New insight into the interaction between maleic anhydride grafted polypropylene and aluminum foil converted with trivalent chromate: An experimental and DFT study

Abstract

The good adhesion between layers of aluminum (Al)/polymer composite is necessary for the safety of lithium-ion batteries. The Al foil was converted with environmentally friendly trivalent chromate [Cr(III)] to enhance its adhesive strength with the inner adhesive layer. The morphology, composition and adhesive strength with maleic anhydride grafted polypropylene (mPP) of different Cr-converted Al foils were studied. The Cr conversion coating mainly consists of metal oxides and hydroxides and the interfacial adhesion strength is enhanced by 93 % through Cr(III) conversion treatment. The effect of Cr conversion on the acid-base characteristics on the Al was determined through contact angle measurement. The results reveal that Cr conversion increases the acidity of the Al surface. The bonding mechanism at the interface was further studied fundamentally. To study the reaction at the interface mPP/Al foils, a coating-evaporation technique was utilized to fabricate a nano-thick mPP layer on the Al foils. The morphology and thickness of the mPP coating on the substrate were analyzed using atomic force microscopy and the interfacial reaction was characterized through attenuated total reflection-Fourier Transform Infrared Spectroscopy. The bonding mechanism at the molecular level was further investigated by quantum chemical calculations based on density function theory. The results of theoretical calculations further indicate that the strength of the interfacial interaction between mPP and Cr oxides and hydroxides is stronger than that between mPP and Al oxides and hydroxides.