Abstract
Silicic acid, commonly derived from cheap and easily available sodium silicate, has recently received great attention for application in leather industry to produce ecological leather with a cleaner approach. However, leather tanned with silicic acid alone is poor in storage stability, which limits its practical application in leather production. In this work, a new environment-friendly combination tannage based on silicic acid and plant tannin was developed to address this issue along with improving the comprehensive performances of leather. The obtained leather was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and so on. The results showed that compared with leather tanned with silicic acid alone, the leather tanned with this combination method possessed improved thermal stability, enhanced mechanical properties, acceptable softness, appropriate hydrophilicity, and especially enhanced storage stability. More importantly, the combination tanned leather with 1:1 of the mass ratio of silicic acid to vegetable tannin (composed of valonea extract and mimosa extract with the same weight) had more prominent comprehensive performances. In addition, the results demonstrated that hydrogen bonding played an important role in the combination tanning process. Furthermore, the hydrogen bonds generated between phenolic hydroxyl groups of polyphenols with silicon hydroxyl groups of silicic acid molecules inhibited the excessive condensation of Si-OH groups between themselves. Subsequently, the assessment of environmental impact revealed the value of BOD5/COD of the wastewater produced in this combination tanning process is more than 0.3, indicating the chrome-free combination tannage based on silicic acid and plant tannin was an environment-friendly tanning technology. These findings therefore indicated that a new chrome-free tanning method with silicon and biomass materials as main tanning agents has potential practical application prospect in leather production.Graphical abstract
Highlights
The leather industry plays an important role in our daily life
We found that hydrogen bonds between silicon hydroxyl groups of silicic acid and amino groups of collagen fiber play an important role in tanning process, which is consistent with vegetable tanning method to some extent [20]
The combination tanned leather was in possession of improved thermal stability, increased softness, acceptable hydrophilicity, appropriate micro-porous structure, and especially remarkable storage stability, due to the addition of vegetable tanning agent
Summary
The leather industry plays an important role in our daily life. And as an important industrial material product, leather is widely used in many fields, including shoes, clothing and furniture upholstery [1, 2]. Comprehensive properties of the leather are still insufficient, especially lacking enough softness and hydrophilicity, so it should be improved for further practical application It is still an impending requirement for leather industry to find an efficient chrome-free tanning technology that can alleviate the impact on the environment, accelerate sustainable development, and endow leather with acceptable comprehensive performances for practical application. We found that hydrogen bonds between silicon hydroxyl groups of silicic acid and amino groups of collagen fiber play an important role in tanning process, which is consistent with vegetable tanning method to some extent [20]. A chrome-free combination tanning method based on vegetable tanning agent and silicic acid was proposed. This study reported an environmental-friendly and effective combination tanning technology, which would further expand the application of silicon materials in leather tanning, and provide exciting opportunities to the sustainable development of the leather industry
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