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1.
Veneer drying is one of the most important stages in the manufacturing of veneer-based composites such as plywood and laminated veneer lumber. Due to the high drying costs, increased temperatures are being used commonly in plywood industry to reduce the overall drying time and increase capacity. However, high drying temperatures can alter some physical, mechanical and chemical characteristics of wood and cause some drying-related defects. In this study, it was attempted to predict the optimum drying temperature for beech and spruce veneers via artificial neural network modeling for optimum bonding. Therefore, bonding shear strength values of plywood panels manufactured from beech and spruce veneers dried at temperatures of 20, 110, 150 and 180 °C were obtained experimentally. Then, the intermediate bond strength values based on veneer drying temperatures were predicted by artificial neural network modeling, and the values not measured experimentally were evaluated. The optimum drying temperature values that yielded the highest bonding strength were obtained as 169 °C for urea formaldehyde and 125 °C for phenol formaldehyde adhesive in beech plywood panels, while 162 °C for urea formaldehyde and 151 °C for phenol formaldehyde in spruce plywood panels. 相似文献
2.
Alireza Bastani Stergios Adamopoulos Holger Militz 《Wood material science & engineering》2017,12(4):236-241
The shear strength of furfurylated, N-methylol melamine (NMM) and thermally modified wood bonded with emulsion polymer isocyanate, polyvinyl acetate (PVAc), and polyurethane (PU) adhesives was examined. Furfurylation and NMM modification of Scots pine had a significant negative effect on the bonding strength with all adhesives irrespective of the treatment intensity. The obtained low-shear strength values were related to the brittle nature of the wood after modifications rather to the failure of the bondline. PVAc showed a better bonding performance with both furfurylated and NMM modified wood while the combination of furfurylated wood and PU gave the highest reduction in bonding strength (47–51%). Shear strength also decreased significantly after thermal modification in both Scots pine (36–56%) and beech (34–48%) with all adhesives. With the exception of thermally modified beech samples bonded with PU, bondline was found to be the weakest link in thermally modified wood as it was revealed by the wood failure surfaces. Bondline thickness and effective penetration of adhesives did not relate to the shear strength of all modified wood materials. The lower shear strength of modified wood could be attributed to other factors, such as the reduced chemical bonding or mechanical interlocking of adhesives, and the reduced strength of brittle modified wood substrate. 相似文献
3.
This study examines the cyanoethylation and thermoplasticity of several cyanoethylated fiber materials. Cyanoethylated pulps with a degree of substitution of 1.43 have the lowest Vicat softening point. Cyanoethylated poplar with a weight gain of 18.2 % has the lowest melting temperature. Instead of traditional adhesives, cyanoethylated materials can be used to produce wood-based panels because of their good thermoplasticity. Plywood bonded with cyanoethylated pulp has a bonding strength of 2.06 MPa and an average wood failure of 62.7 %. Wheat straw particle board containing 40 % cyanoethylated pulp has an internal bonding strength of 0.49 MPa, a modulus of rupture (MOR) of 33 MPa, and a density between 0.5 and 0.6 g cm?3. Fiberboard containing 40 % cyanoethylated pulp has an internal bonding strength of 0.53 MPa, MOR of 38 MPa, modulus of elasticity of 4,200 MPa, and a density between 0.7 and 0.8 g cm?3. Its swelling in thickness is 41 %. 相似文献
4.
In this paper, the influence of melamine polyphosphate (MPP) and aluminum hypophosphite (AHP) on mechanical properties, flame retardancy and thermal degradation of high-density polyethylene/wood flour composites (HDPE/WF) was investigated. The synergistic effect of MPP and AHP was investigated. Polyethylene grafted with maleic anhydride (PE-g-MAH) was used as coupling agent. The experimental data demonstrated that the HDPE/WF composites with 35 wt% MPP/AHP (3:2) could achieve a LOI value of 29.6 % and UL-94 V-0 rating. In addition, the cone value also revealed that the heat release rate and the smoke production rate were clearly reduced. SEM results showed that the synergistic system (MPP/AHP = 3:2) could form a dense and thick char layer and good adhesion between wood flour and HDPE matrix, which prevented the transfer of heat flux and fuel gases. Incorporation of MPP and AHP improved the thermal stability of HDPE/wood flour as observed from the thermogravimetric analysis results and also enhanced the thermal resistance of char layer at high temperature based on scanning electron microscopy observation. 相似文献
5.
【目的】通过木粉纤维增强生物塑料聚3-羟基丁酸酯-co-4-羟基丁酸酯(P34HB),为生物复合材料的理论研究和生物可降解塑料的广泛应用提供科学依据和理论支持。【方法】以毛白杨木粉和P34HB为原料,采用共混热压法制备P34HB/木粉生物复合材料,基于电子扫描显微镜(SEM)、差示扫描量热法(DSC)、热重分析(TGA)、傅里叶红外光谱(FTIR)、动态热机械分析(DMA)和力学性能分析等手段对其结构和性能进行表征。【结果】随着木粉含量增加,生物复合材料的拉伸强度、断裂伸长率和弯曲强度先增加后减小,冲击强度逐渐下降,拉伸强度、弹性模量和杨氏模量分别增加89%、59%和103%,储能模量E′逐渐增加,tanδ峰值先下降后上升。生物复合材料的高频率模量大于低频率模量,动刚度比静刚度好。相比P34HB,生物复合材料的热分解区间变宽,热解速率变慢,热解剩余质量增加。【结论】随着木粉含量增加,P34HB分子链运动受阻,生物复合材料的储能模量和脆性增大;同时,木粉纤维的成核作用诱导P34HB形成结晶度高、层状结构发达的横晶层,木粉与P34HB之间界面结合力增强,力学性能和热稳定性明显提高。综合考虑,P34HB/木粉生物复合材料的最佳木粉加入量为50%。 相似文献
6.
热氧老化和水浸渍对木粉/HDPE和稻壳粉/HDPE两种复合材料性能的影响 总被引：1，自引：0，他引：1
木粉和稻壳粉是制备木塑复合材料(WPC)常用原料。WPC在使用过程中经常受到热和水分的影响,笔者对比研究了稻壳粉/HDPE和木粉/HDPE两种复合材料经历热氧老化和长时间水浸渍后性能的变化规律。结果表明:木粉/高密度聚乙烯(HDPE)复合材料的弯曲强度和弹性模量都大于稻壳粉/HDPE的;随着热氧老化或水浸渍处理时间的延长,复合材的挠曲性能下降,其中木粉/HDPE复合材的弹性模量下降最为迅速;复合材料表面明度值随着热处理时间的延长而减小,说明颜色变暗,稻壳粉与木粉填充的复合材之间差别不大。通过光学显微镜观察发现,HDPE与稻壳粉或木粉之间都有缝隙存在,为水分和氧气的进出提供了通道。 相似文献
7.
In this research, technological properties of glulam beams made from hydrothermally treated poplar (Populus deltoides) wood were investigated. Poplar wood blocks with dimensions of 6 (r)?×?10 (t)?×?73 (l)?cm3 were cut and hydrothermally treated in a stainless steel reactor at temperatures of 140 and 160°C for a holding time of 30?min. The treated wood blocks were initially air seasoned and then they were dried in a semi-pilot scale vacuum dryer to achieve moisture content (MC) of 12%. Conditioning of the treated and the untreated wood blocks was done prior to adhesive bonding. Afterwards the glulam beams (4 ply) were manufactured using polyurethane. In order to evaluate the physico-mechanical properties of the beams, density, equilibrium moisture content, water repellent effect (WRE), anti-swelling effect (ASE), mass loss (ML), wettability as well as surface roughness due to the hydrothermal treatment were determined in the treated wood and delamination, bond shear strength, tensile strength, MC and moisture-induced stresses as well as strains in cross-section of the beams were determined in the glulam beams. The results revealed that density, ML, ASE, WRE, modulus of elasticity, modulus of rupture and delamination were increasing and the others were decreased due to the hydrothermal treatment. 相似文献
8.
为了研究活性染料对染色单板胶合性能的影响,分别采用环保型低毒脲醛树脂胶和单组分湿固化异氰酸酯胶进行杨木染色单板的胶合,测试染色后杨木单板的润湿性和胶合强度,结果得出:染色处理能够在一定程度上增加单板的孔隙度,有利于黏度较低的胶黏剂的铺展,也有利于改善其胶合性能;对于黏度较大的胶黏剂则影响不明显。 相似文献
9.
Hamidreza Edalat Mehdi Faezipour Volker Thole Frederick A. Kamke 《Wood Science and Technology》2014,48(4):703-712
The importance of adhesion in production of wood-based composites is well-known. Adhesive penetration and interphase morphology play an important role in bond strength and product performance. Many studies offered different methods for interphase characterization and analysis. Both qualitative and quantitative methods have been used to analyze the bondline. Most of the quantitative methods were developed for bonded assemblies of veneer or wood blocks. Adhesive penetration measurement in particulate wood-based composites is the main scope of this study. For this purpose, uniform oriented strand board with veneer strands was produced by the use of phenol formaldehyde resin with 2, 6, and 10 % strand moisture content (MC). The strands were formed into well-organized mats to achieve a uniform structure for the composite. Cross-section specimens were prepared from each board and observed by epifluorescence microscopy. Six positions for growth-ring angle in adhesive joints were denoted to evaluate penetration in different directions of the wood. Four parameters were also determined to quantify resin penetration patterns by counting the quantity of the main anatomical elements of wood, which were filled with resin. Finally, it was determined that this method could recognize the differences between adhesive penetration in boards produced with different level of strand MC. Resin penetration in strands with 6 and 10 % MC was the greatest. Growth-ring angle of the strands influenced penetration as it was increased when both strands meet each other in an oblique position, although this effect was significant only in maximum penetration depth in fibers. 相似文献
10.
Heat treatment is an alternative to the chemical treatment in wood preservation, which has been used to some extent in improving timber quality. However, reduction in strength properties has been one of the major limitations in the use of this technique and therefore investigations on the use of various pre-treatment methods are highly essential. Wood samples from Scots pine were immersed in already boiling water (100°C) for 20 min followed by 2 h of heat treatment at 160 and 200°C. The acidity and strength properties were determined by measurement of pH and static bending test, respectively. There were no significant changes in pH due to preboiling in both heat-treated and untreated wood. Similarly, preboiling did not result in any appreciable differences in strength both before heat treatment and during heat treatment at 160°C. However, for 200°C heat treatment preboiling reduced significantly the degree of strength loss as indicated by 19.4% reduction in modulus of rupture in preboiled wood compared to 26.6% reduction in unpreboiled wood. From the results of this study it is evident that preboiling has a buffering effect on wood during heat treatment and the higher the intensity of heat treatment the higher the significance of the buffering effect of pre-boiling. 相似文献
11.
SEBS-g-MAH和原位接枝MAH对木粉/废旧塑料混合物复合材料力学性能的影响研究 总被引：1，自引：0，他引：1
由聚丙烯（PP）、高密度聚乙烯（HDPE）和聚苯乙烯（PS）组成的混合废旧塑料与木粉经高速混合机混合后,采用双螺杆/单螺杆串联挤出机组制备了木粉/混合废旧塑料复合材料。探讨了马来酸酐接枝苯乙烯-乙烯/丁烯-苯乙烯嵌段共聚物（SEBS-g-MAH）和原位接枝马来酸酐（MAH）对木粉/混合废旧塑料复合材料力学性能的影响。结果表明,与使用MAH和DCP的原位反应共混相比,SEBS-g-MAH显著提高了复合材料的抗冲击性能,但对拉伸和弯曲性能的改善不如原位反应共混显著。总的来说,混合废旧塑料制备的复合材料的力学性能要低于纯塑料混合物制备的复合材料,尤其是拉伸断裂伸长率。微观形态研究表明,添加SEBS-g-MAH和原位接枝MAH均可提高木粉与塑料混合物之间的界面相容性,但与添加SEBS-g-MAH相比,原位接枝MAH能更好的改善PP、HDPE、PS与木粉之间的界面结合。原位接枝MAH可被看作是一种改善木粉与塑料混合物间界面相容性的有效途径。此外,采用动态力学分析（DMA）进一步表征了复合材料的储能模量和阻尼因子。 相似文献
12.
Manuel Raul Pelaez-Samaniego Vikram Yadama Eini Lowell Raul Espinoza-Herrera 《Wood Science and Technology》2013,47(6):1285-1319
The objective of this paper is to review the published literature on improving properties of wood composites through thermal pretreatment of wood. Thermal pretreatment has been conducted in moist environments using hot water or steam at temperatures up to 180 and 230 °C, respectively, or in dry environments using inert gases at temperatures up to 240 °C. In these conditions, hemicelluloses are removed, crystallinity index of cellulose is increased, and cellulose degree of polymerization is reduced, while lignin is not considerably affected. Thermally modified wood has been used to manufacture wood–plastic composites, particleboard, oriented strand board, binderless panels, fiberboard, waferboard, and flakeboard. Thermal pretreatment considerably reduced water absorption and thickness swelling of wood composites, which has been attributed mainly to the removal of hemicelluloses. Mechanical properties have been increased or sometimes reduced, depending on the product and the conditions of the pretreatment. Thermal pretreatment has also shown to improve the resistance of composites to decay. 相似文献
13.
This study examined effects of surface modification with hydrogen peroxide (H2O2) on adhesive bond performance in birch veneer bonded with phenol–formaldehyde resin. The veneer was treated with 5% of H2O2 at 80 °C in the presence of alkali with the objective of improving adhesive bond performance and reducing the resin demand. The effects of the surface modification were determined by surface color measured with a spectrophotometer, bond performance tests with ABES (automated bonding evaluation system) and surface hydrophobicity with sessile contact angle measurements. Results demonstrated that veneer surface became significantly whiter, which also increased in lightness and decreased in redness and yellowness. ABES test revealed that a remarkable increase in bond performance in the treated veneer and the maximum bond strength with the treatment at 60 min, which was nearly twice as high as reference sample (5.42 → 9.94 N/mm2), was obtained. A notable decrease in contact angle measurements was also observed in the treated veneers (0° in 0.5 s). The surface modification of birch veneer with H2O2 + alkali demonstrated greater potential for the improvement of physical characteristics in veneer surface. Other aspects of H2O2 consumption during the treatment are also discussed. 相似文献
14.
用ＵＦ、ＭＵＦ胶制作三种松木胶合板，分别就单板厚度、涂胶量及抽提物含量对胶合性能的影响，松木与柳安混合树种组坯、特殊添加剂对改善胶合性能的作用进行了研究。结果表明：除了老挝松边材ＭＵＦ胶合板以外，１．５和２．０ｍｍ厚的单板胶合强度均达到或超过日本ＪＡＳ普通胶合板的要求。合板胶合强度随单板厚度增加而下降，在一定范围内增加涂胶量可以提高合板胶合强度，混合组坯及施加特殊添加剂具有改善松木单板胶合性能的作用。 相似文献
15.
A conductive and corrosion-resistant wood-based composite was obtained via electroless Ni–W–P plating on birch veneers. The W content of the Ni–W–P coatings obtained under different Na2WO4 concentrations in the plating bath was analyzed. The crystal structure, surface morphology, electrical resistivity, electromagnetic shielding effectiveness, surface wettability, adhesive strength and corrosion resistance of the composite were investigated. Energy-dispersive spectroscopy and X-ray photoelectron spectroscopy results showed that the coating consisted mainly of Ni0, Mo0 and P0 doped with little of their oxides. X-ray diffractometry analysis suggested the obtained coatings contained a nanocrystalline structure. Scanning electron microscopy images showed that the veneer surfaces were covered with uniform and continuous coatings. Birch veneers plated with Ni–W–P alloy exhibited good electrical conductivity with surface resistivity below 200 mΩ/cm2 and shielding effectiveness above 35 dB from 9 kHz to 1.5 GHz. Ni–W–P films firmly adhered to the wood surface. Water contact angle of the composite reached about 130° indicating the hydrophobic surface. The Ni–W–P-plated veneers showed excellent corrosion resistance due to the polarization resistance above 3.1 kΩ/cm2. This study further provides a new method for fabricating multifunctional wood-based composites. 相似文献
16.
为获得无甲醛释放的环保胶合板,将热塑性树脂薄膜(低密度聚乙烯(LLDPE)、聚丙烯(PP)、聚氯乙烯(PVC))用作胶黏剂,并利用空气介质阻挡等离子体对热塑性树脂薄膜进行表面改性处理以提高薄膜与杨木单板的界面相容性,从而获得性能良好的环保胶合板。研究了等离子体处理对胶合板胶合性能的影响,并从等离子体处理对热塑性树脂薄膜表面化学组分及其对胶合板界面形貌的影响分析其胶合机理。结果表明:在等离子体处理功率为4.5 kW、处理时间为8 m/min的条件下处理热塑性树脂薄膜,胶合板的胶合强度得到显著提高,LLDPE/杨木胶合板的胶合强度从0.49 MPa增至0.81 MPa,PP/杨木胶合板的胶合强度从0.65 MPa提高到0.84 MPa,均达到Ⅱ类胶合板标准要求。其中用等离子体处理后PVC与杨木制备的胶合板能满足Ⅰ类胶合板的标准要求,胶合强度达到0.79 MPa。XPS分析表明,等离子体改性热塑性树脂薄膜的表面发生了氧化反应,引入了含氧官能团,提高了薄膜表面极性,有利于提高薄膜与杨木单板之间的相互作用,从而使得胶合板的界面胶合更为紧密,说明等离子体处理后树脂与杨木单板的相容性提高,树脂能在单板表面更好地附着。热塑性树脂薄膜与杨木单板制备的胶合板仅有极微量甲醛释放,其主要源于木材自身,远低于国家标准对人造板甲醛释放限量的要求。研究证明等离子体处理能明显改善热塑性树脂薄膜与杨木单板的界面相容性。 相似文献
17.
《Wood material science & engineering》2013,8(1):13-23
Abstract Thermal modification at elevated temperatures changes the chemical, biological and physical properties of wood. In this study, the effects of the level of thermal modification and the decay exposure (natural durability against soft-rot microfungi) on the modulus of elasticity (MOE) and modulus of rupture (MOR) of the sapwood and heartwood of Scots pine and Norway spruce were investigated with a static bending test using a central loading method in accordance with EN 408 (1995). The results were compared with four reference wood species: Siberian larch, bangkirai, merbau and western red cedar. In general, both the thermal modification and the decay exposure decreased the strength properties. On average, the higher the thermal modification temperature, the more MOE and MOR decreased with unexposed samples and increased with decayed samples, compared with the unmodified reference samples. The strength of bangkirai was least reduced in the group of the reference wood species. On average, untreated wood material will be stronger than thermally modified wood material until wood is exposed to decaying fungi. Thermal modification at high temperatures over 210°C very effectively prevents wood from decay; however, strength properties are then affected by thermal modification itself. 相似文献
18.
Vladimirs Biziks Bruno Andersons Ļubova Beļkova Elīna Kapača Holger Militz 《Wood Science and Technology》2013,47(4):717-735
Birch wood (Betula pendula) samples were treated in a thermal regime (140, 160, 180 °C) for 1 h and investigated by means of scanning electron microscopy (SEM). SEM microimages of the wood cross-section were taken from one and the same place before and after the thermal treatment (magnification 100–2,000×). The results of measurements of areas and linear sizes of the birch wood cells show significant changes, which depend on the thermal treatment conditions and the type of the cell: libriform, tracheid, vessel and ray. After the treatment at 180 °C, the integrity of wood morphological structure begins to break up. Voids and cracks are formed between fibres, thus leading to a decline in the mechanical properties of the wood. 相似文献
19.