Influence of organic Na+-MMT on the dielectric and energy storage properties of maleic anhydride-functionalized polypropylene nanocomposites

Polymer dielectrics with unique advantages of high electrical breakdown strength and high-power energy storage are very essential in the development of advanced thin-film capacitors. Herein, nanocomposite film capacitors with maleic anhydride functionalized polypropylene (PP-g-MAH) as matrix and organic Na+-MMT (org-MMT) as nano-modifier were prepared by simple melt blending and hot pressing method. The polarity of PP-g-MAH was beneficial to the uniform dispersion of org-MMT in the nanocomposites. The addition of org-MMT had no influence on the crystal form of PP-g-MAH but decreased its spherulite size because of the heterogeneous nucleation of org-MMT. Compared with the normal PP, the polar PP-g-MAH behaved a much higher dielectric constant and had a similar dielectric loss. The introduction of org-MMT slightly reduced the dielectric constant of the nanocomposites due to the interfacial chain movement limitation of PP-g-MAH. On the other hand, org-MMT improved the breakdown strength of the nanocomposites due to the inhibited electrical tree development. The PP-g-MAH nanocomposite film with an optimized org-MMT content of 0.4wt% possessed a strong breakdown strength of 530 MV/m, an excellent discharged energy density of 5.21 J/cm3, and high efficiency of 94.9%. This research provides a new direction for the development of PP based thin film capacitor towards energy storage application.