Thermal expansion and shrinkage of epoxy foams during secondary heating

RELEVANCE. Epoxy foams produced by thermal expansion of polymer microspheres show promise as sandwich panel cores. During secondary heating of epoxy foams, significant shrinkage or thermal expansion may occur, depending on the foam composition. Research and prediction of these processes is necessary for the design of sandwich products with epoxy foam cores.
THE PURPOSE. To study the thermal expansion and shrinkage of epoxy foams during secondary heating. To estimate the pressure created in a confined tooling space due to expansion.
METHODS. Dynamic mechanical analysis was used to estimate the glass transition temperature of epoxy foams. The foaming process of microspheres was studied using thermomechanical analysis. Thermal expansion and shrinkage were assessed by measuring the linear dimensions and volume of the foam before and after heat treatment. The pressure during the thermal expansion of foam plastics was assessed using pressure sensors and recorded using the DiamonPlus dielectric composite molding process monitoring system (INASCO).
RESULTS. It was shown that secondary heating of epoxy foam plastics can cause shrinkage or expansion of the material depending on the microsphere content. Thermal expansion pressure increases with increasing foam plastic density.
CONCLUSIONS. The temperature conditions for secondary heat treatment were selected, and thermal expansion studies were conducted for epoxy foam plastics with different microsphere contents and initial densities. It was shown that the initial minimum foam density decreases, while the density after heat treatment increases with increasing microsphere concentration. With an increase in the initial foam plastic density at a constant microsphere concentration, the foam plastic density after heat treatment decreases. For foam plastics with a high initial density and a high microsphere content, anisotropy of expansion and contraction after heat treatment is observed.

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