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Lignin is evaluated as a nature-inspired broad-spectrum sun blocker in sunscreen lotions.

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Five types of industrial lignin are blended with a pure cream and a commercial sunscreen lotion. Lignin is found to significantly boost their sunscreen performance. Photostability of the lignin-modified lotions is analyzed. The results show that hydrophobic lignin has better sunscreen performance than hydrophilic counterpart. Sun protection factor (SPF) of the pure cream containing 10% organosolv lignin (OL) reaches 8.66. Small amount of hydrophobic lignin dramatically increases SPF value of the sunscreen lotions. Adding 1% lignin almost doubles the sun lotion’s SPF. Addition of 10% OL to the lotion boosts its SPF from 15 to 91.61. However, it is also found that hydrophilic lignin tends to demulsify the lotions due to an electrostatic disequilibrium. After 2 h of UV radiation, UV absorbance of all the five lignin-modified sunscreen lotions increases up to the limit of measuring instrument. All the lignin types studied in this work are found to have a general synergistic effect with sunscreen actives in the commercial lotion. An effort is also made to elucidate radical mechanisms of the synergy.

Molecular iodine has been introduced into the alkali lignin (AL) solutions to adjust the π-π aggregation, and the effect of lignin-iodine complexes on the aggregation and assembly characteristics of AL have been investigated by using fluorescence, UV-vis spectroscopy, light scattering, and viscometric techniques. Results show that AL form π-π aggregates (i.e., J-aggregates) in THF driven by the π-π interaction of the aromatic groups in AL, and the π-π aggregates undergo disaggregation in THF-I(2) media because of the formation of lignin-iodine charge-transfer complexes. By using iodine as a probe to investigate the aggregation behaviors and assembly characteristics, it is estimated that about 18 mol % aromatic groups of AL form π-π aggregates in AL molecular aggregates. When molecular iodine is introduced into the AL solutions, lignin-iodine complexes occur with charge-transfer transition from HOMO of the aromatic groups of AL to the LUMO of iodine. The formation of lignin-iodine complexes reduces the affinity of the aromatic groups approaching each other due to the electrostatic repulsion and then eliminates the π-π interaction of the aromatic groups. The disaggregation of the π-π aggregates brings a dissociation behavior of AL chains and a pronounced molecular expansion. This dissociation behavior and molecular expansion of AL in the dipping solutions induce a decrease in the adsorbed amount and an increase in the adsorption rate, when AL is transferred from the dipping solution to the self-assembled adsorbed films. Consequently, the adsorption behavior of AL can be controlled by adjusting the π-π aggregation. Above observations give insight into the occurrence of J-aggregation of the aromatic groups in the AL molecular aggregates and the disaggregation mechanism of AL aggregates induced by the lignin-iodine complexes for the first time. The understanding can provide an academic instruction in the efficient utilization of the alkali lignin from the waste liquor and also leads to further development in expanding functionalities of the aromatic compounds through manipulation of the π-π aggregation.

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CO2/N2-triggered water-dispersible/collectable lignin-g-DEAEMA nanoparticles were successfully synthesized and were used to prepare emulsified/demulsified switchable Pickering emulsions by gas processing under nearly neutral conditions.