Preparation And Electromagnetic Shielding Properties Of Composites Containing Hierarchically Porous Carbon Derived From Loofah

With the advancement of electrical and electronic devices,the requirement of highly efficient electromagnetic shielding materials has become increasingly urgent.Usually,multi-functional carbonaceous materials are ideal candidates as the shielding materials due to their light weight,high strength,good conductivity and strong corrosion resistance.However,the rapid development of industrialization has caused an adverse impact on the ecological environment.Therefore,renewable,environmentally friendly,and inexpensive biomaterials replacing or partially replacing fossil resources and chemical materials are gaining more and more popularity.This dissertation is mainly focused on using the three-dimensional porous natural loofah as an effective carbon resource to manufacture electromagnetic shielding composites,with improved comprehensive performances(compressive resistance,temperature resistance and thermal insulation,etc.)of the composites by hybridizing with other nanoparticles.It is intended to provide a fundamental analysis for its application in the practical environment.In the first part,a combination of carbonized loofah fiber(CLF),graphene nanosheets(GNP)is blended with poly(ether-ether-ketone)(PEEK)matrix to prepare highly efficient electromagnetic shielding composites.A three-dimensional multi-interface conductive network is constructed by the CLF and GNP.The composite exhibits good electromagnetic shielding performance in the X-band region.When adding 9 wt%CLF and 2.5 wt%GNP,the average total shielding effectiveness of the composite reaches 27.1dB.In addition,the obtained composites also have excellent mechanical properties and thermal stability.When the content of CLF is 3 wt%,the compressive strength of the GNP/CLF3/PEEK composite reaches 114.6 MPa.And the 10%mass loss temperature of the obtained composites has reached 550?,showing strong temperature resistance.In the second part,the surface of the CLF is successfully coated with a layer of nickel(Ni@CLF)by electroless plating to improve the conductivity of bio-carbon.And the multi-walled carbon nanotube(MWCNT)is evenly dispersed in the PEEK matrix by an ultrasonic cell disruptor.The three-dimensional conductive network constructed by Ni@CLF and MWCNT is more beneficial for composites to attenuate incident electromagnetic waves.The results show that the conductivity and maximum shielding effectiveness of MWCNT/Ni@CLF/PEEK composite containing 18 wt%Ni@CLF reaches 2.101 S/m and 48.1 dB,respectively.In particular,the composite also exhibits superior compressive properties,and the compressive strength and modulus of the composite reach 145.6 MPa and 2.54 GPa.The comprehensive performance of composites has been effectively improved.In the third part,the free-standing application of the overall carbonized loofah is achieved,and silicon carbide whiskers-coated carbonized loofah sponge(SCLS)electromagnetic shielding composite with high bending strength and good thermal insulation is successfully prepared.A 2.5 mm thick SCLS achieves electrical conductivity of 22.3 S/m and electromagnetic shielding effectiveness of 68.4 dB,which is extremely competitive among those reported porous shielding materials at the same thickness.This outstanding property originates from the formation of a continuous three-dimensional conductive network constructed by the three-dimensional porous structure carbonized loofah sponge and silicon carbide whiskers.More importantly,the flexural strength of 8.4 MPa offered by the SCLSs makes them promising for direct application in the practical environment.Moreover,the carbonized loofah sponge exhibits a polymer-like thermal insulation behavior,achieving a thermal conductivity of only 0.226 W/(m·K)at 300?.In order to further increase the mechanical strength and electrical conductivity of the carbonized loofah sponge(CLS),CVD technology is explored to deposit carbon layers with different thickness on the CLS in the last part.And it combines with the oriented MXene aerogel to prepare high-performance electromagnetic shielding composites.The maximum compressive strength and modulus of CVD carbon-coated CLS skeleton reach 0.939 MPa and 10.881 MPa,and its electrical conductivity reaches 28.34 S/m.The maximum conductivity and average total electromagnetic shielding effectiveness of the prepared composites achieve 43.93 S/m and 70.0 dB,respectively.In summary,natural loofah is an excellent bio-carbon material.And the composites prepared in combination with other functional materials exhibit good electrical conductivity,electromagnetic shielding performance,mechanical properties and thermal stability.Therefore,the porous carbonized loofah has great potential application value in the field of electromagnetic shielding.