High performance cellulose acetate propionate composites reinforced with exfoliated graphene

This paper deals with the preparation, structural characterization, and physical performances of composites composed of biomass-based cellulose acetate propionate (CAP) and exfoliated graphene (EG). As a reinforcing nanofiller, EG is thus prepared by an oxidation/thermal expansion process of natural graphite flakes and it is characterized to consist of disordered graphene platelets. Structural features, thermal stability, mechanical modulus, and electrical resistivity of CAP/EG composites are investigated as a function of EG content. SEM and X-ray diffraction data demonstrate that graphene platelets of EG are well dispersed and exfoliated in the CAP matrix for the composites with up to ∼1 wt.% EG, although they are partially aggregated in the composites with higher EG contents above ∼3 wt.%. Thermo-oxidative stability of CAP/EG composites under active oxygen gas condition is improved substantially due to the gas barrier effect of graphene platelets of EG dispersed in the CAP matrix. Dynamic mechanical modulus of the composites is also enhanced significantly with increasing the EG content. This mechanical enhancement of CAP/EG composites is analyzed by adopting the Halpin–Tsai model. The electrical volume resistivity of CAP/EG composites prepared by melt-compounding is decreased dramatically from ∼10¹⁵ to ∼10⁶ Ω cm by forming the electrical conduction path at a certain EG content between 5 and 7 wt.%.     

Ketotifen controlled release from cellulose acetate propionate and cellulose acetate butyrate membranes

Ketotifen was immobilised in cellulose acetate propionate (CAP) membranes and in cellulose acetate butyrate (CAB) membranes. The characteristics of each system were evaluated under a range of experimental conditions. The topography and uniformity of the membranes was assessed using scanning electron microscopy. The release characteristics associated with Ketotifen were monitored spectrophotometrically. The swelling capacity of the membranes was evaluated and attributed to the combined effects of diffusion and of complex dissociation, during swelling. The materials produced were able to provide controlled release of Ketotifen due to their controlled swelling behaviour and adequate release properties. The results showed that the release of Ketotifen from the CAB membranes is higher but the release from the CAP membranes is more uniform.     

Chemical vapor deposition-derived graphene with electrical performance of exfoliated graphene

While chemical vapor deposition (CVD) promises a scalable method to produce large-area graphene, CVD-grown graphene has heretofore exhibited inferior electronic properties in comparison with exfoliated samples. Here we test the electrical transport properties of CVD-grown graphene in which two important sources of disorder, namely grain boundaries and processing-induced contamination, are substantially reduced. We grow CVD graphene with grain sizes up to 250 μm to abate grain boundaries, and we transfer graphene utilizing a novel, dry-transfer method to minimize chemical contamination. We fabricate devices on both silicon dioxide and hexagonal boron nitride (h-BN) dielectrics to probe the effects of substrate-induced disorder. On both substrate types, the large-grain CVD graphene samples are comparable in quality to the best reported exfoliated samples, as determined by low-temperature electrical transport and magnetotransport measurements. Small-grain samples exhibit much greater variation in quality and inferior performance by multiple measures, even in samples exhibiting high field-effect mobility. These results confirm the possibility of achieving high-performance graphene devices based on a scalable synthesis process.     

High conductive ethylene vinyl acetate composites filled with reduced graphene oxide and polyaniline

A conductive network composed of reduced graphene oxide (RGO) planes and polyaniline (PANI) chains was designed and fabricated by in situ polymerization of aniline monomer on the RGO planes. It was further used for fabrication of conductive composites with a polymer matrix–ethylene vinyl acetate (EVA). The composites achieve improved conductivity at a low filler loading although the host polymer–EVA–is of insulator. For instance, compared to the pure EVA polymer, the conductivity of the composite filled with 4.0 wt.% RGO and 8.0 wt.% PANI increases from 1.2 × 10^?14 S cm^?1 to 1.07 × 10^?1 S cm^?1. In addition, thermal stability of the composites is also enhanced by the filler loading.     

Epoxidised soybean oil polymer composites reinforced with modified microcrystalline cellulose

Microcrystalline cellulose (MCC) grafted with n-octadecyl isocyanate (18C-g-MCC) was introduced as the reinforcing filler in epoxidised soybean oil (ESO) polymer. The wetting characteristics of 18C-g-MCC were evaluated by static contact angle and the results show that the hydrophobicity of MCC was improved by the introduction of nonpolar alkyl groups. The ESO composites were synthesised with different contents of 18C-g-MCC (from 0 to 25 wt%) by a thermally cured method. The reinforcing effects of 18C-g-MCC were evaluated by scanning electron microscopy, mechanical test, dynamic mechanical analysis and thermal stability test. The results show that the tensile strength, the impact strength, Young's modulus, the flexural strength and glass transition temperature of the composites increase gradually with the increase of 18C-g-MCC content, while the elongation at break begins to decrease with 18C-g-MCC content of more than 20 wt%. Contact angle and water absorption analysis of the composites indicate the addition of 18C-g-MCC increases the water absorption of the ESO polymer.     

石墨烯增强铜基复合材料研究进展

石墨烯是一种新兴的二维碳纳米材料,具有良好的力学、导电以及润滑性能,是铜基复合材料中最具潜力的增强体.本文综述了石墨烯增强铜基复合材料的制备工艺,详细分析并归纳了石墨烯增强铜基复合材料的界面结构对于复合材料力学性能的影响及增强机制,总结了石墨烯增强铜基复合材料摩擦学行为研究的最新进展,并深入阐述了石墨烯增强铜基复合材料...     

氧化石墨烯增强水泥复合材料的断裂性能

将氧化石墨烯(GO)加入水泥砂浆中,以提高其抗裂性和韧性.通过三点弯曲梁法测试了GO增强水泥砂浆试件的断裂性能,采用双K断裂模型分析了GO掺量对改性水泥砂浆断裂参数的影响.结果表明:GO提高了水泥砂浆试件的起裂韧度,当GO掺量(与胶凝材料质量比)为0.01％～0.07％时,较对照组分别提高了13.4％、25.4％、24...     

Aging mechanisms in cellulose fiber reinforced cement composites

This paper examines the effects of laboratory scale accelerated aging exposures on the changes in physical and mechanical properties of commercially produced cellulose fiber reinforced cement composites. Two different accelerated aging methods were used to simulate the possible aging mechanisms for which the material may experience under service conditions, both methods being compared to material naturally weathered for 5 yr in roofing. The first aging method consisted of different cycles of water immersion, carbonation, and heating exposures whereas in the second method, cycles of water immersion, heating and freeze-thaw exposures were used. The porosity, water absorption, permeability of nitrogen and compressive shear strength of the composites were examined before and after aging exposures. The surface morphologies of the composites fractured in compression shear tests were examined using scanning electron microscope. Experimental results showed that the compressive shear strength of the accelerated aged composites were related to the microstructures within the composites. Both natural weathering and accelerated aging in CO₂ environment reduced the porosity, water absorption, and nitrogen permeability in the cement matrix, and enhanced the durability of the cellulose fiber-cement composites. The aging test based on artificial carbonation was more effective in simulating natural aging performance of the composites, while the freeze-thaw cycling method failed to induce significant aging effects on the composites even after 21 cycles.     

Atomistic simulations on multilayer graphene reinforced epoxy composites

We use molecular dynamics simulations to characterize multilayer graphene reinforced epoxy composites. We focus on two configurations, one where the graphene layers are parallel to polymer/graphene interface and a perpendicular case, and characterize the in situ curing process of the resin and the thermo-mechanical response of the composites. The yield stress of the composites under uniaxial loading normal to the interface is in all cases larger than that of the bulk polymer even after the constraint of the reinforcement to transverse relaxation is taken into account. While both the parallel and normal configurations have very similar strengths, the parallel case exhibits cohesive yield with strain localization and nano-void formation within the bulk polymer while the case with graphene sheets oriented normal to the interface exhibit interfacial debonding. These two mechanisms lead to different post yield behavior and provide key insight for the development of predictive models of carbon fiber polymer composites.     

石墨烯增强铜基复合材料研究进展

铜(Cu)基复合材料具有优异的力学、热学、电学及耐磨和耐腐蚀等性能,广泛应用于各种工业技术领域。石墨烯(Graphene,Gr)具有二维平面结构和优异的综合性能,是金属基复合材料理想的增强相。石墨烯增强铜基复合材料拓展了铜及其合金的应用范围,适当的制备方法可以使其在保持优异导电导热性能的同时拥有更好的力学性能。石墨烯在铜基体中的存在形式主要以还原氧化石墨烯、石墨烯纳米片或与金属氧化物/碳化物纳米颗粒连接,旨在增强两者之间的界面结合。因此,石墨烯在铜基体中的结构完整性及存在形式直接影响了其性能的优劣。本文综述了Cu/Gr复合材料的制备及模拟方法、复合材料的性能评价及力学性能与功能特性的相互影响规律。指明Cu/Gr复合材料的发展关键在于：(1)分散性与界面结合;(2)三维石墨烯结构的构建;(3)界面结合对力学性能与功能特性的影响及两者间的相互协调。     

Deformation behavior of aluminum alloy matrix composites reinforced with few-layer graphene

Microstructure and mechanical properties of aluminum alloy 2024 (Al2024)/few-layer graphene (FLG) composites produced by ball milling and hot rolling have been investigated. The presence of dispersed FLGs with high specific surface area significantly increases the strength of the composites. The composite containing 0.7 vol.% FLGs exhibits tensile strength of 700 MPa, two times higher than that of monolithic Al2024, and around 4% elongation to failure. During plastic deformation, restricted dislocation activities and the accumulated dislocation at between FLGs may contribute to strengthening of Al2024/FLG composites.     

High performance hybrid PP and PLA biocomposites reinforced with short man-made cellulose fibres and softwood flour

This paper presents the research on hybrid thermoplastic biocomposites reinforced with a combination of short man-made cellulose fibres and softwood flour. The introduced short fibre composites are meant to be processed with injection moulding and may be an alternative to glass-fibre reinforced thermoplastics on account of their comparable specific strengths. The occurring positive hybrid effect enables to substitute up to half the weight of short fibre cellulose reinforcement with softwood flour without a significant reduction of material flexural strength. The flexural modulus of investigated hybrid biocomposites remained approximately at the same level, while impact strength was reduced with increasing softwood flour content. The proposed hybridisation leads to establishing biocomposites of suitable performance with competitive density, price and recycling possibilities in comparison to standard glass fibre reinforced counterparts. Moreover, the application of biobased polymers like polylactide as biocomposite matrix, contributes to the development of so called “green” high performance materials.     

Characterization of kenaf fiber composites prepared with tributyl citrate plasticized cellulose acetate

Cellulose bio-composites have been formed with many matrix polymers; however, a cellulose based matrix offers advantages of enhanced compatibility and environmental conformity. The aim was to use cellulose acetate as matrix since it is readily soluble and more flexible compared with cellulose. Kenaf (Hibiscus cannabinus) was selected as the reinforcement material. Cellulose acetate was dissolved for solution impregnation of the fibers. Plasticized cellulose composites were prepared by addition of tributyl citrate (TBC) to cellulose acetate solutions prior to fiber impregnation. Composites were then compression molded for compaction and fabrication of the composites. The surface morphology, thermal stability and mechanical properties of the kenaf-cellulose acetate composites were characterized. Thermal stability of the composites was limited by evaporation of moisture and TBC, followed by elimination of acetic acid for cellulose acetate. Scanning electron microscopy provided a morphological examination of the composites. Mechanical property measurements demonstrated that modulus of cellulose acetate was increased by kenaf, though the composites were brittle without TBC plasticizer addition.     

石墨烯增强金属基航空复合材料研究进展

本文综述了石墨烯增强金属基航空复合材料的研究现状,归纳了该种复合材料的制备方法,讨论了石墨烯对其性能的影响及机制。指出目前高含量、排列石墨烯增强金属基航空复合材料的研究还比较缺乏,涉及的工艺参数、组织结构、界面化学及高温物理性能等相关问题仍需进一步研究,并提出未来的研究重点应由制备方法等工艺性探讨向微观复合构型设计的思路转变。     

石墨烯/聚酰亚胺复合材料的力学和摩擦学性能

采用氧化石墨烯还原法制备了石墨烯,通过溶液共混法制备了石墨烯增强聚酰亚胺复合材料;研究了石墨烯/聚酰亚胺复合材料的力学和摩擦学性能及摩擦学作用机制。结果表明,随着石墨烯含量增加,复合材料的拉伸强度、断裂伸长率和硬度均呈先上升后下降的趋势,而冲击强度呈先升高而后降低,再升高的趋势。当添加1.0%(质量分数)的石墨烯时,复合材料的拉伸强度和断裂伸长率达到最大值,分别比纯聚酰亚胺提高了149%和652%。石墨烯的加入显著降低了聚酰亚胺复合材料的摩擦系数和磨损率;随石墨烯含量增加,复合材料的磨损率先下降后上升,而摩擦系数先显著降低,尔后平缓减小。随载荷增加,复合材料的磨损率呈平缓下降的趋势;而随滑动速率增加,磨损率呈上升趋势。石墨烯增强的聚酰亚胺复合材料的磨损机理为粘着磨损。     

Tribological properties of copper matrix composites reinforced with homogeneously dispersed graphene nanosheets

Graphene reinforced copper matrix composites (Gr/Cu) were fabricated by electrostatic self-assembly and powder metallurgy. The morphology and structure of graphene oxide, graphene oxide-Cu powders and Gr/Cu composites were characterized by scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction and Raman spectroscopy, respectively. The effects of graphene contents, applied loads and sliding speeds on the tribological behavior of the composites were investigated. The results indicate that the coefficient of friction of the composites decreases first and then increases with increasing the graphene content. The lowest friction coefficient is achieved in 0.3?wt% Gr/Cu composite, which decreases by 65% compared to that of pure copper. The coefficient of friction of the composite does not have significant change with increasing the applied load, however, it increases with increasing the sliding speed. The tribological mechanisms of the composite under different conditions were also investigated.     

Solvent exfoliated graphene for reinforcement of PMMA composites prepared by in situ polymerization

Graphene (GP)-based polymer nanocomposites have attracted considerable scientific attention due to its pronounced improvement in mechanical, thermal and electrical properties compared with pure polymers. However, the preparation of well-dispersed and high-quality GP reinforced polymer composites remains a challenge. In this paper, a simple and facile approach for preparation of poly(methyl methacrylate) (PMMA) functionalized GP (GPMMA) via in situ free radical polymerization is reported. Fourier transform infrared (FTIR), X-ray photoelectron spectra (XPS), Raman, transmission electron microscope (TEM) and thermogravimetric analysis (TGA) are used to confirm the successful grafting of PMMA chains onto the GP sheets. Composite films are prepared by incorporating different amounts of GPMMA into the PMMA matrix through solution-casting method. Compared with pure PMMA, PMMA/GPMMA composites show simultaneously improved Young's modulus, tensile stress, elongation at break and thermal stability by addition of only 0.5 wt% GPMMA. The excellent reinforcement is attributed to good dispersion of high-quality GPMMA and strong interfacial adhesion between GPMMA and PMMA matrix as evidenced by scanning electron microscope (SEM) images of the fracture surfaces. Consequently, this simple protocol has great potential in the preparation of various high-performance polymer composites.     

Surfactant effects on poly(ethylene-co-vinyl acetate)/cellulose composites

Cellulose whiskers, isolated from banana waste fibres, were used as a reinforcement in poly(ethylene-co-vinyl acetate) [EVA] matrices, to develop composites. A non-ionic surfactant, poly(ethylene glycol ether), was used to improve the dispersion characteristics of the cellulose whiskers in EVA/cellulose whisker composites. The influence of the surfactant on the morphology, the mechanical properties and the thermal characteristics of the resultant EVA/cellulose whisker composites has been examined. Theoretical models, namely the Halpin–Tsai model and the Nicolais–Narkis model have been used to provide a basis for comparing the results those were derived from investigations of the tensile properties of the composites.