Injection molding PTFE (Dupont’s Teflon) and UHMWPE

Yes, it can be done; no you might not like the results. PTFE (like UHMW) has never been actively considered injection moldable as a base resin.50% PTFE in PPS as a blend can be molded, just as 50% UHMW in HDPE is moldable.

The issue with unmodified PTFE, unlike UHMW, is that PTFE “grows” by 30% in the gel condition which is the melt condition for both materials. They don’t flow like other thermoplastics. That means you can inject PTFE into a cavity on a conventional molding machine, being careful with processing to avoid melt fracture. But as the resin cools it shrinks by 30% leaving a massively sunk condition. A mold that can contract as the resin melts, like a coining operation, will solve one axis, but not the other two. So, a cavity 6”x6”x 0.5” will become a 4”x4”x 0.35” part. If you want a plate, just plan for the shrinkage, but if you want a 2” diameter hole in the middle there are complications, and two holes are nearly impossible. Also remember that PTFE in its gel state is very corrosive so you will need alloy tooling. Another complication is PTFE is not available as a granule, so you have to wrestle with injection molding a powder.

PFA, also called Teflon by Dupont, is injection moldable with proper steps. It requires alloy injection units and tooling, and a mold heating capability of around 350F or higher. Here the processing trick is to avoid melt fracture which is caused by injection speeds that are too high at mold temperatures that are too low. High shrinkage rates are another obstacle.
Injection molding UHMW is possible even though there are caveats here as well. There are a number of companies that mold UHMW and at least two who have done it for 40 years. You would expect high prices and you would be right because there is a reason why every one isn’t doing it. The first obstacle are delamination, burning, and weld lines. The next obstacle is there can be a “laminar” surface of about .002-.003” that needs to be constantly monitored and corrected. With UHMW at least there are granulated pellets available, and ordinary tool steels can be used. Getting a new application running successfully can take days getting the processing just right after multiple mold tweeks. The industry criticism usually applied to injection molded parts is the decay in molecular weight and increased crosslinking. Starting with a resin of 5,000,000 molecular weight a well molded part will achieve 4,000,000 with only a 20% increase of crosslinking, which is well within the industry standard for compression, or ram extruded UHMW parts. Without giving away trade secrets, keep oxygen away from melt temperature resin to reduce oxidation(burning).

It is far easier to mix 5,000,000 molecular weight UHMW with 50% autocross linkable, low melt flow HDPE to get very comparable results, and it is far more injection moldable.