Lignin-assisted polyesters: sustainable optical filters with high NIR transparency

Optical filters that block visible light but allow near-infrared radiation to pass through (VONIRT) are considered promising for applications in optical detection or information security. However, they have mostly been manufactured using fossil raw materials, often involving environmentally harmful processes.

A Chinese research team has now developed a sustainable alternative: using a simple, highly atom-efficient in-situ polymerisation process, industrial lignin is incorporated into a polymerisable deep eutectic solvent (PDES). This consists of citric acid and 1,6-hexanediol and performs a dual function: it breaks down the ether bonds in the lignin and simultaneously promotes the formation of a cross-linked polyester network.

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Extreme UV shielding, high NIR transmission

Through π–π stacking, lignin forms J-shaped structures which, together with hydrogen bonds, ensure a dense filter structure. The result: almost complete blocking in the UV–visible range (transmission at 400 nm and 600 nm ~0%) with high NIR transmission (~80% at 1,400 nm).

The material also has good mechanical properties, with a tensile strength of 10.6 MPa and a fracture energy of 5.2 MJ m⁻³. Initial applications show potential for NIR photography and optical information security. The process is catalyst-free, easy to implement and an example of sustainable, high-performance filters based on lignin.

Source: Green Chemistry, Issue 26, 2025

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