Adhesion Engineering in Polymer–Metal Comolded Joints with Biomimetic Polydopamine

Abstract

Joints that connect thermoplastic polymer matrices (TPMs) and metals, which are obtained by comolding, are of growing importance in numerous applications. The overall performance of these constructs is strongly impacted by the TPM–metal interfacial strength, which can be tuned by tailoring the surface chemistry of the metal prior to the comolding process. In the present work, a model TPM–metal system consisting of poly(methyl methacrylate) (PMMA) and titanium is used to prepare comolded joints. The interfacial adhesion is quantified by wire pullout experiments. Pullout tests prior to and following surface modification are performed and analyzed. Unmodified wires show poor interfacial strength, with a work of adhesion ( G a ) value of 3.8 J m –2 . To enhance interfacial adhesion, a biomimetic polydopamine (PDA) layer is first deposited on titanium followed by a second layer of a poly(methyl methacrylate- co -methacrylic acid) (P(MMA- co -MAA)) copolymer prior to comolding. During processing, the MAA moieties of the copolymer thermally react with PDA, forming amide bonds, while MMA promotes the formation of secondary bonds and molecular interdigitation with the PMMA matrix. Control testing reveals that neither PDA nor the copolymer provides a substantial increase in adhesion. However, when used in combination, a significant increase in adhesion is detected. This observation indicates a pronounced synergistic effect between the two layers that strengthens the PMMA-titanium bonding. Enhanced adhesion is optimized by tuning the MMA-to-MAA ratio of the copolymer, which shows a maximum at a 24% MAA content and a greatly increased G a value of 155 J m –2 ; this value corresponds to a 40-fold increase. Further growth in the G a values at higher MAA contents is hindered by the thermal cross-linking of MAA; MAA contents above 24% restrict the formation of secondary bonds and molecular interdigitation with the PMMA chains. Our results provide new design principles to produce thermoplastic–metal comolded joints with strong interfaces.

Dopamine-Supported Metallization of Polyolefins─A Contribution to Transfer to an Eco-friendly and Efficient Technological Process

“…Longer deposition yields more irregular layers. From the literature, it is known that on most substrates, longer deposition times lead to the deposition of thicker films with larger PDA globules. , Therefore, the changing morphology of the PDA layers in Figure is interpreted as the increasing amount of PDA deposited on the PE sheets. The rms roughness of the coated substrates is 6 ± 3 nm, that is, in the same order as that of the uncoated PE films because the overall morphology is dominated by the PE lamellae.…”

“…Only few very recent publications deal with technically relevant aspects of PDA as an adhesion promoter at the polymer–metal interfaces. Kafkopoulos used PDA to improve the adhesion of Ti wires in a PMMA matrix; Vasconcelos used PDA for the deposition of Ni–P films on nitrile butadiene rubber. Earlier work studied the bonding between aluminum and glass by PDA and the electroless deposition of Cu on PDA-modified silicon substrates .…”

Synthetic strategies to enhance the long-term stability of polymer brush coatings

“…Nevertheless, the primer cannot be strictly universally applied. Though the polyphenol layers bind strongly to metal(-oxide) substrates 154 and carbon-based materials, 155 they not adhere well to SiO 2 substrates. In fact, this weak adherence to silicon has been utilized to prepare brush-coated polydopamine-based nanosheets.…”

Polydopamine as Adhesion Promotor: The Effect of Thermal Treatment on the Performance of Poly(lactic acid) (PLA)‐Metal Co‐molded Joints

“…For more details on the theoretical background regarding the pullout curve analysis and validation of the model used to calculate G a , please refer to our previous work. [8] Figure 2. Schematic representation of the experimental procedure.…”