Functional shape memory composite nanofibers with graphene oxide filler

In the present study, we prepared a series of graphene oxide (GO) filled shape memory polyurethane (SMPU) nanofibers and systematically investigated the morphological, thermal and mechanical properties, surface wettability, and the shape memory effect (SME) followed by the proposed programming model. The results show that GO can be well dispersed within the SMPU matrix, and the introduction of GO significantly improves the mechanical strength, surface wettability, and thermal stability of the SMPU. Compared with pristine SMPU nanofibrous mats, the prepared SMPU/GO nanofibrous mats have better SME and lower thermal shrinkage. When the loading amount of GO increased to 4.0 wt%, the thermal shrinkage ratio (R_ts) of composite nanofibrous mats could be as low as 4.7 ± 0.3%, while the average fixation ratio (R_f) and recovery ratio (R_r) could be as high as 92.1% and 96.5%, respectively. The study indicates that GO is a desirable reinforcing filler for preparing shape memory nanofibers with improved properties.     

Synergistic effect of boron nitride flakes and tetrapod-shaped ZnO whiskers on the thermal conductivity of electrically insulating phenol formaldehyde composites

Tetrapod-shaped zinc oxide (T-ZnO) whiskers and boron nitride (BN) flakes were employed to improve the thermal conductivity of phenolic formaldehyde resin (PF). A striking synergistic effect on thermal conductivity of PF was achieved. The in-plane thermal conductivity of the PF composite is as high as 1.96 W m⁻¹ K⁻¹ with 30 wt.% BN and 30 wt.% T-ZnO, which is 6.8 times higher than that of neat PF, while its electrical insulation is maintained. With 30 wt.% BN and 30 wt.% T-ZnO, the flexural strength of the composite is 312.9% higher than that of neat PF, and 56.2% higher that of the PF composite with 60 wt.% BN. The elongation at break is also improved by 51.8% in comparison with that of the composite with 60 wt.% BN. Such a synergistic effect results from the bridging of T-ZnO whiskers between BN flakes facilitating the formation of effective thermal conductance network within PF matrix.     

Enhanced conductivity behavior of polydimethylsiloxane (PDMS) hybrid composites containing exfoliated graphite nanoplatelets and carbon nanotubes

Polydimethylsiloxane (PDMS) hybrid composites consisting of exfoliated graphite nanoplatelets (xGnPs) and multiwalled carbon nanotubes functionalized with hydroxyl groups (MWCNTs-OH) were fabricated, and the effects of the xGnP/MWCNT-OH ratio on the thermal, electrical, and mechanical properties of polydimethylsiloxane (PDMS) hybrid composites were investigated. With the total filler content fixed at 4 wt%, a hybrid composite consisting of 75% × GnP/25% MWCNT-OH showed the highest thermal conductivity (0.392 W/m K) and electrical conductivity (1.24 × 10⁻³ S/m), which significantly exceeded the values shown by either of the respective single filler composites. The increased thermal and electrical conductivity found when both fillers are used in combination is attributed to the synergistic effect between the fillers that forms an interconnected hybrid network. In contrast, the various different combinations of the fillers only showed a modest effect on the mechanical behavior, thermal stability, and thermal expansion of the PDMS composite.     

Thermal conductivity of Cu–Zr/diamond composites produced by high temperature–high pressure method

Copper matrix composites reinforced with about 90 vol.% of diamond particles, with the addition of zirconium to copper matrix, were prepared by a high temperature–high pressure method. The Zr content was varied from 0 to 2.0 wt.% to investigate the effect on interfacial microstructure and thermal conductivity of the Cu–Zr/diamond composites. The highest thermal conductivity of 677 W m⁻¹ K⁻¹ was achieved for the composite with 1.0 wt.% Zr addition, which is 64% higher than that of the composite without Zr addition. This improvement is attributed to the formation of ZrC at the interface between copper and diamond. The variation of thermal conductivity of the composites was correlated to the evolution of interfacial microstructure with increasing Zr content.     

Fluorographene/polyimide composite films: Mechanical,electrical, hydrophobic,thermal and low dielectric properties

Nowadays, dielectric materials with excellent mechanical and hydrophobic properties are desired for use in the integrated circuits (ICs). For this reason, low dielectric constant fluorographene/polyimide (FG/PI) composite films were prepared by a facile solution blending method, suggesting that the mechanical, electrical, hydrophobic and thermal properties were significantly enhanced in the presence of FG. With addition of 1 wt% FG, the tensile strength, Young’s modulus and elongation at break were dramatically increased by 139%, 33% and 18% respectively when compared with pure PI film. Furthermore, composite films exhibit superior hydrophobic and thermal stability performance. Especially, the FG/PI film with 0.5 wt% of FG possessing a low dielectric constant of 2.48 and a good electrical insulativity that is lower than 10⁻¹⁴ S m⁻¹. Therefore, by their excellent performance, FG/PI hybrid films represent suitable candidate solutions with applications in the microelectronics and aerospace industries.     

Strong and optically transparent biocomposites reinforced with cellulose nanofibers isolated from peanut shell

Cellulose nanofibers–reinforced PVA biocomposites were prepared from peanut shell by chemical–mechanical treatments and impregnation method. The composite films were optically transparent and flexible, showed high mechanical and thermal properties. FE-SEM images showed that the isolated fibrous fragments had highly uniform diameters in the range of 15–50 nm and formed fine network structure, which is a guarantee of the transparency of biocomposites. Compared to that of pure PVA resin, the modulus and tensile strength of prepared nanocomposites increased from 0.6 GPa to 6.0 GPa and from 31 MPa to 125 MPa respectively with the fiber content as high as 80 wt%, while the light transmission of the composite only decreased 7% at a 600 nm wavelength. Furthermore, the composites exhibited excellent thermal properties with CTE as low as 19.1 ppm/K. These favorable properties indicated the high reinforcing efficiency of the cellulose nanofibers isolated from peanut shell in PVA composites.     

Effects of temperature and clay content on water absorption characteristics of modified MMT clay/cyclic olefin copolymer nanocomposite films: Permeability,dynamic mechanical properties and the encapsulated organic device performance

In the present study, amino-silane modified layered organosilicates were used to reinforce cyclic olefin copolymer to enhance the thermal, mechanical and moisture impermeable barrier properties. The optimum clay loading (4%) in the nanocomposite increases the thermal stability of the film while further loading decreases film stability. Water absorption behavior at 62 °C was carried out and compared with the behavior at room temperature and 48 °C. The stiffness of the matrix increases with clay content and the recorded strain to failure for the composite films was lower than the neat film. Dynamic mechanical analysis show higher storage modulus and low loss modulus for 2.5–4 wt% clay loading. Calcium degradation test and device encapsulation also show the evidence of optimum clay loading of 4 wt% for improved low water vapor transmission rates compared to other nanocomposite films.     

Microstructure and mechanical properties of an Al–TiC metal matrix composite obtained by reactive synthesis

A metal matrix composite has been obtained by a novel synthesis route, reacting Al₃Ti and graphite at 1000 °C for about 1 min after ball-milling and compaction. The resulting composite is made of an aluminium matrix reinforced by nanometer sized TiC particles (average diameter 70 nm). The average TiC/Al ratio is 34.6 wt.% (22.3 vol.%). The microstructure consists of an intimate mixture of two domains, an unreinforced domain made of the Al solid solution with a low TiC reinforcement content, and a reinforced domain. This composite exhibits uncommon mechanical properties with regard to previous micrometer sized Al–TiC composites and to its high reinforcement volume fraction, with a Young’s modulus of ∼110 GPa, an ultimate tensile strength of about 500 MPa and a maximum elongation of 6%.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

Aramid fibers reinforced silica aerogel composites with low thermal conductivity and improved mechanical performance

Aramid fibers reinforced silica aerogel composites (AF/aerogels) for thermal insulation were prepared successfully under ambient pressure drying. The microstructure showed that the aramid fibers were inlaid in the aerogel matrix, acting as the supporting skeletons, to strengthen the aerogel matrix. FTIR revealed AF/aerogels was physical combination between aramid fibers and aerogel matrix without chemical bonds. The as prepared AF/aerogels possessed extremely low thermal conductivity of 0.0227 ± 0.0007 W m⁻¹ K⁻¹ with the fiber content ranging from 1.5% to 6.6%. Due to the softness, low density and remarkable mechanical strength of aramid fibers and the layered structure of the fiber distribution, the AF/aerogels presented nice elasticity and flexibility. TG–DSC indicated the thermal stability reaching approximately 290 °C, can meet the general usage conditions, which was mainly depended on the pure silica aerogels. From mentioned above, AF/aerogels present huge application prospects in heat preservation field, especially in piping insulation.     

An investigation on shape memory behaviours of hydro-epoxy/glass fibre composites

Shape-memory polymers (SMPs) have the capacity to return large strains by external stimuli. Among various SMPs, shape-memory epoxy has received considerable attention because of its superior mechanical and thermal properties as well as excellent shape-memory performance. In this study, short glass fibre-reinforced shape-memory hydro-epoxy composites are developed to improve further the mechanical property of shape-memory epoxy resin. The thermomechanical and shape-memory properties of the developed composite materials are investigated by dynamic mechanical analysis, bend test and shape recovery test. The results indicate that the glass modulus and bend strength of the developed composite materials initially increase and then slightly decrease with increasing short glass fibre content. The glass transition temperature of the developed composite materials does not change with increasing short glass fibre. When the short glass fibre content is less than 4.5 wt.%, full recovery can be observed after only several minutes at different temperatures. The shape-memory property of the composite materials is not affected greatly. However, when the short glass fibre content is more than 4.5 wt.%, the material would be destroyed after deformation.     

Synthesis and properties of sandwiched films of epoxy resin and graphene/cellulose nanowhiskers paper

Graphene (GN)-based composite paper containing 10 wt.% cellulose nanowhiskers (CNWs) exhibiting a tensile strength of 31.3 MPa and electrical conductivity of 16 800 S/m was prepared by ultrasonicating commercial GN powders in aqueous CNWs suspension. GN/CNWs freestanding paper was applied to prepare the sandwiched films by dip coating method. The sandwiched films showed enhanced tensile strength by over two times higher than the neat resins. The moduli of the sandwiched films were around 300 times of the pure resins due to the high content of GN/CNWs paper. The glass transition temperature of the sandwiched films increased from 51.2 °C to 57.1 °C for pure epoxy (E888) and SF (E888), and 49.8 °C to 64.8 °C for pure epoxy (650) and SF (650), respectively. The bare conductive GN/CNWs paper was well protected by the epoxy resin coating, which is promising in the application as anti-static materials, electromagnetic interference (EMI) shielding materials.     

Silane modification on mesoporous silica coated carbon nanotubes for improving compatibility and dispersity in epoxy matrices

A simple synthetic method for placing a mesoporous silica coating on multi-wall carbon nanotubes (CNTs@MS) was developed to improve the surface compatibility with regard to a polar epoxy matrix. In addition, the mesoporous silica shell with silanol groups on the CNTs provides a platform to attach silane molecules (e.g. 3-glycidoxypropyltrimethoxysilane, GPTMS) that enable the CNTs@MS to be incorporated into the epoxy matrix at a content of up to 20 wt.%. The viscosities of the CNTs@MS- and GPTMS-modified-CNTs@MS–epoxy composites are much lower than that of the CNTs–epoxy, and then the voids in the GPTMS-modified-CNTs@MS–epoxy composites are most significantly reduced. The effects of the CNTs@MS and GPTMS-modified CNTs@MS on the mechanical and thermal properties of the epoxy composite are investigated. The results show that the GPTMS-modified CNTs@MS improved the filler–epoxy matrix interaction, and has better compatibility in epoxy than the CNTs@MS. As the surface compatibility and interaction strength increase in the epoxy matrix, the enhancement in storage modulus, thermal conductivity and reduction in the coefficient of thermal expansion are in the following order: GPTMS-modified CNTs@MS > CNTs@MS ≫ CNTs.     

Size-scale effects of silica on bis-GMA/TEGDMA based nanohybrid dental restorative composites

The present study focuses on the effect of size-scale combination of silica on the mechanical and dynamic mechanical properties of acrylate based (50% Bis-GMA and 50% TEGDMA by weight) composites with an aim to overcome the conventional problem of high-volume fraction filling of acrylate based composites, typically used in restorative dentistry. Two classes of light-cured composites based on the size-scale combination of silica (7 nm + 2 μm; 14 nm + 2 μm) as the filler were prepared. FTIR spectroscopy revealed functionality and interactions whereas morphological investigations concerning the state of distribution and dispersion of nano- and micro-silica has been carried out by SEM–EDX Si-dot mapping. The dynamic mechanical properties, compressive, flexural and diametral tensile strengths were characterized. Micromechanical analysis of viscoelastic storage moduli following Kerner composite model has revealed an enhancement in the reinforcement efficiency of the nanohybrid composites based on the filler size-scale combination of 14 nm + 2 μm with 10 wt.% nanofiller loading. The compressive strength of the micro-filled composite (with 2 μm silica only) was found to remain comparable to that of the nanohybrid with 5 wt.% of 7 nm silica and 10 wt.% of 14 nm silica filled composites. Diametral tensile strength has been observed to be influenced by the size-scale combination and extent of nanofiller loading. The effective volume fractions in the composites validating the experimentally determined DTS were calculated following Nicolais–Narkis model. Our study demonstrates the conceptual feasibility of exploring the optimization of size-scale combinations of filler for enhancement in reinforcement efficiency by manipulating the volume fraction of filler induced immobilized polymer chains by resorting to the principle of micromechanics.     

Effect of alkali treatment on interfacial bonding in abaca fiber-reinforced composites

Abaca fibers demonstrate enormous potential as reinforcing agents in composite materials. In this study, abaca fibers were immersed in 5, 10 or 15 wt.% NaOH solutions for 2 h, and the effects of the alkali treatments on the mechanical characteristics and interfacial adhesion of the fibers in a model abaca fiber/epoxy composite system systematically evaluated. After 5 wt.% NaOH treatment, abaca fibers showed increased crystallinity, tensile strength and Young’s modulus compared to untreated fibers, and also improved interfacial shear strength with an epoxy. Stronger alkali treatments negatively impacted fiber stiffness and suitability for composite applications. Results suggest that mild alkali treatments (e.g. 5 wt.% NaOH for 2 h) are highly beneficial for the manufacture of abaca fiber-reinforced polymer composites.     

Grafting of nano-TiO2 onto flax fibers and the enhancement of the mechanical properties of the flax fiber and flax fiber/epoxy composite

In this article, a flax fiber yarn was grafted with nanometer sized TiO₂, and the effects on the tensile and bonding properties of the single fibers and unidirectional fiber reinforced epoxy plates were studied. The flax fiber yarn was grafted with nanometer sized TiO₂ through immersion in nano-TiO₂/KH560 suspensions under sonification. The measured grafting content of the nano-TiO₂ ranged from 0.89 wt.% to 7.14 wt.%, dependent on the suspension concentration. With the optimized nano-TiO₂ grafting content (∼2.34 wt.%), the tensile strength of the flax fibers and the interfacial shear strength to an epoxy resin were enhanced by 23.1% and 40.5%, respectively. The formation of Si–O–Ti and C–O–Si bonds and the presence of the nano-TiO₂ particles on the fiber surfaces contributed to the property enhancements. Unidirectional flax fiber reinforced epoxy composite (V_f = 35.4%) plates prepared manually showed significantly enhanced flexural properties with the grafting of nano-TiO₂.     

Electrostatic self-assembled carbon nanotube/nano carbon black composite fillers reinforced cement-based materials with multifunctionality

Electrostatic self-assembled carbon nanotube (CNT)/nano carbon black (NCB) composite fillers are added into cement mortar to fabricate smart cement-based materials. The grape bunch structure of CNT/NCB composite fillers is beneficial for dispersing CNT/NCB in cement mortar matrix and achieving cooperative improvement effect. The mechanical, electrically conductive, and piezoresistive behaviors of the cement mortar are investigated. The CNT/NCB composite fillers can effectively enhance the flexural strength and electrical conductivity of cement mortars, and endow stable and sensitive piezoresistivity to cement mortar at a low filler content. However, they weaken the compressive strength of cement mortar to some extent. The percolation threshold zone of cement mortar with CNT/NCB composite fillers ranges in the amount of 0.39–1.52 vol.%. The optimal content of CNT/NCB composite fillers is 2.40 vol.% for piezoresistivity and the stress and strain sensitivities can reach 2.69% MPa⁻¹ and 704, respectively.     

Thermomechanical properties of bio-based composites made from a lactic acid thermoset resin and flax and flax/basalt fibre reinforcements

Low viscosity thermoset bio-based resin was synthesised from lactic acid, allyl alcohol and pentaerythritol. The resin was impregnated into cellulosic fibre reinforcement from flax and basalt and then compression moulded at elevated temperature to produce thermoset composites. The mechanical properties of composites were characterised by flexural, tensile and Charpy impact testing whereas the thermal properties were analysed by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results showed a decrease in mechanical properties with increase in fibre load after 40 wt.% for the neat flax composite due to insufficient fibre wetting and an increase in mechanical properties with increase fibre load up to 60 wt.% for the flax/basalt composite. The results of the ageing test showed that the mechanical properties of the composites deteriorate with ageing; however, the flax/basalt composite had better mechanical properties after ageing than the flax composite before ageing.     

Study on thermal properties of graphene foam/graphene sheets filled polymer composites

The polymer composites composed of graphene foam (GF), graphene sheets (GSs) and pliable polydimethylsiloxane (PDMS) were fabricated and their thermal properties were investigated. Due to the unique interconnected structure of GF, the thermal conductivity of GF/PDMS composite reaches 0.56 W m⁻¹ K⁻¹, which is about 300% that of pure PDMS, and 20% higher than that of GS/PDMS composite with the same graphene loading of 0.7 wt%. Its coefficient of thermal expansion is (80–137) × 10⁻⁶/K within 25–150 °C, much lower than those of GS/PDMS composite and pure PDMS. In addition, it also shows superior thermal and dimensional stability. All above results demonstrate that the GF/PDMS composite is a good candidate for thermal interface materials, which could be applied in the thermal management of electronic devices, etc.     

Highly conductive graphene oxide/polyaniline hybrid polymer nanocomposites with simultaneously improved mechanical properties

Graphene oxide (GO) was added to a polymer composites system consisting of surfactant-wrapped/doped polyaniline (PANI) and divinylbenzene (DVB). The nanocomposites were fabricated by a simple blending, ultrasonic dispersion and curing process. The new composites show higher conductivity (0.02–9.8 S/cm) than the other reported polymer system filled with PANI (10⁻⁹–10⁻¹ S/cm). With only 0.45 wt% loading of GO, at least 29% enhancement in electric conductivity and 29.8% increase in bending modulus of the composites were gained. Besides, thermal stability of the composites was also improved. UV–Vis spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) revealed that addition of GO improves the dispersion of PANI in the polymer composite, which is the key to realize high conductivity.