Thickening agent found celebrity between sentimentality and heartache (4,6)

'thickening agent' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'celebrity between sentimentality and heartache' is the wordplay.
'celebrity' becomes 'star' (a star is a celebrity or famous person).
'between' means one lot of letters goes inside another.
'sentimentality' becomes 'corn' (corniness).
'and' means one lot of letters go next to another.
'heartache' becomes 'ch' (I can't explain this - if you can you should believe this answer much more).
'corn'+'ch'='cornch'
'star' put inside 'cornch' is 'CORN STARCH'.

'found' acts as a link.

Can you help me to learn more?