Advances in toughened polymer materials by structured rubber particles

Many polymer materials are brittle and hence susceptible to fracture, especially in the presence of notches, scratches, or internal defects. This limits the application of polymer-based materials across a wide range of technological fields. The toughening of polymer materials by developing a two-phase structure with the use of soft rubber as the dispersed phase has gained considerable attention because of their commercial importance. Over the past several decades, homogeneous rubber microparticle toughening and related toughening mechanisms have been extensively investigated. Currently, rubber toughening is being developed considering the design and control of rubber structures for improving the toughness, and realizing the rigidity-toughness balance with minimal loss of heat resistance of polymer materials. This paper reviews the state-of-the-art research progress of polymer materials toughened by structured rubbers. To provide a general understanding on rubber toughening, we first briefly introduce the classification of polymer materials that require toughening, common strategies for improving the interfacial adhesion between rubber particles and polymer matrices, and homogeneous rubber microparticle toughening of polymer materials. Further, four categories of structured rubber toughening are discussed in detail, which includes heterogeneous rubber microparticle toughening, oriented anisotropic rubber microparticle toughening, rubber nanoparticle toughening and bimodal size distributed rubber particle toughening. Furthermore, the relationship between the structure of rubbers and the properties of modified polymer materials, such as toughness, modulus and heat resistance, is discussed. The influence of the interface or interphase on these properties is highlighted. Finally, future research endeavors and possible directions for further progress in this field are outlined.