Korean researchers have developed to strengthen biodegradable plastics using hemp hurd, an agricultural by-product. The approach is expected to be applicable to other large-volume agricultural residues, including soybean stalks and rice straw.
A research team led by Dr. Hoyong Kim of the Korea Research Institute of Chemical Technology (KRICT) , headed by President Suk-Min Shin, extracted cellulose from discarded stalks of industrial hemp, which is used to produce traditional hemp textiles. The team then applied a drying process that preserves the microfibrillar structure of the cellulose, enabling it to serve as a reinforcing biofiller for biodegradable plastics.
Biodegradable films made from thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT) have attracted attention for use in eco-friendly packaging and agricultural mulch films because they can biodegrade in soil. However, these films tend to tear easily and have limited resistance to moisture. Cellulose obtained from cotton or wood pulp can be processed into microfibrils and used as a reinforcing material, but the additional microfibrillation and processing steps can make such materials costly.
Industrial hemp is currently cultivated in designated Regulation-Free Special Zones, including Andong, Gyeongsangbuk-do. While the outer part of the stalk is used to obtain fibers, the remaining woody core, known as hemp hurd, accounts for roughly 70% of the stalk by weight and has had relatively limited applications. Using discarded hemp hurd as a feedstock for microfibrillated cellulose instead of commercial pulp could reduce both agricultural waste and raw-material costs.
A major challenge, however, is that cellulose microfibrils tend to aggregate tightly when dried using conventional methods. This phenomenon, known as hornification, causes the fine fibrillar structure to collapse as the fibers form strong hydrogen bonds with one another. For a biodegradable film to become stronger, the reinforcing fibers must be uniformly dispersed throughout the polymer matrix so that mechanical stress can be distributed effectively. When the fibers form large aggregates, however, they cannot effectively bear or transfer stress, making the film prone to tearing.
Freeze-drying and spray-drying can help suppress such aggregation, but their high energy consumption and equipment costs make them less suitable for large-scale production. Developing a simple and economical drying process that preserves the fine fibrillar structure while minimizing aggregation has therefore remained a longstanding challenge.
The KRICT team addressed this issue through a two-step physicochemical strategy that retains conventional oven drying while controlling the moisture content of the hemp-derived cellulose and treating its surface with a low-cost chemical agent, alkyl ketene dimer (AKD).
Plant fibers have an intrinsic critical moisture level known as the fiber saturation point (FSP). At this point, free water in the pores of the fibers has been removed, while bound water remains within the cell walls. For plant fibers, the FSP generally corresponds to a moisture content of approximately 30%. Once the moisture content falls below this threshold, bound water begins to desorb, bringing adjacent cellulose microfibrils closer together and promoting strong intermolecular hydrogen bonding and irreversible aggregation.
The research team prepared microfibrillated cellulose from hemp hurd and precisely identified its FSP. The fibers were then milled while maintaining an appropriate moisture level above this critical threshold, allowing processing to take place before severe hornification occurred.
The team further treated the cellulose surface with AKD. The hydrophobic alkyl chains introduced by AKD create steric hindrance between adjacent microfibrils, further suppressing interfibrillar hydrogen bonding during drying. By combining moisture control with AKD surface modification, the researchers were able to preserve the fine fibrillar structure using conventional oven drying, without relying on expensive freeze-drying.
The resulting hemp-hurd-derived cellulose was incorporated at 10 wt% into a TPS/PBAT biodegradable film, and the film's tensile strength was evaluated. Cellulose microfibrils prepared using the conventional drying method improved tensile strength by only 1.5%, whereas the biofiller produced using the newly developed process increased tensile strength by 26.2%. The amounts of water vapor and oxygen passing through the film were also reduced by approximately 17% and 9%, respectively, demonstrating improved moisture and oxygen barrier performance.
The technology could potentially be extended to various other cellulose-rich agricultural residues, including soybean stalks and rice straw, and the research team plans to conduct further studies to broaden its applications.
The research was published in July 2026 in the Chemical Engineering Journal (Impact Factor: 12.5), an international journal in the field of chemical engineering.
