The Study Of Tanning Performance Of Blocked Polyurethane Pre Polymer By Sodium Bisulfite To Collagen

The extensive use of chrome tanning agent in chrome tanning process easily was oxidized from Cr(III) to Cr(VI) which has carcinogenic and induce gene mutations by air, light, heat and others,because of it,leather production lost ecological performance and threaten people health.Over the last decade, green chemistry and technology have become one of the most hot issues and main direction of research for global tannery workers.This paper is based on the thermal and alkali catalysis deblocking mechanism of polyurethane blocked by sulphite,synthesized three kinds of blocked polyurethane prepolymer,which were small molecule polyol-IPDI prepolymer(SP-PCMS), polyethylene glycol-IPDI prepolymer (PEG-PCMS) and DMPA/TA-PCMS.The structure characteristic and thermodynamic performance were characterized by Fourier transform infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TG).SP-PCMS and PEG-PCMS were used as tanning agent to tan bated goat skin hide respectively,the tanning performance and process of this series of production were studied.the best tanning process was explored by single factor experiment and the result showed the best process was 8% dosage,35 ℃, tanning time was 120min and basifying end pH was 9.0 when the softened skin were tanned directly,and the Ts of crust is 73-76℃. In the series product of SP-PCMS, the crust had the highest shrinkage temperature tanned by the blocked pentaerythritol-IPDI prepolymers was 76℃ and it had the best thickening rate and mechanical properties. At the same time, it can be found that shrinkage temperature, thickening rate and physical and mechanical properties increased with functionality increasing. In the series product of PEG-PCMS, the crust had the highest shrinkage temperature tanned by the blocked PEG-2000-IPDI prepolymers was 76℃ and it had the best thickening rate and mechanical properties. In addition, the size of molecular had a great impact on leather properties. Small molecular had a strong permeability, but it had a weak crosslinking with collagen. Big molecular had a bad permeability, and it was easy to form surface tanned, and the tanned crust had a bad shrinkage temperature, thickening rate and physical and mechanical properties.D/T-PCMS was used as chrome tanning assistant due to it had carboxyl group that could combine with Cr. when bated hide was treated by it, the result showed it could restrain swelling degree in acidic solution(the pH is 2.8), and the degree of inhibition increased with it dosage. When the dosage was 1%,the crust had a different swelling degree in acidic solution of salt concentrations less than 5. When the dosage was 2%,the crust had a different swelling degree in acidic solution of salt concentrations less than 2. When the dosage was≥3%,the crust would not swell in acidic solution of free salt. So it could achieve salt-free/less pickling in after process. During the traditional pickling chrome process, tanning performance was studied in the circumstance of chrome agent was 6%. It could be found that crusts shrinkage temperature could increase to more than 113℃, the content of Cr2O3 in the wastewater could down to less 221.5 mg/L,and the assistant tanning effect increased with it dosage. In the salt-free pickling chrome tanning process, the D/T-PCMS dosage was 3%, the result showed that the crusts had a similar performance with conventional chrome crusts. But the absorption rate of chrome agent could increase to 91.8% and 92.8%, and the content of Cr2O3 dropped significantly, it was just one-eighth and one-ninth of traditional chrome tanning. The shrinkage temperature and thickening rate were increased with the dosage of chrome agent, but the absorption rate had a decreasing trend and the content of Cr2O3 in the wastewater has increased. In addition, it could be found by using Scanning electron microscope (SEM) that the grain of leather which dealt with D/T-PCMS were smoother, firmer and more carefully. So it can achieve the purpose of salt-free/less pickling and less chrome tanning when the bated skins dealt with these material,and it has a guiding reference to clean tanning theory and practice.