How can flame-retardant microporous polypropylene foam achieve a synergistic breakthrough in high elasticity and flame retardancy?

The core innovation of flame-retardant microporous polypropylene foam lies in the molecular chain modification technology. The molecular chain of traditional polypropylene (PP) is a linear structure with strong rigidity but insufficient elasticity. By introducing a long-chain branching structure (LCB), researchers form ""physical cross-linking points"" between molecular chains, which not only retains the flexibility of PP but also significantly improves the resilience of the material. Experiments show that the modified PP molecular chain can disperse stress through branching points when subjected to force, and the deformation recovery rate is increased by more than 40% compared with the unmodified material.

Molecular chain modification provides a carrier for the dispersion of flame retardants. Monomers containing flame retardant elements such as phosphorus and nitrogen are connected to the PP main chain through copolymerization to form a "built-in" flame retardant structure. This modification method avoids the problem of poor compatibility between traditional flame retardants and substrates, increases the flame retardant efficiency by 30%, and does not affect the processing performance of the material.

The flame retardant properties of flame-retardant microporous polypropylene foam depend on the uniform dispersion of nano-scale flame retardants. Using in-situ polymerization technology, phosphorus-based flame retardants (such as red phosphorus and APP) with a particle size of less than 50nm are embedded in the PP matrix during the polymerization process. The high specific surface area of ​​nano-scale flame retardants enables them to quickly form a dense carbon layer during combustion, isolating oxygen and heat transfer.

The carbon layer formation process is divided into three stages:

Pyrolysis stage: The flame retardant decomposes to produce phosphoric acid substances, which catalyze the dehydration and carbonization of the PP molecular chain;

Carbonization stage: Phosphoric acid reacts with carbonization products to form a graphitized carbon layer with a dense structure and high strength;

Barrier stage: The thickness of the carbon layer increases with the burning time and eventually completely covers the surface of the material.

Scanning electron microscopy (SEM) observation shows that the thickness of the carbon layer after combustion can reach 20-50μm, and the porosity is less than 5%, which effectively inhibits the spread of flames.

The high elasticity of flame-retardant microporous polypropylene foam comes from its unique microporous structure. Through supercritical carbon dioxide foaming technology, a large number of closed cells with a diameter of 50-100μm are formed inside the material, and the cell wall thickness is about 1-2μm. This structure gives the material excellent energy absorption capacity:
Elastic modulus: Under 10% deformation, the elastic modulus of the material is only 0.5-1.5MPa, which can effectively buffer the impact force;
Energy dissipation: The pore wall undergoes elastic deformation when subjected to force, converting the impact energy into the stretching and bending energy of the molecular chain;
Deformation recovery: After the external force is removed, the pore wall rebounds through the molecular chain to restore its original state, and the residual deformation rate is less than 5%.
In the battery thermal runaway scenario, the high elasticity cushion can absorb the shock wave generated by the expansion or explosion of the battery cell, reducing the damage to the surrounding structure.

The flame retardant properties of flame-retardant microporous polypropylene foam are achieved through the dual mechanisms of "gas phase flame retardant" and "condensed phase flame retardant":
Gas phase flame retardant: The flame retardant decomposes to produce non-flammable gases (such as NH₃, H₂O), dilutes the oxygen concentration, and inhibits the combustion chain reaction;
Condensed phase flame retardant: The carbon layer acts as a physical barrier to isolate oxygen and heat transfer, delaying the thermal decomposition of the material.
The excellent performance of self-extinguishing time of less than 3 seconds is due to the efficient carbonization ability of nano-scale flame retardants. Compared with traditional flame retardant materials, the carbon layer of this material has higher thermal stability and can still maintain structural integrity at 600°C.

In the process of battery thermal runaway, the "buffer-flame retardant" synergistic effect of flame-retardant microporous polypropylene foam is particularly critical:
Initial stage: high elastic cushion absorbs the stress generated by the expansion of battery cells to prevent the battery shell from rupturing;
Thermal runaway stage: the flame retardant begins to decompose, the carbon layer gradually forms, and the heat is isolated from the adjacent battery;
Propagation stage: the dense carbon layer prevents the spread of flames and buys time for the occupants to escape.
Experiments show that in the battery module thermal runaway simulation test, the temperature rise rate of the battery pack using flame-retardant microporous polypropylene foam is reduced by 60%, and the fire spread time is extended to more than 3 times that of the traditional solution.

Application scenarios: Covering the entire field from power batteries to energy storage systems
In the CTP (Cell to Pack) structure, the flame-retardant microporous polypropylene foam acts as a buffer layer between battery modules and can withstand impact forces of more than 1000N without failure. Its high elasticity ensures that the battery modules maintain close contact under vibration conditions and reduces internal resistance; its flame-retardant properties prevent thermal runaway of a single battery from causing a chain reaction.

In grid-level energy storage systems, this material is used for fire isolation between battery clusters. Its lightweight properties (density <100kg/m³) can reduce the overall weight of the energy storage power station, while its flame-retardant properties meet the UL94 V-0 standard, ensuring that the fire does not spread to other battery cells when a fire occurs.

In addition to battery systems, flame-retardant microporous polypropylene foam is also used in:
Seat cushioning layer: provides comfort and collision protection;
Interior insulation layer: reduces temperature fluctuations in the car;
Wire harness protective cover: prevents fires caused by short circuits in wires.