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 ¹H/¹³CNMR. 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°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°C. TGA showed increased char yield for PFA/2MA-50 (15.7 wt.% at 800°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.