Fabrication And Properties Of Thermoplastic Polyurethane Micro/nano Fibrous Membrane With Different Topological Structures

The topological structure exists in any material and comes in a variety of forms,including roughness,geometry,pore structure and so on.For materials with a defined chemical composition,the topology determines the performance and the application field of the material.Therefore,it is of great significance to explore the relationship between topological structure and performance of materials for the development and optimization of product performance.In recent years,electrospun fibrous membranes have been widely used in various fields due to their unique properties,which are closely related to the topological structure of electrospun fibrous membranes.The topological structure of electrospun fibrous membranes includes the groove structure of fiber surface,the distribution and arrangement of fibers,the roughness of fiber membrane surface,the distribution and structure of internal pores,and the macroscopic geometry.These topological structures of electrospun fibrous membranes are usually irregular.For the irregular structure,the conventional Euclidean geometry theory cannot be used,so fractal theory needs to be cited.Therefore,this paper used the template method to prepare fibrous membranes with different topological structures on the surface,and the effects of the fibrous arrangement,pore structure,and surface roughness of the fibrous membrane on the wettability,wicking,air permeability and moisture permeability of the fibrous membrane were investigated.The surface structure of the fibrous membrane was characterized by the fractal dimension.These works aim to provide reference for structure characterization,product design and performance optimization of electrospun fibrous membranes.The specific works included in this paper are as follows:First,micro/nanofibers were prepared by electrospinning using thermoplastic polyurethane(TPU)as raw material and a mixed solvent of N,N-dimethylformamide(DMF)and tetrahydrofuran(THF)as solvent system,respectively.The effects of different concentration,solvent ratio and spinning parameters on the fiber morphology were investigated.The spinning solution system with concentration of 18%,DMF/THF volume ratio of 1:4 and the spinning parameters with voltage of 16 k V,receiving distance of 18 cm and extrusion rate of 0.5 m L/h were selected as the subsequent experimental parameters.The influence of the surface structure and size of the receiving template on the structure of the fibrous membrane were studied.The SEM observation of the prepared fibrous membranes revealed that the electrospun fibrous membrane could successfully "replicate" the structure of the receiving template,and the spinning time and the size of the template would affect the "replication" effect of the surface structure of the fibrous membrane.From this,the appropriate size of the fiber template and the receiving time range were determined.Secondly,considering that the different topological structure and the size of the material would have an impact on the performance of the material,six kinds of interwoven structures and three kinds of groove structure TPU micro/nano fibrous membranes were designed by the template method.Moreover,the surface morphology,pore structure and pore diameter were analyzed.The results showed that the interwoven fibrous membranes exhibited obvious orientation characteristics at the ridge and pit,and the fibers of the groove structure fibrous membrane at the ridge and the groove were oriented in two directions,being perpendicular to each other.The fiber orientation degree of the two structure fibrous membranes would decrease with the decrease of the structure size.The surface roughness of the common structure fibrous membrane,interweaved structure and groove structure fibrous membrane with similar pit size and groove spacing were compared.It was found that the surface roughness of the interwoven fibrous membranes and the groove fibrous membranes were greater than that of the common structure fibrous membranes.In addition,the roughness decreased with the decreased of the structure size and finally closed to the roughness of the common structure fibrous membrane.The surface topography prepared by the template method would affect the pore structure and pore size distribution of the fibrous membranes.The pore size of the interwoven fibrous membranes and the groove fibrous membranes were significantly larger than that of the common structure fibrous membrane,and the pore size of the interwoven fibrous membranes decreased with size,while the pore size of the groove fibrous membranes decreased with the increase of groove spacing size.The fractal dimension of TPU fibrous membrane with different topological structures were calculated,and it was found that the TPU electrospinning micro/nanofiber membrane had fractal characteristics.Comparing the fractal dimension of different structural fibrous membranes,the result showed that the fractal dimension was related to the disorder and complexity of the fiber,and the fiber orientation arrangement would reduce the fractal dimension.Thirdly,the wettability,wicking,air permeability and moisture permeability of the TPU fibrous membranes with different structures and size were investigated.There were significant differences in wicking of fibrous membranes with different structures.The results of wicking experiments suggested that there was no wicking of the common structure TPU fibrous membranes,while wicking of fibrous membranes with topological structure.For the interwoven fibrous membranes with the decrease of the pit size,the wicking height increased at first and then decreases.For the groove fibrous membranes,the wicking was anisotropic.The wicking height in the parallel direction of the groove was larger than the vertical direction of the groove.Additionally,as the groove spacing of the groove increased,the wicking height in the parallel direction increased,while the wicking height in the vertical direction of the groove decreased.In terms of wettability,the contact angle results showed that the contact angle of the interwoven fibrous membranes increased with the decrease of the structure size,and the larger the structure size,the faster the water droplet infiltration.For the groove fibrous membranes,the wettability was anisotropic.The contact angle of fiber membrane with different groove spacing showed the relationship of CA?<CA?.The air permeability and moisture permeability of the fiber membrane with interwoven structure were larger than that of the ordinary TPU fibrous membrane.The air permeability and moisture permeability of the ordinary fiber membrane were 51.122 mm/s and 3562.066 g/m2×d,respectively.The air permeability and moisture permeability of the interwove fibrous membrane with a pit diameter of 580 ?m could reach to 175.568 mm/s and 4978.092 g/m2×d.With the decrease of the pit size,the air permeability and moisture permeability were decreasing.The above results showed that the fiber membranes with different topologies prepared by the template method could regulate the surface wettability,wicking,air permeability and moisture permeability.