Advances in toughened polymer materials by structured rubber particles

doi:10.1016/j.progpolymsci.2019.101160

Progress in Polymer Science

Volume 98, November 2019, 101160

https://doi.org/10.1016/j.progpolymsci.2019.101160 Get rights and content

Abstract

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.

Graphical abstract

This paper reviews the state-of-the-art research progress of polymer materials toughened by structured rubbers. Various structured rubber toughening are introduced in detail. 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. The future research endeavors and possible directions for further progress in this field are outlined.

Introduction

The toughening of polymer materials has been extensively studied over the past several decades because of its commercial importance [[1], [2], [3], [4], [5], [6]]. Some techniques have been and are currently being developed for improving the impact toughness of polymer materials to meet the demand of their practical applications. The most widely studied technique involves the development of a two-phase structure with the use of soft rubber as the dispersed phase [7,8]. The impact toughness of rubber-toughened polymer materials is mainly determined by the rubber phase and the interfacial adhesion between rubber and the polymer matrix. Initially, homogeneous rubber microparticle toughening was investigated for various polymer materials. In this process, the rubber toughening mechanism was gradually established. Overall, under loading, rubber microparticles concentrate stress and cavitate, which facilitates the crazing or shear yielding of polymer matrices around the rubber particles [[9], [10], [11], [12], [13]]. Currently, the toughening of polymer materials is being studied considering the design and control of rubber structures for improving the toughness or realizing the rigidity-toughness balance with minimal loss of the thermal property of polymer materials.

In this study, to provide a general understanding on rubber toughening, we first briefly introduce the classification of polymer materials that require toughening (Section 2), common strategies to improve the interfacial adhesion between rubber and polymer matrices (Section 3), and homogeneous rubber microparticle toughening (Section 4). Further, we present the latest development in structured rubber toughening in detail. According to their internal structure, spatial arrangement, and size, structured rubbers are divided into four groups: heterogeneous rubber microparticles (Section 5), oriented anisotropic rubber microparticles (Section 6), rubber nanoparticles (Section 7), and bimodal size distributed rubber particles (Section 8; refer Fig. 1). Heterogeneous rubber microparticles are further subdivided into one-matrix-core, multiple-matrix-core, one-filler-core, and multiple-filler-core rubbers; wherein the filler core is additional polymer component different from the matrix material. Oriented anisotropic rubber microparticles are subdivided into oriented rod-shaped and oriented flaky rubbers. Rubber nanoparticles are subdivided into spherical and fibrillar rubber nanoparticles. In each section, we discuss the relationship between structures of these rubbers and properties of modified polymer materials, including toughness, modulus, and heat resistance, with some typical examples. We also highlight the influence of interface or interphase on these properties. Finally, we outline future perspectives and possible novel research directions (Section 9).

Section snippets

Classification of polymer materials to be toughened

Various polymer materials have different chain entanglement density, chain stiffness, molecular weight, cross-linking density, crystalline degree, and crystalline form. These diversities lead to their different microscopic deformation modes (localized crazing, localized shear yielding and extensive shear yielding) and macroscopic mechanical behaviors (brittle fracture and ductile fracture) under impact loading [14,15]. Overall, brittle fracture is characterized by a linear load-deflection curve

Common strategies for improving interface adhesion

In order to toughen polymers successfully, good adhesion between polymer and rubber is essential because the deformation response of polymer matrix to rubber is realized through stress transfer at their interface. In this section, we will brief introduce the common strategies for improving the interfacial adhesion in rubber/polymer blends. Overall, the strategies to improve the interface adhesion are divided into adding compatibilizers [22], using reactive rubbers [[23], [24], [25]], and

Toughening by homogeneous rubber microparticles

Over the past several decades, homogeneous rubber microparticle toughening has been widely investigated for various polymer materials. Many reports focus on investigating the effect of rubber content and size on toughening. In this section, we will briefly introduce homogeneous rubber microparticle toughening, which involves rubber content, size, and the related toughening mechanisms. Generally, an increase in the rubber content would increase the toughness of polymer materials, which is

Toughening by heterogeneous rubber microparticles

Heterogeneous rubber microparticles are composite rubber particles with polymer inclusions. According to the property and number of inclusions, they are divided into four types: one-matrix-core, multiple-matrix-core, one-filler-core, and multiple-filler-core rubbers. The filler core is an additional polymer component different from the matrix material. If interfacial adhesion is good enough, the presence of one or multiple cores refines the size of the formed voids through fibrillation of the

Toughening by oriented rod-shaped rubbers

An oriented rod-shaped rubber is produced from spherical rubber/thermoplastic polymer blends by dynamic packing injection molding (Fig. 12a) [154,155]. Initially, the spherical rubber/thermoplastic polymer blend is melted and injected into a hot mold. Further, two pistons move reversibly with the same frequency, and they force the blend melt to move repeatedly in the mold cavity. The generated oscillatory shear stress promotes spherical rubber microparticles to elongate and orientate along the

Toughening by rubber nanoparticles

It is known that resistance to cavitation in rubber particles increases with the decrease in diameter. At the same time, the decrease in rubber diameter, especially down to nanoscale, dramatically increases their specific surface area (Fig. 14a). A large specific surface area would increase the stress transfer efficiency between the polymer matrix and rubber, and generate non-ignorable volume of interphase. In some cases, the interphase, which has different physical properties from the bulk of

Toughening by bimodal size distributed rubber particles

Bimodal size distributed rubber particles are the mixture of a type of large rubber particle and another type of small rubber particle. They toughen some glassy thermoplastic polymers synergistically, which are superior to the counterparts with large or small rubber alone. For example, Alfarraj et al. [282] blended 0.5 μm homogeneous PB rubber-toughened PS with 1.5 μm salami PB rubber-toughened PS. Its impact toughness was higher than the linear average of two unimodal rubber-toughened PS.

Conclusions and outlook

Developing a two-phase structure with soft rubber as the dispersed phase significantly improves the impact toughness of various polymers, such as glassy thermoplastic polymers, pseudo-ductile thermoplastic polymers, and thermosetting polymers. Essentially, the soft rubber particles concentrate stress and cavitate to generate voids in their interior, which facilitate multiple crazing of glass thermoplastic polymers and promote shear yielding of pseudo-ductile thermoplastic polymers and

Acknowledgments

We acknowledge the financial support from the High-level Innovative Talent Project in Hunan Province (2018RS3055), the National Natural Science Foundation of China (51973054, 51403008), and the Fundamental Research Funds for the Central Universities.

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Advances in toughened polymer materials by structured rubber particles

Abstract

Graphical abstract

Introduction

Section snippets

Classification of polymer materials to be toughened

Common strategies for improving interface adhesion

Toughening by homogeneous rubber microparticles

Toughening by heterogeneous rubber microparticles

Toughening by oriented rod-shaped rubbers

Toughening by rubber nanoparticles

Toughening by bimodal size distributed rubber particles

Conclusions and outlook

Acknowledgments

Polymer

Compos Part B Eng

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Prog Polym Sci

Prog Polym Sci

Polymer

Eur Polym J

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Eur Polym J

Polymer

Polymer

Polymer

Polym Degrad Stab

Int J Adhes Adhes

Polymer

Polymer

Prog Org Coat

Eur Polym J

Polymer

Polymer

Eur Polym J

J Mater Process Technol

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer

Polymer