Preparation And Stress Response Of Selective Laser Sintering Polyurethane Conductive Composites

In recent years,selective laser sintering technology(SLS)has become a research hotspot of additive manufacturing processing technology.It has been widely used in aerospace,automobile manufacturing,biology,medical and other application fields.As one of the important 3D printing technologies,SLS has the advantages of high forming speed,high precision,wide material adaptability,and can process complex structural parts.Compared with traditional processing methods,SLS processing products have almost the same performance,and SLS can achieve customized and complex structure processing.Polymer materials that can be processed by SLS include polystyrene(PS),thermoplastic polyurethane elastomer(TPU),polypropylene(PP),polycarbonate(PC),and polyetheretherketone(PEEK),etc.TPU is the only thermoplastic elastomer among them.Recently,conductive polymer composites(CPCs)have become the focus of research on functionalization of polymer materials due to their wide application in sensors.The conductivity of CPCs comes from adding nano-conducting fillers to the polymer materials to form a continuous conductive network in the matrix resin.Under external(stress,temperature,gas,etc.)stimulation,the internal conductive network of CPCs will be reconstructed to present a certain pattern of electrical signals,which is the stimulus response behavior of CPCs.Therefore,CPCs has broad application potential in strain sensor,electromagnetic shielding,temperature sensor and volatile organic gas detection.The resolution and sensitivity of CPCs sensor can be improved by adjusting the CPCs microstructure and conductive network to reduce the conductive percolation threshold.In this thesis,using Graphene(G)and carbon nanotubes(CNTs)as nano-conducting filler,and TPU powders as polymer matrix materials,TPU CPCs used for SLS molding were prepared by ultrasonic dispersion-liquid precipitation method.Then the TPU/G and TPU/G/CNTs CPCs were prepared by SLS.The electrical properties,mechanical properties and stress response behavior of obtained CPCs were studied.The main conclusions of this thesis are as follows:1.TPU/G CPCs powders were prepared by ultrasonic dispersion-liquid phase precipitation method,and TPU/G CPCs were prepared by SLS.The results of SEM show that graphene can be uniformly coated on the surface of TPU particles and with little influence on the particle size.The TPU/G CPCs prepared by SLS have excellent conductivity,and its conductive percolation threshold is 0.2wt%.The excellent flexibility of TPU and the low percolation threshold give the TPU/G CPCs excellent tensile strain response performance.The investigation of graphene,strain rate and strain amplitude showed that the TPU/G CPCs had the wide strain response(GF=75.2?668.3),good deformation recovery and response repeatability.2.The powders of TPU/G/CNTs were prepared by adding mixed conductive fillers,and the TPU/G/CNTs CPCs were prepared by SLS.The conductive percolation thresholds of TPU/G/CNTs composites were 0.1wt% of carbon nanotubes and 0.15wt%of graphene.The method of mixing conductive filler can effectively regulate the conductive network inside the composites and reduce the conductive percolation threshold of the composites.