Physical and mechanical properties of plywood produced with 1.3-dimethylol-4.5-dihydroxyethyleneurea (DMDHEU)-modified veneers of Betula sp. and Fagus sylvatica

The dimensional stability and some mechanical properties were tested in plywood produced with veneers modified with 1.3-dimethylol-4.5-dihydroxyethyleneurea (DMDHEU). The experimental design included Betula sp. and Fagus sylvatica impregnated with 0.8 M, 1.3 M, and 2.3 M DMDHEU. The plywood consisted of five veneers glued with a phenolic resin. Dimensional stability tests were conducted after 10 cycles of soaking/oven-drying to determine volume changes and anti swelling efficiency (ASE). The mechanical properties tested were hardness (Brinell), modulus of elasticity in bending (MOE), bending strength (BS) and work to maximum load in bending (WMLB). The modified samples for both species were considerably more dimensionally stable than the untreated samples. The samples of Betula sp. and F. sylvatica modified with DMDHEU presented a MOE and a BS unaffected by the treatment. The WMLB was consistently lower in the modified samples than in the unmodified samples. As determined by the Brinell method, the DMDHEU-modified plywood of the Betula sp. and F. sylvatica was harder than the unmodified plywood.     

Measurement of wood and bark particles acidity and their impact on the curing of urea formaldehyde resin during the hot pressing of mixed panels

In the manufacture of panels, pH value is an important property to measure, especially when a pH-dependent resin like urea-formaldehyde (UF) is used. It has been proven that UF cures very well and faster in an acidic environment. In this study the acidity (pH value and buffering capacity) of both outer and inner white birch bark particles as well as that of wood particles or fibres used together with those barks as reinforcement for the manufacture of three layers particleboards was measured. The results show a significant difference between the acidity of white birch bark and wood. Barks have a lower pH as well as higher acid and alkaline buffering capacities. It was also found that the pH value of inner white birch bark is lower than that of the outer part. The significant differences observed enabled to realize that inner bark should be separated from outer bark and used separately in mixed panels manufacture. The platen temperature should be reduced when the outer bark is used in the surface of mixed panels to avoid pre-cure or over-cure. This study confirms the linear relationship between the pH and the absolute and relative buffering capacities.     

Utilization of bark flours as additive in plywood manufacturing

Increasing demand for wood based panel products and shortage of wood as raw material have triggered many efforts to utilize residues generated annually by the forest industries including a large portion of bark in panel production. In this study, the effects of using bark flours as additives obtained from different wood species (walnut, chestnut, fir and spruce), having much polyphenol content, on some physical and mechanical properties and formaldehyde emission of plywood panels were examined. Wheat flour, which has been used widely as additive in plywood manufacturing, served as control. Plane tree (Platanus orientalis) logs were obtained for veneer manufacturing. Urea formaldehyde (UF) resin with 55 % solids content was used as adhesive. The bonding shear strength, bending strength, modulus of elasticity (MOE), density, equilibrium moisture content and formaldehyde emission of plywood panels were determined according to related standards. It was found that the use of flours obtained from the barks of chestnut and fir trees in the glue mixture decreased the formaldehyde emission of panels. The bonding strength values of the test panels made using the glue mixture including the flour of walnut and spruce barks as additive were lower than those of the panels with adhesive containing the flour of fir and chestnut barks. The panels manufactured with adhesives including the flour of fir bark gave the highest bending strength and modulus of elasticity values.     

Effects of wood species and adhesive types on the amount of volatile acetic acid of plywood by using desiccator-method

The effects of wood species and adhesive types on the amount of volatile acetic acid and pH values of plywood panels were investigated using high performance liquid chromatography (HPLC). The plywood panels bonded with PF resin emitted more volatile acetic acid than those bonded with UF resins. According to the pH measurement carried out in the absorption solutions for volatile acetic acid emissions, the pH values of beech plywood panels were found to be higher than those of alder plywood panels.     

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.     

Effect of short-term thermomechanical densification of wood veneers on the properties of birch plywood

In this study, the physical and mechanical properties of plywood panels made from pre-compressed birch (Betula verrucosa Ehrh.) veneer were evaluated. Veneer sheets underwent short-term thermo-mechanical (STTM) compression at temperatures of 150 or 180 °C and at pressures of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 or 3.5 MPa for a period of 1 min prior to adhesive being applied and pressed into panels using phenol formaldehyde adhesive at 100 g/m² spread rate; this was one-third less than the adhesive spread used for the control panels (150 g/m²). The pressing pressure was 1.0 MPa, which was almost half of the pressure used for the control panels (1.8 MPa); and pressing time was 3 min, also half of the pressing time used for the control panels (6 min). The results showed that surface roughness of compressed veneer, water absorption and thickness swelling of plywood panels made from compressed veneer were significantly improved. The shear strength values of plywood panels made from compressed birch veneer even with reduced adhesive spread were higher than those of plywood panels made from uncompressed veneer. The findings in this study indicated that compression of birch veneer could be considered as an alternative to produce more eco-friendly (owing to smaller adhesive spread) value-added material with enhanced properties.     

Characterization of a formaldehyde-free cornstarch-tannin wood adhesive for interior plywood

This study investigated the physical properties (rheological and thermogravimetric analysis) of cornstarch-tannin adhesives and the mechanical properties (dry tensile strength and 3-point bending strength) of plywood made using cornstarch-tannin adhesives. This adhesive was evaluated for its utility in interior plywood manufacture. The optimum cure temperature and cure time of cornstarch-tannin adhesives were 170°C and 4?min, respectively. Plywood bonded with formaldehyde-free cornstarch-tannin adhesive exhibited excellent mechanical properties comparable to commercially available phenol-formaldehyde plywood adhesives. It was found that cornstarch-tannin panels which do not contain formaldehyde and with an emission equal to that of heated but unbound wood can be obtained by the use of hexamethylenetetramine (hexamine) as hardener. The work has indicated that an environmentally friendly wood adhesive can be prepared from a natural renewable resource (cornstarch and wattle tannin) for bonding interior-type plywood.     

亚麻织物膨胀型阻燃剂整理

采用聚磷酸铵(APP)和三聚氰胺(MEL)组成的膨胀型复合阻燃剂对亚麻织物进行整理,垂直法燃烧试验、热重分析、扫描电子显微镜分析等表明,当APP和MEL的配比为2∶1,阻燃剂的用量为25%时,亚麻织物的炭损长度低至10.0 cm,极限氧指数高达37%。阻燃整理后,700℃时亚麻织物的质量保留率由不加阻燃剂时的16%增至35%,织物在燃烧时可形成膨胀的发泡焦化炭层,起良好的膨胀阻燃效果。此外,织物的强度、白度、透气性和手感均有一定程度的下降。     

磷/氮阻燃剂对涤纶/棉混纺织物的阻燃整理

为赋予涤纶/棉混纺织物良好的阻燃性能,采用生物质植酸和尿素合成植酸铵盐,通过轧—烘—焙工艺对涤纶/棉混纺织物进行整理。借助傅里叶红外光谱仪对合成阻燃剂植酸铵盐进行表征,并研究了整理后涤纶/棉混纺织物的表面形貌、热稳定性、热释放性能、阻燃性能及其阻燃机制。结果表明:整理后涤纶/棉混纺织物的阻燃性能较好,极限氧指数升高至25.6%,在垂直燃烧测试中能够自熄,炭长降低为12 cm,满足GB/T 17591—2006《阻燃织物》中B₁级阻燃性能的要求;整理后涤纶/棉混纺织物的热稳定性提高,热释放能力降低;植酸铵盐主要通过膨胀型阻燃机制提高涤纶/棉混纺织物的阻燃性能。     

Recycled micronized polyurethane powders as active extenders of UF and PF wood panel adhesives

The addition of micronized polyurethane powders obtained from waste flexible polyurethanes to urea-formaldehyde (UF) resins and to phenol-formaldehyde (PF) resins improves markedly the performance of the panels prepared with these resins, namely plywood and particleboard. Infrared spectrophotometry (FT-IR) indicates that to some limited extent a reaction does appear to occur between micronized PUR waste powder and PF resin when the mix is cured under alkaline conditions. There appears to be no reaction at all instead between acid-setting UF resins and PUR powder. In both cases an active filler or extender effect appears to occur, otherwise the improvement in dry strength of UF–bonded joints cannot be explained. Even when reaction does evidently not occur, the addition of PUR powder improves markedly the water resistance of UF and PF resins. This active extender/filler effect is not due to any isocyanate group being re-generated on heating as both FT-IR and NMR confirm the absence of these groups.     

Improving physical and mechanical properties of new lignin- urea-glyoxal resin by nanoclay

To eliminate toxic formaldehyde from wood based panels, glyoxal, a low volatility and nontoxic aldehyde, was used to react with urea and lignin to prepare a glyoxalated lignin- urea-glyoxal (LUG) wood adhesive resin. Moreover, another objective of this research work was to improve the physical and mechanical properties of the new LUG resins by nanoclay addition. For the preparation of LUG resin, glyoxalated lignin (15 mass%) was added instead of second urea to the urea-glyoxal resin synthesis under acid conditions. The LUG resin so prepared was mixed with 1, 2 and 3 mass% nanoclay by mechanically stirring for 5 min at room temperature. Then, the physicochemical and structural properties of the prepared resins as well as the water absorption and the mechanical properties of the plywood panels bonded with it were measured according to standard methods. The physicochemical test results indicated that the gel time of the LUG resin was markedly slower than that of the UF resin. Plywood panels prepared with the LUG resin also presented lower water absorption as well as weaker shear strength than those prepared with the UF resin. Addition of nanoclay changed the physicochemical properties of the resins as the gelation time of the LUG resin was shorter when adding sodium montmorillonite (NaMMT). Higher shear strength values and lower water absorption were achieved by continuously increasing nanoclay proportion from 1 to 3 mass%. Furthermore, addition of nanoclay had more influence on panels bending strength than their flexural modulus. X-ray diffraction (XRD) analysis also indicated that NaMMT exfoliated completely when mixed with LUG resin.     

Modification of beech veneers with N-methylol melamine compounds for the production of plywood: natural weathering

Beech (Fagus sylvatica L.) veneers were treated with two formulations based on N-methylol-melamine (NMM): (1)?NMM solution (NMM-1, 10% solid content), (2)?fatty acid modified NMM dispersions containing paraffin (with an aluminium salt as catalyst, mNMM-2, 5% solid content). Five veneers were glued with a phenol formaldehyde adhesive to produce plywood. The plywood specimens were weathered outdoors over a period of 18 months according to EN 927-3 (2006). The moisture content of the treated plywood was clearly reduced during the exposure as compared to panels from water treated veneers (controls). As a consequence, the treated plywood displayed higher form stability and less cracks and delamination than the control plywood. Coated, NMM-treated plywood panels displayed remarkable lower degrees of discoloration than the coated controls. These differences between the treated, coated and the coated control panels were not so clearly observed in the case of uncoated panels. The treatment with NMM compounds additionally led to reduced surface colonisation by staining fungi on the indirectly weathered reverse sides of the plywood panels.     

Effect of sanding and coating with UV-cured finishes on the surface roughness, dimensional stability and fire resistance of oriented strandboard

Oriented strandboard was sanded and roller-coated with UV-cured finishes. The effects of these treatments on the surface roughness, dimensional stability and fire resistance of OSB were assessed. Sanding reduced the average roughness of OSB, but it had a smaller effect on maximum roughness because sanded boards still contained surface voids between some strands. Sanded boards absorbed less than half of the coating material of unsanded boards, and when they were finished with a UV-cured coating system consisting of filler, sealer and two top coats they absorbed less water and were almost as dimensionally stable as unsanded and coated boards. The swelling of coated boards after 72 h immersion in water was less than one third of that of uncoated OSB. This reduction in swelling compares favourably with that which can be achieved using chemical or thermal modification of OSB. Coated boards were more fire resistant than uncoated ones, but sanding reduced the fire resistance of OSB (coated and uncoated), possibly because it removed part of the densified surface layer from panels. Hence, we conclude that light surface sanding makes it easier and more economical to apply moisture resistant finishes to OSB using roller coating, but it should not be used prior to application of fire-retardant finishes.     

On the performance of a melamine–urea–formaldehyde resin for decorative paper coatings

The decorative laminates industry is a highly competitive industrial sector. To be profitable, manufacturers of impregnated papers for surface laminated MDF and particleboards need to significantly reduce their production costs. Melamine formaldehyde resin (MF) formulations are commonly used for impregnation and coating of such papers, melamine being an important, but costly raw material used in high quantities. While MF is substituted by cheaper urea formaldehyde resins (UF) in the core impregnation, for paper surface films pure MF is used. Therefore, a further reduction in cost could be achieved if a portion of the melamine in the surface film was replaced by urea. In the present contribution, recent results of technological tests on paper laminates using a novel melamine–urea–formaldehyde resin (MUF) formulation are reported and their performance is compared to traditional surfaces made from MF.     

Mechanical properties of wood treated with PF-pyrolytic oil resins

Jack pine and sugar maple wood samples were treated in a two-step process that involved first a copper chloride or a copper chloride-sodium borate mixture and then a phenol-formaldehyde resin containing a certain percentage of softwood bark pyrolytic oil. Various controls were also prepared for comparison. The modulus of rupture (MOR) of jack pine samples was generally negatively affected by the treatment, the observed values being lower than those of the controls. These values were statistically lower or equal to those of untreated samples. On the other hand, the modulus of elasticity (MOE) of treated jack pine samples was not found to be statistically different from that of the untreated wood. Mechanical properties behaved in a similar way for sugar maple wood. Unlike the other treatments, copper chloride–sodium borate and the resin containing 85% of pyrolytic oil as phenol substitute appeared to slightly improve the mechanical properties of both wood species even if not significantly so. Treatment with PF-pyrolytic oil resin resulted in similar or slightly better mechanical properties when compared to CCA-treated wood. The amount of treating water soluble salts retained in samples after the first treatment had a significant impact on MOR of both wood species and on MOE of sugar maple.     

Weathering of uncoated and coated wood treated with methylated 1,3-dimethylol-4,5-dihydroxyethyleneurea (mDMDHEU)

Scots pine (Pinus silvestris L.) sapwood panels were treated with a methylated 1,3-dimethylol-4,5-dihydroxyethyleneurea (mDMDHEU) causing weight gains of approx. 25% and were exposed to weathering for 18 months. Compared to untreated panels, treatment with mDMDHEUreduced surface discoloration mainly caused by staining fungi. Panels treated with mDMDHEU clearly exhibited lower moisture content throughout the exposure time and lower water uptake in periodical submersion tests. The treatment also reduced deformation (cupping) and crack formation of the panels due to weathering (assessed as waviness and surface roughness). When coated panels were compared, a pre-treatment with mDMDHEU resulted in lower water uptake in periodical submersion tests, less discoloration, minor deformation (cupping) and less crack formation (assessed as waviness and surface roughness). Oil-based coatings did not peel off the mDMDHEU treated panel surfaces as observed for the untreated panel surfaces.     

Investigation of Urea-Melamine-Formaldehyde (UMF) resin penetration in Medium-Density Fiberboard (MDF) by High Resolution Confocal Laser Scanning Microscopy

A confocal laser scanning microscope (CLSM) was used to investigate the distribution and penetration of urea-melamine-formaldehyde (UMF) resin in the fiber when injected through blowline blending in a medium density fiberboard (MDF) pilot plant. Samples were prepared with respect to industrial parameters and were collected at the dryer’s end. The samples were later dyed in a Dye Star-Brilliant Red solution (0.01%) and rinsed with distilled water to remove excess. The samples were scanned with the CLSM to build three-dimensional reconstructions of MDF fiber cross-sections. With proper lenses and optimized CLSM settings, it was possible to obtain fiber reconstructions with a resolution greater than the laser wave length (514 nm). The Zeiss CLSM built-in software image analyzer enabled to rebuild them in rotation on any of the three axes with up to 64 images per rotation. The resin penetration sites were identified using this software option. The penetration sites were numerous and well dispersed. The largest openings (lumen, pits and cracks) were responsible for most of the resin lost by over-penetration. The presence of resin in the cell walls (detected with the CLSM) proves their porosity without giving much information about the resin concentration. Finally, the atomic force microscope (AFM) enabled to recreate the finest surface details for these fibers samples. It was found that the fibrils aggregates orientation and size can influence the resin penetration and distribution. It was concluded that the porous structure of wood fibers and their affinity to water enable the resin to penetrate through capillary force. This phenomenon is stimulated by the high pressure, saturated steam, turbulent flow and heat. When injected in the pilot plant blowline, UMF resin was uniformly distributed over the fiber surface (22.5% coverage). The resin penetration was however important and also occurred in nanometric defaults of the wood fibers. Thus, industrial panels made out of very porous, damaged or small fibers will need more resin to fill the gaps in order to make a strong board.     

Comparison of mechanical properties of oriented strand board made from trembling aspen and paper birch

This study compared the performance of oriented strand boards (OSB) made from trembling aspen, a low-density hardwood species, and OSB made from paper birch, a medium-density hardwood species. The birch strands were thinner than the aspen strands to ensure a comparable specific surface. Three levels of adhesive content were used: 3.5%, 5.0%, and 7.0%. Internal bond (IB) and modulus of elasticity (MOE) and modulus of rupture (MOR) for flatwise and edgewise bending were determined. Both species performed equally well in IB (3.5% adhesive content: 0.46 MPa, 5.0%: 0.60 MPa, and 7.0%: 0.65 MPa). The values of MOE in flatwise bending were slightly lower for birch than for aspen panels (11.8 GPa for aspen and 10.6 GPa for birch), and the MOR values were not significantly different (combined 68.3 MPa). Edgewise bending properties were not significantly different for the two species with a MOE of 10.5 GPa and a MOR of 43.2 MPa.     

尼龙66织物的磷氮复合阻燃整理

摘要:采用有机磷酸酯和含氮阻燃剂复配阻燃体系对尼龙66(PA66)织物进行阻燃整理。探讨了阻燃剂用量及配比、焙烘温度对织物燃烧性能的影响。优化的阻燃整理工艺条件为:含磷阻燃剂和含氮阻燃剂质量比1:3,阻燃剂30%,焙烘温度160℃。经阻燃整理的尼龙66织物具有良好的耐熔滴性,其极限氧指数可达35.0%,损毁长度降至4.2 cm,续燃时间仅为1.04 s,断裂强力仅下降3.6%。热重分析(TGA和DTA)表明,阻燃整理后的PA66织物在燃烧过程中分解温度提前,降解速率变小,残炭量增加;扫描电镜(SEM)发现,燃烧残余物表面有蜂窝状的孔洞。该阻燃体系通过气相阻燃、吸热阻燃及凝聚相成炭阻燃等多重阻燃机制,提高了PA66织物的阻燃性能。     

Thermal conductivity and water vapour transmission properties of wood-based materials

For several wood-based materials (plywood, OSB, melamine faced board (MFB), particle board and fibre board), the thermal conductivity was determined as a function of the temperature (ranging between 10 and 30 °C) and also the moisture content (from an oven-dry sample up to a moisture content at 80% RH). Furthermore, the water vapour resistance factor of these materials as well as of the coating (at MFB) and the diffusion coefficient were determined under dry cup (performance at low humidity dominated by vapour diffusion) and wet cup (performance at high humidity with liquid water and vapour transport) conditions. Thermal conductivity increases with rising temperature, moisture content and density. Moreover, a clear decrease of thermal conductivity was found with decreasing particle size at the same density level, from solid wood over plywood and particle board to fibre board. The water vapour resistance factor of the wood-based materials increases with rising density and decreases with increasing moisture content. An influence of the particle and fibre board thickness was also revealed. In contrast to the remaining materials, an increase of the water vapour resistance factor with increasing moisture content was measured for the coating. The diffusion coefficient decreases with rising density and moisture content.