Preparation, Structure, Properties And Application Of Cr(â…¢)-fe(â…¢) Heterocomplex Tanning Agent

Among so many leather tanning agents, the metal complex tanning agents hold an extremely important post. Up to now, the applied and studied metal complex tanning agents are mainly the chrome complex tanning agents, aluminum complex tanning agents, zirconium complex tanning agents, titanium complex tanning agents, ferrite complex tanning agents, and rare earth complex tanning agents. In the current industrialized tannage, there is no doubt that the chrome tanning agent is standing the leading position in the metal complex tanning agents. The secondary position is occupied by the aluminum tanning agent which has widely been used in the tanning. The following are zirconium tanning agent and titanium tanning agent. However, the ferrite tanning agent has drawn the great controversy. The effects of the tanning property of the tanning agents on the environment and human health will decide the future of the tanning agents. The present complex theory and practice have proved that the tanning property of Cr³⁺ complex tanning agent is superior to that of the other metal complex tanning agents. Chrome, as an element in short supply and the top contaminated heavy metal, will be less or no in the leather tannage, which has become the orientation for leather tannage. Among the few inorganic salines as the tanning agents, ferric salt is the only metal tanning agent without any contamination. Due to the obvious faults existing in the ferrite tanned leather, it is very difficult for the sole ferrite tannage to be industrialized widely. As the reinforcement of environment protection increasingly, ferrite tanning method, as an environment friendly tanning method, has its own special advantages and development potentials. The adoption of chrome ferrite complex tannage is practical and significant.This task study includes five aspects: (1) The valence bond theory, ligand field theory and the molecular orbital theory were used to compare and analyze the characteristics of chrome, ferrite, aluminum and zirconium complexes as the leather tanning agents. This provided the theoretical base leading the study on chrome-ferrite Heterocomplex tanning agents.(2) Using sodium citrate and hsodium tartrate as the representatives of masking agent and bridging agnet for metal complex, the ultraviolet visible spectrophotometry, infrared spectrometry and X-ray powder diffraction method were used to study the masking agent which had the bridging function on forming chrome-ferrite Heterocomplex in the chrome complex and ferrite complex solution systems.(3) By comparing the ligand stable constants of different ligands on Fe³⁺ and Fe2+, this task analyzed that the ligands had some effects on the oxidation-reduciton stability of Fe³⁺/Fe2+, which provided the theoretical evidence to solve the issue of ageing resistance performing in the ferrite tanning leather, and to select masking agent and tanning methods. By pH potentiometric titration, the hydrolysis processes of chrome-ferrite complex, chrome complex and ferrite complex were all observed different. This task compared and studied the ligand of sodium tartrate and sodium citrate had some influences on the alkali-resistance stability of chrome complex, ferrite complex and chrome-ferrite complex. (4) By orthogonal experiment, homogeneity test, range analysis, variance analysis and regression analysis, when the chrome chrome shavings, as the reducing agent, was used to prepare the chrome tanning agent, the amounts of sulphuric acid and the chrome shavings, the reaction time and temperature had the regular effects on the bichromate reduction rate and the alkalinity of the as-prepared chrome tanning agent. All these were set the patterns. Basing on the above-mentioned, the chrome shavings and ferrous sulfate were studied to use used to as the reducing agents, the two-step method was to reduce and synthesize the chrome-ferrite heterocomplex tanning agent. The potentiometric titration, infrared visible spectrum analysis and ions transferring resin separating methods were used to observe the stability, structure and composition of the prepared chrome-ferrite heterocomplex tannign agents. The adoption of the different ageing methods, DSC analysis and the physical and mechanical properties testing were to compare the heat-resistance air ageing, humid ageing, thermal-oxide ageing, thermal stability and physical and mechanical properties of chrome-ferrite tanning agents with those of the ordinary chrome tanning agent and ferrous sulfate tanning leather. The atomic absorption sepctrophotometry and Kjeldahl method were used to test and compare the chrome amount and nitrogen amount in the tanning waste liquid of the novel chrome-ferrite tanning agents. (5) In this study, the self-made chrome-ferrite heterocaryosis complex tanning agents were used to combine and tan with the ten extracts, such as wattle bark, larch, quebracho, chestnut, valonex, tara, sumach, red bayberry, teakwood, and acacia rachi bark and to explore the possibility of chrome-ferrite-vegetable combined tannage and dyeing integration. The computer software of testing and color matching and spectrumphotometer were used to analyze the reflectivity curve and K/S curve of chrome-ferrite-vegetable combined tannage crust to the visible spectrum. The standard method was to test the color fastness of the crust, and observe the heat resistance air ageing, humid ageing, thermal oxide resistance ageing and ultraviolet resistance ageing of the crust. The chrome-ferrite combined tannage technique was optimized. XRPS analysis was used to compare the distribution characteristics of chrome and ferrite elements in the chrome-ferrite-vegetable tanning leather and chrome-ferrite-vegetable tanned leather. DSC analysis was used to compare the heat resistance stability differences of chrome-ferrite tanned leather, chrome-ferrite-vegetable tanned leather the combined tanned leather introducing different synthetic tanned agent and resin tanning agent. FESEM was used to analyze and compare the structure changes and fibril state of the collagen protein under the conditions of difference tanning agents existing. In order to explore the reaction characters of tanning agent and the collagen in the chrome-ferrite-vegetable combined tannage, ultra-violet visible spectrophotometry and infrared spectrum analysis were used to analyze the spectrum characteristics of chrome tanning agent, ferrite tanning agent, chestnut extract, and the components of two of them combination and three of them combination, and to analze the absorption characteristics of the two components of chrome, ferrite and gallic acid solution, three components of them and the powder. The gravimetric method was used to study the reactivity of the different tannig agents and the collagen in the chrome-ferrite-vegetable combined tanning, including eurelon as the collagen amidogent simulator and the cotton cloth as the collagen hydroxyl simulator. By simulating chrome tannage, ferrite tannage, vegetable tannage and their combined tannage, the reactivity of various tanning agents and amidogent and hydroxyl was analyzed. The same methods were used to analyze the reactivity of different tanning agents, deamino hide powder, esterified hide powder and the normal hide powder so as to reveal hthe reactivity of tanning agents and the collagen in the chrome-ferrite-vegetable tannage.After the above study, the conclusion is as follows:(1) H2O, Cl^- and SO₄^2- couldn't have any effects on the electrode potential in Fe³⁺/Fe²⁺ oxidation and reduction. The ligands among OH-, tartaric acid, citric acid, oxalic acid, amino propoinic acid, aminoacetic acid, salicylic acid, sulfosalicylic acid, EDTA (ethylenediamine tetra-acetic acid, resorcin, gallic acid and glucurionic acid had raised greatly the stability of Fe³⁺/Fe²⁺ oxidation and reduction. Their ligands also offered some help for increasing the ageing resistance of ferrite tanned leather.(2)Citric acid and sodium tartaric acid might produce the bridging function between Cr³⁺-Fe³⁺ metal ions so as to form Cr³⁺-Fe³⁺heterocomplex. After ligand, the masking agent made the ligand field where the water molecule liganded with the meal ions changed a lot. The OH- concentration was needed by the water molecule in the inner world when hydrolysis became multiplied. Compared with sodium citric acid-Cr³⁺-Fe³⁺ system, the sodium tartaric acid changed greatly the ligand field of Cr³⁺-Fe³⁺ metal ions so as to let Cr³⁺ and Fe³⁺ have the great possibility to form the hetero-multinuclear complex.(3)As the reducing agent to prepare the chrome tanning agent, the chrome shavings possessed the better repeatability. In a certain range, the amounts of sulphuric acid and chrome shavings, the reaction time and the alkalinity of chrome tanning agent, and the reduction rate of chrome shavings to Cr6+ all had the linear relationship. Using chrome chrome shavings and ferrous sulfate as the reducing agent, the two-step method was used to reduce and prepare the chrome-ferrite heterocomplex tanning agent. The fixed synthetic reaction temperature was 95oC and the time was 120 min. to some extent, adjusting the amounts of sulphuric acid and chrome shavings could reach the purpose that the alkalinity of tanning agents was controlled exactly. The reaction repeatability was better. For the tanning agent with Cr : Fe = 2 : 1, the masking agent with oxide : sodium tartaric acid : sodium citric acid = 1 : 0.43 : 0.11 had a very good complexing effect. The acid radical of the masking agent as the relay radical, could form the chrome-ferrite heterocomplex, which was helpful for the synergistic effect producing between chrome-ferrite complexs. (4)The self-made chrome-ferrite heterocomplex tanning agent and vegetable tanning agent combined tannage could realize the integration of black, brown leather tannage and dyeing so as to decrease the amounts of dyestuff or dispense the dyeing process of the synthesizing dyestuff and decrease the dosage of chrome salt appropriately. If chestnut-chrome-ferrite combined tannage was adopted, the amount of chestnut extract was 5%. The amount of chrome-ferrite tanning agent converting chromic oxide was 1.5% 1.8%. The ferric oxide was 0.7%. The curst showed pure black. The contraction temperature could reach over 100 oC. The feel was full and soft. The grain was fine. The color fastness was better. The comprehensive index by the first vegetable tanning and then chrome–ferrite tanning crust was superior to that of the first chrome–ferrite tannign and then vegetable tanning crust. When the wet blue was tanned by vegetable retanning, the ferric salt coloration didn't change the traditional process and was easy to be accepted by the enterprises. The vegetable extract might involve the ligand between chrome and ferrite. In the vegetable-chrome-ferrite combined tannage, the chrome complex, the ferrite complex and chrome-ferrite heterocomplex all possessed some combination with vegetable tannin. This combination would produce the better synergistic effect to tannage. The vegetable tanning agent had no selectivity to the active perssad radical in the collagen. The chrome and ferrite metal complex tanning agents mainly combined with the carboxyl in the collagen. Therefore, the first vegetable tanning and then metal tanning agent tanning could increase the total combined amount of tanning agents.