Composite Polymers from Leather Waste to Produce Smart Fertilizers

The leather industry is facing important environmental issues related to waste disposal. The waste generated during the tanning process is an important resource of protein (mainly collagen) which can be extracted and reused in different applications (e.g., medical, agricultural, leather industry). On the other side, the utilization of chemical fertilizers must be decreased because of the negative effects associated to an extensive use of conventional chemical fertilizers. This review presents current research trends, challenges and future perspectives with respect to the use of hide waste to produce composite polymers that are further transformed in smart fertilizers. Hide waste contains mostly protein (collagen that is a natural polymer), that is extracted to be used in the cross-linking with water soluble copolymers to obtain the hydrogels which are further valorised as smart fertilizers. Smart fertilizers are a new class of fertilizers which allow the controlled release of the nutrients in synchronization with the plant’s demands. Characteristics of hide and leather wastes are pointed out. The fabrication methods of smart fertilizers and the mechanisms for the nutrients release are extensively discussed. This novel method is in agreement with the circular economy concepts and solves, on one side, the problem of hide waste disposal, and on the other side produces smart fertilizers that can successfully replace conventional chemical fertilizers.

Effect of particle size of leather wastes on the processing, vulcanization, and physico-mechanical properties of natural rubber/leather wastes composites

In this work, the effect of particle size and the content of leather wastes on the processability, vulcanization, and mechanical properties of a natural rubber/leather wastes composites was studied. From a reduction process, leather waste was later sieved to classify particles smaller than 0.6 mm and particles between 0.84 and 2 mm, hereafter called fine and coarse residues, respectively. The morphology of the wastes was analyzed from scanning electron microscopy micrographs. Natural rubber/leather wastes composites with 20, 40, 60, 80, and 100 phr (parts per 100 parts of rubber) of treated leather wastes were obtained in a torque rheometer. Mixtures with coarse wastes exhibited a slightly higher torque than mixtures with the fine wastes; additionally, increasing the wastes content yields in an increased torque during the final stage of the process. The addition of leather wastes increased the vulcanization time and stiffness of the composites; additionally, materials with fine wastes showed lower vulcanization times compared to materials with coarse wastes. Composites with fine leather wastes exhibited higher density and tensile modulus than materials with coarse wastes; however, only the composites with 80 and 100 phr of wastes showed a statistically significant difference in hardness values. The specific energy consumption (SEC) was calculated from the results obtained with the torque rheometer; it was found that for all the formulations the SEC decreased as the phr of leather residues increased. It was found that it is possible to use leather wastes in natural rubber composites, to obtain adequate materials feasible for some applications.

Thermo-Mechanical and Morphological Properties of Polymer Composites Reinforced by Natural Fibers Derived from Wet Blue Leather Wastes: A Comparative Study

The present work investigated the possibility to use wet blue (WB) leather wastes as natural reinforcing fibers within different polymer matrices. After their preparation and characterization, WB fibers were melt-mixed at 10 wt.% with poly(lactic acid) (PLA), polyamide 12 (PA12), thermoplastic elastomer (TPE), and thermoplastic polyurethane (TPU), and the obtained samples were subjected to rheological, thermal, thermo-mechanical, and viscoelastic analyses. In parallel, morphological properties such as fiber distribution and dispersion, fiber–matrix adhesion, and fiber exfoliation phenomena were analyzed through a scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) to evaluate the relationship between the compounding process, mechanical responses, and morphological parameters. The PLA-based composite exhibited the best results since the Young modulus (+18%), tensile strength (+1.5%), impact (+10%), and creep (+5%) resistance were simultaneously enhanced by the addition of WB fibers, which were well dispersed and distributed in and significantly branched and interlocked with the polymer matrix. PA12- and TPU-based formulations showed a positive behavior (around +47% of the Young modulus and +40% of creep resistance) even if the not-optimal fiber–matrix adhesion and/or the poor de-fibration of WB slightly lowered the tensile strength and elongation at break. Finally, the TPE-based sample exhibited the worst performance because of the poor affinity between hydrophilic WB fibers and the hydrophobic polymer matrix.

Trash into Treasure: stiff, thermally insulating and highly conductive carbon aerogels from leather wastes for high-performance electromagnetic interference shielding

Humans have used animal leather materials for thousands of years. Nowadays, the disposal of Cr-containing leather wastes (LWs) has become an urgent problem. Herein, by adopting simultaneously conventional freeze-drying and...

Effect of processing temperatures on the thermal and mechanical properties of leather waste-ABS composites

The effect of varying processing temperatures (200, 220 and 240°C) on the thermal and mechanical properties of uncoated and epoxy-coated chrome-tanned leather wastes-ABS composites has been studied. The results obtained showed that the mechanical properties of the composites decreased as the processing temperature increased. Epoxy-coated leather wastes fibre-ABS (CLWABS) composite yielded better mechanical properties compared to the uncoated leather wastes-ABS composite (LWABS). These results were obtained at an optimized processing temperature of 200°C. Furthermore, the results were confirmed by the field emission scanning electron microscopy (FESEM) studies. The differential scanning calorimetry (DSC) studies revealed that the epoxy-coated leather wastes fibres (CLW) showed higher onset and melting temperatures of 131.8 and 179.35°C than the uncoated leather wastes fibres (LW) with glass transition (Tg) and melting (Tm) temperatures of 128.2 and 169.4°C, respectively. When the LW and CLW fibres were mixed with Acrylonitrile butadiene styrene (ABS), the Tg and Tm of CLWABS composite were found to be 94.9 and 269.8°C, respectively, higher than the LWABS composite with Tg and Tm of 89.1 and 261.6°C, respectively. Thus, this study has demonstrated that utilization of epoxy-coated chrome-tanned leather wastes fibres as fillers in the design of ABS-based composites will help a great deal in addressing the problem of solid waste pollutants in our environment.

Development of Sustainable Strategies for Leather Waste Management through Bacterial Remediation

A new Bacillus species has been isolated and used for treating chrome leather wastes. The activity of Bacillus species is evaluated for the degradability of the Chrome Leather Waste (CLW). An initial CLW substrate concentration at 0.5 and 1%, along with the bacterial strain is studied against the control sample without bacterial strain. The higher proteolytic enzyme production and hydroxyproline release in the CLW containing medium confirms the degradation process, whereas it is significantly less in control samples. The degradation profile of CLW shows higher in 1% CLW as compared to 0.5% CLW. In 1% CLW, the protease activity of the isolated strain has been increased from 1.615 to 5.625 U/mL. In addition to protease activity, the isolated strain also expressed chromate reductase activity. Furthermore, FTIR, TGA, and SEM studies confirm the degradation of leather wastes.