Investigation of the regularities of phase transitions in multicomponent polymer blends

Abstract

The influence of the compatibilizers of an ethylene-vinyl acetate copolymer and sodium oleate on the processes of melting and crystallization and the supermolecular structure of polypropylene/copolyamide blends of composition 20/80, 40/60, and 50/50 wt.% has been investigated. It has been shown that a specific fiberization is clearly realized in the compatibilized blends even for compositions corresponding to the region of phase change. Two to three peaks of crystallization of polypropylene in the blends containing an ethylenevinyl acetate copolymer or sodium oleate have been revealed, which is attributed to the increase in the degree of dispersion of polypropylene as a result of the improvement in the specific fiberization and to the growth in the fraction of polypropylene in the interphase transition layer.It is well known [1] that polymer blends are being used in a modern, simple, and efficient method of modifying them and obtaining products with completely new properties. Thus, for example, processing of polymer blends opens up a completely new avenue for production of ultrafine synthetic fibers (microfibers). We are dealing with the so-called phenomenon of specific fiberization [2], where one (fiberizing) component forms numerous microfibers strictly oriented in the direction of extrusion in the mass of another (matrix) component in the case of flow of a molten blend. The morphology of a polymer blend is determined not only by the microrheological processes (deformation of droplets to liquid jets, disintegration of the latter into droplets, and migration on the radius of the extruder-die orifice) at the stage of processing but also to a large extent by the capacity of the blended polymers for crystallization and by the conditions under which it occurs. Realization of specific fiberization substantially depends on the degree of compatibility of the components of the blend and the possibility of forming a transition layer transferring the deforming force from the matrix polymer to the fiberizing polymer. Commercially produced polymers are thermodynamically incompatible, as a rule. Therefore, in processing their blends, one adds special substances improving their compatibility; they are called compatibilizers [3]. Physicochemical processes in compatibilized polymer blends were investigated in [4,5] in detail, but no consideration was given to phase transitions.This work seeks to study the processes of melting and crystallization in ternary compatibilized polymer blends.Objects and Methods of Investigation. Blends of polypropylene (PP) and copolyamide (CPA) with a ratio of the components of 20/80, 40/60, and 50/50 were used as the objects of investigation. Copolyamide represented a caprolactam-AH (adipic acid and hexamethylene diamine) salt copolymer of composition 50/50. The characteristics of the starting polymers have been given in [4,5]. As the compatibilizers we used an ethylene-vinyl acetate copolymer (EVAC) and sodium oleate. We added EVAC in an amount of 5, 10, 20, and 25% of the PP mass. The amount of ...

High-performance transparent solvent-free silicone resins with stable storage and low viscosity based on new hyperbranched polysiloxanes

“…The performance of a multiphase or multicomponent polymer is closely related to its compatibility. 23,24 In recent years, considerable efforts have been made in improving the compatibility of multiphase polymers. [25][26][27] However, these works mainly focused on thermoplastics and were seldom associated with thermosetting resins.…”