**8. Conclusions**

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 resins.

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 to 3000 psi) and hence a solid die and plunger are required during cold pressing powder into pellet, a relatively lower pressure (500 psi) should suffice during sintering.

A 40% mixture was successfully ram extruded by us into long rods of diameter 17 mm. The rods came out satisfactorily from the points of polish and strength but was dark in color with patches all through the length and volume due to carbon deposition. Due to escape of carbon, the discoloration of ram extruded rod considerably reduced on annealing in air at 400°C in atmospheric pressure as the volatile gases found an easy pathway into atmosphere. This is a significant result and confirms our view that the discoloration is caused by carbon production. The fluorine being a gas produced on disintegration of fluorocarbon perhaps has already escaped during the sintering while carbon in the absence of oxygen has deposited within the rod. Discoloration could be further reduced with acid treatment so off-white recycled PTFE rods could be made with ram extrusion.
