Powder-Based Approaches to Sustainable Development: Plant Material (Lignin) Valorization Strategies

Abstract

Lignin, an abundant aromatic biopolymer, is primarily generated as a by-product from industrial processes such as kraft pulping and lignocellulosic bioethanol production. Traditionally, lignin has been utilized as a combustion fuel for process heat recovery; however, this approach contributes to CO₂ emissions and offers limited value in the context of a carbon-neutral economy. With growing societal and industrial interest in sustainable materials and the reduction of greenhouse gas emissions, lignin is increasingly recognized as a promising renewable feedstock for a variety of high-value applications, including energy storage, construction materials, cosmetics, and polymer composites.

To effectively utilize lignin in such applications, it is essential to precisely control its physicochemical characteristics, particularly particle size and morphology, which directly influence dispersion, reactivity, and processability. Due to lignin’s complex, variable structure and flammability, advanced powder processing technologies are required to ensure both functional performance and operational safety.

This paper introduces a comprehensive approach to lignin powder processing, focusing on two core technologies: fine grinding and dry granulation. For the fine grinding of lignin to particle sizes suitable for applications such as films or fillers in thermoplastic composites—typically requiring a d₉₇ below 10 μm—jet milling systems are employed to ensure high-precision production of ultrafine particles with a narrow particle size distribution. In particular, the fluidized bed opposed jet mill (AFG) developed by Hosokawa Alpine has been demonstrated as an effective technology for achieving the desired specifications.

For coarser applications (e.g., d₉₇ ≈ 20–30 μm), impact classifier mills such as the ACM Pulverizer^® offer an energy-efficient alternative. Experimental data presented in this study demonstrate how particle size and energy consumption are interrelated and highlight the importance of process selection based on target application.

Additionally, to address challenges related to handling, dusting, and bulk density, dry agglomeration using roll compactors has been implemented. This technique produces dust-free, free-flowing granules or briquettes that facilitate storage, transport, and downstream processing.

The integration of powder technologies enables the functional conversion of lignin into industrially viable forms, thereby supporting its transition from a waste stream to a valuable resource. This work emphasizes the role of particle engineering in realizing lignin’s potential as a key material in a circular, low-carbon economy.

Examples of granules and briquettes made from milled lignin.