Optimization of industrial hemp production: Influence of stalk maturity on composition, structure, and processing for sustainable packaging

The growing demand for sustainable packaging materials has increased interest in agro-residue biomass, particularly industrial hemp, as an alternative to conventional fossil-based materials. Freshly harvested, unretted hemp stalks ( Cannabis sativa L. ) collected at 6 (early), 8 (mid), and 10 (late) weeks of growth were pulped using soda and Alcell organosolv processes, followed by three levels of refining. Compositional analysis, together with microscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS), revealed that hemp stem morphology and the spatial distribution of lignin and carbohydrates varied markedly between early and late growth stages. Early-harvested stalks contained a higher proportion of bast fibers and less xylem, whereas late-harvested stalks exhibited thicker cell walls and higher lignin content. Soda pulping achieved greater delignification but lower yields than Alcell, with maximum values of 54% yield and a kappa number of 74 for late-harvested stalks, compared with 68% yield and a kappa number of 98 for Alcell organosolv pulp. Packaging handsheets (120 g/m 2 ) produced from soda pulps showed better mechanical properties compared with those prepared from Alcell organosolv pulps. Among all samples, soda pulps derived from mid-harvested stalks demonstrated the highest mechanical properties, with a tensile index of 72.3 Nm/g and a burst index of 3.8 kPa·m 2 /g. These results indicate that unretted hemp stalks harvested at 8–10 weeks, when combined with an appropriate pulping strategy, offer a shortened and effective pathway to high-performance pulp fibers for packaging such as containerboard and other applications. Optimizing hemp stalk maturity improves fiber structure, pulping performance, and paper strength for sustainable packaging applications. • Hemp stalk maturity strongly affected biomass composition, fiber morphology, and packaging performance. • Less mature stalks had more bast fibers and carbohydrates; mature stalks had higher lignin. • Soda pulping achieved greater delignification, while Alcell pulping yielded more pulp. • Alkaline soda pulping removed lignin more effectively than acidic ethanol–water Alcell. • Pulps from 8 to 10 week stalks showed improved packaging properties.