Nanocellulose by Ammonium Persulfate Oxidation: An Alternative to TEMPO-Mediated Oxidation

Abstract

Ammonium persulfate (APS) mediated oxidation has been used in conjunction with acids under extended reaction times to produce highly crystalline cellulose nanomaterials. Opportunities exist to tailor the surface chemistry and morphological properties of nanocellulose using the economically attractive APS process. Here, the response surface methodology is applied to establish a set of predictable and reproducible guidelines for the synthesis of cellulose nanofibers with specific characteristics. The effect of varying treatment conditions on the APS oxidation of bleached and unbleached wood and non-wood pulps has been assessed by adjusting specifically the APS dosage, oxidation time, and temperature. The surface charge, crystallinity, and aspect ratio of the resulting nanocellulose have been systematically characterized. As-prepared materials exhibited a wide range of carboxylic acid contents on their surface from 0.6 to 1.4 mmol/g, while the crystallinity index changed from 72 to 88%. The morphological characteristics of the cellulose nanofibrils can be varied in the 48–80, 2.7–4.5, and 146–247 nm ranges for the aspect ratio, diameter, and length, respectively. More importantly, the environmentally friendly ammonium persulfate, opposed to TEMPO-mediated oxidation, has been effective at generating similar structural and chemical properties in lignin-containing feedstocks without any pretreatment or adjustment of experimental conditions.

High‐Humidity Shaker Aging to Access Chitin and Cellulose Nanocrystals**

“…In short, sulfate-free radicals formed under mild heating of persulfate can induce hydrolysis as well as oxidation, while the hydroxyl radicals further oxidize the aldehyde into the carboxylic acid. [35,36] An important observation that is seen within all HHSA reactions is the uptake of water within the solid mixture of APS and chitin. To better understand the role of water adsorption in this reaction, we experimentally determined the kinetics of water adsorption within our solid mixture by following its content within the solid sample over the course of 7 days under HHSA (Figure 3) using thermogravimetric analysis (TGA).…”

“…From negative control experiments, it is determined that both the formation of radicals as well as the need for water is essential in this reaction to afford the oxidation of chitin (See Supplemental Information for more details). In short, sulfate‐free radicals formed under mild heating of persulfate can induce hydrolysis as well as oxidation, while the hydroxyl radicals further oxidize the aldehyde into the carboxylic acid [35, 36] . An important observation that is seen within all HHSA reactions is the uptake of water within the solid mixture of APS and chitin.…”

Selective Oxidation of Cellulose—A Multitask Platform with Significant Environmental Impact

“…Highly crystalline cellulose nanofibrils have been successfully obtained using a novel and cost-effective oxidation system, namely ammonium persulfate (APS) under acidic conditions and long reaction intervals [ 157 ]. Thus, it was possible to modify the surface features of nanocellulose and, furthermore, to put together a set of conditions so that the synthesis is predictable and the parameters are reproducible, and, finally, nanofibers with specific properties are allowed.…”

High‐Humidity Shaker Aging to Access Chitin and Cellulose Nanocrystals**

“…In short, sulfate-free radicals formed under mild heating of persulfate can induce hydrolysis as well as oxidation, while the hydroxyl radicals further oxidize the aldehyde into the carboxylic acid. [35,36] An important observation that is seen within all HHSA reactions is the uptake of water within the solid mixture of APS and chitin. To better understand the role of water adsorption in this reaction, we experimentally determined the kinetics of water adsorption within our solid by following its content within the solid sample over the course of 7 days under HHSA (Figure 3) using thermogravimetric analysis (TGA).…”