Transparent Sodium Lignosulfonate/Phosphorylated Sodium Alginate/Cellulose Composite Films with Flame-Retardant and UV to Blue Light-Shielding Performance

While there has been an ongoing effort to develop environmentally friendly multifunctional films made from natural polymers and renewable resources, there are still challenges in realizing versatility through a simple and green process. Here, we use aqueous alkali to rapidly dissolve modified cellulose fibers above 0 °C within minutes to prepare cellulose hydrogel substrate. The modified cellulose can be commercially obtained from carboxymethyl cellulose manufacturing with low cost. Subsequently, a biodegradable multifunctional all-biomass composite film is obtained by wrapping sodium lignosulfonate (LSS) and phosphorylated sodium alginate (PSA) molecules in cellulose hydrogel. The films exhibited excellent UV protection, blocking 86–99.3% of UV-A and 99.6–100% of UV–B radiation. Meanwhile, the films blocked 57.4–90.7% of high-energy blue light (HEBL, 400–450 nm) and maintained 66.2–80% transparency at 600 nm. The films effectively block blue light from sources such as computer screens, mobile phones, and lighting systems by means of light absorption. The films outperformed commercial shielding films in UV and HEBL blocking. Notably, the films acquired excellent flame-retardant performance with the addition of PSA, achieving a high limiting oxygen index (LOI) of 33.3%. In comparison with the original one, the composite film exhibited a 75.6% reduction in peak heat release rate and an 84.6% decrease in total heat release. Moreover, the films have ideal biodegradability and mechanical strength, with a tensile strength exceeding 98 MPa. This sustainable and clean strategy would direct all-biomass films toward diversified applications.