Preparation And Electromagnetic Shielding Performance Of Carbon Nanotubes/polyaniline/waterborne Polyurethane Composite Conductive Coating

With the rapid development and wide application of 5G,AI,IOT and big data,more and more new electronic devices have entered into people’s work and life.However,while electronic devices make life easier and better,they also induce Electromagnetic Interference(EMI)into surrounding environment.EMI not only affects the normal operation of nearby electronic equipment,but also affects the physical and mental health of people.In this context,EMI shielding materials have emerged.Design and develop of low cost and high performance EMI shielding materials has become one of the research hotspots.There are various ways to achieve electromagnetic shielding.Electromagnetic shielding coatings can be applied on the surface of materials which has different shapes and substrate by spraying and brushing to form a conductive solidified film.Electromagnetic shielding coatings not only have good shielding effects,but also have the advantage of relatively low cost,flexible and convenient construction,good applicability and so on.For the preparation of electromagnetic shielding coatings,conductive carbon nanotubes and polyaniline are selected as conductive fillers,and environment-friendly waterborne polyurethane is used as coating matrix resin.One the one hand,the electrically conductive carbon nanotubes and polyaniline endow the coating with high electrical conductivity and electromagnetic shielding performance.On the other hand,in order to eliminate the adverse impact on the flexibility and mechanical properties of the coating by introducing the conductive fillers,waterborne polyurethane with good compatibility and excellent mechanical properties is applied as matrix resin.Firstly,MWCNT/WPU(UC series)and PANI/WPU(UP series)waterborne coatings were prepared by mechanical blending and ultrasonic dispersion which contained industrial multi-walled carbon nanotubes(MWCNT)and conductive polyaniline(PANI)as conductive fillers and waterborne polyurethane as film forming material.Then the corresponding composite coatings were prepared by spraying and curing process.The basic properties,electrical conductivity and electromagnetic shielding properties of the two series coatings were characterized.The effect of MWCNT and PANI as conductive fillers and different filler ratios on the coating properties were investigated.Based on the results,with the incensement of the content of conductive fillers,UC and UP series coatings show better conductivity and electromagnetic shielding effect.With more fillers ratio,the flexibility of the coating decreased significantly.In order to ensure the quality and basic properties of the coating,the appropriate filler ratio need to control within 20 wt%.Compared to UP series coatings,UP series exhibit higher conductivity and electromagnetic shielding effect within the same ratio of conductive filler.The result show that as single filler,MWCNT has better electromagnetic shielding effect than PANI.For UP series,the conductivity and specific electromagnetic shielding efficiency of UP-20 are 9.93×10-4 S m-1and225.28 d B cm2 g-1 respectively.The UC series coatings show best conductivity and specific electromagnetic shielding efficiency at UC-20,the corresponding values are97.79 S m-1 and 983.67 d B cm2 g-1.Compared with PANI,MWCNT can significantly improve the electrical conductivity and electromagnetic shielding effect of coatings.But,based on single filler,the improvement is still relatively limited.Taking MWCNT and PANI as composite fillers into coatings,which is helpful for the formation of a better connected conductive network inside the coating.So,in this chapter,by tuning the ratio of MWCNT and PANI in composite filler,the conductive network could be further improved and achieve better electromagnetic shielding effect.The total filler content is fixed at 20 wt%.MWCNT/PANI/WPU(UCP series)composite coatings with different ratio of MWCNT and PANI were prepared.The basic properties,electrical conductivity and electromagnetic shielding performance were investigated.The coatings have good basic properties after adding composite conductive fillers.The conductivity tends to increase when composite fillers MWCNT and PANI ratio increase from 1: 4 to 4: 1.When the ratio of MWCNT and PANI in composite filler is 4: 1,UCP-41 shows highest conductivity of 101.27 S m-1,which is higher than UC-20.At 8.2 GHz,the specific shielding efficiency of UCP-41 reaches to 1199.99 d B cm2 g-1,which is 20% higher than that of UC-20.PANI has a unique doping mechanism.Secondary doping with macromolecular organic acid camphor sulfonic acid(CSA)can improve the conductivity of PANI.Based on previous chapter,PANI was treated by the method of dedoping-redoping(secondary doping)to obtain CSA doped PANI(A-PANI).Taking MWCNT and A-PANI as composite fillers to prepare MWCNT/A-PANI/WPU(UCAP)series coatings,which total filler content is 20 wt%.Then the impact of different MWCNT and A-PANI ratio on the basic performance,conductivity and electromagnetic shielding efficiency were investigated.Compared to UCP series coatings,UCAP series coatings show higher conductivity at same filler ratio.When the ratio of MWCNT and A-PANI is 4: 1,UCAP-41 show highest conductivity of 151.03 S m-1,which is 50% higher than UCP-41.At8.2 GHz,the specific electromagnetic shielding efficiency of UCAP-41 is 1293.73 d B cm2 g-1,which is 7.8% higher than that of UCP-41.