Preparation of Natural Rubber/Condensed Tannin Semi-interpenetrating Polymer Network Composites by Hematin-Catalyzed Cross-Linking

In this study, the preparation of semi-interpenetrating polymer network (semi-IPN) composites composed of natural rubber and condensed tannin was performed by means of the enzyme-mimetic cross-linking of condensed tannin catalyzed by hematin. Prior to the preparation of the composites, the hematin-catalyzed cross-linking behavior of condensed tannin was evaluated by the TGA measurement. The TGA results indicated that condensed tannin was sufficiently cross-linked by the hematin-catalyzed reaction in the presence of appropriate amounts of 30% (w/v) H₂O₂ aq. to give the relatively thermostable materials. For the preparation of the composites, a solution of condensed tannin and hematin, and subsequently 30% (w/v) H₂O₂ aq. were added to natural rubber latex and the mixture was stirred at room temperature for 10 min to perform the cross-linking of condensed tannin, followed by drying of the reaction mixture at 50 °C for 5 h, which was subsequently put into a heat device and hot-pressed at 100 °C and 20 MPa for 20 min to give the semi-IPN composite. The tensile stress?Cstrain measurement of the composites was conducted to evaluate the mechanical properties, which were changeable depending on the weight ratios of natural rubber to condensed tannin and the amounts of 30% (w/v) H₂O₂ aq. Moreover, the miscibility of the cross-linked tannin with natural rubber in the composite was evaluated by the SEM measurement.