Investigation On The Structure Controlling And Adsorption Property Of Polypropylene-based Porous Composite Membrane Incorporated With Graphite Oxide (GO)

With the rapid development of the science and technology, more and more novel polymeric products have arisen people's attention. The presence of these products, on one hand, improves the living quality of people; on the other hand, a series of inevitable environmental problems have been brought to our planet. Consequently, the worse environment has a negative influence on our daily life and threats our health to a great degree. To date, more attentions have been paid to the water and air pollution, which has been dealt with by researchers in different ways. Among all these methods, the technology of membrane separation and adsorption become one of the most prevalent methods for researchers due to its advantages of high efficiency, low cost, easy operation and so on. However, the structure of the porous membrane is hard to control. The membranes prepared by the traditional methods exhibit no special structures and functions. Therefore, the introduction of functional fillers and improvement of controlling methods are needed to endow the membrane with the high practical value.Polypropylene(PP), as one of the five general engineering plastics, is widely used as the matrix for the functional membrane due to its low cost and excellent comprehensive properties. Numbers of outstanding properties, such as good mechanical property, good dimensional stability, excellent chemical stability and so on, are achieved for the prepared membranes, which have been widely applied in the fields of wastewater treatment and air purification. PP-based porous membrane can be prepared by different methods, such as stretching, thermal induced phase separation, immerse precipitation and so on. And also, the pore parameters of porous membranes, such as porosity, mean pore size, pore connection and so on, can be well controlled by adjusting the processing conditions. Furthermore, the surface modification can largely enhance the surface hydrophilicity of the PP-based porous membrane, which endows the membrane with the good adsorbability. Consequently, the modified PP-based porous membrane has a greater potential in practical application.In this work, the composites were prepared with isotactic PP as the matrix, and the graphite oxide(GO) was incorporated into the matrix through the melt-compounding with (3 nucleating (?-NA) and pore-forming agent (OP-10) as the assistant agents. The PP-based porous membrane was prepared with the composite through the melt-compressing and subsequent uniaxial stretching. The pore structure of the porous membrane could be well controlled through the annealing treatment or adjusting the tensile rate, temperature and strain. Finally, the PP-based porous membrane was modified with allylamine as the monomer and through the plasma sputtering technology. Amounts of hydrophilic groups were grafted on the surface of the membrane through the surface modification, which endows the membrane with the super hydrophilicity and outstanding adsorbability. Main conclusions are as follows:(1) The PP/graphene/?-NA composite was prepared through the melt-compounding, and the crystallization and melting behaviors were investigated. The results show that the layered graphene is well-dispersed in the PP matrix, and the presence of graphene exhibited good nucleating effect for the a phase, which is lower than the nucleating efficiency of P-NA. The synergistic nucleating effect could be obtained with the simultaneous incorporation of graphene and ?-NA. Furthermore, The synergistic nucleating effect is mainly dependent on the crystallization conditions. During the isothermal and non-isothermal crystallization process, the synergistic nucleating effect becomes more obvious as the crystallization temperature and cooling rate increase, respectively. Different melting behaviors are obtained for different samples, and different melting peaks are related to melting behaviors of different crystallites induced by different fillers. Therefore, the crystal structure can be well controlled through changing the component of composites and crystallization conditions.(2) The ?-PP based composite membrane was prepared with the incorporation of a certain content of GO, and then, the porous membrane was further prepared through the uniaxial stretching. The initial morphology of the composite membrane and the influence of pre-treatment and different processing conditions on the its pore formation behavior were investigated in details. The results show that as the tensile temperature and rate increase, the mean pore size of the PP/?-NA/GO (PNG) porous membrane decreases while the porosity is enhanced. Under different processing conditions, the addition of GO always leads to the decreasing mean pore size and increasing porosity, and the porosity enhancement is more obvious at high tensile temperature and rate. The porosity and mean pore size oi PNG porous membrane increase as the tensile strain increases but decrease slightly when the tensile strain is too high. In addition, the annealing treatment can lead to the enhanced porosity, decreasing mean pore size and better pore regularity for the PNG porous membrane.(3) The PP-based porous membrane was successfully prepared with the incorporation of OP-10 through the melt-compounding and subsequent uniaxial stretching. The influence of OP-10 on the pore formation behavior of the membrane was investigated in details. The results show that amounts of initial pores can be introduced into the PP matrix through the incorporation of OP-10, which also inhibits the nucleation of PP and then leads to the formation of crystals with thinner lamella. Compared to PP membrane, the effective porosity of PP/OP-10 membrane can be effectively enhanced through the incorporation of OP-10, and this enhancing effect is more obvious at high tensile strain or high content of OP-10. The presence of initial pores can change the stress distribution of the membrane, which leads to formation of more pores and the better pore connection, and then, the effective porosity can be enhanced effectively.(4) The PP-based porous membrane was successfully prepared with the incorporation of OP-10 and GO through the melt-compounding and subsequent uniaxial stretching. The initial structure, pore formation behavior and pore structures after stretching were investigated. The plasticization of OP-10 can improve the mobility of PP chain segments, which is in favor of the growth and expansion of pores. Also, the well-dispersed GO can leads to formation of more pores through changing the stress distribution of PP matrix on one hand, on the other hand, the chain mobility is impeded due to the presence of GO, which further limits the growth and expansion of pores to a certain degree. The combined effect of GO and OP-10 can leads to the small mean pore size and high porosity, which endow the composite membrane with a great potential in the fields of filtration and separation.(5) With the allylamine as the monomer, PP/GO/OP-10 membrane was successfully modified through the plasma sputtering technology. The physical and chemical structures of the modified membrane were characterized and its adsorbability was also investigated. The results show that a large number of O and N-containing groups are grafted on the membrane surface after the surface modification, which also makes the membrane surface smoother. Finally, the surface hydrophilicity of the composite membrane is improved effectively through the plasma-assisted surface modification, and its static water contact angle decreases to 11.9°, which means that the super-hydrophilicity is obtained. The pore structure and adsorbability can be well controlled through adjusting the sputtering time. As the sputtering time increases, the number, mean pore size and porosity of pores decrease gradually, while the adsorbability for congo red is enhanced to a certain degree, which attributes to the increasing interaction between the dye molecule and the membrane surface.In conclusion, this work provides a highly efficient and environmentally friendly method for the preparation of adsorptive membranes, which can effectively control the microstructure of the membrane and also enhance its adsorbability. This research provides new ideas and methods for the preparations and applications of membranes for water treatment.