 700–730 kg/m³, internal bond 0.50–0.65 N/mm², bending strength 26–35 N/mm², modulusE _b 2700–3000 N/mm². Dealt with are results from former long-term tests in comparison with conventional particle boards for furniture (of lower bending strength). With constant load not graded according to the strength the deflection of these MDF was similar to, or higher than that of the particle boards, their creeping coefficient exceeded that of the particle boards.