Towards novel lignin-based aromatic polyesters: In-depth study of the thermal degradation and crystallization of poly(propylene vanillate)

Abstract

The growing environmental concerns over the excessive emissions of greenhouse gasses and the accumulation of synthetic plastics in terrestrial and aqueous recipients have driven the public, academic and industrial awareness towards the production of novel bio-based polymeric materials. Within this frame, poly(propylene vanillate) (PPV) is an alipharomatic engineering polyester with promising thermal and mechanical properties, produced via a two-step melt polycondensation of 4-(3-hydroxypropoxy)-3-methoxybenzoic acid, a monomer derived from the potentially lignin-based vanillic acid. Herein, a systematic investigation of the non-isothermal crystallization, the thermal stability and the decomposition mechanism of PPV was performed, with the implementation of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS), respectively. The Lauritzen-Hoffman parameters (K and U*) of crystallization were calculated using a combination of the Lauritzen-Hoffman theory and isoconversional methods. The determination of the activation energy, using isoconversional methods, along with the model fitting analysis of mass loss data have led to a first assumption about the thermal degradation profile of the synthesized polyester. Furthermore, decomposition products revealed the two different main degradation mechanisms take place: heterolytic β-hydrogen scission and α-homolytic scission.