Papers by Author: Chun Ju He

Abstract: Polypropylene (PP) membranes were respectively prepared using adipic acid (APA) and Sorbitol (NA-40) as nucleating agent via thermally induced phase separation (TIPS) method. The effects of nucleating agent content and cooling temperature on the structure and performance of membrane were investigated using scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). WAXD spectrogram indicates that three kinds of α, β and γ-form crystal were formed in this preparation process and the relative content of β-form crystal in membrane prepared by NA-40 system is higher than that of membrane formed by adipic acid. SEM images show that porous structure and cellular structure were observed on the surface and cross-section of membrane. The water flux, tensile strength and elongation increase with the addition of nucleating agent content and decrease with cooling temperature rising. This paper aims to choose proper nucleating agent NA-40 and coagulation temperature to improve the properties of PP membranes.

Abstract: The hydrophilic modification of poly (vinylidene fluoride) (PVDF) membrane is achieved by using amphiphilic copolymer poly (2-hydroxyethyl methacrylate)-b-polydimethylsiloxane-b-poly (2-hydroxyethyl methacrylate) (PHEMA-b-PDMS-b-PHEMA) as addictive. The copolymer is synthesized via atom transfer radical polymerization (ATRP) and the membranes are prepared by non-solvent induced phase separation. The addition of amphiphlic copolymer has significant influence on membrane hydrophilicity and anti-fouling property. As the addictive content increasing, the water contact angle is decreased from 92° to 65°, water flux and pure water recovery rate are increased from 52.9L/m2h to 263.3 L/m2h and 71 to 95%, respectively.

Abstract: In order to increase antifouling ability of PVDF membrane, crosslinking PEG as antifouling medium in membrane bulk was studied. PEG with different moleculer weight were crosslinked in membrane solution with TMC as crosslinking agent, ATR demonstrated crosslinked PEG were retained in membrane bulk and surface wetting property was improved with contact angle characterization. According to the dynamic fouling test of BSA solution, the PVDF-T1000 membrane exhibited the best antifouling ability with the FRR value as high as 90%.

Abstract: The interaction between polyacrylonitrile (PAN) and various plasticizer at different temperature was discussed by infrared analysis. At the room temperature, the interaction between nitrile groups of polymer is so strong that the conventional plasticizer propylene carbonate (PC) or new-type plasticizer ionic liquid can’t have interaction with nitrile groups. However, the interaction between nitrile groups weakens at higher temperature, i.e. 160°C, and the interaction between the nitrile groups and IL is formed, which is maintained when natural cooling to 90°C. The interaction between the nitrile groups and IL weakens again when natural cooling to room temperature, it may be attributed to the interaction between IL and water is stronger than that of IL and PAN.

Abstract: Poly (vinylidene fluoride) membranes were prepared from the ternary mixture of PVDF/ 1, 2 - propylene glycol/dimethylacetamidevianon-solvent induced phase separation (NIPS). The effect of the addition of the 1, 2 - propylene glycol content, the Coagulation Bath Temperature and the concentration of PVDF on the performance and structure of the PVDF membranes was studied in the present investigation.The results showed that with increasing polymer concentration, the mechanical strength increased,and the structure of membrane changed from finger-like macro-voids structureto sponge-like structure.It was found that water flux, breaking elongation and tensile strength of the membrane increased with increasing 1, 2 - propylene glycol content, when the content reached 41wt.%, the water flux reaches a maximum.The morphology of PVDF can be improved by the addition of 1, 2 - propylene glycol, which was changed from finger-like structure to sponge-like structure. And the dense skin layer of PVDF membranes became thicker with increasing 1, 2 – propyleneglycol. The tensile strength decreasedfrom 3.3 to 2.1MPa, breaking elongation decreased from 315% to 280% andthe pure water flux increased from 91 to 909 L·m^-2·h^-1. as the coagulation bath temperature (CBT) decreased from 30°C to 5°C.With this condition, the sponge-like hollow fiber membrane hassuccessfully spun.

Abstract: Telechelic polymers have been explored widely because they are precursors for preparing multi-block copolymers, grafted polymers, star polymers, and polymer networks [1-2]. A variety of telechelic polymers with terminals like hydroxy, carboxylic, epoxy groups and carbon–carbon double bond have been prepared by controlled radical polymerization (CRP) techniques including nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT)[3-5].The CRP techniques can not only control the molecular weight but also can be carried out in the presence of many functional groups from monomers, initiators, or chain transfer agents (CTA).

Abstract: In this study, a novel amphiphilic copolymer based on the flexible polydimethylsiloxane (PDMS) macroinitiator was successfully prepared by atom transfer radical polymerization (ATRP). First, the high molecular weight bis (hydroxyalkyl)-terminated PDMS was prepared by hydrosilation reaction between hydrogen-terminated PDMS and 2-allyloxyethanol in the presence of Karstedt’s catalyst. The macroinitiator Br-PDMS-Br was prepared by the reaction between different molecular weight bis (hydroxyalkyl)-terminated PDMS and 2-bromoisobutyry bromide. Then the amphiphilic ABA-type block copolymers of poly [dimethylsiloxane-b-(hydroxylethyl methacrylate)] were initiated by bromide end-capped PDMS with HEMA, under an appropriate catalyst/ligand system of CuCl/bpy. The polymerization proceeded with first-order kinetics. It showed that the reaction system was a controlled/‘living’ polymerization. The triblock copolymers were characterized by FTIR, ¹H-NMR, TGA and GPC techniques. GPC results showed the tribolck copolymer had narrow polydispersity of Mw/Mn (PDI<1.5). TGA results showed the good thermal stability of the triblock copolymer.

Abstract: Polyacrylonitrile (PAN) membranes were prepared via thermally induced phase separation (TIPS) process using polyethylene glycol (PEG) as plasticizing agent and polyvinyl pyrrolidone (PVP) as porogen, which presented high strength, i.e. 6MPa. A systematic study was carried out to investigate the effect of PVP content, PAN concentration and cooling conditions on the pore shape, pore size, water flux and mechanical properties of the membranes, which were characterized by scanning electron microscope, filtration measurement and tensile test. PAN membranes with uniformly distributed pores were fabricated by adjusting the mixed diluent composition. Results of filtration confirm that water flux of PAN membranes mainly depends on the pore structure. Moreover, while PVP content is increased, water flux first increases and then declines, and tensile strength and elongation at break first declines and then increases. In conclusion, the successful application of TIPS provides a new route to the structure modulation and performance enhancement of PAN membranes.

Abstract: Poly (vinylidene fluoride) (PVDF) hybrid membranes reinforced by hydrophilic nanoSiO₂ particles were fabricated from PVDF/N-dimethylacetamide (DMAc)/γ-butyrolactone (γ-BL) system via thermally induced phase separation (TIPS) process. Surface and cross-sectional morphology of membranes were characterized by scanning electron microscope (SEM). The properties such as permeability, mechanical performances and antifouling property were also determined. The results showed that the pore size of membrane surface became smaller, while cross-sectional morphology was changed from bicontinuous structure to cell structure, the pore size became larger and majorities of closed pores became open with the addition of hydrophilic nanoSiO₂ particles in the system. Compared with pure membrane, pure water flux of hybrid membrane increased by 30.3%, i.e. from 290 to 378 L/(m²·h·0.1MPa), antifouling property increased from 63.1% to 80.2%. Meanwhile, tensile strength and elongation at break increased by 70.6% and124%, respectively.

Abstract: Plasticized polyacrylonitrile(PAN) fibers have been chemically impregnated with aqueous solution of KMnO₄ under varying conditions of temperature and time. The effect of modification conditions on the chemical structure and the mechanical properties of precursor fibers are characterized by wide-angle X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscope. The experimental results show that KMnO₄ can be used not only as catalyst for cyclization reaction, but also as plasticizer. The chemical modification between KMnO₄ and PAN can not occur below70°C, the most suitable condition for modification is performed at 80°C for 5 min.