Mechanism and effect of hydroxyl-terminated dendrimer as excellent chrome exhausted agent for tanning of pickled pelt

A combination chrome tanning technology which endows leather high chrome exhaustion and thermal property based on hydroxyl-terminated dendrimer (HTD) is reported. The chrome concentration in effluent, denaturation temperature (Td), enthalpy (ΔH), thermal degradation active energy (Ea), crosslinking degree of wet-blue leathers are determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES), differential scanning calorimetry (DSC), thermal gravimetry analysis (TG-DTG), and X-ray diffraction (XRD), respectively. The element (especially chromium) content and distribution of wet-blue leather are also obtained by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). The results show that the chrome uptake, Td, ΔH and Ea of wet-blue leather tanned with HTD and basic chrome sulphate (HTD-Cr) can reach 94.1%, 117.4 °C and 432.2 J/g, and 153.1 kJ/mol much higher than conventional chrome tanning which is 66.1%, 112.5 °C and 129.2 J/g and 147.2 kJ/mol, respectively. It is because HTD could act as excellent masking agent with good alkaline stability, which slows down the basifying process and promotes chrome penetration towards central of wet-blue leather, resulting in evenly dispersed along the grain layer, middle layer and flesh layer of wet-blue leather. Consequently, crosslinking density of collagen increased, thereby inhibiting the outward diffusion of chrome and improving the chrome uptake. In contrast, for blank trial, the chrome mainly aggregate at grain layer and flesh layer. These results illustrate the chrome tanning promotion mechanism of HTD and provide a valuable insight of developing high exhausted chrome agent based on dendrimer for more sustainable future of leather industry.