Preparation And EMI Shielding Performance Of Carbon Nanotubes-cellulose Composite Paper

The natural science has been developed fast with the third industrial revolution. The electron and electrical technology break through unceasingly. Varieties of electronic instruments and electrical appliances not only are commonly used in our daily life which is surely make our life and working environment more convenient, but also produce serious electromagnetic interference?EMI?. The electromagnetic energy can do inestimably harm to human body and the electronic instruments. So the protection of people and electronic instruments from harm and interference was widely emphasized.Carbon nanotubes?CNTs? have very good mechanics, electromagnetism and electricity characteristics. Carbon nanotubes have a large aspect ratio, light weight, good electrical conductivity, unique one-dimensional tube structure and big bandwidth for microwave-absorption, CNTs are considered as excellent candidate material for microwave-absorption and electromagnetic interference?EMI? shielding. Moreover, CNTs also are good additional material of composite materials with its special mechanics property.This study prepared a kind of whisker CNTs by CVD method. The CNTs were mixed with paper cellulose fibers to fabricate the composite paper by vacuum suction filtration method. The flexible CNTs-cellulose composite paper can perform good electrical conductivity. The size and conductivity of the CNT composite papers can be arbitrarily tailored. CNTs were absorbed on cellulose fibers and embedded in cellulose pulp to forming three-dimensional electrical conductive networks which made the composite papers to perform good EMI shielding effect?SE?. This study focus on the EMI shielding effect of the composite paper based on EMI shielding mechanism.The CNTs were characterized by scanning electron microscopy?SEM?, X-ray diffraction?XRD?, thermal gravimetric analysis?TGA? and Raman spectra. The result shows that the CNTs have a line structure and the diameter of all the CNTs is similar with each other. The purity and crystallinity of CNTs is highly improved after graphitization. The permittivity and permeability of CNTs were tested, the results show that the tangent loss factor of permittivity is high?0.28⁰.44rad?while permeability and tangent loss factor of permeability is low which means that the CNTs can produce excellent EMI shielding due to its electrical properties.The shielding mechanism of the CNTs-cellulose composite paper is mainly from reflection loss and absorption loss, both of them are positive correlate to conductivity of the composite paper. The results show that in range of 175MHz¹500MHz, the EMI SE of graphitized CNTs as conductive additive of composite paper is better than other additives, such as raw CNTs, carbon black, graphite and short carbon fiber.With the loading of CNTs increased from 20wt% to 71wt%,the volume resistivity of papers decreased from 5.41?·cm to 0.466?·cm and the electromagnetic interference shielding effectiveness?SE? of the composite paper increased from 17 d B to 44 d B. The EMI SE increased from 32 d B to 48 d B while the composite paper superimposed from one to four layers with 50wt% CNTs.In order to enhance the EMI SE of composite paper,the magnetic CeO₂ was doped into the composite paper. The conductivity of the composite paper decreased with a loading of CeO₂ from 0.1g to 0.5g. The EMI SE increased at first and then decreased. The EMI SE of the composite paper reached the peak value with a doping of CeO₂ of 0.2g. Carbonization can improve the conductivity of the papers. The EMI SE of the composite paper increased 4d B after carbonization.