Enhanced Thermal and Mechanical Properties of Polyfurfuryl Alcohol Resins Via Diels-Alder Modification with Maleic Anhydride and Epoxy Integration

In this study, poly(furfuryl alcohol) (PFA) was chemically modified by Diels-Alder addition of maleic anhydride (MA; 1, 2, 3, 5, and 15 phr) to increase carbonyl functionality and enable ambient-temperature curing with an amine hardener. Modified PFA (mPFA) samples were cured with a polyamine (HY) and, because carbonyl content alone was insufficient to achieve satisfactory mechanical performance, blended with a commercial epoxy (Araldite LY 5052) at varying weight ratios (10-50 phr). The modification reaction and curing kinetics were followed by FTIR and chemorheology; chemical structure was confirmed by H-1/(CNMR)-C-13. Hardness, tensile (ASTM D638 type V), DMTA and TGA characterized the cured networks. FTIR and rheology showed that 1-3 phr MA produces effective modification and that 30 phr HY is sufficient for ambient curing. Incorporation of 50 phr epoxy substantially improved mechanical and thermal performance: PFA-50 exhibited hardness 253 +/- 2 cycles, tensile strength 7.58 +/- 0.38 MPa, Young's modulus 71.01 +/- 1.19 MPa and Tg 57.48 degrees C, while the best-performing MA-modified formulation (PFA/2MA-50) reached hardness 309 +/- 2 cycles, tensile strength 10.19 +/- 0.54 MPa, Young's modulus 126.9 +/- 2.22 MPa and T-g 66.94 degrees C. TGA showed increased char yield for PFA/2MA-50 (15.7 wt.% at 800 degrees C) versus epoxy alone (9.7 wt.%). DFT calculations (B3LYP/6-31G (d,p), implicit DMF) support amide formation as a favorable curing pathway for MA-modified segments and are consistent with ATR-FTIR assignments. The combined MA modification and epoxy integration yields ambient-curing, mechanically robust PFA-based networks with improved thermal stability, making them promising binders for intumescent coatings.