Effects of particle size and distribution on the mechanical properties of SiC reinforced Al-Cu alloy composites

This paper studied the combined effects of particle size and distribution on the mechanical properties of the SiC particle reinforced Al-Cu alloy composites. It has been shown that small ratio between matrix/reinforcement particle sizes resulted in more uniform distribution of the SiC particles in the matrix. The SiC particles distributed more uniformly in the matrix with increasing in mixing time. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength and elongation. Yield strength and ultimate tensile strength of the composite reinforced by 4.7 μm sized SiC particles are higher than those of composite reinforced by 77 μm sized SiC particles, while the elongation shows opposite trend with yield strength and ultimate tensile strength. Fracture surface observations showed that the dominant fracture mechanism of the composites with small SiC particle size (4.7 μm) is ductile fracture of the matrix, accompanied by the “pull-out” of the particles from the matrix, while the dominant fracture mechanism of the composites with large SiC particle size (77 μm) is ductile fracture of the matrix, accompanied by the SiC particle fracture.     

木粉/聚丙烯木塑复合泡沫材料吸能特性

采用模压法制备木粉/聚丙烯复合泡沫材料,并对不同木粉含量的泡沫材料进行静态压缩、循环压缩、压缩蠕变、动态热机械分析的测试,探讨了不同木粉含量的木粉/聚丙烯复合泡沫材料的能量吸收效果。结果表明: 随着木粉含量的增加,木粉/聚丙烯木塑复合泡沫材料的能量吸收量、能量吸收效率参数、松弛率、循环损耗量、动态力学性能等均呈先升后降的趋势,在木粉质量比为30%时泡沫材料吸能性能达到最佳。     

Effects of chitosan as biopolymer coupling agent on the thermal and rheological properties of polyvinyl chloride/wood flour composites

Chitosan (CS) was opted as a novel biopolymer coupling agent for wood flour polyvinyl chloride composites (WF/PVC) to improve interfacial adhesion. This study mainly aimed at investigating the effects after adding CS of different addition amounts and particle sizes on the thermal and rheological properties of WF/PVC composites by the analyses of vicat softening temperature test (VST), differential scanning calorimetry (DSC), thermogravimetry (TGA) and torque rheometry. The results indicated that an optimum addition amount (30 phr) with the particle size (180–220 mesh) could elevate heat resistance capacity, glass transition temperature of composites as well as thermal stability at the early stage of degradation more effectively. In the aspect of rheological characteristics, longer fusion time, lower fusion torque and higher fusion temperature were showed as the CS addition amount increased and the particle size declined. In order to obtain sufficient compaction and ensure proper blending to compounds during extrusion, the higher pressure needed to be supplied when the addition amount of CS exceeded 20 phr.     

木粉含量对木粉/酯化淀粉/聚乳酸复合材料性能影响

以甘油为相容剂,利用木粉、马来酸酐酯化淀粉和聚乳酸(PLA)进行熔融挤出制备了木粉/酯化淀粉/聚乳酸复合材料。利用XRD和SEM对复合材料的结晶度和断面形貌进行分析表征,以研究木粉含量对复合材料界面相容性的影响;并对复合材料的热稳定性、力学性能、流变性能以及吸水率进行表征。实验结果表明,随着木粉含量的增加,复合材料的界面相容性下降,拉伸强度和弯曲强度增大,断裂伸长率下降,吸水率逐渐增大;TGA测试结果表明木粉的加入使材料的热稳定性下降;流变测试表明木粉用量的增加,使复合材料的储能模量、损耗模量和复数粘度逐渐增加。     

木粉粒径和填量对木塑复合材料力学性能影响研究

采用聚氯乙烯(PVC)树脂和桉木粉(WF)制得PVC木塑复合材料。研究了木粉粒径和填量对PVC木塑复合材料力学性能的影响。结果表明,在一定范围内复合材料的拉伸强度随着木粉粒径的减小先升高后降低,随着木粉填量的增加先降低后升高然后趋于平稳;冲击强度随着木粉粒径的减小先升高后降低,随着木粉填量的增加而降低。当木粉粒径为70～80目,木粉填量为20%(质量分数)时,所得复合材料的力学性能最佳。     

竹粉接枝改性及其对竹粉/PETG复合材料流变行为的影响

采用电子活化再生原子转移自由基聚合（AGET ATRP）法将甲基丙烯酸甲酯（MMA）接枝到竹粉（BF）表面,并采用哈克微量混合流变仪及旋转流变仪考察了竹粉接枝改性前后对竹粉/聚对苯二甲酸乙二醇酯-1,4-环己烷二甲醇酯（PETG）复合材料流变行为的影响。毛细管流变结果表明,竹粉/PETG复合材料属于假塑性流体,呈现剪切变稀的现象;应变扫描结果表明,与未改性竹粉/PETG复合材料体系相比,竹粉经接枝改性后其复合材料体系在更大的应变范围内属于线性弹性行为;频率扫描结果表明,竹粉的接枝改性处理有助于促进竹粉在PETG基体中的均匀分散。     

Investigation of rheological and mechanical properties of wood flour reinforced polypropylene

This study aims to investigate the rheological and mechanical properties of polypropylene when reinforced by wood flour. In the study, wood flour (WF) was added as filling material to polypropylene (PP), and its effects were investigated. The grain size of the wood flour was 300 μm. Wood flour was mixed into polypropylene material at different rates of weight. Viscosity changes of the polypropylene at various temperatures and pressure values of the concentration rates were documented. As a result, viscosity increases as the amount of wood flour filling is increased; yet as temperature, pressure and shear rate are increased, viscosity decreases. The study also focuses on the changes in its mechanical properties of polypropylene reinforced with wood flour. The tensile strength of reinforced polypropylene at varying percentages (wt. 5 %, wt. 10 % and wt. 15 %) was observed to decrease by 11 %, 16 % and 21 %, respectively, compared to that of non‐reinforced polypropylene. Additionally, impact tests showed that the highest energy absorption was in 10 % wood flour reinforced polypropylene.     

PBS/杨木粉全降解木塑复合材料的加工流变性能及其应用研究

采用高级毛细管流变仪,分别测定PBS及PBS/杨木粉全降解木塑复合材料的流变性能,研究了不同挤出温度、不同木粉含量对复合材料加工性能的影响。以流变性能测试为参考,改变加工工艺,采用熔融共混法制备了PBS/杨木粉全降解木塑复合材料,并测试其性能。结果表明,随着木粉用量的增加,体系流动性明显下降,可加工的温度范围越来越窄,大致木粉填充量每提高5%,需要升高5℃才能保证粘度变化不大;不同加工工艺对所制备的PBS/杨木粉木塑复合材料性能有较大影响;综合流变性能和力学性能,木粉含量为30%、35%、40%、45%和50%的PBS/杨木粉全降解木塑复合材料的较佳加工温度分别为120、125、125、130和135℃。     

Effect of SiC particle size on the physical and mechanical properties of extruded Al matrix nanocomposites

In this work, the effect of SiC particle size and its amount on both physical and mechanical properties of Al matrix composite were investigated. SiC of particle size 70 nm, 10 μm and 40 μm, and Al powder of particle size 60 μm were used. Composites of Al with 5 and 10 wt.% SiC were fabricated by powder metallurgy technique followed by hot extrusion. Phase composition and microstructure were characterized. Relative density, thermal conductivity, hardness and compression strength were studied. The results showed that the X-ray diffraction (XRD) analysis indicated that the dominant components were Al and SiC. Densification and thermal conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Scanning electron microscope (SEM) studies showed that the distribution of the reinforced particle was uniform. Increasing the amount of SiC leads to higher hardness and consequently improves the compressive strength of Al–SiC composite. Moreover, as the SiC particle size decreases, hardness and compressive strength increase. The use of fine SiC particles has a similar effect on both hardness and compressive strength.     

Physical,mechanical and morphological properties of polymer composites manufactured from carbon nanotubes and wood flour

The objective of this investigation was to evaluate physical, mechanical and morphological properties of experimental polymer type panels made from single-wall carbon nanotube (SWCNT) and wood flour. The composites with different SWCNTs (0, 1, 2, 3 phc) and maleic anhydride grafted polyethylene (MAPE) (0 and 3 phc) contents were mixed by melt compounding in an internal mixer and then the composites manufactured by injection molding method. The mass ratio of the wood flour to LDPE was 50/50 (w/w) in all compounds. Water absorption, thickness swelling, bending characteristics, impact strength and morphological properties of the manufactured composites were evaluated. Based on the findings in this work the water absorption and thickness swelling of the nanocomposites decreased with increasing with amount of the SWCNTs (from 1 to 3 phc) and MAPE (3 phc) in the panels. The mechanical properties of LDPE/wood-flour composites could be significantly enhanced with increased percentage of MAPE and SWCNTs content. Panels having 2 phc SWCNTs and 3 phc MAPE exhibited the highest impact strength value. Also Scanning Electron Microscope (SEM) micrographs showed that carbon nanotubes can fill the voids of wood plastic composites as well as addition of MAPE and SWCNTs enhanced interaction between the components.     

短切碳纤维表面处理对木粉/高密度聚乙烯复合材料性能的影响

木粉（WF）填充增强高密度聚乙烯（HDPE）复合材料具有良好的环境效益,少量引入短切碳纤维（SCF）可进一步提高其力学性能。为改善SCF与WF/HDPE复合材料中塑料基体的界面结合,提高SCF在WF/HDPE复合材料中的增强作用,采用气相、液相及气液双效氧化3种表面处理方式处理SCF,通过挤出工艺制备短切碳纤维增强木粉/高密度聚乙烯复合材料（SCF-WF/HDPE）,探讨了不同处理方法对SCF-WF/HDPE复合材料性能的影响。SEM观察显示,表面处理增大了SCF的表面粗糙度,可提高其与基体的界面结合;动态力学性能分析证实碳纤维提高了存储模量。测试结果表明：表面处理过的短切碳纤维可使SCF-WF/HDPE复合材料的力学性能、热力学性能和蠕变性能均得到显著提高,其中气相表面处理的效果最好。对比WF/HDPE复合材料,SCF-WF/HDPE的拉伸强度提高了34.5%,弯曲强度提高了23%,冲击强度提高了54.7%。     

Additive manufacturing of mechanical testing samples based on virgin poly (lactic acid) (PLA) and PLA/wood fibre composites

3D printing in additive manufacturing is considered as one of key technologies to the future high-precision manufacturing in order to benefit diverse industries in building construction, product development, biomedical innovation, etc. The increasing applications of 3D printed components depend primarily on their significant merits of reduced weight, minimum used materials, high precision and shorter production time. Furthermore, it is very crucial that such 3D printed components can maintain the same or even better material performance and product quality as those achieved by conventional manufacturing methods. This study successfully fabricated 3D printed mechanical testing samples of PLA and PLA/wood fibre composites. 3D printing parameters including infill density, layer height and the number of shells were investigated via design of experiments (DoE), among which the number of shells was determined as the most significant factor for maximising tensile strengths of PLA samples. Further, DoE work evaluated the effect of material type (i.e., neat PLA and PLA/wood fibres) and the number of shells on tensile, flexural and impact strengths of material samples. It is suggested that material type is the only predominant factor for maximising all mechanical strengths, which however are consistently lower for PLA/wood fibre composites when compared with those of neat PLA. Increasing the number of shells, on the other hand, has been found to improve almost all strength levels and decrease infill cavities. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0211-3     

The utilization of bamboo charcoal enhances wood plastic composites with excellent mechanical and thermal properties

In order to enhance the mechanical properties and thermal properties of wood plastic composites (WPCs), bamboo charcoal (BC) was used as reinforcing filler of WPC, and a series of BC-WPC composites were prepared. The effect of BC and water treatment on water absorptions, morphologies, mechanical properties, the effect of water treatment on mechanical properties and thermal properties of the composites were investigated. The results showed that BC could have strong interfacial interaction in the WPC. The water resistance, flexural properties, tensile properties and thermal properties of BC-WPC were higher than WPC. The flexural and tensile properties were reduced and the impact strength was increased after water treatment. The presence of BC resists the influence of water absorption on composites mechanical properties.     

The effect of pre-softened wood chips on wood fibre aspect ratio and mechanical properties of wood–polymer composites

The objective of this work was to study the effect of chemical pre-treatment and moisture content of wood chips on the wood particle aspect ratio after compounding in a twin-screw extruder and on the mechanical properties of wood–polymer composites (WPCs). Composites with 50 wt.% wood content were manufactured using pre-treated and untreated wood chips. The effect of wood moisture content on composite properties was studied by using dried and undried wood chips. The mechanical properties and fracture surfaces of the composites as well as the microstructure and aspect ratio of wood particles after compounding were studied. The highest wood particle aspect ratio after extrusion was achieved by using pre-treated, undried wood chips as raw material. The chemical pre-treatment was found to enhance the defibration of wood chips as well as the mechanical properties of the composites.     

Morphology,mechanical properties,and dimensional stability of wood particle/high density polyethylene composites: Effect of removal of wood cell wall composition

Variation in the chemical composition of wood cell walls has a significant influence on the properties of wood plastic composites (WPCs). This study investigated the effect of removal of hemicellulose and/or lignin on the mechanical properties and dimensional stability of WPCs. Four types of wood particles with various compositions including native wood flour (WF), hemicellulose-removed particle (HR), holocellulose (HC), and α-cellulose (αC) were prepared and compounded with high density polyethylene (HDPE) in an extruder, both with and without maleated polyethylene. Injection molding was used to make test specimens. The HR-based composites exhibited the best water resistance. The HC-based composites obtained a greater tensile modulus but a lower water resistance. The highest values for tensile strength, elongation at brake, toughness, and impact strength were achieved by the composites filled with αC.     

Effect of lognormal particle size distributions on particle spreading in additive manufacturing

Additive manufacturing (AM) has attracted much attention worldwide in various applications due to its convenience and flexibility to rapidly fabricate products, which is a key advantage compared to the traditional subtractive manufacturing. This discrete element method (DEM) study focusses on the impact of particle polydispersity during the particle spreading process on parameters that affect the quality of the final product, like packing and bed surface roughness. The particle systems include four lognormal particle size distribution (PSD) widths, which are benchmarked against the monodisperse system with the same mean particle diameter. The results reveal that: (i) the solid volume fraction of the initial packed particle bed in the delivery chamber increases then plateaus as the PSD width increases; (ii) regardless of PSD width, the solid volume fraction of the particle bed increases with spreading layer height before compression, but decreases with layer height after compression; (iii) the bed surface roughness increases with PSD width or layer height both before and after the compression of the spreading layer; (iv) the extent of increase in solid volume fraction during compression is correlated with the extent of decrease in bed surface roughness; and (v) the broader PSDs exhibit larger fluctuations of solid volume fraction of the particle bed and bed surface roughness due to greater variability in the arrangement of particles of different sizes. The results here have important implications on the design and operation of particle-based AM systems.     

HDPE/木粉改性复合材料的制备及其长效吸水性能研究

加入HDPE-g-MAH、CG-8831和KH-550制备HDPE/木粉改性复合材料。研究其长效吸水性,发现吸水率随时间延长先快速增加,浸水35 d后缓慢增至平衡,HDPE-g-MAH改性效果最好,其饱和吸水率仅为1.503%。利用Fick第二扩散定律拟合吸水动力学曲线,得扩散系数D的顺序:HDPE-g-MAH增容HDPE/木粉复合材料HDPE/木粉复合材料KH-550改性HDPE/木粉复合材料CG-8831改性HDPE/木粉复合材料。并证明该吸水过程符合Fick第二扩散定律,相关系数R2值达0.99以上。HDPE/木粉改性复合材料尺寸变化系数CDCWCT。     

滑石粉对微孔发泡木粉/聚丙烯复合材料结晶行为及泡孔结构的影响

以滑石粉为成核剂,超临界CO_2为发泡剂,采用间歇釜式方法制备微孔发泡木粉/聚丙烯复合材料。采用DSC、XRD和SEM对微孔发泡木粉/聚丙烯复合材料的结晶行为与泡孔结构进行了测定与分析。结果表明:滑石粉的添加能够提高微孔发泡木粉/聚丙烯复合材料的结晶温度,诱导产生不完善的α晶型;能够提高聚合物基体的熔体黏度,减小泡孔尺寸,增加泡孔密度,促使泡孔尺寸分布更均匀,最终能够形成泡孔密度为1.0×10~9个/cm~3、平均泡孔半径为16.4μm、发泡倍率为18倍、表观密度约为0.055g/cm~3的微孔发泡木粉/聚丙烯复合材料。     

杨木纤维尺寸对热压成型杨木纤维/高密度聚乙烯复合材料力学和蠕变性能的影响

采用热压成型法制备了4种不同尺寸, 即125~180 μm、180~425 μm、425~850 μm和850~2 000 μm的杨木纤维(PWF)/高密度聚乙烯(HDPE)复合材料, 并对PWF/HDPE复合材料进行了弯曲性能测试、冲击性能测试、动态热力学分析(DMA)、24 h蠕变-24 h回复测试和1 000 h长期蠕变测试。结果表明:PWF的尺寸过大或者过小均不利于提高PWF/HDPE复合材料的弯曲性能, 增强效果最好的是425~850 μm PWF/HDPE复合材料, 其弯曲强度达到26.71 MPa, 弹性模量达到2.73 GPa;PWF长度从180 μm增加到2 000 μm, PWF/HDPE复合材料的抗冲击性能变化不大;125~180 μm PWF/HDPE复合材料的抗冲击性能较差;短PWF/HDPE复合材料的抗蠕变性能较差, 不适合在长期负载的条件下工作, 而850~2 000 μm的长PWF/HDPE复合材料的抗长期蠕变性能最好, 且回复率最高, 为78.46%;1 000 h形变仅为0.809 mm, 对比其他尺寸的PWF/HDPE复合材料1 000 h 形变的平均值降低了48.00%。