Performance inhomogeneity of gelatin during gelation process

The structural and performance inhomogeneities of gelatin gel can directly affect its application as a kind of functional material. The structural inhomogeneity of gelatin caused by the uneven and unstable temperature field has been analyzed by the finite element method in our previous work. Further in this paper, the performance inhomogeneity of gelatin which is closely connected with the actual application is numerically analyzed during the gelation process, which includes the inhomogeneities of the optical and mechanical properties of gelatin gels. The time required for reaching the gel point at different spatial grids is exhibited and discussed. The calculated results also show that the equilibrium shear modulus of gelatin is dependent on the thermal history.

Facile synthesis of PtRu/C electrocatalyst with high activity and high loading for passive direct methanol fuel cell by synergetic effect of ultrasonic radiation and mechanical stirring

The PtRu/C electrocatalyst with high loading (PtRu of 60 wt%) was prepared by synergetic effect of ultrasonic radiation and mechanical stirring. Physicochemical characterizations show that the size of PtRu particles of as-prepared PtRu/C catalyst is only several nanometers (2-4 nm), and the PtRu nanoparticles were homogeneously dispersed on carbon surface. Electrochemistry and single passive direct methanol fuel cell (DMFC) tests indicate that the as-prepared PtRu/C electrocatalyst possessed larger electrochemical active surface (EAS) area and enhanced electrocatalytic activity for methanol oxidation reaction (MOR). The enhancement could be attributed to the synergetic effect of ultrasound radiation and mechanical stirring, which can avoid excess concentration of partial solution and provide a uniform environment for the nucleation and growth of metal particles simultaneously hindering the agglomeration of PtRu particles on carbon surface.

Effect of yttrium-rich misch metal on the microstructures, mechanical properties and corrosion behavior of die cast AZ91 alloy

Die cast AZ91-xYmm (x = 0-0.8 wt.%) magnesium alloys with excellent tensile properties and corrosion resistance behavior were successfully prepared by a simple addition of yttrium-rich misch metal (Ymm) to AZ91. Influences of Ymm on the microstructure, mechanical properties and corrosion behavior of AZ91 were investigated. The results showed that addition of Ymm to die cast AZ91 alloy could re. ne the microstructure including primary alpha-Mg and eutectic beta-Mg17Al12. When the content of Ymm reached 0.8 wt.% a small quantity of Al2Y phase would form. The tensile properties were improved greatly with addition of Ymm to AZ91. The creep rate of the AZ91-Ymm alloys, tested at 150 degrees C/50MPa, was one order of magnitude lower than that of AZ91. When addition of Ymm was more than 0.3 wt.%, the salt-spray corrosion resistance of AZ91-Ymm alloys could be 30-40 times of that of AZ91. The improvement of corrosion resistance with addition of Ymm was confirmed by the results of electrochemical polarization experiments. Mechanism of the improvement of mechanical properties and corrosion behavior caused by Ymm was also discussed.

Microstructures, mechanical properties and corrosion behavior of high-pressure die-cast Mg-4Al-0.4Mn-xPr (x=1, 2, 4, 6) alloys

Mg-4Al-0.4Mn-xPr (x = 1, 2, 4 and 6 wt.%) magnesium alloys were prepared successfully by the high-pressure die-casting technique. The microstructures, mechanical properties, corrosion behavior as well as strengthening mechanism were investigated. The die-cast alloys were mainly composed of small equiaxed dendrites and the matrix. The fine rigid skin region was related to the high cooling rate and the aggregation of alloying elements, such as Pr. With the Pr content increasing, the alpha-Mg grain sizes were reduced gradually and the amounts of the Al2Pr phase and All, Pr-3 phase which mainly concentrated along the grain boundaries were increased and the relative volume ratio of above two phases was changed. Considering the performance-price ratio, the Pr content added around 4 wt.% was suitable to obtain the optimal mechanical properties which can keep well until 200 degrees C as well as good corrosion resistance. The outstanding mechanical properties were mainly attributed to the rigid casting surface layer, grain refinement, grain boundary strengthening obtained by an amount of precipitates as well as solid solution strengthening.

Study on the synthesis and performance of hydrogels with ionic monomers and montmorillonite

Two series of the nanocomposite hydrogels were synthesized by in-situ solution polymerization. One pre-gel solution was obtained by directly dispersing the montmorillonite (MMT) powder into aqueous monomer solution and the other pre-gel solution was obtained by mixing monomer aqueous solution and the dispersion of MMT. The structure and performance of two series of hydrogels in dry state were studied by XRD, Raman spectroscopy, TEM and Al-27 MAS NMR. Compressing test results showed that the gel strength of the hydrogels prepared by the latter method was much higher than that by the former method. When acryloyloxyethyl trimethyl ammonium chloride (DAC) was introduced into the system, hydrogels with excellent nanostructure could be synthesized. The result of Al-27 MAS NMR suggested that the chemical environment of aluminum in MMT was changed by the introduction of DAC due to the interaction between the groups of DAC and MMT layers. Thus, the combination of copolymerizing with strong polar monomers and using the dispersion of MMT were the effective ways to obtain tranocomposite hydrogel of MMT and ionic monomers. The nanostructure of the hydrogel improved the gel strength, while the swelling ratio of the hydrogel depended on synergic effects of multifunctional groups.

Microstructures and mechanical properties of Mg-8Gd-0.6Zr-xNd (x=0, 1, 2 and 3 mass%) alloys

Mg-8Gd-0.6Zr-xNd (x = 0, 1, 2 and 3 mass%) alloys were prepared by metal mould casting method, and the microstructures, age hardening responses and mechanical properties have been investigated. The microhardness of the as-cast alloys is increased with increasing Nd content. The age hardening behavior and mechanical properties are enhanced significantly by adding Nd element. The peak ageing hardness of the Mg-8Gd-0.6Zr-3Nd alloy is 103, it is about 1.3 times more than that of the Mg-8Gd-0.6Zr alloy. The aged Mg-8Gd-0.6Zr-3Nd alloy exhibits maximum ultimate tensile strength and yield strength, and the values are 271 and 205 MPa at room temperature, 205 MPa and 150 MPa at 250 degrees C, respectively. Which are about 2 times higher than those of Mg-8Gd-0.6Zr alloy. The improved hardness and strength are mainly attributed to the fine dispersiveness Of Mg5RE and Mg12RE precipitates in the alloy.

Synthesis, properties, and gas permeation performance of cardo poly(arylene ether sulfone)s containing phthalimide side groups

Novel bisphenol monomers (1a-d) containing phthalimide groups were synthesized by the reaction of phenolphthalein with ammonia, methylamine, aniline, and 4-tert-butylanilne, respectively. A series of cardo poly (arylene ether sulfone)s was synthesized via aromatic nucleophilic substitution of 1a-d with dichlorodiphenylsulfone, and characterized in terms of thermal, mechanical and gas transport properties to H-2, O-2, N-2, and CO2. The polymers showed high glass transition temperature in the range 230-296 degrees C, good solubility in polar solvents as well as excellent thermal stability with 5% weight loss above 410 degrees C. The most permeable membrane studied showed permeability coefficients of 1.78 barrers to O-2 and 13.80 barrers to CO2, with ideal selectivity. factors of 4.24 for O-2/N-2 pair and 28.75 for CO2/CH4 pair. Furthermore, the structure-property relationship among these cardo poly(arylene ether sulfone)s had been discussed on solubility, thermal stability, mechanical, and gas permeation properties. The results indicated that introducing 4-tert-butylphenyl group improved the gas permeability of polymers evidently.

Surface-grafted silica linked with L-lactic acid oligomer: A novel nanofiller to improve the performance of biodegradable poly(L-lactide)

A new surface modification method by grafting L-lactic acid oligomer onto the surface silanol groups of silica nanoparticles has been developed. The surface-grafting reaction is confirmed by IR and Si-29 MAS NMR analyses. TEM and SEM results show that grafted SiO2 (g-SiO2) nanoparticles can be comparatively uniformly dispersed in chloroform or PLLA matrix, while the unmodified SiO2 nanoparticles tend to aggregate. The loading of g-SiO2 nanoparticles in poly(L-lactide) (PLLA) matrix greatly improves the toughness and tensile strength of this material. In contrast, the incorporation of un-grafted SiO2 nanoparticles into PLLA leads to the deterioration of its mechanical properties. DSC analysis shows that g-SiO2 nanoparticles can serve as a nucleating agent for the crystallization of PLLA in the composites. SEM characterization shows the tough characteristics and great interfacial combination strength for g-SiO2 (5wt%)/PLLA nanocomposites.

Thermal mechanical and dynamic mechanical property of biphenyl polyimide fibers

High-performance polyimide fibers possess man), excellent properties, e.g., outstanding thermal stability and mechanical properties and excellent radiation resistant and electrical properties. However, the preparation of fibers with good mechanical properties is very difficult. In this report, a biphenvl polyimide from 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydianiline is synthesized in p-chlorophenol by one-step polymerization. The solution is spun into a coagulation bath of water and alcohol via dry-jet wet-spinning technology. Then, the fibers are drawn in two heating tubes. Thermal gravimetric analysis, thermal mechanical analysis, and dynamic mechanical analysis (DMA) are performed to study the properties of the fibers. The results show that the fibers have a good thermal stability at a temperature of more than 400degreesC. The linear coefficient of thermal expansion is negative in the solid state and the glass transition temperature is about 265degreesC. DMA spectra indicate that the tandelta of the fibers has three transition peaks, namely, alpha, beta, and gamma transition. The alpha and gamma transition temperature, corresponding to the end-group motion and glass transition, respectively, extensively depends on the applied frequency, while the beta transition does not.