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

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.