This research explores the synthesis of carboxymethyl cellulose (CMC) for the development of a cost-effective bioplastic film that can serve as a sustainable alternative to synthetic plastic. Replacing plastic packaging with CMC-based films offers a solution for mitigating environmental pollution, although the inherent hydrophilicity and low mechanical strength of CMC present significant challenges. To address these limitations, zinc oxide nanoparticles (ZnO NPs) were employed as a biocompatible and non-toxic reinforcement filler to improve CMC’s properties. A solution casting method which incorporated varying concentrations of ZnO NPs (0%, 5%, 10%, 15%, 20%, and 25%) into the CMC matrix allowed for the preparation of composite bioplastic films, the physicochemical properties of which were analyzed using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The results revealed that the ZnO NPs were well-integrated into the CMC matrix, thereby improving the film’s crystallinity, with a significant shift from amorphousness to the crystalline phase. The uniform dispersion of ZnO NPs and the development of hydrogen bonding between ZnO and the CMC matrix resulted in enhanced mechanical properties, with the film CZ₂₀ exhibiting the greatest tensile strength—15.12 ± 1.28 MPa. This film (CZ₂₀) was primarily discussed and compared with the control film in additional comparison graphs. Thermal stability, assessed via thermogravimetric analysis, improved with an increasing percentage of ZnO Nps, while a substantial decrease in water vapor permeability and oil permeability coefficients was observed. In addition, such water-related properties as water contact angle, moisture content, and moisture absorption were also markedly improved. Furthermore, biodegradability studies demonstrated that the films decomposed by 71.43% to 100% within 7 days under ambient conditions when buried in soil. Thus, CMC-based eco-friendly composite films have the clear potential to become viable replacements for conventional plastics in the packaging industry.

The increasing demand for sustainable, flexible and high-performance humidity sensors is driving the search for biodegradable alternatives to conventional electronic sensors. In this study, we report a highly sensitive capacitive humidity sensor fabricated on a self-standing carboxymethyl cellulose (CMC) bioplastic film, thus eliminating the need for additional substrates or sensing layers. The sensor design, including interdigitated electrode (IDE) geometry and film thickness, was optimized using COMSOL Multiphysics software's simulations to maximize sensitivity and ensure reliable performance. The CMC film was prepared via a dispersion-casting technique, and silver IDEs were directly deposited using aerosol jet printing, thus enabling a low-cost and scalable fabrication process. Comprehensive material characterization confirmed the film's smooth surface, robust electrode adhesion, and excellent flexibility, which allowed it to withstand repeated mechanical deformation. Electrical performance testing of the sensor revealed a marked increase in capacitance with increasing relative humidity (35–100% RH). The sensor achieved a sensitivity of 7110 pF/%RH, significantly outperforming a comparable paper-based reference. The sensor also exhibited a rapid response time of 5.3 s and a recovery time of 9.2 s, while maintaining stable performance under cyclic mechanical stress. The sensor also showed low hysteresis, confirming reversibility and operational stability. Biodegradability assessments under soil burial conditions indicated substantial weight loss and material disintegration, underscoring the environmental compatibility of the sensor. Owing to its high sensitivity, mechanical robustness, eco-friendliness, and cost-effective fabrication, the proposed CMC-based humidity sensor therefore holds significant potential for a scalable, broad spectrum of applications, including smart packaging, environmental monitoring, food safety, health care and wearable electronics.