Process for preparing foamed polymer
The invention pertains to a process for manufacturing a glycerol-tricarboxylic acid polyester foam which comprises the steps of combining glycerol and a tri-carboxylic acid to provide a liquid reaction mixture and contacting the reaction mixture with a substrate under polymerization conditions, wherein the substrate has a top layer comprising one or more of metal, metal oxide, and metal halide. The invention also pertains to a glycerol-tricarboxylic polyester foam, in particular a glycerol-citric acid polyester foam, which has a closed cell foam structure wherein at least 90 vol. % of the foam, preferably at least 95% of the foam, is built up from cells having a diameter below 2 mm. The foamed polyester of the present invention is “green”, biodegradable, and non-toxic, and can be cleanly combusted. It finds application in, int. al., packaging materials, insulation materials, and materials with a short life cycle.
1. Process for manufacturing a glycerol-tricarboxylic acid polyester foam, comprising combining glycerol and a tricarboxylic acid to provide a liquid reaction mixture and contacting the reaction mixture with a substrate under polymerization conditions, wherein the substrate has a top layer comprising one or more of metal, metal oxide, and metal halide.
2. The process according to claim 1 , wherein the tri-carboxylic acid is citric acid.
3. The process according to claim 1 , wherein a strong acid is added to the reaction mixture and/or wherein a strong acid is applied to the substrate prior to contacting the reaction mixture with the substrate.
4. The process according to claim 3 , wherein the strong acid is selected from one or more of hydrochloric acid HCl, hydroiodic acid (HI), hydrobromic acid (HBr), perchloric acid HClO 4 , nitric acid HNO 3 , sulfuric acid H 2 SO 4 , triflic acid, and trihaloacetic acid.
5. The process according to claim 3 , wherein the strong acid is used in an amount of at most 10 mol. %, calculated on the total moles tricarboxylic acid present in the system.
6. The process according to claim 1 , wherein the substrate comprises a top layer of metal, metal oxide, and/or metal halide, wherein the metal is selected from iron, steel, aluminium, copper, zinc, lead, brass, tin, and alloys and other combinations thereof.
7. The process according to claim 1 , wherein the substrate is in the form of a flexible metal material.
8. The process according to claim 1 , wherein the reaction is carried out for at least part of the time above the boiling point of water, that is, above the point where the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.
9. The process according to claim 1 , wherein the reaction mixture is seeded with pulverized polymer particles as seed.
10. The process according to claim 1 , wherein water is added to the reaction mixture in an amount of at least 2 wt. % on the total of acid and glycerol.
11. The process according to claim 1 , wherein the reaction is carried out in the absence of catalyst.
12. The process of claim 5 , wherein the strong acid is used in an amount of at most 8 mol. % calculated on the total moles tricarboxylic acid present in the system.
13. The process of claim 7 , wherein the flexible metal material is a metal foil.
14. The process of claim 13 , wherein the metal foil has a thickness in the range of 1-500 microns.
15. The process of claim 9 , wherein the mixture is seeded with pulverized polymer particles in an amount of 1-30 wt. %.