Process of dough forming of polymer-metal blend suitable for shape forming
Processing of polymer-metal blend composition involving viscosity control under ambient conditions suitable for shape forming and homogeneous green body preparation. The advancement involves effective controlling of the rate of settling of the metal particles in polymer-metal blend under ambient conditions to generate a cost effective and simple process for producing shape formable dough. Advantageously, the present invention provides a rapid, energy saving process involving minimum material loss and utilizing non hazardous solvent system such as water.
1. A process of dough forming of polymer-metal blend compositions with increased viscosity suitable for shape forming comprising:
i) providing polymeric solution and coagulant with or without other additives to provide a polymer-coagulant composition;
ii) subjecting said polymer-coagulant composition to vigorous stirring to increase viscosity by frothing thereby incorporating air bubbles into said polymer-coagulant composition to obtain a porous polymer-coagulant composition; and
iii) thereafter gradually adding the metal powder to said porous polymer-coagulant composition of step ii) above to thereby further increase of viscosity of said metal powder dispersion in porous polymer-coagulant composition and generate a porous shape formable dough under ambient condition with improved viscosity.
2. The process as claimed in claim 1 , wherein the process is carried out with or without foaming agents or fugitives.
3. The process as claimed in claim 1 , comprising:
increasing the viscosity of said metal powder dispersion in polymer-coagulant composition with or without other additives to thereby provide for said dense shape formable dough via high shear mixing with pressure ranging from 1 to 500 MPa preferably upto 100 MPa; and
subjecting the thus obtained dense shape formable dough to shape forming, drying and sintering.
4. The process as claimed in claim 3 , wherein the step of stirring is carried out selectively involving anyone or more of roll mill, mechanical stirring/sigma blender/cone blender/V-blender for bulk volumes and after mixing subjecting the dough to shaping through plastic deformation/yielding above the yield stress of the prepared dough, and finally the dried green body further subjected to heat treatment (sintering) to obtain final dense components optionally involving grinding, polishing or any other shaping/finishing.
5. The process as claimed in claim 4 , wherein the polymer-blend composition (wt %) comprises based on the weight of metal powder:
A) Polymer powder
1-50
B) Solvent
3-30
C) Lubricants
0.1-10
D) Plasticizers
0.1-10
E) Coagulant
0.1-10
F) Other additives
0.1-10.
6. The process as claimed in claim 1 , involving porous shape formable dough comprising:
i) subjecting the thus obtained porous shape formable dough to cast into a predefined lubricated mold for shape forming without further high shear mixing, and drying; and
ii) dried green body being further subjected to heat treatment (sintering) to obtain final porous components.
7. The process as claimed in claim 1 , comprising addition of foaming agents and/or fugitive particles for porosity or increasing pore connectivity in said generated shape formable dough for porous structures, interconnected secondary macropores and wherein sintered density, total porosity, pore size distribution, microstructure, mechanical properties are selectively varied based on selective additives involved.
8. The process as claimed in claim 7 , wherein the polymer-blend composition (wt %) comprises based on the weight of the metal powder:
A) Polymer powder
1-50
B) Solvent
3-30
C) Lubricants
0.1-10
D) Plasticizers
0.1-10
E) Coagulant
0.1-10
F) Other additives
0.1-10
G) Fugitive/foaming agent
upto 15.
9. The process as claimed in claim 1 , wherein the low viscous polymer-metal blend composition is converted into high viscous dough under ambient conditions to generate shape formable dough with the following specifications:
For coagulation dough processing:
Viscosity at shear rate 0.03 (s −1 ): 0.0001 to 1 MPa·s
Yield stress (MPa): 0.0001-2.
10. A process of dough forming of polymer-metal blend compositions with increased viscosity suitable for shape forming comprising:
i) providing metal powder;
ii) adding said metal powder to polymer with or without additives to obtain a polymer-metal blend composition; and
iii) subjecting the said metal polymer-metal blend composition to high shear mixing involving plastic dough processing to thereby generate shape formable plastic dough.
11. The process as claimed in claim 10 , wherein the high shear mixing is carried out with pressure range of 1 to 500 MPa, preferably upto 100 MPa, at low temperature 4° C. to 40° C., preferably at 10° C., for de-agglomeration of polymers and metal powders and wherein the high shear promotes deformation, blending of metal powders within polymer matrix in presence of very low amount of solvent, co-solvent, plasticizer and surfactant along with the applied shear force eliminating possibility of entrapped air bubbles during formation of dense components.
12. The process as claimed in claim 10 , wherein (a) for dense component dough forming composition by weight of metal powder comprises:
A) Polymer Powder
1-50
B) Solvent
3-30
C) Lubricants
0.1-10
D) Plasticizers
0.1-10.
and (b) for porous components dough forming composition by weight of metal powder comprises:
A) Polymer Powder
1-50
B) Solvent
3-30
C) Lubricants
0.1-10
D) Plasticizers
0.1-10
F) Fugitive/foaming agent
1-15.
13. The process as claimed in claim 12 , wherein after the formation of the shape formable dough, the additive/foaming agents are removed by anyone or more of:
(i) formed dough is either heated at 100-600° C. for burning out of the organic/inorganic fugitive particles; or
(ii) dipping within a solvent for leaching out of the soluble polymer/inorganic salts which leaves spaces after removal and turned into foam after sintering.
14. The process as claimed in claim 10 , wherein the low viscous polymer-metal blend composition is converted into high viscous dough under ambient conditions to generate shape formable dough with the following specifications:
for plastic dough processing involving high shear mixing of metal powder and polymer blend composition:
viscosity at shear rate 0.03 (s −1 ): 2 to 100 MPa·s
yield stress (MPa): 2-50.
15. The process as claimed in claim 14 , wherein the dough obtained is selectively worked into dense and/or porous, graded or laminated objects with various shapes including rods, tubes, blocks, spring or other hollow structures along with required surface texturing for metal stent, drug eluting stent, device for lumen stricture, bone plates, bone screws, dental roots and crowns, dental bridges, spinal shunt, hip joints, knee joints and any other structural load bearing supports, metal foams for architectural, automobile, biomedical applications including cancellous bone analogue, dense-porous laminates and gradients for dental roots and bone.