Study Of Properties Of Cellulose Diacetate Spinning Dope And Filtration Properties Of Electrospun Composite Filter Materials

Cellulose diacetate as a cellulose derivatives is poisonless and tasteless, it can absorb toxic substances selectively, it has good properties of antibacterial and bacteriostasis, and it also posseses good biological compatibility and biodegradable properties, so cellulose diacetate is a kind of environmentally friendly materials. The main job of this project is studying the properties of cellulose diacetate spinning dope and the influences of spinning dope on the morphology of as-spun fibers, based on the results, the effects of fiber morphology on filtration properties of cellulose diacetate composite filtration materials are also been explored.Cellulose diacetate flake with different intrinsic viscosity were dissolved in acetone/DMAc which volμme ratio is 3:2, the influences of spinning dope temperature, intrinsic viscosity and mass fraction on the rheological properties of spinning dope were studied, the relationship between rheological properties and morphology of as-spun fibers were also explored. The result shows that as the intrinsic viscosity increases, viscosity of spinning dope increases, non-Newtonian index decreases, structural viscosity index increases, the diameter of as-spun fibers increases and the value of CV increases; as the increase of mass fraction, viscosity of spinning dope increases, the interaction between macromolecules increases, so it must influence the morphology of as-spun fibers.Cellulose diacetate flake(Iv=1.45 dL/g) were dissolved in acetone/DMAc mixed solvent system, the influences of saturated vapor pressure, conductivity, viscosity and surface tension on as-spun fibers were explored. The results show that non-Newtonian index is most close to 1 and structural viscosity index is smallest, when the volμme ratio is 3:2. When using the solvent system which volμme ratio is 3:2, the morphology of as-spun fibers is glossiest and the CV value is smallest. When the value of volμme ratio lower than 3:2, the jet evaporationspeed slows down as the decline of acetone content, even when using pure DMAc as solvent, the fiber collected will adhere; when the value of volμme ratio higher than 3:2, the jet evaporates faster and faster as the increase of acetone content, the diameter and CV value of fibers increase, even when using pure acetone as solvent, the jet will been forbidden.The cellulose diacetate nanofibers were composited with two layers of PET nonwoven substrate and the "sandwich" type nano composite filter materials were made. The influences of fiber morphology, spinning time, spinning voltage and air mass flow on the filtration properties of nano composite filtration materials were explored. The results show that when using uniform nanofiber membrane as filtering functional layer, the filter efficiency is hightest, but the filtration resistance is also higher; when using beaded nanofiber membrane as filtering functional layer, the filtration resistance is much smaller but the filter efficiency is also small. The filter efficiency increases significantly firstly and then slowly, while the filtration resistance increases slowly firstly and then significantly, as the increase of spinning time or voltage. Filtration efficiency increases slowly while filtration resistance increases significantly, as the increase of air mass flow.When using uniform and beaded nanofibers composite membranes as filtering functional layer the nanofiber composite filter material can meet requirement of sub HEPA provided by JB/T 10535-2006, by setting the spinning time as 60 min, spinning voltage as 22 kV and the ratio of nanofibers and bead-string nanofibers as 10:5(v/v).