Final answer:
The key difference is that the neutralization of thio relaxers involves oxidation, whereas hydroxide neutralization is based on an acid-base reaction. Thio relaxers are also noted to be more effective at completely straightening hair due to their disulfide bond reduction capability.
Step-by-step explanation:
The neutralization of thio relaxers differs from hydroxide neutralization primarily in that the neutralization of thio relaxers involves oxidation. Unlike hydroxide relaxers that work by hydroxide ion reactions, thio relaxers use a reducing agent typically ammonium thioglycolate to break down the disulfide bonds in hair. After the hair is reformed on rollers or curlers, an oxidizing agent, usually a dilute solution of hydrogen peroxide, is applied. This agent reestablishes the disulfide bonds, locking the hair into its new shape. In comparison, hydroxide-relaxer neutralization is less about oxidation and more about neutralizing the strong alkaline pH of the straightening agent.
Furthermore, thio relaxers can be seen as more effective at fully straightening the hair due to their ability to reduce disulfide bonds more extensively. Hydroxide relaxers, while still effective, operate through a different mechanism, involving an acid-base neutralization reaction with the hydroxide ions derived from compounds like sodium hydroxide (NaOH), where Na+ acts as a spectator ion.