Investigation of surface tension and contact angles for effective polymer binders based on epoxy oligomers and active diluents

Objectives. This study focused on the quantification of the surface tension and the static and dynamic contact angles of epoxy oligomers, active diluents, and their mixtures of various compositions at different temperatures. The active diluents were aliphatic compounds based on glycidyl ethers, namely laproxides and a laprolate of different structure, functionality, molecular weight, and viscosity. Moreover, the preparation of effective polymer binders (matrices) for composites was explored.

Methods. In this study, the epoxy oligomers ED-20 and DER-330, laproxides 201B, DEG-1, E-181, and 703, laprolate 301, and their mixtures in various compositions were investigated. Their surface tension and the static and dynamic contact angles were determined by the Wilhelmy plate and ring methods on a semiautomatic tensiometer at different temperatures (20–60 °C). The static contact angle was measured on a thin aluminum borosilicate glass plate, and the dynamic contact angles were determined using an installation for measuring surface tension developed by NPO Stekloplastik.

Results. The surface tension and static and dynamic contact angles were obtained for all epoxy oligomers and active diluents, as well as for their mixtures at 20–60 °C. For binders based on systems of epoxy oligomers and active diluents, the impregnation rate of fiber reinforcement was also calculated. The introduction of laproxides or laprolates into the epoxy oligomers led to a decrease in surface tension and contact angles, while the increase in temperature increased the impregnation rate by 10–20 times.

Conclusions. The temperature increase from 20 to 60 °C resulted in a decrease in the surface tension of mixed systems of epoxy oligomers and active diluents by almost two times. In addition, the contact angles changed by only 4°–7°, while the impregnation was significantly improved and the corresponding rate increased by 10–20 times.

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