Research On Performance And Preparation Of Wooden Integrate Absorbing And Reflection Mechanism Electromagnetic Shielding Materials

Wood,which is a natural polymer renewable materials.Through the electroless plating technology,metal coating was formed on the wood surface.This composite not only have good electrical conductivity and electromagnetic shielding performance,but also retain the excellent characteristics of wood.This technology can develop the application field for wood greatly.Nowadays,there still have some problems for electroless plating on wood,such as the kinds of plated metal are few,and the plated wood only reflect the low-frequency electromagnetic wave.In order to overcome those problems,novel wooden integrate absorbing and reflection mechanism electromagnetic shielding materials were developed.Firstly,the electroless plating copper technology was used to form a copper coating on the poplar veneer surface,and further adding nano Fe₃O₄ particles in the process of electroless copper plating to form composite coating.This composite coating can be regred as an electromagnetic wave reflection layer;secondly,the electroless plating NiFe alloy technology was used to form a NiFe alloy coating on the poplar veneer surface,and further using a plurality of electroless plating methods to prepare the electromagnetic wave absorbing layer;finally,those two lays have been prepared the integrate absorbing and reflection mechanism electromagnetic shielding materials.The conclusions were summarized as below:1.The optimum conditions of lectroless plating Cu are as follows:CuSO₄·5H₂O 80 g/L,C₄O₆H₄KNa 40 g/L.EDTA-2Na 20 g/L.HCHO 40 mL/L;pH=11.5;reaction temperature 60 ℃;Time 40 min.Firstly,the surface coating of plated veneer prepared under this conditions has good continuous conductivity,which is the ideal reflective shielding material,the electromagnetic shielding effect is up to 62 dB;secondly,the coating is crystalline structure,the surface resistivity exists apparent anisotropy,the lateral direction measurement was approximately twice than the measurement in the longitudinal direction;thirdly,the poplar veneer surface characteristics changed from hydrophilic to hydrophobic after copper plating.2.In order to further improve the electromagnetic shielding effectiveness of plated veneer,the nano-Fe₃O₄ particles are used to prepare composite plating veneer.The ultrasonic treatment is used to prevent the agglomeration of nano-Fe₃O₄ particles.The optimal ultrasonic treatment parameters are as follows:the concentration of iron oxide was 25 g/L,the ultrasonic time was 70 min,the ultrasonic power was 800 W,and the ultrasonic wave was optimized by the single factor analysis and the response surface method.Compared to ordinary plated veneer,the coating structure becomes smoother and denser,the grain size decreases,the compositive plated veneer has better continuous conductivity,electromagnetic shielding effect improved significantly.At the same time,the surface resistivity decreases and the anisotropy disappears,the saturation magnetization is 3.09 emu/g.3.The structure and performance of the coating are affected by the pH value of solution,and the concentration ratio of（NH₄）₂Fe（SO₄）₂ · 6H₂O and NiSO4 · 6H₂O.When the ratio of Fe:Ni is 5:1（（NH₄）₂Fe（SO₄）₂ · 6H₂O:NiSO4 · 6H₂O = 50:10 g/L）and pH=9.5,plated veneer has the ability to absorb electromagnetic waves,the bandwidth which reflection loss less than-5dB is 2 GHz,the bandwidth which reflection loss less than-10dB is 0.4 GHz,and the minimum absorption reflection loss of the composite was-11.7 dB,it can be regard as an absorption shielding materials.At the same time,the metal deposition of the plated veneer is 38.8 g/m2,the maximum values of saturation magnetization and surface resistivity were 52.37 emu/g and 517 mΩ·cm,respectively,the coatings consisted solely of disciform metal particles.4.In order to broaden the absorption bandwidth and enhance the absorbing ability of plated veneer,the multiply electroless plating method is applied.The electroless plating solution used in the first two electroless plating processes as follows:NiSO4·6H₂O 10 g/L,（NH₄）₂Fe（SO₄）₂·6H₂O 50 g/L,NaH₂PO₂.H₂O 60 g/L,Na₃C₆H₅O7.2H₂O 30 g/L,CH₄N,S 0.5 g/L;the third plating solution is NiSO₄·6H₂O 30 g/L,（NH₄）₂Fe（SO₄）₂·612O 20 g/L,NaH₂P0₂·H₂O 60 g/L,Na₃C₆H₅O₇·2H₂O 30 g/L,CH₄N₂S 0.5 g/L.The bandwidth of plated veneer which reflection loss less than-5dB is 3.5 GHz,the bandwidth of plated veneer which reflection loss less than-lOdB is 1.6 GHz,and the minimum absorption reflection loss of the composite was-24.36 resistivity is 26.3 mΩ·cm,the saturation magnetization is 78.5 emu/g,the bonding strength of the coating is 3.6 MPa,the surface abrasion resistance weight loss is 0.295 g.5.The orthogonal experiment is used to optimize the preparation conditions of Integration reflection absorption plywood.The optimum conditions are as follows:the sizing capacity is 320 g/m2,the cold pressing time is 20 min,and the cold pressing pressure is 1.5 MPa.The flexural strength,flexural strength and elastic modulus of the plywood prepared under these conditions are 1.94,74.35,6912 MPa,respectively.In the 10 kHz to 1.5 GHz,the electromagnetic shielding effect of the integrated plywood exceeds 60 dB;the bandwidth which reflection loss less than-5dB is 6.05 GHz,the bandwidth which reflection loss less than-10dB is 2.01 GHz,and the minimum absorption reflection loss of the composite was-23.71 dB.