Rubber-blend-toughened epoxy resins

The attempt to blend natural rubber with epoxy resins resulted from the abundance of natural rubber and that it was a renewable resource. Nevertheless, interfacial adhesion between natural rubber and epoxy resins was weak due to the hydrophobic nature of natural rubber. Thus, it was an interesting experiment to blend the toughened epoxy resins with synthetic reactive liquid rubber. In order to achieve an efficient stress transfer between rubber and the... 

This study demonstrated that the final destination of the added core-shell rubber particles, in PC, PA, or both, in the PC-PA binary blend can be controlled by properly selecting the chemical structure of the shell in the core-shell rubber. The unreactive MBS rubber tends to reside in the PC phase and near the vicinity of the PC-PA interface. The reactive MBS-MA rubber can have a chemical reaction with PA end groups and can therefore be retained within the PA phase. High-molecular-weight bisphenol A epoxy resin has proved to be an efficient compatibilizer for PC-PA blends. Rubber-toughening of the PC-PA blend in which PC is the matrix is much more effective than with blends in which PA is the matrix. 

One approach to addition of elastomeric tougheners is to select a modifier which is initially soluble in the resin (22) but precipitates as small rubbery spheres as curing progresses. However, this procedure has always resulted in depression of thermal mechanical properties. Alternatively, an immiscible material can be dispersed in the resin by use of physical and chemical interactions of the solvents and catalysts so that a fine dispersion of rubber particles is produced in the epoxy resin prior to cure. It is also possible to produce a stable dispersion by a reactive blending process without the use of a catalyst or solvents. 

Some authors have refused to accept the role of interfacial adhesion on the toughening of thermoset resins. Lavita and co-workers [190] reported that non-reactive rubber can toughen BPA-modified epoxy, but the mechanism was not fully discussed. Huang and co-workers [194] showed that when the second phase consists of micron-size rubber particles, the interfacial bonding has only a modest effect on the fracture properties of blends. 

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