Effect of twin-roll temperature and interface adhesion on ablative performance and char structure of ethylene propylene diene monomer-based ablative insulator

In a novel approach, the effect of twin-roll mixer temperature as well as fiber-matrix interaction on the ablation behavior and carbonized char structure was studied. Different ablative insulators based on ethylene propylene diene monomer (EPDM) were fabricated using a laboratory twin-roll mixer at cold (25 °C) and hot (60 °C) temperatures. Moreover, the effects of hydroxyl-terminated polybutadiene (HTPB), bis(3-triethoxysilylpropyl)tetra sulphane (SI-69) and polyethylene glycol 400 (PEG-400) as coupling agents at 2 and 3 phr levels were assessed. Curing rheometery, physical and mechanical testing, micro and macro-morphology images of insulator and char, thermal assesment and oxyacetylene torch test (T_flame = 3000 °C) were expolited. FE-SEM analysis of charred layers showed that PEG (2) EPDM-Hot, SI-69 (2) EPDM-Hot, and HTPB (3) EPDM-Cold samples (Table 1) formed a loose carbonized layer, which cannot resist under the oxyacetylene flame, resulting in low ablative resistance. The micro-morphology of hot processed samples displayed more compatible interplanar layers. The HTPB Hot (3)-EPDM sample (Table 1) showed a higher T_g (− 49.63 °C), cross-linked density (6.83 10^–4 mol/cm³), tensile strength (5.11 MPa), thermal stability (T_max = 476.60 °C), char layer compression strength (about 600 N at 1.75 mm displacement) and better dispersion of filler in the matrix than the other samples. Remarkably, the use of a hot twin-roll mixer and an appropriate coupling agent simultaneously suggests a synergistic effect in increasing the ablation resistance (the lowest ablation rates of 0.07916 mm/s and 0.3758 g/s) in HTPB Hot (3)-EPDM sample through better distribution and interaction of the fillers with the rubber matrix.