decomposition at 623 K but can cause complete decomposition of
PEEK at 703 K [16]. It is believed that the carbonate functional
group is responsible for the decomposition observed in carbonate
solutions, therefore the replacement of Na2CO3 with another carbonate
species should not significantly alter the effects. Previous
trial experiments showed that the addition of 3.3 mmol ml1
Na2CO3 resulted in considerable quantities of salt residue post reaction.
The solubility of salts in supercritical water is extremely low,
typically leading to the precipitation from solution [17e20].
Consequently the carbonate concentration was reduced greatly
until no residual salt build up post reaction was observed.