Melt Elasticity

Chain Entanglement

Long molecular strands wrap around each other to create a temporary network that resists flow. In resins with high melt elasticity, these entanglements are numerous or involve long branches that prevent the chains from sliding past one other easily.

Processing Consequence

Stored energy leads to greater expansion at the die exit and longer relaxation times during cooling. When melt elasticity is too high, it can cause surface defects like sharkskin because the material snaps back as it leaves the die wall. Conversely, low elasticity can result in part failure during vacuum forming or blow molding because the melt flows too freely.

Quality Metric

Laboraties use the ratio of the storage modulus to the loss modulus as a way to quantify the elastic nature of a batch. This value helps moulders distinguish between different grades of the same resin that might have identical melt flow rates. Monitoring melt elasticity ensures that the material will perform consistently in automated production lines.