Nucleation modalities in poly(lactide), poly(butylene succinate), and poly(ε‐caprolactone) ternary blends with partial wetting morphology

Abstract

Ternary biodegradable polymer blends of poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and poly(ε-caprolactone) (PCL) with the composition 45/10/45 wt% and exhibiting partial-wetting morphology were prepared. In this morphology, the minor phase is present as self-assembled droplets at the co-continuous interface of the other two major phases. The crystallization of the components in the various blends was thoroughly investigated. Differential scanning calorimetry highlighted minor differences in the overall kinetics of a given component in the ternary blend, with respect to the neat polymer. On the other hand, several unusual nucleation mechanisms could be studied by polarized optical microscopy (PLOM). With reference to the major phases, PLA spherulites displayed surface-induced nucleation from the interface with molten PBS or PCL droplets. On lowering the crystallization temperature, the PBS phase effectively nucleated at the interface with previously crystallized PLA domains, forming a transcrystalline morphology. Concerning the minor phase, weak partial-wetting PBS droplets displayed a droplet-to-droplet percolation of the nucleation events. Strongly partial-wetting PCL droplets were confined between previously crystallized PLA and PBS co-continuous phases and, instead, solidified as isolated domains randomly in space. This work provides further insights in the relationship between morphology and crystallization in immiscible ternary blends.

Surface Roughness Enhances Self-Nucleation of High-Density Polyethylene Droplets Dispersed within Immiscible Blends

“…As previously known, the size of the dispersed micro-domains in immiscible blends is crucial and has a strong effect on the final crystallization behavior of the minor phase. 13 , 23 , 24 , 26 − 28 …”

“… 11 , 12 Fenni et al 12 reported the nucleation effect of molten poly(ε-caprolactone) (PCL) and molten poly(butylene succinate) (PBS) on poly(lactic acid) (PLA) self-assembled droplets in their 45/10/45 PCL/PLA/PBS immiscible ternary blend. While in another work, Fenni et al 13 showed that in 45/10/45 PLA/PCL/PBS ternary blends, the PBS continuous phase was able to nucleate at the surface of the previously crystalline PLA. Several factors were claimed to control and affect surface nucleation, such as polarity of the polymers, 14 affinities between different components, 12 states of the interface, and surface roughness.…”

“…Surface nucleation was found to play an important role in the crystallization of immiscible blends (both for the matrix and the dispersed micro-domains). , Several researchers reported that surface nucleation could initiate from solid polymer surfaces as well as from molten surfaces/polymers. , Fenni et al reported the nucleation effect of molten poly­(ε-caprolactone) (PCL) and molten poly­(butylene succinate) (PBS) on poly­(lactic acid) (PLA) self-assembled droplets in their 45/10/45 PCL/PLA/PBS immiscible ternary blend. While in another work, Fenni et al showed that in 45/10/45 PLA/PCL/PBS ternary blends, the PBS continuous phase was able to nucleate at the surface of the previously crystalline PLA. Several factors were claimed to control and affect surface nucleation, such as polarity of the polymers, affinities between different components, states of the interface, and surface roughness. , Regarding this last factor, Dalnoki-Veress and Carvalho found a direct correlation between the nucleation mechanism of the droplets and the roughness of the substrate in their polystyrene/poly­(ethylene oxide) (PS/PEO) systems .…”