The effect of hemicellulose pre-extraction on the wood viscoelasticity and its implications on the fiber separation mechanism in Chemi-mechanical pulping

Abstract

Chemi-mechanical pulping (CMP) is a typical high-yield pulping technology to produce various papers and paperboards due to its high yield and high fiber properties. However, it is challenging to further improve its energy efficiency without the scarification of fiber quality. To attack this challenge, herein we study the effects of different hemicellulose pre-extraction on the viscoelasticity of wood cell wall, the energy efficiency, and product properties in chemi-mechanical pulping (CMP) process. Hardwood was first pretreated by NaOH to hydrolyze the benzyl ester bonds that link lignin with hemicellulose, aiming to partially remove hemicellulose and weaken the inter-fiber connections. Then, the hemicellulose-extracted wood underwent refining. The chemical distributions of wood, fiber morphologies, fiber surface fibrillation, energy consumption, and paper properties were extensively studied. The results showed that a 40.8% removal of hemicellulose corresponded to a 90.3% reduction in wood storage modulus (E’) and a 68.3% decrease in specific refining energy consumption. Moreover, the weaker connections between microfibrils in the secondary layer, caused by hemicellulose extraction, promoted fiber surface fibrillation during pulp refining. The study elucidates the nonnegligible role of hemicellulose as the linking “bridge” between lignin and cellulose. It also provides a new mechanism in addition to the current classic pulping mechanism including lignin chemical/thermal softening and cellulose swelling in both CMP and chemi-thermomechanical pulp (CTMP). This study offers a feasible and efficient approach to extract hemicellulose from hardwood to reduce the refining energy without scarification of fiber quality, therefore, it holds promise for advanced and greener biorefineries.