toughener is a substance that can increase the flexibility of the adhesive film. Some thermosetting resin adhesives, such as epoxy resin, phenolic resin and unsaturated polyester resin adhesives, have low elongation and brittleness after curing. When the bonding part is subjected to external forces, it is easy to crack and expand rapidly, resulting in the cracking of the adhesive layer, which is not fatigue resistant and can not be used as structural bonding.

Therefore, we must try to reduce the brittleness, increase the toughness, improve the bearing strength. Where can reduce brittleness, increase toughness, and does not affect the other main properties of the adhesive material called toughening agent. The toughening agent generally contains active groups, which can chemically react with the resin, and is not completely compatible after curing, sometimes it is also divided into phases, which will obtain a better toughening effect, so that the thermal deformation temperature remains unchanged or decreases little, and the impact resistance is significantly improved.

Some low molecular liquid or plasticizer is added to the resin, although it can reduce brittleness, but the rigidity, strength, thermal deformation temperature is greatly reduced, can not meet the structural bonding requirements, therefore, plasticizer and toughening agent is completely different.

Some linear polymer compounds, can be miscible with the resin, containing active groups, can participate in the curing reaction of the resin, improve the elongation at break and impact strength, but the thermal deformation temperature has decreased, this substance is called flexibizer (flexibizer), commonly used liquid polysulfide rubber, liquid nitrile rubber, Because they are matched with the resin in the right amount, they can be made into structural adhesives, so the flexibizer is also returned to the toughening agent.

Softening and toughening are interrelated and different concepts, but in fact it is difficult to strictly distinguish. Theoretically speaking, toughening is different from toughening. Toughening does not soften the material as a whole, but turns the epoxy resin curing homogeneous system into a heterogeneous system, that is, the toughening agent gathers into spherical particles in the continuous phase formed by the crosslinked network of the epoxy resin to form a dispersed phase. The cracking resistance mutates, the fracture toughness is significantly improved, but the mechanical properties and heat resistance are less lost.

toughening mechanism of

a different type of toughening agent, have different toughening mechanism. Liquid polysulfide rubber can react with epoxy resin, introduce a part of the flexible chain segment, reduce the modulus of epoxy resin, improve toughness, but sacrifice heat resistance.

liquid nitrile rubber, as a toughening agent of epoxy resin, has almost no toughening effect when cured at room temperature, but the bond strength decreases; Only in the medium and high temperature curing system, the toughening and bonding effect is more obvious. Carboxy-terminated liquid nitrile butadiene rubber toughened epoxy resin is compatible before curing and divided into phases after curing to form an "island structure", which can absorb impact energy and basically do not reduce heat resistance.

T99 multi-function epoxy curing agent curing epoxy resin makes the cross-linked structure introduced flexible chain segments, does not produce phase separation structure, and basically does not reduce heat resistance while improving toughness.

thermoplastic resin is continuously penetrated in the epoxy resin network, forming a semi-interpenetrating network polymer, resulting in improved toughness of epoxy resin curing material.

nanoparticle size is 1~100nm, has a large specific surface area, the surface atoms have a very high unsaturated, so the surface activity is very large. The epoxy group has a much greater effect than the van der Waals force on the interface with the nanoparticle, which can cause microcracks and absorb energy well. Nano-sio2 and nano-clay can not only cause silver lines, but also terminate cracks.

At the same time, the nanoparticles have strong rigidity, and the sheaths of the nanoparticles will be deflected or deflected when the cracks expand, absorbing energy and achieving the purpose of toughening. In addition, the nanoparticle has good compatibility with the resin, which improves the dispersion and absorption ability of the matrix to the impact energy, resulting in increased toughness.