Study On Mechanical Modification And Properties Of Polyhydroxybutyrate Nanofibers

Electrospinning technology is one of the most effective methods to prepare nanofibers. The traditional electrospun nanofibers are random arrangement with incomplete crystallization that lead to the poor mechanical properties, which limits its application in many fields. In this paper, we have used the electrospinning method to prepare the polyhydroxybutyrate (PHB) parallel nanofibrous membranes and the carboxylic multi-walled carbon nanotubes (CMWCNT) enhanced PHB nanofibrous membranes, which are used for filtration and adsorption dyes in wastewater. The main works include the following three parts:(1) The preparation of PHB parallel nanofibers. The first method:A rotating drum was used as the collecting device, and the parallel nanofibers with different orientation are prepared by electrospinning technology. The influences of the drum speed on the morphology and mechanical properties of the parallel nanofibers were investigated. The second method:A metal plate as the collecting device was used to prepare PHB nanofibers with the hot stretch post process to improve the orientation of nanofibers. The orthogonal experimental design and response surface model analysis were used to study the effects of the different hot stretch conditions (the stretch temperature, times, stretch force and the membrane thickness) on the morphology and mechanical properties of nanofibers.(2) The preparation of carbon nanotubes reinforced PHB nanofibers. The first method:The PHB/CMWCNT blend nanofibers were prepared by electrospinning. The second method:The CMWCNT-PHB nanofibers were prepared by electrospinning and electrostatic spraying. The third method:The CMWCNT grafted PHB (CMWCNT-g-PHB) was prepared by chemical method with orthogonal experimental design and the PHB/CMWCNT-g-PHB composite nanofibers were prepared with PHB solution by electrospinning. The effects of CMWCNT contents of three doping methods on the morphology and mechanical properties were studied. The optimum conditions of CMWCNT-g-PHB were determined by infrared spectroscopic analysis, X-ray diffraction spectrum, X-ray photoelectron spectroscopy and thermal property analysis.(3) The modified PHB nanofibrous membranes for the filtration and adsorption properties of dye molecules in dye wastewater were investigated. The first method: The composite nanofibrous nano-filtration membranes were prepared with PHB nanofibrous membrane as supporting layer, calcium alginate nanofibrous membrane as barrier layer and the dye adsorption and filtration performance for Brilliant blue were studied. The adsorption kinetics and adsorption isotherm model analysis were used to study the adsorption mechanism of the adsorbents for dye molecule. The second method:The adsorption separation properties of the composite membranes with different CMWCNT doping methods for dyes were studied, including the influence of dye solution concentration and adsorption time on the adsorption capacity. The results showed that the adsorption capacity of the etelectrostatic spraying CMWCNT-PHB nanofibers for Neutral red was reached up to 34.83 mg/g and the removal rate was 98%. The dyes adsorption was in accordance with the first order kinetic model and Freundlich isotherm adsorption model, which belongs to the physical surface adsorption. The flux and rejection rate of the composite membrane for dye Brilliant blue were 32.95 L/m2h and 98.20% respectively, indicating the composite nanofibrous membranes for dyes possess higher adsorption separation and filtration properties.