Solvent-Free Ball Milling Transforms Biochar into Super-Adsorbent Green Coating for Oil Spill Cleanup

New research uses solvent-free ball milling to turn biochar into a hydrophobic coating for hemp fibers, absorbing 14x its weight in oil for sustainable cleanup.

By: AXL Media

Published: Mar 14, 2026, 6:14 AM EDT

Source: Information for this report was sourced from Biochar Editorial Office, Shenyang Agricultural University

Revolutionizing Carbon Modification Through Mechanochemistry

Biochar is a highly versatile, carbon-rich byproduct of biomass pyrolysis, valued for its porous structure and environmental benefits. However, tailoring its surface to repel water—a process known as hydrophobic functionalization—traditionally involves complex chemical reactions requiring large volumes of toxic solvents. A new study published in the journal Biochar introduces a greener alternative: a solvent-free mechanochemical process. By utilizing planetary ball milling, researchers induced direct chemical bonding between biochar and long-chain amine molecules, creating an eco-friendly functional material without the environmental cost of traditional wet chemistry.

The Mechanics of Surface Roughness and Repellency

The innovation relies on a planetary ball mill to mechanically activate the carbon surface, forcing a chemical reaction with octadecylamine. This process introduces long alkyl chains onto the biochar, significantly reducing its polarity. These chains, combined with the natural topography of the biochar, increase surface roughness—a critical physical requirement for high water repellency. This dual-action modification ensures that water droplets cannot penetrate the material, instead resting on the surface in a state of high tension.

Transforming Hemp Fibers into High-Performance Sorbents

To test the practical application of this modified biochar, the team used it as a coating for natural hemp fibers. Using a bio-based solvent derived from citrus waste, the fibers were dip-coated to create a thin, protective layer. Contact angle measurements revealed that the coated hemp achieved a water contact angle of 126°, indicating strong hydrophobic behavior. While untreated hemp fibers are naturally absorbent and quickly become waterlogged, the biochar-coated versions remained dry and buoyant, maintaining their structural integrity when exposed to moisture.