Preparation And Performance Study Of Bacterial Cellulose Nanomembranes/Fibers Based On Mechanophysical Method

Bacterial cellulose(BC)has the advantages of excellent ultrafine threedimensional mesh structure,high water retention,high permeability,biocompatibility,and mechanical strength.Nowadays,BC membrane and fiber materials are mainly made by mechanical crushing or self-assembly,but these practices inevitably destroy the excellent properties of BC.At present,there are relatively few studies on the direct preparation of BC membrane and fiber materials using mechanical-physical methods.In the first part of the thesis,by referring to the process of mechanical stripping to prepare single layer graphene,the original BC dry membranes were firstly produced by solvent replacement and hot-pressing process based on BC hydrogel films.The nanofiber membranes(NFMs)were further prepared by top-down mechanical layered peeling method.The structure,morphology and physical and chemical properties of NFMs obtained after mechanical layer-by-layer peeling were systematically investigated.Further,the BC twisted fibers were prepared by twisting method and the strain sensing fibers were obtained by laminating multi-walled carbon nanotubes(MWCNT).The results were as follows:1)The thickness of NFMs obtained by primary(1st),secondary(2nd)and tertiary(3rd)peeling gradually decreased to 8.0 μm,6.5 μm and 5.0 μm,respectively,which was significantly lower compared with the thickness of original BC dry membrane(41.0 μm).2)The water absorption of all three NFMs increased significantly compared with the original BC dry membrane.The water absorption of 3rd-NFM was the highest,up to 2284%,which was 2.4 times higher than that of original BC dry membrane.The tensile strength of 3rd-NFM was the highest,338.0 MPa,which is 11.7 times higher than that of original BC dry membrane;3rd-NFM twisted fiber had a tensile strength of 401.2 MPa.3)The monitoring of small changes in human movement showed that BC/CNT fiber had good strain sensing performance,which broadens the development prospects of the fiber in the field of wearable sensors.In the second part of the thesis,four different types of BC twisted fibers with diameters of 0.35-0.53 mm were prepared based on BC hydrogel films by borrowing the process of yarn preparation by twisting method.The effects of drying methods(oven-drying and freeze-drying)and twisting sequence on the morphology,structure and physicochemical properties of the fibers were investigated in detail.The results were as follows: 1)Only the wet twisting method could obtain compact and uniformly structured continuous fibers,and the tensile strength and elongation at break of the resulting fibers were up to 199.0 MPa and 24%,respectively.2)The surface of the fibers twisted first was smoother,and the crystallinity was slightly reduced but the crystalline shape did not change compared with the fibers dried first,and the thermal stability did not change significantly.3)Compared with the fibers twisted first,the fibers that underwent the drying process first had greater water absorption,both being as much as three times that of the former.4)Based on the moisture-sensitive mechanism,the twisted composite fibers made by the soaking method has the properties of reversible torsional motion through humidity change and near-infrared light irradiation.It could produce a twisting motion of 0.39 rpm and an untwisting motion of 0.6 rpm,indicating its potential application in the field of artificial muscle fibers.