In this work, the preparation of blends of thermoplastic cassava starch (AT) with poly (epsilon-caprolactone) (PCL) 80/20 p/p and using as compatibilizing agents, starches esterificated with alkyl chains of 18 and 22 carbon atoms (AE-n) in a ratio of 90/10 with respect to starch. The mixtures were prepared by melt extrusion, their morphology was studied by scanning electron microscopy (SEM), being able to observe that the PCL constitutes the continuous phase of the mixture, while the starch particles constitute the dispersed phase and also that both the interaction between both phases, as the adherence between them, is quite weak; its mechanical behavior was analyzed by tensile tests, finding that the use of the compatibilizing agent does not significantly modify the mechanical properties of the mixtures. Lastly, starch contributes significantly to the PCL degradation faster, and it is also observed that the size of the n-alkyl chain of the compatibilizing agent also exerts a small effect during the process.

En este trabajo, se llevo a cabo la preparacion de mezclas de almidon de yuca termoplastico (AT) con poli(e-caprolactona) (PCL) 80/20 p/p y usando como agentes de compatibilizacion, almidones esterificados con cadenas alquilicas de 18 y 22 atomos de carbono (AE-n) en una proporcion de 90/10 respecto al almidon. Las mezclas se prepararon por extrusion en fundido, se estudio su morfologia por microscopia electronica de barrido (MEB) pudiendose observar que la PCL constituye la fase continua de la mezcla, mientras que las particulas de almidon constituyen la fase dispersa y ademas que tanto la interaccion entre ambas fases como la adherencia entre ellas, es bastante debil; su comportamiento mecanico fue analizado mediante ensayos de traccion, encontrandose que el empleo del agente compatibilizante no modifica significativamente las propiedades mecanicas de las mezclas. Por ultimo, el almidon contribuye de forma significativa a que la PCL se degrade con mayor velocidad, observandose ademas que el tamano de cadena n-alquilica del agente compatibilizante tambien ejerce un pequeno efecto durante el proceso. In this work, the preparation of blends of thermoplastic cassava starch (AT) with poly (e-caprolactone) (PCL) 80/20 p/p and using as compatibilizing agents, starches esterificated with alkyl chains of 18 and 22 carbon atoms (AE-n) in a ratio of 90/10 with respect to starch. The mixtures were prepared by melt extrusion, their morphology was studied by scanning electron microscopy (SEM), being able to observe that the PCL constitutes the continuous phase of the mixture, while the starch particles constitute the dispersed phase and also that both the interaction between both phases, as the adherence between them, is quite weak; its mechanical behavior was analyzed by tensile tests, finding that the use of the compatibilizing agent does not significantly modify the mechanical properties of the mixtures. Lastly, starch contributes significantly to the PCL degradation faster, and it is also observed that the size of the n-alkyl chain of the compatibilizing agent also exerts a small effect during the process.

The oxo-degradation process of high-impact polystyrene (HIPS) with 0, 1.5 and 3% w/w of pro-oxidant d2w® was studied. The degradation was conducted in a convection oven employing temperatures of 50, 55, 60 and 65 °C. The process was monitored by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests (i.e., strain at break). Neat HIPS samples did not exhibit significant changes for all conditions evaluated. Samples with oxo-additive exhibited a complex behavior in relation to the rate of degradation; HIPS with 1.5% oxo-additive exhibited faster degradation than samples with 3% oxo-additive at temperatures of 50 and 55 °C, but no significant differences at 60 and 65 °C. FTIR studies showed the evolution of hydroxyl and carbonyl functional groups during degradation and allowed to infer that polybutadiene phase is degraded preferentially. A complete loss of mechanical properties of samples with pro-oxidant was observed with changes occurring faster as temperature increased. Tensile and DSC tests were the most effective techniques for monitoring the degree of decomposition of HIPS, since the results obtained evidenced early structural changes during thermal aging that were undetected by FTIR and TGA at identical exposure times.

ABSTRACTThe oxodegradation of an injection molding grade polypropylene (PP), formulated with 0%, 1.5%, and 3% w/w of a pro‐oxidant additive, was studied. The degradation was conducted in a weathering tester at 60 °C for 40 h. The process was monitored by Fourier transform infrared spectroscopy, standard differential scanning calorimetry, and successive self‐nucleation and annealing. Neat PP samples did not exhibit significant changes during the exposure time employed. PP samples with oxo‐additive presented similar changes independently of the amount of oxo‐degradative additive employed; however, the changes manifested more rapidly in the formulation with higher pro‐oxidant content. Fourier transform infrared spectroscopy studies revealed the presence of hydroxyl and carbonyl functional groups whereas differential scanning calorimetry tests showed the decrease in the melting and crystallization temperatures as a consequence of the chain scission and oxidation reactions taking place during exposure. In addition, the induction time (tid) of the oxo‐degradative process was determined for each technique employed and successive self‐nucleation and annealing was found to be the most sensitive characterization technique to reveal structural modifications in PP samples. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46088.

El objeto de este trabajo es realizar un estudio comparativo de los proceso abioticos de termo-oxidacion en poliolefinas, en particular polipropileno (PP) y poliestireno alto impacto (PSAI). La elongacion a la ruptura es muy sensible a los procesos de degradacion oxidativa. En terminos relativos la velocidad de termo-oxidacion medida a traves del inverso del tiempo necesario para la perdida del 50% de la deformacion a la ruptura es diez veces mayor en el PSAI que en el PP. The objective of this paper is to make a comparative study of abiotic thermo-oxidative degradation in polyolefins: polypropylene (PP) and high impact polystyrene (HIPS). Elongation at break is very sensitive to oxidative degradation processes. In relative terms, the rate of thermo-oxidation measured by the inverse of the time required for the loss of 50% strain at break is ten times higher in HIPS than in PP.

PCL was blended with pristine multiwalled carbon nanotubes (MWCNT) and with a nanohybrid obtained from the same MWCNT but grafted with low molecular weight PCL, employing concentrations of 0.25 to 5 wt % of MWCNT and MWCNT-g-PCL. Excellent CNT dispersion was found in all samples leading to supernucleation of both nanofiller types. Nanohybrids with 1 wt % or less MWCNTs crystallize faster than nanocomposites (due to supernucleation), while the trend eventually reverses at higher nanotubes content (because of plasticization). Rheological results show that yield-like behavior develops in both nanocomposites, even for the minimum content of carbon nanotubes. In addition, the MWCNT-g-PCL family, when compared with the neat polymer, exhibits lower values of viscosity and modulus in oscillatory shear, and higher compliance in creep. These rheological differences are discussed in terms of the plasticization effect caused by the existence of low molecular weight free and grafted PCL chains in the nanohybrids. (c) 2017 Wiley Periodicals, Inc.

The influence of composition and crystallization conditions on the behavior of double crystalline poly (ethylene oxide-b-L-lactide) (PEO-b-PLLA) diblock copolymers is investigated. Poly(L-lactide) contents in the synthesized copolymers vary from 50 to 91%, and the molecular weight of the PLLA block ranges from 2 to 20 kg mol−1, while that of the PEO block is kept constant at 2 kg mol−1. In bulk samples, DSC results show a synergistic interaction between the crystallization processes of the two blocks. The PEO block provides heterogeneities and exerts a plasticizing action which favors the crystallization of the PLLA block with a nucleation efficiency of 30%. In contrast, the subsequent crystallization of the PEO block is subject to two opposing effects: (a) the nucleating action of PLLA crystals and (b) the topological and geometrical constraints imposed by PLLA crystals, especially when the PEO content is 20 wt% or less. In the case of ultra thin films, block copolymers with PEO contents equal or smaller than 20 wt% form distorted PLLA single crystals when crystallized from the melt. However, upon increasing the PEO content in the system to 33 wt% (by blending or copolymerization), the distortions disappear and the angle between the {110} growth faces changes from 140° to 121°, since the PEO block acts as a solvent or plasticizer for the PLLA block during the crystallization process. PEO incorporation can therefore tailor the rate and morphology of PLLA block crystallization. TEM and AFM studies allowed direct observation of the PEO block dendritic crystals on the surface of lozenge-shaped PLLA crystals previously formed during cooling from the melt.

In this paper, the synergistic effects that carbon nanotubes (CNTs) produce on the basic rheological properties and crystallization of polyethylenes with different branch contents and molecular weights was investigated. Multiwalled carbon nanotubes coated with polyethylene (as produced by in situ polymerization) were blended in the melt (in a 1% wt. ratio) with three polyethylene matrices of different molecular weights and branch contents. Transmission electron micrographs demonstrated excellent carbon nanotube dispersion in all samples and the existence of a geometrical percolation network. The rheological and calorimetric properties of the nanocomposites were determined and the results compared to those obtained for neat polyethylene resins. Both Newtonian viscosity and steady-state shear recoverable compliance increased with the addition of CNTs in all cases. However, the increase was strongly dependent on the molecular weight (and dispersity index) of the matrices regardless of the branch content. A novel screening effect of the CNTs network due to the high relaxation times of the matrix with the highest molecular weight was detected. This important result demonstrates that viscoelasticity can hinder the measurement of the rheological percolation threshold of CNTs network depending on the scale of relaxation times involved. Additionally, it was found that in relative terms (comparing each nanocomposite with its neat polyethylene matrix), the M-w values also play a vital role in CNT nucleation besides chain branching content. Both nonisothermal and isothermal nucleation effects caused by CNTs increased as the M-w of the polyethylene matrix decreased in spite of the role played by short chain branches in decelerating their overall crystallization kinetics. The capability for producing more stable lamellae through successive annealing of the nanocomposites as compared to their neat matrices also followed a decreasing trend with molecular weight increases, as indicated by SSA thermal fractionation results. Nevertheless, the presence of branches played a major role, since fractionation quality improved greatly as the branch content increased in the samples, as expected on the basis of the sensitivity of thermal fractionation to the presence of defects along crystallizable sequences.

En este trabajo se evaluo el efecto de un aditivo “oxo” en el comportamiento fisico-quimico de un PP, a diferentes tiempos de termodegradacion acelerada (60°C) y de exposicion a la intemperie. Se extruyeron peliculas de espesor 60±5 μm, con 0; 1,5 y 3,0 % de aditivo “oxo” y se caracterizaron por FTIR, DSC, TGA, RMN y ensayos tensiles. Se observo una disminucion del peso molecular hasta valores del orden de 10 3 g/mol causada por la escision de cadenas y la aparicion de grupos alcohol, carbonilo y dobles enlaces; una disminucion de las temperaturas de fusion (10-18oC) y cristalizacion (»30oC) y cambios en la endoterma multiple de fusion obtenida luego de un fraccionamiento termico (SSA). Tambien se aprecio un comportamiento fragil luego de 5 dias en el horno para un contenido de aditivo “oxo” de 3,0%. Las muestras sometidas a la intemperie presentaron resultados similares pero con menor velocidad de oxidacion con respecto a las sometidas a termodegradacion. This work evaluated the effect of an “oxo” additive on the physicochemical behavior of PP at different times of accelerated thermodegradation (60°C) and natural weathering. Extruded films with thickness of 60±5 μm, mixed with 0; 1,5; and 3,0 % of “oxo” additive were prepared and characterized by FTIR, DSC, TGA, NMR and tensile tests. A decrease of the molecular weight to values in the order of 10 3 g/mol caused by chain scission and appearance of alcohol, carbonyl groups and double bonds were observed, as well as a decrease in melting temperatures (10-18oC) and crystallization temperatures (»30oC) and changes in the multiple melting endotherm that was observed by thermal fractionation (SSA). Tensile tests showed a fragile behavior after 5 days in the oven for a content of oxo additive of 3,0%. The samples subjected to environmental conditions showed similar results with lower oxidation rates than those subjected to thermodegradation.

The mechanical properties of two linear low density and low density polyethylenes containing a pro-oxidant additive were monitored during accelerated aging (60 degrees C in a convection oven) and weather exposure. Tearing tests (trouser) were performed for the first time in polyethylenes subjected to oxo-degradation revealing a transition from an extensible to a non-extensible material, at exposure times when standard tensile tests were not able to detect any changes in the materials. The essential work of fracture (EWF) technique was also applied and the results were in agreement with those of trouser tests. The specific essential work of fracture first increased with exposure time until the sample experienced a transition to a less ductile state where EWF was no longer applicable. EWF and trouser tear tests were more sensitive detecting the onset of degradation probably because they employ notched specimens that impose more critical stress concentration conditions than conventional tensile tests. (C) 2013 Elsevier Ltd. All rights reserved.

This article investigates the influence of a pro-oxidant additive on the accelerated and environmental degradation of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). Extruded cast films (100 mu m) were prepared with various amounts of a pro-oxidant (a so-called "Oxo" additive) (0%, 1% and 2% w/w). The films were subjected to either environmental weathering or air oven aging (60 C) tests for 260 days. The chemical and physical changes induced by aging were monitored by: Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Successive Self-nucleation and Annealing (SSA) thermal fractionation and tensile tests. Neat PE samples did not exhibit significant changes during the period evaluated. Crystallinity obtained from standard DSC tests during accelerated degradation exhibited variations due to a combination between annealing and recrystallization after chain scission. For both accelerated and environmental degradation a complete loss of mechanical properties was obtained although at different exposure times. SSA was shown to be the most sensitive technique applied since it evidenced early structural changes during degradation in LLDPE and LDPE that were undetected by GPC, tensile tests (i.e., strain at break) or FTIR at identical exposure times. SSA tests after accelerated degradation revealed that LLDPE linear sequences in between branching points are substantially more affected at longer exposure times than those in LDPE, a result that may imply differences in degradation mechanisms during the later stages of the degradation process. (C) 2012 Elsevier Ltd. All rights reserved.

In this work, the nucleation and crystallization behavior of melt mixed PCL/CNT nanocomposites has been studied. The mixtures of PCL and pristine MWNTs were prepared by extrusion with different nanofiller contents: 0.3, 0.5, 0.7, 1 and 3%. Standard DSC measurements demonstrated pronounced nucleation effects as well as increases in PCL crystallinity. The nucleation effect saturates at only 0.5% (a value much lower than those previously reported in the literature for similar nanocomposites) indicating that the dispersions obtained were excellent. This was corroborated by both TEM observations and by the determination of a very low dielectric percolation threshold (i.e., 0.3%). In self-nucleation experiments, supernucleation effects were obtained up to a maximum of approximately 200% efficiency. This is the first time that supernucleation effects of this order have been reported for PCL filled with untreated MWNTs, a result that we attribute to the excellent dispersion achieved. Isothermal crystallization experiments performed by DSC showed an increase in the crystallization kinetics of PCL with increases in MWNT content as a consequence of the supernucleation effect. The Avrami equation successfully described the overall crystallization kinetics and while neat PCL exhibited Avrami indexes close to 3, indicating that instantaneously nucleated spherulites were formed, the nanocomposite yielded mostly Avrami index values close to 2, as expected for axialites instantaneously nucleated on the surface of the MWNTs. Remarkably, the temperature dependence of the overall crystallization rate exhibited a dramatic change with MWNT content. This novel effect was described as a crystallization regime change (i.e., from Regime II to Regime III) induced by the presence of the MWNTs in terms of the Lauritzen and Hoffman theory.

In this paper we reexamine recent results obtained by our group on the crystallization of nanocomposites and linear and miktoarm star copolymers in order to obtain some general features of their crystallization properties. Different nanocomposites have been prepared where a close interaction between the polymer matrix and the nano-filler has been achieved: in situ polymerized high density polyethylene (HDPE) on carbon nanotubes (CNT); and polycaprolactone (PCL) and poly(ethylene oxide) (PEO) covalently bonded to carbon nanotubes. In all these nanocomposites a “super-nucleation” effect was detected where the CNTs perform a more efficient nucleating action than the self-nuclei of the polymer matrix. It is believed that such a super-nucleation effect stems from the fact that the polymer chains are tethered to the surface of the CNT and can easily form nuclei. For polystyrene (PS) and PCL block copolymers, miktoarm star copolymers (with two arms of PS and two arms of PCL) were found to display more compact morphologies for equivalent compositions than linear PS-b-PCL diblock copolymers. As a consequence, the crystallization of the PCL component always experienced much higher confinement in the miktoarm stars case than in the linear diblock copolymer case. The consequences of the topological confinement of the chains in block copolymers and nanocomposites on the crystallization were the same even though the origin of the effect is different in each case. For nanocomposites a competition between super-nucleation and confinement was detected and the behavior was dominated by one or the other depending on the nano-filler content. At low contents the super-nucleation effect dominates. In both cases, the confinement increases as the nano-filler content increases or the second block content increases (in this case a non-crystallizable block such as PS). The consequences of confinement are: a reduction of both crystallization and melting temperatures, a strong reduction of the crystallinity degree, an increase in the supercooling needed for isothermal crystallization, a depression of the overall crystallization rate and a decrease in the Avrami index until values of one or lower are achieved indicating a nucleation control on the overall crystallization kinetics.

Successive self-nucleation and annealing (SSA) is applied to thermally fractionate a model hydrogenated polybutadiene. SSA produces discrete and well-separated thermal fractions with distinct melting peaks. The samples are studied by SAXS as a function of temperature. The SAXS profile displays only one scattering peak associated with the interlamellar correlation and is unable to discriminate the multimodal distribution of lamellar thicknesses in the samples. The average lamellar thickness associated with each melting fraction can be estimated from SAXS data at different temperatures. A modified Gibbs-Thomson equation is employed to predict the lamellar thickness from DSC data, giving results consistent with those derived from SAXS.

En este trabajo se presenta un estudio de la cristalizacion isotermica del sistema policaprolactona/nanotubos de carbon de pared multiple, con contenidos de nanotubos que varian entre 0 y 5%. Se realizaron ensayos de Calorimetria Diferencial de Barrido (DSC) que ajustan de manera satisfactoria a la teoria cinetica de cristalizacion de Lauritzen y Hoffman This paper presents an isothermal crystallization study of polycaprolactone/multi-wall carbon nanotube system with nanotube contents ranging between 0 and 5%. Tests were performed by differential scanning calorimetry (DSC). The results can be satisfactorily fitted to the kinetic theory of crystallization of Lauritzen and Hoffman.