Preparation And Application Of Surfaced-Functionalized Nano-SiO₂/Polymer Nanocomposite Tanning Agents

Chrome tanning method is one of the most widely used methods of traditional leather industry,which brings good performance to leather.However,the low absorption rate of chrome tanning agents leads to the waste of heavy metal resources and serious environmental pollution,which restricts the sustainable development of the leather industry.In this study,nanomaterial and nanotechnology are indroduced into the traditional leather industry.A series of inorganic/polymer nanocomposite tanning agents were prepared.The nanocomposite tanning agents improve the hydrothermal stability of tanned leather and reduce the chrome usage evidently.Meanwhile,the excellent physical-mechanical properties of tanned leather are also obtained.The main conclusions are listed as follows:1.Preparation and application of a series of SiO₂/PMAAS nanocomposite tanning agentsDispersible and spherical silica nanoparticles?nano-SiO₂?were prepared with tetraethyl silicate and various surface-modifiers via a simple method.The silica nanoparticles surface-modified with methacryloxy?propyl?trimethoxysilane?denoted as MPS?,dimethyl diallyl ammoniumchloride?denoted as DMDAAC?and polymethylacrylic acid?denoted as PMAA?also known as hydrobic,amphiphilic and hydrophilic modifiers respectively were dispersed in different solvents and polymer matrix and found excellent dispersibility.The obtained MPS-SiO₂,DMDAAC-SiO₂,PMAA-SiO₂ and bare SiO₂ spherical nanoparticles were compared and characterized by Fourier transform infrared spectra?FTIR?,thermogravimetric analysis?TGA?,transmission electron microscope?TEM?and scanning electron microscope?SEM?.Then,a series of nanocomposites?denoted as SiO₂/PMAAS,MPS-SiO₂/PMAAS,DMDAAC-SiO₂/PMAAS and PMAA-SiO₂/PMAAS?were also prepared with the bare or surface-modified silica nanoparticles and a methylacrylic acid-acrylamide-acrylonitrile-salicylic acid tetrabasic copolymer?denoted as PMAAS?and applied in leather tanning.As a result,the physical and mechanical properties,rheological properties and thermal abilities of the leather treated with SiO₂/P,MPS-SiO₂/P,DMDAAC-SiO₂/P and PMAA-SiO₂/P nanocomposite tanning agents are found to be improved in a significant way.Compared with those of leather tanned with the commercial acrylic resin tanning agent?CHINATAN OM?and the synthesized pure tetrabasic copolymer tanning agent,the highest shrinkage temperature of the white wet sheepskin tanned with PMAA-SiO₂/P reaches 76 oC and the thickness increase reaches105%.2.Preparation and application of PASP-K-SiO₂/PAA nanocomposite tanning agentsThe spherical silica nanoparticles?denoted as PASP-K-SiO₂?were firstly prepared with 3-aminopropyltriethoxy silane?KH550?and polyaspartic acid?PASP?as surface-modifiers by sol-gel method.The obtained spherical nano-SiO₂ was well dispersed in water and then compounded with waterborne acrylic resin matrix?denoted as PAA?for preparing a novel nanocomposite tanning agent?denoted as PASP-K-SiO₂/PAA?successfully through a strong mechanical blending.The nanocomposite tanning agent was used to tan pickling white-wet sheepskin.The properties of the tanned leather were characterized by rheological measurements and revealed an evident increase in the storage modulus of the tanned leather compared to those of the leather tanned with PAA.The leather with the addition of PASP-K-SiO₂ nanoparticles also exhibits excellent mechanical properties,high thermal stability and chromium absorption rate.Moreover,the shrinkage temperature of the leather tanned with PASP-K-SiO₂/PAA compounding just 0.2% chromium powder based on the sheepskin weight can reach above 80 oC,which is potentially advantageous in completely replacing or partially replacing toxic chromium tanning agents in traditional leather industry.3.Preparation and application of PEI-SiO₂/Tannin nanocomposite tanning agentsThe spherical superhydrophilic silica nanoparticles?denoted as PEI-SiO₂?were prepared with polyethyleneimine?denoted as PEI?.The obtained spherical nano-SiO₂ was well dispersed in water and then compounded with condensed tannins for preparing novel nanocomposite tanning agents?denoted as PEI-SiO₂/T?through a strong physical blending.The nanocomposite tanning agents were used to tan pickling white-wet sheepskin and the rheological properties of the tanned leather were also measured.The leather with the addition of PEI-SiO₂ nanoparticles exhibits excellent mechanical properties and rheological properties.In addition,the highest shrinkage temperature of the white wet sheepskin tanned with PEI-SiO₂/T reaches 84.7 oC and the thickness increase reacheds 247 %,which meets the requirements for the practiced useage of leather without chrome tanning.