Fixed boundary extrusion orientation crystallization of Teflon 100 – Effect of the die geometry on the resultant extrudate
This investigation is concerned with the determination of the effect of the die geometry and operating conditions on the properties of Teflon 100 ribbon extrudates produced by the Fixed Boundary Extrusion Orientation Crystallization (FBEOC) process. A single screw plasticating extruder in conjunction with a specially designed convergent die was used. A steep temperature gradient was imposed near the tip of the die to control the site of the fluid-solid phase transformation, and 'freeze in' any orientation derived from the elongational flow regime. The die flow passages were coated with a Teflon dispersion (made by Du Pont) to achieve a smooth, slippery surface with low coefficient of friction. Comparative studies were made using dies with die half angles (è) of 10, 15 and 20.5 deg.. DSC measurements and Tensile Test data have brought out that the die half angle has a significant effect on the properties of the resultant extrudates. Over the screw speed range studied, è=20.5 deg. has been the most effective in achieving samples with elevated melting point, improved crystallinity and enhanced mechanical properties. The technique (and the condition) of the Teflon coating on the die flow passages is another factor critical for the successful application of the FBEOC process.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:teflon fixed boundary extrusion orientation crystallization elongational flow regime
Date of Publication:01/01/1982