Influence of drying method on the material properties of nanocellulose I: thermostability and crystallinity

Abstract

The effect of drying method on selected material properties of nanocellulose was investigated. Samples of nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNC) were each subjected to four separate drying methods: air-drying, freeze-drying, spray-drying, and supercritical-drying. The thermal stability and crystallinity of the dried nanocellulose were evaluated using thermogravimetric analysis (TGA) and X-ray diffraction. Supercritical-drying produced NFCs with the least thermal stability and the lowest crystallinity index. Air-drying or spray-drying produced NFCs which were more thermally stable compared with freeze-dried NFCs. The CNCs dried by the three methods (air-drying, freeze-drying, and spray-drying) have similar onset temperature of thermal degradation. The different drying methods resulted in various char weight percentages at 600 A degrees C for the dried NFCs or CNCs from TGA measurements. The dried NFCs are pure cellulose I while the dried CNCs consist of cellulose I and II. The calculated crystallinity indices differ with each drying method. The cellulose II content in CNCs changes as a function of drying method. For the application of nanocellulose in non polar thermoplastics, spray-dried products are recommended according to their higher thermal stability and higher crystallinity index.