Analysis of the sulfuric acid hydrolysis of wood pulp for cellulose nanocrystal production: A central composite design study

Published Date
25 December 2016, Vol.93:76–87, doi:10.1016/j.indcrop.2016.01.048

Nanocellulose: production, functionalisation and applications

Author 

• Shuping Dong ^a,b
• Michael J. Bortner ^b,c
• Maren Roman ^a,b,,

• aDepartment of Sustainable Biomaterials, Virginia Tech, Blacksburg, VA 24061, USA
• bMacromolecules and Interfaces Institute, Virginia Tech, Blacksburg, VA 24061, USA
• cDepartment of Chemical Engineering, Virginia Tech, Blacksburg, VA 24061, USA

Received 20 November 2015. Revised 25 January 2016. Accepted 28 January 2016. Available online 20 February 2016. 

Highlights

• •
  3-factor RSM study of cellulose nanocrystal production by sulfuric acid hydrolysis.
• •
  66–69% yield with 57–58 wt.% sulfuric acid at 64–67 °C for 134–156 min.
• •
  All three factors (acid concentration, temperature, time) are significant.
• •
  Only interaction between hydrolysis temperature and time is insignificant.
• •
  Sulfate group density increases linearly with acid concentration and temperature

Abstract

Cellulose nanocrystals (CNCs) are most commonly prepared by sulfuric acid hydrolysis of a purified cellulose starting material but the effects of hydrolysis conditions on CNC yield and properties are incompletely understood. In this study, we use a rotatable central composite experimental design to elucidate parameter interactions between three design factors, acid concentration (x₁), hydrolysis temperature (x₂), and hydrolysis time (x₃), over a broad range of process conditions and determine their effect on yield and sulfate group density. Parameter ranges are 55–65 wt.% for x₁, 45–65 °C for x₂, and 30–180 min for x₃. Regression models of the experimental yield data reveal significant two-factor interactions of x₁ with each x₂and x_3, whereas x₂ has no significant two-factor interaction with x₃. The models predict maximum yields of 66–69% at optimum process conditions of 57–58 wt.% (x₁), 64–67 °C (x₂), and 134–156 min (x₃). At these conditions, the sulfate group density is predicted to be between 241 and 265 mmol/kg. The sulfate group density is linearly dependent on acid concentration and hydrolysis temperature and not dependent on hydrolysis time. Maximum sulfate group density can only be achieved at the expense of yield. The results presented here provide a foundation for subsequent, sequential optimization using narrower parameter ranges, allowing further optimization of the hydrolysis conditions and potentially enabling higher yield.

Graphical abstract

Keywords

• Cellulose nanocrystals
• Acid hydrolysis
• Central composite design
• Yield
• Sulfate group density

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  Corresponding author at: Department of Sustainable Biomaterials, Virginia Tech, Blacksburg, VA 24061, USA.

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