Crosslinking agents are some of the more commonly used compounding agents for polyurethane foams such as high resilience foams, microcellular elastomers, semi-rigid foams, etc., which have a great effect on improving and adjusting the properties of polyurethane foams. In the plastics industry, cross-linking agents are mainly used in plastics such as epoxy resins, unsaturated polyphenols, phenolic, polyethylene, and polyvinyl chloride. Commonly used crosslinking agents are imidazole crosslinking agents, phthalic anhydride, diethylene triamine, tert-butylperoxyethane, hexamethylenetetramine and the like.
Most of the crosslinking agents are active hydrogen compounds containing polyfunctional groups, such as polyols having a smaller molecular weight and polyamines. A polyol containing an amino group and a tertiary nitrogen atom can also be used as a crosslinking agent. They also have a certain catalytic effect on the reaction of isocyanates and polyols. For example, ethanolamine, bis-2-(hydroxypropyl)aniline, triethanolamine, and alkyl alcohol derivatives of piperazine, and the like. Alcoholamine compounds such as triethanolamine and diethanolamine are common crosslinking agents for systems such as high resilience foams and semi-rigid foams. A low-viscosity polyol having a relative molecular mass of several hundred or less, which is obtained by polymerizing a small molecule polyol or an alcohol amine as a starting agent, can be used as a RIM semi-rigid foam formulation, such as aniline, toluenediamine and ethylene oxide. The resulting low molecular weight aromatic polyol has high activity and can also be used in formulations such as RIM microcellular elastomers and semi-rigid foams.
The purpose of adding a human cross-linking agent in plastic is to cause cross-linking between resin molecules having a linear macromolecule or a branched linear macromolecular structure, and as a result, the molecular structure of the resin is changed from a linear type to a net type or a bulk type. The molecular structure that changes the physical and mechanical properties of the plastic and the rheological properties of the plastic melt.
In most cases during plastic processing, cross-linking of the polymer is carried out by a reaction at the active center (reactive functional group or active site) on the macromolecule or by reaction between the active center and the cross-linking agent. These active centers are all reactive groups having reactivity, and under certain conditions, in the presence of an initiator or a catalyst, the resin molecules can be cross-linked to form a bulk structure.
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