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 degrees), 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.