**Acknowledgements**

**Figure 28.** A 40% repro + 60% virgin PTFE mixture was ram extruded into long rods of diameter 17 mm with the help of a local industry in India. The rods came out fine from the points of polish and strength but was dark in color with

Among all plastics, PTFE has the least stability against ionizing radiation, a property which is used to break down carbon-carbon bonds in the polymer chain in the PTFE scrap and reduce its molecular weight which makes it very brittle and the end product is a white, free-flowing PTFE powder which was found to be useful as lubricant additive in other materials or system such as printing ink, thermoplastics, elastomers, coatings and other lubricants. While the turnings of PTFE scrap before irradiation are tough and elastic, those after irradiation in air crumbles into a powdery material. The molecular weight of irradiated PTFE is in the range of a few tens of thousands to a few hundreds of thousands, compared to several million for the

Unirradiated PTFE scrap could be successfully ground with the help of a commercial shredder and milling machine. A technique based on Shear Extrusion Pulverization based on Bridgeman – Anvil was successfully used to grind PTFE scrap into a fine powder. Suitable pre-heat treatments were arrived at to remove organic and other volatile impurities. Since normal sintering procedures used for molding virgin PTFE did not work with repro filled PTFE, sintering under pressure and ram extrusion techniques were tried to mold them. Repro filled PTFE Discs up to 40% tried so far when kept inside the die and plunger and pressurized with a C-clamp show discoloration which runs through its volume although good surface smooth‐ ness is seen and cracks disappeared totally. This was attributed to carbon production on reaction of volatiles with the die material. The discoloration can, however, be avoided if a pathway can be provided for the escape of volatile gases during sintering under pressure That will need fabrication of a new die and plunger with a series of holes. While high pressure (2000

patches all through the length and volume due to carbon deposition.

**8. Conclusions**

188 Sintering Techniques of Materials

unirradiated resins.

This work was carried out under the TePP-DSIR (New Delhi, India) Techno Entrepreneurship funded project entitled "Development of Filler Grade PTFE powders and Recycling PTFE Scrap Materials". We thank Hindustan Nylons, India for making Ram extruded PTFE rods.
