Network formation and differentiation of chitosan-acrylic acid hydrogels using X-ray absorption spectroscopy and multivariate analysis of Fourier transform infrared spectra

Chitosan-acrylic acid (Cs-AA) hydrogels were prepared by blending different Cs concentrations and AA:Cs ratios. The Cs-AA hydrogel samples were analyzed using synchrotron radiation-induced near edge X-ray absorption fine structure (NEXAFS) and Fourier transform infrared (FTIR) spectroscopies. The characteristics of Cs were observed through the C, O, and N K edges in NEXAFS. Significant shifts in the Cs characteristic features were induced by the addition of AA. The NEXAFS findings confirmed the new covalent and ionic bridges to form the network of the Cs-AA hydrogel. Raw FTIR spectra were used to investigate the different functional groups of each of the macromolecules. The study attempted to discriminate the Cs-AA hydrogels prepared with different Cs wt% concentration and AA:Cs ratio using multivariate approaches. The preprocessed dataset was evaluated using principal component analysis (PCA) and hierarchical cluster analysis (HCA). The PCA and HCA methods showed the possibility of discriminating the Cs-AA hydrogel samples from the control samples and with each other. The approaches further confirmed that the C=O groups found in the range of 1700-1800 cm-1 can be used as an identifier for Cs-AA hydrogel samples prepared using different solution parameters. The use of FTIR coupled with multivariate approaches provided a simple and reliable way to inspect the possible discrimination of Cs-AA hydrogels.