Kinetics Study of the Solid-State Acid Hydrolysis of Chitosan: Evolution of the Crystallinity and Macromolecular Structure

Abstract

The heterogeneous hydrolysis of fully deacetylated chitosan solid samples was carried out with concentrated HCl. The hydrolysis kinetics was studied at different temperatures and HCl concentrations. From 5 to 50 degrees C in the hydrolysis time range up to 50 h, a monomodal distribution of molecular weights was observed connected to the only degradation of amorphous domains. Between 70 and 90 degrees C and for the hydrolysis longest times, a multimodal distribution appeared with the additional hydrolysis of the crystalline phase. The crystallinity index increased from 57 to 73% with the elimination and partial recrystallization of amorphous regions. X-ray diffraction patterns revealed the presence of the anhydrous polymorph, absent in the starting materials only containing the hydrated polymorph. The apparent crystallite width (from the Scherrer equation) of both the anhydrous and hydrated allomorphs did not vary significantly with time despite the increase in the fraction of anhydrous allomorph. Therefore, the hydrolysis in the solid state was complex, revealing several regimes. The activation energy parameters were deduced, and the mechanisms were discussed.

Preparation and Characterization of Chitosan Obtained from Shells of Shrimp (Litopenaeus vannamei Boone)

“…The step size was 0.02${}^{\circ }$. The crystallinity index ($CrI$) was obtained from the ratio of the area of the crystalline contribution ($A_{crist}$) to the total area of the diffractogram ($A_{total}$) as proposed by Osorio-Madrazo et al [38]. For doing so, $A_{crist}$ was first obtained by subtracting the amorphous contribution from $A_{total}$: $\%CrI=100\times A_{crist}/A_{Total}.$…”

Preparation and Chemical/Microstructural Characterization of Azacrown Ether-Crosslinked Chitosan Films

“…Weight- and number-average molecular weights of the starting chitosan (Ch) were characterized by size exclusion chromatography (SEC) coupled to multiangle laser light scattering (MALLS) detection, following the procedure used by Osorio-Madrazo et al [42]. Chitosan solutions at 0.1% ( w / v ) were prepared in an AcOH (0.2 M)/AcONH 4 (0.15 M) (pH 4.5) buffer, used as eluent, then filtered through 0.45 μm pore-size membranes (Millipore, Darmstadt, Germany).…”

Fine microstructure of processed chitosan nanofibril networks preserving directional packing and high molecular weight

“…The CHI crystallinity index CrI was determined from the ratio of the crystalline peaks contribution to the total area of the diffraction patterns (Osorio-Madrazo et al, 2010). Complementary synchrotron SAXS and WAXS patterns in transmission mode were recorded at the BM02/D2AM beamline at the ESRF, Grenoble (photon energy: 16 keV, = 0.7749Å).…”

“…Water content (wt%) ch1-d1 0.40 ± 0.01 1.10 ± 0.03 680 ± 2 1.81 ± 0.02 67.1 ± 0.5 8.12 ± 0.10 ch1-d2 0.10 ± 0.01 1.16 ± 0.03 720 ± 2 1.55 ± 0.01 68.5 ± 0.6 7.73 ± 0.10 ch1 was fully deacetylated by means of a heteregeneous multistep process, involving freeze-pump out-thaw (FPT) cycles in order to improve the deacetylation reaction while limiting the chitosan depolymerization (Lamarque, Cretenet, Viton, & Domard, 2005;Osorio-Madrazo et al, 2010). As shown in Table 1, the molecular weight and crystallinity in the resulting fully deacetylated chitosans ch1-d1 and ch1-d2 were preserved.…”

“…Nevertheless, the preparation of highly crystalline CHI nanofibrils that preserve the native directional structural packing and macromolecular structure is challenging. We previously reported on acid hydrolysis as a method to increase crystallinity of CHI substrates (Osorio-Madrazo et al, 2010;OsorioMadrazo et al, 2011). The deacetylation of chitin nanowhiskers has been proposed to produce CHI nanofibers.…”