Researches on utilization of supercritical fluid technology in vegetable tanning process

The aim of the first part of the thesis was to optimize the extraction parameters of tannins from the acorns by Response Surface Methodology (RSM) and Box-Behnken Design (BBD), and to examine the tanning properties of the tannins produced in optimum parameters. Experiments were planned to evaluate the effect of solvent/feed ratio (20-100 ml/g), time (2-10 h) and solvent mixture ratio (methanol-water) (0-100%) on extraction yield (%), tannin content (%) and total tannin amount (g) of the valonea tannin. The results were examined via 3D response surface plots. Valonea tannin obtained under optimum conditions was also applied to tanning process, and filling coefficient (%) of the tanning and shrinkage temperature (Ts) of the leathers were evaluated by comparing the commercial valonea. Optimum extraction parameters were elicited as 100 ml/g for solvent/feed ratio, 6 hours of process duration and solvent mixture ratio of 62% methanol-38% water. The filling coefficient of the leathers tanned with extracted valonea (57.81%) in optimum conditions and the shrinkage temperature (75.5 oC) was superior to the commercial valonea (52.83%, 73 oC). This shows the significant impact of process optimization. The obtained results prove that the tanning properties of the extracted valonea were satisfactory for the vegetable tanning. In the second part of the study, the effect of the parameters of H2O/CO2 and H2O/CH3OH/CO2 as solvent variables of binary and ternary systems, solvent/feed (S/F) ratio (20 to 100 w/w), time (2 to 3 h) and pressure (10 bar to 200 bar) in subcritical and supercritical CO2 at 80 oC were researched for the production of valonea tannin from the acorn cups of the oak tree by pressurized fluid extraction (PFE) method. Phenolic contents (PCs) (total PCs, non-tanning PCs, tanning PCs) (wt%) of the valonea tannins were examined after PFEs. The results were statistically evaluated by the analysis of variance (ANOVA) and Duncan test, and the differences between the tanning PCs of valonea tannin were focused as the main response for optimization. The best yield of tanning PC (34.73±0.02wt%) was obtained by H2O/CO2 binary solvent system under the conditions of S/F=100 (w/w) at 100 bar for 3 hours with supercritical CO2. Phase equilibria of H2O/CH3OH/CO2 ternary system with different solvent fractions and at different temperatures and pressures were also imaged in the high pressure view cell for the PFE studies. The system showed liquid-liquid-vapor (LLV) phase behavior for all ratios of H2O and CH3OH at 60 oC to 100 oC and 60 to 250 bar with subcritical and supercritical CO2. Third part of the thesis includes the high pressure tanning (HPT) of sheepskins with valonea tannin in supercritical CO2 and aims to examine the diffusion process through the porous skin matrix. % uptake of vegetable tanning agent (VTA) was analyzed for different high pressure vegetable tanning times (2 h to 8 h). Shrinkage temperature (Ts) as thermal stability of the tanned collagen and filling coefficient (%) of pressurized vegetable tanning (PVT) applications on the leathers were also comparatively analyzed. The results showed that vegetable tanning under pressure was successfully carried out for each tanning time and 83.77±0.77% of VTA uptake was obtained for 8 h HPT. PVT experiments showed a satisfactory conversion of the skins to leather and 54.97±0.62% filling coefficient was obtained by 8 h PVT. Scanning electron microscopy (SEM) analysis of the tanned skins has been performed which shows that fiber structure and morphology are not negatively affected by the use of high pressure. Digital microscope views also show the filling coefficient of high pressure tanning application on the skins. The results obtained from high pressure tanning studies were found as highly promsing in terms of the use of supercritical fluid technology in vegetable tanning process for leather industry.