Polymer Blends

Study of PCL comprising binary blends confined in ultrathin films for tissue engineering.

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This work focused on the morphological investigation of miscible polycaprolactone/polyvinyl chloride (PCL/PVC) blends for scaffolds in tissue engineering, which act as templates for tissue regeneration to guide the growth of new tissue. The influence of the blend composition, crystallization temperature and film thickness on the morphology of PCL/PVC blends confined in ultrathin films was studied under isothermal crystallization conditions. At a film thickness of 30 nm, the truncated lozenge-shaped morphology of pure PCL crystals, found when the growth rate is slow, bent with increasing PVC content to form S-shaped or inverted S-shaped crystals, and the curvature increased by lowering the crystallization temperature. Electron diffraction patterns reveal that these crystals are flat-on single crystals with the PCL molecular chains (c axis) in the blends slightly tilted with respect to the lamella normal, while the b direction of the crystal lattice, corresponding to the fast growing direction of the growth front, follows an S line. Upon decreasing the film thickness (<30 nm), the S-shaped or inverted S-shaped crystals transform into four-branch dendritic lamellae. We have discovered that the suppression of crystallization in ultrathin films is not solely due to size effects. There is strong evidence to support the notion that irreversible adsorption of chains at the film surface impairs local chain mobility (relative to the bulk) and hinders crystallization.

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We have extended the work for a systematic investigation of the crystallization and morphological behavior of PCL comprising binary blends in ultrathin films. A series of PCLs comprising miscible blends with PVC, CPE, PC, SAN, PB, PBA, PBMA and PVME were prepared. The miscibility labels of the blends were identified and quantified. The morphology is followed by optical microscopy (OM), atomic force microscopy (AFM), and electron microscopy (TEM). It was found that the truncated lozenge-shaped morphology of the pure PCL crystals was modified in miscible blends, forming regular or inverted S- or C-shaped crystals, and the curvature depended on the nature of the second polymer and increased with blend composition. Moreover, the growth rate decreases with the addition of the second polymer following the same order as the crystal curvature. In contrast, for immiscible blends, no significant changes in kinetics and morphology were observed since a constant crystal growth rate and the same truncated lozenge-shape morphology as pure PCL crystals were observed. Morphological variations and crystallization kinetics are discussed in terms of intermolecular interactions between PCL and the second polymers. Crystallization of the blends in ultrathin films shows a dramatic difference when confined to very small dimensions. The crystallization rates for ultrathin PCL/amorphous blends were strongly depressed—and eventually completely arrested—as the film thickness was reduced.

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[A Mamun, VH Mareau, J Chen, RE Prud'homme, Morphologies of miscible PCL/PVC blends confined in ultrathin films, Polymer (Elsevier Publisher), 2014]

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[A Mamun, CG Bazuin, RE Prud’homme, Morphologies of various polycaprolactone/polymer blends in ultrathin films, Macromolecules (ACS Publisher), 2015]

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