Explosion-proof material - polymer mesh foam.


2020 promises to be an unusual year. The first half of year was too hectic and restless. On afternoon of June 13, a tanker truck on G15 Shenhai Expressway near Liangshan Village, Daxi Town, Wenling City, exploded and ran off expressway, killing 10 people and injuring 117 others. With regards to this incident, we need to deepen our understanding of polymeric materials in order to address issues that we are really facing. Today we will get acquainted with a more practical polymer material for explosion protection of fuel tanks - mesh polyurethane foam.

1. What is mesh polyurethane foam?

Reticulated polyurethane foam is usually a product obtained by one-step foaming by molding polyester or polyester polyol, isocyanate, foaming agent, surfactant and other components, and then networked. The structural form of polyurethane foam is usually a three-dimensional network of interconnections of fibers, usually in form of a dodecahedron. Lines of intersection between surfaces are called meridians. Meridians are common to neighboring polyhedra, forming an anisotropic three-dimensional skeletal structure. The mask formed between meridians disappears after networking.

Figure 1-1 PU net material

Reticulated polyurethane foam is a special type of soft foam. This material has a high degree of disclosure, usually above 97%. It can fill about 70% of fuel tank volume and reduce oil capacity by about 5%. and PPU has good air permeability, softness, sound-absorbing and filtering properties, which allows it to be used as an explosion-suppressing fuel tank filler.

The mesh polyurethane foam used to fill fuel tank must ensure integrity of structure during operation, have certain strength and anti-aging properties.

2. The method of preparing mesh polyurethane foam and mechanism of fire and explosion protection

2.1 Method for making polyurethane mesh foam

One-step preparation of reticulated polyurethane foam: Weigh quantitative amounts of polyester polyol, water, surfactant and other additives according to formula, place them in a container, mix and mix well. Pour isocyanate and physical foaming agent into cup, mix quickly and pour into mold, release mold after foam is initiated and stabilized, and mature to obtain a meshed polyurethane foam product. The specific process flow is shown in Figure 2-1.

Figure 2-1 Flowchart

The choice of polyol type, choice of isocyanate, amount of amine catalyst, surfactant and physical blowing agent all have a certain effect on structure of polyurethane foam. Among them, mesh polyester foam, which has high compressive strength and tensile strength. The ester bonds formed by reticulated polyester foam increase flexibility of polymer chains and reduce cohesive energy of polyester products resulting in lower performance compared to polyester products. MDI is suitable for making high performance foams while TDI is used for general flexible foams.

2.2 Fire and explosion protection mechanism

The explosion-proof mechanism of meshed polyurethane foam can be analyzed from two points of view, as shown in Table 2-2.

3. Conclusion

Using reticulated polyurethane foam to fill a fuel tank is an extremely efficient and feasible method. The fuel tank may cause deflagration and explosion after a fall and a violent impact. According to relevant data, mesh polyurethane foam can cause fuel tank to fall and be trapped. fire 75% reduction in mortality rate can greatly improve people's survival rate. Reticulated polyurethane foam was used to suppress explosion of fighter jet fuel tanks and then gradually applied to transport aircraft; in addition, it was also used in ground combat vehicles and tanks for storing flammable liquids.

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