Organo-modified magnesium hydroxide nano-needle and its polystyrene nanocomposite

Acrylic acid modified magnesium hydroxide nano-needles (AA–Mg(OH)₂) had been synthesized by alkaline injected into magnesium chloride solution at about 0°C in the presence of acrylic acid (AA). Then the polystyrene/magnesium hydroxide nano-needles composite (PS/Mg(OH)₂) had been prepared by the radical copolymerization with styrene in toluene system using AA–Mg(OH)₂ as a macro-monomer. The elemental analysis (EA) and Fourier transform infrared (FTIR) analyses show that the polystyrene had been grafted onto the surfaces of the nano-needles (AA–Mg(OH)₂). The nano-needles (AA–Mg(OH)₂) had better dispersibility in polystyrene matrix as observed by transmission electron microscope (TEM) analysis. The thermal behavior analysis results from the differential scanning calorimetry (DSC) indicated that the magnesium hydroxide nano-needles had lower thermal decomposition temperature than that of the polymer matrix and it is expected that the nano-needles prepared by the proposed method could be used as an environmental-friendly flame retardant.     

Flame-Retarding and Mechanical Properties of Flexible Polyvinyl Chloride with Surface-Treated Lamellar Magnesium Hydroxide

The effects of hydrophobic magnesium hydroxide (Mg(OH)₂) particles, prepared by a surface modification method with oleic acid, on the flame-retarding and mechanical properties of polyvinyl chloride (PVC) were investigated. Comparison between the use of modified and unmodified Mg(OH)₂ in the preparation of PVC composites showed that the former could provide excellent optical and flame-retarding properties. The dispersion of the modified Mg(OH)₂ particles in the PVC matrix was investigated through scanning electron microscopy. Compared with a composite containing unmodified Mg(OH)₂, the rheological and impact strength properties of that containing the modified Mg(OH)₂ filler were found to be significantly improved. These improvements were mostly attributed to the better dispersion of the modified Mg(OH)₂ particles and the strong adhesion between the filler and matrix.     

Effect of Particle Size on the Thermal Stability and Flammability of Mg(OH)2/EVA Nanocomposites

The effect of the Mg(OH)₂ particle size on the thermal degradation and flammability of a model nanocomposite is presented. In order to investigate the effect of particle size on the flammability and thermal stability of materials intended for cable coatings, the ethylene–vinyl acetate copolymer (EVA) was filled with two types of magnesium hydroxide (Mg(OH)₂) with the average particle size 20 nm and 2000 nm. The thermogravimetric experiments performed under nitrogen and air atmosphere did not reveal any substantial effect of particle size on the mechanisms and kinetics of Mg(OH)₂ decomposition. Both types of Mg(OH)₂, at temperatures above 350°C, decomposed endothermally to MgO and H₂O. At the same filler volume fraction, composites with the larger Mg(OH)₂ particles exhibited greater value of the limiting oxygen index (LOI) compared to Mg(OH)₂ nanocomposites. It is proposed that the reduction of Mg(OH)₂ particle size below 200 nm results in the catalytic effect of Mg²⁺ to become more prominent compared to coarser particles. In the case of nano-sized Mg(OH)₂, a large portion of polymer matrix is in direct contact with filler surface due to the high specific surface area of the filler used. Large filler–matrix contact area most probably resulted in the surface-induced catalytic effects of the Mg²⁺ ion on degradation of polyolefins, already described in the literature, accelerating thermal degradation of EVA matrix. This process acts against the flame retarding effect of the Mg(OH)₂ thermal decomposition. Furthermore, larger filler surface of nano-filler led to the indispensable change of the deformation response of EVA compared to the micro-filled composite.     

氢氧化镁对聚苯乙烯燃烧产物的影响

聚苯乙烯和含阻燃剂氢氧化镁的聚苯乙烯复合物在气密性良好的燃烧室中燃烧，燃烧产物分别采用气相色谱和气相色谱/质谱进行分析．结果表明，氢氧化镁对聚苯乙烯燃烧产物有明显的影响．随着氢氧化镁含量的增加，二氧化碳的浓度逐渐降低；残渣中焦碳的含量以及大多数的挥发性和半挥发性有机产物，尤其是聚苯乙烯单体和一些多环化合物明显增加．这意味着氢氧化镁的存在改变了聚苯乙烯的燃烧反应路径，导致了聚苯乙烯的不完全燃烧，降低了可燃性．     

Surface treatment of magnesium hydroxide to improve its dispersion in organic phase by the ultrasonic technique

Micron magnesium hydroxide [Mg(OH)₂] was modified by means of ultrasonic method with stearic acid (SA) as modifier in water. The Fourier transform infrared spectroscopy (FT-IR) and element analysis showed all SA was bonded upon the surface of the Mg(OH)₂ forming a coating layer and no free SA was detected after the modifying process. The thickness of coating SA on the Mg(OH)₂ was determined by X-ray photoelectron spectroscopy (XPS). Compared with the unmodified Mg(OH)₂, the modified Mg(OH)₂ had better dispersion property in xylene, slower sedimentation velocity of dilute suspension in xylene and lower viscosity of suspension in paraffin liquid. The results showed that the modified Mg(OH)₂ could be dispersed much better than the unmodified Mg(OH)₂ in organic phase.     

Self-assembly of metal–organic frameworks and graphene oxide as precursors for lithium-ion battery applications

We fabricated composites of Fe₂O₃/reduced graphene oxide as lithium-ion batteries anode material with controlled structures by employing self-assembly of metal–organic frameworks (MOFs) and polymer-functionalized graphene oxide as precursors. By electrostatic interaction, the negatively charged MOFs, Prussian Blue (PB), are assembled on poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene oxide (positive charge). Then the PB cubes become FeOOH nanosheets when treated with sodium hydroxide. Upon further annealing, the FeOOH nanosheets transform to Fe₂O₃ nanoparticles while the graphene oxide become reduced graphene oxide simultaneously. It was found that the composites have good performance as anode of lithium-ion battery. This work shows a new way for self-assembling MOFs and 2D materials.     

Ultrasound-promoted coating of silk yarn with different morphology of magnesium hydroxide nanostructures

The growth of magnesium hydroxide nanostructures on silk yarn was achieved by sequential dipping steps in alternating bath of magnesium nitrate and potassium hydroxide under ultrasound irradiation. The effects of ultrasound irradiation, concentration, pH and sequential dipping steps on growth of the Mg(OH)₂ nanostructures have been studied. Morphology of the nanostructures, depending on pH and with decreasing pH from 13 to 8, changed from nanoparticle to nanoneedle. Results show a decrease in the particles size as the concentration and sequential dipping steps increased. The physicochemical properties of the nanostructures were determined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and wavelength dispersive X-ray (WDX).     

Dissociation of magnesium oxide and magnesium hydroxide nanoparticles in physiologically relevant fluids

Magnesium oxide (MgO) and hydroxide [Mg(OH)₂] are conventionally considered insoluble in water and stable at high temperatures. However, in this study, we found significant dissociation of MgO and Mg(OH)₂ into ions when they were immersed in different physiologically relevant solutions in the form of 20-nm and 10-nm nanoparticles respectively, under standard cell culture conditions in vitro, i.e., a 37 °C, 5% CO₂/95% air, sterile, humidified environment. The change in Mg²⁺ ion concentrations and pH measured in the physiologically relevant solutions (e.g., Dulbecco’s modified Eagle’s Medium (DMEM), simulated body fluid (SBF), relevant chloride solutions, and deionized water) confirmed their dissociation. Possible mechanisms and contributing factors for dissociation of MgO and Mg(OH)₂ nanoparticles were discussed. The evidence suggests that nucleophilic substitution of OH^? by Cl^? in Mg(OH)₂ is energetically unfavorable and it is more likely that Cl^? plays a role in the stabilization of intermediate forms of MgO and Mg(OH)₂ as it dissociates. The pH and buffering capability of the immersion solutions might have played the most significant role in dissociation of these nanoparticles when compared with the roles of chloride (Cl^?), proteins, and different buffering agents. This article provided the first evidence on the dissociation of MgO and Mg(OH)₂ nanoparticles in physiologically relevant conditions and elucidated possible factors contributing to the observed behaviors of these nanoparticles in vitro, which is important for their potential medical applications in vivo.

Open image in new window

Graphical Abstract Dissociation of magnesium oxide and magnesium hydroxide nanoparticles in physiologically relevant fluids

     

Submicron Ion-Exchange Fibers of Polystyrene and Styrene-Butadiene-Styrene Copolymer Blends

In the present study, submicron ion-exchange fibers (IEFs) of polystyrene (PS) and its blends with styrene-butadiene-styrene block copolymer (SBS) were prepared by electrospinning and postsulfonating modification. Scanning electron microscopy (SEM) images showed that the diameters of the fibers enlarged significantly after treatment and the surfaces become rougher. Mechanical properties analysis showed that the electrospun fibers (EF) and the IEFs from PS/SBS blend fabrics possessed better mechanical performances than those from pure PS. The ion-exchange capacity (IEC) of 4.35 mmol/g and and copper ions (Cu²⁺) adsorption value of 3.08 mmol/g for IEFs from PS/SBS blends were both higher than that of IEFs from pure PS and the conventional IEFs produced by coating or grafting fibrous substrates with functionalized resins or monomers. Dynamic adsorption experiments were made to test the behavior of adsorption for Cu²⁺. The results of dynamic adsorption experiments with Cu²⁺ showed that the IEFs from PS/SBS would quickly purify 3000 ml waste water containing Cu²⁺ (100 mg/L), and the removal rate for Cu²⁺ reached 96.5% even at the flow rate of 12 ml/min. The study provided an absorbent with a high dynamic adsorption capacity for removing Cu²⁺ from waste water.     

X-ray diffraction analysis for isothermal annealed powder Mg(OH)2

In this paper, we use an XRD-based 100% approach method to quantify the activity evolution of phase transformation from annealed powder Mg(OH)₂ to MgO. The sample is chemically synthesized. The isothermal phase transformation is carried out between 300 and 310 °C. The ratio of reacted magnesium hydroxide is applied and compared with different existing models. The Avrami model A_n appears to be the most close-fitting. An order of reaction between 1.5 and 2 is observed that it could be considered as a complex combination of different phenomenon, for which we test different models.     

Effect of fillers on magnesium–poly(ethylene oxide) solid polymer electrolyte

A solid polymer electrolyte (SPE) film consisting of poly(ethylene oxide) (PEO) with magnesium chloride as electrolytic salt and B₂O₃ as the filler has been prepared by solution casting technique. The polymeric film was flexible and self-standing with proper mechanical strength and studied for application in a solid-state rechargeable magnesium battery. The interactions between the filler and PEO chains are studied by differential scanning calorimeter and Fourier transform infrared techniques. Composition of SPE is optimized, and maximum conductivity is obtained at 2 wt% B₂O₃. Filler seems to increase the number of free magnesium cations by decoordinating the bond between magnesium cations and ether oxygen of PEO. Cyclic voltammetry results show the reversible capability of magnesium electrode. Solid-state magnesium cell employing magnesium anode, SPE, and manganese oxide was assembled, and its open circuit voltage is found to be 1.9 V.     

Polymer concentration, shear and stretch field effects on the surface morphology evolution during the spin-coating

Polymer concentration and shear and stretch field effects on the surface morphology evolution of three different kinds of polymers (polystyrene (PS), polybutadiene (PB) and polystyrene-b-polybutadiene-b-polystyrene (SBS)) during the spin-coating were investigated by means of atomic force microscopy (AFM). For PS and SBS, continuous film, net-like structure and particle structure were observed at different concentrations. For PB, net-like structures were not observed and continuous films and radial array of droplets emerged. Moreover, we compared surface morphology transitions on different substrate locations from the center to the edge. For PS, net-like structure, broken net-like structure and irregular array of particles were observed. For SBS, net-like structure, periodically orientated string-like structure and broken-line structure appeared. But for PB, flower-like holes in the continuous film, distorted stream-like structure and irregular distributions of droplets emerged. These different transitions of surface morphologies were discussed in terms of individual material property.     

Increased open‐circuit voltage of ZnO nanowire/PbS quantum dot bulk heterojunction solar cells with solution‐deposited Mg(OH)2 interlayer

An ultrathin Mg(OH)₂ layer was solution‐deposited onto the ZnO nanowires to solve the problem of interfacial charge recombination, caused by the increase of interfacial area in bulk heterojunction (BHJ) PbS colloidal quantum dot solar cells (CQDSCs). This Mg(OH)₂ interlayer efficiently passivated the surface defects of ZnO nanowires and provided tunnel barrier at ZnO/PbS interface. As a result, the charge recombination at ZnO/PbS interface was largely suppressed, proved by the significantly elongated electron lifetime and the increased open‐circuit voltage of the Mg(OH)₂‐involved BHJ CQDSCs. Careful thickness optimization of Mg(OH)₂ interlayer finally brought a ～33% increase in V_oc and ～25% improvement in power conversion efficiency.     

THE 31P NMR INVESTIGATION OF PHOSPHORUS BURNS

为了明确磷烧伤创面及吸收毒性物质的化学形式及分布.作者采用\+\{31\}P NMR波谱,研究皮下注射黄磷、磷酸及磷烧伤后创面残留、肝脏及脑组织吸收的元素磷及其化合物含量.其结果皮下注射非致死与致死剂量的黄磷后,肝脏可测到元素磷的吸收,磷燃烧后创面磷绝大部分转化为磷酸及其结合物,极少部分以元素磷形式存在.致死面积的磷酸烫伤与磷烧伤后肝脏区域磷酸增加4～5倍,未检测到元素磷的波谱,各组脑组织均未检测到元素磷峰,而磷酸峰只有微小的增加.结论为磷烧烧后吸收的主要中毒物质与创面残留的主要化学物质一致,磷烧伤中毒的致死性主要是创面磷酸吸收所致.     

Chemical and microstructural study of the oxygen passivation behaviour of nanocrystalline Mg and MgH2

Nanocrystalline Mg and MgH₂ samples have been prepared by high-energy ball milling and gas phase condensation methods. Starting from these materials in their “as received” state without air exposure, a study of the oxygen and air passivation behaviour was carried out by “in situ” analysis of the samples by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The binding energy and photoemission Auger parameters have been determined for metallic magnesium as well as for magnesium hydride, oxide and hydroxide species. Values of the MgH₂ material were reported for the first time. The study clearly shows the formation of an oxide passivation layer of ca. 3-4 nm in thickness for all the nanocrystalline magnesium samples handled under controlled inert gas atmospheres. A hydroxide like amorphous layer is formed at the topmost surface layers of the nanocrystalline Mg and MgH₂ samples. The implication of these studies for H₂ storage and transport applications of nanocrystalline magnesium is discussed.     

Correlation between the surface chemistry and the atmospheric corrosion of AZ31, AZ80 and AZ91D magnesium alloys

X-ray photoelectron spectroscopy (XPS) was used in order to investigate the correlation between the surface chemistry and the atmospheric corrosion of AZ31, AZ80 and AZ91D magnesium alloys exposed to 98% relative humidity at 50 °C. Commercially pure magnesium, used as the reference material, revealed MgO, Mg(OH)₂ and tracers of magnesium carbonate in the air-formed film. For the AZ80 and AZ91D alloys, the amount of magnesium carbonate formed on the surface reached similar values to those of MgO and Mg(OH)₂. A linear relation between the amount of magnesium carbonate formed on the surface and the subsequent corrosion behaviour in the humid environment was found. The AZ80 alloy revealed the highest amount of magnesium carbonate in the air-formed film and the highest atmospheric corrosion resistance, even higher than the AZ91D alloy, indicating that aluminium distribution in the alloy microstructure influenced the amount of magnesium carbonate formed.     

An optical study of the deposition and conversion of nickel hydroxide films

The deposition and conversion of nickel hydroxide films on platinum in nickel nitrate solution is studied using a self-nulling ellipsometer. The cathodically deposited hydroxide film, α-Ni(OH)₂, has a refractive index of 1.502 — 0.0i. When anodically oxidized, the α-Ni(OH)₂ converts to a film of γ-NiOOH of index 1.502 — 0.27i Alternate oxidation and reduction causes the hydroxide film to convert to β-Ni(OH)₂ with refractive index 1.43 — 0.0i. Oxidation of the β-Ni(OH)₂ produces a film of β-NiOOH with refractive index 1.43 — 0.165i. The conversion processes take place uniformly throughout the film with the film thickness increasing by a factor of 1.43 on oxidation. When further deposition of α-Ni(OH)₂ is attempted on a layer of α-Ni(OH)₂, the layer of β-Ni(OH)₂ converts to α-Ni(OH)₂ before deposition begins.     

Evolution of reactive unsaturated interfacial modifiers for polyolefin based composites

The development of a novel reactive unsaturated interfacial modifier for filled (magnesium hydroxide, aluminium hydroxide and calcium carbonate) polyolefins is reviewed. Initial work explored maleimide functional candidate molecules including 1,3-phenylene dimaleimide (1,3-PDM) and a range of linear alkyl dimaleimides. Most of the dimaleimides were very effective interfacial modifiers in polypropylene and poly(ethylene-co-vinylacetate) (18% w/w vinylacetate) based composites. However, the dimaleimides caused the composites to have a distinct pink/brown colouration apart from when the maleimide groups were spaced by a C12 alkyl chain. The problem with colour and high effective dosage prompted a switch to unsaturated carboxylic acid based systems. The performance of a range of unsaturated carboxylic acids and the hexafunctional monomer trimethylolpropane triacrylate are reviewed, together with a novel oligomeric unsaturated carboxylic acid (OUCA) based system developed by the Noveon Division of Lubrizol Limited. The data obtained from this series of interfacial modifiers, and adsorption studies on 1,3-PDM and OUCA, afforded some insight into the competing factors (such as the strength of adsorption versus ability to form a polymerised interfacial layer and the ability to react with matrix chains) that significantly affect the coupling performance of interfacial modifiers.     

Catalytic properties of gold nanoparticles immobilized on the surfaces of nanocarriers

Gold nanoparticles are immobilized in the hydrophilic coronas of spherical micelle carriers for high catalytic activity. The micelle is formed by self-assembly of block copolymer, polystyrene-b-poly (acrylic acid), in basic aqueous solution (pH 10) and has a polystyrene core and a poly (acrylic acid) corona. The gold nanoparticles are anchored into the poly (acrylic acid) corona by in situ reduction of the mixture of HAuCl₄ and micelle with NaBH₄. The sizes of the gold nanoparticles can be adjusted by changing the content of the HAuCl₄. In the process of catalyzing p-nitrophenol to p-aminophenol, the reaction shows one-order kinetics, furthermore, the reaction rate increases with the concentration of composites as well as reaction temperature. Comparing the composites with polystyrene as core and poly (4-vinylpyridine)/Au as corona, the catalytic activity of the present composites is higher, which is ascribed to their hydrophilic corona structure.     

Effects of Rice Husk Derived Amorphous Silica on the Thermal-Mechanical Properties of Unsaturated Polyester Composites

Rice husk is rich in amorphous silica which has found various applications as a filler in rubbers and plastics. In the research described here silica was extracted from rice husk ash in the form of sodium silicate which was used to produced amorphous precipitated silica (PS) and silica aerogel (SA) using a sol – gel process and supercritical drying. These materials were then physically mixed with unsaturated polyester (UP) resin and cured at room temperature to form polymer composites. The experimental results showed that the UP composites with 30% (volume percent) of SA filler had lower density and better thermal insulation than the composites with the same amount of PS. Thermogravimetric analysis (TGA) results showed that the T_onset of the PS and SA composites were slightly delayed by 15 and 10°C, respectively. The tensile stress-strain curves showed that addition of the fillers reduced the tensile strength, but increased the elastic moduli of the UP matrix. PS filled UP composites exhibit higher moduli (higher stiffness) than that of SA filled UP composites. This was due to agglomeration and poor adhesion of the SA particles to the UP matrix while better dispersion was observed for the PS filled composite.