Chemical Foaming of Carbon Fiber-Polylactic Acid (CF-PLA) Porous Structures and Their Feasibility as EMI Shields in the X-Band

The massive increase in telecommunications infrastructure and devices has recently exacerbated the necessity of developing advanced electromagnetic interference (EMI) shielding solutions. Porous structures based on conductive polymer composites (CPCs) are currently promoted as feasible options for this task. In this scenario, the chemical foaming process shows suitability for easily fabricating CPC foams with closed cells and variable porosity. Nonetheless, the process and the products have not yet been fully explored in the literature for EMI shielding purposes. Hence, this work proposes the fabrication of foams made of polylactic acid with 10wf% carbon fiber (CF-PLA) via chemical foaming. After the process assessment, the morphological and dielectric characterizations of the samples were discussed in the function of the process parameters. The results show that chemical blowing agent (CBA) weight fraction % and temperature were key in obtaining target structural and dielectric requirements enabling EMI shielding. Numerical analyses on CF-PLA foams, modeled according to morphological outcomes, were performed via the integral finite difference time domain (IFDTD) method. The obtained Scattering Parameters and shielding effectiveness (SE), between 0.5 and 12 GHz, highlighted that when foam relative density and air pore density are simultaneously high, the shielding is mainly accomplished through absorption (SE $_{\mathrm {A}} =20$ dB) while reflection is minimized (SE $_{\mathrm {R}} =2$ dB). Scattering Parameters and SE were also measured in the X-band showing good agreement with the numerical findings; indeed, CF-PLA foams with higher relative density and air cell density exhibited a reduction of SER (3dB) and a SEA with maxima up to 30dB.