Polytetrafluoroethylene (PTFE) membranes with three-dimensional interconnected porous networks are usually used as air filters. However, they are easily contaminated by oily aerosols in air filtration, resulting in a decrease in filtration efficiency. Herein, a strategy for the preparation of amphiphobic PTFE membranes with a ring-on -string-like micro/nano structure for air purification was proposed. First, the PTFE fibers were locked by OTS polysiloxane rings to form an OTS layer with ring-on-string-like structure by spraying octadecyltrichlorosilane (OTS) solution on the membrane surface. Subsequently, fluorinated silica (F-SiO2) nanoparticles were sprayed to build the micro/nano structure and the surface with low surface energy. The prepared amphiphobic membrane had high liquid repellency to water (-153), diiodomethane (-136) and hexadecane (-124). Moreover, the membrane amphiphobicity exhibited a high stability, which can be ascribed to the OTS layer. The layer has a special ring-on-string-like structure and can act as an anchor to fix the nanoparticles on the membrane surface because of the strong interaction between OTS and the nanoparticles. The filtration test results showed that the amphiphobic membrane developed possessed high removal efficiency for 0.1, 0.16 and 0.2 mu m particles (> 99.9670%). As for the anti-oil fouling ability, the amphiphobic membrane maintained a pressure drop below 3 kPa in the smoke filtration within 10 min, meaning that the membrane developed had a high anti-oil fouling ability. The developed amphiphobic PTFE membrane in this work has a promising prospect in air purification in oil environments.
双疏表面的研究是目前材料特性研究的热点之一,在分离膜领域,双疏膜的研究主要集中在膜蒸馏方面,用于处理含低表面张力液体的废水,具有分离效率高、抗污染性强和易清洁等优点.重点综述了静电纺丝法、浸涂法、喷涂法、等离子体处理等双疏膜材料的制备技术,并简要介绍了双疏膜在膜蒸馏和空气过滤领域的应用.最后,对这几类常见的双疏膜表面构筑技术的优势与不足进行了总结,并对双疏膜材料的应用和发展进行了展望.
本文利用Nested Logit模型,从绝对质量和相对质量两个角度,对2001-2010年期间中国出口到美国市场上的产品质量和产品质量升级进行了实证测算.实证分析发现:中国整体出口产品质量高于世界平均水平.此外,中国出口产品存在明显的质量升级现象.这主要是由机电仪器与交通工具大类的质量升级所带动的.在此基础上,本文将中国出口产品质量和质量升级与日本、德国、印度、东盟进行了比较分析.研究结论显示:2001-2010年间,与德国、日本、东盟、印度四个经济体的出口产品整体质量相比,中国出口产品整体质量有了明显的提升.
纺织业是中国对外经济贸易中的支柱产业之一,凭借其廉价的劳动力竞争优势在国际市场上占有很大的份额。近年来,中国的劳动力成本不断上升,直接导致纺织品出口价格的提高。本文以出口竞争力指数和纺织品出口额占总额的比重作为衡量的指标,通过建立模型来分析劳动力成本提高对纺织品出口的具体影响,并提出相关的对策分析。
