Title page for ETD etd-05092014-114502


Type of Document Master's Thesis
Author Dong, Shuping
Author's Email Address dongs05@vt.edu
URN etd-05092014-114502
Title Effects of acid hydrolysis conditions on cellulose nanocrystal yield and properties: A response surface methodology study
Degree Master of Science
Department Macromolecular and Science Engineering
Advisory Committee
Advisor Name Title
Maren Roman Committee Chair
Scott Renneckar Committee Member
Timothy E. Long Committee Member
Keywords
  • cellulose nanocrystals
  • sulfuric acid hydrolysis
  • surface charge density
  • ζ-potential
  • particle size
  • yield
  • surface response method
  • central composite design
  • Box-Behnken Design
Date of Defense 2014-04-24
Availability restricted
Abstract
Cellulose nanocrystals (CNCs) are frequently prepared by sulfuric acid hydrolysis

of a purified cellulose starting material. CNC yields, however, are generally low, often

below 20%. This study employs response surface methodology to optimize the hydrolysis

conditions for maximum CNC yield. Two experimental designs were tested and

compared: the central composite design (CCD) and the Box–Behnken design (BBD). The

three factors for the experimental design were acid concentration, hydrolysis temperature,

and hydrolysis time. The responses quantified were CNC yield, sulfate group density,

ζ-potential, z-average diameter, and Peak 1 value. The CCD proved suboptimal for this

purpose because of the extreme reaction conditions at some of its corners, specifically

(1,1,1) and (–1,–1, –1). Both models predicted maximum CNC yields in excess of 65% at

similar sulfuric acid concentrations (~59 wt %) and hydrolysis temperatures (~65 °C).

With the BBD, the hydrolysis temperature for maximum yield lay slightly outside the

design space. All three factors were statistically significant for CNC yield with the CCD,

whereas with the BBD, the hydrolysis time in the range 60–150 min was statistically

insignificant. With both designs, the sulfate group density was a linear function of the

acid concentration and hydrolysis temperature and maximal at the highest acid

concentration and hydrolysis temperature of the design space. Both designs showed the

hydrolysis time to be statistically insignificant for the ζ-potential of CNCs and yielded

potentially data-overfitting regression models. With the BBD, the acid concentration

significantly affected both the z-average diameter and Peak 1 value of CNCs. However,

whereas the z-average diameter was more strongly affected by the hydrolysis temperature

than the hydrolysis time, the Peak 1 value was more strongly affected by the hydrolysis

time. The CCD did not yield a valid regression model for the Peak 1 data and a

potentially data-overfitting model for the z-average diameter data. A future optimization

study should use the BBD but slightly higher hydrolysis temperatures and shorter

hydrolysis times than used with the BBD in this study (45–65 °C and 60–150 min,

respectively).

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