Sequential Isocyanate/Acrylate Functionalization of Cellulose Nanocrystals for Multi‐Performance Advancement in Unsaturated Polyester Composites

ABSTRACT This study develops a functionalization strategy for incorporating cellulose nanocrystals (CNCs) into unsaturated polyester resin (UPR) to simultaneously enhance its strength and toughness. Surface modification of CNCs was achieved through sequential reactions with toluene diisocyanate (TDI) and hydroxyethyl acrylate (HEA), introducing carbon double bonds(CC) to obtain modified CNC (m‐CNC). The m‐CNC was subsequently compounded with UPR to fabricate composite materials. A comprehensive investigation of the composites' morphological features, mechanical performance, and thermal behavior was conducted through transmission electron microscopy (TEM), mechanical testing, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). Experimental results demonstrate that 0.3 wt% m‐CNC incorporation markedly improves UPR's mechanical properties, with the composite exhibiting 23.55% higher tensile strength, 59.01% increased flexural strength, and 96.16% enhanced impact resistance compared to unmodified UPR. DMA characterization revealed that covalent cross‐linking between m‐CNC and the UPR matrix restricts polymer chain mobility, resulting in a 35.4% elevation in storage modulus. TGA data confirmed the heat resistance improvement, showing 12.8°C and 9.3°C increases in thermal decomposition temperatures for m‐CNC/UPR composites relative to pure UPR and unmodified CNCs/UPR systems, respectively. This synergistic modification approach effectively balances structural integrity preservation of CNCs with significant enhancement of UPR's multifunctional performance, demonstrating potential applications in automotive, construction, new energy, and eco‐friendly packaging industries. It emerges as a promising alternative to conventional composite materials.