Bio-degradable foamed products
The method provided produces a bio-degradable foamed material with qualities of uniformity of mechanical and physical properties throughout the product including a foam thickness of up to one meter and a finished foam surface suitable for packaging applications. The parameters for producing such a product are selected from a range of variables which includes wall thickness, mold material, use of a susceptor and the type and composition of a susceptor, the number and arrangement of magnetrons and mold shape. Complex shapes produced by the process are also disclosed.
1. A method of producing a bio-degradable foamed product, with a smooth surface finish and density of about 35 to 100 kg/m 3 the method comprising
preparing a bio-degradable raw material ready for foaming by process of heat and shear;
placing the material into a closed mold to form a moldable assembly;
microwaving at least one said moldable assembly to form a bio-degradable foamed product;
wherein said mold comprises at least one of:
microwave interactive material disposed on at least one internal surface of a cavity in said mold;
microwave interactive material impregnated into the mold material itself; and
combinations thereof such as to enable the internal surface of the mold to be heated substantially uniformly by microwave radiation to a temperature that is greater than a melt temperature of said material being foamed in said mold and high enough to prevent vapour condensation on the surface of the foamed article.
2. A method of producing a bio-degradable foamed product as claimed in claim 1 which utilizes domestic strength magnetrons.
3. A method of producing a bio-degradable foamed product as claimed in claim 1 by semi continuous processing comprising:
(i) moving at least one moldable assembly on a conveyer belt into under a microwave apparatus;
(ii) sealing said microwave apparatus between said belt, walls of said microwave apparatus and a ceiling of said microwave apparatus;
(iii) commencing microwave processing irradiation;
(iv) moving said conveyor belt forward at a speed such that as each moldable assembly finishes microwave processing, the next moldable assembly enters the microwave apparatus.
4. A method of producing a bio-degradable foamed product as claimed in claim 1 by semi continuous processing comprising:
moving at least one moldable assembly on a conveyer belt into a cavity of a microwave apparatus;
sealing said cavity by closing a door thereto;
commencing microwave processing; and
as the piece finishes microwave processing, opening the door is and moving the belt forward such that the next moldable assembly enters the microwave apparatus cavity.
5. A method of producing a bio-degradable foamed product as claimed in claim 1 , wherein the bio-degradable raw material is selected from the group consisting of: renewable natural resources and modifications of such natural resources; non-natural polymerization products of monomers derived from natural resources; non-natural polymerization products of oligomers derived from natural resources; polymers obtained by biotechnological production; and bio-degradable polymers selected from the group consisting of: polyvinyl alcohol (PVA); polycaprolactone; and combinations thereof.
6. A method of producing a bio-degradable foamed product as claimed in claim 1 , wherein the bio-degradable raw material additionally comprises additives selected from the group consisting of: biodegradable plasticizers; nucleating agents; processing aids; and combinations thereof.
7. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the heat and shear generating process is extrusion.
8. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the bio-degradable material prepared in step (a) has a moisture content of 5 to 30% (w/w).
9. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the base mold material is substantially microwave transparent.
10. A method of producing a bio-degradable foamed product as claimed in claim 1 , wherein the base mold material is selected from the group consisting of: a plastic; a ceramic; glass; and combinations thereof.
11. A method of producing a bio-degradable foamed product as claimed in claim 10 wherein said plastic is at least one member selected from the group consisting of: polyethylene (UHMICROWAVEPE); polyacetal; polysulfone (PSU); polypolyetherimide (ULTEM); polyetherketone (PEEK); epoxy resins; polyphenylene ether; polyphenylsulfone (PPSU); and combinations thereof.
12. A method of producing a bio-degradable foamed product as claimed in claim 10 wherein said ceramic is at least one member selected from the group consisting of gypsum (plaster of paris) and china clay.
13. A method of producing a bio-degradable foamed product as claimed in claim 1 , wherein the mold material is reinforced with at least one low dielectric loss material selected from the group consisting of: a filler material with a low dielectric loss; micro-balloons; glass fibres; and combinations thereof.
14. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein said mold material has a dielectric constant of 0 to 10 at a frequency of 2.45 GHz, and a loss factor of 0 to 0.1 at a frequency of 2.45 GHz.
15. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the mold has vent holes.
16. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the microwave interactive material is applied to the mold in a form selected from the group consisting of: a thin film; a liner; a surface coating.
17. A method of producing a bio-degradable foamed product as claimed in claim 1 , wherein the mold acts as a susceptor and microwave interactive material is dispersed throughout the mold material.
18. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the microwave interactive material is selected from the group consisting of: electrically resistive materials; conductive materials; semi-conductive materials; and combinations thereof.
19. A method of producing a bio-degradable foamed product as claimed in claim 18 , wherein the microwave interactive material is aluminium.
20. A method of producing a bio-degradable foamed product as claimed in claim 18 , wherein the microwave interactive material is selected from the group consisting of; carbon black; graphite; silicon; silicon carbide; metal oxides; sulfides; ferromagnetic materials; a dielectric material; and combinations thereof.
21. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the microwave interactive material is ferrite dispersed in silicone rubber or other resinous polymeric material formed into a shape that lines the interior surfaces of the mold.
22. A method of producing a bio-degradable foamed product as claimed in claims 1 wherein the inner mold surface temperature during microwave processing is between about 50° C. and 190° C. as a consequence of the presence of a susceptor or microwave interactive material.
23. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein, under steady state operating conditions, the maximum inner mold surface temperature is between about 50° C. and 190° C. as a consequence of the presence of a selected susceptor or microwave interactive material.
24. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the moldable assembly is moved within the microwave field during foaming.
25. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the energy density in said microwave apparatus is about 0.001 to 10 W/cm 3 during processing.
26. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the internal rate of heating within the material during foaming is controlled to about 0.1-20° C. per second temperature rise.
27. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein said microwave is operated, during processing, at a frequency of about 100 MHz to 5 GHz.
28. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the power for the microwave apparatus is up to about 100 kW.
29. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the nominal microwave frequency, power level and energy density remain the same for different shaped foamed objects.
30. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the nominal microwave frequency, power level and energy density are adjusted dependent on the shape of the foamed product to be produced.
31. A method of producing a biodegradable foamed product as claimed in claim 1 wherein rapid depressurization is used in conjunction with microwave irradiation during step (c).
32. A method of producing a biodegradable foamed product as claimed in claim 1 wherein elevated pressure is used in conjunction with microwave irradiation during step (c).
33. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein the mold further comprises microwave interactive material disposed on at least one internal surface of a cavity in said mold.
34. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein, the temperature of the inner mold surface is between about 80° C. and about 120° C.
35. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein, the temperature of the inner mold surface is about 120° C.
36. A method of producing a bio-degradable foamed product as claimed in claim 1 wherein, the biodegradable foam product has a wall thickness of up to 1 meter.
37. A method of producing a bio-degradable foamed product as claimed in claim 1 which comprises using water as a blowing agent.