Study On Electromechanical Sensing Characteristics Of Graphene/Multi-Walled Carbon Nanotube Compounded Modified Natural Rubber Composites

Carbon nanomaterials such as graphene(GE)and multi-walled carbon nanotubes(MWCNTs)are often used to prepare conductive composites due to their excellent electrical conductivity.Carbon nanomaterials can form conductive networks at low doping levels,resulting in composites with low permeation thresholds and excellent performance in strain sensing.However,the performance enhancement of composites modified by a single carbon nanofiller is very limited,and the permeation threshold is high in some matrices,which makes the filler difficult to disperse in the polymer matrix,thus making the composite more difficult to process and seriously affecting the mechanical properties of the material.It is shown that two or more carbon nanofillers can form a stable conductive network with synergistic effects in the polymer matrix to obtain better strain sensing properties and better mechanical properties.In this paper,MWCNTs/NR,GE/NR and GE/MWCNTs/NR composites with resistance/strain response properties were prepared by adding MWCNTs or GE to natural rubber(NR)in different ratios by solution blending method.The dispersion of different carbon nanofillers in the NR matrix was characterized by field emission scanning electron microscopy(FE-SEM)and X-ray diffractometer(XRD),and the influence law of single and compound fillers on the force-electrical properties of the composites was analyzed.The strain sensitivity of different composites under static loading effect,as well as the cyclic rate and strain amplitude under dynamic loading effect on the strain sensing behavior of the materials were investigated.The effects of the cyclic rate and strain amplitude on the strain sensing behavior of the material under dynamic loading were investigated.Finally,the interfacial interactions between the GE/MWCNTs composite fillers and the NR matrix were investigated by Fourier infrared spectroscopy(FTIR)and Raman spectroscopy(Raman).The experimental results show that there is a synergistic effect between GE and MWCNTs,and the conductive network composed of the two significantly reduces the conductive permeation threshold of the composites,and the composites have the best conductivity when the ratio of the two is 1:1,and the permeation threshold is only 2.23 wt%,which is 36.3%and 10.8%lower compared to MWCNTs/NR and GE/NR composites,respectively.In addition,the GE/MWCNTs/NR composites exhibited better mechanical properties than MWCNTs/NR and GE/NR composites,and the tensile strength of 1GE/1MWCNTs/NR composites was 304.57%and 223.23%higher than that of MWCNTs/NR and GE/NR composites,respectively,at 5 wt%filler content;all composites The elongation at break of all composites decreased with the increase of filler content and the 100%strain modulus increased with the increase of filler content,which proved that the carbon nanofillers contributed to the stiffness improvement of the composites and the GE/MWCNTs/NR composites had greater stiffness than the two composites.In addition,the resistance/strain sensitivity of GE/MWCNT/NR composites was better than that of MWCNT/NR composites,with the highest sensitivity at GE/MWCNT=1/1,and showed a large strain response range;during dynamic cyclic loading,GE/MWCNTs/NR composites had good resistance response for large deformation(>100%).In the dynamic cyclic loading process,the GE/MWCNTs/NR composite has good stability,repeatability and monotonicity for large deformation(>100%),and the sensitivity of resistance/strain response increases simultaneously with the increase of loading rate.According to the microscopic morphology analysis,the synergistic binding force between GE,MWCNT and rubber molecular chains promoted the dispersion of the filler in the matrix,resulting in a more favorable interfacial interaction between the filler-matrix,which was conducive to the structural stability of the conductive network and lowered the permeation threshold of the composites,resulting in significantly better resistance/strain response stability,sensitivity and monotonicity of the composites than that of the single nano-carbon modified composites.Combining all the data,it was determined that the material properties are optimal for the GE and MWCNT compound ratio of 1:1,which is a guideline for the development of structural health monitoring sensors for large deformations.