Integrated FTIR, DSC, and TGA analyses of structural evolution and thermal behavior in maleic anhydride-modified polylactic acid prepared by reactive melt processing

This study investigates the structural and thermal responses of maleic anhydride-modified polylactic acid (PLA) prepared through peroxide-initiated reactive melt processing using integrated Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The objective was to determine how MA content is associated with the local spectral environment, thermal-transition and crystallization behavior, and thermal stability of PLA. FTIR analysis revealed progressive variations in band intensity, broadening, asymmetry, and localized spectral distribution with increasing MA content, particularly in the carbonyl and fingerprint regions, while the characteristic PLA absorption framework remained identifiable. A weak shoulder at approximately 1630–1650 cm -1 was interpreted cautiously as a localized spectral variation rather than definitive evidence of a newly formed chemical structure. DSC showed lower glass transition temperatures (T g ) of 53.4–56.2 °C for the modified formulations compared with 64.8 °C for neat PLA and distinct cold-crystallization peaks (T cc ) at 95.3–97.5 °C, while melting temperatures (T m ) remained within 174.5–176.7 °C. TGA showed that the temperature at 5% mass loss (T 5 %) decreased from 342.1 °C for neat PLA to 320.1–339.2 °C for the modified formulations, whereas the maximum degradation temperature (T max ) remained comparatively stable at 368.8–372.5 °C. Collectively, the integrated FTIR–DSC–TGA results demonstrate that MA-containing reactive melt processing is associated with distinct changes in spectral, thermal-transition, crystallization, and early-stage thermal responses, while key PLA characteristics remain identifiable. This integrated interpretation provides a basis for understanding how formulation changes are reflected across complementary spectral and thermal responses, supporting future studies on modified PLA materials.