Research On The Structure-activity Properties Of Three-dimensional Graphene/polyurethane Composites

Flexible force sensor has been widely used in aerospace,industrial production,marine exploration,bioengineering,medical health and other fields due to its good ductility,flexibility,portability and ability to cope with various measurement environments.Traditional flexible force sensors generally have many problems such as low sensitivity,poor resolution,weak stability,and poor controllability of force sensitive materials.Therefore,the development of force-sensitive composite materials with good physical properties and piezoresistive response behavior has certain scientific value.In this paper,graphene oxide(GO)is used as the three-dimensional conductive network skeleton precursor,thermoplastic polyurethane(TPU)is used as the filling material,and the mutual bite type three-dimensional graphene/polyurethane composite material(GA/TPU)is prepared by vacuum impregnation method.The characterization of the microstructure and physical properties of three-dimensional graphene aerogel(GA)and GA/TPU composites reveals the synergy between GA and TPU.The multi-walled carbon nanotubes(MWCNT_S)were introduced by self-assembly method to form the modification of GA structure.The effects of MWCNT_S on GA pore size and polyurethane composite molding were studied.Finally,the piezoresistive respon se and stability performance of polyurethane composites were tested by self-made piezoresistive test platform.The change mechanism of three-dimensional continuous conductive network structure in polyurethane composites under external load was analyzed.Experimental results show:(1)The GA formed by the precursor of 12 mg/mL GO exhibited the best conductivity,and the volume resistivity was as low as 7.25×10~3?·cm.The three-dimensional network skeleton of GA in the GA/TPU composite was current-carrying.Sub-migration provides multiple paths,increasing TPU conductivity by approximately eight orders of magnitude.At the same time,the three-dimensional network skeleton of GA is also a good channel for the phonon of the heat transport medium.Therefore,the introduction of GA improves the thermal stability of the polyurethane material,and the highest purity of the polyurethane material is 52°C.Appropriate amount of GA has a mechanical strengthening effect on TPU materials,and it is the best at 8 mg/mL GO content.(2)Comparison of drying experiments showed that the volume shrinkage rate at atmospheric pressure was as high as 95%,and the freeze-drying could maintain the original shape well,and the volume shrinkage rate was as low as 5%.High-temperature heat treatment significantly improves the three-dimensional network conductivity of graphene,and can eliminate a small amount of oxygen-containing functional groups in GA.Comparing the composite materials prepared by the blending method and the vacuum impregnation method,it was found that the vacuum-impregnated composite material has better conductivity and thermal conductivity than the blended composite material which accounts for the proportion of the same graphene sheet filler.(3)MWCNTS acts as a sheet support in GA,and the pore size increases to 1.2mm.Compared with TPU,the electrical,thermal and mechanical properties of GA-CNT_S/TPU have been improved.The thermoplastic polyurethane composited with GA-CNT_S has an electrical conductivity increase of 9 orders of magnitude and a minimum volume resistivity of 7.31×10~3?·cm.In the range of 0-10%by weight,with the increase of the proportion of hydroxylated multi-walled carbon nanotubes(MWCNT_S-COOH),the thermal decomposition temperature of GA-CNT_S/TPU gradually increased,and the highest value reached 347°C.When 10wt%of MWCNT_S-COOH was added,GA-CNT_S increased by 15.7%compared with GA stress at 30%strain,and GA-CNT_S/TPU increased by 56.4%compared with TPU at 30%strain.(4)The percolation thresholds of GA/TPU and GA-CNT_S/TPU were 0.06 wt%and 0.048 wt%,respectively.In the piezoresistive response,hysteresis and stability tests,GA/TPU and GA-CNT_S/TPU were found to exhibit two piezoresistive responses in the 50%strain range.In the stability test,the hysteresis value of the GA-CNT_S/TPU composite increased by 0.2%after 80 cycles of testing,indicating that the GA-CNT_S/TPU composite has the advantage of being a flexible force sensitive substrate.