Bubble Wall Rupture Model for Open Cell Structure in Starch/Fiber Heterogeneous Composites

Starch/fiber heterogeneous composites were prepared through thermos-cavity foaming machine. Open cell structures are widely distributed in the heterogeneous composites. Bubble wall rupture is an inevitable stage in the formation of open cells. Different from the conventional models to explain the bubble wall rupture from the energy and the wave point of view, this study suggests the local thinning ultimate stress model to reveal the bubble wall rupture from the stress perspective. The local stress of the starch bubble wall is increased with the thinning of the bubble wall. The bubble wall ruptures when local stress exceeds the ultimate surface tension. Starch slurry retraction occurs after bubble wall rupturing. The elastic retraction drives partially open cells to fully open cell morphologies in the starch/fiber heterogeneous composite. The developed mechanism was validated by starch/fiber slurry with different viscosities to design a novel biodegradable composite with fully open cell structures.