Polydopamine-coated lignin nanoparticles in polysaccharide-based films: A plasticizer, mechanical property enhancer, anti-ultraviolet agent and bioactive agent

The potential of polysaccharide film as an alternative to petroleum-based plastics is being closely watched. To solve the defects of poor water resistance, poor flexibility and no bioactivity of polysaccharide-based films, polydopamine-coated lignin nanoparticles (LNP@PDA) were prepared and loaded on polysaccharide matrix to obtain composite films. LNP@PDA has good biocompatibility and can be dispersed homogeneously in polysaccharide matrix. The tight entanglement and hydrogen bonding between LNP@PDA and pectin promoted the formation of dense structure in film, and allowed the films to exhibit a nano-scale rough surface (7.61–20.90 nm). Composite films have higher mechanical strength (35.76 MPa) and water contact angle (92.42°), and exhibit unique antioxidant and antibacterial activities. Even without the addition of any plasticizers, the composite film exhibits attractive flexibility that is not present in polysaccharide-based films. When LNP@PDA loading exceeded 5%, composite films almost completely blocked the UVA (400-320 nm), UVB (320-275 nm) and UVC (275-200 nm) spectra and remained so after 24 h of UV irradiation, which demonstrated their excellent UV resistance and photostability. Furthermore, the universality results verify that LNP@PDA is also suitable for other different polysaccharide-based (such as starch, sodium alginate, agar, carrageenan, carob gum) films. Interestingly, the shear-thinning property of the film-forming fluid allows it to be sprayed through a sprayer bottle onto the surface of fruit or food packaging. These results suggest that LNP@PDA can be loaded into polysaccharide-based films as plasticizers, mechanical property enhancers, anti-UV agents, antioxidants and antimicrobial agents. This provides a brand-new strategy for producing high-performance polysaccharide-based food active packaging/coating.