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Understanding accessibility and interactions of clay nanoparticles with collagen fibers is an important fundamental issue for the conversion of collagen to leather matrix. In this study, we have investigated the diffusion and binding of Laponite into the collagen fiber network. Our results indicate that the diffusion behaviors of Laponite into the collagen exhibit the Langmuir adsorption, verifying its affinity for collagen. The introduction of Laponite leads to a shift in the isoelectric point of collagen from ∼6.8 to ∼4.5, indicating the ionic bonding between the positively charged amino groups of the collagen and negatively charged Laponite under the tanning conditions. Fluorescence microscopy, atomic force microscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and wide-angle X-ray diffraction analyses reveal that Laponite nanoparticles can penetrate into collagen microstructure and evenly distributed onto collagen fibrils, not altering native D-periodic banding patterns of collagen fibrils. Attenuated total reflectance-Fourier transform infrared and Raman spectroscopy detections further demonstrate the presence of noncovalent interactions, namely, ionic and hydrogen bonding, between Laponite and collagen. These findings provide a theoretical basis for the use of Laponite as an emerging tanning agent in leather manufacture.

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In this work, a novel eco-friendly wet-white tanning approach based on tetrakis­(hydroxymethyl) phosphonium sulfate (THPS) and synthetic Laponite clay nanoparticles has been developed to reduce potential HCHO risk as well as to improve leather performances. Our results indicate that the hydrothermal stability enhancement of the leather and the HCHO release are closely related to the dosage of THPS and final float pH in the THPS-based wet-white tanning process. The introduction of Laponite can cause distinct increase in shrinkage temperature (T s) of the combination tanned leather and reduced HCHO contents, implying the presence of synergistic effects between THPS and Laponite. The wet-white tanning system of 2.5% THPS combined 3% Laponite by two-bath method at final pH ∼4.5 is thus optimized, conferring the leather with a T s above 85 °C. Laponite clay nanoplatelets can be evenly bound between collagen fibrils without altering the native D-periodic banding patterns. Moreover, the novel combination tanning not only improves yellowing resistance and lightfastness but also enhances strength properties of the wet-white leather. These findings provide a potential application of Laponite to meet growing demands for reasonable tanning materials and related technologies toward eco-friendly leather manufacture.

This paper presents the comprehensive evaluation results of physical and environmental performances for a novel wet-white (chrome-free) leather manufacturing. The tanning process is optimized as 15 wt% tannic acid (TA) combination with 4 wt% Laponite nanoclay, giving the leather with shrinkage temperature (Ts) above 86 °C. Inductively coupled plasma-atomic emission spectrometry (ICP-AES) measurements indicate that Laponite can be evenly and tightly bound within the leather matrix, which is further confirmed by scanning electron microscopy and energy dispersive X-ray (SEM-EDX) spectroscopy analysis. The resultant wet-white leathers have reasonable good physical properties that can meet the standard requirements for furniture leather without containing hazardous Cr(VI) and formaldehyde. Further life cycle assessment (LCA) studies shows that tanning process is the main contributor to environmental impact categories in the wet-white tanning process, and tannic acid is the most significant substance factor. Compared to conventional chrome tanning, the wet-white tanning process exhibits much lower abiotic depletion potential (ADP), and reduced global warming potential (GWP) and human toxicity potential (HTP) impacts due to the nature of vegetable tanning; whereas, GWP excluding biogenic carbon and energy consumption are higher owing to prolonged run time.Peer ReviewedPostprint (published version