Understanding the self-polymerization mechanism of dopamine by molecular simulation and applying dopamine surface modification to improve the interfacial adhesion of polyimide fibers with epoxy resin matrix

The object of this paper is to interpret the self-polymerization mechanism of dopamine by molecular simulation and use dopamine polymerization to modify the surface properties of polyimide fibers for improving its interfacial adhesion strength with the epoxy resin matrix. Theoretically, the molecular simulation results of calculated energy band gaps and infrared spectrum of the intermediate products generated in the dopamine self-polymerization process confirmed that the spontaneity of self-polymerization of dopamine and the occurrence of intramolecular cyclization and intermolecular polymerization in the self-polymerization process of dopamine. Moreover, the interaction between polyimide and poly(dopamine) was simulated, and the calculated results showed that the interaction between them depended on hydrogen bonding and was verified by ultrasound treatment. Experimentally, the effect of dopamine treatment concentration on the surface properties of polyimide fibers was investigated. Obviously, after a relatively high dopamine concentration treatment, the surface roughness and surface energy of polyimide fibers were largely improved and the number of active groups on polyimide fibers surface were increased, which were altogether conducive to enhance the adhesion strength of polyimide fibers with the epoxy resin matrix.

Preparation of R-BABP Polyimide Fibers via Wet Spinning of Polyamide Acid

A polyamide acid (PAA) based on diamine 4,4'-bis (4-aminophenoxy) diphenyl and 1,3-bis (3',4-dicarboxyphenoxy) benzene dianhydride was synthesized. PAA fibers were obtained by wet spinning. Then, these fibers were converted into polyimide by thermal imidization. Dependence of the structure and properties of fibers on the die drawing and the composition of the coagulation bath was studied. It is shown that the composition of the coagulation bath has a significant effect on the morphology and mechanical properties of polyimide (PI) fibers. To obtain defect-free fibers, a coagulation bath consisting of ethylene glycol/ethanol at 50/50 vol. % was found to be optimal. An increase in the die drawing of fibers from 1 to 2 times leads to an increase in tensile strength and strain at break of the polyimide fibers.