Non-isothermal cold crystallization kinetics of leather polymer composites for additive manufacturing

Abstract The tannery industry generates substantial amounts of solid leather residues, posing environmental challenges due to their protein-rich composition and, in the case of tanned leather, heavy metal content like chromium, lead and cadmium. This study is part of a broader project aiming to valorise leather residues through the development of adapted formulations for different additive manufacturing (AM) techniques. Specifically, it focuses on investigating the cold crystallization behaviour of leather polymer composites (LPC) with a polylactic acid (PLA) matrix, intending to develop LPC filaments for fused filament fabrication, an AM technique. Two LPC formulations, LPC10 PLA and LPC15 PLA with 10% and 15% (in volume) of leather powder, respectively, were prepared. Differential scanning calorimetry assessed the cold crystallization behaviour at four different heating rates (2.5, 5, 7.5 and 10 °C min −1 ). The addition of leather particles accelerated the crystallization rate, resulting in well-defined exothermal peaks compared to neat PLA. Avrami, Ozawa and Liu’s kinetic models were employed, with Avrami and Liu’s models successfully describing the crystallization behaviour, while Ozawa’s method failed. Both models indicated a faster crystallization rate and the formation of three-dimensional crystalline structures in the presence of leather particles, suggesting their role as nucleating agents. Activation energy values determined by Friedman’s model, and polarized optical microscopy images also corroborate such behaviour. This research aims to demonstrate the potential for valorising leather residues through AM applications while revealing their crystallization behaviour. Graphical abstract