Thickness swelling and water absorption of WPC after immersion in cold and boiling water

Thickness swelling (TS), water absorption (WA) and edge swelling (ES) of 20 mm flat-pressed wood–plastic composites (WPC) panels with a wood flour (WF) content of 50 and 70 % manufactured using an industrial single-daylight press and samples of a high pressure laminate (HPL) compact panel were determined after immersion in cold water according to EN 317 and boiling water according to EN 438 in order to propose, describe and verify a method to (1) measure TS, WA and ES more quickly than by applying EN 317 and (2) to make the properties of WPC and HPL comparable to each other. TS, WA and ES of WPC panels determined after immersion in cold and boiling water were found to correlate with a correlation coefficient of 95–99 % equating 24 h (EN 317) and 0.5 h (EN 438) to factor x. Properties of WPC panels with WF content of 50 % were found to be comparable, respectively superior to those of HPL.     

Preparation and characterization of wood-plastic plywood bonded with high density polyethylene film

This paper presents a study on the potential use of high density polyethylene (HDPE) film as wood adhesive for formaldehyde-free plywood. The physical–mechanical properties of the plywood, including thickness swelling (TS), water absorption (WA), tensile shear strength, modulus of elasticity and modulus of rupture were evaluated. Results show that HDPE film dosage positively affects the properties when ranging from 61.6 to 246 g/m². The performance of these panels was comparable to those of plywood made with commercial urea–formaldehyde (UF) resins. Comparisons of the dimensional stability between the two plywood demonstrated that 7-day TS and WA values of the panels bonded with UF resins were 5.10 and 23.5 % higher than those bonded with HDPE film, confirming the suitability of HDPE for the use as adhesive in wood-based composites intended for indoor applications subjected to high moisture. DMA tests show that HDPE bonded plywood was significantly inferior in thermal stability at 120 °C and above while it presented almost the same dynamic mechanical properties as UF plywood when the temperature was lower than 100 °C, making it suitable to be used as geothermal floor.     

Optimising the properties of OSB by a one-step heat pre-treatment process

Heat-treatment of solid wood to increase its dimensional stability and durability is well known and established in the industry. To enhance the application of wood-based panels (e.g. for exterior application) their durability against moisture and fungal decay has to be improved. In this paper a possibility is shown, how to adapt a heat treatment process on wood-based panels. Two different temperatures were applied on strands of Scots pine, before hot-pressing oriented strand board. The mechanical properties show an influence of the applied temperature on the strands and of the adhesive used for the panel. The thickness swelling is reduced (Fig. 3), resulting in increased dimensional stability. The process temperature has a major influence; with an increased pre-treatment temperature the thickness swelling is reduced. The internal bond strength was not affected by the pre-treatment.     

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.     

Estimation of physical and mechanical properties of agro-based particleboards by near infrared spectroscopy

Partial least square regression (PLS-R) calibrations based on near infrared (NIR) spectroscopic data were developed in order to predict mechanical and physical properties of agro-based particleboards. The panels were manufactured using Eucalyptus and Pinus wood particles and sugar cane bagasse. The following panel properties were evaluated according to standard methods: modulus of elasticity (MOE), modulus of rupture (MOR), internal bonding (IB) strength, water absorption (WA24H), and thickness swelling (TS24H) after 24 hours of immersion. NIR spectra information was measured on samples cut from each particleboard and correlated with their physical and mechanical properties by PLS-R to build predictive NIR models. The NIR models for IB, WA24H and TS24H presented satisfactory coefficient of determination (0.73; 0.72 and 0.75, respectively.) The key role of resins (adhesives), cellulose, and lignin for NIRS calibrations of mechanical and physical properties of the particleboards is shown. These models can be useful to quickly verify such properties in unknown agro-based particleboards.     

Tailor made OSB for special application

The purpose of this study was to develop speciality oriented strand board (OSB) with high stiffness for use in products such as engineered wood flooring (EWF). Three-layer oriented strand boards were manufactured from two feedstocks of strands: a mixture of 90% aspen (Populus tremuloides) and 10% of paper birch (Betula papyrifera), and 100% of small diameter ponderosa pine logs (Pinus ponderosa). The OSB panels were manufactured under a factorial design of three resin contents, two density profiles, and three weight ratios for the face and core layers. Tests to determine density, bending modulus of elasticity (MOE), internal bond (IB) and thickness swelling (TS) were performed according to ASTM standard D 1037-06a. The results showed that the higher values of bending MOE for panels made from aspen/birch mixture and ponderosa pine, 8190 and 9050?MPa, respectively, were obtained for the same combination of factors. Such high bending MOE values are very close to Baltic birch (Betula pendula) plywood, a product known for its high stiffness. The effect of resin content on IB is more pronounced for panels made from ponderosa pine than panels made from the aspen/birch mixture. Thickness swelling of panels made from ponderosa pine strands is higher than thickness swelling of panels made from a mixture of aspen and birch strands. The results indicate the potential to tailor an OSB for a specific application such as EWF.     

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.     

Properties of oriented strandboard made of wood species from Brazilian planted forests: Part 1: 80 mm-long strands of Pinus taeda L.

This research is part of a general study on the properties of oriented strandboard (OSB) using wood strands of species from Brazilian planted forests. The OSB industry is the latest wood related activity established in Brazil. In this particular part of the study, 80 mm long strands of Pinus taeda L. were bonded using two resin types (urea-formaldehyde and phenol-formaldehyde) at two levels of resin content (5% and 8%) to produce three-layer cross-aligned OSB to a face to core layer ratio of 1:2 and target density of 0.75 g/cm³. Physical and mechanical properties of the boards were evaluated according to ASTM standard D 1037-96a (1997) and the results compared to standards available as requirements for commercial structural panels. The results indicate that all the mechanical properties evaluated were above the requirements set forth by the Canadian standard CSA O437.0 (1993) for structural panels. The results of Janka hardness were in average 4 folds higher than the minimal requirements for Grade R-1 waferboard. Screw withdrawal values were also above the minimum required by grade M-3 of ANSI A208.1 standard (1993). Nevertheless, values of thickness swelling and water absorption were very high. The low dimensional stability may be related to the high density of the boards (“springback” effect) and also to the fact that no wax was used.     

Comparative properties of bagasse, canola and hemp particle boards

Residues of Bagasse (Saccharum officinarum L.), canola (Brassica napus L.) and hemp (Cannabis sativa L.) as well as industrial wood chips in various proportions from 0–100% were used as raw materials for the main component of the middle layer in urea formaldehyde bonded particle boards. The results reveal that most of the investigated mechanical-technological properties of the boards achieved the requirements of EN 312-2 (2003). Only increasing the percentage of canola chips usage in the middle layer to more than 30% negatively affect the internal bond (IB) properties. Comparing the water absorption (WA) and thickness swelling (TS) values, the boards containing up to 50% bagasse and hemp reach similar values to the ones of the reference boards, while increasing the amount of canola leads to more and more disadvantageous WA and TS. In summary, the results reveal that agri-fibers can be used for making composite panels conforming to the standards (EN 312-2 2003). One possible application for these panels could be the production of furniture.     

Dimensional stability and irreversible thickness swell of thermally treated oriented strandboards (OSB)

This paper discusses thickness swell and irreversible thickness swell properties after immersion in water for 24, 48, 96 and 168 h, changes in equilibrium moisture content (EMC) and determination of dimensional changes associated with changes in relative humidity of laboratory-made methylene diphenyl diisocyanate (MDI)-bonded oriented strandboards (OSB). It was observed that thermal post-treatment of said OSB had a positive effect on the above mentioned properties. As far as thickness swell and irreversible thickness swell are concerned, it could be shown that the thermally modified variants generally performed better, i.e. lower values than the respective untreated ones for all four immersion periods and MDI dosages of 3.0, 4.0 und 5.0 %. It was furthermore noticeable that the swelling potential was not exhausted after immersion for 24 h and a prolonged immersion period led to significant increases in respective thickness swelling values. The EMC was decreased and the determination of dimensional changes associated with changes in relative humidity showed that thermally post-treated OSB displayed lower thickness changes when “drying“(from 65 to 30 % relative humidity; RH) as well as when “moistening“(from 65 to 85 % RH) than the untreated controls. For all of the above mentioned properties it can be concluded that the influence of the post-treatment temperature proved to be greater than the reduction of the hydrophobing agent from 1.0 to 0 %.     

Properties of MDF from black spruce tops as affected by thermomechanical refining conditions

Wood composite industry has focused on traditional wood fibre resources such as logs, wood chips and sawmill-residues for panel manufacturing. It is becoming necessary now for the wood composite panel industry to look for ways to utilize non-traditional forest resources such as forest residuals for panel manufacturing. A full factorial experimental design with two factors: retention time of preheating and steam pressure of thermal mechanical refining and three levels with 3, 5, 7 minutes of retention time and 6, 9, 12 bar of steam pressure was carried out in the MDF pilot plant of Forintek Canada Corp. in Quebec City of Canada to evaluate the effect of refining conditions on the properties of MDF panels made from the tops of black spruce (Picea mariana). The results from this study indicate that black spruce tops could be a good raw material for MDF manufacture. The effects of steam pressure of thermomechanical refining on modulus of elasticity (MOE), thickness swelling (TS), water absorption (WA) and linear expansion (LE) were considerable. The effect of retention time of preheating on internal bond strength (IB) was significant. The effects of retention time as well as the interaction between retention time and steam pressure were also significant for modulus of rupture (MOR).     

Hydrothermal treatment of strand particles of pine for the improvement of OSB panels

The aim of this study was to evaluate the effect of hydrothermal treatment in strand particles of pine used for oriented strand boards (OSB) production. Strand particles of pine were hydrothermally treated at 130, 150 and 170 °C for 7 and 21 min, for the determination of chemical composition, pH, equilibrium moisture content, particles mass loss, and contact angle of these particles with phenol–formaldehyde resin. Afterwards, OSB panels were produced using 8% phenol–formaldehyde resin, with a nominal density of 0.7 g/cm³, and pressing cycle at 170 °C and 3.14 MPa for 8 min. Then, the panels were kept in climate chamber until mass stabilization for the determination of their physical and mechanical properties, and for comparison with the European standards. The hydrothermal treatment in the particles decreased carbohydrate, especially mannan, xylan and arabinans, resulting in reduced equilibrium moisture content, pH, and contact angle, and increasing buffer capacity and mass loss. In OSB panels, treated particles caused the drop in the equilibrium moisture content and reduction of the thickness swelling of the panel, without reducing the mechanical strength, making the hydrothermal treatment very attractive. The hydrothermal treatment at 170 °C for 7 min allowed the resulting OSB panel being classified into the categories 1 and 2 of the European standard, expanding its range of use.     

Effect of radiata pine juvenile wood on the physical and mechanical properties of oriented strandboard

This work analyzes the impact of radiata pine (Pinus radiata D. Don) juvenile wood on the physical and mechanical properties of oriented strandboards (OSB). Radiata pine logs were obtained from 10 trees of a 26-year old managed stand located in the 8th Region of Chile. The experimental design considered the proportion of juvenile wood and strand orientation as independent variables. OSB panels of 0.4 m×0.4 m×12 mm were produced and tested. The results show that the juvenile wood proportion has a significant impact on the physical and mechanical properties of OSB. Strands orientation had a significant impact on all the properties studied with the exception of the modulus of elasticity in bending. However, this impact was small in all cases and would not change panel grade with the exception of linear expansion. In this case, panels made from tangential strands showed a higher linear expansion. According to these results, radiata pine juvenile wood can be used for the manufacturing of OSB up to a proportion of 70% of the oven-dry wood weight without significant losses of the physical and mechanical properties if the juvenile wood strands are located in the surface layers.     

Material properties and nondestructive evaluation of laminated veneer lumber (LVL) made from Pinus oocarpa and P. kesiya

This study aimed at evaluating the mechanical, physical and biological properties of laminated veneer lumber (LVL) made from Pinus oocarpa Schiede ex Schltdl (PO) and Pinus kesiya Royle ex Gordon (PK) and at providing a nondestructive characterization thereof. Four PO and four PK LVL boards from 22 randomly selected 2-mm thickness veneers were produced according to the following characteristics: phenol-formaldehyde (190 g/m²), hot-pressing at 150°C for 45 min and 2.8 N/mm² of specific pressure. After board production, nondestructive evaluation was conducted, and stress wave velocity (v ₀) and dynamic modulus of elasticity (E _Md ) were determined. The following mechanical and physical properties were then evaluated: static bending modulus of elasticity (E _M ), modulus of rupture (f _M ), compression strength parallel to grain (f _c,0), shear strength parallel to glue-line (f _v,0), shear strength perpendicular to glue-line (f _v,90), thickness swelling (TS), water absorption (WA), and permanent thickness swelling (PTS) for 2, 24, and 96-hour of water immersion. Biological property was also evaluated by measuring the weight loss by Trametes versicolor (Linnaeus ex Fries) Pilát (white-rot) and Gloeophyllum trabeum (Persoon ex Fries.) Murrill (brown-rot). After hot-pressing, no bubbles, delamination nor warping were observed for both species. In general, PK boards presented higher mechanical properties: E _M , E _Md , f _M , f _c,0 whereas PO boards were dimensionally more stable, with lower values of WA, TS and PTS in the 2, 24, and 96-hour immersion periods. Board density, f _v,0, f _v,90 and rot weight loss were statistically equal for PO and PK LVL. The prediction of flexural properties of consolidated LVL by the nondestructive method used was not very efficient, and the fitted models presented lower predictability.     

The effects of a two stage heat treatment process on the properties of particleboard

Steam pre-treatment can effectively improve the dimensional stability of panel products such as particleboard and fiberboard. At temperatures above 200–210 °C steam pre-treatment might result in a significant reduction of the bond strength of the panel product. The results of an effective two stage heat pre-treatment process, in which treatment temperatures below 200 °C are used, are given in this paper. The variations in process conditions which affect the particleboard properties are described in detail. A two- stage heat pre-treatment with temperatures below 200 °C appears to improve the dimensional stability of panel products. The process conditions used have an effect on thickness swelling and internal bond properties of the particleboard prepared, especially during the first process stage (hydrothermolysis). The best results were obtained with wood particles which were only thermolysed (without curing).     

Shape- and dimensional stability of solid wood panels made from heat-treated lime wood strips

The paper presents the results of an experimental research performed with solid wood panels made from heat-treated and untreated lime wood (Tilia cordata Mill.) strips and then subjected to open-air exposure for 3 months. The dimensions of the panels were measured by means of an OPTODesQ Measurement Table, first after conditioning and sanding, then after each month of open-air exposure in order to assess their shape- and dimensional stability. After 3 months, the panels made from heat-treated wood strips showed up to 70% lower volumetric swelling and up to 143% lower flatness deviation than the panels made from untreated strips.     

The effect of silicone on some properties of flakeboard

Waxes are used as water repellent in wood composites, and there are only limited alternative water-repellent systems for wood composites. The aim of this study was to investigate the effectiveness of a silicone compound as a water repellent for flakeboard and to compare the properties of boards made with silicone treated flakes to those made with commercial wax treated flakes. Three levels of silicone and wax application rates were used (0.25, 0.5, and 1%). The hydrophobic nature of silicone-treated flakes was evaluated by measuring the contact angle and the rate of water absorption (WA) on the surface of the wood flake. The internal bonding strength (IB), the modulus of elasticity (MOE) and modulus of rupture (MOR) in bending regime, the WA, and the thickness swelling at edges of boards were evaluated. Results obtained showed that IB, MOE and MOR decreased as the concentration of silicone on the flakes increased from 0.25% to 1%. The IB, MOE and MOR of panels made with 0.25% silicone-treated flakes were comparable to boards made with 1% wax-treated flakes. Thickness swell at edges and WA were significantly reduced as the amount of silicone increased. No significant difference was found for the thickness swelling at edges and the WA between panels made with 1% silicone-treated flakes and 1% wax-treated flakes. The silicone treated flakes had high water repellency.     

Peuchtebedingte Längenänderungen von Holzwerkstoffen in Plattenebene

A review of important factors influencing hygroscopic inplane swelling and shrinkage of wood-based panels (panel structure and components, measurement method, specimen size, conditioning of specimens) is given. Measurements of in-plane swelling and shrinkage on resin- and mineral-bonded particleboard, wet and dry process fibreboard, OSB, three-layer solid wood panel, and plywood are reported. The direct transfer of specimens from standard climate (20 °C/65% rel. humidity) to a dry (20/35) and a humid (20/85) climate, respectively, was compared with a two-step conditioning process involving intermediate steps, i.e. 20/75 and 20/50, respectively. In-plane swelling and shrinkage as well as equilibrium moisture contents of the panels at 20°C and 35, 50, 65, 75, and 85% relative humidity, respectively, are tabulated. From the results, important conclusions can be drawn with regard to a revision of EN 318. They also emphasise the influence of the conditioning procedure on swelling and shrinkage, and show that a quick test renders reliable results with regard to quality control on wood-based panels.     

应力释放对刨花板尺寸稳定性的影响

研究了热压过程中内应力的形成机理和板材内部应力状态,探讨了内应力释放对刨花板尺寸稳定性的影响,提出了减小内应力和提高尺寸稳定性的工艺措施。     

In-treatment cooling during thermal modification of wood in soy oil medium: soy oil uptake, wettability, water uptake and swelling properties

Thermal modification of wood is a process which has gained wider acceptability as an alternative to chemical treatment in wood preservation. In order to maximize the benefits of this technique several options have been adopted including the use of soy oil in transferring the heat to the wood. Available information on thermal treatment in general and the oil method in particular show that there is need for further investigations on the possibilities of improving the available options in order to evolve new techniques. Thermal treatment of ponderosa pine (Pinus ponderosa P Laws ex C Laws) and black spruce (Picea mariana (Mill) BSP) in soy bean oil was carried out at 220 °C for 2 hours followed by cooling inside the hot oil 180 °C and 135 °C. The surface wettability, (contact angle), amount of oil uptake, water absorption and thickness swelling were determined thereafter. The oil uptake ranged from 88 to 93.3% in the permeable ponderosa pine sapwood and from 6.1 to 11.3% in the refractory black spruce with the uptake increasing with cooling time but decreasing with increasing depth of wood in both species. Thermal modification in soybean oil increased the wettability of the surface to water (reduced contact angle). However, there were no significant changes to the surface energies due to in-treatment cooling, as determined by contact angles of water, glycerol, ethylene glycol, and formamide. There were reductions in the hydrophilic behaviour and swelling of wood as a result of the thermal treatment; in-oil cooling resulted in greater hydrophobicity and dimensional stability in the wood. In both species, there were greater reductions in water uptake and swelling with increasing cooling time.