Construction and performance of polyethyleneimine modification on cellulose nanocrystal surface and reducing end groups.

Cellulose nanocrystals (CNCs) possess excellent mechanical strength, high crystallinity, and intrinsic biocompatibility, but their limited surface reactivity and weakly active reducing end groups restrict their application in functional materials. In this work, CNCs were modified with polyethyleneimine (PEI) to enhance surface functional density. The grafting of PEI onto CNCs significantly increased the availability of nucleophilic sites, strengthened the interaction between PEI and the aldehydic reducing ends, and enabled efficient crosslinking. As a result, PEI-modified CNCs displayed markedly enhanced properties, the surface-modified CNC-PEI(S) exhibited a zeta potential increase to ~ -28.3 mV, improved dispersion stability with an average particle size of 204.8 nm, and a maximum formaldehyde adsorption capacity of 11.8 % within 20 min at room temperature. It showed a fluorescence intensity enhancement responsive to formaldehyde concentrations ranging from 2 to 400 ppm. In contrast, the reducing-end modified CNC-PEI(R) demonstrated superior performance, with a formaldehyde removal efficiency of up to 55.3 % under the same conditions and a linear fluorescence response to low formaldehyde concentrations (20-400 ppb). Both materials retained the chiral nematic structure of native CNCs and exhibited significant thermal stability, with the maximum degradation temperature of CNC-PEI(S) reaching approximately 325 °C. These functionalized CNCs were successfully fabricated into freestanding films and integrated into a portable, low-cost detection device for rapid, visual quantification of aqueous formaldehyde under UV light. These findings demonstrate that PEI-functionalized CNCs provide a versatile platform for constructing high-performance bio-based materials suitable for environmental sensing and pollutant adsorption, offering a sustainable alternative to conventional detection and remediation technologies.