Molecularly Designed Heterocyclic Additives for Mechanically Reinforced Biodegradable Nanocomposites

Biodegradable polymer/cellulose nanofiber (CNF) nanocomposites are promising sustainable materials, but mechanical reinforcement requires effective control of CNF dispersion, matrix–filler adhesion, and, in blend matrices, phase compatibility. Here, we report molecularly designed heterocyclic additives for two related reinforcement challenges: CNF dispersion and interfacial adhesion in a single poly(butylene succinate) (PBS) matrix, and simultaneous CNF dispersion and blend compatibilization in an immiscible poly(butylene adipate-co-terephthalate)/poly(lactic acid) (PBAT/PLA) matrix. In the first system, an isosorbide-derived heterocyclic additive was synthesized to modify CNFs for PBS nanocomposites. Its heterocyclic and urethane motifs promoted hydrogen bonding with CNFs, enabling their exfoliation and uniform distribution and enhanced matrix-filler adhesion. The resulting film showed increases of 18.6%, 33.3%, and 77.1% in tensile strength, elongation at break, and toughness, respectively, compared with neat PBS. In the second system, this concept was extended to an immiscible PBAT/PLA blend by synthesizing a heterocycle-containing additive with PLA oligomer blocks. In this structure, the heterocyclic and urethane moieties provided hydrogen bonding with CNFs to improve dispersion and matrix–filler adhesion, whereas the PLA blocks enhanced segmental affinity with the PLA-rich domain for PBAT/PLA compatibilization. The resulting film achieved a tensile strength of 19.37 MPa, elongation at break of 579.61%, Young’s modulus of 155.27 MPa, and toughness of 403.62 N/mm². Molecular simulations and FT-IR analysis using model systems supported the proposed interaction mechanisms. These results demonstrate that molecularly designed heterocyclic additives can be structurally tailored to the matrix architecture, offering a strategy for mechanically reinforced biodegradable nanocomposites based on single-polymer matrices or immiscible polymer blends.