From leather wastes to leather: enhancement of low quality leather using collagen recovered from leather tanned wastes

Leather industry produces huge amounts of solid wastes. In the last decade, several methods for the recovery and valorization of these wastes were developed, mainly focused on the extraction of collagen using chemical methods. The extracted collagen, due to its poor quality, is mostly used in agriculture as a nitrogen source ingredient of fertilizers. This study aims to apply collagen, extracted from leather tanned solid wastes using a recently reported new process based on enzymatic hydrolysis, as filling agent for low quality leather. Thanks to the enzymatic hydrolysis, collagen can be extracted without affecting its integrity and, therefore, its quality. In order to use the extracted collagen as filler for low quality leather, an enzymatic mediated cross-linking reaction between collagen and casein was developed. The enzymatic cross-linking reaction was added as an additional phase of the re-tanning process or as a replacement of one of the re-tanning steps. To evaluate the filling effect, thickness of the treated leather was measured and infrared and microscopy analyses were performed, comparing the new methods to the traditional standard one. The mechanical properties of the filled leather were tested and the sensorial features, such as fullness and touch feelings, were estimated through a panel test. Results suggest the high potential of extracted collagen to be employed back in leather processing both as additive and as substitutive filler. Graphical abstract Aims and goals of the research study: comparison between re-designed (green workflow) and traditional re-tanning process (grey workflow).