Bioinspired Adhesion Promoters for the Metalization of Polyethylene: A Comparison between Polydopamine and Tannic Acid

Recently, polydopamine (PDA) was introduced as a bioinspired adhesion promoter for the metalization of plastics to substitute for the environmentally critical chromic acid etching. A more economical and environmentally friendly alternative to PDA with similar chemical functionalities is tannic acid (TA). The present study compares the efficiency of PDA and TA as adhesion promoters for the electroless metalization of polyethylene with nickel. PDA and TA are applied under the same conditions; the effects of pretreating the substrate with oxygen plasma, PDA/TA deposition time, and thermal post-treatment on the film formation are investigated, as well as the influence of accelerating the deposition by addition of metal ions or UV radiation. The chemistry of the film formation is analyzed by surface-sensitive spectroscopic methods, X-ray photoelectron spectroscopy (XPS), a newly developed surface-sensitive combination of multiple reflection attenuated total reflection (MATR) with nonlinear surface-enhanced infrared absorption (SEIRA), and contact angle measurements. The PDA- and TA-coated substrates are metalized; the quality and adhesion of the metal layer are evaluated. Under optimal conditions, both adhesion promoters ensure high metalization quality and a good metal–polymer adhesion strength of about 3.5–4 N/mm 2 but TA requires a more elaborate process, i.e., longer deposition times or deposition accelerated by metal ions and postannealing.