Enhancement of dielectric constant in polymer-ceramic nanocomposite for flexible electronics and energy storage applications Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-17 Sunil Kumar, Sweety Supriya, Manoranjan Kar
The polymer nanocomposites have potential applications in flexible electronics due to its interesting dielectric properties. Hence, flexible nanocomposite films of polyvinylidene fluoride (PVDF) polymer and barium hexaferrite (BHF) nanoparticles with high dielectric constant were prepared by the solution cast method. The dielectric behavior of the materials has been understood by employing the impedance spectroscopy techniqe. The co-existence of α and β phases of PVDF has been observed from the XRD (X-ray Diffractometer) and FTIR (Fourier-transform infrared spectroscopy) analysis. The ratio of α and β phases of PVDF has a great influence on dielectric, ferroelectric and energy storage density of PVDF-BHF nanocomposites and, it depends upon the concentration of BHF in the nanocomposites. FE-SEM (Field Emission Scanning Electron Microscopy) micrographs reveal that the microstructure of the composite depends upon the concentration of BHF in the PVDF matrix. Dielectric properties of nanocomposite highly depends on microstructure of the PVDF-BHF nanocomposite. This observation has been well explained by considering the BLCs (Barrier Layer capacitances) model. Interestingly, the dielectric constant has been enhanced eighteen (18) times at 1 KHz to that of dielectric constant of PVDF. The dielectric constant increases due to the electrostatics and interfacial interaction between the local electric field of the BHF nanoparticle and CH2/CF2 dipole of PVDF chain. The present study opens a new window for the possible use of PVDF-BHF nanocomposite in dielectric and energy storage device applications.
Highly enhanced electromechanical properties of PVDF-TrFE/SWCNT nanocomposites using an efficient polymer compatibilizer Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-13 Kie Yong Cho, Hyunchul Park, Hyun-Ji Kim, Xuan Huy Do, Chong Min Koo, Seung Sang Hwang, Ho Gyu Yoon, Kyung-Youl Baek
PVDF-TrFE/SWCNT nanocomposites with outstanding electromechanical properties were produced using P3HT-PMMA block copolymers as a compatibilizer between PVDF-TrFE and SWCNT. P3HT-PMMA block copolymer coated SWCNT (PTMCNT) was first prepared to utilize π-π stacking interactions between SWCNT and the P3HT block segment. The obtained PTMCNTs are highly compatible with the PVDF-TrFE matrix due to strong hydrogen bonding interaction between the polymer matrix and the PMMA block segment on the surface of SWCNT, leading to a very low percolation behavior at 0.05 wt% of SWCNT in PVDF-TrFE. The obtained electroactive PVDF-TrFE/SWCNT nanocomposites showed ca. 50 times increased electromechanical thickness strain, ca. 3200 times increased elastic energy density, and ca. 400 times increased electrical-to-mechanical energy conversion rate in comparison to those of pristine PVDF-TrFE at the relatively low electric field (50 Vppμm-1). These outstanding properties result from the ultra-low percolation of SWCNT along with uniform local field distribution in PVDF-TrFE, which kept not only intrinsic properties of PVDF-TrFE such as all-trans formed crystalline phase and softness but also enhanced electrical properties including dielectric constant.
CNT-PAN hybrid nanofibrous mat interleaved carbon/epoxy laminates with improved Mode I interlaminar fracture toughness Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-12 Volkan Eskizeybek, Adem Yar, Ahmet Avcı
Interleaving laminated composites with electrospun nanofibrous mats comes out as a promising micro--scale strategy to strengthen interlaminar regions of laminated composites. The aim of this study is to evaluate the synergetic contribution of nano- and micro-scale mechanisms on interlaminar delamination. For this, carbon nanotubes (CNTs) reinforced polyacrylonitrile (PAN) electrospun hybrid mats were successfully fabricated and utilized as interleaves within the interlaminar region of carbon/epoxy laminated composites. The Mode I interlaminar fracture toughness values were enhanced up to 77% by introducing CNTPAN nanofibrous interleaves. Specifically, the nano-scale toughening mechanisms such as CNTs bridging, CNTs pull-out, and sword-sheath increased the Mode I fracture toughness by 45% with respect to neat PAN nanofibrous interleaves. The related micro- and nano-scale toughening mechanisms were evaluated based on the fracture surface analysis. Atomic force microscopy was also utilized to quantify the magnitude of surface roughness changes on the interlaminar region with respect to multi-scale interleaving reinforcement and correlate surface roughness changes due to crack deflection to increased fracture toughness.
Strong, transparent and flexible aramid nanofiber/POSS hybrid organic/inorganic nanocomposite membranes Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-10 Fang Wang, Yadong Wu, Yudong Huang, Li Liu
Mechanical performance, transparency and thermal stability still remain the dominating constraints for the application of polymeric composite membranes. Thus, the research and development of co-effectively strong, transparent and heat-resistant membranes are necessary and significant for promoting practical outcomes. POSS NPs is incorporate into the structure of aramid nanofibers (ANFs) to synthesize the ANFPs nanocomposite membranes with different amounts of POSS by vacuum-assisted flocculation. FT-IR and XPS were applied to characterize the structure of composite membranes. Upon the addition of POSS, the surface topological structures of composite membranes were not affected, and they retained excellent transparency and flexibility. The mechanical properties of ANFPs membranes could be altered by changing the POSS content, in which the POSS served as a cross-linking agent between nanofibers, and ANFPs composite membrane presented the optimal tensile strength with 6 wt% POSS embedding in the nanocomposite. Besides the excellent mechanical performance and transparency, the unique thermal assets of ANFs and POSS further enabled the membranes with high thermal stability. Based on these results, it could be concluded that the ANFPs membranes developed here might provide the alternative materials for the practical application of strong, transparent and heat-resistant membrane.
Macro-mechanical damage modeling of fibrous composite materials accounting for non-linear material behavior Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-10 G.A. Abu-Farsakh, A.M. Asfa
In the present paper, a new macro-mechanical model for tracing damage-evolution in composite materials is proposed. The present model represents a new extension and a new approach to a previous model (Ghazi-Farid model), which can be applied for a general state of stress. The model is verified by comparing its results with those corresponding to Ghazi-Farid model for different composite materials and it seems to give very close correlations. The proposed model can be applied to both elastic and inelastic materials as well as generally orthotropic fibrous composite nonlinear-materials. It was concluded that shear damage is always higher than any other damage types due to the high nonlinear-material shear behavior, which causes high plastic strain-energy density. Damage in a composite lamina causes a reduction in its stiffness. Therefore, a new quantum-damage variable is proposed: '' tangential quantum-damage variable '' to quantify the overall-damage in a composite lamina. Percentage reduction of composite stiffness depends mainly on the amount of resulting damage irrespective of fiber-orientation angle. So, a new trend for the behavior of composite materials is introduced which states that the relation between damage-evolution and corresponding stiffness-reduction follows a certain behavior and it is independent of fiber-orientation. Each composite material has a unique trend which is verified using three different composite materials; Boron-Epoxy-Narmco 5505, Graphite-Epoxy 4617/Modmore-II, and Carbon-Epoxy AS4/3501–6. A new damage-term is introduced as: "directional damage-variable", to simplify tracing damage in the case of a uniaxial off-axis loading. The new damage-variable was used to predict damage-evolution in the three laminas made of the indicated composite materials. It is concluded that, Graphite-Epoxy 4617/Modmore-II has the minimum damage at all stress levels and Boron-Epoxy-Narmco 5505 has the maximum damage. The importance of the new damage-term makes it easier to predict damage and make preferences between several composite materials subjected to uniaxial off-axis loading.
Thermoelectric and mechanical properties of PLA/Bi0·5Sb1·5Te3 composite wires used for 3D printing Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-10 Jizhe Wang, Hongze Li, Rongxuan Liu, Liangliang Li, Yuan-Hua Lin, Ce-Wen Nan
Thermoelectric (TE) composite wires with polylactic acid (PLA) as the matrix and Bi0·5Sb1·5Te3 (BST) as the filler are synthesized by extruding. The effects of silane coupling agent KH570, plasticizer ATBC, and conductive additive multi-walled carbon nanotubes (MWCNTs) on the composition, TE, and mechanical properties of the composite wires are systematically studied. It is necessary to add KH570 into the composite wires to make the actual BST loading the same as the designed value. The addition of ATBC greatly increases the flexibility of the composite wires and improves the wires' mechanical properties. When the BST loading increases from 35.8 to 87.5 wt%, the flexural modulus increases from 1684.0 to 4379.8 MPa and the flexural strength monotonically decreases from 50.1 to 13.4 MPa. In aspect of TE properties, the power factor PF of the composite wires increases with the increase of the BST loading, and the maximum Seebeck coefficient reaches 200 μV K−1. When MWCNTs are added into the composite wires, the electrical conductivity is significantly enhanced and thus the PF of the wires is raised. The highest PF of 11.3 μW m−1 K−2 is obtained for the wire containing 81.3 wt% BST and 4 wt% MWCNTs. A TE figure of merit ZT of 0.011 is obtained at room temperature. The excellent TE properties and satisfactory mechanical properties of the BST/PLA composite wires make them a promising candidate used for 3D printing of TE devices.
A highly stretchable and stable strain sensor based on hybrid carbon nanofillers/polydimethylsiloxane conductive composites for large human motions monitoring Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-10 Yanjun Zheng, Yilong Li, Kun Dai, Yan Wang, Guoqiang Zheng, Chuntai Liu, Changyu Shen
Stretchable strain sensors have promising potentials in wearable electronics for human motion detection, health monitoring and so on. A reliable strain sensor with high flexibility and good stability should be designed to detect human joints motions with a large deformation. Here, a simple and facile solution mixing-casting method was adopted to fabricate a highly stretchable strain sensor based on composites mixing polydimethylsiloxane (PDMS) with hybrid carbon nanotubes (CNTs) and carbon black (CB) conductive nanofillers (CNTs-CB). Bridged and overlapped hybrid CNTs-CB nanofillers structure was achieved in the composite on the basis of the morphology observation. In monotonic stretching test, the CNTs-CB/PDMS composites strain sensors exhibited high stretchability, strain-dependent sensitivity in a wide strain sensing range (ca. 300% strain) and an excellent linear current-voltage behavior. During stretching-releasing cycles, the strain sensors presented excellent repeatability, good stability and superior durability (2500 cycles at 200% strain). Combined with the above outstanding strain sensing performances, the fabricated stretchable strain sensors were attached onto different joints of human body to monitor the corresponding human motions, demonstrating their attractive perspective in large human motions detection.
Mechanical response of carbon/epoxy composite sandwich structures with three-dimensional corrugated cores Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-10 Guo-dong Xu, Zhi-hai Wang, Tao Zeng, Su Cheng, Dai-ning Fang
A novel three-dimensional (3D) corrugated core sandwich structure was designed and fabricated by auto-cutting process. Mechanical behaviors and failure mechanism of 3D corrugated core sandwich structures were investigated. Analytical models were developed to estimate the strength, stiffness and dominant failure modes. In order to demonstrate sensitivity of the graded parameters on mechanical behaviors of 3D corrugated core sandwich structures, the specimens with different graded parameters were fabricated and tested under compression and bending loads. Results showed that the graded parameters have obviously influences on the mechanical properties and failure modes of 3D corrugated core sandwich structures. The predictions were also compared with the experiments and the results showed good agreements. Failure maps were constructed to illustrate the controlling failure mechanisms in various regions with different parameters.
Quantized prediction of coefficients of thermal expansion of 3-D CNT-Graphene junctioned carbon nanostructures Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-10 Sangwook Sihn, Ajit K. Roy, Barry L. Farmer
A computational finite element analysis based on a structural molecular mechanics approach was conducted to predict effective coefficients of thermal expansion (CTE) of a novel three-dimensional carbon nanostructure, pillared graphene structure (PGS), which is constituted with several graphene sheets and single-walled carbon nanotubes. Four sets of representative unitcell models were developed atomistically having different geometric parameters of pillar length and inter-pillar distance in the PGS. Periodic boundary conditions were applied to periodic unitcell geometries to yield consistent results. Parametric study shows that both pillar length and inter-pillar distance significantly affect the effective in-plane and through-thickness CTEs. The PGS with smaller inter-pillar distance and larger pillar length yields higher in-plane CTEs, while that with larger inter-pillar distance and smaller pillar length yields higher through-thickness CTE. The calculation yields negative through-thickness CTE at low temperatures (T<100T<100 K) for all sets of PGSs, which is associated with the curvature at the junction.
Synergetic effects of thin plies and aligned carbon nanotube interlaminar reinforcement in composite laminates Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-09 Estelle Kalfon-Cohen, Reed Kopp, Carolina Furtado, Xinchen Ni, Albertino Arteiro, Gregor Borstnar, Mark N. Mavrogordato, Ian Sinclair, S. Mark Spearing, Pedro P. Camanho, Brian L. Wardle
Thin-ply carbon fiber laminates have exhibited superior mechanical properties, including higher initiation and ultimate strength, when compared to standard thickness plies and enable greater flexibility in laminate design. However, the increased ply count in thin-ply laminates also increases the number of ply-ply interfaces, thereby increasing the number of relatively weak and delamination-prone interlaminar regions. In this study, we report the first experimental realization of aligned carbon nanotube interlaminar reinforcement of thin-ply unidirectional prepreg-based carbon fiber laminates, in a hierarchical architecture termed ‘nanostitching’. We synthesize a baseline effective standard thickness laminate using multiple thin-plies of the same orientation to create a ply block, and we find an ∼15% improvement in the interlaminar shear strength via short beam shear (SBS) testing for thin-ply nanostitched samples when compared to the baseline. This demonstrates a synergetic strength effect of nanostitching (∼5% increase) and thin-ply lamination (∼10% increase). Synchrotron-based computed tomography of post mortem SBS specimens suggests a different damage trajectory and mode of damage accumulation in nanostitched thin-ply laminates, notably the complete suppression of delaminations in the nanostitched region. Finite element predictions of damage progression highlight the complementary nature of positive thin-ply and nanostitching effects that are consistent with an ∼15% improvement in Modes I and II interlaminar fracture toughness due to the aligned carbon nanotubes at the thin-ply interfaces.
Conducting α-Fe2O3 nanorod/polyaniline/CNT gel framework for high performance anodes towards supercapacitors Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-09 Zhaokun Yang, Aidong Qiu, Jun Ma, Mingqing Chen
Thick-electrode design toward high energy density per device is of particular importance for supercapacitors to store large amounts of energy, but this remains a seemingly insurmountable challenge due to sluggish electron transport. The challenge is addressed herein by developing an electrically and ionically conducting framework which consists of α-Fe2O3 nanorods, multi-walled carbon nanotubes (CNTs) and polyaniline (PANi) hydrogel. The interconnecting composite framework is formed by in situ polymerizing aniline on the surface of α-Fe2O3 nanorods and CNTs; the nanorods are found to well disperse in the matrix. The framework can provide low-resistance, continuous transport pathways for both electrons and electrolyte ions in the entire electrode system, maximizing the energy use of the nanorods. An anode of ∼100 μm in thickness is fabricated using the composite framework, corresponding to a mass loading of 9.3 mg cm−2. It delivers high area capacitance of 2434.7 mF cm−2 and cycling capacitance retention of 96.3% after 10,000 cycles. This work would shed light on the design of thick electrodes toward high-capacity energy storage devices.
Interfacial designing of PP/GF composites by binary incorporation of MAH-g-PP and lithium Bis(trifloromethanesulfonyl)imide: Towards high strength composites with excellent antistatic performance Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-09 Senlin Gu, Huanhuan Liu, Xuan Li, Claude Mercier, Yongjin Li
High strength Polypropylene (PP)/glass fiber (GF) composites with excellent antistatic performance were prepared by binary incorporation of maleic anhydride grafted polypropylene (MAPP) and lithium bis(trifloromethanesulfonyl)imide (Li-TFSI) into PP/GF composites. Li-TFSI was used as antistatic agents and MAPP was added as the interfacial binder between GF and PP matrix. It was found that the interface between PP and GF can be tuned by the binary addition of MAPP and Li-TFSI. The mechanical properties of PP/GF composites are enhanced drastically with the addition of MAPP. However, Li-TFSI induces the decreasing of the mechanical properties with enhanced antistatic performance of the composites. The investigation showed that Li-TFSI, as a high polar agent, breaks the physisorbed silane on the glass fiber, which induces the deterioration in the strengthening effects of MAPP. At the same time, the Li-TFSI is absorbed on the surface of GF and the ions are ready to move along the GF, so the antistatic performance is achieved. The specific interactions between Li-TFSI, GF and MAPP make it possible to design the interface of PP/GF composites by the binary incorporation of MAPP and Li-TFSI. Therefore, high performance PP/GF composites with both excellent antistaticity and high strength can be achieved.
An in-situ formable and fibrils-reinforced polysaccharide composite hydrogel by self-crosslinking with dual healing ability Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-08 Bihua Ye, Shuyun Zhang, Riwang Li, Lihua Li, Lu Lu, Changren Zhou
Novel in-situ formable and fibrils-reinforced polysaccharide-based composite hydrogels with dual healing ability were prepared by a facile, one-pot approach with maleilated chitosan (CS-MA) and thiol derivatised sodium alginate (SA-SH), via Michael addition reaction and ionic interaction. The unique fibrils network working as reinforcement fillers were attributed to the electrostatic interaction of CS-MA with SA-SH. This CS-MA/SA-SH composite hydrogel can self-heal cracks through dynamic disulfide exchange in 12 h at 37 °C without any external intervention. Noteworthy, fast healing ability inside hydrogels or with porous scaffolds within 1 min can be obtained via the introduction of calcium ions. Moreover, tunable shapes can also be obtained via dual cross-linking, providing advantages to optimize the fibrils-reinforced composite gels system for more biomedical applications. In addition, cell viability and proliferation showed that both of the gels before and after healing with Ca2+ possessed good cytocompatibility.
Toward biomimetic porous poly(ε-caprolactone) scaffolds: Structural evolution and morphological control during solid phase extrusion Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-08 Hua-Mo Yin, Yan-Fei Huang, Yue Ren, Peng Wang, Baisong Zhao, Ji-Hua Li, Jia-Zhuang Xu, Zhong-Ming Li
Two-dimensional oriented scaffolds bear spatial limitation to regenerate three-dimensional (3D) tissues despite showing the ability to guide cell alignment and elongation. By combining solid phase extrusion (SPE) of co-continuous blends with phase removal, we prepared an interconnected 3D porous poly(ε-caprolactone) (PCL) scaffold with oriented pores. To better regulate structure of these distinctive scaffolds, structural evolution of co-continuous blends in the convergent die during SPE was investigated in this study. Morphological observation manifested that the elongation deformation of co-continuous blends proceeded along the extrusion direction in the converging die continuously. Due to the extrusion temperature below the melting point of the matrices, the aligned co-continuous phase was maintained to form the uniformly oriented pores after phase extraction. Unlike consecutive deformation of phase morphology, the change in the crystalline structure of PCL involved two stages divided by the critical deformation distance (∼10 mm). At stage I (<10 mm), spherical crystals of PCL transformed into ellipsoidal shape owing to plastic deformation. At stage II (>10 mm), organized PCL lamellae formed along the extrusion direction as a result of crystal fragmentation and rearrangement. On the basis of anterior cognition, effects of processing parameters on porous morphology were further explored. It was revealed that extrusion draw ratio and annealing time were more effective to regulate pore orientation and size of aligned porous scaffolds than extrusion temperature. The tunable morphological structure of biomimetic scaffolds is of vital importance to broaden their applications for tissue repair.
Dispersion of nanoparticles in polymer matrices with well-designed ligands as dispersant/emulsifier/comonomer Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-08 Yong Ding, Yu Chen, Junping Zheng
Dispersing nanoparticles in polymers is a key requirement for the development of polymer-matrix composites. In this study, cationic ligand and anionic ligand were designed to serve as dispersant, emulsifier and comonomer in different stages of nanocomposites preparation. Commercial BaTiO3, TiO2, Ag and Al2O3 nanoparticles were incorporated and dispersed uniformly in polystyrene (PS) and polymethyl methacrylate (PMMA) matrices by designed cationic/anionic ligand. As dispersants, the sizes of nanoparticles aggregates were reduced from thousands of nanometers to dozens of nanometers by cationic/anionic ligand. Then ligands served as emulsifiers to prepare polymer nanocomposites. At the end of emulsion polymerization, the ligands copolymerized with polymer matrices. At this stage, the sizes of nanoparticles in polymer matrices fell to several nanometers. After hot-pressing, nanoparticles maintained the stable dispersion state in polymer matrices. The tensile strength of P(MMA-co-VDAC)/BaTiO3 increased by 77% compared with PMMA. The thermal decomposition temperature of P(St-co-MAMS)/Al2O3 was improved by 24 °C compared with PS. A facile and efficient approach was exhibited for preparing polymer nanocomposites with a large variety of chemically different nanoparticles in diversified polymer matrices.
A novel expandable porous composite based on acetalized polyvinyl alcohol and calcium sulfate used for injectable bone repair materials Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-08 Hongyu Du, Yudong Zheng, Wei He, Yi Sun, Yansen Wang
Carbon nanotube-reinforced carbon fibre-epoxy composites manufactured by resin film infusion Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-06 Mostafa Yourdkhani, Wenjiao Liu, Simon Baril-Gosselin, François Robitaille, Pascal Hubert
Effective dispersion of carbon nanotubes (CNTs) in the polymer matrix of fibre-reinforced composites is challenging due to the re-agglomeration and filtration of CNTs that occur during the processing of composite materials. In this study, resin film infusion (RFI) process is used for manufacturing composite laminates and investigating the degradation of CNT dispersion during high-temperature processing of a thermoset fibre-reinforced composite. Dispersion stability is investigated by studying the re-agglomeration of CNTs in the resin caused by variations in resin physiochemical properties. Filtration of CNTs by fibre tows is studied by investigating two layup strategies. The effect of CNT dispersion on the mechanical and electrical properties of composites is evaluated by performing compression-after-impact experiments and electrical conductivity measurements.
Tailored glass fiber interphases via electrophoretic deposition of carbon nanotubes: Fiber and interphase characterization Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-06 Qi An, Sandeep Tamrakar, John W. Gillespie Jr., Andrew N. Rider, Erik T. Thostenson
Electrophoretic deposition (EPD) has been used to deposit carbon nanotubes (CNTs) onto glass fibers to strengthen the fiber/matrix interphase of glass/epoxy composites. CNTs were functionalized using ultrasonicated ozonolysis followed by polyethyleneimine (PEI) treatment, creating a stable, aqueous dispersion suitable for EPD. Single E-glass fiber filaments were successfully coated with the functionalized CNTs using EPD. Single fiber tensile and microdroplet debond tests were conducted to investigate the tensile properties of the CNT modified E-glass fibers and their interfacial structure and properties in an epoxy matrix, respectively. Weibull analysis of the fiber testing revealed no detrimental effects resulted from the CNT coating, with some evidence to suggest slightly improved strength. Microdroplet tests revealed changes in the fracture modes due to the application of the CNT coating. The interfacial shear-sliding shifted from the fiber/resin interface to the CNT/resin interphase for the CNT modified fibers. Higher effective interfacial shear strength corresponded to the results where fracture propagated deeper into the CNT-rich interphase layer, confirming the trends observed in previous model interphase studies.
Novel three-component nanocomposites with high dielectric permittivity and low dielectric loss co-filled by carboxyl-functionalized multi-walled nanotube and BaTiO3 Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-06 Shanshan Guana, Hai Li, Shugao Zhao, Laina Guo
In this work, a novel ternary polydimethylsiloxane (PDMS)-based nanocomposite co-filled by carboxyl-functionalized multi-walled nanotube (cMWCNT) and BaTiO3(BT) nanoparticle were developed. The hybrids cMWCNT-BT was realized via the hydrogen bonding (H-bonding) interaction between –COOH groups of cMWCNT and the -OH groups of BT. Compared with the binary composite of BT/PDMS and cMWCNT/PDMS, the results showed that the kind of three-component nanocomposites had high dielectric permittivity and low dielectric loss. Different from cMWCNT, the hybrids cMWCNT-BT have good dispersion in PDMS matrix, forming many micro-capacitors and interfaces, and thus leading to remarkably high dielectric constant. Meanwhile, BT on the surfaces of cMWCNT reduce the direct contact of cMWCNT, resulting in reduced dielectric loss. More important, the BT and cMWCNT had a synergistic effect on dielectric permittivity of the cMWCNT-BT/PDMS composite. Therefore, the dielectric properties of the novel ternary composite can be improved by optimizing the synergistic effects between the charge storage behavior of the ferroelectric phase and the charge transport behavior of the conductive phase.
Advanced piezoresistive sensor achieved by amphiphilic nanointerfaces of graphene oxide and biodegradable polymer blends Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-06 Roberto Scaffaro, Andrea Maio, Giada Lo Re, Antonino Parisi, Alessandro Busacca
This work focuses on the preparation of a piezoresistive sensor device, by exploiting an amphiphilic sample of graphene oxide (GO) as a compatibilizer for poly (lactic acid) (PLA)-Poly (ethylene-glycol) (PEG) blends. The presence of GO determined a high stiffening and strengthening effect, without affecting toughness, and allowed a good stability of mechanical properties up to 40 days. Moreover, GO endowed the materials with electrical properties highly sensitive to pressure and strain variations: the biodegradable pressure sensor showed a responsivity of 35 μA/MPa from 0.6 to 8.5 MPa, a responsivity around 19 μA/MPa from 8.5 to 25 MPa. For lower pressure values (around 0.16–0.45 MPa), instead, the responsivity increases up to 220 μA/MPa in terms of ΔI/ΔP (i.e. (ΔI/ΔI0)/P close to 1 kPa−1). Furthermore, this novel sensor is able to monitor submicrometric displacements with an impressive sensitivity (up to 25 μA/μm in terms of ΔI/ΔL, or 70 in terms of (ΔI/I0)/ε). We implemented a model able to predict pressure changes up to 25 MPa, by monitoring and measuring variations in electrical conductivity, thus paving the road to use these biodegradable, ecofriendly materials as low-cost sensors for a large pressure range.
Low cost and facile preparation of robust multifunctional coatings with self-healing superhydrophobicity and high conductivity Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-06 Kunlin Chen, Weiwei Gou, Le Xu, Yan Zhao
Superhydrophobic and conductive multifunctional coatings have been receiving great attention in recent years due to their wide potential applications. Nevertheless, a simple and cost-effective approach is still lacked. Herein, photocatalytic TiO2 nanoparticles and graphite particles were blended with fluorinated polysiloxane and methyltris(methylethylketoxime)silane, and followed by simply spraying onto various substrates for superhydrophobic functionalization under ambient-drying, in which the graphite particles and TiO2 nanoparticles could not only lead to the micro/nano-roughness structures for coatings but also endow the coatings with the conductivity and photocatalysis. These as-prepared coatings are not only superhydrophobic but also have the high conductivity. They also can be coated on the fabrics for the oil/water separation and deposited on flammable objects as the fire-shielding layer. This multifunctional coating is robust under the external taped or pressed forces and very stable whether in the acid-alkali and salty environment or during long hours of UV irradiation. And most of all, this coating could repair its superhydrophobicity even after mechanically abraded or polluted with organics. The design and fabrication of this multifunctional coating may find immediate usage in a wide range of areas.
Mechanically strong polyimide / carbon nanotube composite aerogels with controllable porous structure Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-05 Wei Fan, Lizeng Zuo, Youfang Zhang, Ye Chen, Tianxi Liu
Developing aerogels with controllable pores, outstanding mechanical properties and excellent thermal stability still remains a key challenge in evolution of aerogels. In the present work, polyimide (PI) composite aerogels with controllable porous structures and tunable multi-functions have been fabricated with the addition of carbon nanotubes (CNTs) with different functional groups and aspect ratio via an eco-friendly freeze-drying method followed by a thermal imidization process. The interactions between PI chains and CNTs can form crosslinking points through physical or chemical bonding, which could overcome the expansive force in the ice crystal growth process and the capillary force during ice sublimation, thus forming a three-dimensional porous structure. Through increasing the content of functional groups on CNTs, the PI/CNT composite aerogels show enhanced structural stability with a less shrinkage (<20%) during processing, further resulting in improved mechanical properties. As a result, the PI composite aerogels exhibit low density (∼0.1 g cm−3), improved compression modulus (33.5 MPa), and high thermal stability (above 580 °C), showing great potential for application as lightweight and high-performance materials. Additionally, this work develops a new strategy to realize the controllable preparation and tunable properties of polymer aerogels by utilizing nanofillers as an effective crosslinking agent.
Largely enhanced electrical conductivity of layer-structured silver nanowire/polyimide composite films by polyaniline Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-05 Fang Fang, Gui-Wen Huang, Hong-Mei Xiao, Yuan-Qing Li, Ning Hu, Shao-Yun Fu
Electrical conductivity (σ) and mechanical properties are two major concerns for layer-structured films used in electronic devices. It is unavoidable to significantly reduce the mechanical integrity of layer-structured films for adjoined conducting-layer and polymer layer and also greatly increase the cost for expensive conductive fillers in order to enhance σ by simply increasing conducting filler content. This paper reports for the first time the preparation of silver nanowire (Ag-NW)/polyimide (PI) layer-structured composite films with greatly enhanced σ and maintained good mechanical properties by polyaniline (PANI) utilized in the PI substrate layer to regulate its potential barrier for the purpose of reducing the tunneling resistance between Ag-NWs. Consequently, σ is greatly enhanced by up to 8.7 times (over 1000 S/cm) while the high tensile strength of the layer-structured conducting composite film is maintained by 95% (over 75 MPa) via introduction of PANI at low contents up to 20% of PI. This work provides a simple strategy for development of high-quality thin films for electronic devices simultaneously possessing high σ and good mechanical properties.
A facile approach to constructing efficiently segregated conductive networks in Poly(lactic acid)/Silver nanocomposites via silver plating on microfibers for electromagnetic interference shielding Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-04 Kai Zhang, Hai-Ou Yu, Kai-Xin Yu, Yuan Gao, Ming Wang, Jiang Li, Shaoyun Guo
Here, a facile approach to constructing efficiently segregated conductive networks in the poly(lactic acid)/silver (PLA/Ag) nanocomposites were developed by coating Ag particles on PLA microfibers and then compression molding. The electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) of the nanocomposites were obviously enhanced by these efficiently conductive networks because of the well Ag coating layers on PLA microfibers. Furthermore, the electrical conductivity and the EMI SE of the nanocomposites increased with increasing the coating amount of Ag particles, which can be easily tuned by controlling the coating time. It was found that the chain-structured PLA/Ag nanocomposites with coating time of 7 min with 5.89 vol.% Ag particles possessed the remarkable electrical conductivity of 254 S/m and outstanding EMI SE of 50 dB at 8.2–12.4 Hz when the testing samples with the thickness of 1.5 mm, which far surpassed the targeted value of 20 dB for commercial applications. The excellent EMI shielding properties of the nanocomposites were ascribed to the unique segregated chain-structures, which provide enormous interfaces to reflect, scatter and adsorb the electromagnetic waves many times. The PLA/Ag nanocomposites with segregated networks were also found to be an absorption dominated EMI shielding mechanism.
Unraveling crack stability and strain localization in staggered composites by fracture analysis on the shear-lag model Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-03 Zhongliang Yu, Junjie Liu, Xiaoding Wei
Bio-inspired composites can achieve excellent toughness while maintaining their strength through hierarchical microstructure designs combining strong and brittle reinforcements and soft yet ductile matrices. The interfaces between reinforcements and matrices transfer loads through shear deformation and deflect cracks along themselves to dissipate a considerable amount of energy. In this way, the catastrophic failure, which is common in monolithic reinforced materials due to the severe stress concentration near the defects, is deferred in hierarchical composites. Yet, recent computations and experiments suggest that strain localization arising from the unstable crack propagation along interfaces leads to the composites failure. In this study, fracture analysis is carried out on staggered composites with the brick-and-mortar structure. An analytical formula predicting the onset of strain localization emerges from the analysis and is validated by finite element analysis. Furthermore, showing good agreements with independent tensile tests on multi-layer graphene assemblies, our model demonstrates its applicability to explain the strain localization in composites consisting of interfaces that function through re-formable bonds. Characteristic length scales emerging from the analysis can be used to guide the composites design to optimize material toughness and ductility.
Silkworm silk fibers vs PEEK reinforced rubber luminescent strain gauge and stretchable composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-03 Luca Valentini, Silvia Bittolo Bon, Lorenzo Mussolin, Nicola Pugno
In the present study we demonstrate how the sensitive property of the constituent parts of silkworm silk fiber can be applied to the field of soft composite materials. It concerns the structural and intrinsic functional characteristics of silk vs. the macroscopic property and the realization of functional composites. Silk fiber reinforced silicone rubber (SR) composites have been fabricated with different fiber lengths. The key structural features of silk made of stiff nanocrystals, including hydrogen bonded β-strands and β-sheet nanocrystals, when embedded in a softer matrix demonstrate that the tensile strength as well as the stiffness of the composites are higher than those measured for SR reinforced with synthetic polyether-ether-ketone fibers. Moreover, the intrinsic luminescence of protein nanocrystals permits the direct observation of the deformation with accurate measurement of the strain in the composite. Based on the intrinsic properties of such natural hierarchical material, these findings will allow to transfer the engineering of composite materials, particularly, soft functional composites, to a new applications ranging from strain measurements in biological tissue to monitoring tool in structural composites.
Fabrication and testing of composite corrugated-core sandwich cylinder Compos. Sci. Technol. (IF 4.873) Pub Date : 2018-01-02 Wanxin Li, Fangfang Sun, Weiyi Wei, Debo Liu, Xi Zhang, Ming Li, Hualin Fan
To get a strong, stiff and weight efficient cylindrical shell, carbon fiber reinforced corrugated-core sandwich cylinders (CSCs) were designed and made. The corrugated-core is made up of corrugated cylindrical shell and manufactured by mould hot pressing method. Split forming and integral filament winding forming methods were applied to make the CSC separately. Effects from non-wrapped and wrapped cylindrical ends were investigated individually. Uniaxial compression tests were performed to reveal the strength and failure mode. Split forming method makes the CSC stiffer but integral filament winding forming method makes the CSC stronger. With non-wrapped ends, the cylinders fail at end delamination and the load carrying capacity is 289.7 kN and 373.7 kN, respectively. The load is improved to 415.6 kN and 491.4 kN, respectively, when the cylinder is end-wrapped. Skin fracture controls the failure of the CSCs with wrapped ends and makes them stronger. Meanwhile, the load carrying ability of the CSC is stronger than lattice truss-core sandwich cylinders (LTSCs). Benefiting from the high axial load carrying ability of the CFRC corrugated shell, strength of the designed CSC failing at skin fracture improves at a magnitude of 50% compared with the referenced LTSC.
All-aromatic SWCNT-Polyetherimide nanocomposites for thermal energy harvesting applications Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-29 Lazaros Tzounis, Maruti Hegde, Marco Liebscher, Theo Dingemans, Petra Pötschke, Alkiviadis S. Paipetis, Nikolaos E. Zafeiropoulos, Manfred Stamm
The thermoelectric properties of amorphous and semi-crystalline high-performance polyetherimide–SWCNT nanocomposites are reported for the first time. Nanocomposites based on a non-linear polyetherimide (PEI) model system, labeled aBPDA-P3, with 0.6, 4.4 and 10 vol% SWCNTs remained amorphous after the addition of SWCNTs. In contrast, SWCNTs induced crystallization in a linear PEI model system labeled as ODPA-P3. The (thermo)mechanical properties were fully characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMTA). The electrical conductivity was studied by four-probe measurements and showed higher values for the ODPA-P3 films reaching 20 S/m at 10 vol% of SWCNTs. The thermoelectric performance revealed by Seebeck coefficient (S) measurements showed values of 40 and 55 μV/K for the 0.6 and 4.4 vol% ODPA-P3 SWCNT nanocomposites, while 16 and 47 μV/K for aBPDA-P1 amorphous films. This difference has been attributed to SWCNT–induced crystallization in ODPA-P3 matrix. The PEI-SWCNT nanocomposites are ideal candidates as flexible films and coatings for large area thermal energy harvesting, where high temperature gradients exist. Potential applications can be envisaged in the aerospace, automotive and micro-electronics sectors.
Electric field-induced alignment of nanofibrillated cellulose in thermoplastic polyurethane matrix Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-29 Shuman Xu, Dingyao Liu, Qin Zhang, Qiang Fu
Nanofibrillated fibers (NFC) has been largely used as reinforcing filler to improve the properties of polymer matrix because of their unique properties such as high aspect ratio, good aqueous stability, high specific strength and stiffness. However, the full potential of NFC as reinforcing agent has not been realized because of its poor dispersion and random distribution in polymer matrix. In this work, we demonstrate the importance of alignment of NFC to determine the mechanical properties of polymer via applying alternative current (AC) electric field and using thermoplastic polyurethane (TPU) as the matrix. The TPU/NFC nanocomposites were prepared via solution casting method and the effect of parameters of the applied electric field (amplitude, frequency as well as the duration of application) on the orientation degree of NFC and the final properties of TPU/NFC nanocomposites are systematically investigated. It was found that NFC could be easily oriented under effect of AC due to electric induced polarization. The prepared anisotropic TPU/NFC composites exhibit 2.07 and 1.82 times increase of tensile strength and elongation at break in the parallel direction than that in the vertical direction for the anisotropic samples, respectively. It was also interesting, to find that the samples with aligned NFC exhibit an increased dielectric constant with lower dielectric loss, which could provide an idea to fabricate high performance dielectric materials.
Surface modified BaTiO3 nanoparticles by titanate coupling agent induce significantly enhanced breakdown strength and larger energy density in PVDF nanocomposite Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-28 Penghao Hu, Shengmin Gao, Yangyang Zhang, Liang Zhang, Chengchen Wang
Dielectric capacitors are promising in micro-electronics, portable equipment and hybrid electric vehicles due to their specific features of flexibility, ultrahigh operating voltage and fast charging-discharging rate. The dielectric properties of polymer-based nanocomposite are much related to the interface binding between fillers and matrix. In this work, a surface modification approach employed newfound titanate coupling agent was developed to improve the compatibility between BT nanoparticles and PVDF matrix. After treated by the modifier TC-2, a coating layer contained with active organic groups was formed on the surface of BT nanoparticles. Benefited from the improved dispersibility and compatibility of modified BT nanoparticles in PVDF matrix, the breakdown strength of the nanocomposites was much enhanced. The monodisperse mBT-2 nanoparticles treated with appropriate amount of modifier dramatically enlarged the breakdown strength from 397 kV/mm for neat PVDF to 517 kV/mm for 4 vol% mBT-2 loading nanocomposite. Compared with BT/PVDF, the improvements on the energy storage performance in mBT-2/PVDF are significant. The maximum discharged energy density of 11.27 J/cm3 for 4 vol% loading mBT-2/PVDF is nearly double of that for 4 vol% loading BT/PVDF, and the energy efficiency for mBT-2/PVDF is also increased. The modification method originally represented here has great potential in developing high energy density nanocomposites for advanced applications.
Highly conductive nanocomposites based on cellulose nanofiber networks via NaOH treatments Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-28 Chuchu Chen, Mengmin Mo, Wenshuai Chen, Mingzhu Pan, Zhaoyang Xu, Haiying Wang, Dagang Li
Developing functional nanocomposites with the utilization of the sustainable natural resources (e.g. cellulose) is one most importance strategy. In this study, a novel method was developed and used to fabricate flexible conductive nanocomposite. The key innovation of this method is that carbon nanotubes (CNTs) was incorporated into cellulose nanofiber (CNF) gel which processed by alkali treatment. We found that the gelation process caused the shrinking of CNF/CNT gel-film, which result in forming a robust 3D network structure. While the shrinking attributed to constructing high density CNTs electron transport pathways and achieve improved electrical conductivity. Results clearly show that CNFs, a dispersing agent, were used to well-dispersed the CNTs in the nanocomposite. After the alkali treatments, the as-prepared CNF/CNT gel-film had a conductivity of 5.02 S/cm, which is almost 3-fold higher than the CNF/CNT film (without alkai treatment), at 20 wt% CNTs. Conductivity of the CNF/CNT gel-film was further improved to as high as 17.04 S/cm, when adding 50 wt% CNTs. Morphology investigation exhibited that CNFs and CNTs formed into a high density 3D network affording adequate electron transport pathways, and giving the gel-film remarkable electrical conductive properties. Additionally, in lights of its excellent electrical performance, low cost, and environmental friendliness, the CNF/CNT gel-film may have a promising application in the flexible electrodes and conductive papers.
Enhanced thermal and fire retardancy properties of polypropylene reinforced with a hybrid graphene/glass-fibre filler Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-27 Dimitrios G. Papageorgiou, Zoe Terzopoulou, Alberto Fina, Fabio Cuttica, George Z. Papageorgiou, Dimitrios N. Bikiaris, Konstantinos Chrissafis, Robert J. Young, Ian A. Kinloch
The thermal stability and flame retardancy properties of polypropylene (PP) nanocomposites containing graphene nanoplatelets (GNPs), glass fibres (GFs) or a hybrid mixture of the two fillers were investigated. The GNPs enhanced the thermal stability of the nanocomposites by at least 48 °C as a result of the nanoconfinement of the polypropylene chains and the prevention of the emission of the gaseous molecules during decomposition. Pyrolysis combined with gas chromatography and mass spectroscopy showed that the decomposition mechanism of the polymer was not altered by the presence of the nanofillers and the alkenes that comprised of 3n carbon atoms were the main degradation products. Cone calorimetry tests revealed a significant delay of the ignition under irradiation with the addition of GNPs to the PP. Furthermore, the GNPs lowered the combustion rate of the PP due to the formation of a carbonaceous protective layer that acted as a barrier to heat and mass transfer. The lightweight materials prepared show promising results for applications where high thermal stability along with fire retardancy are a prerequisite, such as parts for vehicles or aircraft.
Flexible films of poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)/SnS nanobelt thermoelectric composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-27 Xuejiang Cheng, Lei Wang, Xin Wang, Guangming Chen
Organic polymer/inorganic thermoelectric (TE) composites are emerging green energy materials for diverse applications including harvesting waste or low-quality heat, local cooling, sensing and wearable electronics. Here, we report flexible films of new TE composites by employment of SnS nanobelt into polymer matrix. First, the SnS nanobelts with high purity were prepared by a convenient hydrothermal process. Then, the poly (3,4-ethylenediox-ythiophene): poly (styrenesulfonate) (PEDOT:PSS)/SnS nanobelt composites were obtained by a solution mixing procedure aided by ultrasonication. The structure and morphology of the SnS nanobelts as well as the PEDOT:PSS/SnS composites were characterized by X-ray diffraction (XRD) and field-emission scanning electroscopic (FESEM) techniques. The effects of the SnS content and the dispersing agent (organic solvent) on the dispersion state and the TE performance for the composites were investigated. The highest power factor at room temperature reached 27.8 ± 0.5 μW m−1 K−2 for the PEDOT:PSS/SnS nanobelt composite prepared in N,N-Dimethylformamide. The present study opens a novel avenue to exploit of excellent polymer TE composites by introduction of inorganic nanoparticles with large Seebeck coefficients.
Simultaneously improved electromagnetic interference shielding and mechanical performance of segregated carbon nanotube/polypropylene composite via solid phase molding Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-27 Hong-Yuan Wu, Li-Chuan Jia, Ding-Xiang Yan, Jie-feng Gao, Xiao-Peng Zhang, Peng-Gang Ren, Zhong-Ming Li
Conductive polymer composite with segregated structure has been well demonstrated to achieve high electromagnetic interference shielding effectiveness (EMI SE) due to the selectively distributed electrical nanofillers to establish desirable conductive networks. Nevertheless, the formation of segregated structure in low-melt-viscosity semi-crystalline polymer is still challenged and the segregated composite always suffers poor mechanical performance. Herein, elevated pressure and temperature were utilized to make a typical semi-crystalline polymer, polypropylene (PP), hold solid phase to restrict the diffusion of carbon nanotube (CNT) into its interior. Segregated CNT networks were facilely constructed in the resultant CNT/PP composite and imparted it with a superior EMI SE of 48.3 dB at 2.2 mm thickness and 5.0 wt% CNT loading, the highest EMI shielding level among the reported CNT/polymer composites at equivalent material thickness and CNT loading. Moreover, the elevated pressure and temperature effect dramatically increase the compressive, tensile, and flexural strength (modulus) of the CNT/PP composite by 133% (65%), 74% (130%) and 53% (50%), respectively, in comparison to those for conventional segregated CNT/PP composite, really overcoming the major mechanical shortcoming in the development of segregated composites for EMI shielding. Our work provides a facile strategy to fabricate the efficient EMI shielding and robust material with the construction of typical segregated structure in low-melt-viscosity semi-crystalline polymers.
A polymer-coated calcium chloride hexahydrate/expanded graphite composite phase change material with enhanced thermal reliability and good applicability Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-27 Kunjie Yuan, Yan Zhou, Wanchun Sun, Xiaoming Fang, Zhengguo Zhang
A novel polymer-coated composite PCM was prepared by mixing the CaCl2·6H2O/EG composite particles with a photo-curing polymer, followed by irradiating the mixture under UV light to make the polymer cured. It is shown that the surfaces of the composite particles have been sealed by the polymer. And the melting and freezing enthalpy values of the obtained polymer-coated CaCl2·6H2O/EG composite PCM are as high as 113.2 and 114.1 J g−1, respectively, and its melting point is quite close to that of CaCl2·6H2O. After experiencing 500 heating-cooling cycles, polymer-coated CaCl2·6H2O/EG exhibits the decreases only by 1.68% and 0.52% in the enthalpies of melting and freezing, much less than 25.54% and 30.55% for CaCl2·6H2O/EG, respectively, revealing much enhanced thermal reliability. The applicability of the uncoated and polymer coated CaCl2·6H2O/EG composite PCMs was investigated by directly mixing them with gypsum powder and water, followed by forming into plasterboards. It is found that, the plasterboard containing polymer coated CaCl2·6H2O/EG not only exhibits superior thermal performance for delaying temperature rise over the one with CaCl2·6H2O/EG but also possesses much better thermal reliability. These good characteristics render the polymer-coated CaCl2·6H2O/EG composite PCM with great potentials in building energy conversation.
Sustainable packaging biocomposites from pPolylactic acid and wheat straw: Enhanced physical performance by solid state shear milling process Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-26 Shuangqiao Yang, Shibing Bai, Qi Wang
As a sustainable and inexpensive agricultural byproduct, wheat straw has gained major interest as filler in green composites in recent years, but previous studies about PLA/wheat straw composites have reported modest enhancement or even major reduction in physical performance. Here, we report a new method for both production cellulose nanofibrils and achieving excellent dispersion in composites free of solvent for the first time, and enhanced physical performance is obtained via solid state shear milling process (SSSM). The SSSM pretreatment process led wheat straw an ultrafine particle size and even the separation of cellulose nanofibrils from micro-sized pristine cellulose fibers. Both optical and electron microscopy revealed that composites made by SSSM process exhibit excellent dispersion of hemicellulose, lignin and cellulose nanofibrils which derived from wheat straw. Such PLA/wheat straw composites exhibited fast crystallization rate with 0.8 min crystallization half-time and 41.4% crystallinity, leading major enhancement in flexural modulus which exceed the known value reported in the literature. In addition, a heat deflection temperature of 73 °C is observed with 30%wt wheat straw, which is much higher than neat PLA. Furthermore, high water vapor permeability is observed in composites, enabling food packaging applications especially for respiring fresh products such as fruits and vegetable. The approach presented in this paper highlights a novel technique for recovering wheat straw in producing value-added products.
Graphite nanosheets - polypropylene composites from in toluene delaminated graphite using atactic polypropylene as dispersant Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-26 A. Rosehr, D. Griebe, G.A. Luinstra
Composites of polypropylene (PP) and graphite nanosheets (GN) are prepared by melt blending PP with a master batch of GN suspended in atactic polypropylene (Mw = 129.000 g/mol). aPP/GN master batches were obtained by wet ball-milling graphite in toluene using the aPP as dispersant. The procedure gives single flakes of GN with crystallite out-of-plane thickness as low as 17.7 nm. PP/aPP/GN composites were obtained with finely dispersed GN, predominantly as single nanosheets from master batches containing aPP dispersant and graphite. Crystallization of the iPP in the composites is facilitated by the presence of aPP and GN. PP spherulites are formed as the graphitic fillers act as strong nucleating agents: the dimensionality of the crystal growth (n = 2-3) and the crystallinity increases with increasing filler content in isothermal and non-isothermal crystallizations. The yield strength of the composites can be enhanced up to 20% by the presence of GN; the presence of aPP counteracts a decrease in elongation at break. Composites prepared from parent graphite or GN without aPP show larger aggregates of nanosheets in the composites.
A new low moduli dielectric elastomer nano-structured composite with high permittivity exhibiting large actuation strain induced by low electric field Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-26 Feixiang Zhang, Tiefeng Li, Yingwu Luo
Dielectric elastomers (DEs) are able to deform significantly in response under an external electric field. DE actuators have promising applications in many emerging fields such as biomimetic robots, haptic devices, tunable lens, and loudspeakers. Practical applications of DE devices are limited by the extremely high electric field and the high pre-stretch. Herein, we have designed and fabricated a new type of soft DE composites of partially reduced graphene oxide (RGO)/polystyrene-b-poly (n-butyl acrylate)-b-polystyrene triblock copolymer (SBAS). An extremely soft SBAS was tailor-made as the elastic matrix. A facile colloidal blending method, i.e. simply mixing the SBAS latex with GO aqueous dispersion, was used to fabricate the nano-structured composite with a segregated network of RGO nanosheets. The design strategy led to the DE composite film of 1.5 wt% RGO/SBAS owning low modulus (0.51 MPa), high relative permittivity (∼11) and relatively high dielectric breakdown strength (33 kV/mm). The DE composite film exhibited 21.3% maximum area actuation strain at relatively low electric field strength 33 kV/mm without pre-stretch.
Effects of elevated loading rates on mode I fracture of composite laminates using a modified wedge-insert fracture method Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-26 Solver I. Thorsson, Anthony M. Waas, Joseph Schaefer, Brian Justusson, Salvatore Liguore
In this paper, experimental results for rate dependence of interlaminar mode I fracture of a polymer matrix composite laminate are presented. A modified wedge-insert fracture (MWIF) method for conducting mode I fracture testing at elevated loading rates is used. A correction factor has been introduced to the modified beam theory method for measuring the mode I interlaminar fracture toughness using the MWIF method. The experimental method was successfully verified against the most widely used standardized method at quasi-static loading rates. Mode I interlaminar fracture testing was conducted at loading rates ranging from 0.01 mm/s to 3600 mm/s. A reduction in fracture toughness with rate was seen. The fracture behaviour at elevated rates differed from the lower rates. The effect of bridging (and process zone) lengths on the fracture toughness were seen decreasing drastically with increased loading rate.
Competing mechanisms in the unfolding failure in composite laminates Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-26 J.M. González-Cantero, E. Graciani, B. López-Romano, F. París
Highly-curved laminates are prone to fail by delamination when they are loaded under a bending moment which tries to flatten the laminate. This failure, commonly called unfolding failure, has been traditionally associated with the tensile interlaminar stresses which appear in the laminate, due to its high curvature. However, some specimens failing by unfolding present a maximum interlaminar tensile stress, at the failure instant, much lower than other specimens with different thicknesses or stacking sequences. This fact has been commonly associated with a thickness dependence of the interlaminar tensile strength for which no physical explanation can be found in the literature, although sometimes it has been attributed to manufacturing defects, which are assumed to be higher in thinner laminates. The present work considers the idea of a second failure mechanism named induced unfolding, which assumes that an intralaminar failure is responsible for the failure onset. Therefore, in some cases, the unfolding failure starts as an intralaminar crack which, under a high enough interlaminar tensile stress, propagates instantaneously, causing the delamination and the final failure. Analysing the results of a test campaign, proofs of the occurrence of this kind of failure on L-shape CFRP laminates of UD plies are reported.
Chemical treatment of wood fibers to enhance the sound absorption coefficient of flexible polyurethane composite foams Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-26 Hyeon Choe, Giwook Sung, Jung Hyeun Kim
Polyurethane foams are commonly used as sound absorption materials in the automobile industry because their well-defined structure allows for effective absorption of sound waves through air friction and the structural vibration of cell walls. In this study, chemically treated wood fibers were incorporated into the polyurethane foams to improve their sound absorption coefficient by enhancing the compatibility between the wood fibers and the polyurethane matrix. The open porosity of the composite foams was strongly dependent on the chemical treatments of wood fibers as well as the wood fiber contents in the composites, and it was related to the air-flow resistivity and tortuosity of the foam materials. Model calculations revealed that high air-flow resistivity led to a high sound absorption coefficient, which agreed well with experimental observations. Therefore, for achieving high sound absorption performance in composite foams, no more than the optimum amount of a coupling agent must be used to improve the interfacial compatibility between the wood fibers and the polyurethane matrix. The use of excessive amount of the silane coupling agent led to intramolecular agglomeration, thus negatively affecting the sound absorption behavior.
Significantly improved rubber-silica interface via subtly controlling surface chemistry of silica Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-24 Chengfeng Zhang, Zhenghai Tang, Baochun Guo, Liqun Zhang
It has been commonly acknowledged that particle dispersion and interfacial interactions are vital in determining the ultimate performance of polymer composites. However, the interplay between dispersibility and interfacial interaction in polymer composites has not been explicitly unraveled. In this contribution, a series of silica with controlled surface chemistry are prepared to reveal the effects of subtle change in surface property of filler on the structures and mechanical performance of the rubber composites. On the basis of thermodynamic theory, the dispersibility of modified silica in rubber is quantitatively evaluated by using surface energy. The modified silica was introduced into styrene-butadiene rubber (SBR) to investigate the effects of surface modification on the dispersion of silica and interfacial interaction of the rubber composites. It has been demonstrated that subtle change in surface chemistry of silica drastically improves its dispersibility in rubber matrix, leading to much improved accessible surfaces and hence much complete interfacial reaction. At very low grafting content (0.2 molecule/nm2), improved modulus (44%) and wet-traction (54%), together with reduced rolling-resistance (11%), are concurrently observed.
Post-functionalization of carboxylic polyethersulfone composite membranes Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-23 Chen Wang, Yuan Xu, Shudong Sun, Changsheng Zhao
Herein, a new and facile approach by in situ cross-linking polymerizationcoupled with a post-functionalization procedure was developed to prepare functional PES composite membranes to improve its over-all performance as hemodialysis membrane. In our strategy, poly(acrylate acid-co-2-hydroxyethyl methacrylate) P(AA-co-HEMA) as a macromonomer, was firstly synthesized by free radical copolymerization, then blended in PES solution and in situ cross-linked polymerization via the reaction of the hydroxy group of HEMA and the isocyanate group of 4,4′-diphenylmethane diisocyanate (MDI) to prepare the carboxylic membranes. To further enhance the hemocompatibility, the carboxylic membranes were post-functionalized by grafting sulfonic acid groups onto the membrane surfaces via a “grafting from” method. The chemical compositions and surface morphologies of the prepared membranes were investigated by ATR-FTIR, XPS, SEM and AFM. After introducing the functional groups, the surface hydrophilicity of the membranes was significantly improved, demonstrated by the reduced water contact angles (WCAs) and enhanced permeability. The decreased protein adsorptions and higher flux recovery ratios (FRRs) revealed that the modified membranes showed improved protein antifouling property. The improvement of hemocompatibility was confirmed by the inhibited platelet adhesion, prolonged clotting times, and suppressed blood-related complement activation. Moreover, the post-functionalized membranes also showed good cytocompatibility. In general, the in situ cross-linking technique is a suitable route in the field of membrane modification for its facile and easy operation; and the post-functionalization operation could endow the membranes with efficiently improved properties.
Pseudo-ductility in flexural testing of symmetric ±45° angle-ply CFRP laminates Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-20 M.C. Serna Moreno, S. Horta Muñoz, A. Romero Gutiérrez, C. Rappold, J.L. Martínez Vicente, P.A. Morales-Rodríguez, J.J. López Cela
Pseudo-ductility could be sought in composite structures to avoid their brittle behaviour and, consequently, to withstand higher levels of external loading due to an extended non-linear response. This mechanism has been deeply examined in the literature for angle-ply laminates submitted to uniaxial tests. Nonetheless, the pseudo-ductile effects could appear also under flexural loading because tension and compression are applied in different regions of the cross-sections simultaneously. In this sense, bending testing presents a higher degree of complexity introduced by the variation of the strain through the cross-section thickness. Taking this into account the main scope of this work is to understand, describe, predict and optimise the pseudo-ductile flexural response of symmetric ±45° angle-ply laminates consisting of unidirectional and continuous CFRP plies. The outcome of three-point bending tests is reviewed analytically and experimentally. The analytical study considers the different behaviour of the material under tension and compression as well as the neutral fibre deviation from the mid-height plane. During testing the full normal strain field is acquired by means of a DIC system while strain-rosettes help to complete the data. The post-process based on microscopic characterization using SEM technology allows to observe the procedure of damage initiation and its evolution. Finally, the determination of the stacking sequences that minimise the bending-twisting coupling but favour the pseudo-ductile response is developed applying optimisation techniques with design purposes.
Crystallization and morphological and crystal structures of PP in an in situ microfibrillar composite of modified PA66 with PP Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-19 Linghe Cheng, Jingwu Wang
An in situ-profiled microfibril-reinforced composite of modified polyamide 66 (mPA66) with polypropylene (PP) was prepared using a non-conventional compatibilization technique. The scanning electron microscope morphological observations showed in situ-generated, profiled microfibrils with a non-uniform diameter distribution and very rough surfaces with many pits and knots. The pits and knots were confirmed by the compatibilizer diffusion determined by the energy dispersive spectrum analysis. The presence of the PA66-profiled microfibrils shows the significant nucleation ability of the PP crystallization. Differential scanning calorimetry observations illustrated that the profiled microfibrils can accelerate the crystallization rate and increase the crystallization temperature. Obvious transcrystallization layers were observed through a polarized optical microscope. The β-crystalline phase of PP and larger, long period lamellar stacks were identified by small and wide-angle X-ray scattering measurements, respectively. These observations were very different from those of the simply blended samples of PP/PA66 in the presence or absence of the compatibilizer. Thus, the profiled microfibrils and improved interface adhesion may account for the powerful influence of PP on the crystallization and crystal structure.
Glass fiber/epoxy composites with integrated layer of carbon nanotubes for deformation detection Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-16 P. Slobodian, S. Lloret Pertegás, P. Riha, J. Matyas, R. Olejnik, R. Schledjewski, M. Kovar
An entangled multiwalled carbon nanotube film (Buckypaper) embedded in a polyurethane membrane was integrated into a glass fiber reinforced epoxy composite by means of a vacuum infusion to become a part of the composite and to give it a strain self-sensing functionality. In order to increase the strain sensing, pristine nanotubes were either oxidized by KMnO4 or Ag particles were attached to their surfaces. Moreover, the design of the carbon nanotube/polyurethane sensor allowed a formation of a film of micro-sized cracks, which increased its reversible electrical resistance and resulted in an enhancement of the strain sensing. Prestaining of the sensor with Ag-decorated nanotubes increased its sensitivity to strain, which was quantified by a gauge factor, more than hundredfold in comparison with the sensor with pristine nanotubes. The tests revealed that the integrated strain sensing exhibited a long-term electromechanical stability, which was linked to the level of strain in the host glass fiber/epoxy composite.
Improved electromechanical properties of silicone dielectric elastomer composites by tuning molecular flexibility Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-14 Dan Yang, Shuo Huang, Mengnan Ruan, Shuxin Li, Yibo Wu, Wenli Guo, Liqun Zhang
Silicone rubber (SR) composites exhibited significantly improved electromechanical properties via tuning the molecular flexibility by adding plasticizer. To decrease the enhanced elastic modulus of SR composites filled with high-dielectric-constant BaTiO3 (BT) particles, silicone oil (SO) plasticizer was incorporated into the BT/SR composite to weaken the intermolecular interactions and break the structure of the filler network as result of swelling effect. The obviously decreased elastic modulus resulted in a high electromechanical sensitivity β and a relatively large actuated strain of 10.6% for 20 phr BT/SR composite filled with 50 phr SO at a low electric field of 25 kV/mm, approximately 380% increase compared to that of pure SR at the same electric field of 25 kV/mm. The result indicates that tuning flexibility of composites is a good strategy to obtain high-performance dielectric elastomers.
Investigations on electrophoretic deposition of carbon nanotubes on glass textures to improve polymeric composites interface Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-14 A. Haghbin, G.H. Liaghat, A.M. Arabi, H. Hadavinia, M.H. Pol
Multiscale prediction of thermal conductivity for nanocomposites containing crumpled carbon nanofillers with interfacial characteristics Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-13 Seong Yun Kim, Han Gyeol Jang, Cheol-Min Yang, B.J. Yang
The importance of the thermal conductivity of engineering plastics reinforced with nanofillers is increasing in various industries, and the need for a model with which to make reliable predictions continues. We propose a micromechanics-based multiscale model that considers multi-shaped nanofillers to predict the thermal conductivity of composites. The distribution of each phase is assumed to be probabilistically distributed, and the Kapitza resistance at the interface between the filler and matrix was calculated by means of a molecular dynamics simulation. A polybutylene terephthalate (PBT) composite system embedded with multi-walled carbon nanotubes (MWCNTs) was used in a specific simulation. Composites containing MWCNTs of different lengths were also fabricated to obtain appropriate experimental results for the verification of the proposed model. Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and field-emission scanning microscopy (FE-SEM) were carried out to confirm that the selected materials could suitably be compared. Finally, the proposed model was applied to the finite element method to examine the heat flux of the composites according to the constitutive properties, and their results were compared to the experimental results.
Virtual testing framework for hybrid aligned discontinuous composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-13 J. Henry, S. Pimenta
The inherent brittleness of conventional high-performance composites can be addressed by the use of discontinuous fibres or hybridisation of fibre-types. In this paper, we propose the first models in the literature to predict the stress-strain curve of hybrid discontinuous composites, with either a brick-and-mortar or an intermingled-fibre microstructure. The models consider a shear-lag stress-transfer between the hybrid reinforcement units, and show that this stress transfer becomes less efficient with hybridisation. The model for intermingled-fibre hybrids also considers stochastic fibre strengths and fibre fragmentation, and can therefore predict a brittle or pseudo-ductile response of hybrid discontinuous composites as observed experimentally, as well as hybrid effects. These models can be used to perform virtual testing and microstructural design of hybrid aligned discontinuous composites.
Comparison of ATH and SiO2 fillers filled silicone rubber composites for HTV insulators Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-09 Yang Xue, Xiao-fei Li, Dong-hai Zhang, Hao-sheng Wang, Yun Chen, Yun-fa Chen
To enhance the electrical and mechanical properties of silicone rubber (SIR) in the field of high-voltage insulation, conventional fillers such as aluminum hydroxide (ATH), fumed silica and precipitated silica have been used for many years. In this work, SIR composites filled with ATH, irregular SiO2 (IS) and sphere SiO2 (SS) were prepared by mechanical blending, and the effects of filler type and filler shape on mechanical, electrical and thermal properties of SIR composites were systematically investigated. Compared with ATH-SIR composites, SS-SIR composite exhibited better electrical and mechanical properties. It showed that the tensile strength of SS-SIR composites was up to 6.6 MPa, which was nearly 2-folded compared to ATH-SIR composite. According to the loss tangent results in combination with tensile fracture surface observation, the interfacial interaction between SiO2 fillers and SIR is stronger than that between ATH and SIR, and the dispersion is better in SiO2 fillers filled SIR composites than that in ATH filled composite. The breakdown strength of ATH-SIR composite is only 18.9 kV mm−1, while those of IS-SIR and SS-SIR composites are 24.9 and 24.8 kV mm−1, respectively. Among the three SIR composites, SS-SIR composite has lowest dielectric permittivity and dielectric loss. Compared with ATH-SIR composite, the SiO2 fillers filled SIR composites have the lower thermal conductivity ranging from 30 °C to 150 °C, but they exhibit the better arc aging resistance due to the good thermal stability and thermal conducting property at high temperature. Moreover, the SS-SIR composite exhibits the better arc aging resistance than IS-SIR composite.
Microscopical observations of inter-fibre failure under tension Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-09 Elena Correa, María Inmaculada Valverde, María Luisa Velasco, Federico París
The numerical study of the inter-fibre failure at micromechanical level predicts the appearance of different stages in the development of this damage mechanism; these studies have also allowed the main features of each stage (such as the interfacial debond length and the kinking angle) to be identified. The development of experimental studies aiming to check the relevance of the aforementioned numerical results is crucial. Based on this, this research focused on the tensile test under different loading levels of specimens manufactured from carbon-epoxy cross-ply symmetrical laminates. The microscopic observation of the 90° layers leads to the analysis of the appearance of the transverse cracks as a function of the load, the identification of the previously numerically predicted stages of the mechanism of damage, the measurement of key parameters and the evaluation of the influence of nearby fibres. A clear connection between the numerical and experimental results has been found.
Poly (ether ether ketone) - Silicon carbide composite adhesives for elevated temperature applications of stainless steel joints Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-09 Ajay Kumar Kadiyala, Jayashree Bijwe
In the present work, the performance of a series of adhesives based on poly (ether ether ketone) (PEEK)/reinforced with micro-sized silicon carbide (SiC) particles for metal-metal joints was investigated. The size effect for SiC particles was studied by developing two composite adhesives with 3 wt. % of nanoparticles (NPs) (50–60 nm), and other with an equal amount of microparticles (MPs) (20 μm). The influence of particles on retention of adhesive strength at elevated temperature was studied in detail. The inclusion of MPs increased the bond strength of adhesives almost by 2 times and 15 wt. % was found to be optimum. At elevated temperatures, the adhesive strength decreased for all compositions. Interestingly the adhesive strength of composite adhesive at 300 °C was similar to the adhesive strength of virgin PEEK at ambient temperature. MPs performed better than NPs, which was correlated to agglomeration and shape of particles. SEM studies revealed that inclusion of hard fillers led to crack growth inhibition and resisting shearing during lap shear test of joints.
Enhanced thermal conductivity and mechanical property through boron nitride hot string in polyvinylidene fluoride fibers by electrospinning Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-09 Dong-Li Zhang, Jun-Wei Zha, Wei-Kang Li, Chao-Qun Li, Si-Jiao Wang, Yongqiang Wen, Zhi-Min Dang
The electrospun polyvinylidene fluoride (PVDF) based modified boron nitride (m-BN) composite with high thermal conductivity and flexibility mechanical property was successfully fabricated by electrospinning method. The uniform dispersion and ordered orientation of m-BN in the m-BN/PVDF composites form a hot string, denoted as a series of thermal conduction fillers, in the direction of the fiber. Hence, the thermal conductivity of the m-BN/PVDF film could reach to 7.29 W m−1K−1 with the addition of 30 wt% m-BN. Besides, the obtained composites also show improved mechanical properties with the tensile strength of 24.06 MPa, low dielectric permittivity of 2.45 and dielectric loss of 0.0242 @ 103 Hz. Therefore, this work provides a new route to prepare the high thermal conductivity films with potential application as flexible power devices.
Evaluation of elastic-plastic response of discontinuous carbon fiber-reinforced thermoplastics: Experiments and considerations based on load-transfer-based micromechanical simulation Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-06 M. Nishikawa, A. Fukuzo, N. Matsuda, M. Hojo
The present study investigated nonlinear elastic-plastic stress-strain relationships of discontinuous carbon fiber-reinforced thermoplastics (CFRTPs) using experiments and numerical simulations. In the experiments, we conducted uniaxial tensile tests and three-point bending tests for two types of CF/PA6 (carbon fiber/polyamide 6) specimen: injection-molded specimens with short fiber length and aligned fiber orientation, and compression-molded specimens with long fiber length and random fiber orientation. Comparison of the experiment results indicated that the injection-molded specimens exhibited a nonlinear stress-strain response, while the compression-molded specimens exhibited an almost linear response. These results implied that long discontinuous fibers effectively increased the yielding point of composites, even if the composites had random fiber orientation, which eliminated orientation dependence on mechanical properties of the composites. Furthermore, we attempted to simulate elastic-plastic stress-strain relationships of discontinuous CFRTPs in an effort to understand the effect of the microstructure, including fiber length. For this purpose, we employed fiber-based simulations to deal with the microstructure of fibers and matrix and the constitutive law of the matrix. The simulated results indicated that fiber length influences the nonlinearity of the stress-strain relationships of discontinuous CFRTP composites.
Cellulose nanofiber aerogels impregnated with bio-based epoxy using vacuum infusion: Structure, orientation and mechanical properties Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-06 Tuukka Nissilä, Sakari S. Karhula, Simo Saarakkala, Kristiina Oksman
Cellulose nanofiber aerogels were used as preforms that were impregnated with a bio-epoxy resin via a widely used vacuum infusion process. The simple and straightforward nanocomposite processing approach resulted in an almost 70% improvement in the storage modulus of the polymer with only an 11.7 wt% cellulose nanofiber content. The nanofibers were well dispersed in the polymer matrix and the fiber structures were anisotropically aligned. The impregnation time of the aerogels was also significantly lower than that of the more commonly used nanopapers. It was thus shown that environmentally friendly and mechanically robust nanocomposites could be produced by impregnating cellulose nanofiber aerogels with a thermosetting resin using a processing approach that has potential to be scaled up for commercial use.
Sensitivity, influence of the strain rate and reversibility of GNPs based multiscale composite materials for high sensitive strain sensors Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-05 R. Moriche, A. Jiménez-Suárez, M. Sánchez, S.G. Prolongo, A. Ureña
The addition of functionalized graphene nanoplatelets (f-GNPs) into the epoxy resin of glass fiber multiscale composite materials creates an electrically conductive network. This electrical network is highly sensitive to strain induced in the material. For this reason, it is a competitive material to be used in structural health monitoring (SHM). Sensitivity of multiscale composite materials is ∼50 under tensile loads and the behavior under compression loads differs, making possible the detection of different load conditions. Independency of the strain rate is related to the enhanced interface between f-GNPs and the epoxy matrix due to functionalization. Additionally, the electrical behavior is reversible without the loss of efficiency in sensorial properties.
A linear and large-range pressure sensor based on a graphene/silver nanowires nanobiocomposites network and a hierarchical structural sponge Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-02 Xuchu Dong, Yong Wei, Song Chen, Yong Lin, Lan Liu, Jing Li
It is challenging to manufacture pressure-sensing materials that possess linearly sensitive regime, high sensitivity, and large-range detection for the development of artificial intelligence products. Herein, a very simple approach is proposed to fabricate piezoresistive sensors based on hierarchical structure sea sponges and composites conductive networks of polydopamine reduced graphene oxides and silver nanowires. The hierarchical structures of porous sea sponges including the contacting of multi-scale porous skeletons and the bending of nodes vary synchronously, resulting in the linear relationship between applied compress strain and resistances, Moreover, the as-prepared pressure sensor exhibits a high sensitivity (S = 0.016 kPa−1 at 0-40 kPa) and a large area detection range (gauge factor = 1.5 at 0-60% strain). The synergetic effect of the composites conductive network endows the sensor with excellent reproducibility (>7000 loading/unloading cycles) and fast response time (<54 ms). In addition, demonstrate various applications of pressure sensor for health monitoring ranging from human leg to foot activities (such as toes on points, Restless Legs Syndrome (RLS) and walking).
Effect of electrical stress on glass fiber reinforced polymer used in high voltage composite insulator under wet environment Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-02 Yanfeng Gao, Xidong Liang, Yingyan Liu
The effect of electrical stress on glass fiber reinforced polymer under wet condition has been investigated in the present study. A specially designed and fabricated test setup was used through which the current passing through the GFRP rod during the test was recorded. Based on the changes in morphology of GFRP rod surface and development trend of current, the degradation process of GFRP rod caused by electrical stress under wet condition was divided into four consecutive stages, namely degradation inception stage, hydrolysis stage, carbonization stage and breakdown stage. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and X-ray Photoelectron Spectroscopy (XPS) analyses were employed to provide the physical and chemical properties of GFRP at different stages. The results showed that the degradation process of GFRP caused by electrical stress under wet condition progressively developed in the form of degraded channel, in which the epoxy resin matrix deteriorated significantly. The occurrences of hydrolysis, oxidation, pyrolysis and carbonization of epoxy resin matrix could be observed sequentially in the degradation process of GFRP during the test. With the development of the degradation process of GFRP, the content of epoxy resin matrix continued to decrease and the relative content of highly oxidized carbons (C-O, C=O and O-C=O) in epoxy resin matrix on GFRP surface increased before the carbonization process and then decreased in the carbonization process. The present study is helpful for better understanding of the electrical performance of GFRP used in high voltage composite insulator as well as in other electrical applications.
Effect of discontinuities in bamboo fibre reinforced epoxy composites Compos. Sci. Technol. (IF 4.873) Pub Date : 2017-12-02 D. Perremans, E. Trujillo, J. Ivens, A.W. Van Vuure
This paper performs a systematic study of the effect of various unidirectional fibre patterns, ranging from different overlapping lengths of adjacent fibre bundles to a complete randomization of the position of individual fibre ends. The study is benchmarked with the mechanical behaviour of a fully continuous unidirectional bamboo fibre-epoxy composite and will show the feasibility of using UD discontinuous technical bamboo fibres in continuous preforms for high-end composites applications. The study shows that the tensile stiffness is hardly influenced by the discontinuity patterns, while the introduction of randomized fibre end discontinuities (individual fibres with segment length 50 mm) leads to a preservation of 85% of the longitudinal tensile strength in comparison with a UD continuous bamboo fibre composite.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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