Enzyme-assisted pretreatment of PA12 for sustainable Plating on Plastics: Replacement of Cr⁶⁺ etching and Pd activation

Plating on plastics (PoP) is broadly used in automotive, electronics, and household appliances to improve mechanical strength, corrosion protection, and surface aesthetics. Effective pretreatment of polymer surfaces is required to enable electroless deposition of a conductive Ni-P layer, which acts as the foundation for subsequent electroplating. However, established industrial processes depend on Cr⁶⁺-based etching solutions and Pd-containing activators, raising serious environmental, health, and economic concerns due to the toxicity of Cr⁶⁺ and the high cost of Pd. Among polymeric materials, ABS and polyamides (e.g. PA6, PA66, PA12) are most frequently used in PoP applications.

In this study, chromic acid etching is replaced by an enzyme-based pretreatment using a protease (alcalase) and Pd-based activation is replaced by Ni salt-based activation which is more cost-effective. Alcalase is an alkaline serine protease capable of cleaving amide bonds and was therefore selected for the enzymatic pretreatment of PA12 surfaces, introducing polar functional groups that promote effective activation for subsequent electroless Ni-P deposition. The enzymatic pretreatment conditions were systematically optimized by varying the enzyme-containing solution temperature, enzyme concentration, and immersion time. Surface chemistry, morphology and adhesion were evaluated by FT-IR spectroscopy, water contact angle measurements, SEM/EDS and pull-off adhesion tests. The results showed the formation of uniform, thin and well-adhered Ni-P conductive layer on enzyme-treated PA12 substrates, highlighting the potential of protease-assisted pretreatment as a sustainable alternative for PoP.