In this work, the rheological properties and the sagging behavior of different grades of PP have been studied to assess their suitability in thermoforming operations.
The sagging resistance of PP and ABS was studied by measuring the polymer's melt strength using a Gottfert "Rheotens" Melt Strength Tester as described previously .
In thermoforming processes, the sagging of a polymer sheet is an extensional deformation.
The sagging behavior of PP and ABS was studied in an air circulating oven that was set at a temperature of 190[degrees]C.
In the sagging experiment, a sheet sample was put in the oven for 12 minutes to ensure a distinguishable amount of sagging could be obtained for different polymers without tearing of the polymer sheet.
The local extension ratio of the ABS sample could not be measured accurately because ABS gave very little sagging and there was insignificant deformation of the grids.
When paint starts sagging, it forms "tears" underneath the holes.
The amount of sagging and leveling in a drying paint is strongly related to the time-integrated film fluidity (or total film flow).