Chemical Modification of Plasticized Lignins Using Reactive Extrusion

Area of Science:

• Polymer Chemistry
• Biomaterials Science
• Chemical Engineering

Background:

• Kraft lignin (KL) is an abundant lignocellulosic byproduct with potential for chemical modification.
• Traditional methods for lignin esterification often involve solvents and batch processes, limiting efficiency.
• Developing sustainable and efficient lignin valorization pathways is crucial for a circular bioeconomy.

Purpose of the Study:

• To investigate the esterification of plasticized Kraft lignin (KL) with succinic and maleic anhydrides using reactive extrusion (REX).
• To characterize the structure and properties of the resulting lignin esters.
• To compare REX modification with conventional batch processes for lignin valorization.

Main Methods:

• Kraft lignin (KL) was plasticized using DMSO, glycol, and glycerol.
• Esterification was performed using succinic and maleic anhydrides via reactive extrusion (REX).
• Structural and chemical characterization employed Solid-state 13C CP-MAS NMR, FT-IR, 31P NMR, and HSQC NMR spectroscopy.
• Molecular weight changes were analyzed by GPC/SEC, and thermal properties by TGA.

Main Results:

• DMSO, glycol, and glycerol were identified as effective plasticizers for lignin in REX.
• REX primarily targeted and esterified the aliphatic OH groups of lignin, forming monoesters.
• REX-modified lignin esters exhibited altered molecular weight and thermal properties compared to batch-modified samples.
• REX demonstrated superior efficiency and speed compared to traditional batch modification methods.

Conclusions:

• Reactive extrusion (REX) is a viable, fast, solvent-free, and continuous method for Kraft lignin valorization.
• The REX process enables efficient esterification of lignin's aliphatic hydroxyl groups, yielding novel lignin-based polymers.
• This approach offers a sustainable pathway for upgrading lignin into value-added materials.