Bioinspired Adhesion\nPromoters for the Metalization\nof Polyethylene: A Comparison between Polydopamine and Tannic Acid

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