Effect of organosilane incorporation on the structure and adhesive performance of lignin-based non-isocyanate poly(urea-urethane) networks

Lignin-based non-isocyanate polyurethanes (NIPUs) are emerging as a sustainable alternative to conventional polyurethanes; however, their implementation is limited by insufficient control of microphase organisation and interfacial performance. In this work, the effect of (3-aminopropyl)trimethoxysilane (APTMS) incorporation on the structure and properties of lignin-derived NIPUs is investigated, with the aim of establishing a relationship between network architecture, intermolecular interactions and interfacial behaviour. NIPUs were synthesised via the polycondensation of bio-based lignin polyols with dimethyl carbonate and hexamethylenediamine, followed by incorporation of APTMS (5–25%). Spectroscopic analysis revealed that APTMS induces a reorganisation of hydrogen-bonded domains, leading to changes in microphase separation and associated intermolecular interactions within the polymer network. These structural variations directly influence stress transfer at the interface, resulting in a significant increase in dry shear strength measured by automated bonding evaluation system (ABES), with values 85–120% higher than those of the silane-free systems. In most cases, intermediate silane contents balanced stiffness and interfacial strength, although the optimum depended on the lignin-derived backbone. Thermal stability, analysed by thermogravimetric methods combined with isoconversional kinetics, indicated that degradation behaviour is governed by the relative abundance and organisation of urea-rich domains. Overall, organosilane induced microphase reorganisation tailors interfacial and thermal performance of lignin-based NIPUs, offering further insights into the structure property relationships in lignin-based polymer network.