Method for producing expanded thermoplastic polymers
An improved process for fabricating expanded thermoplastic polymers (eTP) starting from non-expanded TP is disclosed whereby said process has improved thermal control, uses preferably environmentally friendly foaming gasses, avoids anisotropy and sticking of the eTP during the processing and minimises the duration of the charging step.
1. A method for producing expanded thermoplastic polymeric material, said method comprising at least following steps:
a) placing a non-expanded thermoplastic polymer material in an autoclave, said autoclave being partly filled with a liquid and wherein the non-expanded thermoplastic polymer material not being in contact with said liquid;
b) increasing the pressure in the autoclave by introducing at least one gaseous fluid at a temperature within the autoclave below the melting temperature of the non-expanded thermoplastic polymer material;
c) allowing the non-expanded thermoplastic polymer material to reach a saturation state; thereby forming a saturated non-expanded thermoplastic material
d) submerging the saturated non-expanded thermoplastic material into the liquid, and then
e) decreasing the pressure in the autoclave such that the submerged saturated non-expanded thermoplastic polymer material expands to form the expanded thermoplastic polymer material.
2. The method according to claim 1 , wherein the gaseous fluids are selected from N 2 and/or CO 2 .
3. The method according to claim 1 , wherein the gaseous fluids comprise low thermal conductivity gases selected from Hydro Chloro Fluoro Carbons (HCFC's), Chloro Fluoro Carbons (CFC's), Hydro Chloro Fluoro Olefins (HCFO's), Hydro Fluoro Olefins (HFO's), (cyclo)-alkanes.
4. The method according to claim 1 , wherein the liquid in the autoclave is reactive or non-reactive towards the non-expanded thermoplastic polymer material.
5. The method according to claim 1 , wherein the non-expanded thermoplastic polymer material is reactive or made reactive towards the liquid in the autoclave.
6. The method according to claim 1 , wherein the gaseous fluids in the autoclave further comprise additives which are reactive towards the non-expanded thermoplastic polymer material and can result in modification of the thermoplastic polymer during the charging step.
7. The method according to claim 1 , wherein the liquid in the autoclave further comprises additives which are reactive towards the non-expanded thermoplastic polymer material and can result in modification of the non-expanded thermoplastic polymer material during step (d).
8. The method according to claim 1 , wherein the thermoplastic polymer material is a thermoplastic polyurethane material.
9. The method according to claim 1 , wherein the non-expanded thermoplastic polymer material is a thermoplastic polyurethane pellet having an average diameter in the range 0.2 to 10 mm.
10. The method according to claim 1 , wherein the non-expanded thermoplastic polymer thermoplastic polymer material is a thermoplastic polyurethane pellet having an average diameter in the range 0.5 to 5 mm.
11. The method according to claim 1 , wherein in step (b) the pressure within the autoclave is above the supercritical limits of the gaseous fluids.
12. The method according to claim 1 , wherein the pressure within the autoclave ranges from 1-25 MPa in step (b).
13. The method according to claim 1 , wherein the temperature within the autoclave is above the supercritical limits of the gaseous fluids and below the melting temperature of the thermoplastic material.
14. The method according to claim 1 , wherein the temperature within the autoclave ranges from 30-250° C.
15. The method according to claim 1 , wherein step (c) is performed at controlled pressure and temperature within the autoclave until saturated non-expanded thermoplastic polymer material is achieved.