Solvent-free processing of lignin into robust room temperature phosphorescent materials

Area of Science:

• Materials Science
• Polymer Chemistry
• Biomass Valorization

Background:

• Developing room temperature phosphorescent (RTP) materials from sustainable biomass resources via solvent-free methods presents significant challenges.
• Lignin, a complex biopolymer, exhibits poor solubility in common organic solvents, hindering its direct incorporation into functional materials.
• Existing methods for RTP material synthesis often involve harsh chemicals or complex procedures, limiting their environmental friendliness and scalability.

Purpose of the Study:

• To develop a novel, solvent-free method for producing room temperature phosphorescent (RTP) materials derived from lignin.
• To investigate the interactions between lignin and specific liquid monomers for efficient material processing.
• To demonstrate the potential of the resulting RTP materials in practical applications such as inks, coatings, and anti-counterfeiting technologies.

Main Methods:

• Lignin was dissolved in a mixture of 2-hydroxyethyl acrylate (HEA) and urethane dimethacrylate (UDMA) liquid monomers.
• UV irradiation was used to initiate the polymerization of HEA and UDMA, creating a rigid polymer network incorporating lignin.
• The photoluminescence properties, including phosphorescence lifetime and color tuning via energy transfer with Rhodamine B (RhB), were characterized.
• The developed material was tested for applications as photocured inks, luminescent coatings, and anti-counterfeiting logos.

Main Results:

• A stable, solvent-free system was established by dissolving lignin in HEA and UDMA.
• UV-initiated polymerization successfully converted lignin into a rigid polymer network, activating humidity/water-resistant RTP with a lifetime of 202.9 ms.
• The phosphorescence color was tuned to red by incorporating Rhodamine B (RhB) through targeted Förster resonance energy transfer (TS-FRET).
• The material demonstrated successful application as photocured, multi-emission RTP inks, luminescent coatings, and a smart anti-counterfeiting logo.

Conclusions:

• A facile, solvent-free method enables the conversion of lignin into high-performance room temperature phosphorescent (RTP) materials.
• The developed polymer network enhances the stability and water resistance of lignin-based RTP, with a significant phosphorescence lifetime.
• The tunable emission color and versatile application potential highlight the material's promise for advanced optical and security features.