Sustainable design and synthesis of high-performance lignin-based sunscreen ingredients

The active ingredients most commonly employed in sunscreens are compounds containing one or two aromatic rings. Lignin is the most abundant renewable aromatic polymer that has the potential to yield low molecular weight aromatic chemicals when strategically depolymerized. Here, the UV absorbance of a series of monomeric and dimeric lignin model compounds (LMCs) were studied. Specifically, vanillin and ferulic acid demonstrated good absorption in the UVB (280-320 nm) range, while the 5-5 dimer showed efficient absorption in the UVA (320-400 nm) range. Based on this, vanillin, ferulic acid and 5-5 dimer were mixed in pairs and dispersed in the oily isoeugenol to prepare LMC hybrid dispersions. Subsequently, demethylated lignin (DL) was synthesized and used to encapsulate the LMC hybrid dispersions via ultrasonic cavitation to prepare DL-based nano-capsules (DLNCs). The DLNCs were used as the only active ingredient in sunscreens, whose sun protection factor (SPF) value could be up to 55 with a dosage of 10 wt%. Due to anti-photolysis property of DL, the SPF value of DLNCs-based sunscreens increased initially and maintained >8 h under UV irradiation. Additionally, the prepared DLNCs exhibited excellent anti-permeability, antioxidant capacity and biocompatibility, making them a potential substitute for conventional petroleum-based sunscreen agents.