Polydopamine surface functionalized submicron ZnO for broadening the processing window of 3D printable PLA composites

The “catalytic degradation” of metal oxides limits the wide application of PLA when PLA needs to be modified by adding metal oxides to achieve desired properties. Zinc oxide (ZnO) is a common and widely used agent as it can be used for many properties, such as antioxidant, antibacterial, etc. However, detrimental effects often exist on the properties of polymers after introducing the ZnO, due to the catalytic degradation. In this study, we used polydopamine (PDA) to construct ZnO@PDA core-shell submicron particles via the self-polymerization of dopamine (DA) in alkaline solution, aimed to produce a surface functionalization that would be used to control the rate of degradation of PLA by ZnO during thermal processing, and promote the preservation of mechanical properties. PLA with different contents of ZnO and ZnO@PDA were prepared by a simple melt extrusion method. The degradation behavior, mechanical properties and antibacterial activity of ZnO/PLA and ZnO@PDA/PLA were investigated. It was found that the incorporation of ZnO@PDA in PLA at different contents exhibits a dramatic control over the degradation rate when compared to that of the ZnO/PLA with the same filler content. Notably, the T(5%) and T(50%) of 3%-ZnO@PDA/PLA increased by 36.4 (o)C and 31.9 (o)C. GPC results showed the molecular weight of 3%-ZnO@PDA/PLA was only reduced by 15.8% after thermal processing. In addition, 3%-ZnO@PDA/PLA can be 3D-printed smoothly. That is to say, the introduction of ZnO@PDA can increase the processing window of PLA/ZnO composites, providing the possibility for materials that need to be included in civil application. Accordingly, ZnO@PDA/PLA samples showed higher tensile strength and elongation at break than that of corresponding ZnO/PLA samples. Regarding the antibacterial behavior, the ZnO@PDA/PLA have more bacterial growth disability effect against Gram(+) bacteria than that of pure PLA.