Other material properties which can be measured and used for simulation include:
The elongational viscosity is a measure of the resistance of the fluid against an applied elongational force. Outside the equipment (i.e. during stretching), the elongational viscosity is the most important material characteritic. Elongational flow is a special type of flow that occurs when the material is accelerated (elongated or stretched). As such, the elongational viscosity can also effect the flow within a die if the material is forced to accelerate rapidly.
It has been found that the elongational viscosity is much more sensitive to the material structure than the shear viscosity and so, it is a more difficult characteristic for resin companies to control during the polymerization process. In general if you have a situation in which two materials have almost identical similar shear viscosity yet, one material (or lot) processes poorly and the other material (or lot) processes well, then it may be a good idea to study the elongational viscosity.
An effect that is becoming more and more important is slip at the wall. One of fundamental assumptions in fluid mechanics is that liquids stick completely to walls, in other words that the velocity at the wall is zero. For polymer melts, that generate high stresses, it can happen that the material does not stick to the wall but it moves slowly (slips) along the wall. This effect is called Wall slip.
This effects is common for rigid PVC but it is also being observed in other polymers that exhibit high shear stress at the wall or with certain additives (i.e processing aids). Wall slip is another characteristics that may need to be measured and included in the simulation of the process.
Other measurement services we can provide:
- Conductivity of the material (for chosen pressures and thermal conditions)
- Melt Fracture
- Die Swelling
- PVT diagrams
- Cross-linking (using UV radiation)