Synthesis and characterization of elastomeric polyurea foam

Abstract

Polymeric foams are ubiquitous in impact mitigation for civilian and military applications; the performance in such loading scenarios can be elucidated through quasi‐static and dynamic mechanical testing. The present study reports on the complex microstructure of newly synthesized polyurea foams exhibiting a hierarchical structure consisting of large perforated semi‐closed spherical cells with a mean diameter of 370 ± 162 μm surrounded by smaller closed, spherical cells with size distribution of 69 ± 18 μm. The stress–strain curves were used to calculate the basic mechanical properties and to predict the dynamic behavior of the foams. Nonlinear regression and finite element analyses were used to calibrate the Ogden hyperfoam model to explicate the hyperelastic behavior. The performance of the polyurea foam was found to outperform a benchmark foam in nearly all the elastic and energy absorbing properties. For example, one variation of the newly synthesized foam stored nearly doubled the energy of the benchmark foam while being 12% lighter. Low‐density polyurea foam was found to decelerate an incoming impact mass with a minimum G‐level that was nearly one third lower than the higher density polyurea and benchmark foams. In all, the behavior of the foam is dependent on the parameters of the fabrication process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48839.

Characterization of Energy Absorption and Strain Rate Sensitivity of a Novel Elastomeric Polyurea Foam

“…As no heat‐activated nor vacuum‐initiated blowing agents are required to synthesize the foams in this work, the process performed here is considered a self‐foaming reaction. [ 10,11,27 ] The mass ratio of diisocyante to diamine was maintained at 1:4, while the dH 2 O was added at a ratio of 8:3 to the latter mixture. The mechanical mixing of these constituents resulted in a foam slurry with a pot life spanning between 3–5 min, i.e., short duration to transfer and shape the foam into the final geometry.…”

“…The weight ratio of the constituents and the poured‐weight can be adjusted to tune the density and, in turn, the foam properties, as discussed in previous studies. [ 10,11,27 ] The polyurea foam used in the following characterizations has a density of 227.3 ± 4.5 kg m −3 . Upon curing, cylindrical foam plugs were obtained using a ≈41 mm circular die‐cutter (Mayhew Pro 66 002) and a hydraulic press (K.R.…”

“…[ 3–9 ] Therefore, a foam with a hierarchical structure composed of regions of open‐cell and others of closed‐cell is optimal for improving the impact‐mitigation ability of structures to absorb the impact energy. [ 10,11 ] Nonetheless, regardless of the cell structure, the foam padding is required to lower the amplitude of the incoming force while broadening the peak of the force‐time history, hence allowing the body to respond with inducing injury naturally. It is important to point out that re‐education in the temporal characteristics of the force‐time history maps directly to linear and rotational accelerations, leading to concussion, as discussed earlier.…”

“…Polyurea foam with a density of 210 kg m −3 (similar to the one investigated herein) was found to exhibit superior impact‐mitigation performance compared to D3O and heavier versions of the same type of polyurea foam. [ 10,11 ] In addition to being efficient in reducing the amplitude of the impact force, polyurea foams were found to broaden the duration of the force‐time history, i.e., improving the impact performance by giving the body more time to react to the impact force while effectively reducing the severity index and head‐injury criteria. [ 11,12 ] Table 1 compares some of the mechanical performance metrics of semi‐closed cell polyurea and closed‐cell D3O foams.…”

“…[ 11,12 ] Table 1 compares some of the mechanical performance metrics of semi‐closed cell polyurea and closed‐cell D3O foams. [ 10,11 ] It also summarizes some of the morphological aspects of polyurea foams.…”