Improvement in compression performance of the polysulfide sealant by thiol‐acrylate reaction

Trimethylolpropanetriacrylate (TMPTA) was added to the polysulfide‐manganese dioxide (PSF‐MnO₂) liquid mixtures as a crosslinker to improve their crosslinking capability. The samples were cured at room temperature for different times and the crosslinking degree was characterized by extraction and swelling tests. Mechanical properties of the cured samples including tensile, compression (stress relaxation, permanent set, and cyclic compression), and dynamic mechanical behaviors were investigated. The results indicated that the TMPTA crosslinker significantly increased the crosslinking degree and the homogeneity of the formed PSF networks. As a result, the tensile and compression stress and relaxation performances of the cured PSF rubber were dramatically improved. This result was also consistent with the results from the swelling, cyclic compression, and dynamic mechanical measurements. Interestingly, the tensile strength of the TMPTA cured samples did not show apparent change when the curing time was longer than 14 days, whereas their compression stress and relaxation performance were growing remarkably from 14 to 60 days. The improved performances were attributed to the high efficiency of thiol‐acrylate Michael addition reaction for the crosslinking. It promoted the curing rate, resulting in good compression properties in a much shorter curing time.POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Synthesis and characterization of manganese dioxide spontaneously coated on carbon nanotubes

Manganese dioxide (MnO₂) was coated on carbon nanotubes (CNTs) by simple immersion of the CNTs into a KMnO₄ aqueous solution. The synthesis mechanism was investigated by in situ monitoring of the reduction potential and pH of the solution and supplementary UV-VIS analysis of ions in the solution. CNTs were found to act as a reducing agent and substrate for the heterogeneous nucleation of MnO₂ in an aqueous KMnO₄ solution. The morphology of the CNTs before and after MnO₂ deposition was examined using scanning electron microscopy, which showed MnO₂ deposited as a thin and uniform layer on the CNTs at an initial pH of 7, but as nano-rods of MnO₂ at an initial pH 1. The MnO₂ was shown to be a Birnessite-type MnO₂ by X-ray powder diffraction and Raman spectroscopy. The thermal stability of the CNTs, examined by thermogravimetric analysis, was improved by the thin, uniform and continuous coating of MnO₂.     

Sintering,crystallization and properties of 2(Mg1−xMnx)O·2Al2O3·5SiO2 ceramics

Mn-substituted cordierites, 2(Mg_1?xMn_x)O·2Al₂O₃·5SiO₂ (x?=?0–1), were prepared from natural components (talc, clay, alumina) and MnO_2. Sintering behavior, phase transformation, and microstructural features of the samples were investigated using X-ray diffraction (XRD), differential thermal analysis (DTA), dilatometric measurements and scanning electron microscopy (SEM) with energy dispersive analysis (EDS). The results of DTA and XRD analysis indicate that MnO₂ is successively reduced to Mn₂O₃ and MnO in the sintering process. Mn²⁺ ions incorporate into the crystal structure of α-cordierite substituting Mg²⁺ ions in octahedral sites and thus increasing the cordierite unit cell volume. Mn promotes the sintering process: the crystallization temperature, melting point, density and open porosity of Mn-substituted cordierites lowered, whereas the shrinkage and medium pore diameter enlarged with an increase in MnO₂ content in the mixture of raw materials. Surface enrichment with Mn with the formation of manganese oxide crystallites was found for the samples with high substitution degree.     

Optimized formulation of an oxidative curing system for liquid polysulfide sealants used in fuel tanks by D‐optimal design method

In this work, the effective parameters in liquid polysulfide curing system were optimized by D ‐optimal design method. Five main components in the formulation, carbon black, vulcanizing agents (MnO₂, Na₂Cr₂O₇, and PbO₂), CaCO₃, fumed silica, and chlorinated paraffin, were selected. Mechanical and chemical properties of the samples were investigated. The results showed that tensile strength, hardness, viscosity, and optimum cure time (t₉₀) presented a suitable coordination with reduced quadratic model. For elongation at break and swelling tests, reduced two‐factor interaction (2FI), and for peel strength, a linear model showed the best correlation. To achieve the desirable properties for liquid polysulfide sealants used in fuel tanks, an optimized amount of the above components in the formulation were used. Finally, MnO₂ curing system, compared with Na₂Cr₂O₇ and PbO₂, was selected as the best choice. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

水溶液中新生态MnO2对苯酚的吸附作用

研究了新生态MnO^₂对水溶液中苯酚的吸附作用.对一些影响因素,如pH、高价正离子Al³⁺和高价负离子PO^3-₄进行了考察,并探讨了反应机理.实验结果表明,新生态MnO₂对苯酚的吸附等温线为“S”形,对苯酚的吸附过程包括表面吸附和孔内扩散两部分.pH在6～9的范围内,随pH升高苯酚吸附量下降,但变化不大;当pH≥10时,苯酚去除率几乎降为零.少量铝离子有利于苯酚的吸附.因为铝离子吸附在新生态MnO₂表面,改变了新生态MnO₂的表面性质,有利于苯酚的吸附.磷酸根离子极易与苯酚络合而带负电荷,不利于新生态MnO₂对苯酚的吸附.     

Characterization of coil coatings by thermal analysis

The interrelationship between the network formation process and performance properties makes cure process studies critically important in the coil‐coating industry. The objective of this work was to introduce thermal analysis into the evaluation of curing of uncured samples and in studies of the glass‐transition temperatures of cured samples. Thermal analysis, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC) were used to characterize gelation and curing of three types of samples: paints, coated sheets, and free films. In addition to the generally used three‐point‐bending and extension geometries, a cup‐and‐plate geometry also was used in analyzing gelation and curing of liquid samples. These thermal analyses are suited to the purpose of characterizing coil coatings. A correlation between PMT (peak metal temperature) and measured T_g (glass‐transition temperature) was found, as well as effectively distinguishing different curing conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2016–2022, 2003     

Promotion effect and mechanism of MnOx doped CeO2 nano-catalyst for NH3-SCR

MnO_x-CeO₂ (denoted as Mn–Ce) nanorod and MnO_x-CeO₂ nanooctahedra catalysts were synthesized by the hydrothermal method and were used for selective catalytic reduction of NO with NH₃. The catalytic performance tests showed that the NO removal efficiency of CeO₂ catalysts was obviously improved after loading MnO_x. The structure and properties of catalysts had been characterized by SEM、TEM、XRD、BET、XPS、H₂-TPR、NH₃-TPD and in situ DRIFTS. It was found that Mn–Ce catalyst were of uniform core-shell structure, higher concentrations of Mn⁴⁺ and Ce³⁺, better reducibility, the increase of weak acid sites. The results of in situ DRIFTS indicated that the NH₃-SCR reaction should obey the E–R mechanism. Moreover, the promotion effect and mechanism of MnO_x doped CeO₂ was demonstrated, which improved the catalytic activity of Mn–Ce catalysts.     

In–situ Characterization and Cure Kinetics in NEPE Propellant/ HTPB Liner Interface by Microscopic FT‐IR

The content distribution of chemical groups and the kinetics of curing process in the micro‐region interfaces of nitrate ester plasticized polyether (NEPE) based propellant/hydroxyl‐terminated polybutadiene (HTPB) based liner were studied by in‐situ diffuse reflection FT‐IR spectroscopy. During the curing process, the content of –NCO groups showed little increase in the liner region toward the interface. It rises quickly through the interface layer and is then stable in the region of the propellant layer, while the content of –NH groups gradually increases from liner to propellant. In the micro‐region between liner and propellant, the –C=O decreases rapidly through interface and then has a slight increase in the propellant region. Migration of nitrate esters appears at the interface of the NEPE propellant/liner at early period of curing, and –O–NO₂ decreases from propellant to liner in the bonding interface micro‐region. A study of curing kinetics indicates that the second‐order reaction model can describe the curing reaction in the bonding interface at the early stage of curing process. The order of apparent curing reaction rate constant (k ) of liner (L point), intermediate point (I point) and propellant (P point) in the interface micron‐region is k L > k I > k P at the same curing temperature. The apparent reaction activation energy (E _a) at L, I, and P points are 39.96, 81.49, and 62.51 kJ mol^–1, respectively, based on the Arrhenius equation.     

Fibrillation of liquid crystalline polymer in polysulfone promoted by increased system elasticity via adding nano-silica

Ternary blends composed of a liquid crystalline polymer (LCP), nano-SiO₂ and polysulfone (PSF) were prepared by melt blending. Very long and perfectly oriented LCP fibrils were in situ formed in capillary flows by adding 5 vol% of nano-SiO₂ to binary PSF/LCP blend. Dynamic rheology analysis indicated that the sharp increase of elasticity was caused by higher content of nano-SiO₂. Then the entrance angle was decreased and elongational stress increased when the polymer melt flowed through the abrupt contraction, which resulted in the fibrillation of LCP in PSF/LCP/nano-SiO₂ system.     

Fabrication of highly sensitive MnO2/F-MWCNT/Ta hybrid nanocomposite sensor with different MnO2 overlayer thickness for H2O2 detection

In this work, we report the development of MnO₂/F-MWCNT/Ta hybrid nanocomposite sensor with different MnO₂ overlayer thickness for the detection of H₂O₂ in real samples. A novel two-step process using e-beam evaporation and spray pyrolysis deposition was adopted for the synthesis of hybrid MnO₂/F-MWCNT/Ta electrodes. SE morphology revealed smaller-sized, compact grains of MnO₂ infiltrated on the outermost walls of MWCNTs. Raman analysis confirmed the existence of carbon nanotubes with abundant structural defects of MnO₂ in the composite. The cyclic voltammetry results displayed a high peak current and narrowed over potential towards the reduction of H₂O₂. The sensor displayed a fast response (<5?s), wide linear range (2–1510?μM) and a low limit of detection (0.04?μM) with significant anti-interfering properties, promising for the development of highly sensitive and reproducible biosensors. The three dimensional nanocomposite sensor also exhibited good recovery (> 98%), thus providing a favourable tool for analysis of H₂O₂ in milk samples.     

Experimental and theoretical study of a fast curing adhesive

In semiconductor industry the application of fast curing adhesives with curing times below 20 s is necessary for cost-effective production of electronic packages at high throughput. For the curing process control as well as for the selection of appropriate adhesives, adequate analytical tools, which enable the measurement of fast curing reactions under package assembly conditions are essential. In this study, the curing behaviour of a commercially available adhesive, chemically based on an epoxy compound was examined by means of dielectric analysis (DEA) and differential scanning calorimetry (DSC). For the DEA method we developed an experimental set-up with similar temporal and thermal conditions as for the observed curing behaviour during the package production process. Formal kinetic analysis was performed of the isothermal DEA and the non-isothermal DSC data and kinetic models and parameters were derived and compared. This study revealed, that both measuring methods, the DEA and the DSC gain important information for characterising this curing system, although different kinetic models were found for the two methods. With the DEA method it was possible to determine an optimal curing temperature for the adhesive at process near experimental conditions.     

Influence of the synthesis conditions on the curing behavior of phenol–urea–formaldehyde resol resins

The curing behavior of synthesized phenol–urea–formaldehyde (PUF) resol resins with various formaldehyde/urea/phenol ratios was studied with differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The results indicated that the synthesis parameters, including the urea content, formaldehyde/phenol ratio, and pH value, had a combined effect on the curing behavior. The pH value played an important role in affecting the shape of the DSC curing curves, the activation energy, and the reaction rate constant. Depending on the pH value, one or two peaks could appear in the DSC curve. The activation energy was lower when pH was below 11. The reaction rate constant increased with an increase in the pH value at both low and high temperatures. The urea content and formaldehyde/phenol ratio had no significant influence on the activation energy and rate constant. DMA showed that both the gel point and tan δ peak temperature (T_tanδ) had the lowest values in the mid‐pH range for the PUF resins. A different trend was observed for the phenol–formaldehyde resin without the urea component. Instead, the gel point and T_tanδ decreased monotonically with an increase in the pH value. For the PUF resins, a high urea content or a low formaldehyde/phenol ratio resulted in a high gel point. The effect of the urea content on T_tanδ was bigger than that on the gel point because of the reversible reaction associated with the urea component. Too much formaldehyde could lead to more reversible reactions and a higher T_tanδ value. The effects of the synthesis conditions on the rigidity of the cured network were complex for the PUF resins. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1368–1375, 2005     

Influences of different gravity environments on the curing process and cured products of carbon‐nanotube‐reinforced epoxy composites

The influences of different gravity environments on the curing process and the cured products of carbon‐nanotube‐reinforced epoxy composites were investigated in this study. Different gravity environments were simulated with a superconducting magnet on the basis of which resin matrix composites with different amino‐functionalized multiwalled carbon nanotube (NH₂‐MWCNT) concentrations of 0.1, 0.3, 0.5, and 1 wt % were tested. Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, thermomechanical analysis (TMA), thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and three‐point bending tests were used to analyze the characteristics of different curing processes and cured products. From the results, we observed that the curing rate of the epoxy composites was influenced by different gravity values, and there was anisotropy in the NH₂‐MWCNT‐reinforced epoxy composites cured in the simulated microgravity environment. More effects of gravity on the curing process and cured products could be obtained through detailed experiments and discussion; this is important and fundamental for improving and enhancing the properties of composite materials used in different gravity environments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41413.     

Studies on MnO2—II. Relationship between physicochemical properties and electrochemical activity of some synthetic MnO2 of different crystallographic forms

The electrochemical activity of a number of synthetic MnO₂ samples of various crystalline modifications has been determined by discharging a thin pellet containing 0.150 g MnO₂ and 0.015 g acetylene black in both NH₄ClZnCl₂ (pH 4.1) and 9M KOH medium. An attempt has been made to find correlations between depolarizing capacity (time to reach 0.6 V) and various physico-chemical properties; such as, density, surface area, lattice parameters, surface OH groups, surface oxygen, magnetic susceptibility etc. Whereas depolarizing capacity for γ-MnO₂ increases with increase in both true and packing (powder) density, capacity tends to decrease with increase in surface area. For other modifications of MnO₂ there exist direct relationships between depolarizing capacity and the various properties of the samples mentioned above. The relationships between lattice parameters and depolarizing capacity indicate that samples with an extended ab plane in general possess higher activity. It has been observed that surface OH groups and surface oxygen when normalised to unit weight are not only important properties in active MnO₂ but are also interrelated.     

Development of MnO<Subscript>2</Subscript>-incorporated high performance aluminum alloy matrix sacrificial anodes

Manganese dioxide, a potential catalyst in many electrochemical reactions, was explored as an effective activator in Al + 5% Zn alloy sacrificial anodes. The catalytic influence of MnO₂ on the anodes was micro-structurally and electrochemically characterized using different electrochemical techniques. The process of incorporation of MnO₂ not only improved the grain size but also the galvanic performance of the anodes significantly. A galvanic performance as high as 80% was achieved by incorporating an optimum quantity (0.5%) of MnO₂ in the anode matrix. High and steady active open circuit potential, very low polarization and substantial reduction in self corrosion were achieved during galvanic exposure tests. Effective activation of the anodes by MnO₂ was also revealed by the results of electrochemical impedance analysis. The tolerance to biofouling on the anode surface was studied by quantifying the number of micro-organisms on the anode surface after immersing in natural sea water containing the micro-organisms.     

Electrodeposited MnO2/Au composite film with improved electrocatalytic activity for oxidation of glucose and hydrogen peroxide

The major drawback of currently used MnO₂ film sensor is the loss of electrical conductivity due to the formation of a poorly conductive MnO₂ layer. To overcome this problem, a coating in which the Au is alloyed with MnO₂ has been developed. The fabrication of the codeposited film electrode of Au and MnO₂ by using a cyclic voltammetric (CV) method was described, and systematic physical and electrochemical characterization was performed. This MnO₂/Au film electrode enhanced MnO₂ electrocatalytic activity. The oxidation process of glucose at the codeposited MnO₂/Au shows a well-defined peak at 0.27 V in alkaline aqueous solution. In contrast, the glucose oxidation at Au modified glassy carbon electrode (GCE) just shows a shoulder wave at 0.42 V. The experimental results indicate that the modification of MnO₂ on the surface of GCE significantly improved the electrocatalytic activity towards the oxidation of glucose. Further study shows that the MnO₂/Au could also effectively catalyze the oxidation of hydrogen peroxide in pH 7.0 phosphate buffer solution (PBS).     

Polypyrrole/MnO2 composites and their enhanced electrochemical capacitance

The composites of polypyrrole (PPY) and MnO₂ have been prepared through chemical oxidation of pyrrole monomer and MnO₂ suspension with ammonium peroxysulfate at low temperature. The morphology and structure of materials were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Transmission electron microscopy (TEM), thermal gravity analysis ‐ differential thermal gravity (TG‐DTG), and X‐ray diffraction (XRD) measurements. The electrochemical properties of the composite were investigated by galvanostatic charge–discharge and electrochemical impedance spectroscopy. The specific capacitance of the composite electrode is 352.8 F/g at a current of 8 mA/cm² in Na₂SO₄ electrolyte of 0.5 mol/L, which is much higher than that of 246.2 F/g and 103.5 F/g of PPY and MnO₂, respectively. A convenient and effective technique has been developed to fabricate composite materials of PPY and MnO₂ promising for designing new capacitors. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Investigation of thermoplastic elastomer (TPE) foaming process using blowing agent by rheological and morphological methods

The effects of a chemical blowing agent (CBA) or an encapsulated physical blowing agent (PBA) on morphological development in ethylene octene copolymer (EOC) matrix using dicumyl peroxide (DCP) as a curing agent were investigated by rheological, mechanical, and morphological methods. Temperature ramp tests were carried out to understand curing and foaming processes. Curing temperature (T_cure) was determined as the crossover temperature where storage modulus G′ coincided with loss modulus G′′ in the rheological point of view. For the CBA, T_cure increased with increasing CBA concentration, whereas for the PBA, T_cure decreased with increasing PBA concentration. Other critical temperatures T_1st, T_2nd by foaming process were determined using the axial normal force. With these critical temperatures (T_cure, T_1st, T_2nd), curing and foaming mechanisms can be estimated. Simultaneously, volume expansions of samples were observed with camera. Morphology and mechanical analysis were conducted on fully cured and foamed ECP (is defined as EOC with DCP) with blowing agent. ECP with the CBA exhibited an irregular open-cell structure, whereas when produced using the PBA, it formed a regular closed-cell structure. Specific tensile strength tended to increase with increasing PBA concentration but as blowing agent concentration increased elongation at break decreased. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47358.     

Time–temperature–transformation cure diagrams of phenol–formaldehyde and lignin–phenol–formaldehyde novolac resins

In this study, the time–temperature– transformation (TTT) cure diagrams of the curing processes of several novolac resins were determined. Each diagram corresponded to a mixture of commercial phenol–formaldehyde novolac, lignin–phenol–formaldehyde novolac, and methylolated lignin–phenol–formaldehyde novolac resins with hexamethylenetetramine as a curing agent. Thermomechanical analysis and differential scanning calorimetry techniques were applied to study the resin gelation and the kinetics of the curing process to obtain the isoconversional curves. The temperature at which the material gelled and vitrified [the glass‐transition temperature at the gel point (_gelT_g)], the glass‐transition temperature of the uncured material (without crosslinking; T_g0), and the glass‐transition temperature with full crosslinking were also obtained. On the basis of the measured of conversion degree at gelation, the approximate glass‐transition temperature/conversion relationship, and the thermokinetic results of the curing process of the resins, TTT cure diagrams of the novolac samples were constructed. The TTT diagrams showed that the lignin–novolac and methylolated lignin–novolac resins presented lower T_g0 and _gelT_g values than the commercial resin. The TTT diagram is a suitable tool for understanding novolac resin behavior during the isothermal curing process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology and thermal/mechanical properties of alkyl‐imidazolium‐treated rectorite/epoxy nanocomposites

A novel organic rectorite (OREC) was prepared by treating the natural sodium‐rectorite (Na‐REC) with ionic liquid 1‐hexadecyl‐3‐methylimidazolium bromide ([C₁₆mim]Br). X‐ray diffraction (XRD) analysis showed that the interlayer spacing of the OREC was expanded from 2.23nm to 3.14nm. Furthermore, two types of OREC/epoxy nanocomposites were prepared by using epoxy resin (EP) as matrix, 2‐ethyl‐4‐methylimidazole (2‐E‐4‐MI) and tung oil anhydride (TOA) as curing agents, respectively. XRD and transmission electron microscope (TEM) analysis showed that the intercalated nanocomposite was obtained with addition of the curing agent 2‐E‐4‐MI, and the exfoliated nanocomposite was obtained with addition of the curing agent TOA when the OREC content was less than 2 wt %. For the exfoliated nanocomposite, the mechanical and thermal property tests indicated that it had the highest improvement when OREC content was 2 wt% in EP. Compared to pure EP, 60.3% improvement in tensile strength, 26.7% improvement in bending strength, 34% improvement in bending modulus, 14°C improvement in thermal decomposition temperature (T_d) and 5.7°C improvement in glass transition temperature (T_g) were achieved. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012