Melt Rheology Suitable for Foaming

When low density foams are produced, the polymer melt must undergo high biaxial extension in order to 

One way to characterise thermoplastic melts is by using a Rheotens machine (31) which subjects an extruded strand of melt to tensile elongation at a fixed velocity while measuring the tensile force. The typical response (melt tensile force versus draw velocity) for branched PP extends to twice as high a draw velocity, with six times the force, than that for linear PP. Alternatively a 

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