Vinyl levulinate (VL) is used as a biobased reactive diluent in styrene (St)-free unsaturated polyester resins (UPR). The reactivity ratios for the radical copolymerization of VL with diethyl fumarate (DEF) are determined by the Jaacks method (r VL 5 0.01 and r DEF 5 0.81 at 60 C in DMSO-d 6 ). The properties of UPRs having a stoichiometric ratio between unsaturated groups from the UPR and either St or VL are compared. Defect-free, slightly yellow, transparent, and rigid thermosets are obtained after a mild curing cycle. Due to unfavorable reactivity ratios about 5.5 wt % of unpolymerized VL remains inside the network and acts as plasticizer. Consequently, compared with St-based ones, VL-based UPRs exhibit lower a relaxation (T a 5 180 and 100 C, respectively), lower elastic moduli at the rubbery plateau (G 0 5 10 8 and 10 7 Pa) and lower mechanical properties as measured by three points bending tests. Strain at break (e f 5 1.8 6 0.2%) and Charpy impact strength (2.7 6 0.3 kJ m 22 ) are comparable independently of the RD chemical nature.
Ultra-high temperature ceramic composites based on carbon fibre, Cf, preforms impregnated with hafnium diboride, HfB 2 , powder and then densified with carbon by chemical vapour infiltration, CVI, have been mechanically tested to measure the room temperature flexural, interlaminar shear, compressive and tensile strengths.
The thermophysical properties of carbon fiber‐based ultra‐high temperature ceramic matrix composites have been determined to aid designers who need these properties when considering using the composites in ultra‐high temperature aerospace applications. The coefficient of thermal expansion (CTE) and thermal diffusivity of the composites were measured parallel and perpendicular to the ply direction; the thermal conductivity was measured using the laser‐flash method and the heat capacity calculated from the relationship between the thermal diffusivity, density, and thermal conductivity. Both the CTE and thermal conductivity showed higher values across the ply and increased with increasing temperature as expected, whilst the thermal diffusivity showed higher values parallel to the ply and increased smoothly with temperature. In addition, two different but related oxyfuel torch tests, based on oxyacetylene and oxypropane, were used to evaluate the thermo‐ablation behavior of the composites. The tests showed how good the composites were at withstanding the ultra‐high temperatures, high heat fluxes, and gas velocities involved.
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