Developing a Tannin-Furanic Foam with Excellent Thermal Insulation and Robust Flame Retardancy via the Synergistic Effect of Phytic Acid

It is p-toluenesulfonic acid (p-TSA) that is commonly used as a catalyst in conventional tannin-furanic foams. However, it does not participate in the crosslinking network and tends to leach out from the foam during use, resulting in a strongly acidic material that may corrode contacting substrates and accelerate material aging. To address this issue, herein, tannin and furfuryl alcohol were used as raw materials, and bio-derived phytic acid (PA) was employed to completely replace p-TSA for the preparation of tannin-furanic foams. The multi-phosphate groups of PA form a stable crosslinked network with tannin, thereby anchoring the catalyst in the foam matrix. Inductively coupled plasma (ICP) and energy-dispersive X-ray spectroscopy (EDS) analyses revealed that the leaching ratio of p-TSA from the foam was as high as approximately 92%, whereas the leaching ratio of PA reached about 78%, demonstrating the superior loading stability of PA. The as-prepared tannin-furanic foam exhibited a compressive strength of 0.137 MPa, which is approximately 49% higher than that of the foam catalyzed by p-TSA. Ignition tests confirmed that the prepared tannin-furanic foam possessed excellent flame retardancy, with a limiting oxygen index (LOI) exceeding 70%, much higher than that of conventional foam (ca. 38%). This study provides an effective route for the development of an eco-friendly tannin-furanic foam material with excellent flame retardancy.