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PTFE Fine Powder: a Dispersion Stirred Until It Curdles (Lontz 1952)
A PTFE dispersion is stable on the shelf, but stirred hard enough it curdles. Fifty seconds at 1000 rpm in a baffled beaker and the polymer floats up as a dry-looking, unwettable crumb. Washed and dried, it is a free-flowing powder for rolling into tape, or for cold lubricated extrusion.
Source: J. F. Lontz (du Pont), US 2,593,583 (1952), Example 1. Lontz started from a dispersion made with disuccinic acid peroxide; ours is Berry's persulfate dispersion, diluted to his 17 %. Picture drawn by Youblob.
Intermediate
1 day
Instructions
1
1
Dilute the dispersion to 17 %
Dilute the dispersion to 17 %
Ours: stir the 34 % dispersion with an equal weight of distilled water to get 17 % solids, the strength Lontz used.
Materials for this step:
Aqueous PTFE Dispersion1 part
Distilled Water1 partTools needed:
Balance Scale
Glass Jars with Lids2
2
Set up the baffled beaker
Set up the baffled beaker
A 1-gallon stainless beaker, 6.5 in across and 7.5 in deep, with four baffles about ⅜ × 1 in hanging from the cover to within 3 in of the bottom. Stirrer: open turbine, 4 blades 1½ in high, 5 in across, reaching to within 1 in of the bottom.
Tools needed:
Baffled Stirred Tank
Stirrer3
3
Stir hard at 176 °F for 50 seconds
Stir hard at 176 °F for 50 seconds
Put in half a gallon of the 17 % dispersion and heat it to 176 °F (80 °C). Run the stirrer at 1000 rpm for 50 seconds (Lontz measured 0.72 hp per gallon). The polymer coagulates and floats, unwetted, on top.
Tools needed:
Baffled Stirred TankStirrer
Hot Plate
Thermometer4
4
Wash hot, then cold
Wash hot, then cold
Pour off the water. Wash the polymer with hot water at 176 °F, then with cold water at 60 °F (16 °C), and drain.
Tools needed:
Baffled Stirred TankThermometer5
5
Dry at 230 °F for 16 hours
Dry at 230 °F for 16 hours
Spread the wet polymer on a 100-mesh screen and dry it in an oven at 230 °F (110 °C) for 16 hours. It comes out a free-flowing granular powder that passes 6–8 mesh.
Tools needed:
Fine Wire Mesh Sieve
Drying OvenGlass Jars with LidsMaterials
2- 1 partPlaceholder
- 1 partPlaceholder
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