防白蚁胶合板的制备及性能研究

目的实现包装人造板的防白蚁功能。方法采用联苯菊酯、溴氰菊酯和高效氯氰菊酯为防白蚁剂,制备具有防白蚁功能的三聚氰胺甲醛树脂胶(MF)速生杨胶合板。研究防白蚁剂对MF胶黏剂的初粘度和胶合强度,白蚁作用方式,胶合板的防白蚁性能和力学性能等的影响。结果所用的防白蚁剂在MF中分散性良好,无分层现象。防白蚁剂对胶合强度有不良影响,溴氰菊酯和高效氯氰菊酯对弹性模量、静曲强度产生不良影响,但其浓度对弹性模量、静曲强度无显著影响。结论当联苯菊酯占MF的质量分数为1.25%,或溴氰菊酯占MF的质量分数为5%,或高效溴氰菊酯占MF的质量分数为2.2%时,胶合板的防白蚁性能最佳,白蚁死亡率达到100%,而且其主要力学性能指标均达到国家标准要求。     

Development and material properties of new hybrid plywood from oil palm biomass

Shortage of wood as a raw material has forced wood-based industries to find alternative local raw materials. Currently, oil palm biomass is undergoing research and development (R & D) and appears to be the most viable alternative. This work examines the conversion of oil palm trunk (OPT) and oil palm empty fruit bunches (OPEFB) into new plywood and analyses its properties. We prepared five-ply veneer hybrid plywood (alternating layers of oil palm trunk veneer and empty fruit bunch mat) with different spread levels (300 g/m² and 500 g/m²) of resins (phenol formaldehyde and urea formaldehyde). We then studied the mechanical and physical properties of the plywood. The results show that hybridisation of EFB with OPT improves some properties of plywood, such as bending strength, screw withdrawal and shear strength. The thermal properties of the plywood panels were studied by thermogravimetric analysis (TGA). The panels glued with phenol formaldehyde with a spread level of 500 g/m² showed better thermal stability than the other panels. Scanning electron microscope (SEM) was used to study the fibre matrix bonding and surface morphology of the plywood at different glue spread levels of the resins. The fibre–matrix bonding showed good improvement for the hybrid panel glued with 500 g/m² phenol formaldehyde.     

The efficiency of tannin as a formaldehyde scavenger chemical in medium density fiberboard

The aim of this study was to determine the effect of tannin content of urea formaldehyde (UF) resin on the panel properties of medium density fiberboard (MDF). Tannin extracted from the bark of white oak (Quercus alba) was added to UF resin at different ratios (based on the resin) to decrease the free formaldehyde content of MDF panels in this study. It was determined that free formaldehyde values of MDF panels decreased when the ratio of tannin content in UF resin increased. However, the modulus of rupture (MOR), modulus of elasticity (MOE), and internal bond strength (IB) of these panels were a little lower, and the thickness swelling (TS) (24 h) and water absorption (WA) (24 h) values were a little higher compared to the control MDF panels.     

Improving core bond strength and dimensional stability of particleboard using polymer powder in core layer

Low density polyethylene powder (LDPE) was used as polymer binder in the core layer of three layer particleboard. In the first phase, six levels of the LDPE powder (5–30 wt.%) based on the composition by weight, were mixed with the core particles with 8 wt.% urea–formaldehyde (UF) resin. In the second phase, the LDPE powder content was kept constant at 10 wt.% in all treatments and the UF resin content applied to the core layer was decreased gradually from 8 to 4 wt.%. Thickness swelling and water absorption of the particleboards significantly decreased with increasing the LDPE content in the core layer. Similarly, incorporation of the LDPE powder into the core layer of the particleboard greatly improved internal bond strength. The flexural properties of the particleboards, the modulus of rupture (MOR) and modulus of elasticity (MOE), were positively affected by increasing LDPE content up to 10 wt.% but the further increment of the LDPE decreased the MOR and MOE. The UF resin content can be reduced in the core layer of the particleboard as a function of increasing the LDPE powder.     

Properties of medium density fibreboard (MDF) from kenaf (Hibiscus cannabinus L.) core as function of refining conditions

The objective of this study was to evaluate physical and mechanical properties of medium density fibreboard (MDF) panels made from kenaf core as function of fibre geometry and refining conditions. Raw material was prepared by using pressure levels of 3, 5 and 7 bar at two heating times, namely 3 and 5 min. The length and width of the fibres were determined employing image analyser. Experimental samples with a target density of 700 kg m⁻³ were produced with 12% of urea formaldehyde as a binder. Physical properties such as swelling in thickness (TS) and water absorption (WA) of the panels in addition to their mechanical properties including modulus of rupture (MOR), modulus of elasticity (MOE) and internal bonding (IB) were evaluated based on MS 1787:2005. Based on the test results, low digestion pressure produced longer fibre length and panels made from these fibres had higher TS with MOR and MOE than those of the others panels. However, the IB properties of samples were low. Panels made from shorter fibre resulted in contradict properties found above. The ideal properties of the samples were found for the panels made having fibre length of 0.81 mm and aspect ratio of 23.4. Such sample had 14.6%, 63.2%, 30.3 MPa, 3619 MPa and 0.66 MPa for TS, WA, MOR, MOE and IB, respectively.     

Properties of laminated panels made from compressed oil palm trunk

This study evaluated physical and mechanical properties of laminated panels made from compressed oil palm trunk (OPT). The OPT were steamed at 130 °C before being compressed and laminated using polyvinyl acetate adhesive at 250 g/m² and 500 g/m² spread rates. The modulus of rupture and compression strength values of laminated panels made from compressed OPT was greater than those of laminated panels made from uncompressed OPT. Surface roughness, water absorption, and thickness swelling of laminated panels made from compressed OPT significantly improved. The findings in this study indicated that compressing of OPT would be considered as an alternative to produce value-added material with enhanced properties.     

Properties of steam treated binderless particleboard made from oil palm trunks

The objective of this study was to evaluate both physical and mechanical properties of particleboard panels manufactured from steamed material of oil palm trunks without using any adhesives. Experimental panels from fine particles and vascular strands of oil palm were manufactured. Modulus of rupture (MOR), internal bond strength (IB), thickness swelling (TS) and water absorption (WA) of the samples were tested based on Japanese Industrial Standards. Bonding quality of such binderless samples was also evaluated by using scanning electron microscope (SEM). Based on the findings on this work steaming of the raw material enhanced overall mechanical and physical characteristic of the samples. The highest MOR values of 8.12 MPa and 25.84 MPa were found for the samples made from fine particles and strands steamed at a temperature of 130 °C for 30 min, respectively. It appears that mechanical properties of the panels reduced when they exposed to beyond 30 min steaming time.     

Mechanical and physical properties of medium density fiberboard panels laminated with thermally compressed veneer

The objective of study was to evaluate some of the physical and mechanical properties of medium density fiberboard (MDF) panels laminated with veneer sheets compressed at different levels of pressure and temperature. Rotary peeled veneer samples of European beech (Fagus orientalis Lipsky) were compressed at temperatures of 150 °C, 180 °C, and 200 °C using 4 MPa and 6 MPa pressure for 8 min. Commercially produced MDF samples also were laminated with such compressed veneer sheets. Both modulus of elasticity (MOE) and modulus of rupture (MOR) of the specimens increased with increasing pressure and press temperature. Bending characteristics of the samples tested parallel to the grain orientation resulted in significantly higher values than that perpendicular to the grain orientation for each manufacturing parameter. Thickness swelling of the samples also was influenced by increased pressure but variation in press temperature did not result in any influence on dimensional stability. The findings of this work provide potential to produce sandwich type panels with improved properties. Initial results found in this study could be used to manufacture laminated panels with a fixed rate of adhesive while controlling press parameters as a function of the magnitude of pressure and temperature.     

Effects of treatment with low molecular weight phenol formaldehyde resin on the surface characteristics of oil palm (Elaeis quineensis) stem veneer

Even though oil palm (Elaeis quineensis) stem (OPS) is highly potential as an alternative raw material in wood industry, it possesses some inferior characteristics. One of the critical weaknesses is a high degree of veneer surface roughness that resulted in high resin consumption during plywood manufacture. The objective of this study was to investigate effects of treatment with low molecular weight phenol formaldehyde (LMWPF) resin on the wettability and surface roughness of OPS veneer. OPS veneers were segregated into two categories namely outer and inner layer veneer, prior to soaking in LMWPF resin solution to obtain weight percent gain of 16–20%. The wettability of OPS veneers was assessed with contact angle measurement according to the sessile drop method. The veneer surface roughness was evaluated by determining the average roughness (R_a), mean peak-to-valley height (R_z), and maximum roughness (R_max) using a stylus profilometer in accordance with DIN standard 4768. The results show that the effect of LMWPF resin treatment on the surface roughness of the veneers is statistically significant. The technique used in the study was able to enhance the surface properties as well as improved the physical and mechanical properties of OPS plywood.     

Effect of coarse aggregate blending on short-term mechanical properties of self compacting concrete

This investigation is mainly focused on finding the unit weight, compressive strength, modulus of elasticity (MOE) and splitting tensile strength (STS) of SCC mixes with different coarse aggregate blending (60:40 and 40:60) (20 mm and 10 mm) and coarse aggregate content (28% and 32%) and these properties were compared to a conventional concrete (CC). All SCC mixes had 35% replacement of cement with class F fly ash. The coarse aggregate blending did not affect the compressive strength of SCC mixes, but it affected the unit weight, MOE and STS of SCC mixes. A new parameter called coarse aggregate points (CAPs) has been introduced to study the effect of coarse aggregate blending in a particular coarse aggregate content on mechanical properties of SCC mixes. It is observed that for the given strength, SCC mixes with the same CAP value have shown similar mechanical properties. The measured MOE of all mixes were compared with ACI 363R and AASHTO LRFD/ACI 318 predicted equations. The measured STS of all mixes were compared with ACI 363R and CEB-FIP predicted equations.     

Cell-wall hardness and Young's modulus of melamine-modified spruce wood by nano-indentation

Samples of spruce wood were infiltrated with a melamine–formaldehyde resin. After curing of the resin, a melamine concentration of 24% (v/v) was measured in the secondary cell walls of melamine treated wood. Nano-indentation tests revealed an average Young's modulus of 16.1 GPa and a hardness of 0.24 GPa for untreated secondary cell walls. In the melamine treated cell walls, an increase in the Young's modulus of 33% to 21.4 GPa was observed. With 115%, i.e. 0.52 GPa, the increase in longitudinal hardness due to melamine–formaldehyde treatment was even more pronounced. This proves clearly that melamine treatment of wood improves mechanical properties of cell walls. Thus, treatment of wood with melamine–formaldehyde resin shows a considerable potential to improve mechanical properties, as desired for applications where large stresses normal to grain arise.     

Some technological properties of wood–styrofoam composite panels

Synthetic resins are widely used in wood based composites manufacturing. Besides their many advantages, most of them contain formaldehyde and a chemical agents that cause environmental problems. Styrofoam known as expanded polystyrene, is used all over the world for various purposes including thermal insulation, packing, coffee cups, fabrication of car parts etc. This study investigated the evaluation possibilities of styrofoam wastes in plywood production as a bonding material. Pine (Pinus pinea) and poplar (Populus deltoides I-77/51) veneers were used to produce wood–styrofoam composite (WSC) and traditional plywood. Urea-formaldehyde adhesive was used as bonding material for traditional plywood panels. Two different types of styrofoam having high density (25 kg/m³) and low density (10 kg/m³) were used as binder in the manufacturing of WSC panels. Bonding and bending strength, modulus of elasticity, density and thermal conductivity of plywood and WSC panels were investigated. Experimental results showed that mechanical properties of panels manufactured with low density styrofoam type were higher than those of panels manufactured with high density styrofoam type. The lowest thermal conductivity among the all panels was found for poplar panels manufactured with high density styrofoam.     

Strong and optically transparent biocomposites reinforced with cellulose nanofibers isolated from peanut shell

Cellulose nanofibers–reinforced PVA biocomposites were prepared from peanut shell by chemical–mechanical treatments and impregnation method. The composite films were optically transparent and flexible, showed high mechanical and thermal properties. FE-SEM images showed that the isolated fibrous fragments had highly uniform diameters in the range of 15–50 nm and formed fine network structure, which is a guarantee of the transparency of biocomposites. Compared to that of pure PVA resin, the modulus and tensile strength of prepared nanocomposites increased from 0.6 GPa to 6.0 GPa and from 31 MPa to 125 MPa respectively with the fiber content as high as 80 wt%, while the light transmission of the composite only decreased 7% at a 600 nm wavelength. Furthermore, the composites exhibited excellent thermal properties with CTE as low as 19.1 ppm/K. These favorable properties indicated the high reinforcing efficiency of the cellulose nanofibers isolated from peanut shell in PVA composites.     

Chemical and physical modifications of rice husks for use as composite panels

Modifications of rice husks surfaces by steam and sodium hydroxide (NaOH) were carried out in order to study the effects of these on the surface functional groups properties and performances of the composite panels bonded with phenol formaldehyde (PF) resin. Comparison was made between untreated and ground rice husks. The removal of carbonyl and silica groups as observed by ATR-FTIR improved the rice husk-resin interfacial bonding as revealed by an increase in the modulus of elasticity to 2.76 ± 0.28 GPa, which is above the minimum value of 2.1 GPa recommended in EN 312-3 standard. On the other hand, steam treatment did not lead to any change in the outer surface chemical functional groups. Still, an increase in the mechanical properties of the composite with increase in steam temperature was observed. This showed that other mechanisms than changes in the surface chemical groups led to improved mechanical properties. TGA thermographs of unmodified and NaOH treated rice husks indicated that untreated rice husks exhibited higher thermal stability compared to rice husks treated with NaOH. The decrease in thermal stability of NaOH treated rice husks is an indication of possible degradation of rice husks by the concentrated NaOH used. This study has shown that the use of complementary testing techniques provides useful structure–property relationship in the understanding of the performance of materials.     

Thermomechanical properties of bio-based composites made from a lactic acid thermoset resin and flax and flax/basalt fibre reinforcements

Low viscosity thermoset bio-based resin was synthesised from lactic acid, allyl alcohol and pentaerythritol. The resin was impregnated into cellulosic fibre reinforcement from flax and basalt and then compression moulded at elevated temperature to produce thermoset composites. The mechanical properties of composites were characterised by flexural, tensile and Charpy impact testing whereas the thermal properties were analysed by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results showed a decrease in mechanical properties with increase in fibre load after 40 wt.% for the neat flax composite due to insufficient fibre wetting and an increase in mechanical properties with increase fibre load up to 60 wt.% for the flax/basalt composite. The results of the ageing test showed that the mechanical properties of the composites deteriorate with ageing; however, the flax/basalt composite had better mechanical properties after ageing than the flax composite before ageing.     

Low shrinkage light curable dental nanocomposites using SiO2 microspheres as fillers

Commercial resin matrixes of dental composites generally utilize diluents such as triethylene glycol dimethacrylate (TEGDMA) to reduce viscosity. However, the diluents exhibited adverse effects such as higher volume shrinkage and diminished mechanical properties of the dental composites. To overcome these adverse effects, developing of both inorganic fillers and resin monomers is necessary to improve the properties of dental composite. In this work, monodispersed silica microspheres with a diameter of 400 nm were synthesized via the Stöber process. The as-prepared particles were silanized with 3-methacryloxypropyltrimethoxysilane (γ-MPS) and used as fillers. Additionally, ethoxylated bisphenol A dimethacrylate (EBPADMA) with lower viscosity and higher molecular mass was introduced as a base resin monomer, which could be used as resin matrixes with a low amount of diluent. Various resin mixtures of EBPADMA, bisphenol A diglycidyl dimethacrylate (Bis-GMA) and TEGDMA were prepared, which had a similar filler content (71 wt.%), and their mechanical properties, volume shrinkage, depth of cure and light transmission were examined. Among them, the resin mixture containing 70% EBPADMA and 30% TEGDMA exhibited the best compression strength (238.1 ± 5.4 MPa), depth of cure (4.02 ± 0.04 mm) and the lowest volume shrinkage (2.27%).     

Multiresponse optimization based on statistical response surface methodology and desirability function for the production of particleboard

It is very difficult to determine the actual level of process parameters responsible for the quality production of particleboard due to the high degree of process variable interactions and lack of robust methodology for optimization. In this study, an attempt was made to optimize the process parameters of particleboard production by using multi-response optimization process. Plackett–Burman factorial design was first employed to eliminate some factors from selected seven important parameters: flake thickness, flake length, dried chips moisture content (MC%), amount of adhesive, pressing time, pressure, and press temperature. By using this screening procedure, three important factors: flake thickness, dried chips moisture content and press temperature were found to have significant effect on particleboard properties. Afterwards, Box–Behnken design was performed as response surface methodology (RSM) with desirability functions to attain the optimal flake thickness, MC% and press temperature that affect modulus of rapture (MOR) and modulus of elasticity (MOE) of particleboard production. The optimized parameters for maximum MOR and MOE determined were found to be: flake thickness, 0.15 mm; press temperature, 182 °C; and dried chip MC% 3.5. Finally, a confirmation study was executed by using optimized levels of parameters which showed well response to the predicted model.     

The effect of alkaline treatment on mechanical properties of kenaf fibers and their epoxy composites

In this work, kenaf fibers were pre-treated in a NaOH solution (6% in weight) at room temperature for two different periods (48 and 144 h). The chemical treatment of kenaf fibers for 48 h allowed to clean their surface removing each impurity whereas 144 h of immersion time had detrimental effect on the fibers surface and, consequently, on their mechanical properties.Untreated and NaOH treated kenaf fibers (i.e. for 48 h) were also used as reinforcing agent of epoxy resin composites. The effect of the stacking sequence (i.e. using unidirectional long fibers or randomly oriented short fibers) and the chemical treatment on the static mechanical properties was evaluated showing that the composites exhibit higher moduli in comparison to the neat resin. As regards the strength properties, only the composites reinforced with unidirectional layers show higher strength than the neat resin. Moreover, the alkali treatment increased the mechanical properties of the composites, due to the improvement of fiber–matrix compatibility.The dynamic mechanical analysis showed that the storage and the loss moduli are mainly influenced by the alkali treatment above the glass transition temperature. Moreover, the alkali treatment led to a notable reduction of tan δ peaks in addition to significant shifts of tan δ peaks to higher temperatures whereas the stacking sequence did not influence the trends of storage modulus, loss modulus and damping of the composites.     

Influence of coupling agent content on the properties of high density polyethylene composites reinforced with oil palm fibers

Oil palm fiber reinforced high density polyethylene (HDPE) composites which can be used in several applications (mechanical part, fiber panel, etc.) were manufactured by twin-screw extrusion followed by compression molding. In particular, the effect of coupling agent (maleated polypropylene, MAPP) concentration (0, 2, 4 and 6 wt.%) was investigated for 30 and 40 wt.% oil palm fiber. Scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FT-IR), dynamic mechanical thermal analysis (DMTA) and mechanical testing (tension and impact) were carried out to determine the effect of fiber and compatibilizer contents. The results showed that compatibilized composites have increased stiffness due to enhanced interfacial adhesion between the fibers and the matrix, as well as better homogeneity (better fiber dispersion) due to chemical bonding. The optimum MAPP content was found to be 4% for the range of conditions tested.     

Properties of solid wood and laminated wood lumber manufactured by cold pressing and heat treatment

Physical, mechanical, and morphological properties of solid wood lumbers which were cold pressed in a press and then heat treated in a kiln. Two different kinds of domestic thinning small-diameter softwood (Ginko biloba L.) and hardwood (Tilia amurensis Rupr.) were used in this study. First 50 mm thick lumbers were cold pressed until 35 mm (30% of control lumber) using a stopper for 5 min. Then the cold pressed lumbers were heat treated in an electric kiln at 180 °C for 6, 12, 24, or 48 h. To increase the utilizability of woods, the LVLs were produced from 4 mm thick veneers prepared from the heat treated lumbers using a veneer saw. Each LVL sample consisted of 5 layers which were subsequently 48 h-, 24 h-, 12 h-, and 6 h-treated veneers and untreated veneer (from top layer to bottom layer). The shrinkage rates of softwood and hardwood were considerably decreased with increasing temperature. The mechanical properties of heat treated samples were better than those of unpressed control samples. The bending strength and modulus of elasticity of the LVLs manufactured from cold pressed and then heat treated lumbers were slightly lower than those of untreated woods. The colour values obtained from the heat treated wood samples showed a clear effect of the temperature on the colour changes.