Influence of the polymorphism of cellulose on the formation of nanocrystals and their application in chitosan/nanocellulose composites

Abstract

In this study, we evaluated the physicochemical properties of the chitosan/nanocellulose composites. Wide-angle X-ray scattering was applied to define the supermolecular structure of the materials, the laser diffracting technique was used to characterize the particle sizes, and scanning electron microscopy was used to evaluate the morphologies of the samples. The tensile properties of the composite films were also determined. Cellulose pulp was mercerized with 16% sodium hydroxide to give only cellulose II. Cellulose I and cellulose II were subsequently hydrolyzed with 64% sulfuric acid. As a result, nanocellulose I (NCC I) from cellulose I and nanocellulose II (NCC II) from cellulose II were produced. The mercerization of cellulose pulp contributed to a significant particle size reduction; more than 50% of the particles of the NCC II sample and only 36% of the particles of the NCC I sample were smaller than 100 nm. Chitosan composite films containing 5, 10, and 20% w/w of nanocelluloses were prepared by a solvent casting method. This was the first study investigating the influence of the crystallographic forms of cellulose on the formation of nanocrystals.

Thermal and mechanical properties of chitosan nanocomposites with cellulose modified in ionic liquids

“…Not only Atef et al but other research groups [61,62] too showed that due to good dispersion, low content of nanofiller (CNC) in polymer matrix (polylactide) is the best in terms of enhancement of mechanical properties. This hypothesis is also supported by this and our previous work [28,40], but stays in opposite to Khan et al [63] who claimed that 5% of CNC is optimal for chitosan. It comes as no surprise that aspect ratio of a filler, its interaction with polymer matrix, and uniform dispersion of filler are the main factors limiting mechanical properties of composites [63].…”

“…Accordingly, it can be concluded that sample of CNC I consisted of slightly larger amount of particles up to 220 nm, but it was also characterized with large volume of micrometric fraction. In the study on acidic hydrolysis of cellulose I and cellulose II [28], it was found that even though fraction of CNC II nanometric particles was higher than of CNC I, the micrometric particles of CNC I were significantly bigger than those of CNC II (max. 3580 and 1990 nm for CNC I and CNC II, respectively).…”

“…Apart from the optimal concentration of the filler, findings of this research stay in opposite to the mechanical results obtained for chitosan filled with acid-derived CNC. Tensile properties of chitosan/acidderived CNC composites [28] indicate that addition of CNC I is more effective than CNC II. The reason for that is probably the fact that the acid-derived CNC I had rather fibrillar structure, while the sample of acid-derived CNC II consisted of spherical or irregularly shaped particles.…”

“…It was already shown that in case of the acid hydrolysis of cellulose its polymorphic form has an influence on the particles sizes of produced nanometric celluloses. The higher yield of nanocrystalline cellulose II was ascribed to different crystallographic structures of starting celluloses and lower crystallinity of cellulose II, which was more susceptible to acid hydrolysis than cellulose I [28]. Still, the influence of polymorphic forms of cellulose on formation of cellulose nanocrystals using ionic liquids has not been reported yet.…”

Chitosan biocomposites with enzymatically produced nanocrystalline cellulose

“…Nonetheless, even chitosan films filled with unmodified nanometric cellulose exhibit high mechanical properties. Chitosan composites filled with 5% of nanocrystalline C I were found to be characterized with better tensile properties than analogous composites with nanocrystalline C II . It is worth emphasizing that in each case values of Young's modulus (YM) and tensile strength (TS) were higher than for pristine chitosan.…”