索氏提取-气相色谱法测定食品纸包装材料中的多氯联苯

建立一种测定食品纸包装材料中多氯联苯的测定方法。采用索氏提取法提取样品,通过浓硫酸净化、无水硫酸钠脱水、浓缩后,用气相色谱-ECD进行测定。并对索氏提取的不同条件进行系统比较,优化实验条件。方法的检出限为0.5 μg/kg,回收率为78%～86%,相对标准偏差小于7%。     

Mechanical and tribological properties of poly(hydroxyethyl methacrylate) hydrogels as articular cartilage substitutes

Poly(hydroxyethyl methacrylate) (p(HEMA)) hydrogels have been proposed as promising biomaterials to replace damaged articular cartilage. A major obstacle to their use as replacement bearing tissue is their poor mechanical properties in comparison with healthy articular cartilage. The purpose of this study was to obtain p(HEMA) hydrogels with physicochemical and mechanical properties close to healthy articular cartilage, by introducing a hydrophilic monomer, namely acrylic acid (AA). Formulations of hydrogels with different amounts of hydrophilic monomer (acrylic acid, AA) were synthesized and tested: p(HEMA), p(HEMA-co-5%AA), p(HEMA-co-25%AA). The macro-mechanical tests were reproduced at nanoscale in order to verify if the superficial properties of the hydrogels are similar to the bulk ones.     

The effect of nano-TiO2 and SiO2 on bonding strength and structural properties of poly (vinyl acetate) composites

Polyvinyl acetate (PVAc) is a thermoplastic polymer widely used in the furniture industry. It has many advantages such as easy processing, cheap, biodegradable; but, resistance to water and hot medium is not enough to the application area. In this study, the effect of nano-TiO₂ and nano-SiO₂ on bonding performance and structural properties of PVAc were investigated. Bonding strength with block shear test and structural properties with thermogravimetric analysis-TGA, X-ray diffraction-XRD, and transmission electron microscopy-TEM of PVAc were determined. The obtained results showed that bonding strength with cooperating both TiO₂ and SiO₂ for 1% and 2% were improved. XRD and TEM results proved to be the homogenously interactions for 1% and 2% between nano fillers and matrix. TGA results showed that thermal stability of PVAc blends was largely improved.     

Synthesis and characterization of iron(III) oxide/polyvinyl chloride/poly(methyl methacrylate) nanocomposites

Polyvinyl chloride/poly(methyl methacrylate) blended and iron(III) nanoparticle polyvinyl chloride/poly(methyl methacrylate) nanocomposites were prepared by solution casting. The iron(III) oxide nanoparticles were prepared using a sol-gel procedure and their particle size was less than 200 nm. Scanning electron microscopy showed that no phase separation occurred and polyvinyl chloride and poly(methyl methacrylate) were miscible. Scanning electron microscopy also showed that the iron(III) oxide nanoparticles were dispersed well within the polymer blend. Thermogravimetric analysis showed three stages for the thermal degradation for polyvinyl chloride/poly(methyl methacrylate) blend and the iron(III) oxide/polyvinyl chloride/poly(methyl methacrylate). The second degradation was possibly due to dehydrochlorination during the thermal degradation of polyvinyl chloride in the blend system. Young’s modulus of the iron(III) oxide nanoparticle filled nanocomposites was from 1987.7–2471.6 MPa, which was higher than polyvinyl chloride/poly(methyl methacrylate) blend (1955.5 MPa). The stress yield (47.9–51.8 MPa) of the iron(III) oxide nanoparticle composites was higher than pure polyvinyl chloride/poly(methyl methacrylate) (47.0 MPa). The cyclic voltammograms of the pure blend and the nanocomposites were compared.     

Electrically conducting polymers: preparation and investigation of oxidized poly(acetylene) by EFTEM

Energy-filtering transmission electron microscopy (EFTEM) was used to demonstrate that the oxidation of poly(acetylene), necessary to produce a highly conducting phase, proceeds homogeneously on a scale of 100 nm to several micrometres. The distribution of the anions BF₄⁻ and PF₆⁻ serves as indicator for the penetration of poly(acetylene) by the oxidizing agent. The sample preparation necessitates prevention of sample degradation by air and moisture. It was possible to synthesize, orientate, oxidize, embed and section poly(acetylene) samples under inert conditions. Only mounting of the grids into the sample holder of the electron microscope was performed under ambient conditions. EFTEM was possible for phosphorus and boron, but not for fluorine owing to irradiation damage leading to loss of fluorine from the sample. Polyvinylbutyral was chosen as the embedding medium because it allows embedding of the sample prior to oxidation. Embedding of a previously oxidized poly(acetylene) sample leads to migration of the anions from the interior of the sample into the embedding medium.     

Structural and mechanical properties of (Cr,Ni) N single and gradient layer coatings deposited on mild steel by magnetron sputtering

Ternary single and gradient layer (Cr, Ni) N thin films were deposited on the mild steel substrate by unbalanced magnetron sputtering technique in order to evaluate mechanical properties for machine tools and automotive applications. Microstructure, chemical composition, surface morphology and phase analysis were carried out using field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction, respectively. Both single and gradient layer of (Cr, Ni) N coatings show a significant increment in mechanical properties such as hardness, adhesion strength and surface roughness along with the reduction of friction coefficient. Mechanical tests revealed that the hardness of the gradient layer increased up to 3.1 times due to the formation of Cr₂N and Ni phase whereas single layer showed the least friction. Single layer CrNiN layer exhibited 27.2% less surface roughness (R_a) in comparison with gradient layer. High values of surface roughness, hardness, thickness and friction could be correlated with high film-to-substrate adhesion (L_c2) for the gradient layer.     

Scratch properties of poly(methyl methacrylate) surfaces: The time‐temperature dependence of friction and hardness

Viscoelastic‐viscoplastic behaviour is usually not taken into account in models describing the scratch properties of polymeric surfaces. In the case of a standard indentation test with stationary tip, the elastic‐plastic boundary and the boundary of the region being subjected to hydrostatic pressure beneath the tip are understood. Such well‐known models have been used in this study to understand the geometry of the groove left on the surface of a viscoelastic‐viscoplastic body by a moving diamond tip. A new apparatus was built that can control the velocity of the tip over the range 1 μm/s to 15 mm/s, at several different temperatures from −10 to +100°C. The material used was a commercial grade of cast poly(methyl methacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress‐ and temperature‐activated process. The values for the activation energy and volumes of the dynamic hardness and of the interfacial shear stress were in good agreement with the mechanical properties usually attributed to PMMA.