Novel water-soluble chitosan derivative prepared by graft polymerization of dicyandiamide: synthesis, characterisation, and its antibacterial property

Novel water soluble chitosan derivative of dicyandiamide chitosan (DCDA-g-CS) was synthesized by grafting polymerization of dicyandiamide DCDA onto chitosan CS. The presence of a new absorption peak in the infrared region of nitrile at 2297 cm⁻¹ and NH at 1635 cm⁻¹ of DCDA-g-CS and the chemical shift of ¹³C NMR at 120 and 162 ppm due to the presence of nitrile and carbon in DCDA clearly shows that the grafting process has taken place. The strong signal in the ¹H NMR at 2.5 ppm could be assigned to the four protons in the amino group of DCDA, further confirms the formation of DCDA-g-CS. The polymer has shown to undergoing three steps of thermal degradation. The first stage was between 30 and 157 °C, followed by degradation step up to 350 °C and continuously degraded up to the high temperature set at 850 °C. The rate of degradation in the second stage which is slightly faster was considered as the rate determining step. The value of T_g was increased to 92.75 °C in DCDA-g-CS due to the considerable amount of DCDA was grafted onto the CS. The DCDA-g-CS was more soluble in water due to the decrease in crystallinity of chitosan after grafting as shown from X-ray diffraction spectra. The DCDA-g-CS shows high antibacterial activity at pH 7.0 and pH 4.0 the minimum inhibitory concentration (MIC) of gram-negative bacteria E. coli ATCC25922, the MIC at pH 7 and pH 4.0 were 62.5 and 125 μg/mL respectively and gram-positive bacteria S. aureus ATCC 29213, the MIC at pH 7 and pH 4 were 62.5 and 125 μg/mL respectively.