Potential of Sorghum Stalk as Climate Resilient Resource for Paper Production

Abstract

Sorghum bicolor is a promising multi-purpose crop for the bioeconomy. To unfold its potential, genotypes must be matched to the respective industrial processes. Five sorghum genotypes were evaluated under contrasting field conditions in Southwest Germany, focusing on the stalk as a source of lignocellulosic biomass for paper production. Dual-purpose hybrids, particularly Ganymed and Tarzan, demonstrated high resilience, maintaining stable biomass and sugar yield under drought stress. Compositional analysis of the stalk showed substantial genotypic differences in extractive, carbohydrate, and lignin contents. Ganymed and Tarzan possessed higher glucose and xylose levels and lower extractives than KIT1 and Hannibal, making them more favorable candidates for biobased processing. Soda pulping results aligned with chemical profiles: Ganymed achieved the highest pulp yield (50.2%) and moderate kappa number (30.5), while KIT1 showed the lowest yield (38.0%) and the highest kappa number (40.3), Tarzan and Zerberus produced pulps with low kappa values (23.5 and 19.8 respectively) but moderately reduced yields due to hemicellulose loss (43.9% and 39.9%, respectively). Paper produced from Tarzan (6.6 mN.m²/g) had high tear indices compared to the other sorghum genotypes. Overall, Ganymed, Tarzan, and Zerberus showed strong suitability as lignocellulosic feedstocks, offering promising options for biorefinery and paper production.