Boulic V., Hesse C., Staropoli M., Verge P., Schmidt D.F., Addiego F.
Polymer Testing, vol. 160, art. no. 109242, 2026
Understanding the mechanical recycling of vitrimers is essential for their effective reuse. A simple recycling strategy consists of grinding vitrimer materials into particles followed by hot pressing into a new shape. However, the relationship between molecular network rearrangement and material integrity during repeated recycling remains poorly understood. In this study, a bio-based polybenzoxazine vitrimer was mechanically recycled to investigate the mechanisms governing network reorganization. The influence of pressure and temperature during the first reprocessing step was examined by dynamic mechanical thermal analysis (DMTA). Pressure showed no significant effect on the viscoelastic behaviour, whereas temperature strongly influenced network homogeneity, increasing the breadth of the glass transition and acting as the key parameter for consolidation optimization. Recycling was subsequently repeated up to five times at the highest processing temperature to evaluate the relationship between network rearrangement and degradation. Repeated thermal exposure led to an increase in crosslink density and loss modulus, accompanied by a reduction in tensile strength and strain at break. These changes are attributed to the catalytic role of tertiary amines within the network. Initially, polybenzoxazine segments are connected through ester bonds linked to poly(ethylene glycol) (PEG<sub>400</sub>) chains. During transesterification-driven network rearrangement, ester groups preferentially react with alcohol groups located near tertiary amines, progressively releasing PEG<sub>400</sub> pendant chains and increasing the network crosslink density. Prolonged thermal exposure further induces PEG<sub>400</sub> cleavage, as evidenced by swelling experiments and subsequent <sup>1</sup>H NMR characterization. This work highlights the critical role of molecular network design in preserving vitrimer integrity and properties during mechanical recycling.
