Polyester is a condensation polymer of dicarboxylic acid and diol.
Example : Polethylene terphthalate is polymer of ethylene glycol and tere phthallic acid.
When a strong acid like HCl or a strong base like NaOH comes in contact with polyester (like spilled on slacks) it causes hydrolysis of polyester and it get converted back to dicarboxylic and diol(the monomers).
the general reaction will be
RCOOR' ---> RCOOH + R'OH
Thus slacks will get teared.
It is a covalent bond because both carbon and oxygen are nonmetals. The formula will be CO² because the electrons between the atoms are being shared equally.
