Preparation, Characterization, and Utilization of Regenerated Cellulose for Reinforcing Natural Rubber Composite

This study examines the reinforcing potential of regenerated cellulose (RC) nanofibers, synthesized via an alkali–urea aqueous system, within a natural rubber (NR) matrix. The physical attributes of the RC nanofibers, including morphology, thermal stability, and swelling behavior, were characterized. RC nanofibers were incorporated into the NR matrix at loadings of 0, 1, 3, and 5 phr to evaluate their effects on composite properties. Results showed that the RC exhibited a honeycomb-like structure with a mean diameter of 33.0 ± 13.2 nm and a crystalline structure consistent with cellulose I (CI = 88.3%). The addition of RC nanofibers increased the bound rubber content and modified the vulcanization behavior of the NR. Mechanical testing revealed significant improvements in hardness, modulus at 100% elongation (M100), and tensile strength, with hardness increasing from 38 to 45 Shore A, M100 from 0.52 to 1.10 MPa, and tensile strength from 10 to 14 MPa, indicating enhanced stiffness and effective stress transfer within the composite matrix. This work demonstrates a novel integration of in situ cellulose regeneration within a latex-stage mixing process, enabling structural transformation from nanofibrils to a honeycomb-like architecture that enhances filler dispersion and rubber–filler interactions without chemical modification.