Sodium Hydroxide/Itaconic Acid Polyamidoamine-Epichlorohydrin Cross-linked Soy Protein Bonded Rhizophora spp. Composites

Abstract

Structural, thermal, and physicochemical performance were studied for sodium hydroxide (NaOH) (12 wt%)/itaconic acid polyamidoamine-epichlorohydrin (IA-PAE) (0 to 30 wt%) cross-linked tissue-equivalent composites made from defatted soy flour, soy protein concentrate, and soy protein isolate-bonded Rhizophora spp. (particle size: 149 µm), to enhance interfacial bonding, stability, and overall material performance. The Fourier transform infrared spectra confirmed effective crosslinking and a reduction in hydroxyl groups, with the formation of ester/ether linkages. Thermal analysis showed improved stability and a higher char yield. Microstructural analysis revealed denser, more homogeneous matrices with enhanced interfacial bonding. Average densities ranged (0.94 ± 0.11 to 1.04 ± 0.20 g/cm3), matched those of water and other commercial tissue substitute biomaterials, while moisture content (6.51 ± 0.19 to 8.06 ± 0.50%) was consistent with JIS A-5908 (2015) limits. Mechanical properties exceeded standards (internal bonding strength (IBS) up to 0.73 ± 0.01 MPa; modulus of rupture (MOR): 19.21 ± 0.50 MPa; modulus of elasticity (MOE): 7.70 ± 0.33 GPa), and dimensional stability improved significantly (water absorption: ≥ 20%, thickness swelling: ≥ 10%). Optimal performance was achieved at 20% IA-PAE. NaOH/IA-PAE crosslinking effectively enhances structural, thermal, and physicomechanical properties, producing sustainable composite particleboards suitable for tissue-equivalent and radiation-related applications.