Preparation of Nontoxic Biodegradable Packaging Materials from Hazardous Leather Shaving Dusts Using Poly(Vinyl Alcohol)

The tanning industry contributes heavily to environmental issues because it produces a large amount of solid waste during processing. Chrome-tanned shaving dust is a type of waste discharged when chrome-tanned leather hides are shaved or buffed. This waste is very harmful to the environment, because it contains chromium compounds. This study aimed to develop a waste valorization strategy in the leather sector, focusing on detoxifying shaving dust and producing biodegradable plastic films. The optimized dechroming conditions, achieved through response surface methodology (RSM), resulted in an impressive 99.98% chromium removal with parameters set at a 5% alkali concentration and 18 h of stirring. Following the dechroming process, collagen extraction was carried out via hydrolysis in an autoclave, yielding 34.6% collagen containing 4.08% hydroxyproline. Subsequently, the preparation of bioplastic films was undertaken using poly(vinyl alcohol) (PVA), citric acid (CA), and chitosan. The bioplastic films were subjected to comprehensive characterization, including FT-IR, thermogravimetric analysis (TGA), water swelling, tensile testing, contact angle measurement, transparency assessment, field emission scanning electron microscopy (FE-SEM) analysis for surface morphology, evaluation of antimicrobial properties, and cytotoxicity testing, to assess their suitability as packaging materials. The film prepared with 30% citric acid exhibited better mechanical properties and underwent thermal cross-linking through heating (80–120 °C) to enhance stability and further improve its physico-mechanical, thermal, antimicrobial, and nontoxic properties. It was observed that the incorporation of collagen enhanced water stability by approximately 75% and significantly increased the tensile strength by approximately 215%, highlighting the importance of adding collagen. The bioplastic film (P4) cross-linked by 120 °C exhibited high water resistance, with only 43.8% solubility after 24 h of swelling in water, a contact angle of 111.2°, a tensile strength of 11.02 MPa, and approximately 295% elongation. These properties surpassed those of non-thermally crosslinked bioplastics, which exhibited 67% solubility, a 66.32° contact angle, 5.35 MPa tensile strength, and 179% elongation. The crosslinked bioplastics also demonstrated antibacterial properties, with 23 and 30 mm zones of inhibition against E. coli and B. subtilis, respectively. Moreover, they exhibited nontoxicity, with over 95% survival of Vero cells, making them suitable for potential applications in food packaging, although transparency decreased slightly compared to that of non-crosslinked film. Chromium recovered from the hydrolysis solution was efficiently utilized in the rechroming process for crust leather preparation. Finished leather from recycled chromium sulfate exhibited properties comparable to those of fresh basic chrome sulfate-rechromed leather. The findings of this study demonstrated the feasibility and effectiveness of implementing circular economy principles in the leather industry, offering a holistic solution to environmental pollution through waste valorization and resource utilization.