Rod- and sphere-shaped cellulose nanocrystals (CNCs) type-II derived from Asclepias syriaca stem residues: composition, morphology, and thermal properties

Abstract

Cellulose nanocrystals or nanoparticles (CNCs) have drawn a lot of attention due to their abundance, biocompatibility, renewability and their excellent mechanical properties paving the way to innovative and sustainable applications. In the present work, the stem residues of Asclepias syriaca L., better known as milkweed and generally regarded as a weed, was used for the first time to extract CNCs with a crystalline structure type-II (CNC-II). Structural, thermal, morphological, and mechanical properties of extracted CNC-II were characterized by means of Fourier transform infrared, X-ray diffraction, scanning electron microscopy, dynamic light scattering, thermogravimetric analysis, and atomic force microscopy (AFM). Asclepias syriaca stem fibers revealed quite similar cellulose content compared with other milkweed species, and stable suspensions made of nanosphere- and nanorod-shape CNC-II were successfully extracted from raw milkweed fibers. In addition, after conversion from cellulose-I to cellulose-II by mercerization, milkweed cellulose-II exhibited higher thermal resistance compared with cellulose-I with degradation temperatures at 328 °C and 310 °C, respectively. Finally, the transversal elastic modulus of individuals CNC-II, as measured by AFM, was found to be in the range of 3.5–27 GPa, which is consistent with reported values for CNC-I or -II in the literature.