Toughened Polyolefin Alloys of Core‐Shell Morphology: Correlations among Processing, Microstructure, Micromechanics, and Macroscopic Mechanical Performance

Polyolefin alloys with superior balance of stiffness, toughness, and processability properties are progressively being developed for structural applications. The technologies employed and design strategies utilized for producing these multicomponent systems have brought about the formation of specific morphological structures in these materials, which are responsible for their far advantageous overall characteristics compared with traditional toughened binary blends. This review examines the state-of-the-art and recent developments in the field of such high-performance toughened polyolefin (mostly polypropylene-based) alloys showing encapsulated (core-shell) morphology. Two families of toughened polyolefin alloys are examined in-detail in this paper: physical blends and reactor alloys. In the case of physical blending approach, the necessity for modification of interfacial and/or rheological characteristics of blends' systems has triggered the formation of composite dispersed droplet morphology in the resulting alloys. The reactor alloy technology usually offers materials with a multi-layered core-shell structure. The impacts of manufacturing parameters, processing conditions, and various microstructural (molecular, architectural, compositional, rheological, and physical) characteristics involved in the production technologies of these multiphase systems on the morphology evolution of resulting alloys are reviewed thoroughly. Then, the impact of ultimate morphology on the macroscopic mechanical behavior of the resulting alloys is discussed. The involved nano- and micro-mechanics of deformations associated with different phase structures and dispersion states of core-shell micro-structures during both high-speed impact and quasi-static fracture mechanics tests are demonstrated. The advantages of reactor alloying method over physical blending, in terms of having far better control over the interfacial interactions, morphological features, and rheological properties for specific applications, are highlighted. This is accomplished through proper design and/or manipulation of polymerization conditions/sequences and engineering the chain architectures. Finally, research perspectives and possible directions for further progress in this field are outlined. Highlights: Toughened polyolefin alloys of core-shell morphologies are reviewed. Both melt blending and reactor alloy technologies are considered. Processing-microstructure-micromechanics-property correlations are presented. Specific attention is paid to the (micro)-mechanical deformation processes. Role of structural and technological factors on properties is discussed in detail.