I received this question yesterday…
We are using Isoplast in a hot runner system. The press was shut down. When the sprue, manifold, and barrel heaters were turned on, the material started oozing as a white material covered in black specs. What would cause this behavior?
The material you are processing is a ETPU (engineering thermoplastic polyurethane) which tends to be prone to degradation, especially when the material is not properly dried.
It is critical that you determined the dewpoint of the material at the hopper and compare the melt temperature, dewpoint, and drying recommendations of the material.
Any time you are using a hot runner system, you are adding more heat and residence time to the material. If the hot runner design is not specifically tailored to reduce stagnation and hot spots, it is very likely that hangups and degradation will occur within the hot runner system.