What are the differences between PMI and PET foam?

In the structural foam material system, polymethacrylamide (PMI) and polyethylene terephthalate (PET) foam occupy an important position due to their unique properties. Although both are closed-cell foams, they differ fundamentally in composition, performance, and application scenarios, profoundly affecting their industrial positioning.

The differences in composition and structure are the root cause of their performance divergence. PMI foam uses methacrylic acid and methacrylonitrile copolymer as the matrix, which is cross-linked to form a thermosetting polymer. Its cells have a polygonal closed-cell structure with a uniform pore size distribution between 100 and 1000 μm. PET foam, on the other hand, is formed by the condensation polymerization of terephthalic acid and ethylene glycol. It is a thermoplastic material; the benzene rings in the molecular chain provide rigidity, while the methylene segments impart flexibility. While it also has a closed-cell structure, the difference in crystallinity significantly alters its brittleness.

The contrast in core properties is even more pronounced. In terms of mechanical properties, PMI foam boasts top-tier specific strength and specific modulus among polymer foams, exhibiting excellent resistance to compressive creep and significantly exceeding the load-bearing capacity of PET at the same density. While PET foam possesses basic shear and compressive strength, it becomes brittle with increased crystallinity. Regarding heat resistance, PMI, after high-temperature treatment, can withstand curing processes up to 190℃, making it suitable for co-curing with resins such as epoxy. PET, on the other hand, can only withstand short periods at 180℃ and is prone to melting due to overheating during cutting and grinding. In terms of processing characteristics, PMI is easy to machine with smooth surfaces, excelling in the molding of irregularly shaped parts. PET, limited by its thermoplasticity, requires more stringent temperature control during processing.

The divergence in application areas reflects their respective value propositions. Due to its high performance, PMI has become the preferred core material in multiple fields, widely used in critical components such as rocket fairings and passenger aircraft rear pressure frames. It is also indispensable in applications requiring both mechanical and electrical properties, such as medical devices and communication antenna covers. PET foam, with its cost-effectiveness and environmental advantages, has established itself in general-purpose fields, achieving large-scale applications in wind turbine blade leading edges, rail transit vehicle bodies, building sandwich structures, and sports equipment. Its recyclable nature further aligns with the needs of low-carbon development.

The difference between economic efficiency and environmental friendliness determines market adaptability. PMI (Polymerized Insulated Material) processes are complex and time-consuming; PET foam can be recycled from materials, not only reducing production costs but also conforming to the concept of a circular economy, possessing the potential to replace traditional materials in large-scale industries such as wind power.

From equipment manufacturing to consumer industries, the differentiated development of PMI and PET foam responds to the diverse needs of different sectors for material performance and cost, jointly driving the upgrading and evolution of the structural foam industry.