Understanding the Concept:
Plasticizers are low-molecular-weight substances added to polymeric coating formulations (such as those used in tablet film coating) to reduce the polymer's glass transition temperature ($T_g$), enhance flexibility, reduce brittleness, and prevent cracking of the coating film.
Functional Ingredient Analysis:
• Dioctyl phthalate: A widely used phthalate ester that acts as an effective plasticizer for various polymers.
• Triacetin (Glycerol triacetate): Frequently used as a hydrophilic plasticizer in pharmaceutical film coatings.
• Triethyl citrate: A citric acid ester commonly utilized as a plasticizer, especially in enteric coating polymers like Eudragit.
• Glucaric acid: A dicarboxylic acid derived from sugar oxidation. It acts as a chemical intermediate, chelating agent, or structural compound, but it does not possess the property profile required to function as a polymer film plasticizer.
Therefore, Glucaric acid is the compound that does not function as a plasticizer.