This study investigates the effectiveness of using cellulose microfibrils (CMFs) synthesized from different acids as reinforcing agents in polyvinyl alcohol (PVA) composites. The research focuses on the morphology, thermal properties, and chemical behavior of the cellulose particles. Citric acid-derived CMFs exhibited the highest yield and aspect ratio, while oxalic acid-derived particles showed the maximum thermal stability. Cast films of PVA reinforced with CMFs were analyzed using Fourier transform infrared spectroscopy (FTIR), thermal degradation temperature (T_d), differential scanning calorimetry (DSC), and tensile strength tests. The addition of CMFs led to significant improvements in the thermal behavior and mechanical properties of the films, with 5% CMF derived from citric acid showing the most substantial increase in Young's modulus. The study highlights the potential of using organic acids for cellulose particle synthesis to enhance the sustainability and performance of PVA composites.This study investigates the effectiveness of using cellulose microfibrils (CMFs) synthesized from different acids as reinforcing agents in polyvinyl alcohol (PVA) composites. The research focuses on the morphology, thermal properties, and chemical behavior of the cellulose particles. Citric acid-derived CMFs exhibited the highest yield and aspect ratio, while oxalic acid-derived particles showed the maximum thermal stability. Cast films of PVA reinforced with CMFs were analyzed using Fourier transform infrared spectroscopy (FTIR), thermal degradation temperature (T_d), differential scanning calorimetry (DSC), and tensile strength tests. The addition of CMFs led to significant improvements in the thermal behavior and mechanical properties of the films, with 5% CMF derived from citric acid showing the most substantial increase in Young's modulus. The study highlights the potential of using organic acids for cellulose particle synthesis to enhance the sustainability and performance of PVA composites.