Manufacture of fully recyclable foamed polymer from recycled material
A solid state foaming process permits the use of up to 100% recycled pre- and post-consumer polymer for the manufacture of foamed polymer material and thermoformed foamed polymer articles. The process enables the optional formation of integral unfoamed skins of controllable depth and crystallinity on foamed polymeric materials suitable for a wide variety of applications. Because this process does not alter the underlying chemistry of the material all scrap from the manufacturing process may be reused without additive to form new foamed polymeric materials and articles.
1. A process for making a shaped article of manufacture from a sheet or roll of a thermoplastic material, wherein the thermoplastic material consists essentially of a virgin thermoplastic material admixed with a previously foamed thermoplastic material, wherein the virgin material and the previously foamed thermoplastic material are of the same chemical composition, and wherein the previously foamed thermoplastic material is in an amount that ranges from about 5% to about 100% by weight of the thermoplastic material, the process comprising at least the following steps:
(a) pressurizing the sheet or roll of the thermoplastic material with a plasticizing gas under a selected pressure and period of time sufficient to yield a reversibly plasticized thermoplastic material, the plasticized thermoplastic material being impregnated with the plasticizing gas;
(b) depressurizing the plasticized thermoplastic material to thereby desorb some of the plasticizing gas from the plasticized thermoplastic material to thereby yield a partially desorbed plasticized thermoplastic material;
(c) partially foaming the partially desorbed plasticized thermoplastic material to yield a plasticized and partially foamed thermoplastic material; and
(d) thermoforming-foaming, while in a thermoforming mold, the plasticized and partially foamed thermoplastic material into the shaped article of manufacture, wherein the step of thermoforming-foaming occurs before the impregnated plasticizing gas concentration falls below about 0.5 percent by weight of the plasticized and partially foamed thermoplastic material, and wherein the plasticized and partially foamed thermoplastic material is additionally foamed by an amount ranging from 2% to 30%.
2. The process of claim 1 wherein the thermoplastic material consists essentially of polyethylene terephthalate (PET).
3. The process of claim 2 wherein the plasticizing gas is carbon dioxide (CO2).
4. The process of claim 3 wherein the shaped article has a width to depth ratio of greater than about 1:1.
5. The process of claim 1 wherein the shaped article of manufacture has an outer skin layer and a foamed interior.
6. The process of claim 1 wherein the shaped article of manufacture is a cup having a wall angle of less than about 35 degrees from vertical.
7. The process of claim 1 wherein the selected pressure ranges from about 0.345 MPa to about 17.2 MPa, and the selected period of time ranges from about 3 hours to about 100 hours.
8. The process of claim 1 further comprising, after the step of thermoforming-foaming, a step of additional heating to thereby increase the crystallinity level of the shaped article of manufacture.