Preparation and morphology of different types of cellulose spherulites from concentrated cellulose ionic liquid solutions
作者：Hongzan Song, Yanhua Niu, Jian Yu, Jun Zhang, Zhigang Wang and Jiasong Heb
關鍵字：cellulose spherulites，ionic liquid
論文來源：期刊
具體來源：Soft Matter, 2013, 9, 3013-3020
發表時間：2013年
Spherulites of microcrystalline cellulose (MCC) have been prepared by using the vapor precipitation
procedure with proper humidity at various temperatures from concentrated microcrystalline cellulose/
1-allyl-3-methylimidazolium chloride (MCC/AMIMCl) solutions, for which AMIMCl is an ionic liquid, a
good solvent for dissolving MCC. Four different types of MCC spherulites have been investigated by
using polarizing optical microscopy (POM), scanning electron microscopy (SEM) and wide-angle X-ray
diffraction (WAXD) technique. POM observations reveal four types of MCC spherulites, i.e., negative and
positive banded spherulites, and negative and positive non-banded spherulites, depending on MCC
concentration and crystallization temperature (Tc). For banded spherulites, both the band spacing and
sizes of spherulites evidently increase with increasing Tc for each MCC/AMIMCl solution. The sizes of
spherulites increase with increasing MCC concentration at a given Tc. The findings imply that MCC
concentration plays a key role in MCC chain reorganizations into positive or negative spherulites, while
the crystallization temperature mainly affects the MCC crystalline lamellar twisting for the formation of
banded spherulites. SEM observation reveals that the formation of negative and positive banded
spherulites is due to different lamellar twisting directions and the formation of non-banded spherulites
is due to the formed radiating fibrillar textures. WAXD profiles confirm that all the four types of MCC
spherulites formed are in the crystalline form of cellulose II family, exhibiting more intense and sharper
diffraction peaks than those of cellulose II family obtained by the dissolution/precipitation process.