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

Aromatic polyimide (PI) is characterized by rigid chains and strong interchain interactions, resulting in poor solubility and non-melting of polymers, so chemical recovery of PI is challenging. Herein, ethylenediamine (EDA) was successfully used for the aminolysis of PI on the surface of flexible printed circuit boards (FPCBs). The PI can be completely degraded at 50 °C for 40 min at a revolution speed of 200 rpm, and the epoxy adhesive and flexible copper clad laminate sheet were separated by simple filtration. The degradation mechanism of PI was proposed and verified by the density functional theory (DFT) method. Intermolecular hydrogen bonding and the vicinal amino moiety of EDA play an important role in activating nucleophiles. DFT calculations show that the formation of the six-membered ring transition state is the rate-determining step during the breaking of the amide bonds. The Gibbs activation energy and the Gibbs reaction energy are 22.90 and 11.73 kcal/mol, respectively. This study provides guidance for the degradation of PI and the recovery of FPCBs.