Abstract
A two-step strategy has been developed to introduce silica nanoparticles into highly porous poly(l-lactic acid) (PLLA) nanofibers. Silica nanoparticles (SiNPs) were firstly synthesized and then modified to be hydrophobic. After PLLA/SiNPs composite fibrous membranes were electrospun and collected, they were re-crystallized by acetone at room temperature for a few minutes. With the re-arrangement of PLLA chains, the nano-/micro-electrospun fibres were transformed from non-porous ones to be porous ones with high surface area. Consequently, SiNPs that were completely covered by PLLA before acetone treatment showed up at the fibre surface. Higher PLLA crystallization also enhanced the Young’s modulus and tensile strength (420 and 8.47 MPa) of the composite membrane. However, incorporation of SiNPs into porous PLLA membranes reduced their modulus and tensile strength (280.66 and 5.92 MPa), but an increase in strain to fracture (80.82%) was observed. Scanning electron microscopy (SEM), focused ion beam SEM, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction were applied to confirm the presence of SiNP in PLLA fibres. The presence of SiNPs inside and outside fibres enhances the hydrophobicity of PLLA/SiNPs nano-fibrous membrane as the water contact angle is greater than 150°. The oil absorption of these porous composite membranes was also tested using four different oils, which can reach the highest absorption capacity when the weight ratio of PLLA and SiNPs is 1:1. The flux of prepared membranes was investigated, and results indicated that SiNPs-loaded membrane effectively enhanced the flux (5200 Lm−2 h−1).
Highlights
The realizing of promise of nanotechnology is dependent on efficient technology for producing nanosized objects which should be prevented from aggregating into larger objects
These results indicate that the surface of the pristine Silica nanoparticles (SiNPs) have been successfully modified by VTMO
Pore formation causes modified SiNPs (M-SiNPs) exposure whilst M-SiNP loading contributes to the formation of flexible chain fibres and reduces the mobility of poly(l-lactic acid) (PLLA) fibres. These results indicate that compared with pristine PLLA fibres, crystallization enhances porous fibres’ Young’s modulus and uniform M-SiNP loading in PLLA fibres plays an important role in enhancing fibres’ tensile strength
Summary
The realizing of promise of nanotechnology is dependent on efficient technology for producing nanosized objects which should be prevented from aggregating into larger objects. Gu et al built a superoleophilic and superhydrophobic SiNPs/polylactic acid (PLA) non-woven fabric via dopamine modification for oil and water separation [39] The disadvantage of this method is that it is hard to deposit particles uniformly on the fibre surface. Natarajan et al [50] prepared porous PLA fibres via adding dimethyl formamide as a non-solvent into electrospinning solution. Most of these pores were formed only on the fibre surface. We report a two-step strategy for porous PLLA nanofibrous membranes loaded with modified silica nanoparticles prepared via electrospinning and recrystallization. PLLA was dissolved and M-SiNPs were dispersed in DCM and DMF mixed solvent to prepare a transparent electrospinning solution at 50 °C under stirring on a hotplate for 1 h. V St where V is the volume of oil, S is the effective area of membrane, and t is the oil pass time
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