epoxy resin has excellent comprehensive properties, including high bonding strength, small curing shrinkage, good dimensional stability and excellent electrical insulation properties, it is an ideal composite matrix. However, due to the high molecular crosslink density and high internal stress after curing, there are shortcomings such as brittleness, fatigue resistance and poor impact toughness. For aviation structural composites, the toughening modification of epoxy resins has always been important Research topics.
1. Toughening of thermosensitive liquid crystal polymer
Restoring epoxy resin with thermosensitive liquid crystal polymer can not only significantly improve the toughness of epoxy resin, but also improve the strength and heat resistance of the system, and has received more research in recent years.
Liquid crystal belongs to a special high-performance thermoplastic polymer. When it is added to an epoxy resin system, it obviously improves the properties of the continuous phase of the epoxy resin, which is conducive to the generation of shear slip bands and micro-cracks under the action of stress. End stress concentration is relaxed, preventing crack propagation. The results show that in the thermosensitive liquid crystal (TCLP)/epoxy resin blending system, controlling the morphology of the liquid crystal is very critical to improve the mechanical properties of the epoxy cured product.
2. Toughening of thermoplastic resin
Toughening of thermoplastic resin is a method that is used more often. Commonly used thermoplastic resins are polyetheretherketone, polysulfone, polycarbonate, etc., which have good heat resistance and high mechanical properties: resins. The toughening mechanism of thermoplastic wax can be described by bridge and crack nail anchor models.
Bridge constraint effect. Thermoplastic resins often have a modulus of resilience comparable to that of epoxy resins and much greater than the elongation at break of the epoxy resin. This allows the plastic particles bridging on the surface of the cracked brittle epoxy resin matrix to propagate crack propagation. Constrain the closing effect.
Crack nail anchor. The particle bridging not only restrains the overall advancement of the crack front, but also the bridging force acting on the crack super ruthenium anchor at the bridging point, so that only the front of the crack is wavy.
Although the toughening effect of thermoplastic resin is higher than that of Jiaotang, if the proper resin is selected, the toughness can be improved, and at the same time, the impact on epoxy temperature and glass transition temperature is small.
The thermoplastic resin can also form a semi-internutrient network structure with epoxy resin. These two total points penetrate each other and merge with each other, thus replacing the toughness of the cured product of epoxy resin. Such as thermoplastic polyurethane (PU) and epoxy resin (EP) mixed and cured, brittle epoxy network and elastic PU molecular chain interpenetrating and entangled together, the elastic interpenetrating network formed in this way plays a role in dispersing stress and strain The effect of which is to prevent the propagation of cracks after the epoxy resin is stressed, increase the tensile strength and elongation at break.
3. Nanoparticle toughening
Nano-composite materials refer to materials in which at least one phase of two or more solid-phase materials is on the order of nanometers. Nanocomposites exhibit excellent and special properties that conventional materials do not have because of their unique size effects, volume effects, and quantum effects. The development of nanocomposites has become a major research hotspot in materials science today.