Principles of minimal wrecking and maximum separation of solid waste to innovate tanning industries and reduce their environmental impact: The case of paperboard manufacture

Solid leather waste can be considered as a composite material highly structured whose organization is intimately connected with the collagen fibers. Any process aimed at destroying such structure is economically and energetically disadvantageous. A more cost-effective approach therefore would be to reuse the solid leather waste avoiding the wrecking stage: Principle of Minimal Wrecking. The maximum efficiency of the method can be achieved if waste separation is so subtle that each waste becomes a homogeneous system, ie raw material for a new production: Principle of Maximum Separation. These general principles have been applied to handle to solid leather waste from a bovine leather industry manufacturing soles and uppers where the separation process has been refined up to post-tanning dyeing stage. The collagen fibers of leather waste were classified on the basis of length and their compatibility with cellulose was morphologically monitored via electronic microscopy and quantitatively analyzed via physical tests. The degree of compatibility was such that no chemical pretreatment of the material was required. Thereby several ternary systems consisting of mixed newspapers, newspapers and leather waste of long fibers at different composition, were prepared for simple mixing. For each formulation a paperboard type was manufactured whose mechanical performance was tested according to ISO recommendations. The system of composition 70% mixed newspapers, 15% newspapers and 15% leather waste with long collagen fibers, exhibited the best performances and the paperboard quality was comparable to one of boxes and packaging commercially used. In addition, release tests proved the complete absence of Cr(VI) in the material. Transforming solid leather waste into new raw material increases the life cycle of the material and drastically reduces its environmental impact.