高分子超滤膜表面改性研究进展

介绍目前对高分子超滤膜进行表面改性的几种方法。

高分子线性柔性链在超滤过程中第一类突变现象的观察

利用一种双层结构的膜屏蔽了每个微孔所产生的流场之间的相互作用,从而首次观测到理论上预计的高分子线性柔性链在超滤过程中的第一类突变现象,即仅当宏观流速高于一宏观阈值时,高分子长链方可通过尺寸远小于链无扰半径的微孔,且该宏观阈值与高分子链的长短无关.另外,实验中的过滤膜含有多个微孔,实验结果显示,当一给定的宏观流速低于宏观阈值时,部分微孔会被无法通过的较长的高分子链堵塞,造成未堵塞微孔中的微观流速大于微观阈值.因此,较短的高分子链可从未堵塞的微孔通过滤膜.

聚丙烯腈超滤膜流动电位的测定

用实验方法测定多孔性高分子超滤 (UF)膜的流动电位。考察不同类型电解质如 Na Cl、KCl、Mg Cl2 、Na2 SO4 和 Mg SO4 等溶液对聚丙烯腈管式 ACP- 0 0 5 3 UF膜的流动电位随浓度的变化关系。结果表明流动电位的大小与电解质种类和浓度有关 ,浓度越大 ,流动电位越小。离子价态对膜的流动电位影响很大 ,阳离子比阴离子对膜流动电位的影响更大 。

聚醚砜和聚偏氟乙烯超滤膜对臭氧的耐受性

通过静态浸泡实验考察了臭氧对聚醚砜(PES)和聚偏氟乙烯(PVDF)超滤膜透水能力、截留性能、力学性能等的影响,分析了与臭氧接触前后膜化学组成和性质的变化,结果表明,室温(20±1)℃下与饱和臭氧水接触2h后,PES膜的透水率增大至原始膜的3倍以上,对腐殖酸(HA)的截留率降至0左右,结合膜表面组成和性质分析,臭氧在氧化亲水添加剂聚乙烯吡咯烷酮(PVP)的同时使PES分子也发生了分解,破坏了PES分离层的结构和功能;对于PVDF膜,与饱和臭氧水接触1h后膜的透水率增大至原始膜的1.4倍左右,对HA截留率由原始膜的61.13%降至41.24%,但与臭氧接触时间进一步延长时膜性能无进一步下降,对膜表面组成和性质的分析表明臭氧对PVDF膜分离层的损伤主要是由于PVP的氧化和流失造成的,PVDF本身未发生分解.PVDF膜分离层对臭氧的耐受性显著高于PES膜,但臭氧使2种膜的力学性能均有明显下降.

Changes of Resistance During Polyelectrolyte-enhanced Stirred Batch Ultrafiltration

The permeation flux or the resistance in the ultrafiltration process is mainly limited by osmotic pressure, and it may originate from various kinds of polymer interactions. However, the real origin of permeation resistance hasn＇t been clarified yet in the light of polymer solution nature. The removal of nitrate contamination by polyelectrolytes was carried out with stirred batch ultrafiltration. The polyelectrolyte concentrations both in permeate and retentate were analyzed with total organic carbon analyzer and permeate mass was acquired by electronic balance connected with computer. The total resistance was calculated and interpreted based on the osmotic pressures in three concentration regimes. In the dilute region, the resistance was proportional to polymer concentration; in the semidilute region, the resistance depended on polymer concentration in the parabolic relationship; in the highly concentrated solution regime, the osmotic pressure factor （OPF） would dominate the total resistance; and the deviation from OPF control could come from the electrostatic repulsion between the tightly compacted and charged polyelectrolyte particles at extremely concentrated solution regime. It was first found that dilute and semidilute concentration regions can be easily detected by plotting the leg-log curves of the polymer concentration versus the ratio of the total resistance to polymer concentration. The new concept OPF was defined and did work well at highly concentrated regime.