Title
The role of formic acid pretreatment in improving the carboxyl content of tempo-oxidized cellulose
Authors
LEI DAI ZHU LONG YONG LV and QUN-CE FENG

Received March 25, 2013
Published Volume 48 Issue 5-6 May-June
Keywords TEMPO, formic acid, pretreatment, native cellulose, carboxyl groups

Abstract
In this report, the application of formic acid pretreatment in oxidizing once-dried celluloses for the production of nanocellulose has been explored for the first time. Fully bleached softwood kraft pulp was pretreated with formic acid solution of various concentrations, and then it was oxidized with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) system. Water-insoluble fractions of carboxyl cellulose (COC) were obtained and their carboxyl contents were between 0.981-1.769 mmol/g cellulose. The oxidized pulp, which had been pretreated with 5% (v/v) formic acid solution, had approximately 10% more carboxyls than the pulp without pretreatment. Moreover, this pretreatment process can be used accompanying other methods (such as NaClO2 post-treatment, borax buffer and/or ultrasonic treatment) to improve carboxyl content of TEMPO-oxidized cellulose. Additionally, the oxidized fibers were converted into nanofibrils (3-7 nm in width and 300-400 nm in length) by homogenizing with a homogenizer.