Effect of radiation dose on the properties of natural rubber nanocomposite

Effect of radiation dose and carbon nanotubes (CNT) on the mechanical properties of standard Malaysian rubber (SMR) was investigated in this study. SMR nanocomposites containing 1–7 phr CNT were prepared using the solvent casting method and the nanocomposites were radiated at doses of 50–200 kGy. The change in mechanical properties, especially, tensile strength (Ts), elongation at break (Eb), hardness and tensile modulus at 100% elongation (M₁₀₀) were studied as a function of radiation dose. The structure and morphology of reinforced natural rubber was investigated by FESEM, TEM and AFM in order to gain further evidence on the radiation-induced crosslinking. It was found that the Ts, M₁₀₀ and the hardness of the SMR/CNT nanocomposites significantly increased with radiation dose; the elongation at break exhibited an increase up to 100 kGy, and a downward trend thereafter. Results on gel fraction further confirmed the crosslinking of SMR/CNT nanocomposites upon radiation.     

Compounding,mechanical and morphological properties of carbon-black-filled natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) blends

Blends of natural rubber/virgin ethylene-propylene-diene-monomer (NR/EPDM) and natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) were prepared. A fixed amount of carbon black (30 phr) was also incorporated. The effect of the blend ratio (90/10, 80/20, 70/30, 60/40 and 50/50 (phr/phr)) on the compounding, mechanical and morphological properties of carbon-black-filled NR/EPDM and NR/R-EPDM blends was studied. The results indicated that both the carbon-black-filled NR/EPDM and NR/R-EPDM blends exhibited a decrease in tensile strength and elongation at break for increasing weight ratio of EPDM or R-EPDM. The maximum torque (S′M_H), minimum torque (S′M_L), torque difference (S′M_H?M_L), scorch time (ts₂) and cure time (tc₉₀) of carbon-black-filled NR/EPDM or NR/R-EPDM blends increased with increasing weight ratio of virgin EPDM or R-EPDM in the blend. SEM micrographs proved that, for low weight ratios of virgin EPDM or R-EPDM, the blends exhibited high surface roughness and matrix tearing lines. The blends also showed a reduction in crack path with increasing virgin EPDM or R-EPDM content over 30 phr. This reduction in crack path could lead to less resistance to crack propagation and, therefore, low tensile strength.     

The effect of gamma irradiation and particle size of CaCO3 on the properties of HDPE/EPDM blends

Mechanical blends formed of 50 wt% of high-density polyethylene (HDPE) and 50 wt% of ethylene–propylene–diene-monomer (EPDM) elastomer have been loaded with 50 wt% of three different particle size of CaCO₃, namely CaCO₃ 300, CaCO₃ 700, and CaCO₃ 2000 whereby the latter has the smallest particle size of ～311, 82 μm. Mechanical, physico-chemical and thermal properties were followed up as a function of irradiation dose for loaded and unloaded blends. The results obtained indicated that the values of tensile strength, tensile modulus at 50% elongation, gel fraction and decomposition temperature increase with increasing irradiation dose. On the other hand elongation at break, permanent set and swelling number were found to decrease with increasing irradiation dose. Moreover, the effect of particle size of CaCO₃ was observed in a limited but apparent upgrading of mechanical, physico-chemical, and thermal properties. The order of semi-reinforcing capacity of three different types of CaCO₃ is as follow: CaCO₃ 2000 > CaCO₃ 700 > CaCO₃ 300 > unloaded blend. Whereby CaCO₃ 2000 has the smallest particle size.     

In situ synthesis of composite MTiO3–Al2O3 coatings via laser zone melting

Laser zone melting was employed in this work to prepare MTiO₃ based coatings over commercial, polycrystalline Al₂O₃ substrates, using the corresponding mixtures of powdered alkaline earth carbonates and TiO₂ as starting materials. In situ synthesis of the series M = Ca, Sr, Ba was studied using a CO₂ laser as the heating source, emitting at 10.6 μm, following substrate preheating to a temperature of 750 °C and sample displacement speed of 500 mm h⁻¹. Microstructure (SEM) and phase composition (XRD) demonstrated in situ formation of crystalline MTiO₃ perovskite (M = Ca, Sr), MAl₂O₄ (M = Ca), MAl₁₂O₁₉ magnetoplumbite type (M = Sr) and MAl₁₄O₂₂ β-alumina type (M = Ba) phases. Substantial interaction with the substrate resulted in stable, 50–150 μm thick, composite coatings.     

Preparation and Characterization of Microwave-absorption of Sarulla North Sumatra Zeolite and Ferric Oxide-filled Polyurethane Nanocomposites

Microwave-absorptive polymeric composite materials are becoming important to protect interference of any communication systems due to the increase in the use of microwave-inducing devices. In this work, the microwave-absorptive polyurethane composites are prepared using natural zeolites of Sarulla North Sumatra and commercial ferric-oxide as fillers. Weight ratio of the natural zeolite to ferric oxide were varied (18:2; 16:4; 14:6; 12:8 and 10:10) by weight. The fillers are prepared using ball milling technique and characterized using Particle Size Analyzer for particle size distribution. The nanocomposites, prepared using in-situ reaction of polyethylene glycol and toluene diisocyanate, is characterized for physical and mechanical properties using tensile strength, thermal properties with TGA techniques, as well as morphological and chemical properties using scanning electron microscopy. Composition and loading of the nanofillers against polyurethane matrices is 20% by weight. Microwave-absorption properties of the nanocomposites is characterized using 8-12 GHz frequency. Tensile strengths of the natural zeolite-ferric oxides polyurethane nanocomposites shows higher values when matrices filled with lower ferric-oxide, which could be due to the nanozeolites have functioned as reinforcement for the polyurethane matrix through polar-polar interaction between the filler surfaces with the matrices. The microwave absorption properties, which investigated by Vector Network Analyzer, of the nanocomposites filled in polyurethane with the ratio of nanozeolite to ferric oxide filler of 12:8 shows reflection loss of – 13.2 dB. This condition was observed at 11.1 GHz.     

Mechanoelectrochemical synthesis of porous Ti-based nanocomposite biomaterials

In this work we have synthesized a new class of nanocomposites based on Ti with the addition of hydroxyapatite (HA) and glass 45S5. The nanocomposites were prepared by mechanical alloying of the pure microcrystalline Ti powders with different amount of ceramics. The powder mixture was milled up to 48 h, pressed and sintered, which resulted in nanocomposite structure with the grain size of about 20–36 nm. The ultra low grain size structure improves mechanical properties of the implants in comparison to commonly used microcrystalline Ti-based implants. For example, the hardness of the Ti-HA nanocomposites reaches a value of 1500 HV and is five times greater than the microcrystalline Ti.To improve bonding of the implants with human tissue, the implants were electrochemically etched in 1 M H₃PO₄ + 2–10% HF electrolyte at 10 V vs. OCP for times up to 60 min. The treatment results in highly porous surface covered with Ti-oxide. The nanocrystalline structure is very useful during etching, due to the easy access of the electrolyte to the large volume of the grain boundaries. The nanocomposites with modified surface show very good corrosion resistance in Ringer’s solution.     

Syntheses and crystal structures of new vanadium(IV) oxyphosphates M(VO)2(PO4)2 with M = Co,Ni

We have extended our research interest on titanium oxyphosphates (M^II(TiO)₂(PO₄)₂, with M^II = Mg, Fe, Co, Ni, Cu, Zn) to vanadium oxyphosphates M^II(V^IVO)₂(PO₄)₂ (M^II = Co, Ni). For each compound two phases, named α and β according to synthesis conditions, have been stabilized at room temperature, then characterized. The four crystal structures M(VO)₂(PO₄)₂ (α and β for M = Co, Ni) have been determined in monoclinic P2₁/c space group using X-ray single crystals diffraction data. Structure of the α phase is derived from the Li(TiO)(PO₄) (orthorhombic Pnma) and LiNi_0.50(TiO)₂(PO₄)₂ (monoclinic P2₁/c) types, with cell parameters: a = 6.310(1) Å, b = 7.273(1) Å, c = 7.432(1) Å, β = 90.43(1)° for M = Co, and a = 6.297(2) Å, b = 7.230(2) Å, c = 7.421(2) Å, β = 90.36(2)° for M = Ni. Structure of the β phase is derived from the Ni(TiO)₂(PO₄)₂-type (monoclinic P2₁/c) with cell parameters: a = 7.2742(2) Å, b = 7.2802(2) Å, c = 7.4550(2) Å, β = 120.171(2)° for M = Co, and a = 7.2691(2) Å, b = 7.2366(2) Å, c = 7.4453(2) Å, β = 120.231(2)° for M = Ni. All these structures consist of a three dimensional (3D) framework built up of infinite chains of tilted corner-sharing [VO₆] octahedra, cross-linked by corner-sharing [PO₄] tetrahedra. The M²⁺ ion (M = Co, Ni) is located in a triangular based antiprism which shares faces with two [VO₆] octahedra. Structural filiation is discussed based on a common structural unit, a sheet where divalent cations M²⁺ (M = Co, Ni) are inserted. A thermal study of the α ? β transition is also presented.     

The reaction of amidinato(pyridine) complexes of molybdenum and tungsten with triethylborane adduct of N-heterocyclic carbene (NHC · BEt3): Investigation on the reactivity of NHC · BEt3 as carbene precursor toward transition metal complexes

The reaction of triethylborane adduct of N-heterocyclic carbene, NHC · BEt₃, (NHC = IⁱPr = 1,3-diisopropylimidazol-2-ylidene (IⁱPr · BEt₃; 1a), NHC = IMes = 1,3-dimesitylimidazol-2-ylidene (IMes · BEt₃; 1b)), which was prepared by the reaction of the corresponding imidazolium salt with one equivalent of LiBEt₃H, with amidinato(pyridine) complex, [M(η³-allyl){η²-(NPh)₂CH}(CO)₂(NC₅H₅)] (M = Mo; 2-Mo M = W; 2-W), was investigated. The reaction of compound 1 with complex 2 under toluene-reflux conditions resulted in the formation of carbene complex [M(η³-allyl){η²-(NPh)₂CH}(CO)₂(NHC)] (M = Mo, NHC = IⁱPr; 3a-Mo, M = Mo, NHC = IMes; 3b-Mo, M = W, NHC = IⁱPr; 3a-W, M = W, NHC = IMes; 3b-W). These complexes were characterized spectroscopically as well as by X-ray analyses. Complex 3a-Mo was formed in various solvents such as 1,2-dimethoxyethane (DME), 1,2-dichloroethane, and acetonitrile under refluxing conditions for 3 h. In toluene, 3a-Mo was obtained in a good yield by heating at 70 °C for only 20 min. Employment of NHC · BEt₃ (1) was found to afford convenient route for the introduction of the carbene ligand to the transition metal complexes.     

Magnetic properties of nitric oxide adsorbed within channel crystals

The crystalline one-dimensional compounds, [M₂(bza)₄(pyz)]_n (bza = benzoate; pyz = pyrazine; M = Cu^II (1)) and [M₂(bza)₄(2-mpyz)]_n (2-mpyz = 2-methylpyrazine; M = Rh^II (2), Cu^II (3)), demonstrate gas absorbency of NO. The amounts of adsorbed NO gas are 0.61 for 1, 0.30 for 2, and 0.23 for 3 per M₂ unit at 195 K (800 Torr). The crystals of 1 adsorbed more NO molecules than did those of 2 and 3. The magnetic susceptibilities of the NO-inclusion crystals indicate that included NO molecules interact antiferromagnetically with neighboring guests without dimerization to N₂O₂. Magnetic behaviors indicated NO aggregation in the narrow 1D channels of 1–3 under unsaturated adsorption conditions.     

Solid solutions: An efficient way to control the temperature of spin transition in heterospin crystals MxCu1 − x(hfac)2L (M = Mn,Ni, Co; L = nitronyl nitroxide)

A series of mixed-metal solid solutions M_xCu_1 − x(hfac)₂L (M = Mn, Ni, and Co) liable to undergo thermally induced spin transitions have been synthesized. The structure and magnetic properties of the compounds have been investigated. By varying the metal to be incorporated in the complex (Mn, Ni, or Co) and the value of x, one can control the character of the magnetic anomaly.     

Enhancement of plant growth stimulation activity of irradiated alginate by fractionation

Alginate with the weight-average molecular weight (M_w) approximately 900 kDa and ratio of M (mannuronate)/G (guluronate) about 1.3 was irradiated by gamma Co-60 in aqueous solution at doses up to 200 kGy. The irradiation dose was shown to be a function for reducing M_w and molecular weight distribution of irradiated alginates. The distribution of oligomer fractions in irradiated products was also investigated by separation using ultrafiltration membranes. The irradiated alginate with M_w approximately 14.2 kDa was found to have a positive influence for growing of barley and soybean. The irradiated oligoalginate fraction with M_w ranging from 1 to 3 kDa displayed the strongest effect on the growth and development of the mentioned plants at low concentration (20 ppm). It is suggested that oligoalginate with M_w in the range 1–3 kDa is a trigger for the growth and development of plants.     

Synthesis and properties of alkaline metal complexes with new overcrowded β-diketiminato ligands

Enaminoimines TbtNHC(Me)CHC(Me)NAr (5, Tbt = 2,4,6-[CH(SiMe₃)₂]₃C₆H₂) bearing a Tbt group were synthesized by the two steps condensation of acetylacetone with bulky amines. Enaminoimines 5 were treated with n-BuLi to give the corresponding lithium β-diketiminates, [Li{TbtNHC(Me)CHC(Me)NAr}] (1). The X-ray structural analysis of [Li{TbtNC(Me)CHC(Me)NMes}] (1c, Mes = mesityl) revealed that it is a monomeric, solvent-free lithium β-diketiminate. The equilibrium between free 1c plus THF and THF-coordinated (1c · thf) was investigated in detail by the determination of the association constant (K_a) in C₆D₆ at 293 K and the Job’s plot. The heavier alkali metal complexes, sodium and potassium β-diketiminates (6c–9c), were prepared by the two routes. THF-coordinated [M{TbtNC(Me)CHC(Me)NMes}(thf)] (6c: M = Na. 7c: M = K) were prepared by the reaction of 5c (Ar = Mes) with MH (M = Na, K). Solvent-free [M{TbtNC(Me)CHC(Me)NMes}] (8c: M = Na. 9c: M = K) were prepared by the reaction of 1c with t-BuOM (M = Na, K).     

Metal–metal bond cleavage of carbene complexes by halogens: The crystal and molecular structures of ax-[Mn2(CO)9{C(OEt)2-thienyl}], [Mn(CO)4(I){C(OEt)2-thienyl}] and eq-[Mn2(CO)9{C(NH2)2-thienyl}]

The metal–metal bond in [M₂(CO)₉{C(OEt)R}] (M = Mn (1), Re (2), R = 2-thienyl (a), 2-bithienyl (b)) is readily cleaved with halogens to afford cis-[M(CO)₄(X){C(OEt)R}] (M = Mn (3), X = I; M = Re (4), X = Br). In the binuclear manganese complex, the carbene ligand is found in an axial position due to steric reasons, whereas the electronically favoured equatorial position is found for the carbene ligands in the corresponding rhenium complexes and in [Mn₂(CO)₉{C(NH₂)thienyl}] (5a), containing a sterically less demanding NH₂-substituent.     

Controlled synthesis of MnSn(OH)6/graphene nanocomposites and their electrochemical properties as capacitive materials

We report the synthesis of novel MnSn(OH)₆/graphene nanocomposites produced by a co-precipitation method and their potential application for electrochemical energy storage. The hydroxide decorated graphene nanocomposites display better performance over pure MnSn(OH)₆ nanoparticles because the graphene sheets act as conductive bridges improving the ionic and electronic transport. The crystallinity of MnSn(OH)₆ nanoparticles deposited on the surface of graphene sheets also impacts the capacitive properties as electrodes. The maximum capacitance of 31.2 F/g (59.4 F/g based on the mass of MnSn(OH)₆ nanoparticles) was achieved for the sample with a low degree of crystallinity. No significant degradation of capacitance occurred after 500 cycles at a current density of 1.5 A/g in 1 M Na₂SO₄ aqueous solution, indicating an excellent electrochemical stability. The results serve as an example demonstrating the potential of integrating highly conductive graphene networks into binary metal hydroxide in improving the performance of active electrode materials for electrochemical energy storage applications.     

Relationship between structure,fluxionality and racemization activity in organometallic derivatives of polyoxometalates

The catalytic activity of several organometallic derivatives of polyoxometalates, especially those of general formula [M₄O₁₆{M′(η⁶-arene)}₄] (M = Mo, W; M′ = Ru, Os), was evaluated in the racemization of secondary alcohols. A link between composition, fluxionality and catalytic activity was established.     

Crucial effect of rubidium cation on catalytic activity of a polycrystalline gold electrode toward oxygen reduction reaction in alkaline media

Catalytic activity of a polycrystalline gold electrode toward oxygen reduction reaction (ORR) in aqueous alkaline media in the presence of various alkali-metal sulfates (M₂SO₄, M = Li, Na, K, Rb and Cs) was investigated by hydrodynamic voltammetry. The fraction of 4e^? pathway in low overpotentials (? 0.1 to ? 0.3 V) depended on the alkali-metal cations (Rb ? Na, K, Cs, Li). A complete 4e^? reduction of O₂ was only attained in the presence of Rb⁺ cation in the solution, which was comparable or even superior to that reported at the Au(100) single crystal electrode.     

Phase behaviour of binary and ternary mixtures for the poly(methyl methacrylate-co-hexafluorobutyl methacrylate) [P(MMA-co-HFBMA)] in supercritical fluorine solvents

In this study, the poly(methyl methacrylate-co-2,2,3,4,4,4-hexafluorobutyl methacrylate) [P(MMA-co-HFBMA)] as a fluoric copolymer was prepared using dispersion polymerization in supercritical carbon dioxide. The characterization for the prepared P(MMA-co-HFBMA) was investigated with varied ratios of MMA vs HFBMA (30:1, 25:1, 22:1 and 20:1), 2,2′-azobisisobutyronitrile (AIBN) amounts (1.0, 2.0, 3.0, and 4.0) wt% and the weight average molar mass (M_w).Experimental cloud-point data at temperatures to 454 K and pressures up to 184 MPa are reported for binary and ternary mixtures of P(MMA-co-HFBMA) in supercritical CH₂F₂, CHF₃ and CHClF₂. Experiments are performed in order to determine phase behaviour of binary system for the P(MMA-co-HFBMA) (mole ratio: 25:1, AIBN: (1.0, 2.0, 3.0 and 4.0) wt%) + supercritical solvents (CH₂F₂, CHF₃ and CHClF₂) mixtures at temperature range from (333 to 454) K and pressure up to 184 MPa. It appears that the {P(MMA-co-HFBMA) + CH₂F₂} mixtures show the upper critical solution temperature (UCST) type behaviour with negative slope, while the {P(MMA-co-HFBMA) + CHF₃} and {P(MMA-co-HFBMA) + CHClF₂} mixtures show lower critical solution temperature (LCST) type curve with positive slope. Cloud-point curves for the P(MMA-co-HFBMA) [mole ratio: 30:1 (M_w = 186,000 g · mol⁻¹), 25:1 (M_w = 176,000 g · mol⁻¹), 22:1 (M_w = 158,000 g · mol⁻¹) and 20:1 (M_w = 126,000 g · mol⁻¹); AIBN: 1.0 wt%) + supercritical (CH₂F₂, CHF₃ and CHClF₂) mixtures show a negative slope for the {P(MMA-co-HFBMA) + CH₂F₂}, and a positive slope for the {P(MMA-co-HFBMA) + CHF₃} and {P(MMA-co-HFBMA) + CHClF₂} mixtures at temperatures to 454 K and pressure up to 184 MPa. Also, the impact of MMA on phase behaviour for the {P(MMA-co-HFBMA) (mole ratio: 25:1; AIBN: (1.0 and 2.0) wt%) + CH₂F₂} mixtures are measured in changes of the (pressure + temperature) slope from UCST behaviour to LCST behaviour, and with MMA co-solvent concentrations of (0.0 to 40.1) wt%.     

High-pressure synthesis and characterization of the alkaline earth borate β-BaB4O7

The new orthorhombic barium borate β-BaB₄O₇ was synthesized under high-pressure/high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C, starting from stoichiometric mixtures of the binary oxides. β-BaB₄O₇ crystallizes in space group Pmnb with Z = 2 and lattice parameters a = 1099.4(2), b = 901.7(2), c = 430.73(9) pm, R1 = 0.0199, and wR2 = 0.0406 (all data). The network-structure is built up exclusively from BO₄-tetrahedra, linked via common corners. Its structural differences to the ambient-pressure phase α-BaB₄O₇ and structural agreements with the isotypic high-pressure phases β-MB₄O₇ (M = Ca, Hg, Sn) and the ambient-pressure phases MB₄O₇ (M = Sr, Pb, Eu) are discussed. β-BaB₄O₇ and a hypothetical BaB₄O₇ in the β-MB₄O₇ (M = Ca, Hg, Sn) structure were studied as high-pressure phases of α-BaB₄O₇, using density functional calculations. The transition pressure of α-BaB₄O₇ into the structure of β-BaB₄O₇ was calculated to 1.5 GPa; the transition pressure of β-BaB₄O₇ into BaB₄O₇ in the β-MB₄O₇ (M = Ca, Hg, Sn) structure to 7.5 GPa.     

Synthesis and characterization of three Cu(II), Zn(II), Cd(II) supramolecular complexes bridged by biphenyl 2,2′-dicarboxylate

Three complexes, M₂(bpy)₂(bpdc)₂·xH₂O [M = Cu, x = 0; M = Zn or Cd, x = 2], have been hydrothermally synthesized by 1,1′-biphenyl-2,2′-dicarboxylic acid (H₂bpdc) with 2,2′-bipyridine (bpy) to form binuclear molecules. In each, the two bpdc groups align the two opposing planar [M(bpy)]²⁺ cations. The molecules are connected by C–H⋯O hydrogen bonds, π–π stacking, and C–H⋯π interactions to form three dimensional supramolecular networks. Furthermore, at room temperature, complex 3 exhibits strong photoluminescence.     

Anthracene-based macrocyclic fluorescent chemosensor for selective sensing of dicarboxylate

An anthracene-based macrocyclic receptor has been designed and synthesized for selective recognition of 1,4-phenylenediacetate (K_a = 3.34 × 10⁵ M^?1). The macrocycle binds 1,4-phenylenediacetate selectively at the charged sites of the receptor with a concomitant increase in fluorescence of anthracene. The interaction properties of the macrocycle were evaluated by ¹H NMR, UV–vis and fluorescence spectroscopic methods.