Foam of polymers
The disclosure pertains to foam of polymers, which can be made by a method for making a polymer foam comprising vacuum or gas-filled compartments by making a solution of 1 to 20% by weight of a polymer in a solvent; adding particles to the a polymer solution; solidifying the polymer wherein the particles are contained by heating, cooling, ageing, or coagulating to obtain a polymer foam or matrix comprising the particles, and obtaining from the polymer matrix the polymer foam containing the compartments; and optionally washing, drying, and/or heating the polymer foam.
1. A method for making a polymer foam comprising vacuum or gas-filled compartments by
a) making a solution of 1 to 20% by weight of a polymer in NMP/CaCl 2 or sulfuric acid;
b) adding particles to the polymer solution; and
c) solidifying the polymer wherein the particles are contained by heating, cooling, ageing, or coagulating to obtain a polymer foam or matrix comprising the particles, and obtaining from the polymer matrix the polymer foam containing the compartments; wherein in step b)
i) the particles are inert hollow particles, wherein the hollow part is the vacuum or gas-filled compartment to give the polymer foam; or
ii) the particles are solid particles that are insoluble in the NMP/CaCl 2 or sulfuric acid to give the polymer matrix; whereby in step c) the solid particles are removed from the polymer matrix after the heating, cooling, ageing, or coagulating by dissolving the solid particles in a second solvent wherein said solid particles are soluble and the polymer is insoluble, to give the polymer foam; or
iii) the particles are expandable particles that upon dissolution in the NMP/CaCl 2 or sulfuric acid in step b) and/or during heating in step c) release gas bubbles to give the polymer foam, wherein the polymer is selected from an aramid.
2. The method according to claim 1 wherein the polymer is selected from poly(p-phenylene-terephthalamide), poly-4,4′-(3,3′-dihydroxy)-bisphenylene-therephthalamide, and co-poly-(paraphenylene/3,4′-oxydiphenylene terephthalamide.
3. The method according to claim 1 wherein the particles are inert hollow particles wherein the inert material is glass or a ceramic material; or the particles are solid particles, wherein the solid is an inorganic salt and the second solvent is water.
4. The method according to claim 3 wherein the particle is an inert hollow particle of glass or of a ceramic material, wherein the hollow part is filled with gas.
5. The method according to claim 1 wherein the particles are beads of which at least 50% by volume has a diameter between 1 and 500 μm.
6. The method according to claim 1 wherein the solidifying step c) is performed in a mold.