Structure and properties of hybrid PLA nanocomposites with inorganic nanofillers and cellulose fibers

Polylactide reinforced with 3 wt% of organo-modified montmorillonite, 5 wt% of stearic acid-modified calcium carbonate nanoparticles, 15 wt% of cellulose fibers (PLA/MMT, PLA/NCC, PLA/CF) and hybrid composites containing 15 wt% of fibers in addition to montmorillonite (PLA/MMT/CF) or calcium carbonate (PLA/NCC/CF) were prepared and examined. The nanoparticles were dispersed in polylactide almost homogeneously; montmorillonite was exfoliated during processing. T_g of polylactide remained unaffected but its cold crystallization was enhanced; the cold-crystallization behavior of the hybrid composites was dominated by nanofillers nucleating ability. The fibers and calcium carbonate decreased whereas exfoliated montmorillonite improved the thermal stability of the materials. Polylactide, PLA/NCC and PLA/MMT exhibited ability to plastic deformation, although the latter the weakest. Tensile behavior of the hybrid composites was strongly influenced by the fibers and similar to that of PLA/CF. All the fillers increased the storage modulus below T_g; that of PLA/MMT/CF and PLA/NCC/CF was improved with respect to polylactide by 50% and 45%, respectively.     

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%。     

Effect of aluminum trihydroxide on flame retardancy and dynamic mechanical and tensile properties of kenaf/poly(lactic acid) green composites

In this work, the effect of aluminum trihydroxide (ATH) on the flame retardancy and dynamic mechanical and tensile properties of kenaf/poly(lactic acid) green composites was explored. Prior to composite fabrication, poly(lactic acid) (PLA) pellets filled with ATH powder at different loadings (0, 10, 20, 30, and 50?wt.%) were processed by using a twin-screw extrusion technique. The green composites were fabricated using the pellets and chopped kenaf fibers by a compression molding method. The kenaf fibers were used as primary reinforcement, and the contents were fixed to 40?wt.% of the total, and the average fiber length was 3?mm long. It was noticeable that the flame retardancy of kenaf/PLA green composite with ATH was improved by 66%, and the storage modulus and tensile modulus were enhanced by 136 and 59%, respectively, compared with the kenaf/PLA counterpart without ATH. It was concluded that the ATH incorporated into PLA by extrusion technique played a significant role not only as flame-retardant but also as secondary reinforcement of kenaf/PLA green composites.     

Dispersion and roles of montmorillonite on structural,flammability, thermal and mechanical behaviours of electron beam irradiated flame retarded nanocomposite

In this work, the effects of montmorillonite (MMT) dispersion and electron beam irradiation on intercalation and flammability-thermal behaviours of alumina trihydrate (ATH) added low density polyethylene and ethylene vinyl acetate (LDPE–EVA) blends were investigated. MMT and ATH added LDPE–EVA blends were compounded using Brabender mixer and compression moulded into sheets. The samples sheets were electron beam irradiated in the dosage range of 0 to 250 kGy. The dispersion and intercalation of nano-MMT in LDPE–EVA matrix were investigated through X-ray diffraction (XRD) analysis. The d-spacing measurements revealed that the addition of nano-MMT has effectively intercalated into polymer matrix and this has enhanced the compatibility of ATH particles and LDPE–EVA matrix. Limiting oxygen index test (LOI) revealed that the incorporation of MMT into ATH added LDPE–EVA blends as improved the flame retardancy up to 26.5 LOI%. Besides, the application of electron beam irradiation were also improved the flame retardancy of the blends by increasing the LOI% for about 2% compared to non-irradiated samples. The application of irradiation dosage up to 250 kGy has rapidly improved the thermal stability of blends by delaying decomposition temperature and also promoting formation of char. The increasing of MMT loading level and irradiation dosage has effectively enhanced tensile strength and Young’s modulus by intercalating polymer matrix into interlayer galleries of MMT particles. Beside, the formation of crosslinking networks in polymer matrix also could further enhance the tensile strength and Young’s modulus. The intercalation effect of MMT particles and formation of crosslinking networks in polymer matrix could improve the thermal and mechanical properties. Consequently, this study has demonstrated that addition of MMT and electron beam irradiation into ATH added LDPE–EVA blends could produce better flammability, thermal and physical properties of ATH added LDPE–EVA blends.     

Properties of poly(lactic acid)/montmorillonite/carbon nanotubes nanocomposites: determination of percolation threshold

Incorporation of rigid nanoparticles is the most effective means of improving polymer properties. Montmorillonite (MMT) and multi-walled carbon nanotubes (MWCNTs) are legendary in this field for their individual exceptional properties. A synergistic phenomenon is induced between these two particles when they are simultaneously incorporated into polymers. At a definite nanofillers concentration, called the percolation threshold, there is a sudden change in nanocomposite properties due to the formation of a 3D-structured network of the nanoparticles within the matrix. In this work, the properties of poly(lactic acid) (PLA) nanocomposites filled with different fractions of MMT/MWCNTs hybrid (0.5–2.0 wt%) were analyzed. In particular, the percolation threshold of the MMT/MWCNTs hybrid was uniquely identified by differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical thermal analysis. The structural studies by X-ray diffraction and Fourier-transform infrared spectroscopy were also associated with the percolation threshold of MMT/MWCNTs in PLA. At 1.0 wt% MMT/MWCNTs concentration, the complete exfoliation of the particles was maintained, and the thermal characteristics such as glass transition, crystallization and melting temperatures reached their plateau at this hybrid concentration. Moreover, the thermal degradation and viscoelastic parameters showed their peak values at this critical point, which is correlated with the formation of the percolation threshold within the matrix. The morphological studies confirmed the homogeneous dispersion of MMT/MWCNTs in PLA up to a concentration of 1.0 wt%. At 2.0 wt% MMT/MWCNTs, few aggregations occurred in the PLA-based composite, confirming that the percolation threshold was formed at a lower concentration of MMT/MWCNTs nanoparticles.

     

Effects of potassium titanate whiskers and carbon fibers on the wear behavior of polyetheretherketone composite under water lubricated condition

The tribological behaviors of polyetheretherketone (PEEK) composite reinforced by carbon fiber (CF) and potassium titanate whiskers (PTW) have been investigated using the pin-on-disk configuration at different applied loads under water lubricated condition. The effects of micrometer carbon fiber and sub-micrometer PTW on the wear properties of the hybrid composite have been discussed. It was found that the PEEK/PTW/CF composite showed excellent tribological performance in water condition. High wear resistance and low friction coefficient were achieved under a wide range of loads. It was revealed that the two fillers worked synergetically to enhance the wear resistance of the hybrid reinforced PEEK composite. The carbon fiber carried the main load between the contact surfaces and protected the matrix from further severe abrasion of the counterpart. At the same time, the exposed PTW out of the polymer matrix around the fiber inhibited the direct scraping between the fiber edge and counterpart tip in some degree, so that the fibers could be less directly impacted during the subsequent sliding process and they were protected from severe damage. In addition, the reinforcement effect of PTW on PEEK could reduce the stress concentration on the carbon fiber-matrix interface, and thereby reduce the CF failure/damage. The reinforcement effect of PTW on PEEK might also restrict the crack initiation and propagation on the surface and subsurface of the composite, and therefore to protect the matrix from fatigue failure during the sliding process.     

碳纤维表面处理对脉冲电磁场作用下碳纤维增强聚乳酸基复合材料降解行为的影响

采用HNO₃氧化对碳纤维进行表面处理,并制备了碳纤维增强聚乳酸基（CF/PLA）复合材料。研究了脉冲电磁场（PEF）对该条件下CF/PLA复合材料降解特性的影响。结果表明,碳纤维的表面处理对PEF作用下CF/PLA复合材料的吸水率、质量保持率、弯曲强度和剪切强度等均有不同程度的影响。分析表明,碳纤维表面处理形成的酯键在受到PEF作用后存在某种改变,进而导致CF/PLA复合材料界面降解行为的特异性。本研究有望提供一种从材料本身和外部条件协同控制的可降解CF/PLA骨折内固定装置解决方案。     

碳纤维在高温下的结构、性能演变研究

针对碳纤维在碳/碳烧蚀防热复合材料中应用的基础问题,论述了不同碳纤维结构、成分、表面特征,及其力学性能和热物理性能的高温演变规律,揭示了碳纤维灰分含量对碳纤维力学性能和热氧化性能的影响。确定了在碳/碳复合材料复合成型过程中,碳纤维结构受基体碳影响的变化规律和碳纤维表面特征对碳/碳材料宏观力学性能的影响。阐明了碳/碳复合材料中碳纤维的力学性能对纤维发生折断烧蚀的阻碍作用和通过控制碳/碳成型最高温度实现提高性能的途径。     

碳纤维形貌结构对其电化学氧化行为及其复合材料界面性能的影响

通过调控原丝工艺,制备得到形貌结构不同、力学性能相近的PAN基碳纤维(CF),用以模拟碳纤维表面光滑与沟槽结构对其电化学氧化行为的影响。研究表明:原始形貌光滑碳纤维在电化学过程中保持形貌能力较强,相同的电化学氧化强度下,其表面氧碳比高于原始表面粗糙的碳纤维,表明其氧化程度高。X射线光电子能谱(XPS)分峰结果表明,二者表面氧含量差别来自于表面羰基含量的差异。力学性能测试结果表明具有沟槽形貌的碳纤维拉伸强度及拉伸模量提高的幅度较大,其中拉伸强度提高最大值为17.3%。将氧化前后的碳纤维制备成碳纤维增强树脂基复合材料,探讨碳纤维形貌结构对其复合材料界面性能的影响。结果表明:由具有沟槽形貌的碳纤维制备得到的复合材料层间剪切强度(ILSS)较高,表明碳纤维表面物理形貌也是影响复合材料界面的重要因素。     

Influence of the interface structure on the thermo-mechanical properties of Cu–X (X = Cr or B)/carbon fiber composites

This study focuses on the fabrication, for power electronics applications, of adaptive heat sink material using copper alloys/carbon fibers (CF) composites. In order to obtain composite material with good thermal conductivity and a coefficient of thermal expansion close to the ceramic substrate, it is necessary to have a strong matrix/reinforcement bond. Since there is no reaction between copper and carbon, a carbide element (chromium or boron) is added to the copper matrix to create a strong chemical bond. Composite materials (Cu–B/CF and Cu–Cr/CF) have been produced by a powder metallurgy process followed by an annealing treatment in order to create the carbide at the interphase. Chemical (Electron Probe Micro-Analysis, Auger Electron Spectroscopy) and microstructural (Scanning and Transmission Electron Microscopies) techniques were used to study the location of the alloying element and the carbide formation before and after diffusion. Finally, the thermo-mechanical properties have been measured and a promising composite material with a coefficient of thermal expansion 25% lower than a classic copper/carbon heat sink has been obtained.     

Influence of cold remote nitrogen oxygen plasma treatment on carbon fabric and its composites with specialty polymers

The parameters controlling performance of a fiber-reinforced polymer composite are type of matrix and fibers, their amount, aspect ratio, fiber orientation with respect to loading direction, fiber–matrix interface, and processing technique. In the case of carbon fiber reinforcement, fiber–matrix interface has always been a serious concern, because of chemical inertness of carbon fibers toward matrix and hence efforts are continued to enhance the fiber–matrix adhesion. A recent technique of cold remote nitrogen oxygen plasma was employed for surface treatment of carbon fabric (CF) to enhance its chemical reactivity and mechanical interaction toward matrix material. Untreated and plasma treated CF were used as bidirectional reinforcement for developing high performance composites with various specialty polymer matrices such as Polyetherimide, Polyethersulfone, and Polyetheretherketone. Treated CF reinforced composites showed appreciable improvement in most of the mechanical properties, which varied with type of plasma, its dozing and matrix used. X-ray Photoelectron Spectroscopy confirmed improvement in O/C and N/C ratio indicating inclusion of Oxygen and Nitrogen on the surfaces of fibers due to plasma treatment, which was responsible for enhanced adhesion. Similarly, Fourier Transform Infrared–Attenuated Total Reflectance Spectroscopy indicated presence of ether, carboxylic, and carbonyl functional groups on the plasma-treated surface of fibers. Raman spectroscopy indicated slight distortion in graphitic structure of treated CF. Scanning Electron Microscopy also indicated changes in the topography of treated CF, indicating enhanced mechanical interlocking with matrix.     

Highly dispersed graphene oxide electrodeposited carbon fiber reinforced cement-based materials with enhanced mechanical properties

Mechanical behavior of carbon fiber (CF) reinforced cement-based materials greatly depends on the dispersion of CF and interfacial properties between the CF and cement matrix. In this study, graphene oxide (GO) was utilized to modify the surface properties of CF, including the roughness, wettability and chemical reactivity, and the graphene oxide/carbon fiber (GO/CF) hybrid fibers were fabricated by a newly designed electrophoretic depositing method. The scanning electron microscopy and contact angle measurement results indicated that GO/CF hybrid fibers not only had a rougher surface which was expected to improve the physical friction when CF was pulled out from cement matrix, but also had a higher wettability surface that made it easier to contact with cement hydrates as nucleation sites. In addition, GO/CF hybrid fibers were capable of high chemical reactivity due to the introduction of GO with many functional groups, which ensured them more likely to interact with cement hydrates due to the hydrogen bonding at interface and therefore benefited to strengthen the bonding between the CF and cement matrix. In terms of mechanical behavior, three-point bending test showed that compared with the CF reinforced cement paste, flexural strength of the GO/CF hybrid fibers reinforced cement paste was enhanced by 14.58%, and could be further improved by 10.53% when the GO/CF hybrid fibers were pre-dispersed in the GO solution and then mixed with cement powders. The larger electrostatic repulsion and steric stabilization led to the better dispersion of GO/CF hybrid fibers in GO solution, which were responsible for the further mechanical enhancement of cement paste. In conclusion, the research outcomes provided a novel way for utilizing GO as both of dispersant and surface modifier to improve the dispersion of CF in cement and strengthen its bonding with cement hydrates, consequently achieving a significant enhancement in the mechanical properties of cement paste.     

稀土Ce接枝碳纳米管-碳纤维多尺度增强体对环氧树脂基复合材料界面性能的影响

将马来酰亚胺官能化的多壁碳纳米管(CNTs)和碳纤维(CF)混合并通过CeCl₃处理,得到CNTs-CF多尺度增强体,采用FTIR、XPS、SEM对增强体的表面物理化学状态进行表征;以环氧树脂(EP)为基体,通过模压法制备CNTs-CF/EP复合材料,对其力学性能和断口形貌进行分析,探讨CNTs-CF多尺度增强体对CNTs-CF/EP复合材料界面性能的影响。结果表明:通过Ce的桥接作用,可以将改性后的CNTs化学接枝在CF表面,以同时解决CF与树脂基体间界面结合弱及CNTs不易分散的问题,有效改善了增强体与基体间的界面性能。因此CNTs-CF/EP复合材料的拉伸强度和杨氏模量较CF/EP复合材料分别提高了36.76%和71.57%;较CeCl₃改性CF(RECF)/EP复合材料分别提高了24.79%和52.17%。采用稀土Ce的化学接枝法成功制备出CNTs-CF多尺度增强体,为获得高级轻质树脂基复合材料提供了一种环境友好的新方法。      

Thermal expansion coefficient and thermal fatigue of discontinuous carbon fiber-reinforced copper and aluminum matrix composites without interfacial chemical bond

Fully dense carbon fiber-reinforced copper and aluminum matrix (Cu–CF and Al–CF) composites were fabricated by hot press without the need for an interfacial chemical compound. With 30 vol% carbon fiber, the thermal expansion coefficients (TECs) of pure Cu and Al were decreased to 13.5 × 10^?6 and 15.5 × 10^?6/K, respectively. These improved TECs of Cu–CF and Al–CF composites were maintained after 16 thermal cycles; moreover, the TEC of the 30 vol% Cu–CF composite was stable after 2500 thermal cycles between ?40 and 150 °C. The thermal strain caused by the TEC mismatch between the matrix and the carbon fiber enables mechanical enhancement at the matrix/carbon fiber interface and allows conservation of the improved TECs of Cu–CF and Al–CF composites after thermal cycles.     

Interfacial shearing strength and reinforcing mechanisms of an epoxy composite reinforced using a carbon nanotube/carbon fiber hybrid

The performance of a composite material system depends critically on the interfacial characteristics of the reinforcement and the matrix material. In this study, the interfacial shearing strength (IFSS) of a composite with an epoxy matrix and a novel carbon nanotube/carbon fiber (CNT/CF) multi-scale reinforcement was determined by single fiber-microdroplet tensile test, and the interfacial reinforcing mechanisms of the composite were discussed. Results show that the IFSS of the epoxy composite reinforced by CNT/CF is as high as 106.55 MPa, which is 150% higher than that of the as-received T300 fiber composite. And the main interfacial reinforcing mechanisms of this novel composite could be interpreted as chemical bonding, Van der Waals binding, mechanical interlocking, and surface wetting.     

表面处理碳纤维增强聚酰亚胺复合材料力学性能

采用空气氧化法和硝酸氧化法对碳纤维进行表面处理,研究了碳纤维(CF)增强热塑性聚酰亚胺(TPI)复合材料的力学性能。采用Boehm滴定方法测定了经过硝酸处理后CF表面酸性官能团数量。结果表明:CF表面酸性官能团的数量随着浓硝酸处理时间的增加而增加;浓硝酸处理效果比空气氧化好,当浓硝酸处理CF的时间为20 min时,CF/TPI复合材料拉伸强度和弯曲强度分别提高10 %和14 %,XPS表明此时CF表面活性官能团比未处理增加35.89 %。AFM表明,浓硝酸对CF表面刻蚀沟明显;SEM表明,CF与TPI基体之间形成良好的界面,CF起到了增强效果。      

Boston ivy-like clinging of dendritic polytetrafluoroethylene nano-ribbons to the surface of carbon fiber

Dendritic PTFE nano-ribbons as peculiar interphases between carbon fibers and PTFE matrix are observed on the fractured surface of CF/PTFE composite, which are about dozens of micrometers in length and not more than 200 nm in width. In the meantime, the dendritic PTFE ribbons have some short talons. This makes it feasible for PTFE ribbons to be firmly clung to carbon fiber surface in a Boston ivy-like manner.     

聚乳酸/蒙脱土纳米复合材料的微波辅助制备与性能研究

采用微波辐照酸活化法制备了酸性蒙脱土(H-MMT),并采用BET、NH3-TPD、热重等分析手段对其结构和性质进行表征。结果表明,改性后蒙脱土的比表面积和孔径增大,表面出现超强酸点位,热力学稳定性增强。将H-MMT与SnCl2进行复配后用于微波辅助原位熔融缩聚制备聚乳酸/蒙脱土(PLA/MMT)纳米复合材料,结果表明,H-MMT同时具备了较好的酸催化及纳米增强作用,以剥离形态存在于高分子基体中,PLA/MMT纳米复合材料的力学、热力学性能得到显著提升。     

Effect of fiber surface treatments on mechanical and abrasive wear performance of polylactide/jute composites

The main focus of this work is to improve the adhesion of jute fiber with polylactide (PLA). For this purpose, surface of the jute fiber was modified by alkali, permanganate, peroxide and silane treatments. The surface modified fibers were characterized by FTIR spectroscopy. Unidirectional composites were prepared with treated jute fibers and PLA matrix by hot pressing of solvent impregnated prepregs. Surface treatments resulted in enhancement of tensile and flexural properties and reduction in Izod impact strength. Dynamic mechanical analysis (DMA) results showed that, treated composites have higher storage modulus and lower tangent delta with respect to untreated composite. The degree of interfacial adhesion between the jute fiber and PLA was estimated using adhesion parameter obtained through DMA data. The results of thermogravimetric analysis (TGA) showed a higher thermal stability for silane treated composites. Experimental results on abrasive wear tests revealed that the wear resistance of composite is sensitive to fiber/matrix adhesion.     

聚氨酯改性聚乳酸/蒙脱土复合材料的制备与表征

采用溶液共混法,用聚氨酯(PU)和蒙脱土(MMT)对聚乳酸(PLA)进行改性.通过综合热分析(TGA＆DSC)、红外吸收光谱(IR)以及力学测试(FP)对改性聚乳酸(PLA)的性能进行了表征.结果显示,聚氨酯和蒙脱土与聚乳酸均有较好的相容性,复合材料的稳定性较好,而且聚氨酯/蒙脱土/聚乳酸复合材料较纯聚乳酸的力学性能有了较明显的提高,强度和韧性均较好.