Controlling distribution of multi-walled carbon nanotube on surface area of Poly(ε-caprolactone) to form sandwiched structure for high-efficiency electromagnetic interference shielding

Electromagnetic interference (EMI) shielding composites with high efficiency, low conductive fillers and easy available have been attracted the wide attention. Herein, the multi-walled carbon nanotubes (MWCNT) were confined distribution in the surface area of poly (epsilon-caprolactone) (PCL) to achieve the sandwiched composites by a two-step melt compression. First, thin PCL/MWCNT (PCLNT) conductive layers and pure PCL layers with different thickness were melt-compressed, respectively. Second, two PCLNT layers at two sides and one PCL layer in the middle were melt-compressed again to form the composites with MWCNTs distribution in the surface area. The sandwiched composites exhibited higher EMI shielding effectiveness (SE) than the conventional PCLNT composites with random distribution of MWCNTs. For example, the EMI SET of the C(15/0/15)-T(0.1/1.0/0.1) composites with 3.5 wt% MWCNTs in the whole composites was 67% and 9% higher than that of the conventional composites with 3.5 wt% and 15 wt% MWCNTs, respectively. Furthermore, the EMI shielding performance of the sandwiched composites depended on the thickness of the conductive surface area and the concentration of MWCNTs. The excellent EMI shielding was found in the composites with thick surface area and high MWCNT loadings on a whole. In addition, the asymmetrically sandwiched composites which the surface area in two sides had the different concentration of MWCNTs were fabricated to investigate the effect of the conductivity in front layers on EMI shielding. The higher reflection loss happened in the composites with the higher conductivity in front layer, which resulted in the higher EMI shielding performance.