Cellulose Etherification with Glycidol for Aqueous Rheology Modification

Cellulose ethers are an important class of cellulose derivatives extensively used as rheology modifiers in aqueous applications ranging from personal care products and pharmaceuticals to paints and construction materials. 2,3-Dihydroxypropylcellulose (DHPC) is a water-soluble cellulose ether that can be derived from the reaction of cellulose and glycidol in a process that is less hazardous than other cellulose ether syntheses, which use volatile compounds under regulatory scrutiny such as methyl chloride and ethylene oxide. In the present work, the synthesis of DHPC was investigated using cellulose and glycidol under heterogeneous slurry conditions. Cellulose was activated in an organic solvent spiked with aqueous sodium hydroxide and then reacted with glycidol at near-ambient temperatures (30–40 °C) for short reaction times (1–4 h). The products were isolated by filtration and characterized by a variety of commonly available tools including NMR spectroscopy, size-exclusion chromatography, turbidimetry, and rheology. The reaction was optimized to afford a product with good solubility and viscosity in water with minimal input of NaOH and glycidol. Several reaction parameters were investigated including time and temperature, solvent identity and composition, and reagent loading and concentration. While past studies on cellulose etherification have identified some key process parameters, this report leverages modern high-sensitivity instrumentation to develop relationships between the process, chemical structure, and performance. DHPC with moderate levels of substitution by glycidol (molar substitution between 1.0 and 2.0) gave the best balance of solubility and viscosity enhancement. Overall, this work demonstrates that a high-quality cellulose ether can be obtained in mild conditions and high yield without the need for operationally costly procedures such as precipitation or dialysis.