Fabrication of advanced “green” composites using potassium hydroxide (KOH) treated liquid crystalline (LC) cellulose fibers

Advanced green composites having excellent strength and stiffness were fabricated using liquid crystalline (LC) cellulose fibers and soy protein isolate (SPI) resin. Further, LC cellulose fibers were treated with potassium hydroxide (KOH) to improve their tensile strength and Young’s modulus by increase the crystallinity of cellulose. The improvements were significant when the treatment was carried out while keeping the fibers under tension. The Young’s modulus (stiffness) of the LC cellulose fibers increased by about 33 % from 47.8 to 63.7 GPa and the strength increased by about 18 % from 1483 MPa to 1749 MPa. X-ray diffraction (XRD) study of the LC cellulose fibers showed over 50 % increase in crystallinity after the KOH treatment. The mechanical properties of the LC cellulose fiber-reinforced composites were also high and improved further when the KOH treated fibers were used. With 65 % fiber volume it should be possible to obtain composites with strength above 1020 MPa and modulus of over 37 GPa, making them truly advanced green composites that could be used for structural applications.     

The effect of heat treatment temperature and time on the microstructure and mechanical properties of PAN-based carbon fibers

The influence of heat treatment temperature from 1400 to 2840 °C and time from 1.2 to 12.0 min on the structure and mechanical properties of polyacrylonitrile carbon fibers was studied. It was observed that the Young’s modulus increased with increasing temperature and time, but the tensile strength exhibited different variation trends with the different processing methods. For a fixed time of 1.2 min, the strength dropped from 4.6 GPa at 1400 °C to 2.6 GPa at 2840 °C, (~43.5 %) as opposed to a 63.9 % increase in Young’s modulus. However, when the treatment time was increased to 6.0 min at 2500 °C, the tensile strength decreased only by 1.9 %, from 3.71 to 3.64 GPa, versus a nearly 20.0 % increase in Young’s modulus. The same situation was found for treatment at 2000 and 2700 °C. Raman spectroscopy and uniform stress model analysis show that the degree of covalent cross-linking between the graphene planes decreased as temperature increased, while it remained almost constant as treatment time was increased. It is believed that during heat treatment of a carbon fiber, the cross-linking collapses at the beginning but the crystalline size keeps growing with prolonging time, so the tensile strength decreases little with further heat treatment while tensile modulus keeps increasing.     

Effect of hot stretching graphitization on the structure and mechanical properties of rayon-based carbon fibers

The influence of hot stretching graphitization on the structure and mechanical properties of rayon-based carbon fibers was studied. It was observed that the Young’s modulus of the treated fibers increased with heat treatment temperature (HTT) and hot stretching stress, to 173 GPa by 158.2 % through hot stretching at 2700 °C under stress of 270 MPa compared to that of the as-received carbon fiber. Meanwhile the tensile strength increased to 1.75 GPa by 73.3 % through hot stretching at 2700 °C under 252 MPa. The field emission scanning electron images showed markedly increased roughness on the external surface and bigger and more compacted granular morphologies on the cross section of the treated fibers with increasing HTT. The preferred orientation of graphitic layers was improved by hot stretching, and the higher the HTT, the stronger the effectiveness of the hot stretching. The crystallite sizes grew and the crystallite interlayer spacing decreased obviously with increasing HTT but changed just slightly with increasing stretching stress. The analysis based on uniform stress model and shear fracture theory proposed that the improvement of tensile strength and Young’s modulus for rayon-based carbon fiber was mainly due to the increased preferred orientation and nearly unchanged shear modulus between planes with increasing HTT during hot stretching graphitization, which was much different from polyacrylonitrile-based carbon fibers.     

The Effect of Shear Mixing Speed and Time on the Mechanical Properties of GNP/Epoxy Composites

The aim of this study was to examine the effect of shear mixing speed and time on the mechanical properties of graphene nanoplatelet (GNP) composites. Shear mixing is cited in the literature as one method of making a good dispersion of nanofillers in a polymer that breaks down agglomerates into smaller particles and in the case of GNP can exfoliate layers of graphene. In this paper 0.1 to 5 wt% GNP was mixed with epoxy at different speeds and for different lengths of time. The composites were then cured and the tensile strength and Young’s modulus was measured. Optical microscopy was performed to examine the dispersion of the GNP in the epoxy. The results show that the shear mixing speed and time affect the size of agglomerates, which has an impact on the mechanical properties of the composite. At 3000 rpm and 2 h of mixing the average size of agglomerate was 26.3 μm (30 % reduction compared to that of 1000 rpm and 1 h duration), the tensile strength of epoxy was not affected by the addition of GNP, while a 12 % increase was recorded for the Young’s modulus. It is also found that functionalisation of the surface of the GNP improves the bond formed between the GNP and the resin that enhances its mechanical properties with no effect on the size of the agglomerates. Acetone was used to improve the GNP dispersion and found that shear mixing 5 wt% of GNP with acetone increases the Young’s modulus up to 3.02 from 2.6 GPa for the neat epoxy, an almost 14 % rise.     

Characterization of the viscoelastic behavior of bismaleimide resin before and after exposure to high temperatures

Creep and high strain rate mechanical properties, shrinkage strain, and thermal properties of a bismaleimide neat resin after exposure to a high temperature in air were evaluated and compared with the corresponding properties for a pristine resin. Under tension at a strain rate of 6×10^?4 s^?1, the Young’s modulus decreases and Poisson’s ratio increases with temperature, measured up to 310 °C. The tensile creep behavior was determined at stress levels of 12, 24, and 33 MPa at elevated temperatures. At each stress level, the creep compliance curves at different temperatures were shifted horizontally to form a master curve. These creep compliance master curves are nearly identical, indicating a linearly viscoelastic behavior up to 33 MPa. The bismaleimide resin was also exposed to air at other temperatures of 245, 260, and 280 °C for 1500 hours. After exposure to a high temperature, three regimes were observed in the resin through optical micrographs: an outer layer showing darker color, an interior that nearly maintained its original color, and a transition (or reacting) region in between. The average shrinkage on surface was determined as 3.4 % strain after 1500 hours of exposure to 260 °C in air. Compression at a high strain rate using a long split Hopkinson pressure bar shows that the bulk bismaleimide resin is rather insensitive to the exposure to a high temperature, exhibiting only a slight reduction in mechanical properties after 1500 hours of exposure to 245 °C. The uniaxial creep compliance of the neat resin was converted into the Young’s relaxation modulus, which was then used to calculate the Young’s modulus under tension at the strain rate and temperatures involved, and a good agreement was achieved between the calculated results and the experimental data, indicating that the rate-dependent Young’s modulus is the representation of viscoelastic properties.     

紫外光辐射固化共混改性环氧树脂复合材料的力学和热老化性能

利用湿法手工铺叠工艺和紫外光固化技术,制备以双酚A环氧树脂E-44与有机硅环氧树脂ES-06共混改性光敏树脂体系为基体的玻璃布增强复合材料,测试并分析比较了复合材料的力学和热老化性能.结果表明,在光敏树脂基体中加入链转移剂以及对光固化后的复合材料进行加压后固化处理,均能显著提高复合材料的性能.采用E-44与ES-06质量比为2:1的共混改性树脂体系制备的复合材料的力学性能和耐热老化性能最佳,其拉伸强度达到146.6 MPa,拉伸模量为19.4GPa,弯曲强度为152.5MPa,层间剪切强度达到16.2 MPa.     

High-performance nanocomposite films: reinforced with chitosan nanofiber extracted from prawn shells

An optically transparent prawn shell with intact original shape and substantial morphological detail was developed in this study as well as the corresponding nanocomposite film. Chitosan nanofibers could be got through deacetylated reaction following a series of simple mechanical treatments under neutral condition. Polyethersulfone (PES) resin was used as matrix to prepare chitosan-nanocomposite film during the impregnated process. FE-SEM images showed that chitosan nanofiber were highly uniform and forming interweaved network structure, with the average wide mostly less than 30 nm. Compared with pure PES, light transmission of the obtained nanocomposite was 84.5 % with only 4.2 % transmission loss. Furthermore, the addition of chitosan nanofiber significantly improved the CTE of the neat PES to 16 ppm/K from room temperature to 140 °C with the fiber content was 60 wt%. Young’s modulus and tensile strength of the PES resin increased from 1.3 to 3.9 GPa and 39 to 91 MPa, respectively, which was attributed by the reinforcement effect of nanostructure chitosan fibers. These unique characteristics of the chitosan/PES nanocomposite would lead to a number of potential applications in some high-tech areas and are a promising move toward the environmental protection of marine-river-waste utilization.     

耐高温异构聚酰亚胺树脂及其复合材料

采用改性的单体反应物聚合法(MPMR)合成了一系列低黏度、耐高温异构聚酰亚胺树脂, 研究了树脂预聚物分子质量对树脂的高温流变行为、固化后热氧化稳定性的影响, 并对树脂的分子结构及其复合材料的加工工艺性能、力学性能进行了表征。结果表明: 树脂预浸液常温储存期大于两个月, 亚胺化后PI-2纯树脂最低黏度为154 Pa·s, 固化后树脂质量损失5%的温度大于560 ℃; 石英纤维/PI-2树脂基复合材料在室温和500 ℃的弯曲强度分别为917、197 MPa, 弯曲模量分别为29、22 GPa, 拉伸强度分别为760、341 MPa, 拉伸模量分别为32、31 GPa, 压缩强度分别为570、95 MPa, 层间剪切强度分别为62、10 MPa。      

‘Green’ composites Part 1: Characterization of flax fabric and glutaraldehyde modified soy protein concentrate composites

Fully biodegradable, environment friendly ‘green’ composites were prepared using glutaraldehyde (GA) modified soy protein concentrate (MSPC-G) and flax fabric. Soy protein concentrate (SPC) polymer has low tensile properties, poor moisture resistance and is brittle. SPC polymer with 15% glycerin, as an external plasticizer, exhibited fracture stress and Young's modulus of 17 and 368 MPa, respectively. SPC polymer was cross-linked with GA to increase its tensile properties and improve its processability as a resin to manufacture flax fabric-reinforced composites. GA reacts with the free amine groups in SPC to form crosslinks. MSPC-G showed 20% increase in fracture stress and 35% increase in Young's modulus as well as improved moisture resistance compared to SPC. Besides the mechanical properties, MSPC-G was also characterized for its thermal stability and dynamic mechanical properties.Composite laminates, approximately 1 mm thick, were made using flax fabric and MSPC-G polymer. Composite specimens were prepared with two different orientations, namely, 0° or 90°. The laminates exhibited a Young's modulus of 1.01 and 1.26 GPa in the longitudinal and transverse directions, respectively. The experimental values were compared with the theoretical predictions using pcGINA^© software and showed good agreement. The composite specimens also showed good adhesion between flax fabric and MSPC-G resin.     

Influence of ethylene glycol vapor annealing on structure and property of wet-spun PVA/PEDOT:PSS blend fiber

In this study, blend fibers composed of poly(vinyl alcohol) and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) were prepared via wet-spinning technology. Ethylene glycol (EG) vapor annealing was employed to improve the electrical conductivity and tensile properties of blend fibers. The effects of EG vapor annealing on structures and properties of blend fibers were investigated in detail by analyzing the changes in chemical constituent and structure, molecular structure, surface morphology, surface chemical composition, electrical conductivity, and tensile properties. FTIR spectroscopy indicates that EG vapor annealing does not change the chemical constituent and structure of blend fibers. Raman spectroscopy shows that vapor annealing leads to conformational changes of PEDOT chains from benzoid structure to quinoid structure. AFM and SEM images show that surface morphology of blend fibers become smoother after vapor annealing. XPS measurement shows that EG vapor annealing induces significant phase separation between PEDOT and PSS, forming an enriched PSS layer on the surface of blend fibers, thus leading to a thinner insulating PSS layer between PEDOT grains. This conformational change is beneficial to improve the electrical conductivity of blend fibers. The resultant blend fiber reached conductivity up to 20.4 S cm^?1. The mechanical properties of blend fibers were also improved by EG vapor annealing, with the Young’s modulus and tensile strength increasing from 3.6 GPa and 112 MPa to 4.4 GPa and 132.7 MPa, respectively.     

Modeling and mechanical performance of carbon nanotube/epoxy resin composites

The effect of multi-walled carbon nanotube (MWCNT) addition on mechanical properties of epoxy resin was investigated to obtain the tensile strength, compressive strength and Young’s modulus from load versus displacement graphs. The result shows that the tensile strength, compressive strength and Young’s modulus of epoxy resin were increased with the addition of MWCNT fillers. The significant improvements in tensile strength, compressive strength and Young’s modulus were obtained due to the excellent dispersion of MWCNT fillers in the epoxy resin. The dispersion of MWCNT fillers in epoxy resin was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis.Also, Halpin–Tsai model was modified by considering the average diameter of internal/external of multi-walled nanotube and orientation factor (α) to calculate the Young’s modulus of multi-walled carbon nanotubes (MWCNTs)/epoxy resin composite. There was a good correlation between the experimentally obtained Young’s modulus and modified Halpin–Tsai model.     

Tensile properties of elephant grass fiber reinforced polyester composites

Elephant grass stalk fibers were extracted using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were incorporated in a polyester matrix and the tensile properties of fiber and composite were determined. The fibers extracted by retting process have a tensile strength of 185 MPa, modulus of 7.4 GPa and an effective density of 817.53 kg/m³. The tensile strength and modulus of chemically extracted elephant grass fibers have increased by 58 and 41%, respectively. After the treatment the tensile strength and modulus of the fiber extracted by retting have decreased by 19, 12% and those of chemically extracted fiber have decreased by 19 and 16%, respectively. The composites were formulated up to a maximum of 31% volume of fiber resulting in a tensile strength of 80.55 MPa and tensile modulus of 1.52 GPa for elephant grass fibers extracted by retting. The tensile strength and the modulus of chemically extracted elephant grass fiber composites have increased by approximately 1.45 times to those of elephant grass fiber composite extracted by retting. The tensile strength of treated fiber composites has decreased and the tensile modulus has shown a mixed trend for the fibers extracted by both the processes. Quantitative results from this study will be useful for further and more accurate design of elephant grass fiber reinforced composite materials.     

Interfacial strength and debonding mechanism between aerogel-spun carbon nanotube yarn and polyphenylene sulfide

The interfacial bonding properties between the carbon nano-tubes yarn and polyphenylene sulfide are investigated using the micro-bond test. Carbon nano-tubes yarn fabricated by floating catalyst chemical vapor deposition with a high Poisson’s ratio of 3.5, and high-performance thermoplastic resin polyphenylene sulfide are used as matrix. In order to improve the tensile strength of the yarn so as to get sufficient data points for the micro-bond test for interfacial bonding strength, a pretreatment that combines drafting and dichloromethane shrinking processes is applied. The pretreated carbon nano-tubes yarn shows a 23% increase in tensile strength (from 117 to 144 MPa) and a 260% increase in initial Young’s modulus (from 0.8 to 3.2 GPa). The effective interfacial shear strength is calculated to be 13.1 MPa and analyzed based on fracture mechanism of a mixed failure mode.     

CIP/GF/CF/EP吸波复合材料的制备及力学性能

为制备兼具力学性能和电磁吸收性能的结构型吸波材料,采用真空辅助成型工艺设计制备一种以羰基铁粉(CIP)为吸收剂,玻璃纤维(GF)为透波层,碳纤维(CF)为反射层,环氧树脂(EP)为基体的吸波复合材料。研究了不同质量比CIP/EP对吸波复合材料力学性能和微波吸收性能的影响。通过FTIR和DSC分析可知CIP未与EP发生化学反应。SEM结果表明CIP能够在EP树脂基体中均匀分散,不趋向于纤维表面。力学测试分析结果显示:当CIP/EP质量比达到30%时,CIP/GF/CF/EP复合材料的力学性能最佳,拉伸强度为347.56MPa,拉伸模量为25.99GPa,较纯GF/CF/EP复合材料提升了4.3%和5.7%;弯曲强度为339.6MPa,弯曲模量为23.7GPa,较纯GF/CF/EP复合材料提升了18.2%和71.2%。矢量网络分析可知复合吸波板的吸波性能随CIP含量的增加而增加,且吸波损耗反射峰值朝低频段移动。     

碳纤维三维编织复合材料的结构对拉伸和弯曲性能的影响

研究了碳纤维四步法三维四向、三维五向编织结构复合材料的拉伸和弯曲性能,以及结构参数-编织角的变化对其拉伸和弯曲性能的影响,并与层合复合材料作了对比性研究.结果表明,三维编织复合材料具有良好的力学性能,其拉伸强度可达810MPa、拉伸模量可达95.6GPa,弯曲强度可达829.03MPa、弯曲模量可达67.5GPa.同时,编织角和编织结构对复合材料性能有较大的影响.随着编织角的增大,复合材料的拉伸、弯曲强度和模量均减小;三维五向结构的拉伸、弯曲强度和模量均高于四向结构;在纤维体积含量相近的情况下,通过对编织角的设计,可以设计三维编织复合材料的性能.     

Effects of VC additives on densification and elastic and mechanical properties of hot-pressed ZrB<Subscript>2</Subscript>–SiC composites

In this study, highly dense ZrB₂-20 vol% SiC composites with 3–10 wt% VC additives were prepared by hot-pressing at 1750 °C for 1 h under a pressure of 20 MPa in a vacuum. The densification behavior and elastic and mechanical properties of the obtained composites were examined, and the effect of the VC content on the densification and the properties is analyzed. The addition of VC promotes the activation of densification mechanism at a lower temperature and inhibits the growth of ZrB₂ and SiC grains during the sintering. In addition, the elastic moduli, hardness and fracture toughness that measured in the obtained composites are constant and independent of the VC content, with a shear modulus of ~ 220 GPa, Young’s modulus of ~ 500 GPa, hardness of ~ 20 GPa and fracture toughness of ~ 4.4 MPa m^1/2. On the other hand, the flexural strength of the composites decreased as the VC content increased from 3 to 7 wt% and then it increased with further increasing the VC content to 10 wt%, with strength values of 620–770 MPa.     

原位聚合法制备连续玻璃纤维增强PCBT复合材料及其性能

采用环状对苯二甲酸丁二醇酯(CBT)原位聚合制备了连续玻璃纤维(GF)增强聚环状对苯二甲酸丁二醇酯(PCBT)复合材料。考察了聚合反应中催化剂用量对PCBT结晶度以及GF/PCBT复合材料力学性能的影响。当催化剂用量为0.5%(质量分数)时, PCBT的结晶度为53%, GF/PCBT的力学性能达到最佳, 拉伸强度为522 MPa, 拉伸模量为27 GPa, 弯曲强度为481 MPa, 弯曲模量为24.8 GPa, 层间剪切强度(ILSS)为43 MPa。SEM观察表明, 发现催化剂用量为0.5%时, 树脂与纤维的结合性较好。进一步研究了淬火和退火后处理对复合材料力学性能的影响。发现复合材料退火处理后具有较好的力学性能, 其中拉伸强度为545 MPa, 弯曲强度为495 MPa。     

高强高模聚酰亚胺纤维/环氧树脂复合材料力学性能与破坏机制

以高强高模聚酰亚胺（PI）纤维为增强体,以航空级环氧树脂（EP）为基体,通过热熔法制备预浸料并采用热压罐成型技术制备了PI/EP复合材料层合板,对其力学性能和破坏形貌进行了分析。结果表明:高强高模PI纤维与EP具有良好的界面结合力,PI/EP复合材料的层间剪切强度为65.2 MPa,面内剪切强度为68.6 MPa;良好的界面结合状态能充分发挥PI纤维优异的力学性能,PI/EP复合材料的纵向拉伸强度达1 835 MPa,弯曲强度为834 MPa;PI/EP复合材料纵向拉伸破坏模式为散丝爆炸破坏,同时由于高强高模PI纤维还具有优异的韧性和较高的断裂伸长率,PI/EP复合材料从受力到失效断裂的时间较长;PI/EP复合材料纵向压缩破坏模式为45°折曲带破坏。高强高模PI/EP复合材料为航空航天先进复合材料增加了一个全新的选材方案。      

玻璃纤维增强聚氯乙烯(GFRPVC)复合材料的研究

本文考察了玻璃纤维增强聚氯乙烯(GFRPVC)中玻璃纤维的表面处理及加入量对力学性能的影响.并用SEM对GFRPVC的界面及其对GFRPVC力学性能的影响进行研究.结果表明:当玻纤为30wt%时,GFRPVC板的拉伸强度为110MPa,弯曲强度为190MPa,为刚性聚氯乙烯(RPVC)的两倍;拉伸模量为8.8GPa,弯曲模量为8.9GPa,是RPVC的三倍;悬臂梁缺口冲击强度达140J/m,接近RPVC的四倍;达到了一般工程塑料的性能水平.热膨胀系数下降到2.23(×10-5)℃-1,HDT增加到84℃.     

Effect of sintering temperature and cooling rate on the morphology, mechanical behavior and apatite-forming ability of a novel nanostructured magnesium calcium silicate scaffold prepared by a freeze casting method

In this research, sol–gel-derived nanostructured calcium magnesium silicate (merwinite)-based scaffolds were fabricated by water-based freeze casting method. The effect of cooling rate and sintering temperature on pore sizes and mechanical characteristics of the scaffolds was studied. Microstructure and surface morphology of scaffolds were also observed by scanning electron microscopy before and after various time intervals of soaking in simulated body fluid. The results showed that increasing temperature at the constant rate led to increasing the parameters of volume and linear shrinkage, strength (σ), and Young’s modulus (E) but decreasing porosity. This increase was significant for strength and Young’s modulus. In addition, with the increase of rate at the constant temperature, the parameters of volume and linear shrinkage and also porosity decreased whereas strength and Young’s modulus increased significantly. According to the obtained mechanical results, the best mechanical properties were achieved when the scaffold was prepared at cooling rate and sintering temperature of 277.15°K/min and 1623.15°K, respectively (E = 0.048 GPa and σ = 2 MPa). These values were closer to the lower limit of the values for cancellous bone. The acellular in vitro bioactivity revealed that different apatite morphologies were formed on the surfaces for various periods of soaking time when the scaffolds prepared at the freezing temperature of 277.15°K/min and at the two different sintering temperatures. The favorable mechanical behavior of the porous constructs, coupled with the ability of forming apatite particles on the surface of scaffold, indicates the potential of the present freeze casting route for the production of porous scaffolds for bone tissue engineering.