Ethylene Propylene Rubber Domain Morphology Tuning for Low Temperature Container Impact Survival
Tuning EPR domains to 0.4-0.8 microns with 45 percent ethylene content ensures sub-zero container shock survival at minus 30 degrees Celsius.
Mooney Viscosity Matching
Meaning
The process of aligning the melt viscosities of elastomeric modifiers and thermoplastic matrices during polymer compounding ensures the creation of a fine and uniform rubber dispersion. This mooney viscosity matching is critical for the production of tough materials like super-tough nylons or impact polypropylene copolymers. When the viscosities of the two phases are close to each other the shear forces of the compounder can break the rubber down into small droplets.
If the viscosities are too far apart the rubber cannot be dispersed properly.
Mixing Efficiency
The size of the dispersed rubber droplets depends on the shear stresses transferred from the matrix during mixing. Through mooney viscosity matching the shear transfer is optimized which allows the elastomer to be deformed and broken down into sub-micron particles. These small particles are necessary for achieving high impact strength in the final moulded part.
If the elastomer is much more viscous than the matrix the shear forces will bypass it and the rubber will remain as large clumps. This clumping lowers the impact resistance and can cause surface defects.
Processing Constraint
Moulders must pay close attention to the melt viscosity of modified resins during injection moulding. Even when mooney viscosity matching is achieved during compounding the difference in shear rates between the compounding and moulding stages can affect the final dispersion. If the melt temperature is set too high the matrix viscosity may drop faster than the rubber viscosity which can cause the rubber particles to run together.
This coalescing can lead to uneven properties across the moulded part. Moulders must balance melt temperature and injection speed to preserve the distribution.
Melt Homogeneity
Consistent viscosity between the matrix and the modifier is also important for maintaining a stable and uniform flow during the filling of the mould. When the resin lacks mooney viscosity matching the uneven flow can lead to jetting or surface splay in the finished part. These defects are not just cosmetic because they can also act as stress concentrators and lead to early part failure.
Using regrind can further complicate this because the thermal history of the recycled material can alter its flow properties and upset the viscosity match. For this reason compounders must carefully monitor the viscosity of both phases to ensure consistent performance. By keeping the viscosities aligned they can produce a material that flows well and provides excellent impact resistance in every part.