Structure–process–yield interrelations in nanocrystalline cellulose extraction

In order to improve the extraction of nanocrystalline cellulose (NCC) from sulfuric acid hydrolysis of chemical pulps, we have studied the effect of hydrolysis conditions on the degree of polymerization (DP), the extent of sulfation, morphological, and solid‐state characteristics of the extracted materials vis‐à‐vis yield. Our results demonstrate that sulfation plays a significant role in (i) determining the yield of, and (ii) imparting the unique solid‐state characteristics to, the extracted, H₂O‐insoluble cellulose nanomaterial from sulfuric acid hydrolysis. The hydrolysis process is itself proven to be highly reproducible, and NCC with high crystallinity (>80%) and a yield between 21% and 38% could be extracted from a fully bleached, commercial softwood kraft pulp using 64 wt.% sulfuric acid at 45–65°C after freeze drying. The NCC aggregates, with iridescent patterns typical of chiral nematic materials, are parallelepiped rod‐like structures which possess cross‐sections in the nanometer range and lengths orders of magnitude larger, resulting in high aspect ratios. The Ruland–Rietveld analysis was employed to precisely resolve X‐ray diffraction patterns and obtain information on crystallite size, crystalline and amorphous areas, and crystallinity of the extracted materials.