Biodegradable and industrially compostable injection molded microcellular flexible foams, and a method of manufacturing the same
A process for injection molded microcellular foaming various flexible foam compositions from biodegradable and industrially compostable bio-derived thermoplastic resins for use in, for example, footwear components, seating components, protective gear components, and watersport accessories wherein a process of manufacturing includes the steps of: producing a suitable thermoplastic biopolymer or biopolymer blend; injection molding the thermoplastic biopolymer or biopolymer blend into a suitable mold shape with inert nitrogen gas; controlling the polymer melt, pressure, temperature, and time such that a desirable flexible foam is formed; and utilizing gas counterpressure in the injection molding process to ensure the optimal foam structure with the least amount of cosmetic defects and little to no plastic skin on the outside of the foamed structure.
1. A method for manufacturing a flexible foam, the method comprising:
forming a molten polymer from a thermoplastic masterbatch, the thermoplastic masterbatch comprising one or more biodegradable thermoplastic polymers;
mixing a supercritical fluid with the molten polymer to create a single-phase solution;
introducing the single-phase solution into a mold cavity of a molding apparatus, the molding apparatus having at least one pressure sensor for sensing a pressure in the molding apparatus;
foaming the single-phase solution in the mold cavity by allowing the supercritical fluid to come out of solution, thereby forming a flexible foam; and
pressurizing the mold cavity with a counterpressure gas during foaming of the single-phase solution, wherein a dosing amount and hold time of the counterpressure gas in the mold cavity is controlled by a computer-controller that receives data from the at least one pressure sensor,
wherein the flexible foam has a density in a range of about 2 lbs/ft 3 to about 10 lbs/ft 3 .
2. The method of claim 1 , wherein the one or more biodegradable thermoplastic polymers comprise one or more of polylactic acid, poly(butylene adipate-co-terephthalate), polycaprolactone, polyhydroxy alkanoate, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate, or combinations thereof.
3. The method of claim 1 , wherein the one or more biodegradable thermoplastic polymers are selected from the group consisting of polylactic acid, poly(butylene adipate-co-terephthalate), polycaprolactone, polyhydroxy alkanoate, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate, and combinations thereof.
4. The method of claim 1 , wherein the one or more biodegradable thermoplastic polymers are produced from plant-derived feedstocks.
5. The method of claim 1 , wherein the thermoplastic masterbatch does not include ethylene vinyl acetate.
6. The method of claim 1 , wherein the one or more biodegradable thermoplastic polymers do not cross-link during manufacturing of the flexible foam.
7. The method of claim 1 , wherein the supercritical fluid comprises supercritical nitrogen.
8. The method of claim 1 , wherein the supercritical fluid comprises supercritical carbon dioxide.
9. The method of claim 1 , wherein the supercritical fluid is introduced at a pressure in the range of about 150 bar to about 300 bar.
10. The method of claim 1 , wherein pressurizing the mold cavity with the counterpressure gas prevents gas bubbles from breaking through a surface of the flexible foam during foaming of the single-phase solution.
11. The method of claim 1 , wherein pressurizing the mold cavity comprises pressurizing the mold cavity in the range of about 5 bar to about 50 bar for a length of time between 1 second to 25 seconds with the counterpressure gas.
12. The method of claim 1 , wherein introducing the single-phase solution into the mold cavity of a molding apparatus comprises contacting a surface of the mold cavity with the single-phase solution.
13. The method of claim 12 , further comprising controlling a temperature of the surface of the mold cavity with a dynamic mold temperature control system that is configured to provide hot and cold thermal cycling.
14. The method of claim 13 , wherein the dynamic mold temperature control system comprises one or more heating elements and one or more cooling elements coupled to the molding apparatus.
15. The method of claim 1 , wherein the mold cavity has a shape such that the flexible foam is formed in the mold cavity in a shape of a shoe component.
16. The method of claim 15 , wherein the shoe component is selected from one or more of a shoe sole, a shoe midsole, or a shoe insole.
17. The method of claim 1 , wherein the flexible foam is entirely biodegradable and/or entirely industrially compostable.