Chitosan Cross-Linking with a Water-Soluble, Blocked Diisocyanate. 1. Solid State

Abstract

The present investigation focuses on the synthesis and application of a cross-linking agent that is compatible with the solubility characteristics of chitosan. A water-soluble, blocked-diisocyanate was prepared as a bisulfite adduct to 1,6-hexamethylene diisocyanate, which proved to be stable for several weeks in aqueous, acidic chitosan solutions at room temperature. Thermal cross-linking of chitosan as cast, dried films was investigated by varying the NCO/NH(2) ratio from 0.0 to 1.2. Spectroscopic (IR), thermal (TGA), swelling, and structural (WAXD) studies indicated that chitosan was cross-linked in a concentration-dependent manner under mild thermal conditions: 60 degrees C for 24 h. Cross-linking inefficiency was concluded to be due to lack of mobility of the reacting species in the solid state. In a preliminary study, the enzymatic degradation with Chitinase (E. C. 3.2.1.14) from Streptomyces griseus was found to be the greatest for non-crosslinked chitosan, followed by chitin, and then by cross-linked samples.

Chitin-chitosan nanocomposite gels: reinforcement of chitosan hydrogels with rod-like chitin nanowhiskers

“…The final yield of product (white powder) was 84%. Chemical shift values in 1 H and 13 C nuclear magnetic resonance (NMR) spectra were similar with those in Welsh et al 30 . …”

“…29,30 Hexamethylene diisocyanate (6.73 g, 40 mmol) was added to Na 2 S 2 O 5 (8.36 g, 44 mmol) solution in deionized water (15.5 ml), and the mixture was stirred for 20 h at room temperature. The white precipitate formed by pouring the turbid mixture into acetone was collected by suction filtration and dried in vacuo.…”

New crosslinkers for electrospun chitosan fibre mats. I. Chemical analysis

“…Addition of HDACS made the CS/TFA solution turbid without an observed colour change. Amounts added for both HDACS [25,26] and ECH [21,27,42] were based on previous studies on CS films or hydrogels. Keeping in mind that the CS used is 75 per cent DD, the crosslinker amounts used here were modified to estimate a 1 : 1 molar ratio of amine : crosslinker group.…”

“…Genipin was purchased from Wako Pure Chemicals Industry, Ltd., (Japan). HDACS was prepared using the protocol reported by Welsh et al [25]. All aqueous solutions were prepared with doubly distilled water.…”

“…HDACS crosslinks CS at the NH 2 group of the polymer, creating a urea linkage [25] (figure 1g). When fully crosslinked, this appears as a strong peak at around 1650 cm 21 [25].…”