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 Tg 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.