Thermal decomposition behavior of γ‐irradiated poly(vinyl acetate)/poly(methyl methacrylate) miscible blends

Miscible polymer blends based on various ratios of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were prepared in film form by the solution casting technique using benzene as a common solvent. The thermal decomposition behavior of these blends and their individual homopolymers before and after γ‐irradiation at various doses (50–250 kGy) was investigated. The thermogravimetric analysis technique was utilized to determine the temperatures at which the maximum value of the rate of reaction (T_max) occurs and the kinetic parameters of the thermal decomposition. The rate of reaction curves of the individual homopolymers or their blends before or after γ‐ irradiation displayed similar trends in which the T_max corresponding to all polymers was found to exist in the same position but with different values. These findings and the visual observations of the blend solutions and the transparency of the films gave support to the complete miscibility of these blends. Three transitions were observed along the reaction rate versus temperature curves; the first was around 100–200°C with no defined T_max, which may arise from the evaporation of the solvent. The second T_max was in the 340–380°C range, which depended on the polymer blend and the γ‐irradiation condition. A third transition was seen in the rate of reaction curves only for pure PVAc and its blends with PMMA with ratios up to 50%, regardless of γ‐ irradiation. We concluded that γ‐irradiation improved the thermal stability of PVAc/PMMA blends, even though the PMMA polymer was degradable by γ irradiation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1773–1780, 2006     

Electrochemical properties of cathode materials LiNi1−y Co y O2 synthesized using various starting materials

LiNi_1−y Co _y O₂ samples were synthesized at 800 °C and 850 °C, by the solid-state reaction method, using the starting materials LiOH·H₂O, Li₂CO₃, NiO, NiCO₃, Co₃O₄ and CoCO₃. The LiNi_1−y Co _y O₂ synthesized using Li₂CO₃, NiO and Co₃O₄ exhibited the α-NaFeO₂ structure of the rhombohedral system (space group ). As the Co content increased, the lattice parameters a and c decreased. The reason is that the radius of the Co ion is smaller than that of the Ni ion. The increase in c/a shows that a two-dimensional structure develops better as the Co content increases. The LiNi_0.7Co_0.3O₂ synthesized at 800 °C using LiOH · H₂O, NiO and Co₃O₄ exhibited a larger first discharge capacity of 162 mAh g⁻¹ than the other samples. The cycling performances of the samples with the first discharge capacity larger than 150 mAh g⁻¹ were investigated. LiNi_0.9Co_0.1O₂ synthesized at 850 °C using Li₂CO₃, NiO and Co₃O₄ showed excellent cycling performance. Samples with larger first discharge capacity will have a greater tendency for lattice destruction due to expansion and contraction during intercalation and deintercalation, than samples with smaller first discharge capacity. As the first discharge capacity increases, the capacity fading rate thus increases.     

Molecular weight studies of the γ‐irradiation degradation of poly(methyl methacrylate) doped with poly(p‐sulfanilamide)

The protection of some poly(methyl methacrylate) (PMMA) samples against γ rays was investigated in the absence and presence of poly(p‐sulfanilamide). Pure PMMA (without additives) and PMMA–poly(p‐sulfanilamide) blend samples were irradiated with γ rays for different exposure doses (5, 15, 25, 35, 50, 75, and 100 kGy). The viscosity‐average molecular weights were determined and thin‐layer chromatography measurements were carried out after each irradiation dose. The maximum protection against γ rays was found when 1% poly(p‐sulfanilamide) was used. The radiation chemical yield for main scission (G_s) was calculated and had lower values in the case of 1% poly(p‐sulfanilamide). The energy absorption per scission was maximum for 1% poly(p‐sulfanilamide), and this confirmed the obtained G_s data. From thin‐layer chromatography studies, it was observed that both the retention factor (R_f) values and polydispersity of the PMMA samples increased with an increasing exposure dose. The effect of γ irradiation on PMMA films doped with 1% poly(p‐sulfanilamide) was investigated with UV spectroscopy after the extraction of the additives. A change in the intensity of the absorption bands with an increasing irradiation dose was recorded. It is suggested that PMMA films doped with this type of polymer can be used as dosimeters. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Change of the properties of nanostructured MoO3 thin films using gamma-ray irradiation

Thin films of Molybdenum trioxide (MoO₃) were deposited on glass substrates by the spray pyrolysis at 500?°C and the samples were then exposed to gamma γ radiation doses by ⁶⁰Co radioisotope at different doses (0.1, 10 and 50 kGy). The effects of gamma irradiation on the properties of MoO3 thin films were investigated. The XRD pattern and Raman spectroscopy of as-deposited MoO₃ samples show an orthorhombic structure related to α-MoO₃ with (0k0) preferred orientations. Uv‐vis spectra were studied to investigate the transmission measurements of MoO₃ films. The optical energy band gap and Urbach energy were found to be gamma-dose dependent. Photoluminescence measurements at room temperature using 300?nm wavelength excitation were investigated. SEM images indicate the formation of α-MoO₃ nanorods.     

Effect of calcination temperature on structural,vibrational, optical,and rheological properties of zirconia nanoparticles

ZrO₂ nanoparticles (NPs) were prepared by a simple, versatile, and an efficient methodology based on microwave. The synthesized NPs were calcined at temperatures ranging from 100 °C to 600 °C. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), FT-IR spectroscopy, Far-IR spectroscopy, Raman spectroscopy, and UV-vis absorption spectroscopy. The results clearly showed the presence of purely monoclinic phase of zirconia when the calcination temperature exceeds 400 °C. The experimental results showed that the viscosity of zirconia NPs in ethylene glycol (EG) increases with increasing the particle volume fraction and decreases with increasing temperature.     

Charge–discharge curves and discharge capacities of LiNi1−yCoyO2 synthesized from lithium carbonate and nickel and cobalt oxides

LiNi_1?yCo_yO₂ (y=0.1, 0.3, and 0.5) were synthesized by a solid-state reaction method at 800 °C and 850 °C using Li₂CO₃, NiO, and Co₃O₄ as the starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were then investigated. For samples with the same composition, the particles synthesized at 850 °C were larger than those synthesized at 800 °C. The particles of all the samples synthesized at 850 °C were larger than those synthesized at 800 °C. LiNi_0.5Co_0.5O₂ synthesized at 850 °C had the largest first discharge capacity (159 mA h/g), followed in order by LiNi_0.7Co_0.3O₂ synthesized at 800 °C (158 mA h/g) and LiNi_0.9Co_0.1O₂ synthesized at 850 °C (151 mA h/g). LiNi_0.9Co_0.1O₂ synthesized at 850 °C had the best cycling performance with discharge capacities of 151 mA h/g at n=1 and 156 mA h/g at n=5.     

Optical,Structural, Electrical Characterization of (Polyvinyl Alcohol–Carboxymethyl Cellulose-Manganese Dioxide) Nanocomposite Fabricated via Laser Ablation

Polyvinyl alcohol (PVA)/Carboxymethyl cellulose (CMC)/Manganese dioxide (PVA/CMC/MnO₂ NPs) nanocomposite were produced by one-pot laser ablation route. PVA/CMC/MnO₂ NPs nanocomposite were prepared with different content of manganese dioxide nanoparticles. The formation of MnO₂ is confirmed by appearing diffraction peaks at 2θ?=?26.4°, 28.4°, 37.2°, 42.5°, 56.4°, 72.2° according to JCPDS No. 24-0735 which agreed with previous literature. The increasing of laser ablation time causes a change of all bands intensities. All the above conclusions affirmed the formation of Mn–O and their complexation with PVA/CMC blend. The ultraviolet and visible (UV/Vis.) measurements showed enhanced in the optical properties as the ratio of Manganese dioxide nanoparticles enhanced. The absorption edge is changed towards lower photon energy sides when MnO₂ NPs are added to the PVA/CMC. The AC conductivity was enhanced after the addition of MnO₂ NPs. The values of the ε′ and ε? of the synthesized samples increased as the ratio of Manganese dioxide nanoparticles increased, which is attributed to an increase in the current films' ion conduction. The obtained results demonstrate the benefits of using MnO₂ NPs as a filler to improve polymeric systems and suggest it for optical and electrical applications.

     

Effect of electron-beam irradiation followed by annealing on the physical properties of poly(vinyl alcohol)–chitosan blend films at different weight ratios

The aim of this study was to examine the effect of electron-beam irradiation followed by annealing on the physical properties of poly(vinyl alcohol) (PVA)–chitosan (CS) blend films. Solution-cast films containing various ratios of polymers were exposed to irradiation doses of 26, 39, and 52 kGy at room temperature and then annealed at 100 °C. The results show that at all doses, with an increase in the weight ratio of CS, the gel content of the samples decreased, and the water absorption of the samples increased. The irradiation dose ranged from 26 to 39 kGy; this led to an increased gel content and a decreased degree of swelling in the samples. However, at 52 kGy, an increase in the amount of swelling was observed. X-ray diffraction analysis and scanning electronic microscopy images of the samples revealed that the increase in the irradiation dose reduced the crystallinity and increased the surface heterogeneity, respectively. The tensile strength of the blends decreased with decreasing PVA–CS weight ratio. This property of the samples increased with dose from 26 to 39 kGy and decreased at 52 kGy. The elongation at break of the samples decreased with both an increase in the irradiation dose and a decrease in the CS content. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47820.     

Factors influencing thermal,mechanical, optical,and adhesive properties of segmented poly(imide siloxane) copolymers films

Poly(imide siloxane), block and blend copolymer, were synthesized using different methods to explore the influence of siloxane chains. The flexible siloxane chains enrichment on surface of copolymer, enhance hydrophobic and adhesive with copper foil. It also improves light transmittance of polyimide film in the visible light region. The effect of different preparation methods on the aggregation in polymers and on polymer properties, especially adhesion and water absorptivity, are also discussed. The imidization temperature and synthesis method (blend and block) during the reaction has a significant effect on the properties of the product, especially thermal properties (T _g values are 207 °C for block and 180 °C for blend) and mechanical properties (elongation of 130% for block and 50% for blend). The bonding strength of polymer films used as hot melt adhesive was also tested. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48148.     

Study of crystallization behavior of neat poly(vinylidene fluoride) and transcrystallization in carbon fiber/poly(vinylidene fluoride) composite under a temperature gradient

The crystallization behavior of poly(vinylidene fluoride) (PVDF) and transcrystallization in carbon fiber (CF)/PVDF composite were investigated under a temperature gradient. The crystallization temperature (T_c) was controlled in the range of 110–180 °C. For neat PVDF, the results showed that exclusive γ phase formed at T_c above 164 °C, but coexisted with α phase at T_c ranging from 137 to 160 °C. The promotion of γ phase to nucleation of α phase at low T_c was observed for the first time. For CF/PVDF composite, a cylindrical transcrystalline (TC) layer formed on the surface of CF when T_c was between 137 and 172 °C. The TC layer was exclusively composed of γ phase at T_c above 164 °C. The hybrid nucleation was dominated by γ phase though some α phase nuclei emerged on the surface of CF when T_c was in the range of 144–160 °C. As T_c decreased, competition between the hybrid nucleation of α and γ phase became more intense. The γ phase nuclei was soon circumscribed by the rapidly developed α phase when T_c was below 144 °C. Furthermore, some α phase nuclei were induced at the surface of the γ phase TC layer, and developed into α phase TC layer when T_c was in the range of 146–156 °C, which resulted in a doubled TC layer of α and γ phase at the interface of the composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43605.     

Morphology and crystallization of poly(ethylene terephthalate)

The melting behaviour and the morphology of poly(ethylene terephthalate) crystallized from the melt are reported. In general, dual or triple melting endotherms are seen, and single endotherms are seen when the samples are crystallized above 215°C for long times. The location of the uppermost endotherm was found to be constant below T_c = 230°C, and above that temperature the location depends on T_c. Therefore, we have shown that samples of PET which are crystallized above T_c = 230°C contain perfect crystals only; below T_c = 230°C, they contain perfect and imperfect crystals. Scanning electron microscopy showed that the perfect crystals are the dominant lamellae in the spherulitic structure, while the imperfect crystals are the subsidiary lamellae in the spherulitic structure, The amorphous regions are located between individual lamellae.     

High‐Temperature Electrical Conductivity of LaCr1−xCoxO3 Ceramics

LaCr_1?xCo_xO₃ solid‐solution ceramics (x = 0.0–0.3) were prepared by pressureless sintering of a submicrometer powder. The powder was synthesized by a modified glycine nitrate process at 800°C. The electrical conductivity of the material sintered at 1600°C was measured by AC four‐wire method from room temperature to 1200°C. While undoped (x = 0) LaCrO₃ revealed semiconductivity dominated by thermally activated mobility of small polarons over a vast temperature range, substitution of Co for Cr gave rise for a pronounced enhancement of conductivity at temperatures >200°C. XPS analysis showed that the concentration of Cr⁴⁺ on the Cr‐site and Co²⁺ at the Co‐site increased with Co substitution suggesting a thermally activated redox reaction Cr³⁺ + Co³⁺→Cr⁴⁺ + Co²⁺ to create additional charge carriers. Thus, Co doping offers a high potential for designing the electrical conductivity making LaCr_1?xCo_xO₃ an interesting resistivity material for high temperature applications.     

Synthesis of cathode material LiNi<Subscript>1-<Emphasis Type="Italic">y</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>O<Subscript>2</Subscript> by a simplified combustion method

The optimum conditions for synthesizing LiNi_1-y Co _y O₂ (y=0.1, 0.3 and 0.5) by a simplified combustion method, in which the preheating step is omitted, and the electrochemical properties of these materials were investigated. The optimum condition for synthesizing LiNi_0.9Co_0.1O₂ by the simplified combustion method is calcination at 800 °C for 12 h in air in 3.6 mole ratio of urea to nitrate. The LiNi_0.9Co_0.1O₂ synthesized under these conditions shows the smallest R-factor{(I ₀₀₆+I ₁₀₂)/I ₁₀₁} and the largest I ₀₀₃/I ₁₀₄, indicating better hexagonal ordering and less cation mixing, respectively. The LiNi_0.7Co_0.3O₂ synthesized at 800 °C for 12 h in air in 3.6 mole ratio of urea to nitrate has the largest first discharge capacity 156.2 mA h g⁻¹ at 0.5C and shows relatively good cycling performance. This sample shows better hexagonal ordering and less cation mixing than the other samples. The particle size of the LiNi_0.7Co_0.3O₂ is relatively small and its particles are spherical with uniform particle size.     

Effect of sol-gel and solid-state synthesis techniques on structural,morphological and thermoelectric performance of Ca3Co4O9

Two methods of obtaining calcium cobalt oxide (Ca₃Co₄O₉) thermoelectric materials were studied: (I) solid state synthesis (SS) followed by high-energy ball-milling (HEBM) and (II) modified sol-gel method (SG). The obtained powders were heated at 900?°C for 12?h. They were subsequently compacted using spark plasma sintering (SPS). The crystal structure and morphology were characterized by X-ray diffraction and scanning electron microscopy. The calculated average crystallite sizes, before and after SPS, alter from 43 to 61?nm and from 38 to 41?nm, for the SS and SG powders, respectively. XRD studies of the obtained powders revealed presence of Co₃O₄ secondary phases, which turned into metallic cobalt after SPS. Thermoelectric measurements of sintered samples were performed in the range, 50–500?°C. The maximum Seebeck coefficient is 120?µV/K and 110?µV/K, for the SS and SG synthesized samples, respectively. The highest ZT was found to be 0.02 and 0.04 at 500?°C for the SS and SG samples, respectively.     

Hydrothermal synthesis of cobalt-doped vanadium oxides: Antimicrobial activity study

Cobalt-doped vanadium oxide (CoVOx) nanocomposites were synthesized using facile hydrothermal sol-gel method. The final products were annealed at 500?°C in the furnace for 2?h under vacuum and air, which led to Co₃(VO₄)₂, CoV₂O₆ and pure V₂O₅ powders respectively. The nanoparticles (NPs) were characterized by X-ray Diffraction and Scanning Electron Microscopy (SEM). The magnetization behavior of the samples shows step–like increase for CoV₂O₆ material while the magnetic moment is quasi saturated at 2?T for Co₃(VO₄)_2.The antibacterial activity of CoVOx nanocomposites was tested against two gram negative and two gram positive bacterial isolates. The bacterial strains were treated with increasing concentrations of NPs (0–3.5?mg/ml) for 24?h. The cell viability was assessed using Alamar Blue assay to monitor the response and health of the cells in culture after treatment with various pathogens. Among the three NPs tested, Co₃(VO₄)₂ and CoV₂O₆ showed enhanced anti-bacterial activity on the four isolates compared to V₂O₅ which manifests an activity on E.coli at the highest dosage.     

Structural characterization and electrochemical properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> anode materials synthesized by a hydrothermal method

Cobalt oxide [Co₃O₄] anode materials were synthesized by a simple hydrothermal process, and the reaction conditions were optimized to provide good electrochemical properties. The effect of various synthetic reaction and heat treatment conditions on the structure and electrochemical properties of Co₃O₄ powder was also studied. Physical characterizations of Co₃O₄ are investigated by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller [BET] method. The BET surface area decreased with values at 131.8 m²/g, 76.1 m²/g, and 55.2 m²/g with the increasing calcination temperature at 200°C, 300°C, and 400°C, respectively. The Co₃O₄ particle calcinated at 200°C for 3 h has a higher surface area and uniform particle size distribution which may result in better sites to accommodate Li⁺ and electrical contact and to give a good electrochemical property. The cell composed of Super P as a carbon conductor shows better electrochemical properties than that composed of acetylene black. Among the samples prepared under different reaction conditions, Co₃O₄ prepared at 200°C for 10 h showed a better cycling performance than the other samples. It gave an initial discharge capacity of 1,330 mAh/g, decreased to 779 mAh/g after 10 cycles, and then showed a steady discharge capacity of 606 mAh/g after 60 cycles.     

Irradiation crosslinking of PVC–ENR blend Effect of efficient radical scavenger

Abstract

The irradiation induced crosslinking of 50:50 poly (vinyl chloride)–epoxidised natural rubber (PVC–ENR) blend was studied in the presence of 0–1·5 pphr antioxidant Irganox 1010. The samples were irradiated using a 3·0 MeV electron beam machine at doses ranging from 20 to 200 kGy in air and room temperature. The gel fraction, tensile strength T _s, modulus at 100% elongation M ₁₀₀, elongation at break E _b, hardness, and resilience were used to follow the irradiation induced crosslinking of the blend. The decline in gel fraction, T _s, M ₁₀₀, hardness, and resilience and the concurrent increase in E _b with increasing antioxidant indicated the inhibition of irradiation induced crosslinking by the antioxidant used. The improvement in aging properties of the blend with the addition of the antioxidant is also reported. It was evident from FTIR that Irganox 1010 is involved in the stabilisation of the blend against irradiation induced degradation.     

Characterization of gamma irradiated polyethylene films by DSC and X‐ray diffraction techniques

The effect of gamma radiation on the thermal behavior and crystalline structure of low density polyethylene (LDPE) has been investigated using differential scanning calorimetry (DSC) and X‐ray diffraction techniques (XRD). Gamma irradiation was carried out in atmospheric air to a maximum dose of 883 kGy. DSC results of the heating run from room temperature up to 150 °C showed that the melting temperature (T_m), and onset temperature of LDPE film decrease linearly with increasing irradiation dose. However, upon cooling LDPE film from 150 °C to room temperature, the crystallization temperature (T_c) and onset temperature were found to decrease non‐linearly with increasing irradiation dose up to 500 kGy and then tended to level off. The change in heat of fusion (ΔH_f) with irradiation dose was found to proceed with different behaviour, two stages, with a kink at irradiation dose of about 500 kGy, being observed. This suggests the occurrence of degradation and crosslinking at low and high doses, respectively. However, parameters of the X‐ray diffraction pattern such as number of diffraction patterns, peak position (2θ) and width of the diffraction pattern, support the results of DSC measurements. © 2000 Society of Chemical Industry     

Improvement of Physicochemical Properties of Rubber Blends Between Nonirradiated and Irradiated Rubber Latexes by Radiation Vulcanization

Abstract

Nonirradiated natural rubber latex (NRL) and irradiated (12 kGy) rubber latex were blended in ratios of 100:0, 85:15, 65:35, 50:50, 35:65, 15:85, and 0:100 (v/v) to improve properties of the rubber latex. The blends were irradiated using different irradiation doses (0–20 kGy) in the presence of a radiation vulcanization accelerator (RVA), normal butyl acrylate (n-BA). The physicochemical properties of the nonirradiated latex, irradiated latex, and blend films were determined after leaching with distilled water. It was observed that the tensile strengths of the blend films increases with an increase in the content of the irradiated proportion and radiation doses. The composition of the blends and the doses of radiation were optimized. The maximum tensile strength (31.41 MPa) was found for the 50:50 composition of the blend with a 5 kGy radiation dose. The 100:0 blends, when irradiated, give the highest tensile strength (27.69 MPa) with 12 kGy but a 15:85 nonirradiated blend gives the tensile strength of 26.18 MPa.     

Synthesis and thermal stability of (Co,Ni)O solid solutions

(Co,Ni)O solid solutions are considered as promising protective materials of O₂-evolving anodes for Al production. In this context, two solid-state synthesis methods, namely high-energy ball milling (HEBM) and calcination, have been evaluated for the synthesis of (Co,Ni₎O solid solutions. In all cases, Co_xNi_1−xO solid solutions can be formed over the whole composition range. However, undesired WC contaminant is observed using the HEBM method due to the erosion of the milling tools. Their thermal stability in air has been analyzed by thermogravimetric analyzes (TGA) complemented by X-ray diffraction (XRD) analyses. It is shown that Co_xNi_1−xO solid solutions are stable at 1000°C over the whole composition range whereas they are only stable for x ≤ 46 and x ≤ 22 at 800°C and 700°C, respectively. For higher Co contents, the formation of Co₃O₄ is observed. This is a relevant information for their future use for Al production, which can be done at different temperatures (~700-1000°C) depending of the electrolyte composition.