Formation of an Organic Rigid Core–Soft Shell Structure Based on the Melting Temperature Difference between the Core and the Matrix by Reactive Processing: A Facile Strategy for Highly Efficient Polymer Toughening

Abstract

Rubbery core–shell particles (usually rigid core and soft shell) demonstrate superior toughening efficiency to classical homogeneous rubber counterparts for glassy polymers, but such a toughener has been rarely exploited by the simple reactive processing strategy. Here, a feasible construction strategy of the core–shell particle with high shape stability in a glassy polymer is proposed by feat of melting temperature (T_m) difference between the core and the matrix. Taking the ethylene-methyl acrylate-glycidyl methacrylate terpolymer (EGMA)/polylactide (PLLA) toughening system as an example, poly(butylene terephthalate) (PBT) (higher T_m than T_m of PLLA matrix) was incorporated and utilized as a rigid core via reactive processing. First, PBT and EGMA were premixed at 240 °C and then blended with PLLA at 190 °C. It can be envisaged that the shape and size of spherical PBT particles could be immobilized and maintained during the subsequent melt processing owing to the higher melting temperature (205–230 °C) than that of PLLA (160–180 °C). The dual grafting of rigid PBT (premade) and molten PLLA (in situ) chains onto EGMA leads to the in situ formation of controllable core (PBT)–shell (EGMA) particles in the PLLA matrix. The obtained core (PBT)–shell (EGMA)-toughened PLLA blends exhibited high toughening efficiency (the notched impact strength of the core–shell particle-toughened PLLA is as high as 87.7 kJ/m², about 15 times higher than that of homogeneous EGMA-toughened PLLA blend) as well as synergistically enhanced heat resistance and crystallization rate. The underlying origin of the impact toughening mechanism was clearly elucidated. This simple core–shell particle construction strategy can be generally applied to other engineering plastic toughening systems. More importantly, this work established a platform for further investigation on organic rigid core–soft shell particles for polymer toughening and reactive blending.