Preparation And Properties Of Polyurethane Flexible Conductive Composites Based On Direct Writing 3D Printing

3D printing technology has the advantages of high manufacturing efficiency,strong scalability and low cost,and has great flexibility in configuring various printing inks,and will not be constrained by factors such as the type of printing materials.Waterborne polyurethane(WPU),as an environmentally friendly polymer resin,has good compatibility with many fillers,is easy to modify,and can be combined with suitable conductive fillers to give it conductive ability.WPU-based flexible conductive composites are applied to the field of direct-writing 3D printing,the performance of 3D printing flexible conductive composites is studied,and the 3D printing process is explored,which can solve the problem of limited flexibility of printing materials and broaden their application in the field of flexible electronics.In this paper,WPU was used as the matrix,and the conductive fillers graphene(GR)and carbon black(CB)were modified by surface modification and dispersion technology to prepare WPU flexible conductive composites for direct 3D printing.The effects of different contents of GR and CB on the mechanical properties and electrical conductivity of the composites were studied.The effects of 3D printing process parameters on the mechanical properties and electrical conductivity of WPU composites were investigated by single factor and orthogonal experiments.(1)The non-covalent functional modification of GR was carried out by selecting different dispersants to determine the best dispersant to prepare stable GR dispersion.The results showed that the dispersion ability of polyvinyl alcohol(PVA)aqueous solution to GR was strong,which significantly improved the compatibility of GR and WPU.CB was covalently modified by silane coupling agent(KH550).The CB before and after modification was characterized by infrared spectroscopy(FTIR),particle size test(DLS)and scanning electron microscopy(SEM).The results of DLS showed that the average particle size of CB particles modified by KH550 was about 620 nm,and the particle size distribution was between 400-900 nm,which was narrower than that of unmodified CB,and the dispersion was improved.The comparative analysis of the FTIR diagram of CB before and after modification proves that CB modification is successful The results of SEM showed that most of the CB modified by KH550 were uniformly dispersed single particles with regular arrangement,less agglomeration and better dispersion.(2)Waterborne polyurethane/graphene(WPU/GR)flexible conductive composites were prepared,and the effects of GR on the mechanical properties and electrical conductivity of the composites were studied.The performance test results showed that the conductivity of WPU/GR flexible conductive composites was 2.6 X 10-7 S/m when the dispersant was not added and the GR content was 2%.On this basis,it was found that when the mass ratio of WPU:PVA aqueous solution was 80:20,the conductivity of WPU/GR flexible conductive composites was 4.5 × 10-5 S/m,which was two orders of magnitude higher than that of the composites without dispersant.The tensile strength of composite materials increased by 116%compared with undispersed additives;The thermogravimetric test results show that the thermal stability of the composite is 54℃ higher than that of pure WPU,and the addition of GR can significantly improve the heat resistance of WPU.Waterborne polyurethane/carbon black(WPU/CB)flexible conductive composites were prepared.The effects of CB on the mechanical properties and electrical conductivity of the composites were studied,and the conductive mechanism of the composites was explored.When CB was unmodified and the content was 3%,the conductivity of WPU/CB flexible conductive composites was 1.16×10-4 S/m.The conductivity of WPU/CB flexible conductive composites modified by KH550 was 1.79×10-3 S/m,which was 10 times higher than that of unmodified composites.When the CB content is 2%,the tensile strength of the composite is increased by 175%compared with the unmodified composite.The thermogravimetric test results show that the thermal stability of the composite is 65.1℃ higher than that of pure WPU,and the addition of CB significantly improves the heat resistance of WPU.(3)The process parameters of direct 3D printing WPU-based flexible conductive composites were explored.The effects of different process parameters(wall thickness,closed surface thickness,filling rate,printing speed)on the electrical conductivity and mechanical properties of the samples were investigated by controlling a single variable.Taking the electrical conductivity and mechanical properties of the composite material as the inspection index,the optimal parameter level combination is determined by orthogonal experiment to optimize the performance of the parts.The comprehensive experiment shows that the WPU-based flexible conductive composites fabricated by direct writing 3D printing have good conductivity and mechanical properties under the conditions of edge width of 0.8 mm,closed surface thickness of 0.8 mm,filling rate of 80%and printing speed of 60 mm/s.On this basis,the conductive properties of WPU-based flexible conductive composites formed by traditional methods and 3D printing were compared.It is found that the conductivity of 3D printed WPU/GR and WPU/CB flexible conductive composites is better than that of composites prepared by traditional methods,and the conductivity of WPU/CB flexible conductive composites is increased by 1～2 orders of magnitude compared with traditional methods.