Bio-Based Deproteinized Natural Rubber/Alginate/Poly(vinyl alcohol) Films with Ca2+-Mediated and Tannic Acid-Induced Crosslinked Networks for Biodegradable Adhesive Materials

In this study, biodegradable adhesive composite films based on deproteinized natural rubber/alginate/poly(vinyl alcohol) (DPNR/ALG/PVA) were developed through Ca2+-mediated ionic crosslinking and tannic acid (TA)-induced hydrogen bonding interactions. DPNR/ALG/PVA mixtures were ionically crosslinked through ALG-Ca2+ interactions, cast into films, and subsequently immersed in TA-containing ethanol/water cosolvent systems. Treatment in a 75:25 ethanol/water solution at a PVA/TA weight ratio of 1:7 for 12 h produced stable films with a high gel fraction. The TA-treated DPNR/ALG3/PVA40 film exhibited gel fraction of 91.01 ± 0.79%, higher than that of the untreated film (71.22 ± 1.62%), indicating improved network stability after TA treatment. FTIR analysis confirmed the incorporation of ALG and PVA within the DPNR matrix and suggested the formation of interactions involving TA. Increasing ALG content from 1 to 5 phr enhanced swelling capacity, reaching 241.81 ± 22.30%, whereas increasing PVA content (20–80 phr) improved tensile strength from 3.51 ± 0.10 to 6.39 ± 0.43 MPa. Moreover, the PVA-TA network improved adhesive performance, increasing lap shear strength from 1.23 ± 0.20 to 1.83 ± 0.12 MPa and peel strength from 70.37 ± 15.10 to 280.94 ± 68.45 N/m. Soil burial tests revealed the biodegradability of composite films, with no recoverable residue detected after 180 days. These results demonstrate the potential of the developed composites as biodegradable adhesive materials for biomedical applications.