Durability of Aluminium Adhesive Joints Bonded with a Homopolymerised Epoxy Resin

The durability of epoxy-aluminium joints that use a homopolymerised epoxy resin was studied, and the effects of relative humidity, temperature, and salt concentration were analysed. The adhesive properties were measured by lap-shear tests, and the water uptake of the epoxy resin was determined by gravimetric measurements. Ageing and degradation effects on the epoxy resin and on the aluminium substrates were also analysed.

The homopolymerised epoxy resin absorbs little water (1.5 wt%) because of its nonpolar network structure. The water uptake is enhanced by increasing relative humidity and temperature; however, the joint strength remains constant because of epoxy plasticization. A saline environment is damaging to the adhesive joints, because of metal corrosion, but was not significantly harmful to the epoxy resin, because of a lower diffusion coefficient of salt water. The T_g decrease of the epoxy adhesive due to water absorption depends only on the amount of absorbed water and is independent of the hydrothermal ageing conditions.     

Mechanical properties of cork: Effect of hydration

Cork is known to exhibit low permeability to liquids and gases, imputrescibility and good mechanical properties, with a remarkable elasticity. These properties make this material particularly interesting for sealing wine. We focused in this study on the compression properties of cork along the radial and tangential direction at 25 °C under atmospheric pressure when cork is stored in various relative humidity environments, from 0% to 100%.The direction of compression significantly affected the Young’s modulus, with a higher value for the radial direction. This corresponds to the orientation of the lenticels which reinforce the rigidity of the material when the strain is applied along their growth direction. More surprising is the effect of water sorption in cork on its mechanical property. Both radial and tangential directions exhibit the same behavior when the relative humidity is increasing. First the Young’s modulus is constant up to 50% relative humidity (RH) with mean values around 37 MPa and 22 MPa for radial and tangential directions, respectively. Then, above this point, the increase in water content leads to a decrease in material rigidity which is attributed to water clusters formations. For high moisture contents, the anisotropy of cork is reduced: Young’s moduli are of 10.5 MPa and 6.6 MPa for radial and tangential orientations, respectively.Differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA) allowed to identify a glass transition temperature (T_g) in cork over a broad range of temperatures, depending on the moisture content and giving a T_g-midpoint from −8 °C to 3 °C. Moreover, a secondary transition was observed by DMTA at approximately −80 °C, for 50% RH.     

Tributyl citrate oligomers as plasticizers for poly (lactic acid): thermo-mechanical film properties and aging

Poly (lactic acid), PLA, is a biodegradable thermoplastic that can be produced from renewable resources. The polymer is of interest for production of films for packaging applications. However, plasticization of PLA is required in order to obtain films with sufficient flexibility. PLA was blended with tributyl citrate (TbC) and two oligomers of TbC that were synthesized by transesterification of tributyl citrate (TbC) and diethylene glycol (DEG). Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) were used to investigate the dynamic mechanical and thermal properties of the blends. All the plasticizers investigated decreased the glass transition temperature of PLA, and the reduction was the largest with the plasticizer having the lowest molecular weight. The PLA matrix became saturated with plasticizer at a certain concentration and phase separation occurred; the higher the molecular weight of the plasticizer, the lower the saturation concentration. Aging of the blends at room temperature for several months induced partial phase separation in the material. It was observed that the morphological stability of the blends was enhanced when the plasticizer concentration was reasonably low, i.e. 10-15 wt%.     

Influence of plasticizer contents on the properties of HEC-based solid polymeric electrolytes

Solid polymeric electrolytes were obtained by the plasticization process of hydroxyethylcellulose (HEC) with different quantities of glycerol and addition of lithium trifluoromethane sulfonate (LiCF₃SO₃) salt. The samples were prepared in the form of transparent films with very good adhesion properties. These films were characterized by X-ray diffraction, thermal analysis (DSC) and UV-NIR spectroscopy. The ionic conductivity measurements were obtained by impedance complex spectroscopy as a function of both salt contents and temperature. The best conductivity values of 1.07 × 10⁻⁵ S/cm at 30 °C and 1.06 × 10⁻⁴ S/cm at 83 °C were obtained for the samples of HEC plasticized with 48% of glycerol and containing [O]/[Li] = 6. These results show that plasticized HEC is a very good material to be used for the preparation of new solid polymeric electrolytes.     

添加元素对Fe3Al金属间化合物高温性能的影响

本文对Ｆｅ３Ａｌ金属间化合物的高温力学性能和氧化性能进行了研究。硼、钛、铬等元素对改善Ｆｅ３Ａｌ的高温强度是非常有效的。但元素铬的加入稍许降低了６００℃以上时的抗氧化性。     

己内酰胺/氯化镁复配增塑聚乙烯醇的性能研究

采用己内酰胺/氯化镁为复配增塑剂,通过流延法制备出了增塑改性的聚乙烯醇(PVA)膜。采用DSC、TGA、XRD分析和力学性能与熔体流动性能测试的方法考察了己内酰胺/氯化镁复配增塑剂对PVA性能的影响。结果表明:氯化镁与己内酰胺复配具有良好的协同增塑效应,其对PVA的增塑效果优于单独使用己内酰胺;复配增塑剂能够有效破坏PVA分子间的氢键,降低PVA的结晶度;加入复配增塑剂后,PVA的熔点降低,热稳定性提高,熔体流动性有所改善,拉伸强度降低,断裂伸长率上升。     

Plasticization of chitosan membrane for pervaporation of aqueous ethanol solution

The process of pervaporation in which two components diffuse through a nonporous polymer membrane was modelled when one of the penetrants can exert a plasticization action to the membrane material. Thereat a phenomenological model was employed for describing the plasticization effect on the diffusivities for penetrants in the membrane. The sorption equilibria and permeation fluxes for aqueous ethanol solutions in a chitosan membrane were measured, and the permeation fluxes for water were compared with those predicted by the proposed model. The concentration of sorbed water was linear with its weight fraction (x₄) in the feed solution, whereas the permeation flux of water was. affected by the plasticization action of sorbed water to the polymer. This plasticization effect on the diffusion process can be simulated in terms of the proposed phenomenological model.     

Study of thermal annealing on Matrimid fiber performance in pervaporation of acetic acid and water mixtures

Unlike the case for low-sorbing gas molecules such as N₂ and O₂, Matrimid^® hollow fibers swell significantly in acetic acid (HAc) and water mixtures. Acetic acid was found to plasticize the polymer and facilitate the passage of the ‘slow’ molecule, acetic acid, while not affecting the ‘fast’ molecule, water, as significantly. The membrane selectivity of water over HAc inevitably decreased with increasing HAc content in the feed for the standard membrane. Sub-T_g (glass transition temperature) thermal annealing was used to stabilize large bore size defect-free Matrimid^® hollow fibers by suppressing the HAc-induced plasticization. The resulting membrane selectivity was increased up to 95 using a 520 μm outer diameter/325 μm inner diameter and 20 cm long defect-free annealed fiber with acceptable water flux (1.6 kg/m² h) for 20 wt% HAc concentration feed streams at 101.5 °C. Micro-fluorescence spectra provide strong support for the notion that thermal annealing can reduce the free volume and promote the formation of charge transfer complexes. As a consequence, the improved rigidity of the polymer chains increases the polymer discrimination of shape and size for penetrants, although no chemical reaction occurs with thermal annealing.     

超临界二氧化碳对聚合物的增塑作用及应用

简要介绍了超临界二氧化碳的性质及其与聚合物的相互作用 ,着重论述了超临界二氧化碳对聚合物的增塑作用及应用 ,包括小分子渗透、溶胀聚合、抽提分级、聚合物脱挥及微孔材料的制备等     

The effect of CO<Subscript>2</Subscript> in free-radical polymerization of 2,2,2-trifluoroethyl methacrylate

Carbon dioxide is an effective diluent for increasing the free volume of polymer. It has useful advantages with reductions of viscosity, surface tension and with an increase of diffusion into polymer. These properties are available in polymer processing and particle designing. We carried out free-radical polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) with AIBN as the initiator in carbon dioxide. This experiment was performed at fixed temperature (343 K), stirring speed and weight of monomer+initiator. Only weight ratios of carbon dioxide were changed. Molecular weight and T_g showed a minimum at 14.1 MPa and increased in the higher final pressure.