Improvement in the toughening of polymer composite materials through the incorporation of a rubber phase has become one of the most important issues in the field of polymer science and technology.

Polymer composites are stiff because of the highly rigidity chains of the polymer matrix; this leads to brittleness and poor resistance to crack initiation and propagation.Brittleness has been a drawback for many engineering materials and can cause premature failure during application.Among the existing methods of achieving toughened composites,the incorporation of a rubber phase has been found to be more favorable in imparting a high toughness to rigid polymer composites. Improvements in the toughness and associated elongation at break are due to the presence of rubber particles, which lead to an increase in the dispersion and distribution of the rigid filler inside the polymer matrix. Meanwhile, the surface characteristics of the rigid filler, the chemical nature of the rubber, and the polymer matrix represent the key parameters in the filler–polymer, rubber–polymer and rubber–filler interactions.

Epoxidized natural rubber (ENR) is a material that possesses high toughness properties relative to original natural rubber (NR) with a nominal reduction in the other mechanical and thermal properties because of the presence of epoxy groups on the backbone chains. ENR has high oil-resistance properties and gas-barrier properties and a high toughness relative to NR; this results from the existence of epoxy groups distributed randomly along the backbone rubber chains. The introduction of ENR particles in a plastic matrix apparently improves the toughness of the resulting plastics; this makes them suitable for application in automotive, aerospace, thermal, and electrical insulating systems.The major products of ENR/plastic blends are in closed mold forms, such as sponges, curing tubes, carpet underlays, connectors, curing flaps, bumpers, heavy duty pads, seals, gaskets, and wheels.

Furthermore, ENR blends are also used as pressure-sensitive adhesives, adhesive tapes, packaging tapes, surgical tapes, and plasters.Currently, ENR has been used as a rubber-toughened material in a number of thermoplastic and thermoset composites. The utilization of ENR as a rubber-toughened material in composite materials began with poly(vinyl chloride) (PVC). Subsequently, other thermoplastics and thermosets, including polyamide 6 (PA6), polypropylene (PP), poly(lactic acid) (PLA), and epoxy resin have also been used.

To obtain high impact properties, a rubbery phase should exist within the composite system, in which rubber particulates are dispersed uniformly throughout the matrix phase. The interaction takes place between the functional groups of the components; this, in turn, transfers the load via shear stress from the matrix to the rubber particles.

Several factors influence the toughening properties; these include the rubber particle size and diameter, type and concentration of rubber, interfacial adhesion between the rubber particles and the matrix, blending method, and processing conditions. Several authors have concluded that the rubber particle size is one of the main factors controlling toughening; tests on blends containing rubber particles with a range of sizes have shown that toughening preferentially depends on the rubber particles.Voids are more likely to form within rubber particles when the stress conditions are highly triaxial, as they are near crack tips, and toughening will not take place before a certain volume strain is reached.

Early studies of rubber toughening in polymers have highlighted a close relationship between the rubber particles and shear modulus; this is explained by differences in the cavitation stresses throughout the matrix body. However, the stress fields surrounding rubber particles hardly affect the mechanical properties of the elastomer.

The rubber toughening should be governed by the particle volume strain and a balance between the stored volume energy, void surface energy, and the work required to stretch the rubber surrounding the void biaxially. It is also currently accepted that the effect of the rubber phase itself correlates with the matrix ductility and that the rubber's intrinsic properties play an important role in determining the yield conditions in the matrix.Therefore, toughened plastics have been tailored with suitable concentrations of the rubber phase to prepare materials that can withstand a high load or impact. 

PVC is one of the earliest polymers to which ENR was added to improve its impact properties. It is recognized that PVC is very brittle at room temperature. Some modifications are thereby required to obtain a modified PVC that can be molded into many products used today; hence, this process enlarges PVC's field of application.The blend of PVC with ENR-50 was reported to produce a miscible blend, which formed a single thermodynamic phase because of the formation of hydrogen bonds between the PVC and ENR molecules. This miscible blend of PVC and ENR-50 was a rare case, and it later received the most attention.The interaction between the epoxy groups of ENR with the chlorine groups of PVC led to miscibility. However, only partial miscibility was observed in a blend of ENR-25 with PVC.