Microstructure and mechanical properties of WC–C nanocomposite films

WC–C nanocomposite film was prepared by using a hybrid deposition system of r.f.-PACVD and DC magnetron sputtering. W concentration in the film was varied from 5.2 to 42 at.% by changing the CH₄ fraction of the mixture sputtering gas of Ar and CH₄. Hardness, residual compressive stress and electrical resistivity were characterized as a function of W concentration. Raman spectroscopy, XRD and high resolution TEM were employed to analyze the structural change in the film for various W concentrations. In the present W concentration range, the film was composed of nano-sized WC particles of diameter less than 5 nm and hydrogenated amorphous carbon matrix. Content of the WC particles increased with increasing W concentration. However, the mechanical properties of the film increased only when the W concentration was higher than 13 at.%. Structural analysis and electrical conductance measurements evidently showed that the increase in hardness and residual stress occurred as the WC particles were in contact with each other in the amorphous carbon matrix.     

Effects of nanosilica and titanium oxide on the performance of epoxy–amine nanocoatings

Different types of composite coatings were prepared by the blending of colloidal nanosilica (SiO₂) and titanium dioxide (TiO₂) in epoxy resin to investigate their coating performances. A fixed amount of silica nanoparticles (20 wt %) and different amounts (5, 10, and 15 wt %) of microsized TiO₂ particles were used in the coatings. The functional groups of the formulated coatings were confirmed by Fourier transform infrared spectroscopy. These results indicate that the SiO₂–TiO₂ particles interacted well with epoxy. Scanning electron microscopy images of the composite coatings revealed a good dispersion of TiO₂ particles at a lower amount of loading; this improved the adhesiveness, glass-transition temperature, thermal stability, and chemical resistance properties. At higher loadings, the performances decreased. The composite coatings were also characterized by their UV radiation-absorption properties with an ultraviolet–visible spectrophotometer. Interestingly, this property was found to be enhanced at higher loadings. An impressive result was noticed in the nanocomposites in terms of oxygen transmission rate performance compared to that of the neat epoxy. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47901.     

Effects of hard-segment compositions on properties of polyurethane–nitrolignin films

Segmented polyurethane (PU) films from castor-oil-based PU prepolymer with different hard-segment compositions and nitrolignin (NL) were synthesized. Diisocyanates (DIs), such as 2,4-tolylene DI (TDI) and 4,4′-diphenylmethane DI (MDI), 1,4-butanediol (BDO) as a chain extender, and trimethanol propane (TMP) as a crosslinker were used to obtain PU films containing NL (UL) which were named as UL–TB for TDI and BDO, UL–TT for TDI and TMP, UL–MB for MDI and BDO, and UL–MT for MDI and TMP, respectively. The mechanical properties and thermal stability of the films were characterized by a tensile test and thermogravimetric analysis, respectively. The MDI-based UL films exhibited a higher tensile strength (σ_b) and thermal stability than TDI-based UL. However, the recoverability of the TDI-based UL films was better than that of others. The UL films with TMP (UL–TT and UL–MT) had higher σ_b and lower breaking elongation (ϵ_b) than the UL films with BDO (UL–TB and UL–MB), caused by enhancement in the crosslinking network of hard segments and microphase separation between soft and hard segments. The values of σ_b and ϵ_b of the UL films that contained NL were much higher than those of the PU films, which indicates that the introduction of NL increased the interaction between hard segments by crosslinking. The hydrogen bonding in the UL films was studied by infrared spectroscopy, which indicated that MDI favored the formation of hydrogen bonds, especially in the ordered domain. Differential scanning calorimetry, dynamic mechanical analysis, and wide-angle X-ray diffraction indicated that the UL films were compatible as a whole, but microphase separation existed between soft and hard segments and significantly affected the mechanical properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3251–3259, 2001     

Ion beam induced evolution of surface morphology and optical properties of SnO2–ZnO nanocomposite thin films

SnO₂–ZnO nanocomposite thin films, prepared by a simple carbothermal reduction based vapor deposition method, were irradiated with 8 MeV Si³⁺ ions for engineering the morphological and optical properties. The surface morphology of the nanocomposites was studied by atomic force microscopy (AFM), while the optical properties were investigated by photoluminescence spectroscopy (PL) and Raman spectroscopy. AFM studies on the irradiated samples revealed growth of nanoparticles at lower fluence and a significant change in surface morphology leading to the formation of nanosheets and their aggregates at higher fluences. A tentative mechanism underlying the observed ion induced evolution of surface morphology of SnO₂–ZnO nanocomposite is proposed. PL studies revealed strong enhancement in the UV emissions from the nanocomposite thin film at lower fluence, while a drastic decrease in the UV emissions along with a significant enhancement in the defect emissions has been observed at higher fluences.     

Demineralized whey–gelatin composite films: Effects of composition on film formation,mechanical, and physical properties

In this study, the objective was to prepare and characterize films with different concentrations of demineralized whey (3–10%) and gelatin (1–3%) containing glycerol (10–70%) as a plasticizer and chitosan or nanochitosan as an additive. Mechanical properties, thickness, grammage, opacity, moisture content, water, and ethanol solubilities of the obtained films were determined. The formation of films without glycerol and gelatin was not possible. A higher gelatin concentration led to more desirable mechanical properties. Thickness, grammage, opacity, and moisture content remained almost constant after increasing gelatin concentration. Heightening glycerol concentrations raised water and ethanol solubility. Despite presenting high water solubility, the films showed low ethanol solubility. The formulation containing whey (3%), glycerol (20%), gelatin (3%), and chitosan (0.1%) resulted in the highest performing film concerning physical and mechanical aspects. Through Fourier transform infrared spectroscopy analysis, it was possible to observe the displacement and the frequency reduction of the band near 3,300 cm⁻¹, revealing different protein interactions. It indicates that hydrogen bonds occur between the amino group and  OH of the protein molecules reducing film hydrophilicity. Contact angle measurements also showed a less hydrophilic character. The films present the potential to prolong the shelf life of food, such as dairy products.     

Effects of vinyltrimethoxy silane on thermal properties and dynamic mechanical properties of polypropylene–wood flour composites

The viability of vinyltrimethoxy silane was investigated as a coupling agent for the manufacture of wood–plastic composites (WPC). The effect of silane pretreatment of the wood flour on the thermal and the dynamic mechanical properties and thermal degradation properties of the composites were studied. Moreover, the effect of organosilane on the properties of composites was compared with the effect of maleated polypropylene (MAPP). DSC studies indicated that the wood flour acts as a PP-nucleating agent, increasing the PP crystallization rate. In general, pretreatment with small amounts of silane improved this behavior in all the WPCs studied. Thermal degradation studies of the WPCs indicated that the presence of wood flour delayed degradation of the PP. Silane pretreatment of the wood flour augmented this effect, though without significantly affecting cellulose degradation. Studies of dynamic mechanical properties revealed that the wood flour (at up to 30 wt %) increased storage modulus values with respect to those of pure PP; in WPCs with a higher wood flour amount, there was no additional increase in storage modulus. Pretreatment of the wood flour with silane basically had no effect on the dynamic mechanical properties of the WPC. These results show that with small amounts of vinyltrimethoxy silane similar properties to the MAPP are reached. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Studies on the effects of γ-radiation on the mechanical properties of Nylon 6–12 fibers

Summary Commercial nylon 6–12 fibers were subjected to various doses of -radiation. The mechanical and some thermal properties, as compared to those of non-irradiated fibers, show changes which are discussed in terms of the radiation-matter interactions.     

Effects of annealing temperature on the microstructure,optical, ferroelectric and photovoltaic properties of BiFeO3 thin films prepared by sol–gel method

Bismuth ferrite thin films were prepared via sol–gel spin-coating method and the effects of annealing temperature on microstructure, optical, ferroelectric and photovoltaic properties have been investigated. The results show that the bismuth ferrite thin films annealed at 550 °C is single phase and the grain size increases with the rise of annealing temperature. The band gap of bismuth ferrite thin films annealed at 550–650 °C is between 2.306 eV and 2.453 eV. With the rise of the annealing temperature, the remnant polarization gradually decreases and the coercive electric field increases. The short circuit photocurrent density decreases with the rise of annealing temperature, and the open circuit photovoltage and the power conversion efficiency of bismuth ferrite thin films annealed at 550 °C are higher than the thin films annealed at higher temperature.     

Effects of SiC content on the densification,microstructure, and mechanical properties of HfB2–SiC composites

To investigate the effects of SiC on microstructure, hardness, and fracture toughness, 0, 10, 20, and 30 vol% SiC were added to HfB₂ and sintered by SPS. Upon adding SiC to 30 vol%, relative density increased about 4%; but HfB₂ grain growth had a minimum at 20 vol% SiC. This may be due to grain boundary silicate glass, responsible for surface oxide wash out, enriched in SiO₂ with higher fraction of SiC. By SiO₂ enrichment, the glass viscosity increased and higher HfO₂ remained unsolved which subsequently lead to higher grain growth. Hardness has increased from about 13 to 15 GPa by SiC introduction with no sensible variation with SiC increase. Residual stress measurements by Rietveld method indicated high levels of tensile residual stresses in the HfB₂ Matrix. Despite the peak residual stress value at 20 vol% SiC, fracture toughness of this sample was the highest (6.43 MPa m^0.5) which implied that fracture toughness is mainly a grain size function. Tracking crack trajectory showed a mainly trans-granular fracture, but grain boundaries imposed a partial deflection on the crack pathway. SiC had a higher percentage in fracture surface images than the cross-section which implied a weak crack deflection.     

The effects of NbC nanoparticles synthesized by combustion method on the mechanical properties of Cu–NbC nanocomposite

In the first stage of this work, the master nanocomposite of niobium carbide (NbC)–Cu (ceramic-based nanocomposite) was synthesized by a mechanically induced magnesiothermic combustion in the Nb₂O₅/CuO/Mg/C system. Ignition time in this system was recorded to be ∼28 min of milling. In the second stage, appropriate amounts of NbC–Cu nanocomposite powder were mixed with pure copper powder to prepare Cu-based nanocomposite with 0, 5, 10, 15, and 20 volume fraction of NbC. The final metal matrix nanocomposite powder was sintered by spark plasma sintering method. The density of nanocomposite specimens decreased with increasing the percentage of NbC nanoparticles, while the microhardness of specimens increased with increasing nano-NbC content. Regarding the tensile test, the sample Cu–10 vol.% NbC nanocomposite with a strength of 372 MPa (∼63% higher than that of nonreinforced copper) was the best composition, and the nanocomposite strength decreased at higher NbC concentrations, mostly due to the agglomeration and nonhomogeneous distribution of reinforcing nanoparticles.     

Effects of the γ-irradiation strength and basalt additive content on the mechanical performance and dielectric response of polypropylene films

In this study, we investigated the effects of high-dose γ-ray irradiation on the mechanical and dielectric properties of polypropylene (PP)–basalt thick films. PP–basalt thick-film composites with various basalt contents from 0.5 to 10.0% were prepared by a hot-press method. The samples were exposed to γ radiation at different doses in the range 3–25 kGy. The mechanical properties of the samples, such as the Young's modulus, tensile strength, percentage strain at break, and energy at break, were examined in the context of the γ-irradiation process. Although the maximum elasticity was obtained for the unirradiated 0.5% basalt-added composite, the 6 kGy γ-irradiated PP–1.0% basalt sample exhibited the highest elasticity properties among all of the composites. The best mechanical properties, including the ultimate tensile strength and energy at break values, were achieved for the 12 kGy γ-irradiated neat PP. The dielectric properties of the PP–basalt composites were also investigated in the 100 Hz to 15 MHz frequency region at room temperature. According to the analysis of the dielectric properties, the 3 kGy γ-irradiated neat PP may have potential for microelectronic device applications that require low dielectric constant and dielectric loss materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47414.     

Effect of yttria substitution on structure,optical and mechanical properties of (Gd,Y)2O3–MgO nanocomposite ceramics

A citrate-nitrate combustion method was applied to synthesize fine composite Gd_2-xY_xO₃-MgO (x = 0, 0.02, 0.2, 0.3, 0.4, 0.6) nanopowders. Y₂O₃ substitution inhibited Gd₂O₃ phase transition from cubic structure to monoclinic structure during sintering, thereby stabilizing its cubic structure to room temperature. This approach led to nanocomposite ceramics with a grain size of about 190 nm and increased the transmittance to 85% over the 3–5 μm wavelength range when x = 0.3. However, the addition of Y₂O₃ weakened the mechanic properties of the nanocomposite ceramics.     

Influence of mono- and triple (Cr–La–Ba) doping on the mechanical,optical and gas diffusion properties of corundum

The effect of triple doping with chromium, lanthanum and barium on the mechanical, degassing and gas diffusion properties of fine-crystalline corundum synthesized in a supercritical water fluid was studied. The influence of chromium monodoping on the mechanical and optical properties of fine-crystalline corundum was also investigated. It was found that even small amounts of dopants of lanthanum and chromium during triple and monodoping of corundum significantly improve its mechanical properties (increase the abrasive ability) and reduce it several times the content of volatile gas-liquid impurities, which contributes to increase transparency of the resulting ceramics. The role of the interaction of a chromium impurity with oxygen vacancies in corundum on the increase in the static strength of crystals was suggested. The diffusion coefficients of water in doped corundum were determined. Comparison of the degassing and diffusion properties of corundum doped with La, Cr, Ba with undoped corundum and corundum doped with lanthanum was carried out. The results obtained contribute to the creation of new materials based on doped corundum with high abrasive, luminescent, and gas diffusion characteristics.     

The influence of nanoadditives on surface, permeability and mechanical properties of self-organized organic–inorganic nanocomposite coatings

Transparent and colorless nanocomposite coatings were prepared from a hybrid organic–inorganic matrix and several inorganic nanofillers. The products are characterized by a high degree of self-assembling of the matrix which was prepared from an epoxy-functional organosilicon precursor and an oligomeric diamine. Unmodified and chemically modified montmorillonite, bentonite, laponite, and colloidal silica were used as nanofillers, differing in shape, size, and origin. The nanoadditive concentration in coatings was always 0.5 wt%. Solid-state NMR (¹³C and ²⁹Si CP/MAS) spectroscopy was used for estimation of polyaddition and polycondensation degree in the polymer matrix in order to evaluate its structure changes caused by interaction with the nanoadditives. The influence of the kind of additive on the dynamic mechanical properties, gas permeability, and surface properties (topography, roughness) is discussed.     

Effects of density on the mechanical properties of spark plasma sintered β-SiC

The influence of density on the hardness value of β-SiC samples was studied based on Knoop and Vickers indentation tests. Hardness measurements were performed on additive-free spark plasma sintered SiC samples in the [80%–95%] density range and on highly dense samples (>99%) sintered with very low content of sintering aids. Results revealed that the density has a strong influence on the hardness value, which increases of about 7 GPa between samples presenting densities of 80% and 95% and even reaches 21 GPa under 2 kg with Knoop indenter for the densest samples sintered with very low content of sintering aids. These results allowed us to give a comprehensive model-supported analysis of the mechanical properties of spark plasma sintered β-SiC with controlled porosity that currently does not exist in the literature. The calculation of Young modulus and toughness further resulted in encouraging properties for our samples with regards to mechanical and ballistic performances.     

Effects of NCO:OH ratio on the mechanical properties and chemical structure of Kraft lignin–based polyurethane adhesive

ABSTRACT

This work aimed to evaluate the influence of the aliphatic and aromatic hydroxyl level on the polyurethane adhesive property and chemical structure. This adhesive was obtained through the reaction of technical Kraft lignin (TKL) as polyol with diphenylmethane diisocyanate (MDI). Thus, lignopolyurethane adhesives were obtained with NCO:OH ratios of 0.8:1.0, 0.9:1.0, 1.0:1.0, 1.1:1.0, and 1.2:1.0. Initially only the TKL aliphatic hydroxyl level was taken into consideration in the stoichiometry in order to define the mass ratio between MDI and polyol. Subsequently, lignopolyurethane adhesive was obtained using the same NCO:OH ratios considering TKL total hydroxyls’ level, and aromatic and aliphatic hydroxyls. The chemical structures of the synthesized adhesives were analyzed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹³C NMR). The mechanical property of the adhesively bonded joints, comprising wood substrates and synthesized adhesives, was measured using single lap shear tests. Results illustrated that by increasing the NCO:OH ratio, there is an increase in the free isocyanate content leading to higher shear strength values. Higher free isocyanate content leads to MDI dimer formation in the lignopolyurethane structure.     

Effects of carbothermal prereduction temperature and Co content on mechanical properties of WC–Co cemented carbides

WC–Co cemented carbides were prepared via an in situ synthesis method, including the carbothermal prereduction of WO₃ and Co₂O₃ to remove all oxygen and a subsequent carbonization-vacuum sintering process. The experimental results revealed that as the prereduction temperature increased from 1000 to 1200°C, the grain sizes of WC in WC–6Co and WC–12Co cemented carbides increased from .91 to 1.09 and .97 to 1.19 μm, respectively. Further, the fracture toughness of the sintered WC–6Co and WC–12Co cemented carbides increased from 9.97 to 10.83 and 11.11 to 18.30 MPa m^1/2, respectively. In contrast, the hardness of the WC–6Co and WC–12Co cemented carbides decreased from 1477 to 1368 and 1351 to 1184 HV₃₀, respectively. For a given prereduction temperature, an increase in Co content can improve the fracture toughness while lowering the hardness. In addition, an increase in the prereduction temperature or Co content led to an increase in the grain size of WC, which resulted in a transgranular fracture as the dominant mode.     

Influence of hydrogen functionalization on the fracture strength of graphene and the interfacial properties of graphene–polymer nanocomposite

Using molecular dynamics and classical continuum concepts, we investigated the effects of hydrogen functionalization on the fracture strength of graphene and also on the interfacial properties of graphene–polymer nanocomposite. Moreover, we developed an atomistic model to assess the temperature and strain rate dependent fracture strength of functionalized graphene along various chiral directions. Results indicate that hydrogen functionalization at elevated temperatures highly degrade the fracture strength of graphene. The functionalization also deteriorates the interfacial strength of graphene–polymer nanocomposite. Near-crack-tip stress distribution depicted by continuum mechanics can be successfully used to investigate the impact of hydrogen passivation of dangling carbon bonds on the strength of graphene. We further derived a continuum-based model to characterize the non-bonded interaction of graphene–polymer nanocomposite. These results indicate that classical continuum concepts are accurate even at a scale of several nanometers. Our work provides a remarkable insight into the fracture strength of graphene and graphene–polymer nanocomposites, which are critical in designing experimental and instrumental applications.