Ultrasound-assisted synthesis of β-cyclodextrin/hydroxyapatite composites as a green and safe additive for enhancing leather properties

This study presents an ultrasound-assisted synthesis of β-cyclodextrin/hydroxyapatite composites to be used as green and safe auxiliaries in the tanning process. A combination of spectroscopic and non-spectroscopic techniques such as DLS (dynamic light scattering), ZP (zeta potential), XRD (X-ray diffraction), SEM (scanning electron microscopy) and ATR-FTIR (attenuated total reflectance-Fourier transform infrared spectroscopy) were used to thoroughly characterize the eight composites obtained by varying the ultrasound process parameters. While not cytotoxic, all composites had strong antibacterial action against Brevibacterium lines, Staphylococcus aureus, Escherichia coli, and Staphylococcus epidermis. All composites underwent lab-scale tanning tests, but only those exhibiting the most suitable set of tanning abilities underwent pilot-scale testing. The composites' interaction with the collagen matrix was assessed by micro-DSC (micro-differential scanning calorimetry), TG/DTG/DTA (thermal analysis), 1H unilateral NMR (proton nuclear magnetic resonance), ATR-FTIR, in-situ temperature synchrotron-based XRD and standard tests (UNI EN ISO 3380: 2015, UNI EN ISO 2589: 2016, UNI EN ISO 105- B02:2014). Thermal stability, dye penetration, thickness, colour fastness, surface appearance and microbiological protection were all improved for the leather treated with a small amount of composite added to the wet finish float. These findings demonstrate the benefits of β-cyclodextrin/hydroxyapatite composites as safe and sustainable tanning additives.