Origin of Transcrystallinity and Nucleation Kinetics in Polybutene-1/Fiber Composites

This work presents an in-depth study of fiber-induced nucleation and crystalline morphology in polybutene-1/single-fiber composites. The nucleation ability of various fibers, including carbon, glas..

Sequential crystallization and morphology of triple crystalline biodegradable PEO-b-PCL-b-PLLA triblock terpolymers

et al.The sequential crystallization of poly(ethylene oxide)-b-poly(ε-caprolactone)-b-poly(l-lactide) (PEO-b-PCL-b-PLLA) triblock terpolymers, in which the three blocks are able to crystallize separately and sequentially from the melt, is presented. Two terpolymers with identical PEO and PCL block lengths and two different PLLA block lengths were prepared, thus the effect of increasing PLLA content on the crystallization behavior and morphology was evaluated. Wide angle X-ray scattering (WAXS) experiments performed on cooling from the melt confirmed the triple crystalline nature of these terpolymers and revealed that they crystallize in sequence: the PLLA block crystallizes first, then the PCL block, and finally the PEO block. Differential scanning calorimetry (DSC) analysis further demonstrated that the three blocks can crystallize from the melt when a low cooling rate is employed. The crystallization process takes place from a homogenous melt as indicated by small angle X-ray scattering (SAXS) experiments. The crystallization and melting enthalpies and temperatures of both PEO and PCL blocks decrease as PLLA content in the terpolymer increases. Polarized light optical microscopy (PLOM) demonstrated that the PLLA block templates the morphology of the terpolymer, as it forms spherulites upon cooling from the melt. The subsequent crystallization of PCL and PEO blocks occurs inside the interlamellar regions of the previously formed PLLA block spherulites. In this way, unique triple crystalline mixed spherulitic superstructures have been observed for the first time. As the PLLA content in the terpolymer is reduced the superstructural morphology changes from spherulites to a more axialitic-like structure.We gratefully acknowledge funds received through the following projects: “MAT2014-53437-C2-P, MAT2012-31088 (Spanish-MINECO and EU)”, UPV/EHU (UFI 11/56) and GIC IT-586-13, IT-654-13 (Basque Government).Peer Reviewe

Controlling the isothermal crystallization of isodimorphic PBS-ran-PCL random copolymers by varying composition and supercooling

In this work, we study for the first time, the isothermal crystallization behavior of isodimorphic random poly(butylene succinate)-ran-poly(e-caprolactone) copolyesters, PBS-ran-PCL, previously synthesized by us. We perform nucleation and spherulitic growth kinetics by polarized light optical microscopy (PLOM) and overall isothermal crystallization kinetics by differential scanning calorimetry (DSC). Selected samples were also studied by real-time wide angle X-ray diffraction (WAXS). Under isothermal conditions, only the PBS-rich phase or the PCL-rich phase could crystallize as long as the composition was away from the pseudo-eutectic point. In comparison with the parent homopolymers, as comonomer content increased, both PBS-rich and PCL-rich phases nucleated much faster, but their spherulitic growth rates were much slower. Therefore, the overall crystallization kinetics was a strong function of composition and supercooling. The only copolymer with the eutectic composition exhibited a remarkable behavior. By tuning the crystallization temperature, this copolyester could form either a single crystalline phase or both phases, with remarkably different thermal propertiesPeer ReviewedPostprint (published version

Super nucleation and orientation of poly (butylene terephthalate) crystals in nanocomposites containing highly reduced graphene oxide

The ring opening polymerization of cyclic butylene terephthalate into poly (butylene terephthalate) (pCBT) in the presence of reduced graphene oxide (RGO) is an effective method for the preparation of polymer nanocomposites. The inclusion of RGO nanoflakes dramatically affects the crystallization of pCBT, shifting crystallization peak temperature to higher temperatures and, overall, increasing the crystallization rate. This was due to a super nucleating effect caused by RGO, which is maximized by highly reduced graphene oxide. Furthermore, combined analyses by differential scanning calorimetry (DSC) experiments and wide angle X-ray diffraction (WAXS) showed the formation of a thick {\alpha}-crystalline form pCBT lamellae with a melting point of ~250 {\deg}C, close to the equilibrium melting temperature of pCBT. WAXS also demonstrated the pair orientation of pCBT crystals with RGO nanoflakes, indicating a strong interfacial interaction between the aromatic rings of pCBT and RGO planes, especially with highly reduced graphene oxide. Such surface self-organization of the polymer onto the RGO nanoflakes may be exploited for the enhancement of interfacial properties in their polymer nanocomposites

Poly(lactic acid) stereocomplexes based molecular architectures : synthesis and crystallization

This review presents the state of the art of complex macromolecular architectures based on polylactide stereocomplexes (PLA-sc) from the viewpoint of synthesis and crystallization. First, we discuss the nomenclature, synthesis, epimerization, and lactide (LA) properties as a bio-derived cyclic dimeric monomer comprising two chiral carbons. Among several polymerization methods, catalytic ring-opening polymerization (ROP) is the most common and versatile technique to access stereoregular (isotactic) PLA, which is the prerequisite to preparing PLA-sc. Combined with other living and controlled/living polymerization techniques, ROP of LA has yielded various PLA-sc-based macromolecular architectures, including copolymers, stars, graft, cyclic, brush, and hybrid materials. New approaches to synthesizing monodisperse discrete oligoLA are also discussed. We show that a small change in the architectures, microstructures, molecular weight, or other chemical and physical modifications affects the behavior of PLA-sc. Moreover, the crystallization of PLA-sc, after more than 30 years of study, still presents many challenges. The crystalline morphology is also a subject of debate. Recent findings suggest a new crystalline unit cell for PLA-sc. Adding a third component or changing chain architecture can significantly modify the properties of the formed PLA-sc. The complex relationship between flexibility, nucleation, diffusion, and the interactions needed for the joint crystallization of the enantiomers constitutes a very large source of variables. As a result, PLA-based stereocomplex materials can be tailored by manipulating one or several of these variables

Clinical and pharmacological profile of benznidazole for treatment of Chagas disease

Introduction: Chagas disease (CD) is one of the most neglected public health problems in the Americas, where <1% of the estimated 6 million people with the infection have been diagnosed and treated. The goal of treatment is to eliminate the parasite, decrease the probability of cardiomyopathy and other complications during the chronic stage of infection, and interrupt the cycle of disease transmission by preventing congenital infection. Currently, only benznidazole (BZN) and nifurtimox are recognized by the World Health Organization as effective drugs for treatment of CD. In this paper, we provide an overview of the clinical pharmacology of BZN. Areas covered: This review covers the historical background, chemistry, mechanism of action, pharmacokinetics, preclinical research, resistance, clinical research, toxicology, adverse effects, and current regulatory status of BZN. Expert commentary: Ongoing investigations aim to optimize BZN therapy by adjusting the current standard regimen or by combining BZN with new chemical entities. These studies are assessing alternatives that improve safety while maintaining or increasing the efficacy of BZN. Timely diagnosis and antitrypanosomal treatment are critical components of programs to eliminate CD as a public health problem, and can dramatically reduce the heavy burden of morbidity and mortality caused by the disease.Fil: Müller Kratz, Jadel. No especifíca;Fil: García Bournissen, Facundo. Gobierno de la Ciudad de Buenos Aires. Hospital General de Niños "Ricardo Gutiérrez"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Forsyth, Colin J.. No especifíca;Fil: Sosa-Estani, Sergio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Epidemiología y Salud Pública. Instituto de Efectividad Clínica y Sanitaria. Centro de Investigaciones en Epidemiología y Salud Pública; Argentin

Optical cavity tests of Lorentz invariance for the electron

A hypothetical violation of Lorentz invariance in the electrons' equation of motion (expressed within the Lorentz-violating extension of the standard model) leads to a change of the geometry of crystals and thus shifts the resonance frequency of an electromagnetic cavity. This allows experimental tests of Lorentz invariance of the electron sector of the standard model. The material dependence of the effect allows to separate it from an additional shift caused by Lorentz violation in electrodynamics, and to place independent limits on both effects. From present experiments, upper limits on Lorentz violation in the electrons' kinetic energy term are deduced.Comment: 17 pages revte

Improving the Mechanical Performance of LDPE/PP Blends through Microfibrillation

Polyolefins (polyethylene (PE) and polypropylene (PP)) are the most abundant polymers found in plastic solid waste. They are expensive to separate, and recycling them in the form of blends is not viable due to their immiscibility and incompatibility. Following the idea of the circular economy where waste is turned into raw materials for manufacturing technological products using minimum energy, a solution is proposed for the poor behavior of immiscible PE/PP blends by taking advantage of their immiscibility to transform them into microfibrillar composites (MFCs). PE/PP blends with an 80:20 content ratio were studied, emulating the ratio found in municipal waste. A microfibrillar structure was achieved through an unusual combination of common industrial processing techniques: Extrusion, drawing, and injection. The performance of the resulting fibrillar materials was evaluated by means of tensile, fracture, and impact tests, and the results were compared with those of unstretched blends (UBs) with droplet morphology. The effect of adding a compatibilizer was also evaluated. The results were promising as the performance of the MFCs was much better than that of the nonfibrillated blends, and a synergistic effect between the addition of the compatibilizer and microfibrillation process was observed. It seems that this type of processing has great potential for large-scale application in immiscible recycled polyolefin blends in which the final properties can be improved by modifying their morphology, obviating the need to separate these polymers in mixed waste streams.Fil: Rosales, Caren Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Aranburu, Nora. Universidad del Pais Vasco. Polymat.; EspañaFil: Otaegi, Itziar. Universidad del Pais Vasco. Polymat.; EspañaFil: Pettarin, Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Bernal, Celina Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnología en Polímeros y Nanotecnología. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnología en Polímeros y Nanotecnología; ArgentinaFil: Müller, Alejandro J.. Universidad del Pais Vasco. Polymat.; EspañaFil: Guerrica Echevarriá, Gonzalo. Universidad del Pais Vasco. Polymat.; Españ

Rheology and Tack Properties of Biodegradable Isodimorphic Poly(butylene succinate)-Ran-Poly(ε-caprolactone) Random Copolyesters and Their Potential Use as Adhesives

The sole effect of the microstructure of biodegradable isodimorphic poly(butylene succinate)-ran-poly(ε-caprolactone) random copolyesters on their rheological properties is investigated. To avoid the effect of molecular weight and temperature, two rheological procedures are considered: the activation energy of flow, Ea, and the phase angle versus complex modulus plots. An unexpected variation of both parameters with copolyester composition is observed, with respective maximum and minimum values for the 50/50 composition. This might be due to the peculiar chain configurations of the copolymers that vary as a function of comonomer distribution within the chains. The same chain configuration variations are responsible for the isodimorphic character of the copolymers in the crystalline state. Tack tests, performed to study the viability of the copolyesters as environmentally friendly hot melt adhesives (HMA), reveal a correlation with rheological results. Tackiness parameters, particularly the energy of adhesion obtained from stress-strain curves during debonding experiments, are enhanced as melt elasticity increases. Based on the carried-out analysis, the link microstructure-rheology-tackiness is established, allowing selecting the best performing HMA sample considering the polymer chemistry of the system.We acknowledge the financial support from the BIODEST project; this project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 778092. This work has also received funding from the Basque Government through grant IT1309-19

Isothermal Crystallization Kinetics and Morphology of Double Crystalline PCL/PBS Blends Mixed with a Polycarbonate/MWCNTs Masterbatch

Published ArticleIn this work, the 70/30 and 30/70 w/w polycaprolactone (PCL)/polybutylene succinate (PBS) blends and their corresponding PCL/PBS/(polycarbonate (PC)/multiwalled carbon nanotubes (MWCNTs) masterbatch) nanocomposites were prepared in a twin-screw extruder. The nanocomposites contained 1.0 and 4.0 wt% MWCNTs. The blends showed a sea-island morphology typical of immiscible blends. For the nanocomposites, three phases were formed: (i) The matrix (either PCL- or PBS-rich phase depending on the composition), (ii) dispersed polymer droplets of small size (either PCL- or PBS-rich phase depending on the composition), and (iii) dispersed aggregates of tens of micron sizes identified as PC/MWCNTs masterbatch. Atomic force microscopy (AFM) results showed that although most MWCNTs were located in the PC dispersed phase, some of them migrated to the polymer matrix. This is due to the partial miscibility and intimate contact at the interfaces between blend components. Non-isothermal di erential scanning calorimetry (DSC) scans for the PCL/PBS blends showed an increase in the crystallization temperature (Tc) of the PCL-rich phase indicating a nucleation e ect caused by the PBS-rich phase. For the nanocomposites, there was a decrease in Tc values. This was attributed to a competition between two e ects: (1) The partial miscibility of the PC-rich and the PCL-rich and PBS-rich phases, and (2) the nucleation e ect of the MWCNTs. The decrease in Tc values indicated that miscibility was the dominating e ect. Isothermal crystallization results showed that the nanocomposites crystallized slower than the neat blends and the homopolymers. The introduction of the masterbatch generally increased the thermal conductivity of the blend nanocomposites and a ected the mechanical properties