An Integrated TG-TOFMS, Non-Negative Matrix Factorization, and Kendrick Mass Defect Framework for Analyzing the Thermo-Oxidative Degradation of Cellulose Nanofiber-Reinforced Polypropylene

Abstract Cellulose nanofiber-reinforced polypropylene (CNF/PP) composites are promising lightweight and high-performance materials. Reliable assessment of their service life requires quantitative elucidation of thermo-oxidative degradation-induced structural changes. This study presents a novel analytical approach that combines thermogravimetric analysis with time-of-flight mass spectrometry (TG-TOFMS), non-negative matrix factorization (NMF), and Kendrick mass defect (KMD) analysis (TG-NMF-KMD) to elucidate molecular-level structural changes and quantitatively assess the progression of thermo-oxidative degradation in CNF/PP. TG-TOFMS enabled the sensitive and simultaneous detection of weight-loss behavior and temperature-dependent high-resolution mass spectra of evolved degradation products from CNF/PP. However, interpretation of these mass spectra was challenging due to the presence of overlapping signals within similar temperature ranges. To address this issue, NMF was applied to deconvolute the mass spectra into components with distinct evolutionary behaviors. Subsequent KMD analysis revealed the molecular compositions of the pyrolysis products corresponding to each component. The combined TG-NMF-KMD approach enabled clear differentiation between ion series originating from undegraded PP and CNF and the degradation-derived components associated with different oxidation stages of PP. Degraded CNF contributed only minor components, thereby facilitating interpretation of the evolution profiles of each ion series. Furthermore, NMF fitting enabled quantitative evaluation of degradation progression based on the weight fractions of the degradation components. This was achieved by fitting the derivative thermogravimetric profiles to the evolution profiles of each ion series. Overall, the TG-NMF-KMD approach provides a powerful framework for elucidating degradation mechanisms and quantitatively analyzing degradation in multicomponent polymer composites.