# Development and Characterization of Tailored Polyurethane Foams for Shock Absorption
## 3 Results
### Cellular Polyurethane Evaluation  
#### 3.4.1 Evaluation of Stiffness and Apparent Density  
Data demonstrate that polyurethane foam material's evident apparent density specifically impacts the cell structure. The cell volume, compression power, and elongation at break increase with apparent density. We tested its rigidity and apparent density after creating a collection of foams of parallelepiped form. These results are described in Figure 14. The findings showed that the hardness was proportional to the density. The denser the sample was, the harder it was.  
The interpretation of the bubbles involved in producing this delivery cellular of polyurethane, development, and stabilization processes is exceedingly complicated. Looking at foam structure in the examined density range can help predict mechanical characteristics more effectively [57].  
The last two SEM images compare the microstructure of the second and sixth polyurethane foam samples, representing the smallest and largest apparent density ratio (Figure 15).  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Samples** & **Dimensions** & **Maximum** & **Minimum** & **Average Cell** \\ \hline \multirow{2}{*}{PUR\_1} & Diameter (\(\mu\)m\({}^{2}\)) & 224.94 & 58.59 & 138.35 \(\pm\) 22 \\  & Area (\(\mu\)m\({}^{2}\)) & 60,965.2 & 16,950.09 & 36,449.02 \\ \hline \multirow{2}{*}{PUR\_2} & Diameter (\(\mu\)m\({}^{2}\)) & 132.28 & 32.65 & 76.64 \(\pm\) 17 \\  & Area (\(\mu\)m\({}^{2}\)) & 16,760.99 & 3918.89 & 10,205.01 \\ \hline \multirow{2}{*}{PUR\_3} & Diameter (\(\mu\)m\({}^{2}\)) & 122.7 & 29.15 & 57.27 \(\pm\) 11 \\  & Area (\(\mu\)m\({}^{2}\)) & 32,399.06 & 1124.84 & 6764.04 \\ \hline \multirow{2}{*}{PUR\_4} & Diameter (\(\mu\)m\({}^{2}\)) & 128.26 & 27.01 & 63.82 \(\pm\) 17 \\  & Area (\(\mu\)m\({}^{2}\)) & 19,348.27 & 1281.34 & 7241.19 \\ \hline \multirow{2}{*}{PUR\_5} & Diameter (\(\mu\)m\({}^{2}\)) & 194.07 & 83.72 & 137.64 \(\pm\) 22 \\  & Area (\(\mu\)m\({}^{2}\)) & 72,771.57 & 14,014.35 & 35,205.52 \\ \hline \multirow{2}{*}{PUR\_6} & Diameter (\(\mu\)m\({}^{2}\)) & 123.17 & 29.01 & 72.07 \(\pm\) 22 \\  & Area (\(\mu\)m\({}^{2}\)) & 21,395.45 & 3307.8 & 12,464.61 \\ \hline \end{tabular}
\end{table}
Table 7: Calculation of radii values of polyurethane foam cells and filler material.  
Figure 14: The influence of bulk density-assigned hardness on the structure of polyurethane foams (PUR).  
Foam measurements demonstrate shaped cells through scanning electron microscopy (Figure 15). The foam cells appear spherical and partially open in the studied density range (0.07-0.34). The foam density is regulated by the gas produced during the reaction. They influence the amount and scale of cells. From the cell diameter distribution (Figure 16) obtained from the picture study, the Gaussian distribution can be modified to evaluate its width and average diameter. The cell average size is 15 lm for relative density above 0.34, with a small distribution.  
Foams with densities from 0.18 to 0.23 all have a cell-size distribution that increases as the density declines, and their typical size is far greater than that of foam of 80 lm. The average size of the lowest density foam (0.07) for an equal distribution is 105 lm.