1. Why PP Hollow Formwork Does Not Need Release Agent
Wooden formwork must be coated with release agent because wood surfaces have capillary pores. Cement slurry from concrete penetrates these pores and forms "mechanical interlocking." Without release agent, the formwork sticks firmly and cannot be removed.
In contrast, the surface of PP hollow plastic formwork is a smooth, dense, non-polar polymer structure, creating a natural "chemical isolation layer" between the formwork and concrete:
Extremely Low Surface Energy: The surface energy of PP material is approximately 30mN/m, far lower than that of concrete slurry (about 70mN/m). Cement slurry cannot wet or penetrate the surface, much like water droplets rolling off a lotus leaf. Concrete simply cannot "grip" the formwork surface.
Chemical Inertness: PP is a saturated hydrocarbon compound that does not chemically react with alkaline substances in concrete such as calcium hydroxide and silicates. There is no "chemical bonding."
No Capillary Pores: The plastic surface lacks the microporous structure found in wood, so cement slurry cannot embed itself to form mechanical interlocking force.
Conclusion: Applying release agent is not only unnecessary but may actually damage the smooth surface layer of PP, making it more prone to sticking in subsequent uses.
2. Why It Can "Automatically Detach"
This utilizes the physical principle of thermal expansion coefficient difference:
Thermal Expansion Coefficient of PP: Approximately 100-150×10⁻⁶/°C
Thermal Expansion Coefficient of Concrete: Approximately 10-14×10⁻⁶/°C
The difference between the two is nearly 10 times. During pouring, concrete hydration releases heat and temperature rises. The PP formwork expands far more than the concrete, creating a tiny gap between them. During the later curing stage, as temperature drops, PP contracts more significantly, further widening the gap.
Result: A natural "separation layer" forms between the formwork and concrete. The formwork can be completely removed without hammering or with just a light tap. The minimum demolding time is only 1/4 of that required for traditional wooden formwork.
