Engineering of Adhesion at Metal-Poly(lactic acid) Interfaces by Poly(dopamine): The Effect of the Annealing Temperature

Control over adhesion at interfaces from strong bondingto releasebetween thermoplastic polymers (TPs) and metal oxides is highly significantfor polymer composites. In this work, we showcase a simple and inexpensivemethod to tune adhesion between a TP of growing interest, poly(lacticacid) (PLA), and two commercial metal alloys, based on titanium andstainless steel. This is realized by coating titanium and stainlesssteel wires with polydopamine (PDA), thermally treating them undervacuum at temperatures ranging from 25 to 250 & DEG;C, and then comoldingthem with PLA to form pullout specimens for adhesion tests. Pulloutresults indicate that PDA coatings treated at low temperatures upto a given threshold significantly improve adhesion between PLA andthe metals. Conversely, at higher PDA annealing temperatures beyondthe threshold, interfacial bonding gradually declines. The excellentcontrol over interfacial adhesion is attributed to the thermally inducedtransformation of PDA. In this work, we show using thermogravimetricanalysis, X-ray photoelectron spectroscopy, Fourier transform infrared,and C-13 solid-state NMR that the extent of the thermaltransformation is dependent on the annealing temperature. By selectingthe annealing temperature, we vary the concentration of primary amineand hydroxyl groups in PDA, which influences adhesion at the metal/PLAinterface. We believe that these findings contribute to optimizingand broadening the applications of PDA in composite materials.