Fabrication And Electromagnetic Shielding Performance Of MWCNTs/Fe₃O₄/NR/NBR Composites

Electromagnetic pollution has a non-negligible impact on people's physical health and the normal operation of highly sensitive equipment.Metal shielding materials has been unable to meet the actual application needs due to high density,easy corrosion and difficult to process.The development of excellent flexible electromagnetic shielding materials has great significance.In this thesis,the natural rubber(NR)and nitrile rubber(NBR)was selected as matrix,MWCNTs and Fe₃O₄ nanoparticles were used as functional fillers.The NR/NBR(50/50)blends filed with MWCNTs was considered as the object and the effect of MWCNTs content on the mesoscopic morphology,conductivity,mechanical and electromagnetic shielding properties was investigated at first.Afterwards,the two kinds of Fe₃O₄nanoparticles with different sizes were prepared by solvothermal method.It was incorporated into rubber matrix filled with CNT.The morphology and content of Fe₃O₄ on the mechanical and electromagnetic shielding properties were compared with the Commercial grade Fe₃O₄.Finally,the Fe₃O₄@MWCNTs hybrid filler was prepared with the ratio of the relative quality 1:2.55by means of in-site synthesis method.This hybrid filler was incorporated into the NR/NBR(50/50)blends and made 6phr Fe₃O₄@15phr MWCNTs/NR/NBR(50/50)compound,and then the mesoscopic morphology and electromagnetic properties were studied.The main results were as follows:For the mesoscopic structure,there is segregation behavior for the MWCNTs in the NR/NBR(50/50)matrix,and the segregation state was influenced by multiple factors,such as thermodynamics,kinetic and MWCNTs content.The MWCNTs will be located at the interface of the two rubber phases from NR phase with increase of MWCNTs content.The mesoscopic structure affected the mechanical properties to some degree.When the MWCNTs content is not more than 9phr,the tensile strength of the system increased and the its elongation at break kept almost constantly with increase of MWCNTs content.When the content of MWCNTs is more than 9phr,the tensile strength of system almost kept constantly,but its elongation at break decreased obviously with increase of MWCNTs content.For the electromagnetic properties,both the conductivity and electromagnetic shielding property increased with increase of MWCNTs content.When the MWCNTs content was up to 15phr,the conductivity and the total electromagnetic shielding property are 1.4*10^-2 S cm^-1and 26 d B.The electromagnetic shielding mechanism was controlled by reflection.Meanwhile,the absorption loss was mainly from conductivity loss,when the MWCNTs content is not more than 9phr.However,both the conductivity loss and the polarization loss contributed to the absorption loss,when the MWCNTs content was more than 9 phr.The conductivity and electromagnetic shielding effectiveness of the compounds were improved by means of filling Fe₃O₄,compared with unfilled system.The electromagnetic shielding effectiveness of the S1-Fe₃O₄ filled system was the highest.The main shielding mechanism was the reflection loss and the main source of the absorption effectiveness was the dielectric loss for the three filled systems.The size of rubber phases decreased obviously in the F-Fe₃O₄ filled system,compared with that in the other two systems.The lowest tensile strength and elongation at break appeared in the F-Fe₃O₄ filled system.However,the stress at definite strain was the highest in this system.Meanwhile,the S1-Fe₃O₄filled system had the highest tensile strength and elongation at break.But the stress at definite strain was the lowest.The Payne effect of the high content S4-Fe₃O₄ filled system was higher than that of the low content S4-Fe₃O₄filled system.The conductivity almost were the same for the two systems,but the low content S4-Fe₃O₄ filled system had the higher electromagnetic shielding effectiveness.The Fe₃O₄@MWCNTs hybrid filler was prepared with relative quality 1:2.55between the ratio of Fe₃O₄and MWCNTs by means of in-situ synthetic method.In which,the Fe₃O₄ was attached to the surface of MWCNTs in the form of polycrystal microballoon,closely combined with the MWCNTs.However,the max of the total shielding effectiveness was only 7.17 d B for the 6phr Fe₃O₄@15phr MWCNTs/NR/NBR(50/50)compound filled with this kind of hybrid filler.It could not absorb the electromagnetic wave,which was arising from the incomplete conductivity network.Therefore,the mixing technology should be explored further.