Dispersion,thermal and mechanical properties of polypropylene/magnesium hydroxide nanocomposites compatibilized by SEBS-g-MA

Isotactic polypropylene (PP)/nano-magnesium hydroxide (nano-MH) composites with 10 wt.% maleic anhydride grafted styrene–ethylene-butylene–styrene tri-block copolymer (SEBS-g-MA) as a compatilizer were prepared by melt extrusion compounding and injection molding. The effects of SEBS-g-MA on dispersion of nano-MHs in PP matrix and interfacial adhesion were studied in order to prepare highly filled PP/MH nanocomposites. The results showed that SEBS-g-MA improved both dispersion of nano-MHs and interfacial adhesion in PP/MH nanocomposites with up to 40 wt.% nano-MHs. The elastic moduli of PP/SEBS-g-MA /MH nanocomposites increased marginally and tensile yield strengths were almost invariant with nano-MH loading. Significant impact toughening of these ternary nanocomposites was, however, achieved due to the cavitation of SEBS-g-MA/MH particles and expansion of voids as well as plastic deformation of the PP matrix.     

Structural characterization and thermal and mechanical properties of poly(propylene carbonate)/MgAl-LDH exfoliation nanocomposite via solution intercalation

Poly(propylene carbonate)/MgAl layered double hydroxide (PPC/MgAl-LDH) exfoliated nanocomposites were synthesized by solution intercalation of PPC into the galleries of organic modified MgAl-LDH (OMgAl-LDH) in cyclohexanone. The crystal morphological structures, thermal degradation behavior, and mechanical properties have been studied by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, and thermogravimetric analysis (TGA). The nanoscale dispersion of OMgAl-LDH layers in the PPC matrix has been verified by the disappearance of d_0 0 1 XRD diffraction peak of OMgAl-LDH and the observation of TEM image. The TGA data give evince that the thermal degradation temperature of the exfoliated PPC/MgAl-LDH nanocomposites with 1% OMgAl-LDH is 10 °C higher than that of pure PPC resin when 20% weight loss was selected as a point of comparison. The data from the mechanical test show that the tensile strength of the PPC/MgAl-LDH nanocomposites with 5% LDH is 36.9 MPa, which is 72% and 30% higher than those of pure PPC resin and simple mixed sample with the same content of LDH, and its Young’s modulus is 1303 MPa, which is 57% and 21% higher than those of the same two samples, respectively.     

Effects of organo-modified montmorillonite on the tribology performance of bismaleimide-based nanocomposites

Poly(allyl condensed polynuclear aromatic-bismaleimide) (ACOPNA–BMI) with different loadings of an organo-modified montmorillonite (OMMT) nanocomposites were successfully prepared via in situ suspension polymerization. Exfoliation/intercalation phenomena were detected using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Positive effects of the exfoliated platelets on the wearable and thermal behaviours were achieved by varying the OMMT load. The lowest friction coefficient of ACOPNA–BMI/2.0 wt.% OMMT was 0.46 at a wear rate of 0.508 × 10^− 6 mm³/Nm, which was superior to that of pure ACOPNA–BMI copolymer resin. The thermostabilities of the materials were assessed by thermogravimetric analysis (TGA). The temperature at the maximum rate of thermal decomposition of ACOPNA–BMI/3 wt.% OMMT was 480 °C, which was much higher than that of the pure ACOPNA–BMI copolymer (436 °C). The nanocomposite obtained, which is a suitable wearable material, can be widely used for protecting drilling tools in petroleum engineering applications due to its thermostability and good self-lubrication properties.     

Investigation of physical and chemical properties of polypropylene hybrid nanocomposites

Hybrid nanocomposites fabricated based on an optimized physical and chemical properties modified polypropylene (PP)/polypropylene grafted maleic anhydride (PP-g-MA) with varied concentrations (1–7 wt% at a step of 2 wt%) of organoclay, montmorillonite (MMT). The morphology of the nanocomposites was studied by scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It was found that partly intercalated and partly exfoliated structure (intercalated–exfoliated structures) existed in the system. The degree of exfoliation is a key factor to determine the reinforcement efficiency. The ratio of exfoliation to intercalation plays an important role in determining the properties of PP nanocomposites and only completely exfoliated silicate layers can significantly improve the properties. PP hybrid nanocomposites showed good thermal stability in the thermogravimetric analysis (TGA). Introduction of ∼3% MMT in the nanocomposites increased the onset temperature of degradation by 27.5 °C compared to that of pure PP, while the 5 wt% MMT resulted the maximum hardness in these nanocomposites. The solvent resistance of PP hybrid nanocomposites slightly increased with increasing the clay content.     

Influence of the epoxidation degree of a polystyrene–polybutadiene–polystyrene (SBS) triblock copolymer on the compatibilization with an organomodified nanoclay

In this work, the addition of organophilic-modified montmorillonite into polystyrene–polybutadiene–polystyrene (SBS) triblock copolymers was investigated with and without the use of epoxidized SBS as a compatibilization agent. The nanocomposites were prepared by melting mixture at 60 rpm and 130 °C. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), tensile tests, and dynamic-mechanical analysis (DMA). XRD and TEM showed the formation of an intercalated dispersion of clay platelets oriented on the SBS surface. The AFM showed the typical lamellar microstructure of the styrene and butadiene phases of SBS. The estimation of the average distance between the styrene lamellae by AFM analysis showed that the platelets are anchored between the phases, and this structural feature caused an increase in elastic modulus. DMA analysis showed that the T _g of butadiene decreased in the nanocomposites. The decrease of the T _g and the increase in the elastic modulus are correlated to mechanisms at the micro- and the macro-scales, respectively. The decrease in the T _g indicates flexibilization at the interface, whereas the intercalation of the platelets restricted the interphase macroscale deformation.     

Synergistic effect of carbon black and nanoclay fillers in styrene butadiene rubber matrix: Development of dual structure

Styrene butadiene rubber (SBR) based hybrid nanocomposites containing carbon black (CB) and organo-modified nanoclay (NC) was prepared. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the presence of intercalated, aggregated, and partially exfoliated structures. Incorporating 10 phr NC to the control SBR containing 20 phr CB resulted 153% increase in tensile strength, 157% increase in elongation at break and 144% stress improvement at 100% strain, which showed synergistic effect between the fillers. The dynamic modulus reinforcement of nanocomposites was examined by the Guth, Modified Guth, and Halpin–Tsai equations. For predicting CB filled nanocomposite modulus, the contribution of modified intercalated structure of clay and the ‘nano-unit’ (dual structure) comprising CB–NC should be considered.     

The origin of defects formation in nanosized zirconia

In the present work, we provide evidence of an increase in the Zr³⁺ paramagnetic center concentration under colloidal transformation in ZrO₂ prepared by the totally inorganic sol–gel method. The samples of thermally treated (100–950 °C in air) ZrO₂ precipitates and dried sol–gel products—xerogels—were examined by TEM, XRD, DTA, EPR and IR-spectroscopy. Under the same heat treatment condition, the concentration of Zr³⁺ (axially symmetric signal at g_⊥ = 1.977–1.979 and g₆ = 1.958–1.963) became higher in the xerogel samples rather than in precipitate samples and reached the maximum (∼ 10¹⁸ g^− 1 in xerogel) after calcinations at 500 °C in air.     

Mechanically improved and optically transparent polycarbonate/clay nanocomposites using phosphonium modified organoclay

The present study deals with the properties of polycarbonate (PC)/clay nanocomposites prepared through melt and solution blending at two different clay loadings (0.5 phr and 1 phr) with preserved optical transparency of PC. The organoclay was prepared by exchanging the Na⁺ ions presented in the clay galleries of Na-MMT with butyltriphenylphosphonium (BuTPP⁺) ions, and denoted as BuTPP-MMT. The outstanding thermal stability of the BuTPP-MMT (∼1.44 wt% loss at 280 °C, after 20 min), concomitant with the increase in gallery height from 1.24 nm to 1.83 nm, proved its potentiality as nanofiller for melt-blending with PC. The X-ray diffraction analysis (XRD) revealed the destruction of the ordered geometry of aluminosilicate layers in the nanocomposites. However, from direct visualization through transmission electron microscopy, a discernible amount of clay was found to be localised in PC matrix in the 1 phr clay loaded nanocomposites (TEM). The differential scanning calorimetric (DSC) study revealed a nominal increase in glass transition temperature (T_g) of the PC in the nanocomposites. The thermal stability of the nanocomposites was increased with increase in clay loading. The nanocomposites possessed improved tensile strength and modulus than that of the virgin PC and the properties were related to the amount of clay loading and degree of clay dispersion. The dynamic mechanical analysis (DMA) revealed that the storage modulus increased in both the glassy and rubbery region with increase in clay loadings in the nanocomposites. Moreover, the optical transparency of the PC was retained in the PC/clay nanocomposites without development of any colour in the nanocomposites.     

Superparamagnetic cobalt-ferrite-modified carbon nanotubes using a facile method

Cobalt ferrite (CoFe₂O₄)/carbon nanotube (CNT) magnetic nanocomposites were synthesized by a facile solvothermal method. X-ray powder diffractometry (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), High-resolution electron microscopy (HRTEM) analyses demonstrate that cubic CoFe₂O₄ nanoparticles were immobilized on the external surfaces of the CNTs. Vibrating sample magnetometer (VSM) measurements indicated that the nanocomposites at room temperature were superparamagnetic with a saturation magnetization of 29.6 emu g^?1.     

Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nanoclay-filled epoxy matrix

The mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading, and the improvement of flexural modulus was at the expense of a reduction in flexural strength. The quasi-static fracture toughness increased, whereas the impact fracture toughness dropped sharply with increasing the clay content.Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed the trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. Both the initiation and propagation values of mode I interlaminar fracture toughness of CFRP composites increased with increasing clay concentration. In particular, the propagation fracture toughness almost doubled with 7 wt% clay loading. A strong correlation was established between the fracture toughness of organoclay-modified epoxy matrix and the CFRP composite interlaminar fracture toughness.     

Properties of silane grafted polypropylene/montmorillonite nanocomposites

Polypropylene/montmorillonite nanocomposites were prepared by melt compounding using organosilane modified polypropylene (PP-g-VTES) as compatibilizing agent. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), tensile modulus, and Izod impact strength. Addition of PP-g-VTES improved clay dispersion, as shown by the distribution of platelets per particle, and improve the interaction between clay and polymer matrix. Crystallization peak temperature (T_p) was increased in 10 °C using PP-g-VTES as compatibilizing agent. However the crystallization process and its rate were unmodified. The tensile modulus of compatibilized nanocomposite is 1.5 times higher compared to pure PP.     

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (T_g) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T_5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10⁻² S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K.     

Combination effect of carbon nanotubes with graphene on intumescent flame-retardant polypropylene nanocomposites

A novel polypropylene (PP) nanocomposite was fabricated by the incorporation of intumescent flame retardant (IFR), carbon nanotubes (CNTs) and graphene into the PP matrix. Results from TEM indicate that IFR, CNTs and exfoliated graphene nanosheets are dispersed finely in the PP matrix, which is supported by the XRD analysis results. Thermogravimetric (TGA) results show that the addition of IFR, CNTs and graphene improved the thermal stability and the char yields of PP. The PP/IFR/CNTs/RGO nanocomposites, filled with 18 wt% IFR, 1 wt% CNTs and 1 wt% graphene, achieve the limiting oxygen index value of 31.4% and UL-94 V0 grade. Cone calorimeter data reveal that combustion behavior, heat release rate peak (PHRR) and average specific extinction area (ASEA) of PP decrease substantially when combination effects of IFR, CNTs and graphene intervene. For the PP/IFR/CNTs/RGO nanocomposites, the PHRR exhibits an 83% reduction and the time of ignition is delayed 40 s compared with neat PP.     

Investigation of the effect of nanoclay and processing parameters on the tensile strength and hardness of injection molded Acrylonitrile Butadiene Styrene–organoclay nanocomposites

Polymer–clay nanocomposites have attracted considerable interest over recent years due to their dramatic improved mechanical properties. In the present study, compatibility of Acrylonitrile Butadiene Styrene (ABS) and organically modified montmorillonite nanoclay (Cloisite 30B) and composition capability of them are investigated. Polymethylmethacrylate (PMMA) in varying amount (0, 2, and 4 wt%) is used as the compatibilizer. In order to produce nanocomposite parts, the material is first compounded using a twin-screw extruder and then injected into a mold. The effect of the nanoclay percentage and processing parameters on the tensile strength and hardness of nanocomposite parts is also explored using Taguchi Design of Experiments method. Nanoclay content (in three levels: 0, 2 and 4 wt%), melt temperature (in three levels: 190, 200 and 210 °C), holding pressure (in three levels: 80, 105 and 130 MPa) and holding pressure time (in three levels: 1, 2.5 and 4 s) are considered as the variable parameters. Moreover, distribution of nanoclay layers is analyzed using Wide Angle X-ray Diffraction (XRD) test. XRD results displayed that with the presence of PMMA, nanoclay in ABS matrix is compounded in more exfoliated and less intercalated dispersion mode. Adding PMMA also leads to a remarkable increase in the fluidity of the melt during injection molding process. Results also illustrated that nanocomposites with medium loading level (i.e. 2%) of nanoclay have the highest tensile strength, while the highest hardness number belongs to nanocomposites with 4 wt% nanoclay. Obtained results also indicated that injection temperature has the most important effect on tensile strength and hardness of ABS–clay nanocomposites.     

Role of silanized halloysite nanotubes on structural,mechanical properties and fracture toughness of thermoset nanocomposites

This study investigates the structure/property relationship of thermosetting unsaturated polyester (UPE) filled with pristine halloysite (HNT) and vinyltrimethoxysilane-treated halloysite nanotubes (s-HNT) nanocomposites. The dispersion of particles and morphological structures of the nanocomposites were examined using TEM and XRD analysis as well as Fourier Transform Infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) and mechanical properties were characterized. The evaluation of stress intensity factor (K_Ic) was measured based on linear elastic fracture mechanics (LEFM) and single-edge notch bending (SENB) geometry to identify the role of silanized halloysites on toughening improvement. It was found that modifying UPE matrix with HNT or s-HNT changed the crystalline structure of the UPE nanocomposites, indicating a high degree of halloysite orientation. Uniform dispersed halloysites are observed in the s-HNT/UPE versus skewed-like clusters in the HNT/UPE nanocomposite. The introduction of HNT or s-HNT up to 5 wt.% induced higher mechanical properties and improved fracture toughness associated with a shift in toughening mechanisms from a highly brittle fracture for neat UPE into matrix shear yielding and zone shielding mechanisms with the presence of halloysite particles in the nanocomposite.     

Microstructure characterization,mechanical properties,compressibility and sintering behavior of Al-B4C nanocomposite powders

In the present work, Al-xB₄C nanocomposite (x = 0, 1, 2, 3, 4 and 5 in wt%, having the average B₄C size of 50 nm) were prepared using a high-energy ball mill. The milling times up to 16 h were applied. Then, the microstructural evolutions, mechanical properties, compressibility and sintering behavior of nanocomposites were investigated. The changes in powders morphology and microstructure during the milling process were characterized by laser diffraction particle size analyzer (LDA), SEM, XRD, EDS and TEM techniques. Compressibility and sintering behavior of milled powders compacted under different pressures (100–900 MPa) and at different sintering temperatures (500, 550 and 600 °C) were also studied. The pressing behavior of the nanocomposites was analyzed using linear compaction equations developed by Heckel, Panelli-Filho and Ge. The results showed the significant effects of B₄C amounts and sintering temperatures on the compressibility and sintering behavior of nanocomposites. The increase in the B₄C amount led to a decrease in both the compressibility rate and the sinterability of specimens. The maximum compression strength of 265 MPa and Vickers hardness of 165 VHN were obtained for Al-5 wt.% B₄C nanocomposite milled for 16 h followed by sintering at 600 °C.     

Fatigue fracture of friction-stir processed Al–Al3Ti–MgO hybrid nanocomposites

This paper presents experimental results on the fatigue properties of Al-matrix nanocomposites prepared by the friction stir processing (FSP) technique. An Al–Mg alloy (AA5052) with different amounts (∼2 and 3.5 vol%) of pre-placed TiO₂ nanoparticles were FSPed up to 6 passes to attain homogenous dispersion of nano-metric inclusions. Microstructural studies by electron microscopic and electron back scattering diffraction (EBSD) techniques showed that nano-metric Al₃Ti (50 nm), TiO₂ (30 nm), and MgO (50 nm) particles were distributed throughout a fine-grained Al matrix (<2 μm). Consequently, a significant improvement in the tensile strength and hardness was attained. Uniaxial stress-controlled tension–tension fatigue testing (R = 0.1) were utilized to evaluate the fatigue behavior of the prepared nanocomposites. The results were compared with the un-processed (annealed) and FSPed alloy without pre-placing TiO₂ particles. It was found that FSP of the aluminum alloy increased the fatigue strength (at 10⁷ cycles) for about 28% and 32% compared with the annealed specimen when the concentration of the reinforcing particles was 2 and 3.5 vol%, respectively. Fractographic analysis determined a ductile fracture behavior with deep-equiaxed dimples for the annealed and FSPed alloy. The facture surface of the nanocomposites revealed a combined ductile–brittle fracture mode with finer dimples. The mechanism of the fatigue fracture and the role of nano-metric inclusions were elaborated.     

Nb2O5 hollow nanospheres as anode material for enhanced performance in lithium ion batteries

Nb₂O₅ hollow nanospheres of average diameter ca. ～29 nm and hollow cavity size ca. 17 nm were synthesized using polymeric micelles with core–shell–corona architecture under mild conditions. The hollow particles were thoroughly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermal (TG/DTA) and nitrogen adsorption analyses. Thus obtained Nb₂O₅ hollow nanospheres were investigated as anode materials for lithium ion rechargeable batteries for the first time. The nanostructured electrode delivers high capacity of 172 mAh g^?1 after 250 cycles of charge/discharge at a rate of 0.5 C. More importantly, the hollow particles based electrodes maintains the structural integrity and excellent cycling stability even after exposing to high current density 6.25 A g^?1. The enhanced electrochemical behavior is ascribed to hollow cavity coupled with nanosized Nb₂O₅ shell domain that facilitates fast lithium intercalation/deintercalation kinetics.     

Impedance spectroscopy characterization of relaxation mechanisms in gold–chitosan nanocomposites

Au–Chi nanocomposites with different AuNPs additions were investigated. The dispersion of AuNPs in polymer matrix was observed using s-SNOM analysis. The dielectric properties as a function of temperature show two relaxation processes: (1) a primary α-relaxation process, at low temperatures; (2) a second low frequency relaxation at temperatures between 70 °C and 150 °C identified as the σ-relaxation often associated with short range ion mobility. In nanocomposite films, the σ-relaxation process overcomes the α-relaxation process so that the glass transition is no longer detected. The dielectric nonlinear properties (tunability) shown an increase of dipolar moment with AuNPs additions and this results are in good correlation with matrix modification in FTIR investigation.     

Synthesis and electrochemical properties of nanosized LiFeO2 particles with a layered rocksalt structure for lithium batteries

Layered rocksalt-type LiFeO₂ particles (O3-LiFeO₂) with average particle sizes of ca. 40 and 400 nm were synthesized by an ion exchange reaction from α-NaFeO₂ precursors. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images confirmed the formation of nanosized O3-LiFeO₂. 40-nm LiFeO₂ exhibited a higher discharge capacity (115 mAh g^?1) than 400-nm LiFeO₂ (80 mAh g^?1), and also had better rate characteristics. The downsizing effect and cation disorder between the lithium and iron layers may have improved the electrochemical activity of the LiFeO₂ particles. Transmission electron microscopy (TEM) observation indicated a phase transition from O3-LiFeO₂ to a cubic lattice system during the electrochemical process. The cubic lithium iron oxide exhibited stable electrochemical reactions based on the Fe²⁺/Fe³⁺ and Fe²⁺/Fe⁰ redox couples at voltages between 4.5 and 1.0 V. The discharge capacities of 40-nm LiFeO₂ were ca. 115, 210, and 390 mAh g^?1 under cutoff voltages of 4.5–2.0 V, 4.5–1.5 V, and 4.5–1.0 V, respectively.