The Major Key Takeaways

Sustainable engineering materials demand viable alternatives to petrochemical-based colorants. In his doctoral thesis, “Biocolorants for engineering materials,” Juha Jordan of Aalto University explores the functionality and endurance of natural colorants in plastics, wood coatings, and aluminum. The research features several natural options, but biochar, derived from industrial waste, emerges as a major contender for coloring thermoplastics like polylactic acid (PLA), showcasing both environmental and performance benefits that are critical for modern engineering applications.

Biochar is highlighted in this work not just for its color, but for its origins in the forest industry’s waste stream. The black pigment is produced by pyrolyzing wood chip mixtures. This approach directly addresses sustainability goals by repurposing a low-value industrial byproduct, thus avoiding the significant land and water use associated with growing dedicated dye crops. Furthermore, studies have shown that biochar pigment presents a reduced carbon footprint compared to commercial pigments. Its derivation from such an abundant, low-cost side stream positions biochar as an optimal feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More for sustainable and economically viable biocolorant production pathways.

In the study involving polylactic acid (PLA), a renewable thermoplastic, biochar was mixed with the polymer through extrusion and injection molded into test rods. Visually, the incorporation of biochar successfully yielded an evenly colored, opaque black appearance. After 168 hours of continuous Xenon light exposure—simulating prolonged exposure to indoor lighting conditions—the biochar-colored specimens maintained excellent color stability, earning a “good” lightfastness rating comparable to the uncolored reference. This demonstrated that biochar is a technically sound and practical coloring agent for thermally processed plastics.

The role of biochar extended beyond aesthetics into crucial functional enhancements. The research assessed polymer degradation by measuring the change in the carbonyl index (CI) of the PLA matrix after light exposure. The uncolored PLA exhibited the highest degradation, but the addition of biochar provided substantial photoprotection, showing a dramatically lower change in the CI value. This protective capability is a significant finding, showcasing biochar’s ability to safeguard the polymer.

Furthermore, biochar acted as an effective reinforcing filler. Tensile tests revealed that the biochar-colored PLA, along with kraft lignin and madder extract, provided statistically significant improvements in the ultimate tensile strength of the polymer compared to uncolored PLA. This suggests that biochar particles, even at the low concentration required for coloring (0.1 w-%) , can reinforce the matrix, helping to distribute mechanical stress. This multifunctionality—coloring, protecting against UV light, and improving strength—establishes biochar as an exceptionally promising and versatile biocolorant for engineering materials.

The combined technical performance of biochar—its good color quality, adequate lightfastness, and valuable functional advantages derived from a low-value, high-volume waste stream —makes it a standout solution for sustainable engineering. It illustrates the potential for industrial symbiosis, transforming an environmental burden into a valuable resource. The findings encourage adventurous researchers and entrepreneurs to further explore this unexplored field and transform academic research into meaningful ecological and societal benefits.

Source: Jordan, J. (2025). Biocolorants for engineering materials (Doctoral thesis, Aalto University). Aalto University publication series Doctoral Theses 198/2025.