Yuhai Guo

Structural Characteristics and Properties of Silk Fibroin/Poly(lactic acid) Blend Films

This paper describes the preparation and characterization of blend films composed of regenerated silk fibroin (SF) and poly(lactic acid) (PLA). FT-IR and XRD of the SF/PLA blend films with different ratios indicated that the secondary structural transition of SF from Silk I to Silk II was induced upon blending with PLA. The effects of SF/PLA blend ratios on the mechanical and physical properties of the blend films were investigated. Compared to pure SF film, the mechanical and thermal properties of the blend films were improved, and surface hydrophilicity and swelling capacity decreased due to the secondary structural transition of SF to Silk II. Among the blend films with different ratios, the SF/PLA blend film with 7 wt% PLA content showed excellent mechanical properties. Meanwhile, the BSA adsorption amount on the blend film increased with the increase of PLA content. In vitro cell adhesion test showed that the blend film was a good matrix for the growth of L929 mouse fibroblast cells. Consequently, controlling the PLA content in the SF film can improve the mechanical and physical properties of the SF film and provide a promising opportunity to widen potential application of SF in the biomaterials field.

Nano-TiO2 induced secondary structural transition of silk fibroin studied by two-dimensional Fourier-transform infrared correlation spectroscopy and Raman spectroscopy.

By sol–gel processing, regenerated nano-TiO2/SF (silk fibroin) composite films were synthesized. The experimental results revealed that the nano-TiO2 particles were well dispersed in the regenerated silk fibroin. Using FT-IR and Raman spectroscopy, the secondary structures of these composite films with concentrations of 0, 0.2, 0.4, 0.8 and 1.6 wt% were characterized. Concentration-perturbed two-dimensional (2D) correlation spectra were calculated for the spectra in the 1800–1600 cm−1 region. To investigate nano-TiO2 particles induced changes in the secondary structure and hydration, the slice spectra were calculated from the synchronous and asynchronous spectra, respectively. The transmittance IR and Raman spectra measurement indicated that the secondary structure of the pure silk film was mostly random coil and α-helix, while the composite films were β-sheet. With increasing nano-TiO2 content, the secondary structure of composite films was changed from typical Silk I to typical Silk II. However, it was found that the transition of the SFs secondary structures would be restrained by excessive nano-TiO2 (over 0.8%) introduced into the composite SF films. Through the FT-IR absorbance and 2D correlation spectra, it was demonstrated that the formation of nano-TiO2 particles could induce the partial transformation of SF conformation from Silk I to Silk II.

Effect of the degree of hydrolysis and polymerisation on the melting process of thermoplastic poly(vinyl alcohol)

ABSTRACT In this work, the thermoplastic poly(vinyl alcohol) (TPVA) blend films were efficiently prepared using pure poly(vinyl alcohol) (PVA) and caprolactam–MgCl2 ·6H2O via the aqueous method on the condition of achieving the melting process of PVA. The effect of the degree of polymerisation (DP) and hydrolysis (DH) of PVA on plasticisation was studied using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, differential scanning calorimeter, and thermo gravimetric analysis. The plasticising effect increases initially and then decreases with the increase of DP owing to the destruction of hydrogen bonding and the decrease in regularity in PVA. The plasticising effect increases with the increase in DH, because the plasticiser weakens the hydrogen bonding of intro-intra molecular in PVA, which is confirmed by the shift of the –OH characteristic peak of FT-IR spectra. The thermal processing windows increase owing to the coordination effect between hydrogen bonding and crystallinity. TPVA-1799 had the largest thermal processing window (120°C) and the molten filament was extruded, which were both significant for melt spinning. GRAPHICAL ABSTRACT

Surface microstructure evolution of polytetrafluoroethylene microporous materials by a casting–lyophilization–calcining (CLC) method

This study aims at manipulating the surface microstructure of polytetrafluoroethylene (PTFE) microporous materials via a novel casting–lyophilization–calcining (CLC) process. In the CLC process, the emulsion consisting of polyvinylidene fluoride (PVDF), sodium dodecyl benzene sulfonate (SDBS) and distilled water was firstly poured onto the surface of the PTFE microporous materials and then the PTFE materials covered by the emulsion were sintered after removal of the distilled water by lyophilization. The results indicate that a compact thin PVDF layer can be easily constructed on the surface of the PTFE microporous materials by controlling the wetting state transition, which can be easily handled by regulating the SDBS concentration in the CLC process. The bubble point is enhanced owing to the compact PVDF layer on the surface, leading to a higher collection efficiency. In addition, the average pore size, porosity and thickness can be easily manipulated by controlling the SDBS concentration and PVDF mass fraction. Finally, the filtration mechanism changes from depth filtration to surface filtration, which brings about a higher air flux recovery. We hope such a novel process could be potentially useful in the surface microstructure regulation of polymer microporous materials with low surface energy.

THE IMPROVEMENT ON THE PROTECTIVE PROPERTY OF PTFE MEMBRANE BY PU COATING AND CO-STRETCHING

A new idea regarding the improvement of the protective property of of PTFE membrane through co-stretching processing technique was put forward in this paper. The structure and properties of PTFE, co-stretching PTFE/PU and PU coated PTFE membranes were researched through SEM, water vapor permeability measurement, together with protective property test. Because of the existence of micro-pores in the PU layer, the WVP of PU coated PTFE laminate is higher than that of co-stretching PTFE/PU laminate with same PU layer thickness. In contrast to PU coated PTFE, the co-stretching PTFE/PU membrane could absolutely prevent the virus from penetrating to the skin of the wearer because the PU layer is nonporous after the heat treatment. It has been proven that this laminate could prevent virus from staining the skin of human and provide satisfactory wearing comfort.