November 2019 Abstracts

Application of Nonionic Gemini Aliphatic Polyurethane Surfactant for Improving the Performance of Vegetable Tanned Leather

by Shuangquan Lai, Yong Jin, Liangjie Shi, Shenghua Wang and Heng Yang

Vegetable tanned leathers with good embossing, air permeability, natural look and pleasing firm handle properties have applied in many goods with multiple uses. However, the performances of vegetable tanned leathers still need a further improvement. In this work, a kind of nonionic gemini aliphatic polyurethane surfactants (GPUs) with different hydrophobic chain lengths as a retanning agent combined with polyacrylic acid (PAA) for condensed tannin tanned leathers to improve their performances. The effects of the alone or combined use of the PAA and GPU, the hydrophobic chain length of GPU, and the offer percentage of retanning agent were studied by evaluating the organoleptic properties, shrinkage temperature, mechanical properties of the obtained leathers. The best performance was found in the leather retanned with PAA and 12-GPU-550 complex retanning agent, and the mechanical properties of leather could be improved when the total offer percentage was controlled at 4 wt%. Moreover, the collagen fibers morphologies and lightfastness properties of leathers retanned with different retanning agents were investigated. The results showed that the total color difference ΔE and the yellowness index Δb decreased significantly with the introduction of 12-GPU-550, and the leather retanned with PAA and 12-GPU-550 complex retanning agent showed the lowest value of ΔE, demonstrating that the lightfastness properties were improved significantly. Therefore, it was an attractive way to combine use of PAA and 12-GPU-550 as complex retanning agent, which can improve the mechanical and lightfastness properties of vegetable tanned leathers simultaneously.

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Effect of Prepolymerization of Acrylic Acid Under High Gravity on the Properties of Acrylic Resin Retanning Agent

by Xin Shu, Weixing Xu, Bi Shi and Jian Zhou

The effects of prepolymerization of acrylic acid (AA) in rotating packed bed (RPB) on the molecular weight and molecular weight distribution of polyacrylic acid (PAA) were investigated. Results showed that, compared with conventional polymerization in stirred tank reactor (STR), the prepolymerization in RPB followed by polymerization in STR produced PAA with lower weight-average molecular weight (Mw) and polydispersity index (PDI). The Mw of PAA decreased with increasing rotational speed of RPB from 800 rpm to 1400 rpm. Therefore, the use of RPB might be an effective strategy to control the molecular weight and molecular weight distribution of PAA. For exploring the value of this technology in preparing PAA retanning agent, PAAs were synthesized by using STR (STR-PAA, Mw=476,615 Dal, PDI=3.36) and RPB (RPB-PAA, Mw=193,386-288,321 Dal, PDI=1.55-1.86), and their performances in retanning were evaluated. Results showed that RPB-PAAs with low Mw had high absorptivity in wet blue and achieved a good filling property for leather because they could permeate into numerous microstructures of collagen fiber network. As for RPB-PAAs, high PDI led to a satisfactory selective filling property. The fullness, mechanical property, isoelectric point, and dyeability of leather were also affected by PAAs with different Mw and PDI. This work demonstrated the considerable influences of the molecular weight and molecular weight distribution of PAA on retanning property. A method to control these parameters was also presented.

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Deep Treatment of Ammonia Nitrogen Tannery Wastewater by an Electro-Fenton System

by Hui Chen, Li-Wei Chen, Shu-Qing Li, Yao Hu, Zhi-Hua Shan, Rui Dai, and Jie Yi

The effect of an Electro-Fenton system on the deep treatment of ammonia nitrogen (NH3-N) and corresponding removal rate was investigated in this article. By using simulated ammonia nitrogen wastewater, it included a Cl- concentration of 3000 mg/L, SO42- concentration of 100 mg/L according to conventional leather wastewater conditions. Furthermore, Cl- and SO42- can be used as supporting electrolyte. After pretreatment, the ammonia nitrogen concentration kept about 100 mg/L. The optimal treatment conditions of Electro-Fenton system were obtained throughout single factors experiments. The current density was 150 A/m2, the reaction time was 30 min, the plate spacing distance was 40 mm, and the reaction temperature was adjusted to 40°C. After flocculation treatment of leather wastewater, the ammonia nitrogen concentration was 142.11 mg/L, and the tanning wastewater was further treated with an Electro-Fenton system. The final ammonia nitrogen concentration was 11.23 mg/L, which meets the first-level wastewater discharge standard. The removal rate was 92.10%, which indicated that the Electro-Fenton system is one kind of clean, feasible and sustainable treatment method for the deep treatment of ammonia nitrogen in tannery wastewater.

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High-efficiency Bio-degreasing Technology for Leather Making – Characterization of Catalytic Hydrolysis Properties of Lipases Towards Fats Based on Greasy Skin Powder Substrate

by Fengxiang Luo, Shan Li, Shencai Pan, Chunxian Zhang, Cai Huang and Biyu Peng

Bio-degreasing technology based on the use of lipases has attracted more attention in the leather industry. Although lipases have been applied in leather making in the past, the previously reported lipase degreasing ratio is still not very high, i.e. less than 60%. In order to correctly understand the mechanism of lipase degreasing and to choose lipases and optimize the degreasing process for achieving efficient degreasing, a novel method of evaluating the catalytic hydrolysis properties of lipases towards skin fats based on a greasy skin powder substrate in an aqueous medium was established. This simulated the actual leather degreasing process and detected the amount of fatty acids produced. The special substrate was prepared; the determination conditions were optimized; then the performances of several typical lipases were evaluated. The results revealed that the lipase performances determined by the novel method were quite different from the standard method using emulsified olive oil substrate. There was a strong product-inhibition characteristic in the catalytic hydrolysis reaction of lipase, and the inhibition concentration of fatty acids varied with the lipase type, thus the maximum hydrolysis ratio of fats was only 67%. The lipases exhibited “super-activity” at pH around 9.5. This occurred because the fatty acids produced transformed into soluble soaps, thus the product-inhibition was weakened. According to the above results, a two-step lipase processing was made, i.e., beginning at pH 7.5 then 9.5. The hydrolysis ratio of fats rose to 82.57% from 46.23%, and the degreasing ratio increased from 50.78% to 89.68%. The new method with better repeatability can be used as a tool to correctly select lipases and optimize process parameters for lipase degreasing.

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