Characterisation and modelling of CNT–epoxy and CNT–fibre–epoxy composites

Abstract

This research presents an experimental and theoretical investigation on the effects of carbon nanotube (CNT) integration within neat epoxy resin (nanocomposites) and a carbon fabric–epoxy composite (multiscale composites). An approach is presented for the prediction of mechanical properties of multiscale composites. This approach combines woven fibre micromechanics (MESOTEX) with the Mori-Tanaka model which was used for the prediction of mechanical properties of nanocomposites in this research. Nanocomposite and multiscale composite samples were manufactured using cast moulding, resin infusion, and hand lay-up process. The CNT concentrations in the composite samples were from 0 to 5 wt-%. The samples were characterised using tensile, shear and flexural tests. The discrepancy between the theoretical predictions and the experimental observations was hypothesised to be due to dispersion and bonding issues and SEM images are presented in support of the hypothesis.     

Production and investigation of structure and properties of polyethylene–polylactide composites

Under conditions of shear deformations, low-density polyethylene (LDPE) and polylactide (PLA) composites are obtained in rotor disperser. The production of these composites allows one to use polymers derived from natural raw and to reduce the cost of the materials on their base. The addition of rigid PLA leads to increase in elastic modulus from 200 for LDPE to 1190 for LDPE–PLA (50:50 wt %) composites and in tensile strength from 13.3 for LDPE to 17.8 for LDPE–PLA. By differential scanning calorimetry method, it is shown that LDPE and PLA are incompatible. Using X-ray diffraction analysis, it is found that degree of crystallinity of composites decreases from 46.1 at 50:50 wt % to 36.9 at 80:20 wt % component ratios with the rise in LDPE content. Tests on fungus resistance show that the composites containing 50 wt % PLA are more resistant than the composites containing 30 wt % PLA. First by gel-permeation chromatography method, it is shown that composite degradation after exposure in soil is accompanied by the PLA chain scission and depolymerization with formation of monomers and dimers (M _w of PLA decreases from 118,860 to 80,100). The obtained composites can be applied as packaging materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47598.     

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.     

Colloidal Stability and Sintering of Yttria–Silica and Yttria–Silica–Alumina aqueous suspensions

The aim of this work was to produce dense yttrium silicate materials by slip casting, with more than 90% of Y₂SiO₅ phase. The rheological behaviour of concentrated aqueous slips was studied considering the effect of the dispersing additives, solids content and pH. The densification kinetics was examined as a function of temperature and time, and the reactions were analysed in the light of the equilibrium phase diagrams. Deflocculation of the slips was achieved by either an electrostatic mechanism using tetraethylammonium hydroxide, thus requiring a high concentration of base, and by a polyelectrolyte through an electrosteric mechanism, which provided more reliable results. In the binary system Y₂O₃–SiO₂, a very low grade of sintering was obtained at 1600°C. The use of alumina allows sintering through a liquid phase, reaching 90% theoretical density.     

Polymer-Salt Synthesis of Photoactive Bactericide ZnO–Ag and ZnO–SnO2–Ag Nanopowders and a Study of Their Structure and Properties

Glass Physics and Chemistry - This paper describes the low-temperature polymer-salt synthesis of ZnO–Ag nanopowders and presents the results of studying their structure, morphology, and...     

Electrocaloric and pyroelectric properties of PZT and PMN–PNN–PZT thin films

The electrocaloric effects (EC) of PZT and PMN–PNN–PZT films were evaluated. PZT and PMN–PNN–PZT thin films with a thickness of 500 nm were fabricated by state-of-the-art chemical solution deposition from a precursor solution with PZT and (PMN?PNN)/PZT=30/70. The polarization hysteresis loop was found to be slim and nonlinear, with smaller hysteretic behavior compared with PZT. The pyroelectric properties evaluated from polarization change and current measurement show that the properties of PMN–PNN–PZT films are superior to those of non-doped PZT films. The electrocaloric temperature changes ΔT due to applied ΔE were calculated. PZT and PMN–PNN–PZT films exhibited ΔT of 2.1 K and 3.6 K at 237.5 °C under a field of 500 kV/cm, respectively. Thermal-electrical energy converters based on pyroelectric effects were investigated for energy harvesting and possible use in ultralow-power sensor modules. The possibilities of pyroelectric energy harvesting using these PZT films were also investigated.     

Synthesis and characterizations of BNT–BT and BNT–BT–KNN ceramics for actuator and energy storage applications

Dielectric and ferroelectric properties of 0.93Bi_0.5Na_0.5TiO₃–0.07BaTiO₃ (BNT–BT) and 0.93Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–0.01K_0.5Na_0.5NbO₃ (BNT–BT–KNN) ceramics were studied in detail. An XRD analysis confirmed the single perovskite phase formation in both the samples. Room temperature (RT) dielectric constant (ε_r) ~1020 and 1370, respectively at 1 kHz frequency were obtained in the BNT–BT and BNT–BT–KNN ceramics. Temperature dependent dielectric and the polarization vs. electric field (P–E) studies confirmed the coexistence of ferroelectric (FE) and anti-ferroelectric (AFE) phases in the BNT–BT and BNT–BT–KNN ceramics. Substitution of KNN into the BNT–BT system decreased the remnant polarization, coercive field and the maximum strain percentage. The energy storage density values ~0.485 J/cm³ and 0.598 J/cm³ were obtained in the BNT–BT and BNT–BT–KNN ceramics, respectively. High induced strain% in the BNT–BT ceramics and the high energy storage density in the BNT–BT–KNN ceramics suggested about the usefulness of these systems for the actuator and the energy storage applications, respectively.     

The preparation and properties of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics

Two series (N-9 and N-18 series) of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics were designed. Nominal compositions of the glass samples in equivalent percent (eq%) are xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 91O: 9 N and xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 82O: 18 N (x=0, 2, 4, 6), respectively. The obtained samples were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Densities, Vickers hardness, fracture toughness, glass transition temperature, and thermal expansion coefficient data were established for each sample. Effect of Zr and N content on glass network structure, thermal and mechanical properties was investigated. It was found that the addition of zirconia is effective in preparing Y–Si–Al–O–N oxynitride glasses with lower glass transition temperature and higher hardness.     

A study of the acidic and catalytic properties of pure and sulfated zirconia–titania and zirconia–silica mixed oxides

Protonated pyridine (PyH⁺) was not found on ZrO₂ (Z) or ZrO₂–TiO₂ (ZT), but was detected on sulfated oxides (ZS, ZTS) by IR spectroscopy. In contrast, ZrO₂–SiO₂ samples containing about 30–80 mol% ZrO₂ showed Brønsted acidity both in nonsulfated (ZS) and sulfated (ZSS) forms. The total acidity was determined by NH₃TPD. Introduction of sulfate ions increased the sitespecific catalytic activity (TOF) in the conversion of cyclopropane or nhexane. The effect of sulfate ions was more significant on samples rich in zirconia. Results suggest that Zr is homogeneously distributed in ZS samples rich in silica. Zirconiabound dimeric sulfate, generating strong acidity, could not be formed in these preparations due to the absence of fairly large ZrO₂ domains.     

Preparation and properties of Ge–Ga–La–S–AgI chalcogenide glass

Chalcogenide glasses of 65GeS₂–(25–x)Ga₂S₃–10AgI–xLa₂S₃ (x=0, 1, 3, and 5 mol%) were fabricated through the traditional melt-quenching method. The effects of addition of La₂S₃ on physical, thermal and optical properties of the glass system were investigated. The results showed that the fabricated glasses possess considerably high glass transition temperature, exhibit improved mechanical property and excellent infrared transmission. A redshift at the visible absorbing cut-off edge is observed with increasing of La₂S₃ content. The direct and indirect optical band gap values are also calculated. Raman spectra analysis indicated that the band at 265 cm⁻¹ decreased in amplitude and a new peak at 230 cm⁻¹ was detected manifesting the formation of La-S bond in the network. In addition, the mid-infrared emission at 3.74 µm of the glasses doped with Tm³⁺ ions was achieved. The results indicated that the glasses are promising materials for mid-infrared applications such as imaging, remote sensing and lasers.     

Thermal and combustion behavior of phosphorus–nitrogen and phosphorus–silicon retarded epoxy

A novel trizine ring-based phosphorus–nitrogen flame retardant, 1,3,5-tris(3-(diphenylphosphoryl)propyl)-1,3,5-triazinane-2,4,6-trione (PN), was synthesized by the reaction of diphenylphosphine oxide and triallyl isocyanurate with triethylborane as catalyst. Chemical structure of the target compound was confirmed by Flourier transform infrared spectrum, nuclear magnetic resonances, matrix-assisted laser desorption/ionization time-of-flight mass spectrum measurements. The newly developed PN was used in the flame retardancy of o-cresol novolac epoxy/phenolic novolac hardener system. For comparison, another analogous phosphorus–silicon flame retardant, [(1,1,3,3-tetramethyl-1,3-disiloxanediyl)-di-2,1-ethanediyl]-bis(diphenylphosphine oxide) (PSi), was also applied in the same system. Experimental results revealed that PN showed superior flame retardant efficiency to that of PSi. In addition, the incorporation of flame retardants was in favor of the char formation during the thermal degradation process of epoxy thermosets. With the same flame retardant content, the char residue of epoxy thermosets with PSi was higher than that of epoxy thermosets with PN at 750 °C. Cone calorimeter results indicated that PN contributed to gas phase flame retardancy while PSi was more likely to take part in flame retardancy in the condense phase. X-ray photoelectron spectroscopy data revealed that the binding energies of phosphorus changed in different ways in PN and PSi after combustion. This implied that phosphorus exhibited different combustion behaviors when combined with nitrogen or silicon.     

Sintering and microstructure of mullite–Mo composites

Mullite–Mo composites of different compositions (0–100 vol.% Mo) were sintered to near theoretical density by pulse electric current sintering (PECS). The densification behaviour and the microstructure of mullite–Mo composites as a function of Mo content were studied. The addition of 10 vol.% Mo significantly enhanced the strength and toughness of monolithic mullite to 556 MPa and 2.9 MPa m^1/2, respectively. SEM observations revealed the modification of discrete isolated Mo particles to continuosly interconnected network with the increase in the Mo content. Mo grains were located at the grain boundaries as well as inside the mullite grains. The addition of Mo to monolithic mullite led to a change in the fracture mode.     

Microstructure and mechanical properties of TiC–TiN–Zr–WC–Ni–Co cermets

Cermet cutting tools are widely used for semi-finishing and finishing work on steel and cast iron. However, their brittleness is still an unavoidable limitation for their utilizations. Zirconium was added to improve the fracture toughness of Ti(C, N) based cermets. The microstructure and the fracture surfaces of cermets were studied by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results reveal that Zr dissolved and formed solid solutions during the sintering process. The amount of grains with typical core/rim structure decreases and that of coreless grains increases with increasing Zr addition. Moreover, the fracture toughness is improved clearly due to the increased amount of the coreless grains, the spinodal decomposition in cermets, as well as the crack deflection and crack branching mechanisms. Additionally, hardness and relative density were also measured, respectively.     

Synthesis and Structural Analysis of Co–Zn–Cd Ferrite by Williamson–Hall and Size–Strain Plot Methods

The work aimed at studying the structural properties of Cd-doped cobalt zinc ferrite (Co_0.5Zn_0.5Cd_0.2Fe_1.8O₄) prepared by simple, low-cost solid-state reaction method and characterized by XRD techniques. The X-ray analysis confirms the formation of ferrite particles with a cubic spinel structure. Crystallite size D, lattice constant a, micro strain ε, X-ray density Δ_X, dislocation density ρ _D , hopping lengths (L_A and L_B), bond lengths (A–O and B–O), ionic radii (r_A and r_B), texture coefficients [TC(hkl)], and mechanical properties are also reported.     

Effects of duty cycle and pulse frequency on microstructures and properties of electrodeposited Ni–Co–SiC nanocoatings

In this study, Ni–Co–SiC nanocoatings were fabricated using pulse current electrodeposition (PCE) method. Effects of duty cycle and pulse frequency on surface appearance, microstructure, phase structure, wear behavior, and corrosion resistance of as-deposited Ni–Co–SiC nanocoatings were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, nanoindentation, and both wear and corrosion tests. Results indicate that numerous small-sized grains formed on Ni–Co–SiC nanocoatings at 20% duty cycle to provide smooth, uniform, and fine microstructures. The content of SiC nanoparticles in Ni–Co–SiC nanocoatings decreased from 11.2 wt% to 7.4 wt% as duty cycle increased from 20% to 60%. However, the content of SiC nanoparticles in Ni–Co–SiC nanocoatings increased from 6.3 wt% to 9.7 wt% as pulse frequency increased from 100 Hz to 300 Hz. Ni–Co–SiC nanocoatings prepared at pulse frequency of 300 Hz and duty cycle of 20% exhibited average microhardness of 934.4 Hv and average thickness of 43.2 μm. Weight loss of Ni–Co–SiC nanocoatings at 300 Hz was only 17.2 mg, indicating significant wear resistance. In addition, Ni–Co–SiC nanocoatings produced at duty cycle of 20% and pulse frequency of 300 Hz exhibited the maximum impedance, indicating optimal corrosion resistance.     

Sol–gel preparation and characterization of nano-crystalline lithium–mica glass–ceramic

The nano-crystalline lithium–mica glass–ceramic with separated crystallite size of 13 nm was prepared using sol–gel technique. In such a process, the structural evolutions and microstructural characteristics of the synthesized samples were investigated through X-ray diffraction, transmission electron microscopy, thermal analysis and Fourier transform infrared spectroscopy. It was found that the crystallite size of the mica obtained from sol–gel method is smaller than the one synthesized via conventional melted method. The XRD results also showed that the crystallization of mica occurred above 675 °C and it could originate from MgF₂ so that the next stage will also be the transformation from mica to norbergite and norbergite to chondrodite. The activation energy of the crystallization and Avrami factor were measured as 376.7 kJ mol^?1 and 2.3, respectively. It is found that the bulk crystallization could be considered as the predominant crystallization mechanism for the glass–ceramic.     

Ignition of droplets of coal–water–oil mixtures based on coke and semicoke

To permit expansion of the resource base and utilize industrial waste, coal–water–oil fuels may be prepared on the basis of coke and semicoke, as well as common petroleum derivatives (fuel oil and spent compressor, turbine, and transformer oils). The minimal oxidant temperature corresponding to stable ignition of coal–water–oil slurries is established. Typical variation in fuel temperature in the course of reaction is determined, as well as the delay time of ignition and the total combustion time for individual droplets of such fuel suspensions. For droplets of initial size 0.5–1.5 mm, the influence of the various factors (droplet size, oxidant temperature, and concentration of the components) on the threshold (minimum) temperature and inertia of ignition is studied. It is shown that stable ignition of coke and semicoke in such fuel is possible at moderate oxidant temperatures: 700–1000 K.     

Influence of wrapping on some properties of MWCNT–PMMA and MWCNT–PE composites

The melt processing technique was used to elaborate composites made with a polymer matrix [polymethylmethacrylate (PMMA) or polyethylene (PE)] and multiwall carbon nanotubes (MWCNT). Nanotubes were wrapped by amphiphilic block copolymer (PE–co-polyethylene oxide) in aqueous solution to facilitate the dispersion and the handling. Morphology and physical properties (thermal, mechanical, electrical, and rheological) of the resulting composites were investigated. The wrapping of MWCNT allowed a good dispersion of these nanoparticules in the polymer matrices. Physical properties such as thermal degradation, mechanical behavior, and conduction are improved. The use of wrapped MWCNT allows to reduce drastically the melt viscosity of the blends of crystalline PE composites whereas it is almost non efficient for amorphous PMMA ones.     

Evaluation of Physicochemical and Antifungal Properties of Polylactic Acid–Thermoplastic Starch–Chitosan Biocomposites

Biocomposites of polylactic acid, thermoplastic starch, chitosan powder, and chitosan lyophilized powder were prepared using an extrusion process. The color, thermal, structural, mechanical, morphology, and antimicrobial properties were evaluated. The addition of thermoplastic starch and chitosan (chitosan powder and chitosan lyophilized powder) produced significant changes in color and heterogeneous surface morphology of the polylactic acid biocomposites. The thermal, mechanical, and morphometric properties of the material showed changes with the addition of thermoplastic starch and chitosan (chitosan powder and chitosan lyophilized powder). The biocomposites formulated with chitosan powder and chitosan lyophilized powder showed antifungal activity when evaluating this property. The biocomposites produced could be used in packaging applications.     

Synthesis and characterization of potassium humate–acrylic acid–acrylamide hydrogel

A novel potassium humate–acrylic acid–acrylamide (KHA–AA–AM) superabsorbent polymer was prepared from the reaction among leonardite potassium humate, acrylic acid and acrylamide by free radical initiating process using ammonium persulfate as the initiator and N, N′-methylene bisacrylamide as the crosslinker. Various effects of synthesis conditions on superabsorbent polymer were studied and the optimal reaction condition was obtained with crosslinker concentration 0.44–0.74 wt%, initiator concentration 1.12–2.22 wt%, n(KOH)/n(AA) 0.51–0.70, monomer concentration 10.95–12.59 wt%, graft reaction temperature 83 ± 1°C, monomer mole ratio of acrylic acid to acrylamide 1.42–2.30, and potassium humate content 17.54 wt%. Under the optimal conditions, the solution absorbency of KHA–AA–AM superabsorbent polymer to deionized water, tap water, 0.5% carbamide solution and 0.9% NaCl solution were 733–756, 161–284, 786–825, and 76–83 g/g, respectively.