Contrasting thermal behavior and low-temperature flexibility of PDMS-grafted and poly(2-ethylhexyl acrylate)-grafted polyurethane

Polydimethylsiloxane (PDMS) was grafted onto polyurethane (PU) to form a P series, and 2-ethylhexyl acrylate (EHA) was graft-polymerized onto PU to form an E series. The spectroscopic, thermal, tensile, shape memory, and low-temperature flexibility properties of the P and E series were compared. With an increase in the PDMS content, the T_g of the P series gradually increased, whereas the T_g of the E series was not affected by an increase in the EHA content. The tensile strength of the P and E series sharply increased with the PDMS or EHA content without a significant decrease in tensile strain. The shape recovery of the P and E series remained high after four repeated tests. However, shape retention of the P series significantly decreased with an increase in the PDMS content. Finally, the P series demonstrated excellent low-temperature flexibility from ?35°C compared with the E series and control PUs.     

Preparation and characterization of electrostrictive polyurethane films with conductive polymer electrodes

All-polymer electrostrictive soft films were developed for the first time by depositing conductive polymer (polypyrrole) directly on both sides of solution-cast electrostrictive polyurethane elastomer films. The final composite films are flexible with strong adhesion between the polyurethane film and the conductive polymer electrode. The conductivity (sheet resistivity ∼1000 Ω/□), of the polymer electrode is appropriate for its intended use. The compatible interface between the polypyrrole electrode polymer and the electrostrictive polyurethane significantly improves the acoustic and optical transparency of these composite films, compared with using a metal electrode film. The all-polymer films also exhibit comparable dielectric properties to gold-electroded polyurethane films in the temperature range from −40^°C to +80^°C. The temperature range covers the soft segment glass transition temperature of the polyurethane elastomers, which is about −20^°C. The films also show large electric field induced strain responses which are dependent on film thickness and measurement frequency. The electrostrictive characteristics in the all-polymer films show similarities to those of the films with gold electrodes under identical measurement conditions. © 1998 John Wiley & Sons, Ltd.     

Retention, kinetics and thermodynamics profile of cadmium adsorption from iodide medium onto polyurethane foam and its separation from zinc bulk

The sorption behaviour of 2.5 × 10⁻⁵ M solution of Cd(II) on polyurethane foam (PUF) from iodide medium have been investigated. The conditions were optimized from aqueous solutions of different pH (1-10) and of acids of varied concentration (0.01-1.0 M). The maximum concentration of KI was found to be 0.24 M and equilibration time was established to be 20 min. The data successfully followed the Freundlich and Dubinin-Radushkevich (D-R) isotherms at low metal ion concentration while Langmuir isotherm followed at higher metal ion concentration. The Freundlich parameter 1/n = 0.66 ± 0.02 have been evaluated whereas D-R isotherm yields the sorption free energy E = 10.5 ± 0.1 kJ mol⁻¹ indicating ion exchange type chemisorption. The monolayer coverage (XL) constant of Langmuir isotherm was found to be 23.7 ± 0.4 mg g⁻¹. The numerical values of thermodynamics parameters enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) indicated the endothermic and spontaneous nature of sorption. The Scatchard plot analysis was tested to evaluate the binding sites of the PUF and stability constants of sorption were determined. On the basis of these parameters, the sorption mechanism was discussed. Among the foreign ions tested, Pb(II), Hg(II), cyanide and nitrite should be absent. The clean separation of Cd(II) from Zn(II) ions in the ratio 1:250, respectively, was achieved by column chromatography.     

Synthesis of novel hierarchical ZSM-5 monoliths and their application in trichloroethylene removal

A self-supporting ZSM-5 monolith with a hierarchical porosity was prepared using polyurethane foam (PUF) as a structural template and a hydrothermal synthesis procedure. The synthesized monolith was characterized and investigated towards the adsorption and catalytic oxidation of trichloroethylene (TCE). Adsorption of TCE was studied gravimetrically and oxidation of TCE was studied using a vapor-phase down-flow reactor. Monolithic ZSM-5 displayed good sorption properties and completely oxidized TCE. Conversion levels of 50% and 90% were achieved at reduced temperatures (by ~50 ℃) when compared with the conversion temperatures obtained from the powder counterparts. Besides the activity of the monolith towards TCE adsorption and oxidation, it was stable and enhanced diffusion, thereby reducing pressure drops to a great extent owing to its hierarchical porous nature.     

油墨用聚氨酯树脂的研究

研究用于印刷油墨的单组分溶剂型聚氨酯树脂，考查聚合物多元醇和异氰酸酯对树脂微观形态、机械性能以及印刷适应性和附着性等性能的影响。结果表明：聚酯型树脂的附着性较好，4，4-二甲苯甲烷二异氰酸酯(MDI)基树脂的附着性较佳。     

含气量对激光空泡在刚性壁面空蚀的影响

采用强脉冲激光器设计液体环境下刚性壁面空蚀实验平台,改变液体中含气量,利用高速相机观察不同含气量条件下激光空泡在壁面附近的脉动过程,并对刚性壁面造成的空蚀结果进行了观测。实验研究发现,随着液体中相对空气含量的提高,激光空泡脉动的最大尺寸增大,空泡的膨胀运动变剧烈,溃灭运动速度降低,空泡的溃灭强度降低,从而影响到溃灭冲击波和壁面微射流对刚性壁面的冲击速度,减弱了壁面空蚀,而液体中含气量的提高能够降低激光空泡对刚性壁面的空蚀程度。     

空心微珠/Al复合材料的动态压缩力学性能和吸能特性

利用分离式霍普金森压杆（split Hopkinson pressure bar,SHPB）系统对空心微珠体积分数为0.4的空心微珠/1199Al复合泡沫在1 700~2 900s^-1应变率范围内的动态压缩力学性能、吸能性能进行了研究,还利用SEM扫描电镜对压缩试件断口进行微观组织分析,与准静态条件下材料的压缩力学性能及压缩变形机制进行了对比。结果表明,空心微珠/1199Al复合泡沫是一种应变率敏感材料,与准静态结果相比,在高应变率下复合材料的流动应力和塑性应变有明显的增大,应变率硬化效应对复合材料的流动应力的影响明显大于应变硬化的影响。复合材料的准静态和动态压缩变形机制存在一定差异,动态载荷作用下,空心微珠/1199Al复合泡沫内部空心微珠的压缩和基体材料的充填同时发生,组分之间具有良好的协调变形能力。

     

A study on the glass transition behavior and morphology of semi-interpenetrating polymer networks

The epoxy resin/polyurethane semi-IPN was prepared and the glass transition behavior of the semi-IPN was discussed with DSC and DMA methods. The results show that the two glass transition temperatures (T_g) referring to epoxy resin and polyurethane respectively get closer. Between the two T_g there exists another T_g related to the interface between the two polymers. SEM indicates that this semi-IPN has a two-phase continuous structure which changes with different weight compositions. This is also proved by testing the Young's modulus. It is found that the IPN system has a cellular structure. Comparatively, the compatibility between the two polymers is the best when the weight ratio of EP/PU is 70/30. © 1996 John Wiley & Sons, Inc.     

含泡沫铝防护结构的超高速撞击数值模拟研究

 泡沫铝是一种新型航天器防护材料,拥有良好的抵御空间碎片超高速撞击的特性。模仿泡沫金属的生产原理,建立了泡沫金属微结构几何模型,结合自编的光滑质点流体动力学程序进行了超高速撞击数值仿真,通过与实验结果的对比,验证了模型的有效性。提出了两种含泡沫铝的空间碎片防护结构,即填充泡沫铝结构和夹层泡沫铝结构。对这两种结构分别进行了仿真计算,获得了其撞击极限曲线。分析结果表明,在空间碎片防护领域涉及的大部分撞击速度区间内,填充泡沫铝结构的防护性能优于夹层泡沫铝结构。