Heyun Wang

Surface chemistry, topology and desalination performance controlled positively charged NF membrane prepared by polydopamine-assisted graft of starburst PAMAM dendrimers

A novel and facile method to prepare surface chemistry, topology and separation performance controlled positively charged nanofiltration membranes by polydopamine-assisted grafting of starburst PAMAM onto polyethersulfone (PES) membranes was introduced. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), zeta potential and water contact angle measurements were applied to characterize the morphology and chemical composition changes of the resultant membranes. The result of the salt rejections followed the sequence: R (MgCl2) > R (MgSO4) > R (NaCl) > R (Na2SO4), which indicated a PAMAM grafting membrane with a positively charged surface. The MgCl2 rejections of the resultant membrane increased with increasing PAMAM generation numbers (G0, G1 and G2) and reached 83.67%, 90.53% and 93.15%, respectively. The resultant membrane possessed a good structural stability and anti-fouling properties, which were determined by the long-term testing. This facile, mild and highly controllable polydopamine-assisted PAMAM grafting modification may find broad applicability in preparing positively charged NF membranes with tunable properties to meet potential needs.

Molecular chain model construction, thermo-stability, and thermo-oxidative degradation mechanism of poly(vinyl chloride)

Thermo-oxidative degradation of poly(vinyl chloride) (PVC) is inevitable during its processing. We focused on the relationship between the structure and properties of PVC, as well as on the thermal-oxidative degradation mechanism of PVC. Two models, the unsaturated and oxygen-containing structure models, were successfully constructed by pretreatment under different atmospheres. The thermal stability of treated PVC was determined by thermogravimetric analysis. An X-ray photoelectron spectroscopy (XPS) processing method was also used to analyze the type of functional groups that may be produced during thermal-oxidative degradation, whereas XPS and Fourier-transform infrared (FTIR) spectrometry were used to determine the trend in the content variation of functional groups of samples. The two structure models revealed that the thermal properties were greatly influenced by oxygen-containing groups compared with the unsaturated structures, and the position of oxygen molecule attack on the PVC main chain is not primarily located on the unsaturated structure or the α carbon atom of the unsaturated sides. XPS and FTIR results can possibly provide evidence for the thermo-oxidative degradation mechanism of PVC. Moreover, a carbonyl group was generated when the methylene or methine structure was attacked by an oxygen molecule, rendering the PVC resins unstable.

UV-Visible Spectrophotometry for the Determination of Conjugated Polyene Structures of Poly(vinyl chloride) in 1,2-Dichloroethane

The article presents an improved UV-visible spectroscopic analysis to determine the types and contents of conjugated polyene structures in poly(vinyl chloride) (PVC) chains based on the derived formulas in 1,2-dichloroethane solution. Due to the restriction of delocalized π electrons by the interaction forces among PVC chains, the effect of concentration was investigated, and the best resolution was achieved when vinyl chloride structure unit concentration (Cvc) was 0.08 mol/L. Compared with the results of the film method, the solution method showed better resolution and lower deviation, especially for low contents of tetraene, pentaene, and hexaene in PVC chains.

Construction of chain segment structure models, and effects on the initial stage of the thermal degradation of poly(vinyl chloride)

The thermal degradation of poly(vinyl chloride) (PVC) is inevitable during its processing and is directly related to the initial stage of the thermal stability of PVC. This paper focuses on the influence of the segment structures that include a conjugated polyene sequence structure and internal allylic chloride structure on the initial stage of the thermal degradation of PVC. The conjugated polyene sequence structure and internal allylic chloride structure were the structural models successfully constructed via thermal and alkali treatment methods through the long chain of PVC directly. Ultraviolet-visible spectroscopy (UV-Vis) was used to analyze the type and content of the conjugated polyene structure. Nuclear magnetic resonance spectroscopy (1H-NMR) was used to determine the variation trend in the content of internal allylic chlorine structures because of the oxygen-containing structure excluded by Fourier-transform infrared spectrometer (FTIR) characterization. The thermal stability of the treated PVC was also determined through thermogravimetric analysis (TGA). The comparison between the two structural models revealed that the internal allylic chloride structure greatly influenced the initial thermal stability as an initiation point in the PVC chain, thereby leading to thermal instability.

Hydrophilic surface modification of DPVC nanofibrous membrane by free-radical graft polymerization

We introduced a novelty and mild method for preparing four different hydrophilic polymers (PVP, PAA, PDMAEMA, and PAM) grafted to DPVC fibrous membrane surface. To increase active sites and improve the grafting efficiency of hydrophilic polymer on PVC membrane, PVC resin was slightly dehydrochlorinated, forming a few conjugated double bonds. A minor reduction in the DPVC average molecular weight in a short dehydrochlorination time exerted minimal influence on the DPVC electrospinning process and fiber morphology. Results of ATR-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and surface wettability of modified membranes proved that hydrophilic polymers were successfully grafted covalently on the surface of the DPVC nanofibrous membrane. The hydrophilicity of the modified DPVC fibrous membrane was evidently improved. This hydrophilic DPVC fibrous membrane may fulfill potential requirements in tissue engineering and wastewater treatment.