Synergistic Toughening Effect Research Articles

Synergistic delamination toughening of composites using multi-scale carbon reinforcements

Multi-scale toughening is a key strategy employed by biological systems, made of intrinsically brittle constituents, to achieve high damage tolerance. This paper presents an investigation of the synergistic enhancements to the mode I interlaminar fracture toughness of fibre-polymer composite laminates using multi-scale carbon reinforcements. By combining carbon nanofibres (CNFs) dispersed in the matrix and z-pins in the laminate thickness at various contents, an extra mechanism of energy dissipation occurs. This additional mechanism synergistically improves the laminate's resistance to delamination growth under mode I loading. Addition of the nanofibres in the matrix increases the interfacial strength and frictional energy dissipation during z-pin pull-out, thus generating a greater-than-additive toughening effect that would not have existed should either the nanofibres or the z-pins been deployed alone. The results reveal that the magnitude of the synergistic toughening effect was dependent on the volume fraction and combinations of CNFs and z-pins used; where synergy values ranged between 24 and 69% over the expected additive toughness value. A numerical model was developed to successfully predict the crack growth resistance and the synergistic toughening effect with filler content of the multi-scale composites.

Synergistic Toughening Effect of Nucleating Agent and Annealing Treatment and Morphological Research on Block Copolymerization Polypropylene

ABSTRACTThe toughening effects of α and β nucleating agents (α-NA and β-NA) and annealing treatment on block copolymerization polypropylene (PPB) were ascertained. The synergistic effect of β-NA and the annealing treatment at 130°C for 3 h impacted the toughness greatly for all test temperatures (−15, 0 and 23°C), specifically, the notched Izod impact strength tested at −15°C increased from 7.3 kJ/m2 to 30.1 kJ/m2. Moreover, the addition of α-NA or the annealing treatment also improved the toughness of PPB. The changes of the crystallite morphology and multiphase structure play an important role on the toughening.

Microstructure and toughening mechanisms of Al2O3/(W, Ti)C/graphene composite ceramic tool material

To toughen the Al2O3 matrix ceramic materials, Al2O3/(W, Ti)C/graphene multi-phase composite ceramic materials were fabricated via hot pressing. The effects of the graphene nanoplates (GNPs) content on microstructure and mechanical properties were investigated. Results showed that the fracture toughness and flexural strength of the composite added with just 0.2 wt% GNPs were markedly improved by about 35.3% (~ 7.78 MPa m1/2) and 49% (~ 608.54 MPa) respectively compared with the specimens without GNPs while the hardness was kept about 24.22 GPa. However, the mechanical properties degrade with the further increase of GNPs’ content owing to the increased defects caused by agglomeration of GNPs. Synergistic toughening effects of (W, Ti)C and GNPs played an essential role in improving the fracture toughness of composites. By analyzing the microstructures of fractured surface and indentation cracks, besides GNPs pull-out, crack deflection, crack bridging, crack branching and crack arrest, new toughening mechanisms such as break of GNPs and crack guiding were also identified. Furthermore, interface stress can be controlled by means of stagger distributed strong and weak bonding interfaces correlated with the distribution of GNPs.

Bio-inspired layered nanolignocellulose/graphene-oxide composite with high mechanical strength due to borate cross-linking

Inspired by the borate cross-linking used by higher plants to strengthen their intercellular structure, high mechanical strength-layered composites based on borate cross-linked nanolignocellulose/graphene-oxide platelets were developed. Borate treatment and graphene deposition on nanolignocellulose surface were carried out by a mechanochemical method. The borate content is used in very low in these composites. The orderly layered structures produced by the flow-directed assembly of individual nanolignocellulose/graphene oxide platelets resulted in a synergistic toughening effect. The bending strength and elasticity modulus of the produced composites were ∼1.5 times higher than those of pure nanolignocellulose; they were also superior to those of lignin-based materials and comparable to those of medium density fiberboard (MDF) with resin. Such high-strength layered composites have potential as load-bearing materials in structural applications.

Bioinspired Reduced Graphene Oxide/Polyacrylonitrile‐Based Carbon Fibers/CoFe2O4 Nanocomposite for Flexible Supercapacitors with High Strength and Capacitance

AbstractFor the first time, zero‐dimensional (0D) CoFe2O4 nanoparticles, one‐dimensional (1D) polyacrylonitrile‐based carbon fibers (PBCF), and two‐dimensional (2D) reduced graphene oxide (RGO) nanosheets were used as building blocks to create an integrated ternary nanocomposite paper with a nacre‐like microstructure for flexible supercapacitors. Inspired by the “mortar‐brick” toughening mechanism of nacre, hydrogen and covalent bonding were further introduced into the bioinspired paper with 0D CoFe2O4, 1D PBCF, and 2D RGO to realize increased mechanical properties through the synergistic toughening effects of the interfacial interactions of hydrogen and covalent bonding. These collaboratively lead to enhanced mechanical properties such as high tensile strength, exceptional toughness, and eminent electrical conductivity. When used as a free‐standing flexible electrode, the bioinspired interconnected 3D network exhibits an outstanding volumetric capacity of 240 F ⋅ cm−3 at 10 mV ⋅ s−1 and an excellent cycle life of 2000 cycles for a flexible symmetric supercapacitor device (SSCD). Remarkably, the fabricated flexible SSCD can be cycled reversibly in the voltage range of −1 to 0 V and shows a maximum energy density of 33.33 mW ⋅ h cm−3, suggesting great potential for practical applications in flexible energy storage devices.

Synergistic effects of thermoplastic and nanoclay on the performance properties and morphology of epoxy resin

The present work investigates the properties and morphology of nanobent/poly(methyl methacrylate) (PMMA)/epoxy resin hybrid nanocomposites which were successfully prepared by solvent and ultrasonication methods. Nanobent ZS1 were added in amount of 1, 2, 3, and 4 wt% and 5, 10, and 15 wt% for PMMA. The fracture toughness (impact strength and critical stress intensity factor) and flexural properties were evaluated for epoxy composites. Obtained results showed improvement of the epoxy resin mechanical properties due to the addition of PMMA and nanobent. Composites containing 5 wt% of polymeric modifier or 1 wt% nanobent exhibited maximally improved properties. In the case of hybrid composites, synergistic effect was obtained with flexural strain at break and flexural energy to break of hybrid nanocomposite based on 1 wt% nanobent and 5 wt% PMMA. However, epoxy nanocomposites based on 2 wt% nanobent and 5 wt% PMMA showed synergism with IS and brittle fracture energy toward the composites with one modifier. Fourier transform infrared (FTIR) spectra analysis confirmed interactions between incorporated modifiers and reactive groups of the epoxy matrix. Moreover, scanning electron microscope (SEM) micrographs of hybrid epoxy nanocomposites exhibited a morphology with large plastic yielding associated with significant roughness of the fracture surface with embedment of nanobent in the polymer system. This study clearly demonstrates that the improvement of mechanical properties of the epoxy resin could be attributed to the synergistic toughening effect of PMMA and nanobent without deterioration of thermal stability. POLYM. COMPOS., 39:E2540–E2551, 2018. © 2018 Society of Plastics Engineers

Multiple Synergistic Toughening Graphene Nanocomposites through Cadmium Ions and Cellulose Nanocrystals

AbstractRobust and functional graphene‐based nanocomposites are attractive in flexible electric devices. Herein, a strong and conductive bioinspired graphene‐based nanocomposite is demonstrated via multiple synergistic toughening effect from graphene oxide (GO), cellulose nanocrystals (CNC), and cadmium ion (Cd2+). The multiple synergistic toughening effect can be realized from building blocks of 2D GO nanosheets and 1D CNC, interface interactions of hydrogen bonding from CNC and ionic bonding from Cd2+, resulting in integrated graphene‐based nanocomposites with high strength, and toughness as well as electrical conductivity. This ternary synthetic graphene‐based nanocomposite possessing outstanding physical properties provides a clear vision in the application of flexible electric devices. Furthermore, this bioinspired strategy could also serve as a guideline for the development of high‐performance graphene‐based nanocomposites in the future.

Synergistic toughening of nanocomposite hydrogel based on ultrasmall aluminum hydroxide nanoparticles and hydroxyapatite nanoparticles

The development of hydrogels combining superior mechanical property attracts researchers' attention in recent years. Here, a novel nanocomposite hydrogel is prepared by one‐step photo‐polymerization of acrylic acid (AA) and N,N‐dimethylacrylamide (DMAA) in the presence of hydroxyapatite nanoparticles (HAp NPs) and aluminum hydroxide nanoparticles (Al(OH)3 NPs). The resulting transparent hydrogel exhibits ultrahigh toughness of 28.3 MJ m−3, high strength of 2.8 MPa, large elongation of 1300%, excellent self‐recovery and good biocompatibility. The crosslinking mechanism is contributed to the ionic coordination interaction between cations absorbing on the surface of nanoparticles and carboxyl groups of the polymer chain, and the synergistic toughening effect between HAp NPs and Al(OH)3 NPs is responsible for improving the strength and toughness simultaneously. Furthermore, this synergistic toughening strategy may provide a universal method for designing and constructing high strength nanocomposite hydrogels in many applications, especially for artificial cartilages. POLYM. COMPOS., 40:942–951, 2019. © 2018 Society of Plastics Engineers

Electrically Insulated Epoxy Nanocomposites Reinforced with Synergistic Core–Shell SiO2@MWCNTs and Montmorillonite Bifillers

AbstractWith unique physicochemical properties, multiwalled carbon nanotubes (MWCNTs) have enabled major achievement in polymer composites as reinforcing fillers. Nevertheless, high conductivity of raw MWCNTs (R‐MWCNTs) limits their wider applications in certain fields, which require outstanding thermal conductivity, mechanical, and insulation properties simultaneously. In this article, silica (SiO2) coated MWCNTs core–shell hybrids (SiO2@MWCNTs) and organically modified montmorillonite (O‐MMT) are employed to modify epoxy (EP) simultaneously. The epoxy‐clay system is cured by using anhydride curing agent. The impact strength and flexural strength of final nanocomposites are greatly improved. Meanwhile, the final composites remain in high electrical insulation. Compared to mixed acid treated MWCNTs (C‐MWCNTs) (0.5 wt%)/EP nanocomposites, the volume resistivity of the O‐MMT(4 wt%)/SiO2@MWCNTs(0.5 wt%)/EP nanocomposites increases more than six orders of magnitude. Synergistic toughening effect occurs when using core–shell SiO2@MWCNTs and MMT bifillers. The electrical insulation is attributed to the suppressed electron transport effect by SiO2 layer on the CNTs surface, and the blocked conductive CNTs network by the buried 2D structural O‐MMT. The SiO2@MWCNTs core–shell hybrids also benefit to decrease the dielectric constant and dielectric loss of CNTs/EP composites. This work provides guidance to using CNTs as reinforcement fillers to toughen the polymers for electric insulating applications.

Preparation and Characterization of (Mo, W)Si2-SiC Composites by In Situ Microwave Reaction Sintering

MoSi2-based materials are considered potentially useful for making high-temperature structural parts. In this work, (Mo, W)Si2-SiC composites have been successfully prepared in situ by microwave reaction sintering of the elemental reactants. Benefiting from the lower sintering temperature and faster densification procedure, the as-prepared composites have finer microstructures compared to the analogs prepared by conventional reaction sintering, resulting in a significant improvement of mechanical properties. The flexural strength, Vickers hardness and fracture toughness of 10%SiC/10%WSi2/80%MoSi2 are as high as 302.81 MPa, 8.55 GPa and 8.90 MPa m1/2, respectively, which are also better than those of monolithic MoSi2 and 10%SiC/90%MoSi2 composite due to the synergistic strengthening and toughening effects of W alloying and SiC second phase.

Synergistic Toughening Effect of Olefin Block Copolymer and Highly Effective β-Nucleating Agent on the Low-Temperature Toughness of Polypropylene Random Copolymer

In the present work, the synergistic toughening effect of olefin block copolymer (OBC) and a highly effective β nucleating agent (NA)-Calcium salt of pimelic acid (CaPim) on polypropylene random copolymer (PPR) was studied. Mechanical tests showed that with the introduction of 0.1 wt % CaPim, there was almost no change in the low-temperature (below 0 °C) toughness of PPR. Although introduction of OBC could obviously improve the toughness at 23 °C, high content is needed to effectively toughen PPR at low temperature. By coadding OBC and CaPim, PPR/OBC/NA blends showed not only great enhancement of toughness over the temperature range tested but also lower OBC content of undergoing brittle-ductile transition compared with PPR/OBC blends. The crystalline structure, crystallization behavior and phase morphology were investigated to explore the possible synergistic toughening mechanism. The high β-crystal content formed in PPR matrix and the finer distribution of OBC phase might be responsible for the superior...

Super toughened immiscible poly(l-lactide)/poly(ethylene vinyl acetate) (PLLA/EVA) blend achieved by in situ cross-linking reaction and carbon nanotubes

Toughening modification is always one of the main subjects of structural materials. A small quantity of dicumyl peroxide (DCP) and carbon nanotubes (CNTs) were simultaneously introduced into an immiscible poly(l-lactide)/poly(ethylene vinyl acetate) (PLLA/EVA) blend through melt compounding processing. The presence of chemical cross-linking structure in the polymer components and the physical network of CNTs were demonstrated through a series of direct and indirect characterization methods. The results demonstrated that DCP and CNTs exhibited synergistic toughening effects and the dynamically vulcanized blend composites exhibited excellent impact toughness. This work provides an alternative way to improve the impact toughness of an immiscible polymer blends.

Synergistic toughening effect of β-nucleating agent and long chain branching on polypropylene random copolymer

β-nucleated long chain branched (LCB) polypropylene random copolymers (PPRs) were prepared via reactive extrusion by introducing β nucleating agent (NA), dicumyl peroxide (DCP) and various contents of 1, 6-Hexanediol diacrylate (HDDA) into PPR. Results of Fourier infrared spectroscopy (FTIR) and the rheological properties demonstrate the existence of LCB polypropylene. Mechanical properties including impact strength, tensile strength and elongation at break were studied. The crystal structure, morphology and crystallization behavior were investigated via wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM) and differential scanning calorimetry (DSC). Non-isothermal crystallization kinetics using the Jeziorny method was also studied. The results show an increased LCB degree with increasing HDDA amount. For the sample with a moderate LCB level, synergistic toughening effect of NA and LCB is achieved without deterioration of yield strength or elongation at break, partially because of its higher β-phase content and much smaller spherulite size. It exhibits the minimum values of Tc and Zc1, and the maximum values of t1/2 and n1 in the primary stage of crystallization, regardless of the cooling rate, indicating a slower crystallization rate and more complicated nucleation and crystal growth model.

Integrated ternary artificial nacre via synergistic toughening of reduced graphene oxide/double-walled carbon nanotubes/poly(vinyl alcohol)

The synergistic toughening effect of building blocks and interface interaction exists in natural materials, such as nacre. Herein, inspired by one-dimensional (1D) nanofibrillar chitin and two-dimensional (2D) calcium carbonate platelets of natural nacre, we have fabricated integrated strong and tough ternary bio-inspired nanocomposites (artificial nacre) successfully via the synergistic effect of 2D reduced graphene oxide (rGO) nanosheets and 1D double-walled carbon nanotubes (DWNTs) and hydrogen bonding cross-linking with polyvinyl alcohol (PVA) matrix. Moreover, the crack mechanics model with crack deflection by 2D rGO nanosheets and crack bridging by 1D DWNTs and PVA chains induces resultant artificial nacre exhibiting excellent fatigue-resistance performance. These outstanding characteristics enable the ternary bioinspired nanocomposites have many promising potential applications, for instance, aerospace, flexible electronics devices and so forth. This synergistic toughening strategy also provides an effective way to assemble robust graphene-based nanocomposites.

Synthesis and mechanical properties of high impact polystyrene with in situ bulk polymerization toughened by one‐pot Nd‐based styrene–isoprene–butadiene terpolymer rubber

ABSTRACTHigh impact polystyrene (HIPS) resins were obtained with in situ bulk polymerization toughened by styrene–isoprene–butadiene terpolymer rubber (SIBR). SIBR prepolymer was prepared through selective polymerization of styrene (St), isoprene (Ip), and butadiene (Bd) in St with [Nd]/[Al]/[Cl] catalyst. Nd‐based catalyst exhibited more favorable activity toward conjugated diene other than St, resulting in St solution of random SIBR with high cis‐1,4 stereoregularity and low St content, which was directly exposed to the free radical polymerization of St to generate HIPS. Effect of toughened rubber and the initiators [difunctional (D2) and trifunctional (T3)] were examined to attain HIPS possessing mechanical properties as follow: impact strength, 0.9–24.8 kJ/m2; tensile strength, 16.0–27.5 MPa; and elongation at break, 7.4–107.0%. Increasing SIBR matrix in HIPS improved the impact strength and decreased tensile strength. The fracture surface morphologies of HIPS specimens were studied by notched impact tests and scanning electron microscopy (SEM), illustrating that the incremental SIBR matrix presented synergistic toughening effect of crazing to enhance the ductile fracture behavior. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43979.

Synergistic toughening effect of chlorinated polyethylene and acrylic resin on SAN/ASA blends at low temperature

ABSTRACTStyrene–acrylonitrile copolymer (SAN)/acrylonitrile–styrene–acrylate terpolymer (ASA) blends (75/25, w/w) were toughened by blending with chlorinated polyethylene (CPE) and acrylic resin (ACR) at three different temperatures (−30, 0, and 25 °C). When the testing temperature was 0 and 25 °C, CPE played a key role in improving the impact strength of blends instead of ACR. However, an obvious synergistic toughening effect of CPE and ACR was observed at −30 °C: when both 10 phr CPE and 15 phr ACR were added, the impact strength of the blends reached a peak at 7.50 kJ/m2, which was about two to three times higher than when 25 phr CPE or 25 phr ACR was introduced into the blends individually. Scanning electron microscopy, dynamic mechanical analysis, and surface energy measurements were used to investigate the toughening mechanism. Furthermore, other mechanical properties and the heat distortion temperatures were evaluated. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43958.

Bioinspired Ternary Artificial Nacre Nanocomposites Based on Reduced Graphene Oxide and Nanofibrillar Cellulose.

Inspired by the nacre, we demonstrated the integrated ternary artificial nacre nanocomposites through synergistic toughening of graphene oxide (GO) and nanofibrillar cellulose (NFC). In addition, the covalent bonding was introduced between adjacent GO nanosheets. The synergistic toughening effects from building blocks of one-dimensional NFC and two-dimensional GO, interface interactions of hydrogen and covalent bonding together result in the integrated mechanical properties including high tensile strength, toughness, and fatigue life as well as high electrical conductivity. These extraordinary properties of the ternary synthetic nacre nanocomposites allow the support for advances in diverse strategic fields including stretchable electronics, transportation, and energy. Such bioinspired strategy also provides a new insight in designing novel multifunctional nanocomposites.

In-situ toughened CFRP composites by shear-calender orientation and fiber-bundle filtration of PA microparticles at prepreg interlayer

Epoxy matrix toughened by polyethersulfone (PES) and polyamide (PA) microparticles was designed and the in-situ interlaminar toughened carbon fiber/epoxy composites were fabricated. Synergistic toughening effect of PES and PA on epoxy matrix was achieved due to semi-IPN structure of PES toughened matrix and uniform dispersion of PA microparticles. Shear-calender orientation of PA microparticles was found during prepreg processing and the microparticles remained on the surface of prepreg due to fiber-bundle filtration. The in-situ formed toughening interlayer of PA microparticles and interfacial bonding between PA and epoxy matrix were detected, which resulted in enhanced fracture toughness, CAI, and transverse flexural strength of the composite based on the PES/PA synergistically toughened matrix. SEM images of fracture morphology of the composite showed evidence of enhanced plastic deformation created by PES and PA, and crack deflection and bridging by PA microparticles.

Integrated Ternary Bioinspired Nanocomposites via Synergistic Toughening of Reduced Graphene Oxide and Double-Walled Carbon Nanotubes.

With its synergistic toughening effect and hierarchical micro/nanoscale structure, natural nacre sets a "gold standard" for nacre-inspired materials with integrated high strength and toughness. We demonstrated strong and tough ternary bioinspired nanocomposites through synergistic toughening of reduced graphene oxide and double-walled carbon nanotube (DWNT) and covalent bonding. The tensile strength and toughness of this kind of ternary bioinspired nanocomposites reaches 374.1 ± 22.8 MPa and 9.2 ± 0.8 MJ/m(3), which is 2.6 and 3.3 times that of pure reduced graphene oxide film, respectively. Furthermore, this ternary bioinspired nanocomposite has a high conductivity of 394.0 ± 6.8 S/cm and also shows excellent fatigue-resistant properties, which may enable this material to be used in aerospace, flexible energy devices, and artificial muscle. The synergistic building blocks with covalent bonding for constructing ternary bioinspired nanocomposites can serve as the basis of a strategy for the construction of integrated, high-performance, reduced graphene oxide (rGO)-based nanocomposites in the future.

Toughening effect of ultrahigh molecular weight polyethylene and compounded α/β nucleation agents on isotactic polypropylene by different processing methods

The improvement in the toughness of isotactic polypropylene by introducing ultrahigh molecular weight polyethylene and further blending it with compounded α/β nucleation agents were studied. According to the results, the polyethylene with higher molecular weight and dissolving method have affected the toughening of isotactic polypropylene. For isotactic polypropylene/nucleation agent blend, the Izod impact strength increases by 93.5% with a slight decrease in the tensile strength. When both nucleation agents and polyethylene are added, the synergistic toughening effect is more remarkable, and the Izod impact strength is about 232% higher than that of pure isotactic polypropylene.