Study On The Preparation, Modification And Properties Of Electrospun Poly (Vinyl Chloride) Fibers

Electrospinning is a very important method to fabricate ultrafine fibers. Poly(vinyl chloride) (PVC) is the second most commonly used polymer. Its electrospun fibers may find great potential applications at many aspects of industry and enviromental protection.In this study, PVC ultrafine fibers were produced by electrospinning. The effects of polymer molecular weight, solution concentration, the grafted sodium N, N - diethyldithiocarbamate (NaETC) and the solvent ratios on the morphology and diameter of the PVC fibers were studied. The measures, such as mixed solvents, solvent treatment, heat treatment and multi-walled carbon nanotubes were applied to improve the mechanical strength of the electrospun fibrous membranes. After the graft copolymerization of acrylic acid on the surfaces of PVC-ETC and PVC fibrous membranes using ultraviolet (UV) irradiation and heat treatment, the PVC-g-PAA fibrous membranes were used for the adsorption of cationic dye. The morphology, microstructure, properties and cationic dye adsorption of the modified electrospun membranes were examined by infrared spectroscopy, scanning electron microscopy, thermogravimetry, universal testing machine and ultraviolet-visible spectrophotometry.The results show that,(1) The PVC molecular weight determines its fibers morphology directly, and the electrospinnability of PVC was improved by the substitution of PVC with NaETC, and the fiber diameter and its distribution was decreased with the increase of DMF fraction in mixed solvents, and the average diameter reduced from 2μm down to 300nm. Long uniform PVC ultrafine fibers was obtained by electrospinning 10% PVC in THF/DMF(30/70) mixed solvent, and the electrospinning process was relatively steady.(2) The mechanical strength of PVC electrospun fibrous membranes are greatly improved by four methods: mixed solvent, solvent treatment, heat treatment and multi-walled carbon nanotube reinforcement. After solvent and heat treatments, the membranes were partially welding with each other, and also the density of the membranes changed. The tensile strengths of the membranes increased as inverse type"S"distribution with the increase of solvent time, while it increased in a parabolic way with the increase of treatment temperature. The tensile strength and elongation at break of the membranes firstly increased and then decreased with the increase of MWCNTs content. This was the results of its orientation reinforcement at low content and its aggregation at high content. When the content of MWCNTs was 3wt%, the tensile strength and elongation at break reached the maximum, 10.23MPa and 72.09% respectively.(3) The PVC-g-PAA fibrous membranes were prepared by using grafting copolymerization under UV irradiation or heating on the surface of PVC fibers. After the modification, the diameter of the fibers became large, and also the surface became rough. The graft rate firstly increased and then decreased with the increases of monomer concentration and polymerization temperature.(4) Cationic dye adsorption of PVC-g-PAA ultrafine fibrous membranes demonstrates high adsorption rate and efficient removal as compared with pure PVC fibrous membranes. The equilibrium sorption capacity Qe increased with the increases of the grafting rate, the initial dye concentration and solution temperature. The adsorption of the pure PVC membranes followed Freundlich isotherm, whereas the adsorption of modified membranes followed Langmuir isotherm.The feature and innovations are as follows:(1) The PVC-ETC ultrafine fibers were made by electrospinning. The polymer molas mass was increased very much while its polydispersity was decreased after the ETC group was connected to PVC chains. Therefore, the electrospinnability of PVC was improved. (2) Solvent treatment, heat treatment and multi-walled carbon nanotube reinforcement all remarkably improved the mechanical strength of PVC electrospun fibrous membranes.(3) After the graft copolymerization of acrylic acid on the surface of PVC-ETC fibrous membranes using UV irradiation or heat treatment, the modified fibrous membranes showed remarkable improvement in the adsorption of cationic dye.(4) The compilation of the adsorptions of synthetic cationic dye waste water with PVC and modified PVC fibrous membranes would serve as a reference for further investigation in the wastewater treatment.