Mixing‐sequence controlled selective localization of carbon nanoparticles in PLA/PCL blends

Abstract

This work proposes modifying the adding sequence of components during the production of poly(lactic acid) (PLA) and poly(ε‐caprolactone) (PCL) ternary systems with multiwalled carbon nanotubes (CNT) or graphene nanoplatelets (GN), in order to analyze the nanoparticles’ selective localization in terms of the competition between different factors, such as kinetics, thermodynamics, rheology, and geometry. In the studied system, the PLA's viscosity is higher than the PCL's and the difference in interactions between the CNT or the GN/PLA and the CNT or the GN/PCL is small, meaning the viscosity effects could dominate. However, other factors, such as thermodynamics and geometry, can be observed to compete with the rheological factor, depending on the mixing sequences. Depending on the processing time, a competition between thermodynamics and rheological factors could be observed when the nanoparticles had contact first with the thermodynamically favored phase. The competition between geometrical and rheological factors was observed in the presence of GN in the PLA phase, in the system in which the GN was added first to the PLA phase, which is the phase of lowest affinity. POLYM. ENG. SCI., 59:323–329, 2019. © 2018 Society of Plastics Engineers

Effects of processing conditions on hybrid filler selective localization, rheological, and thermal properties of poly(ε‐caprolactone)/poly(lactic acid) blends

“…However, since the polymers' melting points largely differ, 59 °C for the PCL and 168 °C for the PLA, as well as their viscosities, 43 Pa s for the PLA and 3 Pa s for the PCL (the capillary rheometer curve is shown in Supporting Information Section S1), and since all blend components were simultaneously added into the extruder, the TiO 2 or the hBN were expected to be first localized in the PCL phase, and, through the driving force generated by the thermodynamic preference, they would migrate to the PLA phase or to the interface, respectively. Such behavior can be related to the nanoparticle's geometry, which hinders the migration through the interface . The migration was obstructed by the hBN tactoids, impairing the movement through the PCL polymer chains …”

“…Such behavior can be related to the nanoparticle's geometry, which hinders the migration through the interface. 12,13,38 The migration was obstructed by the hBN tactoids, impairing the movement through the PCL polymer chains. 34 For the purpose of direct comparison to the ternary systems, 33,34 all four components (PCL/PLA/TiO 2 /hBN) were added simultaneously into the extruder.…”

“…Many factors have been studied to explain the nanoparticles' localization in immiscible polymer blends. Among such, the thermodynamic factors that account for the components' interfacial tension; the processing conditions including the mixing sequence, temperature, time, and shear rate; rheological factors such as the polymers' viscosity and elasticity; and the nanoparticles' intrinsic characteristics, such as surface aspect ratio and functionalization …”

“…Among such, the thermodynamic factors that account for the components' interfacial tension; the processing conditions including the mixing sequence, temperature, time, and shear rate; rheological factors such as the polymers' viscosity and elasticity; and the nanoparticles' intrinsic characteristics, such as surface aspect ratio and functionalization. 5,7,8,[10][11][12][13][14][15][16][17][18][19] The factors responsible for the nanoparticles' localization in ternary systems and the changes in those systems' morphology and properties have been extensively studied. However, there are only a few works on quaternary systems (hybrid fillers in an immiscible polymer blend) in the literature, which do not systematically study the factors responsible for the nanoparticles' localization and the influence of different localization on the properties of these quaternary systems and their influence on the nanocomposites' properties.…”

“…9,23,27 The PCL/PLA blend has been widely studied, showing great application potential in the areas of packaging and biomedicine, among others, being the most popular and largely researched biodegradable polymer. 13,17,[28][29][30][31][32] The combination of PLA with PCL has shown an improvement in mechanical strength and processability when compared to the pure PCL and an increase in toughness and ductility when compared to the PLA. 21,[29][30][31][32] Furthermore, such properties of PCL/PLA blends can be further enhanced with the addition of nanoparticles.…”