Preliminary study of the effects of EVA coupling agents on properties of wood-plastic composites

As a hot-melt adhesive, ethylene-vinyl-acetate （EVA） has been used in many industrial applications. But studies of the application of EVA in wood-plastic composites （WPC） are relatively few, so we have investigated the proposition of whether EVA is a suitable coupling agent for WPC or not. The results show that EVA with 8% VA is not a suitable coupling agent, because it reduces the mechanical properties of WPC without any significant effect on its physical properties. With an increase in the amount of wood powder, the mechanical properties of WPC decrease and the ability of water absorption of WPC increases.

Nanolignin,a Coupling Bio-Agent for Wood-Plastic Composites

The influence of nanolignin coupling bio-agent on some characteristics of polypropylene-wood flour composites was studied.Thus,nanolignin was prepared by the acidic method,and then different ratios of it(0,1,3 and 5 wt%)were added to a polypropylene-wood flour mixture.After mechanically mixing wood flour,nanolignin,and polypropylene,the mixture was injection molded.ASTM methods were used to measure the structural properties of nanolignin,and prepared composites’water absorption,thickness swelling,bending modulus,and bending,tensile and impact strengths.Transforming the original lignin to nanolignin did not change the chemical bonds of the material.The addition of nanolignin yielded improved mechanical and physical properties of the composites prepared.Higher strength and dimensional stability are presented by nanolignin-containing composites when comparing them with those prepared with normal lignin.Nanolignin was shown by SEM(Scanning Electron Microscope)observation to be uniformly dispersed within the polymer matrix.Wood polymer composites(WPCs)with nanolignin exhibited comparable properties with the control samples prepared using maleic anhydride polypropylene(MAPP).

Chemical characterization of smoke from the production process of wood-plastic composites

The chemical composition of unpleasant smell, emitted from the production process of wood-plastic composites using Manchurian ash sawdust （Fraxinus mandschurica Rupr.） and polypropylene powder as the raw material, was investigated. Wood sawdust and polypropylene powder were subjected to heat treatment to 290℃ during 8 min （the conditions were similar to those employed on an industrial scale）. The emitted compounds were collected and analyzed by gas chromatography-mass spectrometry （GC-MS）. The analytical results showed that the unpleasant smell was emitted from the pyrogenation of wood sawdust rather than from the polypropylene powder. Nine types of compounds （hydrocarbons, ethers, phenols, aldehydes, ketones, alcohols, acids and their derivatives, furan and its derivatives, and nitrogen-containing compounds） were collected in the gas phase during heating. Among those 126 components detected by GC-MS, 112 compounds were identified.

Performance Analysis of Plant Shells/PVC Composites under Corrosion and Aging Conditions

To make full use of plant shellfibers(rice husk,walnut shell,chestnut shell),three kinds of wood-plastic com-posites of plant shellfibers and polyvinyl chloride(PVC)were prepared.X-ray diffraction analysis was carried out on three kinds of plant shellfibers to test their crystallinity.The aging process of the composites was conducted under 2 different conditions.One was artificial seawater immersion and xenon lamp irradiation,and the other one was deionized water spray and xenon lamp irradiation.The mechanical properties(tensile strength,flexural strength,impact strength),changes in color,water absorption,Fourier transform infrared spectroscopy(FTIR),and microstructures of the composites before and after the two aging experiments were analyzed.The results showed that the chestnut shell had the highest crystallinity,which was 42%.The chestnut shell/PVC composites had the strongest interface bonding,the least internal defects,and the best general mechanical properties among the three composites.Its tensile strength,bending strength and impact strength were 23.81 MPa,34.12 MPa,and 4.32 KJ·m^(-2),respectively.Comparing the two aging conditions,artificial seawater immersion and xenon lamp irradiation destroyed the quality of the combination of plant shellfibers and PVC,making the internal defects of the composites increase.This made the water absorption ability and changes in the color of the composites more obvious and led to a great decrease in the mechanical properties.The general mechanical properties of the chestnut shell/PVC composites were the best,but their water absorption ability changed more obviously.

Property changes of wood-fiber/HDPE composites colored by iron oxide pigments after accelerated UV weathering

Four kinds of iron oxide pigments were added into wood-fiber/high-density-polyethylene composites （WF/HDPE） at three different concentrations, to determine the effects of pigments on the changes in the color and mechanical properties of the composites before and after UV accelerated weathering. HDPE, wood fibers, pigments and other processing additives were dry-mixed in a high-speed mixer. The mixtures were extruded by two-step extrusion process with a self-designed twin-screw/single-screw extruder system. Color of the samples was determined according to CIE 1976 L^＊a^＊b^＊ system by a spec- trophotometer and the bending properties were tested to evaluate the mechanical properties before and after accelerated UV weathering. The result shows that the modulus of elasticity of WF/HDPE did not obvi- ously changed after incorporating with the pigments, but the bending strength increased. After accelerated aging for 2000 h, both color and mechanical properties significantly changed. Iron oxide red and black performed better than the other two pigments, and the pigments dosage of 2.28% in the composites is favourable.

The properties of flax fiber reinforced wood flour/high density polyethylene composites

Flax fiber(FF) was used to reinforce wood flour/high density polyethylene composites(WF/PE).WF/PE particles were uniformly mixed with FF via high-speed mixing and then extruded with a single screw extruder to prepare FF reinforced WF/PE composites(FF/WF/PE).Mechanical testing,dynamic mechanical analysis,scanning electron microscopy(SEM),creep measurement and Torque rheology were used to characterize the resulting composites.The results indicate that the mechanical performance of the composites could be remarkably improved by adding a limited amount of FF.The flexural strength and modulus increased by 14.6 and 51.4%,respectively(FF content of 9 wt%),while the unnotched impact strength could be increased by 26.5%(FF content of12 wt%).The creep resistance and toughness of thecomposite was markedly improved without changing the plastic content of the composite material.

Effect of an antioxidant on the life cycle of wood flour/polypropylene composites

This study assessed the life cycle of biocomposites with antioxidants by repeated processing.The effects of antioxidants on the life cycle of wood flour/polypropylene(PP)composites were determined by analyzing their mechanical and thermal properties.The composites were repeatedly processed for seven times with pelletizing and extruding.An antioxidant,pentaerythritoltetrakys 3-(3,5-ditert-butyl-4-hydroxyphenyl)propionate,was used.The mechanical strength of the biocomposites decreased after reprocessing.Fourier transformed infrared analysis showed that thermo-oxidative aging occurred during reprocessing.The thermal performance of the resulting composites decreased because of reprocessing.Wood flour/PP has a long lifetime and antioxidants can slow the thermo-oxidative and mechanical degradation during reprocessing.

Decorative Wood Fiber/High-Density Polyethylene Composite with Canvas or Polyester Fabric

Wood-plastic composite is an environmentally friendly material,due to its use of recycled thermoplastics and plant fibers.However,its surface lacks attractive aesthetic qualities.In this paper,a method of decorating wood fiber/high-density polyethylene(WF/HDPE)without adding adhesive was explored.Canvas or polyester fabrics were selected as the surface decoration materials.The influence of hot-pressing temperature and WF/HDPE ratio on the adhesion was studied.The surface bonding strength,water resistance,and surface color were evaluated,and observation within the infrared spectrum and under scanning electron microscopy was used to analyze the bonding process.The results showed that the fabric and WF/HDPE substrate could be closely laminated together depending on the HDPE layer accumulated on the WF/HDPE surface.The molten HDPE matrix penetrates canvas more easily than polyester fabric,and the canvasveneered composite shows a greater bonding strength than does the polyester fabric-veneered composite.A higher proportion of the thermoplastic component in the substrate improved the bonding.When the hot-pressing temperature exceeded 160°C,the fabric-veneered WF/HDPE panels had greater water resistance,although the canvas fabric changed more obviously in terms of fiber shape and color,compared with the polyester fabric.For the canvas fabric,140°C–160°C was a suitable hot-pressing temperature,whereas 160°C–180°C was more suitable for polyester fabric.The proportion of the thermoplastic component in the composite should be not less than 30%to achieve adequate bonding strength.

Mechanical Properties of a Wood Flour-PET Composite Through Computational Homogenisation

This work proposes to study the effective elastic properties(EEP)of a wood-plastic composite(WPC)made from polyethylene terephthalate(PET)and Chilean Radiate pine’s wood our,using nite element simulations of a representative volume element(RVE)with periodic boundary conditions.Simulations are validated through a static 3-point bending test,with specimens obtained by extruding and injection.The effect of different weight fractions,space orientations and sizes of particles are here examined.Numerical predictions are empirically conrmed in the sense that composites with more wood our content and bigger size,have higher elastic modulus.However,these results are very sensitive to the orientation of particles.Voigt and Reuss mean-eld homogenisation approaches are also given as upper and lower limits.Experimental tests evidence that exural strengths and ultimate tensile elongations decrease respect to 100%PET,but these properties can be enhanced considering particle-size distributions instead of a xed size of wood our.

Study on Water Resistance of Polydopamine Treatment Wood Flour/Polypropylene Composites

This paper aims to investigate the water absorption of wood flour/polypropylene composites and its effects on dimensional stability and crystallization properties. Wood-plastic composites (WPCs) makes using polydopamine modified wood flour (WF-D), virgin polypropylene, maleic anhydride-grafted polypropylene (MA) and antioxidant, by using hot-pressing moulding. Water absorption (WA), thickness swelling (TS) and failure of flexural properties of the composites have studied for a range of immersion times. It is found that the WA and TS have increased with WF content and immersion time. The water absorption and thickness swelling of WPCs are 0.85% and 0.99%, respectively, after 8 days immersion. With the prolonging of immersion time, the impact strength, flexural strength and flexural modulus of WPCs increase first and then decrease. The impact strength decreases from 3.32 kJ/m2 to 2.94 kJ/m2, the retention rate is 88.55%;the flexural strength and flexural modulus by 68.58 Mpa and 3.92 Gpa, respectively. WPCs crystallization and thermal properties decrease slightly. Microstructures of the composites are examined to understand the mechanisms for the wood-plastic interaction which affects the water absorption and thickness swelling. Our work demonstrates that using polydopamine treatment wood flour for preparing WPCs can be an efficient way to improve the water resistance of WPCs.

Effect of Different Reinforcing Fillers on Properties,Interfacial Compatibility and Weatherability of Wood-plastic Composites

Utilization of biochar in plastic based blends offers a sustainable way to renewable materials as well as value-added use of wood waste.To investigate the interfacial compatibility and weatherability properties of biochar composites,four types of Wood-Plastic Composites(WPC)were prepared by an extrusion process.The mechanical properties,water absorptions,thermal and viscoelastic properties,and rheological behavior of the composites were also evaluated.The decolorizing carbon(NA)composite melts showed the higher modulus and viscosity,indicating better melt strength.The NA composites performed the best in tensile properties(strength of 2&6 MPa and modulus of 3.4 GPa)and had strong interfacial interaction between particles and the matrix.The degree of HDPE crystallinity in the biochar and carbon composites decreased relative to Douglas-fir(DF)composites,while the thermal properties of the composites improved compared with DF composites.For the water resistance,the DF composites displayed the highest water absorption(3.7%)and thickness swell(2.9%).During accelerated weathering tests,longer exposure time increased the color change and lightness,especially for DF composite.NA and biochar composites resulted in improved photostability.This study opens up a pathway to utilize effectively the renewable biochar as reinforcing filler in WPC in outdoor applications.

Effect of wood dust type on mechanical properties, wear behavior, biodegradability, and resistance to natural weathering of wood-plastic composites

The present work reports the inclusion of different proportions of Mango/Sheesham/Mahogany/Babool dust to polypropylene for improving mechanical,wear behavior and biodegradability of wood-plastic composite(WPC).The wood dust(10%,15%,20%by weight)was mixed with polypropylene granules and WPCs were prepared using an injection molding technique.The mechanical,wear,and morphological characterizations of fabricated WPCs were carried out using standard ASTM methods,pin on disk apparatus,and scanning electron microscopy(SEM),respectively.Further,the biodegradability and resistance to natural weathering of WPCs were evaluated following ASTM D5338-11 and ASTM D1435-99,respectively.The WPCs consisting ofBabool and Sheesham dust were having superior mechanical properties whereas the WPCs consisting of Mango and Mahogany were more wear resistant.It was found that increasing wood powder proportion results in higher Young's modulus,lesser wear rate,and decreased stress at break.The WPCs made of Sheesham dust were least biodegradable.It was noticed that the biodegradability corresponds with resistance to natural weathering;more biodegradable WPCs were having the lesser resistance to natural weathering.

No-formaldehyde Wood-plastic Composite Plywood in China

As a new product invented by the Research Institute of Wood Industry, no-formaldehyde wood-plastic composite plywood is the harvest of the cross-study on wood-plastic composite and plywood industry, It has no formaldehyde emission, with an excellent environment-friendly performance and a good bonding quafity. This paper analyses the strongpoints and market of this wood-plastic composite plywood.

基于CFD与风洞试验的边主梁涡振气动措施

为能够快捷且经济地完成开口类钝体桥梁断面涡振制振气动措施的选型,以一座边主梁叠合梁斜拉桥为背景,采用“CFD(computation fluid dynamics)数值模拟选型+风洞试验验证”的思路对其涡振制振气动措施选型进行研究.该桥原设计主梁断面在常遇风速下存在显著涡激振动,为完成气动措施的初步选型,采用CFD数值计算对原设计断面的流场进行模拟,通过研究原设计断面的旋涡脱落状态确定主要旋涡抑制对象,进而有针对性地模拟了3种气动措施(下中央稳定板、导流板与风嘴)对主要脱落旋涡的抑制作用,通过将各断面旋涡脱落状态与三分力系数进行对比分析,得到各断面涡振性能的相对优劣关系,并最终选取风嘴与下中央稳定板结合而成的组合气动措施进行风洞验证试验.试验结果表明:该组合气动措施能够有效抑制梁体在各风攻角下的涡激振动,且在+5°风攻角下,通过风洞试验得到的导流板、下中央稳定板、风嘴组合气动3种措施对原设计断面涡振振幅的减小作用依此递增,分别为2.7%、27.7%与87.4%,制振能力高低关系与数值模拟结果相一致;本次数值模拟结果符合预期要求,未来可针对不同类型桥梁断面进一步扩展数值模拟与风洞试验结果对比的数据集,以期更为准确、快捷地完成气动措施的选型.

不同界面下梁端直剪型锚栓钢板剪切承载力试验研究

开展梁端直剪型锚栓钢板剪切承载力加固试验研究。试验序列包含1个对比试验段、5个剪切承载力加固试验段。试验参数包括界面条件和钢板高度。结果表明:受力过程中钢板与混凝土之间的黏结界面终会剥离,不同黏结界面不影响剪切承载力;增加钢板高度和配套的直剪型锚栓数量能有效提高混凝土梁的剪切承载力。直剪型锚栓钢板剪切承载力加固存在2种机制,约束机制通过限制斜裂缝宽度提高剪切承载力,而组合受力机制通过钢板将一部分剪力直接传入支座。加固钢板高度较小时以约束机制为主,加固钢板高度较大时,2种加固机制联合发挥作用。

深江铁路洪奇沥公铁大桥主桥设计关键技术

研究目的:洪奇沥公铁大桥是深江铁路的控制性工程,主桥采用主跨808 m公铁合建斜拉桥一跨跨越洪奇沥水道,上层布置8车道城市快速路,下层布置4线铁路。结合建设条件、结构特点及使用性能,对主桥结构体系、主梁横断面及结构形式、索-塔锚固结构、施工方法等关键技术展开研究,确定技术合理可行和经济节约的设计方案。研究结论:(1)首创了短边跨叠合板-桁组合梁斜拉桥结构体系,主桥长度减少20%,节省工程投资;(2)首次在4线铁路公铁合建斜拉桥上采用倒梯形双主桁截面,桥面布置紧凑、受力明确;(3)提出的边跨主梁采用矩形钢管混凝土叠合板-桁组合结构,集结构受力和锚固压重于一体,施工便捷;(4)发明了“自平衡交叉锚固+齿块锚固”的索-塔混合锚固方式,技术经济性高;(5)钢主梁创新采用“纵向大节段+横向分块”施工方法,解决了超宽超高超重整节段钢桁梁运输受既有桥净空限制的难题;(6)本研究成果可为公铁合建桁梁斜拉桥设计提供参考或借鉴。

声发射技术在复合材料壁板压-剪复合载荷疲劳试验损伤扩展监测中的应用

利用声发射技术对某飞机复合材料机身壁板压-剪复合载荷疲劳试验中位于壁板长桁上的两处初始损伤开展了连续跟踪监测,试验过程中对各监测通道声发射信号的幅值、能量、计数等特征参数进行实时统计分析,在试验中成功监测到其中一处损伤的扩展,为试验结论分析提供了重要数据支撑。

汽车B柱复合材料加强件的性能及拓扑优化研究

为探索复合材料在汽车B柱等安全部件中的应用,文中以汽车B柱玻纤尼龙复合材料加强件为例,通过仿真实验验证了其在安全性和轻量化上的性能,并通过对复合材料加强件进行耐撞性拓扑优化实现了加强件的减重降本设计。研究结果表明,玻纤尼龙复合材料加强件相比钢材方案显著提升了B柱的耐撞性,并实现单侧B柱1.15 kg的减重效果,而优化后的玻纤尼龙复合材料加强件在保证B柱耐撞性能的同时,实现减重248.8 g,原料成本降低27.5%。为玻纤尼龙复合材料加强件的应用和耐撞性拓扑优化技术在降本轻量化领域的推广提供了重要参考。

电动工具塑件的复合二次抽芯注塑模具设计

根据电动工具结构件镂空的结构特点,结合其成型生产的技术要求,设计一副包含了三边侧向抽芯的复杂注塑模具。选择侧向复合二次抽芯机构解决塑件一侧倒扣和内扣组合结构的脱模问题,侧向复合二次抽芯结构中的内缩镶件机构设计精巧,模具空间占用少,采用研磨工艺制作,使其尺寸精度达到IT5级;选择2个平滑块侧分型抽芯结构的方式脱出塑件另外两侧边的倒扣和主体胶位,充分利用滑块达到分步脱模的目的,同时,配合斜顶抽芯顶出机构的设计,有效解决了镂空结构状塑件容易粘模和顶出困难的难题。模具经过实际生产验证,结构的合理性、生产的顺畅性、品质的稳定性均达到模具批量生产的要求。

深江铁路洪奇沥公铁两用大桥主桥方案构思与总体设计

深江铁路洪奇沥公铁两用大桥主桥采用(3×100+808+3×100)m超短边跨钢-混组合混合梁斜拉桥,一跨跨越通航水域。该桥公铁分层布置,上层布置8车道城市快速路,下层布置4线铁路。主梁采用倒梯形双主桁截面,桥面布置紧凑、受力明确、经济性好。中跨主梁采用板桁-箱桁组合结构钢梁,桥面结构参与主桁受力,具有高效综合性能。边跨主梁采用矩形钢管混凝土叠合板-桁组合梁,融结构受力和锚固压重于一体,叠合板采用32 cm厚预制板+40 cm厚现浇层。钢-混结合段采用“钢格室+承压板”构造,钢-混结合面位于桥塔向中跨侧4.6 m。桥塔采用H形混凝土塔,基础采用35根直径4.0 m的大直径钻孔灌注桩。斜拉索采用标准抗拉强度2000 MPa的平行钢丝成品索,最大规格为PES(C)7-547。索梁锚固采用副桁弦杆节点兜底钢锚箱结构,传力可靠、抗疲劳性能好。索塔锚固创新地采用自平衡交叉混合锚固技术,以适应大规格斜拉索锚固。钢桁梁采用“纵向分段、横向分区”制造、运输、现场吊装的施工方案。