Morphologies of ultrathin films of nine poly(ε-caprolactone)/polymer miscible and immiscible binary blends have been investigated under isothermal crystallization conditions by real time atomic force microscopy, optical microscopy, and electron diffraction techniques. It was found that the truncated lozenge-shape morphology of the pure poly(ε-caprolactone) (PCL) crystals is modified in miscible blends, forming regular or inverted S- or C-shaped crystals, the curvature depending on the nature of the second polymer and increasing with blend composition. Moreover, the growth rate decreases with the addition of the second polymer following the same order as the crystal curvature: PVC > CPE(48%) > SAN(25%) > PC > SAN(9.5%) > PVME. 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 are obtained at all compositions. Kinetic and morphological changes in miscible blends are discussed in terms of PCL/polymer intermolecular interactions since the growth rate decreases and the curvature increases with the addition of polymers of increasing interactions.

Advanced composite materials used in high-tech fields are widely reinforced with carbon fibers. One of the growing application areas for carbon fibers is their reinforced composites which are used to replace metallic automotive parts. This reduces carbon footprint through weight reduction, which is a strategy pursued globally to reduce the environmental impacts of passenger vehicles. In this study, we assess the reinforcement potential of recycled carbon fibers in a polypropylene (PP) homopolymer with high strength and flowability. The highly crystalline PP homopolymer with low impact properties was used to minimize intrinsic plasticity penalty associated with fiber reinforcement and ascribe the impact strength enhancement solely to extrinsic toughening mechanisms. The reinforced composites are manufactured through extrusion compounding followed by injection molding. Modification of the transition phase connecting the bulk matrix with the bulk carbon fibers led to 78% enhancement in the strength of the composites, compared to the unmodified composites, without any loss in other properties. Compared to a commercial steel bonnet, the compatibilized composites reinforced with recycled carbon fibers exhibited superior specific strength accompanied by ∼87% weight reduction. Morphological analysis showed that all the extrinsic toughening mechanisms are effectively used by the recycled fibers in the reinforced composites.

A quantitative analysis method for the distribution of noncrystalline poly(butadiene) component in poly(ε-caprolactone)/poly(butadiene) (PCL/PB) binary blends have been analyzed by advance application of Raman spectroscopy, optical microscopy, and differential scanning calorimetry (DSC) techniques. Thin films of different compositions of PCL/PB binary blends were prepared from solution and isothermally crystallized at a certain temperature. After calibration with real data, quantitative analyses by Raman spectroscopy revealed the amorphous PB are trapped inside the PCL crystals. Polarized optical microscopy and real time atomic force microscopy were used to collect data for the crystal morphology and crystal growth rate. For pure PCL crystals, a morphology of truncated lozenge shape was observed, independent of crystallization temperature and regardless of the blends compositions. For the pure PCL and their blends, almost unique crystal growth rate was found. The miscibility behaviors using DSC were drawn through melting point depression method. The Hoffman-Weeks extrapolations of the blends were found to be linear and identical with those of the neat PCL. The interaction parameter for the blends indicating that the PCL and PB blends have no intermolecular interaction, confirming the blends are immiscible. Despite the immiscibility of the blend, the PCL crystals do not bend during the growth process and do not reduce the growth rate as they do for miscible blend systems.

The thermal effects on crystallization kinetics and the band morphology of absorbable poly(p-dioxanone) (PDS) were studied in detail with TGA, AFM, DSC and polarized optical microscopy techniques. The polymer film was crystallized with isothermal and non-isothermal conditions over a wide temperature range, cooling from the melt at 140°C (beyond the equilibrium melting temperature but below the degradation temperature). With the isothermal crystallization process, a well-defined spherulitic morphology of the PDS polymer, linearly growing in all directions with time, was observed. A microstructure analysis by polarized optical microscopy and AFM revealed that the crystallized PDS shows large spherulites with band morphology, the nucleation density decreases and the spacing between the band increases with crystallization temperature. The periodic band morphology of the spherulites is related to edge-on and flat-on lamella orientation. The crystallization temperature dependent spherulite growth rate displayed a bell-shaped curve, showing a highest spherulite growth rate at 60°C, explained by classical nucleation theory. These results allowed a good understanding of the thermal and morphological properties of the PDS polymer over a wide temperatures range in both isothermal and non-isothermal conditions. Additionally, the crystallization and melting behaviors of the PDS polymer were studied and compared for the future application of blending with other compatible polymers, e.g. poly(ε-caprolactone).

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