Thermo-mechanical properties of an anti bacteria coating material based on a hybrid composite geopolymer-chitosan

Abstract

The main objective of this study was to examine the effect of a chitosan addition on the thermo-mechanical properties and microstructure of a geopolymer-chitosan composite, as well as the growth activity of bacteria on the surface. Chitosan was produced by the demineralisation (DM) and deproteination (DP) of a shrimp shell powder using a dilute sodium hydroxide (NaOH) solution and hydrochloric acid (HCl), followed by deacetylation (DA) using a dilute NaOH solution. Geopolymer pastes were produced through the alkaline activation of metakaolin. The metakaolin was obtained by dehydroxylating kaolin at 750 °C for 4 h. The chemical composition and the functional groups of the chitosan were examined by X-ray diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FTIR), respectively. The results showed that a high-quality chitosan was produced. The hybrid composites were produced by adding chitosan powder into a geopolymer paste at 0.1, 1.5, and 2.0 wt. % of chitosan relative to the mass of the metakaolin. The mixture was then moulded, cured at 70 °C for 2 h and then stored in the open air for 28 days before being subjected to XRD and Scanning Electron Microscopy (SEM) analyses. Differential Scanning Calorimetry (DSC) and Flexural Strength measurements were conducted to investigate the thermo-mechanical properties of the composites. The results showed that the geopolymer paste was a very strong binder to the chitosan and produced composites with high thermal resistance and excellent flexural strength. The Total Count Plate (TCP) tests showed that the addition of 1.5 wt. % of chitosan powder produced the most effective composite to limit the growth of the bacteria.