Multi-stimuli Responsive Porous Polypropylene Membranes Prepared By Photografting With Poly (N-isopropylacrylamide) And Poly (α-methacrylic Acid)

Polypropylene (PP) is one kind of ideal membrane materials, which has many advantages such as a high performance, non-toxic, good biological compatibility, high intensity and solvent resistance. However, in general, it also has some defects involving low surface energy, hydrophobicity, and the chemical inertness, and nonpolar etc, which limit its application. The present work is to modify the PP membrane by photografting method and then improve its functionality to widen the application domains.At present, the researches on functional switchable membrane mainly have focused on the single responsive membrane modified surfacely by plasma and high-energy radiation grafting methods et al. The modification methods are unfit for the preparation of dual response porous membrane with block grafting polymers. Accordingly, in the present work photo-grafting method was adopted to prepare the functional modification of the PP microporous membrane (basement membrane). The modified membrane will present a dual responsiveness to temperature and to pH value due to the grafting of a block polymer chain.In this work, firstly, a random copolymerization gelatin of poly (NIPAAm-co-MAA) was prepared by cross-linked polymerization, and the influences of correlated conditions were investigated, and then the responsive performances of the gelatin were researched. In addition, a new theoretical model of gelatin was established basing on the Flory-Huggins osmotic pressure theory and Donnan balance theory, to explain the responsive mechanismThen the photo-grafting method was used to introduce the PNlPAAm (poly N-isopropyl acrylamide) and PMAA (poly methyl-acrylic acid) polymers orderly, and form the di-block grafting structure, i.e. the PP-g-PNIPAAm-b-PMAA membrane prepared. In this section, the major influencing factors on the photo-grafting including the monomer concentration,the radiation time and the temperature were investigated in details, and the modified membrane was characterized with ATIR and SEM. The results show that the grafting chains bond to membrane surface by covalent bond, the grafting polymer covers the surface and then fills the membrane holes with the increasing of grafting fields, and the holes will be plugged when the grafting fields is high enough.Finally, the pure water flux test was carried out to measure the flux of the prepared PP-g-PNIPAAm-b-PMAA membrane. The relationship between membrane grafting fields and the water flux was studied under different temperatures and pH values, which could explain by a flux model of the di-block grafting membrane. In addition, the effect of membrane pore size on the grafting fields and pure water flux was also investigated, and dynamic contact angles (normal temperature, in neutral water) of the membrane before and after modification were tested. The results indicate that the grafting membrane has the dual responsiveness to the temperature and the pH, and the hydrophilicity of the membrane surface is also enhanced.