Efficient Aminolysis of Polyimide for Chemical Recovery of Flexible Printed Circuit Boards

Aminolysis of polyimide on the surfaceof flexible printedcircuit boards was achieved using ethylenediamine under mild conditions. Aromaticpolyimide (PI) is characterized by rigid chains and stronginterchain interactions, resulting in poor solubility and non-meltingof polymers, so chemical recovery of PI is challenging. Herein, ethylenediamine(EDA) was successfully used for the aminolysis of PI on the surfaceof flexible printed circuit boards (FPCBs). The PI can be completelydegraded at 50 & DEG;C for 40 min at a revolution speed of 200 rpm,and the epoxy adhesive and flexible copper clad laminate sheet wereseparated by simple filtration. The degradation mechanism of PI wasproposed and verified by the density functional theory (DFT) method.Intermolecular hydrogen bonding and the vicinal amino moiety of EDAplay an important role in activating nucleophiles. DFT calculationsshow that the formation of the six-membered ring transition stateis the rate-determining step during the breaking of the amide bonds.The Gibbs activation energy and the Gibbs reaction energy are 22.90and 11.73 kcal/mol, respectively. This study provides guidance forthe degradation of PI and the recovery of FPCBs.