Geometric and mechanical characterization of ribbed FRP rebars

The paper discusses the advantage of fiber-reinforced polymer (FRP) rebar for application in concrete because of its light weight, high strength, high corrosion resistance and durability. Different options of shaping the wave-like texture of FRP bars for concrete bonding are considered. The diameter measurement problem of ribbed FRP bars is examined, and a proprietary procedure is suggested to determine the equivalent diameter and elastic modulus of ribbed FRP bars. The tensile strength (889–1197 MPa) obtained herein is greater than the longitudinal flexural strength (566–822 MPa), which is due to the ribs, contrary to the case of plain bars. The elastic modulus values obtained (40–61 GPa) are in agreement with the known literature data.     

The effect of monolithic zirconia thickness on the degree of conversion of dental resin cements: ATR-FTIR spectroscopic analysis

The purpose of this study was to evaluate the effect of monolithic zirconia thickness on degree of conversion (DC) of different resin cements. Five groups (1 mm, 1.5 mm, 2 mm monolithic zirconia, veneered zirconia substructure, and lithium disilicate) of disk-shaped ceramic specimens (14 mm in diameter) were prepared (n = 6). Three dental resin cements (Variolink II light-cured, Variolink II dual-cured and Zirconite dual-cured) were tested to evaluate their DC under each ceramic group. FTIR spectra were recorded using Attenuated Total Reflectance-Fourier Transform Infrared Spectrometer (ATR-FTIR). The DC% was calculated by ratio of infrared absorbance values of aliphatic and aromatic peaks for uncured and cured states. Data were statistically analyzed by Analysis of Variance (ANOVA) and post hoc Tukey tests (a = 0.05). DC of dental resin cement specimens under monolithic zirconia decreased with increasing thickness. For Variolink II light-cured cement, the highest DC found under lithium disilicate and the lowest DC observed under veneered zirconia specimens. Zirconite which is recommended for cementation of zirconia revealed the highest DC when polymerized under monolithic or veneered zirconia. Under lithium disilicate specimens, DC of Zirconite was similar with light-cured resin cement.     

Developing a thermomechanical and thermochemical model for investigating the cooling rate effects on the distortion of unsymmetrical viscoelastic polymeric composite laminates

An experimental and semi-analytical study of distortion of asymmetric composite laminates with different cooling rates and lay-ups has been presented. In this study, thermomechanical constitutive equations of thin composite laminates are developed using basic viscoelastic constitutive law considering chemical and thermal effects with time-temperature dependent material properties. To solve a fully scouple problem, both the thermochemical and thermomechanical constitutive equations are formulated. The general heat conduction equation known as the Fourier-Biot equation, viscoelastic laws, Boltzmann superposition principle and composite equations are utilized to formulate thin composite laminates. A static model with constant properties in ambient temperature and a transient model by obtaining constitutive equations are simulated. Results are compared with experimental data. Changing lay-up from cross-ply to angle-ply and then quasi isotropic will increase the value of maximum distortion. Results indicated that the increasing cooling rate will increase the value of the maximum distortion. The differences between FEM results with static analysis of different lay-ups and experimental specimens that cooled in the oven, environment and refrigerator is about 3%, 35% and 55% respectively. The differences between FEM simulation with transient analysis of different lay-ups and experimental specimens that cooled in the environment and the refrigerator is less than 9%.     

Synthesis and characterization of carboxymethylcelluloses from non-wood pulps II. Rheological behavior of CMC in aqueous solution

This paper concerns the rheological behavior of carboxymethylcelulloses(CMC) derived after one and two successive steps from different non-woodbleached cellulose pulps. CMC rheological characterization was achieved in0.1M NaCl solution, as a function of polymer concentration. Theevidence of a critical concentration (C* < 1 g/L) is discussedfromsteady shear and dynamic experiments. Rheological properties of the CMC werefound to depend on the cellulose source reactivity and on their degree ofsubstitution (DS). Higher molecular weight of initial cellulose was accompaniedby higher apparent intrinsic viscosity of the CMC produced. Depending on theCMCconcentration and on the degree of etherification, the system behaves as asolution or as a gel. In the case of abaca CMC sample, it is shown that afteronly one step of chemical modification and above a polymer concentration of20 g/L, the system behaves as a gel. The gel behavior was studied asafunction of temperature. In the temperature range from 25 to 45°C, the rheological behavior was found to remain almostconstant due to the existence of dispersed swollen aggregates. This unusualcharacteristic represents an advantage for applications such as oil recovery inthe petroleum industry, where viscosity of the recovered fluid should not diminishwith temperature.     

Determination of degree of conversion as a function of depth of a photo-initiated dental restoration composite—III application to commercial Prodigy Condensable™

In this third work, we evaluated the degree of conversion (DC) versus depth of dental filling composite named Prodigy Condensable™ using infrared spectroscopy. Confirming previous results, there was a gradual reduction of DC with increasing depth but the composite exhibited extreme values of DC, an upper value (45.9%) on the surface and a lower one (6.1%) at a depth of 5 mm. The composite presented the worst performance among materials studied. The composite formulation was 80% of inorganic fillers and BisfenolA/dimethacrylate (BisGMA) (18%)/triethyleneglycoldimethacrylate (TEGDMA) (2.0%) as monomers. As stated before, type/ratio/viscosity of monomers and type, amount, size and size distribution of fillers all together had an important role in the cure reaction contributing to the final performance of the composite.     

The modification and characterization of maleic anhydride-styrene-methyl metacrylate terpolymer by poly(ethylene adipate)

In this study, the functionality of maleic anhydride was utilized in the maleic anhydride-styrene-methyl metacrylate (MAStMMA) terpolymer. First, the polyester of poly(ethylene adipate), PEA, polycondensation copolymer was synthesized from ethylene glycol and adipic acid monomers. PEA was then modified on its maleic anhydride units in the MAStMMA terpolymer which has been synthesized previously. This modified copolymer was characterized by FTIR (Fourier Transform Infrared spectroscopy). The viscosimetric and thermomechanical characterization of MAStMMA terpolymer and its modified copolymer were also performed and the results were compared. The modified copolymer obtained was found to be more elastic and more soluble, and had lower viscosity and density.     

Effects of monomer structure and imidization degree on mechanical properties and viscoelastic behavior of thermoplastic polyimide films

Two thermoplastic polyimides based on a common diamine (3,4′-ODA) were synthesized using different dianhydrides, namely ODPA and BPDA by a two step method. Molecular weight was controlled by using PA as an end capping agent. Effects of imidization degree on the mechanical properties and viscoelastic behavior of thermoplastic polyimide films were investigated. Film samples with varying degrees of imidization were characterized using FTIR, DMTA and tensile properties testing. It was found that two polyimides have different rates of imidization because of difference in monomer reactivity and molecular structure. It was observed that with an increase in imidization degree there was a decrease in thermoplastic response and a change in viscoelastic behavior from liquid-like to solid-like. With increase in imidization degree the tensile modulus and tensile strength of the films were increased, whereas elongation at break and tensile breaking energy were found to decrease after a certain imidization temperature.     

超支化聚醚的支化度对玻璃化转变温度的影响

聚合物的分子结构对聚合物性能影响很大.支化度不同的同种聚合物,必须通过不同的催化体系合成,很难得到既具有相近分子量又具有不同支化度的系列聚合物样品,因此对聚合物性能与支化度的依赖关系的研究报道不多.     

Influence of different functionality degree grafting monomers on polypropylene melt radical branching reaction and their structure

Long‐chain–branched polypropylene (LCBPP) is one of polypropylenes (PPs) with high melt strength and good melt elasticity. Recently, due to its outstanding properties, LCBPP have been attracted increasingly attention in the field of development and characterization by the researchers all over the world. In this study, LCBPP was prepared by the melt radical branching reaction in a torque rheometer. The influences of various acrylate monomers with different functionality degrees on the structure and melt performance of PP products were investigated. The results indicated that grafting monomers with different functionality degrees made diverse influences on the branching density and branching chain length of branching PP products. With the increase of the functionality degree of grafting monomers, the branching level of PP products increased gradually and the “multiplicity” of branches became increasingly obvious. Besides, a higher reactivity of pentaerythritol triacrylate with hydroxyl than the similar molecular structured pentaerythritol tetraacrylate was confirmed. Furthermore, due to the high reactivity of dipentaerythritol penta(hexa)acrylate, branching and crosslinking reaction occurred simultaneously during the reaction process. As a result, the gel content increased and finally formed highly star branching structures with a shape of “dense and short.”     

The influence of sulfonation degree on the thermal behaviour of sulfonated poly(arylene ethersulfone)s

Initial decomposition temperature (T_i), apparent activation energy of degradation (E_a) and glass transition temperature (T_g) of some low molar mass (M_n ≈ 8000 g mol⁻¹) sulfonated poly(arylene ethersulfone)s s-(PAES)s were determined to check their dependence on sulfonation degree (SD). The results obtained were compared with those for unsulfonated poly(arylene ethersulfone) PAES. In order to have an accurate control of the chemical structure, a pre-sulfonation route was followed for the preparation of sulfonated compounds. The thermal behaviour of the investigated s-(PAES)s as well as that of PAES appears not to be influenced by the environment (flowing nitrogen or static air atmosphere) of degradation. Both T_i and T_g values of s-(PAES)s were higher than those of PAES and increased quite linearly as a function of sulfonation degree. An analogous linear trend was observed for the apparent degradation energy of s-(PAES)s, but the values found were largely lower than those of unsulfonated homopolymer. The results are discussed and interpreted.     

高取代度淀粉磷酸酯的理化性质及结构表征

以磷酸二氢钠、磷酸氢二钠的混盐为酯化剂,干法制备高取代度木薯淀粉磷酸酯(CSP-HDS)。研究表明,取代度不同时,产物的表观粘度、糊透明度、凝沉性、冻融稳定性均不相同。与木薯淀粉相比,酯化反应后产物粘度增大,糊透明度、凝沉性及冻融稳定性得到改善。XRD分析表明酯化反应主要发生在淀粉分子的非结晶区,对结晶区破坏不明显;SEM分析显示酯化后大部分淀粉颗粒保持原来形貌,仅少数团粒受到侵蚀。     

Conjugates between minor groove binders and Zn(II)-tach complexes: Synthesis,characterization, and interaction with plasmid DNA

A new family of conjugates between a Zn(II)-tach complex and (indole)₂ or benzofuran-indole amide minor groove binders connected through alkyl or oxyethyl linkers of different lengths has been prepared. The conjugates bind strongly to DNA. However, the complexation to DNA to promote the Zn(II) catalyzed hydrolytic cleavage of the DNA results instead in its inhibition. This inhibition effect has been confirmed also using Cu(II). Modeling studies suggest that in the most stable complex conformation, the minor groove binder and the linker lie in the minor groove hampering the interaction between the metal complex and the phosphate backbone of DNA. Therefore, the linear arrangement of minor groove binder-linker-metal complex appears to be effective to ensure tight binding but unproductive from a hydrolytic point of view.     

Catalytic conversion of propan-2-ol and butan-2-ol on carbon nanotubes with different carbon structures

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不同金属离子层状双氢氧化物制备及表征

本文采用恒定pH值共沉淀法制备六种层板金属离子不同的层状双氢氧化物(LDH).通过傅立叶变换红外光谱仪(FT-IR)、X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对LDH进行了表征,并利用热重分析(TG)研究了LDH的热分解行为.研究表明,不同金属离子对LDH的层间距、晶粒尺寸等参数有一定影响,团聚程度也有较大的差异.     

Synthesis,characterization, molecular modeling,and DNA interaction studies of a Cu(II) complex containing drug of chronic hepatitis B: adefovir dipivoxil

A new copper(II) complex [Cu(adefovir)₂Cl₂], where adefovir = adefovir dipivoxil drug, was synthesized and characterized by using different physicochemical methods. Binding interaction of this complex with calf thymus DNA (ct-DNA) has been investigated by multi-spectroscopic techniques and molecular modeling study. The complex displays significant binding properties of ct-DNA. The results of fluorescence and UV–vis absorption spectroscopy indicated that, this complex interacted with ct-DNA in a groove-binding mode, and the binding constant was 4.3(±0.2) × 10⁴ M^?1. The fluorimeteric studies showed that the reaction between the complex and ct-DNA is exothermic (ΔH = 73.91 kJ M^?1; ΔS = 357.83 J M^?1 K^?1). Furthermore, the complex induces detectable changes in the CD spectrum of ct-DNA and slightly increases its viscosity which verified the groove-binding mode. The molecular modeling results illustrated that the complex strongly binds to the groove of DNA by relative binding energy of the docked structure ?5.74 kcal M^?1. All experimental and molecular modeling results showed that the Cu(II) complex binds to DNA by a groove-binding mode.     

Synthesis, characterization and properties of a novel fluorinated methacrylate polymer

A fluorinated monomer of 2-(2,2,2-trifluoroethoxy)ethyl methacrylate (FEMA) was prepared by a “one pot” process and then a novel fluorinated methacrylate polymer, poly[2-(2,2,2-trifluoroethoxy)ethyl methacrylate] (PFEMA), was successfully synthesized via miniemulsion polymerization using cetyltrimethyl ammonium bromide (CTAB) as emulsifier, hexadecane (HD) as co-stabilizer and 2,2′-azobisisobutyronitrile (AIBN) as initiator. The chemical structure of PFEMA was characterized by FT-IR, ¹H NMR and ¹⁹F NMR. GPC results show that the number average molecular weight (M_n) of PFEMA was as high as 8.5 × 10⁵ g/mol and the polydispersity index (PDI) was only 1.3. SEM and DLS characterizations showed that the morphology of PFEMA latex was uniform spheres with the diameter of about 110–125 nm. It was also found that PFEMA has high thermo-stability (T_d > 200 °C), low glass transition temperature (T_g = 13.0 °C), and nice hydrophobicity (θ_water = 99.9°). Comparison studies on PFEMA and poly(2,2,2-trifluoroethyl methacrylate) show that an introduced functional group (–CH₂CH₂O–) has a significant effect on lowering T_g and improving hydrolysis resistance without impairing surface properties.     

Synthesis and characterization of arylene ether imide reactive oligomers and polymers containing diaryl alkyl phosphine oxide groups

The diamine monomer bis(m-aminophenyl) methyl phosphine oxide (DAMPO) was synthesized via nitration and reduction of diphenyl methyl phosphine oxide. Rigorous purification of this monomer enabled its utilization in the synthesis of high molecular weight poly(ether imide)s. Both thermoplastic materials and thermosetting systems, endcapped with either phthalic or phenylethynylphthalic anhydride, respectively, have been produced. Major emphasis has been placed on polyimides derived from 2,2′-bis(4-(3,4-dicarboxyphenoxy) phenyl) propane dian- hydride, also known as bisphenol-A dianhydride, or BPADA. High molecular weight homo- and copolyimides based on BPADA/DAMPO had glass transition temperature values in the range of 215–223°C, and were totally amorphous. They displayed higher modulus and tensile strength values than the polyetherimide control based on meta-phenylene diamine and also generated high TGA char yields in air. Phenylethynyl crosslinkable materials were effectively cured at 380°C to produce networks that are ductile, very solvent resistant and also generate high char yields, which suggest their possible utilization in fire resistant matrix systems. © 1998 John Wiley & Sons, Ltd.     

Synthesis and characterization of 2,2‐bis(methylol)propionic acid dendrimers with different cores and terminal groups

Three sets of aliphatic polyester dendrimers based on 2,2‐bis(methylol)propionic acid (bis‐MPA) were synthesized. Two of the sets had benzylidene terminal groups and either a trimethylolpropane or triphenolic core moiety. The last set had acetonide terminal groups and a triphenolic core moiety. Benzylidene‐[G#1]‐anhydride and acetonide‐[G#1]‐anhydride were used as the reactive building blocks in the construction of all dendrimers. The large excess of building blocks used in the coupling reactions initially resulted in considerable material loss. This waste was eliminated through the development of a recycling method. ¹H and ¹³C NMR and matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) analysis were used to verify the purity of all compounds. Size exclusion chromatography (SEC) was used, as well as MALDI‐TOF, for molecular weight determinations. The SEC measurements were conducted with a universal calibration method and an online right‐angle laser light scattering detector. Measured dendrimer molecular weights were close to their theoretical molar masses. Observations were also made of the hydrodynamic radius and intrinsic viscosity for the different dendrimers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1758–1767, 2004     

Synthesis and characterization of new poly(arylene ether)s containing heterocyclic units. II.

A series of new poly(arylene ether)s, containing naphthalene, pyridine, and quinoline units have been prepared by solution condensation polymerization. The synthesis involves nucleophilic displacement of aromatic dihalides with aromatic potassium bisphenates in an anhydrous dipolar aprotic solvent at elevated temperatures. The polymers, having inherent viscosity from 0.24 to 1.32 dL/g, were obtained in quantitative yield, have excellent thermal stability as shown by 10% weight loss temperatures in nitrogen and air (above 450 and 430°C, respectively) and high glass transition temperatures (in the range of 150–220°C). The introduction of quinoline moieties in the polymer backbone positively influences the thermal properties, such as high T_g/T_m ratios. © 1995 John Wiley & Sons, Inc.     

Crosslinking and characterization of commercially available poly(VDF-co-HFP) copolymers with 2,4,4-trimethyl-1,6-hexanediamine

Fluorinated copolymers are well known for their large range of applications. These applications can be improved by grafting or crosslinking of several agents. The mechanism of crosslinking of hexamethylene diamine and 2,4,4-trimethyl-1,6-hexanediamine is well known and occurs in four different steps. To elaborate a film of commercially available poly(VDF-co-HFP) copolymer crosslinked by 2,4,4-trimethyl-1,6-hexanediamine, a step of press cure under air is necessary. Temperature, time and pressure were optimised by regarding the solubility of the press cured films, the mechanical properties, the swelling rate in methyl ethyl ketone, and the degradation of the films. The best temperature, time and pressure for press cure were 150 °C, from 15 to 30 min, and 20 bars, respectively. Other properties of crosslinked poly(VDF-co-HFP) copolymers containing 10 mol.% and 20 mol.% of HFP were characterized. First, all films were insoluble in concentrated HCl. Secondly, swelling rates of different amounts of diamine crosslinked copolymers were measured in ethylene carbonate/dimethyl carbonate and in methyl ethyl ketone; it was proved that the higher the molar percentage of diamine, the higher the crosslinking density, so the lower the swelling rate. Concerning thermal properties, glass transition temperature mainly increased when the amount of diamine increased. Thermal stability measurements showed a higher decomposition temperature when the percentage of diamine was very low (5 mol.%). Finally, mechanical properties were measured by dynamic mechanical analysis; the storage tensile modulus (E′) of a diamine crosslinked Kynar^® copolymer versus temperature exhibited a high drop because Kynar^® was a highly amorphous copolymer. Moreover, the higher the amount of diamine, the higher the rubbery modulus.