Claims:We claim:
1.A process for Recycling of PTFE Scrap Materials by Sintering under Pressure or Ram Extrusion comprises:
pulverising/grinding unirradiated PTFE scrap;
a grinder based on pressure shear pulverization (PSP);
suitable die materials;
wherein PTFE scrap is converted into a free-flowing powder and sintering under pressure or Ram extruded the ground powder into rods / products with desired strength.
2. The mechanism as claimed in claim 1, wherein pre-heat treatments above the melting point and suitable acid treatments are performed to remove volatiles which discolour the finished products made from repro.
3. The mechanism as claimed in claim 1, wherein exhibit that no need to mix virgin PTFE powder with powdered scrap powder and 100% of repro is possible.
4. The mechanism as claimed in claim 1, wherein reveal that the mechanical strength, density and other parameters of the recycled products are comparable to those of the virgin PTFE products.
, Description:Grinding PTFE scrap which is a very tough and slippery high melting plastic. Temperature and duration to which the scrap/ground powder is to be heat treated before sintering are unknown and acid cleaning to be carried out especially when PTFE is hydrophobic. Further major complication involves sintering under pressure and the removal of discoloration produced therein.
That it is possible to recycle PTFE after pulverization without any irradiation but after ram extrusion and their mechanical strength are better than virgin PTFE! Second vital clue came from literature which said that the reprocessed PTFE has to be heat treated above its melting point at least twice to remove volatile impurities. Once ground, it is treated with acid to dissolve organics after which it is washed and re-heated – to vaporize any volatiles.
Shear Extrusion Pulverisation based on Bridgeman –Anvil
After considerable efforts, it was found that Shear extrusion pulverisation based on Bridgeman–Anvil effectively pulverize the PTFE scrap into fine powder form. This technique is also known as double disc mill, solid state pulverization (SSP) or Pressure shear pulverization (PSP). It is a physio-chemical process in which cohesive forces within the polymer are broken down by means of mechanically induced stress. The process is based on “Bridgeman phenomenon” and is realized inside a specially designed pulveriser. In PSP, the polymer is subjected to simultaneous action of axial compression and shear stress between two engraved discs (working surface) made of suitable metal alloys. The process is realized below the melting point of polymers so the technical properties of recycled polymers remain unchanged after polymerization. The PTFE scrap had to be shredded (long threads to be cut into small threads) before pulverization, otherwise the long threads will get entangled with the rotating shaft of the pulveriser.