My friend you say that (thermal degradation ) this mean the driving force of your reaction is the temperature

you can study the effect of pH on decarboxylation at isothermal temperature

I assume you mean deprotonated (anion) or not (neutral). If you have a carboxylate anion what will happen to the charge once the carbon dioxide leaving group is removed? The decarboxylation of sodium carboxylates proceeds via a slightly different mechanism to avoid this, producing an inorganic carbonate instead of carbon dioxide (http://www.chemguide.co.uk/organicprops/acids/decarbox.html).

If it is "pyrolysis", the mechanism indicates it depends on pH.

i decarbolxylate some compounds and in my exprience it depends to pH.

when u add acid to reaction with diffrent percent,u will find it's depend.

in mechanistic viewpoint decarboxylation mechanism have a enol-keto intermediate that acidic condition more stable it.protonation of the carbonyl, break the O-H bond and form the p bond, break the C-C and make the C=C. Note the concerted nature of this reaction and the cyclic transition state.

Q. Rev. Chem. Soc., 1951,5, 131-146

DOI: 10.1039/QR9510500131

I think the decarboxylation reaction depends on the chemical environment of the carboxyl group and the adjacent group that can catalyze decarboxylation process ...

Many things you can try to use in decarboxylation reaction like :

1.try to do reaction in acidic medium and basic medium ...follow your reaction by tlc or hplc to check if the reaction give promissing progress or not

2. Try to do reaction at isothermal temperature and constant pH but at reduced pressure according to leuchatelear prenciple