In Situ Experimental Study of the Hydrolysis Kinetics of Poly(Butylene Adipate‐Co‐Terephthalate) in the Molten State

ABSTRACT

Poly(butylene adipate‐co‐terephthalate) (PBAT) is a representative biodegradable aliphatic–aromatic copolyester, and its hydrolysis is a key process controlling both environmental degradation and chemical recycling. However, the hydrolysis behavior of PBAT above its melting point remains insufficiently understood, particularly with respect to in situ mechanistic observation and kinetic quantification. In this study, high‐temperature hydrolysis of PBAT was investigated at 260°C–320°C using a fused silica capillary reactor coupled with in situ optical microscopy and Raman spectroscopy. Optical observations showed that PBAT transformed into a molten droplet at approximately 120°C and subsequently underwent progressive shrinkage and complete hydrothermal degradation during isothermal treatment at elevated temperatures. Raman spectra indicate preferential cleavage of aliphatic ester segments, producing 1,4‐butanediol‐related aliphatic species and, by stoichiometric inference, adipic acid, whereas terephthalate‐rich aromatic fragments persisted as poly(butylene terephthalate)‐like oligomers and terephthalic acid‐related products. Kinetic analysis based on the time‐dependent evolution of droplet area showed a sigmoidal “slow–fast–slow” profile, which can be described by a Logistic‐type model and is consistent with autocatalytic hydrolysis promoted by accumulated carboxylic acid end groups. The apparent activation energy derived from microscopy (90.8 kJ mol ⁻¹ ) is higher than that from Raman spectroscopy (73.5 kJ mol ⁻¹ ), as the former captures the comprehensive process of melt hydrolysis and decomposition, whereas the latter specifically tracks the evolution of hydrolysis products. These results provide in situ mechanistic evidence and kinetic parameters for understanding the temperature‐accelerated hydrolysis and hydrothermal recycling of PBAT.