Enabling simultaneous reprocessability and fire protection via incorporation of phosphine oxide monomer in epoxy vitrimer
Zhenyu Huang, Wenyu Wu, Daniele Roncucci, Carolina Polisi, Valentin Rougier, Sandro Lehner, Milijana Jović, Daniel Rentsch, Sithiprumnea Dul, Karin Brändli Hedlund, Véronique Michaud, Zhengzhou Wang, Sabyasachi Gaan
Abstract
The conception of epoxy thermosets with both reprocessability and flame retardancy delineates a new horizon in polymer science, offering a material solution that is not only superior in fire safety but is also environment friendly. Herein, a flame-retardant epoxy vitrimer (EV) was prepared using partially bio-based IADPPO (diphenylphosphine oxide itaconic anhydride) and citric acid as curing reagents via a solvent-free process. Their incorporation created covalent adaptable networks (CANs) in the matrix which promote reprocessability and recyclability. The EV exhibits excellent thermal stability with high initial decomposition temperature (T-5wt% ∼308°C) and high glass transition temperature (Tg ∼107°C), similar to the blank EV (115°C). The flame retardancy, mechanical properties, transesterification-based reprocessability, and flame-retardant mechanism were investigated. The EV containing 3 wt% phosphorus (EV IADPPO 3P) achieved UL-94 V0 classification with a limiting oxygen index (LOI) of 27 %, while the virgin sample Blank EV (without phosphorus) burned completely. Additionally, increased flexural strength of 79 % was observed for EV IADPPO 3P compared to Blank EV. Furthermore, the flame-retardant EV showed high malleability and reparability that could be thermomechanically reprocessed without sacrificing the thermal, mechanical, and flame-retardant properties. Thus, the newly developed epoxy vitrimer is not only fire-safe but fulfills the sustainability goals of today's society.