Rapid solid-state foaming
Disclosed, among other things, are ways to manufacture reduced density thermoplastics using rapid solid-state foaming and machines useful for the saturation of plastic. In one embodiment, a foaming process may involve saturating a semi-crystalline polymer such as Polylactic Acid (PLA) with high levels of gas, and then heating, which may produce a reduced density plastic having high levels of crystallinity. In another embodiment, a foaming process may produce layered structures in reduced density plastics with or without integral skins. In another embodiment, a foaming process may produce deep draw structures in reduced density plastics with or without integral skins. In yet another embodiment, a foaming process may utilize additives, blends, or fillers, for example. In yet another embodiment, a foaming process may involve saturating a semi-crystalline polymer such as Polylactic Acid (PLA) with high levels of gas, and then heating, which may produce a reduced density plastic having high levels of crystallinity.
1. An article, comprising:
a non-laminated polymer sheet including at least 60% by weight of a polylactic acid polymer material, the non-laminated polymer sheet having a first outer region, a second outer region, and an inner region disposed between the first outer region and the second outer region,
the first outer region and the second outer region including cells having a first average dimension, and
the inner region including elongated cells having a second average dimension, the second average dimension greater than the first dimension, wherein the elongated cells have a length to width aspect ratio of at least 3:1, and
wherein the cells in the first outer region, the second outer region, and the inner region are formed by heating the non-laminated polymer sheet after the non-laminated polymer sheet has been exposed to a gas at a pressure of at least 500 PSI for a predetermined time period less than 15 minutes, the predetermined time period sufficient to at least partially saturate the non-laminated polymer sheet with the gas.
2. The article of claim 1 , wherein the non-laminated polymer sheet withstands deformation when at least one of the first outer region and the second outer region are exposed to a temperature of at least 180° F.
3. The article of claim 1 , wherein the first average dimension is 50 micrometers or less.
4. The article of claim 1 , wherein the second average dimension is at least 51 micrometers.
5. The article of claim 1 , wherein the non-laminated polymer sheet is heated for a period of 15 to 60 seconds after being exposed to the gas.
6. The article of claim 1 , wherein the first outer region and the second outer region have a higher level of crystallinity than the inner region.
7. The article of claim 1 , further comprising:
an additive.
8. The article of claim 7 , wherein the additive is a crystallizing additive.
9. The article of claim 7 , wherein the additive is selected from the group consisting of polybutyl succinate, polycaprolactone and polyhydroxyalkanoate.
10. The article of claim 1 , wherein the non-laminated polymer sheet includes filler.
11. The article of 10 , wherein the filler is a biodegradable filler selected from the group consisting of talc, algae, wood pulp, and starch.
12. The article of claim 1 , further comprising:
a skin disposed on at least one of the first outer region and the second outer region.
13. The article of claim 1 , further comprising:
a coating disposed on at least one of the first outer region and the second outer region.
14. The article of claim 1 , further comprising:
a solid core disposed in the inner region.
15. The article of claim 1 , wherein the non-laminated polymer sheet is a non-planar formed shape.