WE CLAIM:
1. A chemical blowing agent for foaming a thermoplastic polymer precursor, for example
PVC plastisol or a polymer resin in an extrusion process,
said chemical blowing agent comprising a functionalized particulate bicarbonate, wherein said functionalized particulate bicarbonate contains at least one additive, and wherein said additive in the functionalized particulate bicarbonate comprises rosin acid, any derivative thereof, any salt thereof, or any combinations thereof, preferably comprises abietic acid, dihydroabietic acid, neoabietic acid, a rosin acid ester, or mixtures thereof, more preferably comprises abietic acid, dihydroabietic acid, or mixtures thereof
2. The chemical blowing agent according to Claim 19 wherein the blowing agent does not contain any further blowing agent which is an exothermic blowing agent, or wherein the chemical blowing agent does not contain a compound which liberates nitrogen gas during heating, or wherein the chemical blowing agent does not contain a compound which liberates ammonia gas during heating.
3. The chemical blowing agent according to Claim 1 or 2, wherein the functionalized particulate bicarbonate comprises at least one additional additive selected from
one or more polymers;
one or more amino acids, any derivative thereof, and salts thereof;
one or more inorganic salts;
one or more oils;
one or more fats;
one or more resin acids, any derivative thereof, and salts thereof;
one or more fatty acids, any derivative thereof, and salts thereof;
a carboxylic or polycarboxylic acid, derivative thereof (such as esters), or salts thereof;
one or more soaps;
one or more waxes; or
any combinations thereof; preferably selected from at least one polymer which more preferably is selected from the group consisting of polyoxyalkylenes and derivatives thereof including polyethylene glycols, poly(meth)acrylates and derivatives thereof, polyvinylalcohol, polysaccharides and combinations thereof; and even more preferably from the group consisting of polyvinylalcohol and polyoxyalkylenes and derivatives thereof including polyethylene glycols.

4. The chemical blowing agent according to any of Claims 1 to 3, wherein the fïmctionalized particulate bicarbonate comprises at least 50% by weight and less than 100% by weight of the bicarbonate component, and firom 50% or less to 0.02% by weight of at least one of said additive.
5. The chemical blowing agent according to any of Claims 1 to 4, wherein the functionalized particulate bicarbonate comprises at least 65% by weight and less than 100% by weight of the bicarbonate component, and from 35% or less to 0.02% by weight of at least one of said additive.
6. The chemical blowing agent according to any of Claims 1 to5 wherein the particles of the functionalized particulate bicarbonate have a partiele size distribution of D50 of more than 1 um and at most 250 um, preferably at most 100 urn, more preferably at most 60 urn, yet more preferably at most 40 um, yet most preferably at most 25 um.
7. The chemical blowing agent according to any of Claims 1 to 5, wherein the particles of the functionalized particulate bicarbonate have a partiele size distribution of D50 of at most 1 um.
8. The chemical blowing agent according to any of Claims 1 to 7, wherein the functionalized particulate bicarbonate is obtained by at least one of the following processes:
by spray-drying (also known as atomization), wherein the additive is dissolved in the bicarbonate-containing solution.
- by grinding or co-grinding (also known as milling or co-milling) with the additive(s) in emulsion or powder form;
- by spray coating and granulation within a fluidized bed,
- by spray agglomeration within a fluidized bed,
- by spray chilling (e.g., spray cooling, spray freezing),
- by roller compaction, and/or
- by extrusion, including simultaneous mixing/extrusion;
optionally folio wed by subjecting the thus obtained functionalized particulate bicarbonate to milling to reduce its mean partiele size; preferably obtained by grinding, extrusion, and/or spray coating with the additive(s); more preferably obtained by grinding and/or extrusion with the additive(s).
9. The chemical blowing agent according to any of Claims 1 to 8, further comprising an
second compound which liberates CO2 upon heating, said second compound being selected
from the group consisting of a carboxylic or polycarboxylic acid, derivative thereof (such as
esters), or salts thereof, wherein said second compound optionally is functionalized with at

least one additive which is different or the same as the one in the functionalized particulate bicarbonate, preferably the same additive, and wherein said second compound preferably is at least one of:
fümaric acid,
tartaric acid,
citric acid, citrates (such as sodium hydrogen citrate, disodium citrate), or esters of citric
acid; or combination thereof.
10. The chemical blowing agent according to any of Claims 1 to 9, wherein the functionalized particulate bicarbonate further comprises silica, preferably comprises amorphous silica, more preferably comprises amorphous precipitated silica.
11. A foamable polymer composition, comprising a polymer, optionally a foaming stabilizer, and the chemical blowing agent according to any of Claims 1 to 10, wherein the polymer is a PVC, a polyurethane, a polyolefin, or a polyamide.
12. The foamable polymer composition according to Claim 11, further comprising an exothermic chemical blowing agent, preferably selected from the group consisting of ADCA (azodicarbonamide), OBSH (4,4'-oxybis(benzenesulfonyl hydrazide)), DNPT (dinitrosopentamethylene tetramine), PTSS (p-toluene semicarbazide), BSH (benzene-4-sulfonohydrazide), and TSH (toluene-4-sulfonohydrazide), 5-PT (5-phenyltetrazole), more preferably comprising ADCA.
13. The foamable polymer composition according to Claim 11 or 12, being a foamable PVC plastisol composition, wherein the polymer comprises a PVC resin.
14. The foamable polymer composition according to Claim 11, being a foamable PVC plastisol composition, wherein the polymer comprises a PVC resin, and, which preferably does not contain ADCA(azodicarbonamide), BSH (benzenesulfonylhydrazide), and/or TSH (p-toluenesulfonylhydrazide).
15. A process for manufacturing a polymer, comprising heating the foamable polymer composition according to Claim 11 or 12 which comprises the functionalized particulate bicarbonate at a temperature suitable for liberating C02 gas and melting the polymer during a gelation time at a temperature above glass transition temperature Tg and/or above melting temperature Tm of the polymer which is less than 130 seconds.

16. A foamed polymer obtained by the process of Claim 15, wherein the polymer is a PVC, a polyurethane, a polyolefin, or a polyamide.
17. A process for manufacturing a PVC foamed polymer, comprising heating the foamable PVC polymer composition according to Claim 13 or 14 which comprises the functionalized particulate bicarbonate and the PVC resin at a temperature suitable for liberating C02 gas and melting the PVC polymer during a gelation time from 90 seconds to 120 seconds at a temperature from 190 to 210°C, preferably from 200 to 210°C, to pro vide a foamed PVC polymer, wherein the foamable PVC polymer composition preferably is spread coated on a surface before heating and melting, and wherein the PVC foamed polymer has an expansion ratio of at least 270, preferably at least 280, more preferably at least 300 and/or has a density of less than 0.6 g/cm3, preferably less than 0.55 g/cm3, more preferably at most 0.5 g/cm3.
18. A process for manufacturing a polymer, comprising heating the foamable PVC plastisol composition according to Claim 13 or 14 which comprises the functionalized particulate bicarbonate at a temperature suitable for liberating C02 gas and melting the PVC resin during a gelation time, wherein said gelation time with the chemical blowing agent comprising the functionalized particulate is less than the gelation time that would be obtained with a chemical blowing agent liberating N2, all other components in the foamable PVC plastisol composition being the same.
19. A foamed PVC obtained by the process of Claims 17 or 18.