Polyimide chemistry

Sealing Insulation and Protection

P84® polyimides are known for their high thermal resistance characterised by a glass transition temperature of 315°C as well as their non melting properties. The permanent flame retardancy of P84® is classified by the LOI (Limiting Oxygen Index) of 38 percent O2.

P84® polyimide fibres show a very low thermal conductivity. In combination with the high specific surface area and the fact that P84 felts are quite bulky the construction offers excellent insulation capabilities.

Application areas for P84® fibers



Insulating material

P84® fibers having a unique multilobal cross section which offers a much higher specific surface compared to round fibers are the ideal base material for insulation products.

Needle felts made of P84® polyimide fibers quilted to a light weight P84® fabric are used as thermal insulation inside of fire fighter jackets. The soft handling of P84® in addition to the thermostable and non flammable properties are reasons for their usage in protective clothing.

P84® polyimide fibers show a tendency to shrink extensively if heated above the glass transition temperature of 315 °C. By varying the temperature and the type of initial fiber structure (nonwoven, fabric, knit wear etc.) it is possible to produce light weight but stable mechanical structures which achieve the stiffness of thermoplastic LDPE without additional adhesives or binders. During the heat treatment high contraction forces generate bonds between the single fibers forming self supporting structures.

Using a nonwoven the structure is influenced by the density and thickness of the felt, the temperature of the process and the allowed rate of shrinkage. Achieved densities reach from 0.19 g/cm³ up to 0.96 g/cm³ for semi-rigid to rigid fiber boards. The boards are used in insulation applications in rubber and plastics processing. They are compression resistant and can be machined like wood and easily fabricated into custom insulation packages for areas that could not be insulated without high effort before. Tools for extrusion, thermoset compression and injection molding processing are targets for insulation with this new developed product.

Rigid insulation boards out of P84® fibers are known under the brand Pyropel®.

Braided Packings

P84® is an excellent choice for use in the sealing industry due to high thermostability, a good chemical resistance, a high dimensional stability and pressure resistance even at high temperatures, good flexibility which minimizes shaft wear and a low heat expansion index.

Evonik Fibres supplies P84® multifilament yarns to e.g. Lenzing Plastics GmbH, who impregnate the yarns with PTFE dispersion and oil for the braiding industry. P84® packings have gained reputation as an asbestos substitute in applications :

- where pure PTFE packings do not meet mechanical requirements
- where the high strength of p-aramid yarns is not required but better resistance against acidic conditions is of advantage

Fabrics and knitwear

P84® polyimide fibers are mainly used in fabric blends with major objective on best possible protection and wear comfort. Main blending partners are Viscose FR and p-Aramides.

Fabric weights from 175 g/m2, different blend ratios and different structures can be adapted exactly to each specific application. The fabrics are used as outer shell for suits and jackets for fire fighters, army and industry. Tests confirm no afterglowing and afterburning as well as minimum smoke and no toxic formation and emission.

Turnouts made of P84® and p-Aramide blends offer superior flame and heat protection, strength, durability and provide greater mobility. NFPA tests have shown that the fabric maintains its strength and flexibility even after flashover.