This study valorizes onion peel, an agro-industrial by-product rich in phenolic compounds and structural carbohydrates, for the development of cassava starch-based biodegradable films. The films were prepared using the solution casting method; a cassava starch matrix was mixed with a 2.5% glycerol solution and heated to 85 °C for 30 min. A separate solution of onion peel powder (OPP) in distilled water was prepared at 25 °C. The two solutions were then combined and stirred for an additional 2 min before 25 mL of the final mixture was cast to form the films. Onion peel powder (OPP) incorporation produced darker and more opaque films, suitable for packaging light-sensitive foods. Film thickness increased with OPP content (0.138–0.218 mm), while moisture content (19.2–32.6%) and solubility (24.0–25.2%) decreased. Conversely, water vapor permeability (WVP) significantly increased (1.69 × 10⁻⁹–2.77 × 10⁻⁹ g·m⁻¹·s⁻¹·Pa⁻¹; p < 0.0001), reflecting the hydrophilic nature of OPP. Thermal analysis (TGA/DSC) indicated stability up to 245 °C, supporting applications as food coatings. Morphological analysis (SEM) revealed OPP microparticles embedded in the starch matrix, with FTIR and XRD suggesting electrostatic and hydrogen–bond interactions. Mechanically, tensile strength improved (up to 2.71 MPa) while elongation decreased (14.1%), indicating stronger but less flexible films. Biodegradability assays showed slightly reduced degradation (29.0–31.8%) compared with the control (38.4%), likely due to antimicrobial phenolics inhibiting soil microbiota. Overall, OPP and cassava starch represent low-cost, abundant raw materials for the formulation of functional biopolymer films with potential in sustainable food packaging.

\begin{abstract} This study aims to address the effect of date kernel powder (DKP) as reinforcement obtained from Touggourt oasis, Algeria, on the elastic properties of biocomposites based on two prepared DKPs with grain size 300 $\mu$m and 500 $\mu$m mixed on epoxy (ER) matrix. The weight percentage of powders with 5\%, 10\%, and 15\% was used to obtain epoxy matrix (ER)/date kernel powder (DKP) biocomposites. The effects of DKP size on the elastic properties of ER/DKP biocomposites, such as ultrasonic wave velocities (longitudinal and shear), longitudinal modulus, shear modulus, bulk modulus, Young’s modulus of elasticity, ultrasonic microhardness, Poisson’s ratio, and acoustic impedance, were determined using the ultrasonic through-transmission method. In addition, the two biocomposites prepared to analyze the chemical changes in the functional groups and their morphology were studied using X-ray diffraction and optical microscopy, respectively. The results of ultrasonic characterization of the ER/DKP biocomposites showed that there is a significant relationship between the sizes of DKP and elastic constant values. In addition, the experimental results illustrated that the optimum weight percent of DKP reinforcement in neat ER for excellent mechanical behavior of ER/DKP biocomposites is 5\% and 10\% for 300 $\mu$m and 500 $\mu$m, respectively. \noindent\textbf{Keywords:} Date kernel powder (DKP), Bio-sourced materials, Ecofriendly materials, Ultrasonic characterization, Elastic constants \end{abstract}