High Degree Of Hydrogen Research Articles

Harsh environment resistible and recyclable thermoplastic polyurea adhesive based on stable and density hydrogen bonds

Adhesives are crucial in a variety of applications, including transportation, building, electronics, aerospace and even human organs etc. However, tens of millions of tons of adhesives used world widely couldn’t be recycled due to the chemically crosslinked structure, especially for those used in harsh environments. Here, we synthesized a self-healing thermoplastic polyurea with ultra-high hydrogen bonding by ending capped with UPy and excellent harsh environment resistible and recyclable capability by utilizing PDMS as the only soft segment. For a property balanced sample, PDMS-12, it exhibited high degree of hydrogen bonding association of 92.5 % at 30 ℃ and gradually decayed after 80 ℃, after which its adhesion was stimulated as revealed by rheological test. If the pure PDMS-12 was immersed in water, pH = 1 acid, pH = 14 alkali, oil, and simulated seawater for up to 30 days, its initial adhesion strength declined between 48 % and 70 %. When it was already glued between different matrixes, the lap shear strength dropped by 0.7 % to 80 %, depending on the types of matrixes and liquid environments. Nonetheless, the remaining adhesion strength was always strong enough to lift weights of ∼ 5.0 kg and can be reused after cleaning. What’s more, a 0.5 mm glue coating could successfully protect a glass bulb from an impact of 0.5 kg weight at approximately −196 ℃, proving its potential application in fragile fields like electrical industry.

Gas cluster etching for the universal preparation of polymer composites for nano chemical and mechanical analysis with AFM

Atomic force microscopy (AFM) based techniques that probe nanomechanical and nanochemical features are valuable tools for studying composite surfaces at high-resolution. However, the application of AFM, particularly at resolutions less than 50 nm per pixel, is limited to sample surfaces that are smooth relative to the tip dimensions and damage-free. As a result, high-resolution AFM is limited in technologically relevant polymer composite systems where current sample preparation techniques can fail to produce the necessary pristine surfaces. Here, we apply gas cluster ion beam (GCIB) etching to prepare composite materials for nanomechanical and nanochemical analysis. We demonstrate that the GCIB can effectively remove material and produce damage free surfaces for composites comprised of PMMA or PS confined in the 7 nm diameter pores of an organosilicate matrix. AFM-IR measurements on the etched region indicate a high degree of hydrogen bonding between the carbonyl groups of the confined PMMA and the hydroxyl groups on the pore walls, while maps of loss tangent can identify the 7 nm polymer domains within the organosilicate matrix. This work demonstrates that GCIB is an effective tool for nanocomposite surface preparation and could enable a new range of materials to be studied with AFM at high resolution.

An atomistic insight into reactions and free-energy profiles of NH3 and Ga on GaN surfaces during the epitaxial growth

Precursor molecules (NH3 and Ga compounds) along with carrier gas (H2 or N2) used to grow GaN structures bring a large amount of hydrogen atoms which affect the growing mechanism of GaN. This has a non-negligible effect of the chemistry and diffusivity of precursors and dissociation products. To encompass the experimentally difficulty in of unraveling such a complicated reaction mechanism, we resort to first principles molecular dynamics modeling, providing an atomistic insight into two major issues. The first one is the evolution of H atoms after the adsorption and dissociation of NH3 on the growing GaN surface. The second issue is to shed light on the role of passivating hydrogen at growth conditions for a typical GaN Ga-rich (0001) surface. In the first case, reaction pathways alternative to the product of molecular hydrogen (H2) can be realized, depending on the initial conditions and morphology of the surface, resulting in an adsorption of H atoms, thus contributing to its hydrogenation. In the second one, instead, we show how the presence of passivating H atoms at the surface, corresponding to a relatively high degree of hydrogenation, contribute to limit the diffusivity of Ga adatoms at the typical growth temperatures.

Zirconium promoter effect on catalytic activity of Pd based catalysts for heterogeneous hydrogenation of nitrile butadiene rubber

Three PdZr bi-component catalysts supported on modified silica have been successfully synthesized via different Zr introduction methods and utilized for the hydrogenation of nitrile butadiene rubber (NBR) to produce high value-added hydrogenated NBR. It is demonstrated that the introduction of Zr can lead to the formation of small-sized and electron-rich Pd nanoparticles and the order of adding Zr can significantly affect the catalytic activity. In particular, the PdZr bi-component catalyst obtained by introducing Zr followed by adding Pd is found to be more stable on the silica support, which exhibits a high hydrogenation degree of 90.9% with 100% selectivity to CC bond, close to the single Pd catalyst with double Pd contents. The electronic structure and reaction mechanism analysis from density functional theory calculations further reveal that the addition of Zr component leads to negatively charged Pd species with lower energy barrier for the hydrogenation of CC bond. Our findings provide a useful guidance for the design of efficient and low-cost bi-component catalysts for the selective hydrogenation of unsaturated polymers.

One-step Synthesis of End-Functionalized Hydrogenated Nitrile-Butadiene Rubber by Combining the Functional Metathesis with Hydrogenation.

End‐functionalized hydrogenated polymers obtained from nitrile‐butadiene rubber (NBR) yield new materials with suitable properties for a number of applications as sealing material and adhesives. We investigated the one‐step synthesis of ester end‐functionalized hydrogenated nitrile‐butadiene rubber (EF‐HNBR) by combining the functional metathesis with the hydrogenation of NBR in the presence of the 2nd generation Grubbs catalyst and a functionalized olefin as a chain transfer agent (CTA). We established the operating conditions for the effective production of saturated functional polymers with a high degree of hydrogenation, high chemo‐selectivity and moderate molecular weight. The structures of the products were confirmed by FT‐IR and 1H‐NMR spectroscopy, rubber molecular weight, and distribution determined by using gel permeation chromatography (GPC); their thermal properties were determined by thermo‐gravimetric analysis (TGA) and different scanning calorimetry (DSC).

Chitosan coated polyacrylonitrile nanofibrous mat for dye adsorption

Chitosan is a promising natural-derived polymer for dye adsorption owing to its rich source, good biodegradablity and high adsorption capacity. However, electrospinning of pure chitosan nanofiber needs high concentration of acid solution and the electrospinning productivity is very low due to its high degree of hydrogen bonding and polycationic nature. To solve the problem, the chitosan coated polyacrylonitrile nanofibrous mat (CPNM) was successfully prepared via a two-step fabrication process of polyacrylonitrile electrospinning and a subsequent chitosan coating. The chitosan was homogeneously adhered onto the PAN nanofibers, which improved the hydrophilicity and adsorption capacity of Acid Blue-113 significantly. The adsorption of Acid Blue-113 on CPNM fitted the pseudo-second-order kinetics model well, and the maximum adsorption capacity of CPNM calculated from the Langmuir isotherm model was 1708 mg/g with the average fiber diameter of 189 nm. The CPNM demonstrate the virtue of simple fabrication process, high adsorption capacity and good reusability, which is a promising adsorbent for dye removal.

Regulation of the degree of hydrogenation and electrochemical properties of graphene generated by electrochemical cathodic exfoliation by using different solvents

Hydrogenated graphene has attracted much attention because its properties can be tuned by varying the degree of hydrogenation. In this work we adjusted the degree of hydrogenation of hydrogenated graphene by using different solvents in the electrochemical cathodic exfoliation process. Interestingly, the graphene obtained by exfoliation in different solvents showed a range of electrochemical performances. The characterization data indicated that the highest level of hydrogenation was observed with the sample produced in N,N-dimethylformamide (G-DMF). Moreover, the G-DMF also showed superior electrochemical performance in terms of electron-transfer rate and sensitivity towards ascorbic acid, which is attributed to the fact that it has most catalytic active defect sites, induced by the high degree of hydrogenation. In addition, the sample produced in propylene carbonate (G-PC) showed the lowest density of defects, while the sample produced in dimethyl sulfoxide (G-DMSO) did not appear to have any electrochemical benefits. Overall, the results suggest a route to the scalable production of graphene with a tunable degree of hydrogenation using a facile and simple strategy.

Nitrile Butadiene Rubber Hydrogenation over a Monolithic Pd/CNTs@Nickel Foam Catalysts: Tunable CNTs Morphology Effect on Catalytic Performance

In heterogeneous catalyst systems, catalytic performance was often negatively influenced by mass transfer limitations in which macromolecular reactants cannot diffuse into the inner pores to attach active sites. Carbon nanotubes (CNTs) with no-porous structure were the promising supports to solve the problem. In this work,CNTs were directly prepared by the CVD (chemical vapor deposition) method on nickel foam (NF). The morphology of the as-synthesized CNTs were effectively tailored by varying temperature for growing CNTs. The prepared CNTs composites (CNTs@NF) with good mechanical strength were employed as a palladium catalyst (Pd/CNTs@NF) for nitrile butadiene rubber (NBR) hydrogenation, where a high degree of hydrogenation (HD) was accomplished via Pd/CNTs@NF catalyst. The HD for fifth reuse was only slightly reduced, demonstrating its great recyclable activity. Remarkably, the structured Pd/CNTs@NF catalyst could be easily separated from the hydrogenated products, avoiding the necessity of filtration f...

Hydrogenated graphene as support of Pd nanoparticles with improved electrocatalytic activity for ethanol oxidation reaction in alkaline media

A new class of ethanol electrooxidation catalyst was developed based on Pd nanoparticles supported by hydrogenated graphene (HG). The catalytic activities of Pd/HG with different hydrogenation degree (annealed at 60, 300, 800 °C respectively) were also carefully studied. Test results suggested that Pd/HG-60 exhibited super activity for electrocatalytic ethanol oxidation to Pd/HG-300 and Pd/HG-800. Moreover, Pd/HG-60 showed the highest electrochemically active surface area (EASA) among these obtained catalysts. The characterization data indicated that hydrogenated graphene with high hydrogenation degree was more favorable to promote the formation and dispersion of small Pd nanoparticles. In turn, highly dispersed Pd nanoparticles have strong electronic interaction with graphene support, which contributes to high EASA resulting in better electrocatalytic activity for ethanol oxidation reaction in alkaline media.

Stable and recyclable Pd catalyst supported on modified silica hollow microspheres with macroporous shells for enhanced catalytic hydrogenation of NBR

In this work, a stable and recyclable Pd catalyst supported on N-containing silane coupling agent modified silica hollow microspheres with macroporous shells (Pd/N-SHMs) was successfully prepared and used for the selective hydrogenation of nitrile-butadiene rubber (NBR) with enhanced catalytic performance. The results showed that Pd/N-SHMs possessed small-sized and well-dispersed Pd nanoparticles (NPs) and the macroporous shells were beneficial for the diffusion of macromolecular NBR, and thus with such a catalyst, the reaction could occur under mild conditions and high hydrogenation degree (96.6%) with 100% selectivity to C=C was obtained. The prepared catalyst could be easily recycled and reused with a high efficiency. More importantly, because of the strong coordination between Pd and diamine ligands, Pd NPs could be anchored steadily over the support and only 5.0 ppm Pd residues was detected in products. This reaction was considered as pseudo-first order at high H2 pressures, and the reaction activation energy was calculated to be as low as 18.1 kJ/mol. Our contribution is to provide an efficient and recyclable supported Pd catalyst, which may promote the development of heterogeneous catalytic systems for unsaturated macromolecular hydrogenation.

Unrevealing the effect of different dispersion agents on the properties of ethylene–propylene copolymer/halloysite nanocomposites

The properties of polyolefin nanocomposites strongly depend on the dispersion level of the nanoparticles and the addition of dispersion agents contributes to improving their performance. In this study, the morphology and the mechanical properties of heterophasic ethylene-propylene copolymer/halloysite nanocomposites were tailored by using two hydrogenated hydrocarbon resins: 90% and 100% hydrogenated and two compatibilizing agents: poly(propylene-g-maleic anhydride) and poly(ethylene-octene-g-maleic anhydride). The transmission electron microscopy indicated that the best dispersion of the halloysite nanotubes was achieved when hydrogenated hydrocarbon resins and poly(propylene-g-maleic anhydride) were used simultaneously. All nanocomposites showed an increase in mechanical stiffness and the most pronounced increase of 46% in the Young modulus was achieved with the system containing halloysite, poly(propylene-g-maleic anhydride) and the hydrocarbon resin with the higher degree of hydrogenation. Poly(ethylene-octene-g-maleic anhydride) caused the halloysite nanoparticles to concentrate preferentially in the rubber domains, wherein these hindered the crystallization of polypropylene and polyethylene chains, as showed by atomic force microscopy. In this case, the composite exhibited both high stiffness and improved toughness. These results highlight the key role of dispersion agents in promoting a good balance in the mechanical properties of resulting nanocomposites based on halloysite particles and heterophasic ethylene-propylene copolymers.

Macroporous hollow silica microspheres-supported palladium catalyst for selective hydrogenation of nitrile butadiene rubber

Abstract A potential high durable heterogeneous catalyst for the industrial selective hydrogenation of nitrile butadiene rubber (NBR) has been established by immobilizing palladium (Pd) nanoparticles on macroporous hollow silica (MHS) microspheres in the present work. Compared with the Pd nanoparticles supported on macroporous hollow silica (Pd/MHS) via conversional incipient wetness impregnation with different free chelating reagents (HCl or EDTA) catalysts, the Pd nanoparticles supported on the modified macroporous hollow silica (Pd/M-MHS) catalyst showed better distribution of Pd nanoparticles and catalytic performance. High hydrogenation degree (HD) toward the –CH CH– group of 97% was achieved in acetone solution at 70 °C with H 2 pressure of 4.5 MPa for 6 h, while the nitrile (–C N) group had not been hydrogenated in the reaction. And there was no obvious change in the relative molecular weight and polydispersion index of the product in comparison with the raw NBR. The HD for the 5th reuse was 90.5%, remaining more than 93% of its HD for the original time, demonstrating its high durable activity.

Magnesium hydride film formation using subatmospheric pressure H2 plasma at low temperature

MgH2 films were prepared using pure hydrogen plasma under subatmospheric pressures ranging from 13.3 to 53.3 kPa (100–400 Torr). The prepared films were characterized by scanning electron microscopy, x-ray diffraction (XRD), and temperature programmed desorption measurements. The ratio of MgH2 to Mg in the prepared films was evaluated, as the degree of Mg hydrogenation, by XRD analysis. The plasma was found to be indispensable for the preparation of thick MgH2 film near normal hydrogen pressure. Hydrogen plasma exposure treatment after Mg film formation had only a very small effect on thick MgH2 film formation, despite the use of subatmospheric pressure hydrogen plasma with high H atom density. Simultaneous supply of Mg and atomic hydrogen was found to be important in preparing thick MgH2 films. Therefore, the surface reaction between Mg and H appears to play an important role in the growth process. The flux ratio (ΓH/ΓMg) of atomic H and Mg required to prepare highly hydrogenated Mg was found to be more than 100. The resulting degree of hydrogenation of the prepared MgH2 film was as good or better than that of commercial powders. MgH2 film prepared on Si substrate exhibited growth with (211) preferred orientation as the deposition rate was decreased, and a columnar structure along the growth direction. The deposition rate reached 2.9 μm/min while still maintaining a high degree of hydrogenation.

Synthesis of polybutadiene-silica nanoparticles via differential microemulsion polymerization and their hydrogenated nanoparticles by diimide reduction

Polybutadiene (PB)–SiO2 nanoparticles were successfully synthesized via differential microemulsion polymerization. The core-shell structured PB-SiO2 nanoparticles were designed to achieve a monodispersion with reduced nanosilica aggregation. A high monomer conversion (81.5%), grafting efficiency (78.5%) and small particle size (27 nm) with narrow size distribution was obtained under optimum reaction conditions when using an extremely low surfactant concentration, 5 wt% based on monomer. The PB-SiO2 latex could be hydrogenated by diimide reduction in the presence of hydrazine and hydrogen peroxide to provide hydrogenated polybutadiene (HPB)–SiO2. A high hydrogenation degree of 98.6% was achieved at a ratio of hydrazine to hydrogen peroxide of 0.75:1, and showed a maximum degradation temperature of 469.6 °C resulting in excellent thermal stability. A new nanocomposite of PB-SiO2 and HPB-SiO2 could be used as a novel nanofiller in natural rubber. Especially, NR/HPB-SiO2 composites had improved mechanical and thermal properties, and exhibited good resistance toward ozone exposure.

Thermodynamic study of the partitioning of methyl and propyl parabens in some organic solvent/buffer systems

The thermodynamic quantities of partitioning of methyl paraben (MP) and propyl paraben (PP) were studied at five temperatures in several organic solvent/buffer systems, namely, 1-octanol (ROH/W), isopropyl myristate (IPM/W), chloroform (CLF/W) and cyclohexane (CH/W). In all cases, the values of the mole fraction partition coefficient (Ko/wx) were greater than unity; therefore, the standard Gibbs free energies of transfer are negative indicating a high affinity of MP and PP for all the organic media evaluated. The Ko/wx values were approximately 470-fold and 1700-fold higher in the ROH/W system with respect to the CH/W for MP and PP, thus indicating a high degree of hydrogen bonding contribution to partitioning. Otherwise, in the case of the IPM/W system, the Ko/wx values were in the orders of 0.48 or 0.30 of those observed in ROH/W, whereas, in the case of CLF/W system, the Ko/wx values were in the orders of 0.03 to 0.04 of those observed in ROH/W. On the other hand, enthalpies and entropies of transfer of PP from water to organic solvents were all positive but in the case of MP the quantities were variable, negative or positive as well. These results could indicate some degree of participation of the hydrophobic hydration on the MP and PP partitioning processes.

Hydrogenation of acrylonitrile-butadiene rubber latex using in situ synthesized RhCl(PPh3)3 catalyst

Catalytic hydrogenation of acrylonitrile-butadiene rubber (NBR) latex was achieved by using in situ synthesized RhCl(PPh3)3 catalyst. Water-soluble rhodium salt (RhCl3) was used as the catalyst precursor which was reacted in situ with triphenylphosphine (PPh3) to form RhCl(PPh3)3. Compared with using solid RhCl(PPh3)3, hydrogenation of NBR latex using the in situ RhCl(PPh3)3 showed a faster hydrogenation reaction. Based on the retention of catalyst in the polymer, it was revealed that the efficiency of in situ synthesis and the diffusion of the catalyst from the aqueous phase into the polymer particles were crucial in achieving the required high degree of hydrogenation. As a result, it was discovered that by introducing a small amount of alcohol (e.g. RhCl3=0.52mmol/L, PPh3=18mmol/L, ethanol/total NBR latex=1/10 volume ratio) to the feed latex, the in situ synthesized catalyst could be used in the hydrogenation reaction very efficiently.

Facile synthesis of hydrogenated carbon nanospheres with a graphite-like ordered carbon structure

We report a synthesis of hydrogenated carbon nanospheres (HCNSs) via a facile solvothermal route at low temperatures (60-100 °C), using CHCl3 as the carbon source and potassium (K) as the reductant. Selective cleavage of the relatively lower stable C-Cl bonds (compared to C-H bonds) of the carbon precursor (CHCl3) by K metal results in the growth of HCNSs. The diameter of HCNSs ranges from 40 to 90 nm. The HCNSs have a graphite-like ordered carbon structure in spite of their high degree of hydrogenation. The HCNSs exhibit an average Brunauer-Emmett-Teller (BET) surface area of 43 m(2) g(-1), containing a small amount of mesopores and macropores in the structure. The nanospheres' sample as an anode material for lithium ion batteries (LIBs) has been studied. It exhibits a high discharge capacity (3539 mA h g(-1) in the first cycle, 978 mA h g(-1) after 50 cycles) and good cycling stability, demonstrating advantages as a promising candidate for anode materials in LIBs. The high capacity of the HCNSs is due to their unique nanostructures and high percentage hydrogenation, as well as hydrogenation induced structural defects.

Homogeneous catalytic hydrogenation of hydroxyl-terminated liquid nitrile rubber

It was difficult to obtain high degree of hydrogenation of hydroxyl-terminated liquid nitrile rubber (HTBN) by using homogeneous noble metal catalyst because the hydroxyl (OH) in HTBN was likely to cause catalyst poisoning. In this study, with hexamethyl disilylamine protecting OH, a good yields of hydrogenated HTBN was synthesized through the use of homogeneous metal catalyst. The effects of catalyst concentration, reaction time, hydrogen pressure, and temperature on the hydrogenation of HTBN were investigated and obtained the following optimum process parameter values: catalyst mass fraction of 0.8%, reaction time of 8 h, pressure of 1.6 MPa, and temperature of 100°C. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to characterize the hydrogenation product of the protected HTBN, indicating that under certain conditions a high degree of hydrogenation of HTBN can be achieved. Only the carbon–carbon double bonds (CC), not the CN bonds, are subject to hydrogenation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Preparation and characterization of waterborne polyurethaneurea composed of C9-diol-based polyester polyol

A series of polyurethaneurea (PUU) aqueous dispersions were prepared with C9-diol-based polyester polyol (POA) and/or poly(neopentylene adipate) polyol (PNA). The particle size and viscosity of the PUU aqueous dispersions consisting of POA were close to those of a comparable system prepared with PNA, and the high-temperature stability and freeze–thaw stability for all the aqueous dispersions were excellent. The PUU film prepared only with the POA exhibited the lowest water-absorbing amount, the highest tensile strength (51.3 MPa), and the best hydrolytic stability across all PUU films studied. The experimental results also showed a high degree of hydrogen bonding for urea groups and a perfect, ordered structure of hard segments in this kind of PUU film, resulting in excellent water-resistance performance and mechanical properties.

Characterization of Hydrogenated Fullerene Mixture of C60Hx and C70Hx

A commercially available hydrogenated mixture of fullerenes (HMF) composed of 77% C60Hx and 22% C70Hx has been analyzed by liquid chromatographic analysis (HPLC), electronic absorption, FT-IR spectroscopy, solubility and by thermal analysis (TGA). The results confirm that the HMF is composed by a mixture of C60Hx and C70Hx with a high degree of hydrogenation. The hydrogen content of the HMF was found 6.12% by combustion elemental analysis, suggesting that hydrogenated fullerenes are mixed with hydrogenated fullerene fragments derived from the cage breakdown due to the forcing conditions used in the synthesis (high pressure and high temperature hydrogenation). The HMF is stable in air for a relatively long time of exposure. Under N2, it starts to decompose at 478°C. The maximum decomposition rate under N2 occurs at 522°C. An attempt was made to resolve the C-H stretching band of HMF by recording the FT-IR spectrum at -180°C.