Preparation and properties of microfibrillated cellulose polyvinyl alcohol composite materials

This work reports the preparation of MFC–PVA composite films, and the thermal and mechanical properties of these films. Microfibrillated cellulose (MFC), which was separated from kraft pulp by a mechanical process, was used as the reinforcement in polyvinyl alcohol (PVA) matrix. This MFC reinforcement has an interconnected web-like structure with fibrils having a diameter in the range of 10–100 nm, as observed by TEM. MFC–PVA composite films were created by casting from a water suspension to produce a homogeneous dispersion of MFC in the polymer matrix. DMA shows an increase of the storage modulus in the glassy state with increasing MFC content, but a more significant increase in modulus is detectable above the glass transition temperature. There is a steady increase in both the modulus and strength of the composite films until a plateau is reached at 10 wt% MFC. The thermal stability of the PVA composite films is slightly increased with the addition of MFC.

As a result of this research, it has been shown that MFC is an excellent reinforcement comparable to cellulose nanowhiskers. Furthermore, by combining MFC with PVA in addition to good mechanical properties, this composite has good chemical resistance and biodegradability. The water soluble characteristics of PVA combined with a water dispersion of MFC are also easily processable.     

On the mechanical characterization of carbon nanotube reinforced epoxy adhesives

In this work, the mechanical properties of carbon nanotube reinforced epoxy adhesives are investigated experimentally. The investigations are intended to characterize the physical and mechanical properties of nano-reinforced structural epoxy adhesives and to further highlight some of the complex phenomena associated with these materials. We describe the dispersion methodology used to disperse the carbon nanotubes into the considered adhesive and provide details pertaining to adherent surface preparation, bondline thickness control and adhesive curing conditions. Furthermore, the following tests are described: (i) dogbone tensile testing, (ii) tensile bond testing, (iii) double lap shear and (iv) double cantilever beam fracture toughness testing. The experimental observations indicate a critical carbon nanotube concentration in the vicinity of 1.5 wt% that results in the largest improvements in the measured properties. At concentrations exceeding this critical value, the properties begin to degrade, in some cases, to levels below that of the pure epoxy. Advanced electron microscopy techniques and rheological assessments indicate that this is mainly due to the agglomeration of the carbon nanotubes at higher concentrations as a result of increased resin viscosity and the consequent resistance to dispersion.     

A strategy for improving mechanical properties of a fiber reinforced epoxy composite using functionalized carbon nanotubes

Carbon fiber reinforced epoxy composite laminates are studied for improvements in quasi static strength and stiffness and tension-tension fatigue cycling at stress-ratio (R-ratio) = +0.1 through strategically incorporating amine functionalized single wall carbon nanotubes (a-SWCNTs) at the fiber/fabric-matrix interfaces over the laminate cross-section. In a comparison to composite laminate material without carbon nanotube reinforcements there are modest improvements in the mechanical properties of strength and stiffness; but, a potentially significant increase is demonstrated for the long-term fatigue life of these functionalized nanotube reinforced composite materials. These results are compared with previous research on the cyclic life of this carbon fiber epoxy composite laminate system reinforced similarly with side wall fluorine functionalized industrial grade carbon nanotubes. Optical and scanning electron microscopy and Raman spectrometry are used to confirm the effectiveness of this strategy for the improvements in strength, stiffness and fatigue life of composite laminate materials using functionalized carbon nanotubes.     

激光改性纤维对其增强环氧树脂复合材料力学性能的影响

利用激光对玻璃纤维、玄武岩纤维和碳纤维进行表面改性后,以环氧树脂为基体,分别制备三种纤维增强环氧树脂复合材料。利用SEM和万能试验机对表面改性前后的碳纤维形态、力学性能及三种纤维/环氧树脂复合材料的力学性能和断面形貌进行表征,研究了纤维激光表面改性对三种纤维及其增强环氧树脂复合材料力学性能的影响。结果表明:激光表面改性对碳纤维/环氧树脂复合材料的力学性能提升最高,其拉伸强度最大提高了77.06%,冲击强度最大提高了31.25%,玄武岩纤维/环氧树脂复合材料的力学性能提升次之,而玻璃纤维/环氧树脂复合材料的力学性能有所下降。因此,激光进行表面改性适用于碳纤维和玄武岩纤维。     

Influence of different carbon nanotubes on the mechanical properties of epoxy matrix composites – A comparative study

Carbon nanotubes (CNTs) in general are considered to be highly potential fillers to improve the material properties of polymers. However, questions concerning the appropriate type of CNTs, e.g., single-wall CNTs (SWCNT), double-wall CNTs (DWCNT) or multi-wall CNTs (MWCNT), and the relevance of a surface functionalisation are still to be answered. This first part of the study focuses on the evaluation of the different types of nanofillers applied, their influence on the mechanical properties of epoxy-based nanocomposites and the relevance of surface functionalisation. The nanocomposites produced exhibited an enhanced strength and stiffness and even more important, a significant increase in fracture toughness (43% at 0.5 wt% amino-functionalised DWCNT). The influence of filler content, the varying dispersibility, the aspect ratio, the specific surface area and an amino-functionalisation on the composite properties are discussed and correlated to the identified micro-mechanical mechanisms.     

Fracture toughness of the nano-particle reinforced epoxy composite

Although thermoset polymers have been widely used for engineering components, adhesives and matrix for fiber-reinforced composites due to their good mechanical properties compared to those of thermoplastic polymers, they are usually brittle and vulnerable to crack. Therefore, ductile materials such as micro-sized rubber or nylon particles are added to thermoset polymers are used to increase their fracture toughness, which might decrease their strength if micro-sized particles act like defects.In this work, in order to improve the fracture toughness of epoxy adhesive, nano-particle additives such as carbon black and nanoclay were mixed with epoxy resin. The fracture toughness was measured using the single edge notched bend specimen at the room (25 °C) and cryogenic temperature (−150 °C). From the experimental results, it was found that reinforcement with nano-particles improved the fracture toughness at the room temperature, but decreased the fracture toughness at the cryogenic temperature in spite of their toughening effect.     

MWCNTs对碳纤维非褶皱无纺布/环氧层合板力学性能的影响

将羧基化多壁碳纳米管(MWCNTs)添加到TDE85环氧树脂中,然后与碳纤维非褶皱无纺布(C-NCF)复合,制备成[0°/90°/+45°/-45°]_S层合板。采用三点弯曲、短梁剪切和单边切口弯曲测试方法以及动态力学性能分析方法,研究了不同含量的MWCNTs对层合板弯曲性能、层间剪切强度(ILSS)、Ⅱ型层间断裂韧性(G_ⅡC,以及玻璃态转变温度(T_g)的影响。并采用SEM对Ⅱ型试样的断面进行分析。结果表明,MWCNTs的加入显著提高了NCF层合板的力学性能。与空白试样相比,当MWCNTs在树脂中的质量分数为2.0%时,弯曲强度和模量分别提高了约26%和6%;当MWCNTs的质量分数为0.5%时,ILSS、G_ⅡC、T_g分别提高约14%、27%和14%。     

Effect of carbon nanotube and aluminum oxide addition on plasma-sprayed hydroxyapatite coating's mechanical properties and biocompatibility

This study reports on the synthesis of novel bioceramic composite coating of hydroxyapatite (HA) reinforced with carbon nanotubes (CNTs) and aluminum oxide (Al₂O₃) using plasma spray technique. Fracture toughness of HA–20 wt.% Al₂O₃ improved by 158% as compared to HA coating whereas HA–18.4 wt.% Al₂O₃–1.6 wt.% CNT showed an improvement of 300%. Carbon nanotubes provided reinforcement via rebar mechanism. Human fiber osteoblast cell-growth studies showed that biocompatibility of the coating remained unaltered, as Al₂O₃ retained its bio-inertness and CNT, its bioactivity, within the composite coatings. Composite coating showed lower attachment, but higher proliferation rate, for the osteoblast cells, which has been attributed to the surface roughness. An optimized relation between coating composition, its biocompatibility and mechanical properties was established to predict the most suited coating material for orthopedic implants. HA–Al₂O₃–CNT composite coating displayed most improved mechanical properties while retaining its biocompatibility.     

埋入光纤对CFRP抗弯性能影响实验研究

埋入光纤传感器的碳纤维复合材料作为一种智能材料,集智能,耐腐蚀及比强度高等优异性能于一体而倍受关注.其应用的前提是二者的相容性.在应用中,CFRP主要承担弯曲载荷,所以在我们的实验中,仅对埋入光纤对CFRP弯曲性能的影响作研究.通过埋入不同直径光纤,不同光纤埋入方向,不同光纤涂层以及不同光纤根数等对CFRP弯曲强度影响的试验,以确定埋入光纤对CFRP弯曲性能影响的程度以及如何使之减到最小,为工程优化应用提供依据.     

Effect of fiber surface texture on the mechanical properties of glass fiber reinforced epoxy composite

The effect of fiber sizing and surface texture on the strength and energy absorbing capacity of fiber reinforced composites has been evaluated at two length scales using the macromechanical quasi-static punch shear test and the micromechanical microdroplet test methods. E-Glass/SC-79 epoxy composite laminates with four different fiber sizing formulations with various degrees of chemical bonding and surface texture have been investigated. The failure modes during perforation and different energy dissipating damage mechanisms were identified and quantified. The punch shear strength and the total energy absorption per unit volume of composite with hybrid sizing have increased by 48% and 100% over the incompatible sizing. These results showed linear correlations with the interphase properties reported earlier by the authors (Gao et al., 2011) and provided a methodology for developing new sizing by tailoring chemical bonding and the fiber surface texture at the fiber–matrix interphase for improving both strength and energy absorption of composites.     

微胶囊层间增韧碳纤维/环氧树脂复合材料力学性能的超声导波评价

选用微胶囊作为改性材料,采用热压机层压成型工艺制备出微胶囊层间增韧T300碳纤维/环氧树脂(CF/EP)复合材料.通过双悬臂梁(DCB)Ⅰ型层间断裂试验评估了CF/EP复合材料的增韧效果.利用超声导波技术对普通CF/EP复合材料和增韧CF/EP复合材料层间力学性能进行评价.通过SEM对CF/EP复合材料层间断面微观形貌...     

超低温介质对碳纤维增强树脂基复合材料力学性能的影响

针对超低温介质液氮和液氧对碳纤维增强树脂基复合材料(CFs/EP)力学性能的影响进行研究,将T700碳纤维和CFs/EP在液氮和液氧中处理120h,采用X射线光电子能谱(XPS)和SEM分析碳纤维表面元素和表面形貌的变化;并研究液氧和液氮处理后碳纤维和复合材料试样的力学性能。结果表明,在经液氮处理后的碳纤维表面,上浆剂有明显损伤产生,而经液氧处理后的碳纤维表面则没有损伤出现;两种超低温介质处理对碳纤维单丝拉伸强度、表面元素及其含量的影响几乎没有区别;经液氮和液氧超低温介质处理后,CFs/EP拉伸强度均有所下降,且两者下降率接近,分别约为15.26%和14.38%;弯曲强度均有大幅提高,且提高率接近,分别约为56.18%和57.81%。因此,液氧和液氮处理对CFs/EP力学性能的影响基本没有区别。     

Toughening of carbon fiber-reinforced epoxy polymer composites utilizing fiber surface treatment and sizing

Toughening of fiber-reinforced epoxy composites while maintaining other mechanical properties represents a significant challenge. This paper presents an approach of enhancing the toughness of a DGEBA/mPDA-based carbon fiber-reinforced epoxy composite, without significantly reducing the static-mechanical properties such as flexural properties and glass transition temperature. The impact of combining an UV-ozone fiber surface treatment with an aromatic and aliphatic epoxy fiber sizing on composite toughness is investigated. Carbon fiber-epoxy adhesion was increased as measured by the single fiber interfacial shear test. The Mode I composite fracture toughness was enhanced by 23% for the UV-ozone fiber surface treatment alone. With the addition of an aromatic and aliphatic fiber sizing, the composite fracture toughness was further increased to 50% and 84% respectively over the as-received, unsized fiber. The increased fiber/matrix adhesion also improved the transverse flexural strength.     

3-Phase hierarchical graphene-based epoxy nanocomposite laminates for automotive applications

Two different types of graphene flakes were produced following solution processing methods and dispersed using shear mixing in a bifunctional (A) and a multifunctional (B) epoxy resin at a concentration of 0.8 and 0.6 wt%, respectively. The graphene/epoxy resin mixtures were used to impregnate unidirectional carbon fibre tapes. These prepregs were stacked (seven plies) and cured to produce laminates. The interlaminar fracture toughness (mode-I) of the carbon fiber/graphene epoxy laminates with resin B showed over 56% improvement compared with the laminate without graphene. Single lap joints were prepared using the laminates as adherents and polyurethane adhesives (Sika 7666 and Sika 7888). The addition of graphene improved considerably the adhesion strength from 3.3 to 21 MPa (sample prepared with resin A and Sika 7888) highlighting the potential of graphene as a secondary filler in carbon fibre reinforced polymer composites.     

单向碳纤维增强树脂基复合材料的超低温力学性能

采用真空袋-热压罐工艺制备单向碳纤维增强树脂基复合材料(CFs/EP)层合板,并将高低温试验箱与万能试验机相结合,通过合理使用低温胶和低温引伸计,并在降温过程中实施应力-应变实时调零等关键技术,在室温和液氧超低温度(-183℃)下对单向CFs/EP层合板进行拉伸和弯曲试验,研究了其超低温力学性能,并根据室温和超低温试验后试样的微观和宏观特征,揭示了超低温环境下复合材料力学性能变化机制。结果表明,与室温力学性能相比,单向CFs/EP层合板超低温拉伸强度下降约为9.5%,而拉伸模量上升约为6.2%,主要是由于超低温环境下,树脂的收缩使绝大部分碳纤维与树脂间形成了强界面,拉伸后试样呈"劈裂式"破坏形式,无法使每根纤维都充分发挥其强度,拉伸强度下降,同时超低温也限制了树脂大分子链的运动,所以导致单向CFs/EP层合板拉伸模量上升;单向CFs/EP层合板超低温弯曲强度和弯曲模量分别提高约54.75%和11.64%,这是由于单向CFs/EP层合板的常温和超低温的弯曲破坏形式均为分层剪切破坏,超低温下复合材料的界面增强,提高了单向CFs/EP层合板抵抗剪切分层的能力,进而使CFs/EP的弯曲性能得到提高。     

Synchronous effects of multiscale reinforced and toughened CFRP composites by MWNTs-EP/PSF hybrid nanofibers with preferred orientation

MWNTs-EP/PSF (polysulfone) hybrid nanofibers with preferred orientation were directly electrospun onto carbon fiber/epoxy prepregs and interlaminar synchronously reinforced and toughened CFRP composites were successfully fabricated. With MWNTs-EP loading increasing, the oriented nanofibers were obtained accompanying with enhanced alignment of inner MWNTs-EP. Flexural properties and interlaminar shear strength of composites were improved with increasing MWNTs-EP loadings, whereas fracture toughness attained maximum at 10 wt% MWNTs-EP loading and then decreased. Based on these results, multiscale schematic modeling and mechanism schematic of hybrid nanofibers reinforced and toughened composites were suggested. Due to the preferred orientation of nanofibers, MWNTs-EP was inclined to align vertically to carbon fiber direction along the in-plane of interface layer. The proposed network structures, containing four correlative phases of MWNTs-EP/PSF sphere/carbon fiber/epoxy matrix, contributed to simultaneous improvement of strength and toughness of composites, which was realized by crack pinning, crack deflection, crack bridging and effective load transfer.     

阳极氧化工艺对纤维-铝合金层板力学性能的影响

通过改变铝合金表面阳极氧化工艺参数,研究了阳极氧化电压和时间对玻璃纤维-铝合金(GLARE)层板抗拉强度和层间剪切强度的影响.通过SEM观察了铝合金表面Al2O3多孔膜和层板断面形貌,分析了铝合金/树脂胶接界面对层板力学性能的影响.结果表明,阳极氧化电压为20 V时,GLARE层板抗拉强度和层间剪切强度随着阳极氧化时间延长而增大,在20 min时出现最大值,继续延长阳极氧化时间,层板强度随之下降;阳极氧化时间为20 min时,GLARE层板抗拉强度和层间剪切强度随着阳极氧化电压增大而增大,在20V时出现最大值,继续增大电压,强度随之下降.     

Dielectric properties and noncontact damage detection of plain-woven fabric glass fiber reinforced epoxy matrix composites using millimeter wavelength microwave

Electromagnetic wave reflections from glass fiber reinforced epoxy matrix composites with 0°/90° and ±45° fiber oriented plain-woven glass fabric (PW-GFRP-0/90, PW-GFRP-±45) at incident angles of 30°, 40° and 50° were measured in the frequency range 50-75 GHz using a free-space reflection measurement system. The complex dielectric constants of both composites were calculated using a simple transmission line theory. The complex dielectric constants of PW-GFRP-0/90 and PW-GFRP-±45 are similar and were measured to be ε′ = 4.61 ± 0.01 and ε″ = 0.16 ± 0.002, respectively.The damage stored in PW-GFRP-0/90 and PW-GFRP-±45 was also evaluated by dielectric constant changes using the same system at an incident angle of 30°. For both composites, ε′ decreased with increasing applied stress and damage parameter. The dielectric constant change is effective for detecting the damage stored in composites and can be used to quantitatively evaluate the damage.     

天然细菌纤维素增强不饱和聚酯树脂复合材料的制备及性能

将天然纤维-细菌纤维素（BC）作为增强材料加入不饱和聚酯树脂（UPR）基体中,采用RTM工艺制备BC/UPR复合材料,并对其力学性能、吸湿性能进行了研究。通过紫外辐照方法探讨了BC/UPR复合材料的降解性能。研究结果表明:通过对细菌纤维素的表面改性,在亲水性的天然纤维和疏水性的高聚物基体之间形成了化学键结合,提高了BC/UPR复合材料的力学性能;BC纤维体积分数的增加也有助于提高力学性能, 当纤维体积分数为20%时,该复合材料拉伸强度最高可达152.9MPa; BC/UPR复合材料的吸湿过程符合Fick定律,吸湿可导致力学性能下降; BC/UPR复合材料吸收光能后,表面含氧官能团数量增加,发生一定程度的光降解。      

阳极氧化工艺对纤维-铝合金层板力学性能的影响

通过改变铝合金表面阳极氧化工艺参数, 研究了阳极氧化电压和时间对玻璃纤维-铝合金(GLARE)层板抗拉强度和层间剪切强度的影响。通过SEM观察了铝合金表面Al₂O₃多孔膜和层板断面形貌, 分析了铝合金/树脂胶接界面对层板力学性能的影响。结果表明, 阳极氧化电压为20 V时, GLARE层板抗拉强度和层间剪切强度随着阳极氧化时间延长而增大, 在20 min时出现最大值, 继续延长阳极氧化时间, 层板强度随之下降; 阳极氧化时间为20 min时, GLARE层板抗拉强度和层间剪切强度随着阳极氧化电压增大而增大, 在20 V时出现最大值, 继续增大电压, 强度随之下降。