Preparation process for directional nanocellulose-gelatin-barium ferrite aerogels and the effect of pore structure on electromagnetic signal attenuation

Abstract

Electromagnetic interference (EMI) is a type of pollution emitted from all electronic and electrical equipment. Consequently, electromagnetic pollution is widespread and continuously increasing with rapidly developing and increasing electronics. Therefore, the demand for effective shielding materials to protect the reliability of electronic devices is high. The shortcomings of metals as shielding materials have shifted the attention to composite materials with light weight, chemical stability, low cost, and sustainability. Lately, porous composites based on nanocellulose have been attracting significant attention. Cellulose is an abundant, renewable, biodegradable biopolymer and therefore a highly potential raw material for producing sustainable electronics.

The aim of this thesis was to investigate the preparation process and properties of nanocellulose fiber/gelatin/barium hexaferrite (CNF/G/BaFe) aerogel composites fabricated for EMI shielding. The work focused on creating different pore structures by freeze drying process and studying the effect of the achieved pore structures on the attenuation capability of the composite material. Additionally, the dispersion of BaFe into the aerogel matrix was explored utilizing sonication and milling treatments. Multiple characterization methods were utilized in this work. Electron microscopy was used to investigate the pore structure of the aerogels and the morphology of BaFe, XRD analysis was employed to expose BaFe composition after different treatments, and compressive strength tests were performed to evaluate the mechanical strength of the aerogel materials. Permittivity and permeability were measured with waveguide equipment and shielding efficiency (SE) was calculated based on the obtained data.

Dispersion of BaFe turned out to be difficult and none of the tested treatments provided the desired result. Sonication was stated to be the most suitable dispersion method since it did not inflict any undesirable side effects. Three different aerogel structures were successfully prepared utilizing different freezing temperatures and temperature gradients. The pore size was proven to be an important parameter influencing the attenuation capability of the composite materials. The anisotropic aerogels possessing small pores achieved higher shielding efficiencies compared to randomly structured aerogels with large pores. The concentration of BaFe also influenced the attenuation properties. Increasing BaFe concentration increased the shielding performance of the material. The pore structure was additionally demonstrated to affect the mechanical properties of the aerogels. Overall, the prepared aerogels were mechanically strong and elastic, but the unidirectional structure performed best.

The prepared CNF/G/BaFe aerogel composites achieved relatively low attenuation capabilities and cannot be used as shielding materials as is. However, this work paved the way for further development of sustainable electronics based on cellulose and barium ferrite. More research is needed to improve the BaFe distribution inside the aerogel structure and to increase the total shielding efficiency. Investigating suitable conducting components to pair with BaFe in EMI shielding composites is important for further studies.