Cellulose nanocrystals (CNCs) are ideal rheological modifiers for aqueous oil and gas extraction fluids. When hydrolyzed with sulfuric acid, CNCs with sulfate half ester groups are produced, which impart surface charge and colloidal stability. As a result, aqueous CNC suspensions have uniform and predictable properties in ambient conditions. At elevated temperatures, however, properties of CNC suspensions drastically change and there is only a limited amount of data elucidating these changes. This work examines the effects of heat on CNC suspension properties and enables researchers to both understand and predict CNC performance for high temperature applications. Alternative CNC hydrolysis methods are also examined to produce CNCs which will maintain colloidal stability at high temperatures. CNCs were produced using single acids (sulfuric and phosphoric) as well as acid blends. A TEMPO-mediated oxidation was also performed on CNCs hydrolysed with sulfuric acid. The resulting six CNC types were heated at various temperatures between 100°C and 200°C in a sealed reactor. The effects of these high temperature and pressure conditions on CNC suspension properties such as uniformity, colloidal stability, rheology and color were studied. Additionally, CNC properties such as degree of polymerization (DP), surface charge density and crystallinity were studied before and after heat treatments. CNCs underwent few morphological changes; their DP and crystallinity were unchanged under the conditions tested. Their surface charge density; however, was significantly decreased after heat treatment which resulted in loss of colloidal stability and aggregation of CNCs. The largest changes in both CNC particle and CNC suspension properties were observed for CNCs hydrolysed with sulfuric acid. CNCs hydrolysed with acid blends as well as CNCs with surface carboxyl groups were less affected and maintained colloidal stability at higher temperatures. As such, this study elucidates CNC suspension behavior after heat exposure and demonstrates the production of CNCs with improved high temperature performance.

Predicting the behavior of cellulose nanocrystal suspensions and expanding their use at high temperatures

2019 Spring National Meeting

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