PMI Foam Cores for Liquid Resin Infusion at 130 C and 0.3 MPa

Introduction: In liquid resin infusion and RTM, the 130 °C and 0.3 MPa figures describe the working conditions a closed-cell PMI foam core is built to handle.

When resin flows through a vacuum bag or a closed mold, the foam core inside is doing two jobs at once. It holds the sandwich open as a structural spacer, and it keeps its cells sealed so resin stays out of the interior. Those jobs set real limits, because heat softens a polymer core while pressure squeezes it. Push either one far enough and the core loses thickness, cell shape, or both. The numbers 130 °C and 0.3 MPa mark where a closed-cell PMI core such as Rifeng WF is at home in liquid molding, and understanding them as protection for the core's dimensions and cell structure is far more useful than reading them as a process recipe.

What Liquid Resin Infusion and RTM Ask of a Foam Core

In vacuum infusion, a bag pulls resin across dry reinforcement and down into the part, and the vacuum itself presses the whole laminate stack together. In RTM, resin is injected into a closed cavity, so the core carries the vacuum load plus the mold pressure on top of it. Either way, the core sits in a stack that is being squeezed from both sides. It has to resist that squeeze without thinning, because core thickness drives the bending stiffness of the finished sandwich panel. A core that creeps by a fraction of a millimeter under load changes how the whole part behaves. Heat arrives at the same time. Infusion and RTM resins are usually warmed to lower viscosity so they wet out the fiber and travel through the preform before they gel. That warmth reaches the foam, and a closed-cell foam answers in two ways: the polymer softens, and the gas sealed inside each cell pushes outward a little harder. Together those effects make the core easier to compress under the same process pressure. The temperature limit and the pressure limit are therefore not independent numbers. One sets how soft the polymer is, the other sets how hard the process pushes on it, and the two have to be read together.

Why Temperature and Pressure Limits Protect Core Dimensions

The 130 °C and 0.3 MPa figures are two sides of one balance. Heat lowers the core's stiffness, which gives process pressure more leverage to change its shape. Keeping both numbers inside the stated range keeps core thickness, flatness, and cell walls intact through the warm phases of a molding cycle.

1. How the 130 °C Limit Relates to Core Dimensional Stability

PMI is a rigid polymer, and like most rigid polymers it loses some stiffness as it warms. Below its heat distortion point the loss stays small, and the foam behaves much like the stiff board it is at room temperature. The useful comparison is the gap between the two numbers. Rifeng WF grades show a heat distortion temperature of about or above 180 °C by DIN 53424, while the liquid molding window is capped at 130 °C. That gap is what keeps the core dimensionally stable during warm resin flow. Resin can reach the viscosity the process needs, and the core still holds its thickness because it is working well below the point where it would start to sag under load.

2. Why 0.3 MPa Matters for Closed-Cell Structure Protection

Pressure is where a foam core either keeps its structure or starts to lose it. Every closed cell is a small gas pocket wrapped in a thin polymer wall, and under compression those walls carry the load. A healthy closed-cell core answers moderate pressure with elastic deformation of the cell walls and springs back when the load comes off. Past the point those walls can take, the cells buckle, and buckled cells do not recover. The 0.3 MPa limit keeps the process on the safe side of that transition. It also protects the closed-cell barrier itself. If enough cell walls crush, the core can no longer keep resin out of its interior, and a panel designed to be light starts gaining unwanted weight.

Where Industrial PMI Foam Belongs in Liquid Molding Discussions

Industrial PMI foam sits in liquid molding conversations next to PVC, PET, balsa, and honeycomb, but it earns its place for a specific reason. It combines a high stiffness-to-weight ratio with a closed-cell structure and enough heat resistance to handle warmed resin. That mix makes it a natural fit for wind turbine blade shells, automotive structural panels, and general industrial sandwich parts made by infusion or RTM. Shops that work to a quality management system such as ISO 9001 already document process parameters and check them against material limits, which is the right habit for a structural foam core with a defined temperature and pressure range. Within the Rifeng WF range, the three grades differ mainly by density. Rifeng 52WF at 52 kg/m³ is the lightest and suits panels where stiffness rather than crushing load drives the design. Rifeng 75WF at 75 kg/m³ sits in the middle. Rifeng 110WF at 110 kg/m³ brings noticeably higher compressive, tensile, and shear values, so it fits sections that see concentrated loads. All three are closed-cell, medium-cell PMI foam, all three share the same 130 °C and 0.3 MPa liquid molding limits, and all three handle resin the same way: the sealed cells keep it out of the interior, while the machined surfaces take the resin needed to build the bond.

Conclusion

For anyone learning liquid composite molding, the 130 °C and 0.3 MPa figures are worth remembering as a pair. They mark a working range where a closed-cell PMI core keeps its thickness, keeps its cell walls intact, and holds resin at its cut surfaces rather than letting it soak through the sheet. Read them as the conditions the core is built to handle in resin infusion and RTM, then compare them with the actual resin temperature and mold pressure of the job at hand. When both numbers sit inside the range, the core does its job as a structural spacer and the sandwich panel comes out with the weight and stiffness the design intended.

FAQ

Q：What does the 130 °C limit mean for PMI foam cores in resin infusion?

A：It means resin and tooling can be warmed up to 130 °C without pushing the closed-cell PMI core past its working range. PMI softens gradually as it heats, so the limit marks the point where the core still holds its thickness well enough to survive warm resin flow. It sits comfortably below the heat distortion figure of about or above 180 °C, which is why the core keeps its shape through the warm part of an infusion cycle.

Q：Why is 0.3 MPa an important pressure limit for RTM foam cores?

A：In RTM, the mold pushes resin through the cavity under pressure, and that pressure lands on the core as well. 0.3 MPa is the level the closed-cell structure can take without cell walls buckling. Stay at or below it and the core compresses elastically and returns to shape. Go well past it and cells can crush permanently, which changes panel thickness and opens the interior to resin.

Q：Does a closed-cell PMI core absorb resin during liquid infusion?

A：Some, but only at the cut surfaces. The sealed cells inside the sheet block resin from travelling through the interior. When a core is machined to shape, the cells on the new surface are sliced open, and resin fills those openings to build the bond between core and skin. That surface uptake is part of a sound bond. What the closed-cell structure prevents is resin soaking deeper into the sheet and adding weight.

Sources / References

ISO 9001 - Quality Management Systems | BSI

Integrated Energy Systems Office | Department of Energy

Related Examples

Rifeng WF Medium Cell Size PMI Foam

Further Reading

Lightweight Materials for Cars and Trucks | Department of Energy