Optimizing lignocellulose conversion: A comparative study of alkali-assisted ball milling pretreatment of cotton stalk and corn stover

Abstract

Cotton stalk (CTS) and corn stover (CRS) were pretreated using solid alkali (NaOH or Ca(OH)₂) assisted ball milling (BM). The physicochemical properties of the pretreated materials and their high-solid enzymatic hydrolysis performance were systematically investigated. The interaction between alkali and straw was synergistically enhanced by mechanical force generated during BM, achieving effective lignin removal. NaOH showed superior delignification efficiency compared to Ca(OH)₂ for both straws at same dosages. Analysis of cation exchange capacity revealed higher stability of CTS-Ca²⁺ complex than CRS-Ca²⁺ complex, explaining the more effective lignin removal from CTS than from CRS by Ca(OH)₂. During the alkali/BM process, cellulose showed structural swelling and crystalline destruction. The cellulose of CTS mainly retained its cellulose I crystallinity, whereas most of the cellulose of CRS was converted to an amorphous state. The changes in physicochemical properties and structure effectively improved the enzymatic saccharification efficiency of pretreated straws. Under high-solids loading conditions (20 %) with an enzyme loading of 20 FPU/g, the maximum glucose yields from NaOH-pretreated and Ca(OH)₂-pretreated CTS were 68.52 % and 65.90 %, respectively. The corresponding yields for CRS were 80.43 % and 80.30 %. Partial least squares (PLS) analysis identified straw composition, particularly changes in cellulose, as the dominant factor influencing enzymatic hydrolysis efficiency. This study provided valuable insights for optimizing biomass-specific pretreatment strategies to achieve efficient sugar production.