Electron beam crosslinked gels—Preparation,characterization and their effect on the mechanical,dynamic mechanical and rheological properties of rubbers

Electron beam (EB) crosslinked natural rubber (NR) gels were prepared by curing NR latex with EB irradiation over a range of doses from 2.5 to 20 kGy using butyl acrylate as sensitizer. The NR gels were systematically characterized by solvent swelling, dynamic light scattering, mechanical and dynamic mechanical properties. These gels were introduced in virgin NR and styrene butadiene rubber (SBR) matrices at 2, 4, 8 and 16 phr concentration. Addition of the gels improved the mechanical and dynamic mechanical properties of NR and SBR considerably. For example, 16 phr of 20 kGy EB-irradiated gel-filled NR showed a tensile strength of 3.53 MPa compared to 1.85 MPa of virgin NR. Introduction of gels in NR shifted the glass transition temperature to a higher temperature. A similar effect was observed in the case of NR gel-filled SBR systems. Morphology of the gel-filled systems was studied with atomic force microscopy. The NR gels also improved the processability of the virgin rubbers greatly. Both the shear viscosity and the die swell values of EB-irradiated gel-filled NR and SBR were lower than their virgin counterparts as investigated by capillary rheometer.     

Photo-oxidative degradation of polyethylene: Effect of polymer characteristics on chemical changes and mechanical properties. Part 1—Quenched polyethylene

Photo-oxidative degradation of quenched samples of linear low density (LLD), medium density (MD) and two kinds of high density (HD) polyethylene (PE) films was studied using a medium-pressure mercury lamp. Greater amounts of crosslinking and build up of oxidation products were noticed in LLDPE than the other samples. The primary products of interaction between dienes and oxygen are considered to participate in the initiation of the photo-oxidation reactions. Using the FT-IR difference spectrum technique, the amount of branch concentration in the photo-irradiated PE samples was determined. Oxidation damage at the boundary region between crystalline and amorphous phases is considered to be important in determining the embrittlement time.     

Effects of PVA,agar contents,and irradiation doses on properties of PVA/ws-chitosan/glycerol hydrogels made by γ-irradiation followed by freeze-thawing

Poly(vinyl alcohol) (PVA)/water soluble chitosan (ws-chitosan)/glycerol hydrogels were prepared by γ-irradiation and γ-irradiation followed by freeze-thawing, respectively. The effects of irradiation dose and the contents of PVA and agar on the swelling, rheological, and thermal properties of these hydrogels were investigated. The swelling capacity decreases while the mechanical strength increases with increasing PVA or agar content. Increasing the irradiation dose leads to an increase in chemical crosslinking density but a decrease in physical crosslinking density. Hydrogels made by irradiation followed by freeze-thawing own smaller swelling capacity but larger mechanical strength than those made by pure irradiation. The storage modulus of the former hydrogels decreases above 50 °C and above 70 °C it comes to the same value as that prepared by irradiation. The ordered association of PVA is influenced by both chemical and physical crosslinkings and by the presence of ws-chitosan and glycerol. These hydrogels are high sensitive to pH and ionic strength, indicating that they may be useful in stimuli-responsive drug release system.     

Quantum mechanical modeling of the structures, energetics and spectral properties of Iα and Iβ cellulose

Periodic planewave and molecular cluster density functional theory (DFT) calculations were performed on Iα and Iβ cellulose in four different conformations each. The results are consistent with the previous interpretation of experimental X-ray and neutron diffraction data that both Iα and Iβ cellulose are dominantly found in the tg conformation of the hydroxymethyl group with a H-bonding conformation termed “Network A”. Structural and energetic results of the periodic DFT calculations with dispersion corrections (DFT-D2) are consistent with observation suggesting that this methodology is accurate to within a few percent for modeling cellulose. The structural and energetic results were confirmed by comparison of calculated vibrational frequencies against observed infrared and Raman frequencies of Iα and Iβ cellulose. Structures extracted from the periodic DFT-D2 energy minimizations were used to calculate the ¹³C nuclear magnetic resonance chemical shifts (δ¹³C), and the tg/Network A conformations of both Iα and Iβ cellulose produced excellent correlations with observed δ¹³C values.     

Pore structure and acid properties of high-silica zeolites synthesized with different templates and their catalytic performance in conversion of the propane–butane fraction

The effect of the template on the physicochemical properties of zeolitic catalysts and on the yield and selectivity of formation of aromatic hydrocarbons in conversion of the propane–butane fraction was examined. The zeolitic catalyst sample synthesized with an alcohol fraction as template is characterized by the highest values of the acid site concentration, adsorption capacity, micropore volume, and specific surface area. Therefore, this catalyst ensures the highest, compared to the other samples, conversion of the propane–butane fraction and yield of aromatic hydrocarbons.     

Study of the structure and mechanical properties of hexagonal BaTiO3 thin films prepared by sol鈥揼el processing

Hexagonal barium titanate (HBT) thin films were prepared on borosilicate plate substrates via sol–gel method using the dip-coating process. The structure, texture and morphology of the thin film were analyzed by X-ray diffraction, atomic force microscopy, nanoindentation technique, and transmission electron microscopy. The results showed that the thin film annealed at 700?°C crystallized with BaTiO₃ hexagonal phase and traces of Ba₂TiO₄ (secondary phase). The nanoparticles and the RMS roughness of the sample treated at 700?°C presented high values when compared with those thermally treated at lower temperatures. The hardness and Youngs??modulus of the thin films increased with increasing in grain size, and the thin film annealed at 700?°C with crystallite size about 10?nm presented multiple “pop-in??events during nano-indentation loading curves. The annealing temperature, growth size and surface roughness were discussed in connection with the HBT mechanical properties.     

Influence of “controlled processing conditions” on the solidification of iPP,PET and PA6

In this work reliable experimental data for three semicrystalline polymers (iPP, PA6, PET) crystallised under pressure and high cooling rates are supplied. These results were achieved on the basis of a model experiment where drastic “controlled” solidification conditions are applied. The final objective was to quantify the effect of two typical operating conditions (pressure and cooling rate) on the final properties and morphology of the obtained product. The influence of processing conditions on some macroscopically relevant properties, such as density and micro hardness is stressed, together with the influence of processing conditions on the product morphology, investigated by means of Wide Angle X-Ray Scattering (WAXS). Results on the iPP samples display a decrease of density and micro hardness, due to the pressure increase, in a wide range of cooling rates (from 0.01 to 20°C/s). PET samples exhibit an opposite behaviour with density and micro hardness increasing at higher pressures in the whole range of cooling rates investigated. PA6 samples behave similarly to PET displaying a less significant increase of density and micro hardness with pressure than PET samples.     

Influence of erbium on the structural,optical and magnetic properties of sol–gel Ce: YIG films

Journal of Sol-Gel Science and Technology - Sol–gel Y2.8-xCe0.2Er x Fe5O12 (x?=?0.0, 0.2, 0. 4, 0.6, 0.8 and 1.0) nanofilms were successfully prepared for their potential use in...     

Influence of Ti additions on the martensitic phase transformation and mechanical properties of Cu–Al–Ni shape memory alloys

The effect of Ti additions on the microstructure and mechanical properties of Cu–Al–Ni shape memory alloys (SMA) was studied by means of a differential scanning calorimeter, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), a tensile test, a hardness test, and a shape memory effect test. The experimental results show that the Ti additions have an effective influence on the phase transformation behavior through generating a new phase into the microstructure, which is known as X-phase and/or controlling the grain size. The results of the XRD confirmed that the X-phase is a combination of two compounds, AlNi₂Ti and Ti₃·3Al. Nevertheless, it was found that with 0.7 mass% of Ti, the best phase transformation temperatures and mechanical properties were obtained. These improvements were due to the highest existence of the X-phase into the alloy along with a noticeable decrement of grain size. The Ti additions to the Cu–Al–Ni SMA were found to increase the ductility from 1.65 to 3.2 %, corresponding with increasing the strain recovery by the shape memory effect from 50 to 100 %; in other words, a complete recovery occurred after Ti additions.     

Co-doped ZnO nanoparticles synthesized by an adapted sol–gel method: effects on the structural,optical, photocatalytic and antibacterial properties

Pure and Co-doped ZnO nanoparticles were synthesized with different cobalt levels (1–10 mol%) via adapted sol–gel method using water as solvent and characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and photoacoustic absorption spectroscopy. The results showed that all the samples have hexagonal wurtzite structure, with no evidence of any secondary phases until 10 mol% of the dopant. The average crystallite size of the samples was in the range of 25–50 nm, do not showing significant differences with the increase of the dopant level. However, the band gap energy of the nanoparticles decreases from 2.98 eV (pure ZnO) to 1.95 eV (10 mol% of Co). The photocatalytic activity of the samples was evaluated on the removal of methylene blue under visible light irradiation, which revealed an efficiency reduction by Co-doping ZnO. The antibacterial property was carried out indicating activity of the prepared samples against gram-positive bacteria.     

Influence of the substrate type on the microstructural,optical and electrical properties of sol–gel ITO films

Indium tin oxide (ITO) is recognized as the best transparent and conductive material [transparent conducting oxide (TCO)] until now and its properties are dependent on the preparation method. In the present work ITO films with In:Sn atomic ratio 9:1 were prepared by a sol–gel route on different substrates (microscope glass slides, microscope glass covered with one layer of SiO₂ and Si wafers) for TCO applications. The multilayer ITO films were obtained by successive deposition by the dip-coating method and the films were characterized from the structural, morphological, optical, and electrical points of view using X-ray diffraction, scanning electron microscopy, atomic force microscopy, spectroscopic ellipsometry and by Hall effect measurements, respectively. The results showed that the thickness, optical constants and carrier numbers depend strongly on the type of substrate, number of deposited layers and sol concentration. The optical properties of ITO films are closely related to their electrical properties. The enhancement of the conductivity was possible with the increase of crystallite size (which occurred after thermal treatment) and with the reduction of surface roughness.     

Material design of radiation resistant polypropylene: Part II—Importance of the smectic structure produced by quenching treatment

The effects of quenching on the radiation-induced oxidative degradation and the morphology of isotactic polypropylene were studied. The tensile modulus and yield stress of non-irradiated polypropylene film decrease with decreasing quenching temperature, while the tensile strength is almost constant. Drastic lowering of the elongation at break of the polypropylene film was observed at a characteristic dose of irradiation (critical dose, D_c). The resistance to radiation, as measured by the D_c value, was greater the lower the quenching temperature. The internal crystalline structures were strongly dependent on the quenching treatment, whereas the rate of radiation-induced oxidation was not affected. The higher resistance of polypropylene to radiation was obtained upon decreasing the quenching temperature, thereby increasing the smectic crystalline, or glassy content.     

Influence of the spin acceleration time on the properties of ZnO:Ga thin films deposited by sol–gel method

Journal of Sol-Gel Science and Technology - A detailed study of the structural, morphological, optical, and electrical properties of the spin-coated Ga-doped ZnO (GZO) films in which these...     

Study on the influence of ageing on chemical and mechanical properties of N,N′-dimethyl-N,N′-diphenylcarbamide stabilized propellants

Double-base propellants undergo chemical, physical and mechanical changes upon ageing, leading to changes in ballistic performance and presenting explosive hazards. This report studies the variation of chemical and mechanical properties of aged N,N′-dimethyl-N,N′-diphenylcarbamide (methyl centralite) stabilized propellants in order to simulate and evaluate the natural ageing throughout the artificial one. Therefore, a comparative study of stabilizer depletion, plasticizers content, heat of combustion and mechanical properties such as storage modulus, loss modulus and damping of naturally and artificially aged propellants has been carried out by the following techniques: high-performance liquid chromatography (HPLC), thermogravimetric analyzer (TG), calorimeter of combustion and dynamic mechanical analyzer (DMA), respectively. The results obtained show that all properties are closely connected. In addition, the determination of stabilizer depletion, plasticizers evaporation, decrease of heat of combustion and mechanical properties are very useful for a better understanding of the decomposition and ageing behaviour of propellants. The HPLC investigation of stabilizer has shown good stability of the propellants. The results obtained for DMA have shown that some considerable changes of the mechanical and viscoelastic properties of the propellants occurred during ageing. These results confirm the results obtained by TG for the reduction of the nitroglycerine amount and the decrease of the heat of combustion.     

Influence of Ni nanoparticle addition and spark plasma sintering on the TiNiSn–Ni system: Structure,microstructure, and thermoelectric properties

The electronic and thermal properties of thermoelectric materials are highly dependent on their microstructure and therefore on the preparation conditions, including the initial synthesis and, if applicable, densification of the obtained powders. Introduction of secondary phases on the nano- and/or microscale is widely used to improve the thermoelectric figure of merit by reduction of the thermal conductivity. In order to understand the effect of the preparation technique on structure and properties, we have studied the thermoelectric properties of the well-known half-Heusler TiNiSn with addition of a small amount of nickel nanoparticles. The different parameters are the initial synthesis (levitation melting and microwave heating), the amount of nickel nanoparticles added and the exact pressing profile using spark plasma sintering. The resulting materials have been characterized by synchrotron X-ray diffraction and microprobe measurements and their thermoelectric properties are investigated. We found the lowest (lattice) thermal conductivity in samples with full-Heusler TiNi₂Sn and Ni₃Sn₄ as secondary phases.     

PVC-silica hybrids: effect of sol–gel conditions on the morphology of silica particles and thermal mechanical properties of the hybrids

Hybrid materials from poly(vinyl chloride) (PVC) and silica have been prepared using different conditions by the sol–gel technique. In situ generation of silica network in the PVC matrix was carried out by hydrolysis/condensation of tetraethoxysilane (TEOS) in the matrix. Morphology of the silica particles produced in hybrid films was studied by scattering electron microscopy. The shape of silica particle produced in the matrix was modified by carrying out the sol–gel process under steam on the hybrid films using TEOS. The films were subjected to strain conditions during this process, which produced lamellar shaped particles in the matrix. It was possible to produce platelet type of structure with different aspect ratio by changing the composition and the stress conditions on the films during the steaming process. Addition of a very small amount of γ-glycidoxypropyltrimethoxysilane as compatibilizer drastically reduced the silica particles size in the matrix to nano-level. Thermal–mechanical properties of some of these hybrids were studied and related to the composition, structure and inter-phase interaction between the silica and the matrix.     

Modification of α-ZrP nanofillers by amines of different chain length: Consequences on the morphology and mechanical properties of styrene butadiene rubber based nanocomposites

An aqueous slurry of α-ZrP lamellar nanofillers has been modified by amine type surfactants. The influence of the alkylamine chain length and of the cationic exchange rate on the nanofiller d-spacing has been analyzed. The strength of the interactions formed between the intercalating agent and the filler has been studied by Infra Red Spectroscopy (FTIR), Solid-state Nuclear Magnetic Resonance (³¹P MAS NMR) and Thermogravimetric Analysis (TGA). Different routes allowing to obtain optimized filler properties while minimizing the surfactant weight amount have been proposed from the detailed analysis of the intercalation mechanism. Styrene Butadiene Rubber nanocomposites have been prepared directly from the different slurries of modified α-ZrP. The dispersion of the organophilic α-ZrP in the SBR matrix has been characterized and the mechanical properties of the corresponding nanocomposites have been determined and discussed as a function of the filler modification, of the nanocomposite morphology and of the filler/matrix interfacial properties.