RESUMEN
A set of five vitrimers with glass transition temperatures in the range of 80-90 °C were designed to assess the effect of the network structure and disulfide concentration on their dynamic and mechanical properties, and to find the best performing system overall compared to the commercial Araldite LY1564/Aradur 3486 commercial thermoset system. Vitrimer networks were prepared by incorporating mono- and bifunctional epoxy reactive diluents and an amine chain extender into the Araldite LY1564/4-aminophenyldisulfide system.
RESUMEN
Traditional crosslinked aero grade epoxy resins have excellent thermal-mechanical properties and solvent resistance, but they cannot be remolded, recycled, or repaired. Vitrimers can be topologically rearranged via an associative exchange mechanism, endowing them with thermoplasticity. Introducing dynamic bonds into crosslinked networks to obtain more sustainable thermosets is currently an interesting research topic. While recent research into vitrimers has indicated many advantages over traditional thermosets, an important shortcoming has been identified: susceptibility to creep at service temperature due to the dynamic bonds present in the network. In addition, designing aero grade epoxy vitrimers (similar to RTM6 resin) still remains a challenge. Herein, low creep aero grade epoxy vitrimer with thermal and mechanical properties similar to those of aero grade epoxy resins and with the ability to be recyclable, repairable, and reprocessable, has been prepared. In this manuscript, we demonstrate that aero grade epoxy vitrimer with reduced creep can be easily designed by the introduction of a certain fraction of permanent crosslinks, without having a negative effect on the stress relaxation of the material. Subsequently, the mechanical and relaxation properties were investigated and compared with those of classical aero grade epoxy resin. A high Tg (175 °C) epoxy vitrimer was obtained which fulfilled all mechanical and thermal specifications of the aero sector. This work provides a simple network design to obtain aero grade epoxy resins with excellent creep resistance at elevated temperatures while being sustainable.
RESUMEN
The current drive for sustainability demands recyclable matrices for composite materials. Vitrimers combine thermoset properties with reprocessability, but their mechanical performance in highly loaded applications, for instance, composites for aeronautics, is still to be demonstrated. This work presents the complete mechanical characterization of a new vitrimer reinforced with carbon fiber. This vitrimer formulation consists of functional epoxy groups and a new dynamic disulfide crosslinks-based hardener. The testing campaign for the vitrimer composites encompassed tension, compression, interlaminar shear strength (ILSS), in-plane shear (IPS), open-hole tension (OHT) and compression (OHC), filled-hole compression (FHC) and interlaminar fracture toughness tests under mode I and II. Test conditions included room temperature and high temperature of 70 °C and 120 °C, respectively, after moisture saturation. Tension and flexural tests also were applied on the neat vitrimer resin. The results compared well with those obtained for current aeronautic materials manufactured by Resin Transfer Molding (RTM). The lower values observed in compression and ILSS derived from the thermoplastic veils included as a toughening material. This work demonstrates that the vitrimer formulation presented meets the requirements of current matrices for aeronautic-grade carbon-reinforced composites.
RESUMEN
A compressible regular solution free energy model for describing the phase behavior of weakly interacting binary blends comprising nonrigid polymer nanoparticles and linear-polymer chains (i.e., all-polymer nanocomposites) has been developed by incorporating specific nanoparticle-nanoparticle and nanoparticle-polymer contributions into the original free volume theory for binary polymer blends of Ruzette et al. [J. Chem. Phys. 114, 8205 (2001)]. The extended model allows predicting phase behavior for weakly interacting polymer-nanoparticle/linear-polymer nanocomposites using only pure component properties (nanoparticle and polymer sizes, mass densities, coefficients of thermal expansion, and solubility parameters). The effect of polymer and nanoparticle size, as well as those arising from nanoparticle rigidity, exchange interaction energy and composition on the phase behavior of all-polymer nanocomposites have been systematically investigated. A rich variety of phase diagrams (including upper critical solution temperature-type, lower critical solution temperature-type, and hour-glass shape) are illustrated. Predicted phase diagrams for nonrigid poly(styrene)-nanoparticle (PS-np)/linear-poly(styrene) (l-PS), and branched poly(ethylene)-nanoparticle (PE-np)/l-PS nanocomposites were in excellent agreement with available experimental data.
RESUMEN
Dilution of contact, hard sphere-like, nanoparticle-nanoparticle interactions upon mixing plays a key role in explaining nanoparticle dispersion in athermal all-polymer nanocomposites, as illustrated for polystyrene-nanoparticle/linear-polystyrene blends as a model system.
