Plastic AIDS: toughening mechanism of toughening agent
Plastic AIDS: toughening mechanism of toughening agent
Toughener is a substance that increases the flexibility of the adhesive membrane. Some, thermosetting resin adhesives such as epoxy resin, phenolic resin and the curing of unsaturated polyester resin adhesives after low elongation, brittleness is bigger, when bonding parts under external force is easy to produce cracks, and rapidly expand, result in the crack of the rubber, not fatigue resistance, not for the use of structural adhesive.
Therefore, it is necessary to reduce brittleness, increase toughness, and enhance the bearing strength. Substances that reduce brittleness and increase toughness without affecting the other main properties of adhesives are known as toughening agents. Toughening agent generally contain active group, can react with the resin, cured is not fully compatible, sometimes even split phase, get ideal toughening effect, thermal deformation temperature is constant or dropped, with little, and shock resistance improved significantly. Some low molecular liquid or as plasticizer join resin, although also can reduce the brittleness, but rigidity, strength, heat distortion temperature dropped substantially, can not meet the requirement of the structural adhesive, therefore, plasticizer and toughening agent is completely different.
Some linear polymer compound, miscibility with resin, containing reactive group, can participate in the curing reaction of the resin, improve the elongation at break and impact strength, but the thermal deformation temperature decreased, this material is called a soft agent (flexibizer), commonly used liquid polysulfide rubber, NBR, due to their cooperate with resin in moderation, can be made into structural adhesive glue agent, so will also increase the soft agent in toughening agent and so on. The concept of suppler and toughening is not exactly the same, but it is difficult to distinguish it from each other. Theoretically different toughening with increasing soft, toughening diffusion don't make the material as a whole, but the epoxy resin curing homogeneous system into a multiphase system, namely the flexibilizer gathered into a spherical particle in epoxy crosslinking network structure of the continuous phase, and the formation of dispersed phase cracking resistance mutations, the fracture toughness increased significantly, but the mechanical properties, heat resistance losses small.
The toughening mechanism
Different types of toughening agents have different toughening mechanisms. Liquid polysulfide rubber can react with epoxy resin, introduce some flexible chain segments, reduce the modulus of epoxy resin, improve toughness, but sacrifice heat resistance. As the toughening agent of epoxy resin, liquid acrylonitrile rubber has almost no toughening effect when curing at room temperature. Only the medium high temperature curing system, toughening and bonding effect are obvious. The carboxyl liquid butyronitrile rubber toughened epoxy resin is consistent with the curing before curing, forming an "island structure", which can absorb impact energy and basically not reduce heat resistance. T a 99 multi-functional epoxy curing agent has introduced flexible chain segments in the crosslinking structure, which does not produce a split-phase structure, and has not reduced heat resistance while improving toughness.
Thermoplastic resin is continuously penetrated into the network of epoxy resin, forming a semi-interwoven network polymer, which leads to the improvement of the curing toughness of epoxy resin.
The nanometer particle size is 1~ 100nm, which has a great ratio surface area, and the surface atom is extremely unsaturated, so the surface activity is very large. The epoxidiene group forms far more than van der Waals force on the interface, which can lead to micro-cracks and absorb energy. Nano-sio2 and nano clay can cause both silver and crack. At the same time, nanometer particle has strong rigidity, crack encountered nanoparticles occurred in extension Tuo to or deflection, toughening absorb energy and to achieve. In addition, the nanoparticles and resins have good compatibility, so that the dispersive ability and absorbing ability of the matrix to impact energy increase, resulting in the increase of toughness.
