Fractura de mezclas de policarbonato con acrilonitrilo-butadieno-estireno

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Multifunctional enzymatically generated hydrogels for chronic wound application

The healing of chronic wounds requires intensive medical intervention at huge healthcare costs. Dressing materials should consider the multifactorial nature of these wounds comprising deleterious proteolytic and oxidative enzymes and high bacterial load. In this work, multifunctional hydrogels for chronic wound application were produced by enzymatic cross- linking of thiolated chitosan and gallic acid. The hydrogels combine several beneficial to wound healing properties, controlling the matrix metalloproteinases (MMPs) and myeloperoxidase (MPO) activities, oxidative stress, and bacterial contamination. In vitro studies revealed above 90% antioxidant activity, and MPO and collagenase inhibition by up to 98 and 23%, respectively. Ex vivo studies with venous leg ulcer exudates confirmed the inhibitory capacity of the dressings against MPO and MMPs. Additionally, the hydrogels reduced the population of the most frequently encountered in nonhealing wounds bacterial strains. The stable at physiological conditions and resistant to lysozyme degradation hydrogels showed high biocompatibility with human skin fibroblastsPeer ReviewedPostprint (author's final draft

Kinetics of the thermal degradation of poly(Lactic acid) and polyamide bioblends

Poly(lactic acid) (PLA) and biosourced polyamide (PA) bioblends, with a variable PA weight content of 10–50%, were prepared by melt blending in order to overcome the high brittleness of PLA. During processing, the properties of the melt were stabilized and enhanced by the addition of a styrene-acrylic multi-functional-epoxide oligomeric reactive agent (SAmfE). The general analytical equation (GAE) was used to evaluate the kinetic parameters of the thermal degradation of PLA within bioblends. Various empirical and theoretical solid-state mechanisms were tested to find the best kinetic model. In order to study the effect of PA on the PLA matrix, only the first stage of the thermal degradation was taken into consideration in the kinetic analysis (a < 0.4). On the other hand, standardized conversion functions were evaluated. Given that it is not easy to visualize the best accordance between experimental and theoretical values of standardized conversion functions, an index, based on the integral mean error, was evaluated to quantitatively support our findings relative to the best reaction mechanism. It was demonstrated that the most probable mechanism for the thermal degradation of PLA is the random scission of macromolecular chains. Moreover, y(a) master plots, which are independent of activation energy values, were used to confirm that the selected reaction mechanism was the most adequate. Activation energy values were calculated as a function of PA content. Moreover, the onset thermal stability of PLA was also determined.Peer ReviewedPostprint (published version

PLA/PCL ecoblends: Effect of PCL addition on the toughness of PLA

El comportamiento a fractura de una “Ecoblend” de Poli(Ácido Láctico) (PLA) con Poli(Caprolactona) (PCL) adecuadamente compatilibilizada ha sido estudiado y comparado con el PLA base. El estudio se llevó a cabo sobre probetas de tipo SENB obtenidas a partir de barras prismáticas (4x10 mm) producidas mediante moldeo por inyección. Para asegurar condiciones ideales de fisura aguda y reproducibilidad de resultados, tras el entallado mecánico se agudizó mediante ablación por láser pulsante en femtosegundos (femtoláser). Aplicando la teoría de mecánica de la fractura elástico lineal, el factor provisional de intensificación de tensiones (KQ) y el trabajo específico de fractura (wf) (parámetro alternativo a la resistencia al impacto estandarizada) fueron determinados siguiendo la metodología de monoentalla (a/w=0.45) con 5 réplicas a velocidades de soliticación moderamente altas (1 m.s-1, impacto instrumentado en configuración Charpy). La fase PCL promueve un incremento en 1,5 veces en KQ y de 7 veces en wf. Las evidencias fractográficas revela que la deformación y la cavitación de la fase PCL promueven el alivio de la triaxialidad local, lo que puede causar un aumento de la tensión hidrostática local necesaria para iniciar las crazes y su posterior ruptura en condiciones de impacto. A a bajas velocidades de solicitación (ensayos de tracción), este proceso de cavitación/fibrilación suprime los fenómenos de crazing de la matriz de PLA favoreciendo su cedencia y deformación plástica.Peer ReviewedPostprint (published version

The influence of the clay particles on the mechanical properties and fracture behavior of PLA/o-MMT composite films

In this study, calendered films of polylactic acid/organo-montmorillonite clay (PLA/o-MMT) were prepared and the influence of the clay particles' morphology on the mechanical properties and fracture behavior was evaluated. An image analysis was performed using transmission electron microscopy micrographs to complete the morphological study. The micrographs were taken from ultramicrotomic samples corresponding to the melting flow (MD) and transverse direction (TD) of the films. The micrographs revealed intercalated particles and tactoids, which were in accordance with the wide angle X-ray scattering patterns. Uniaxial tensile tests were performed in the MD and TD directions, finding a slight anisotropy in the films, which was associated with a low level of polymer chain orientation due to the calender processing. The fracture behavior was also evaluated in the MD and TD directions using deeply double-edge-notched tension (DDENT) specimens. The mechanical and fracture tests were evaluated on aging (brittle) and deaging (ductile) films by applying a thermal treatment that consisted of heating above the glass transition temperature of the PLA and subsequent quenching. For ductile PLA composite films, the reinforcement effect promoted by the clay particles was not so evident.Peer ReviewedPostprint (author’s final draft

Extruded-calendered sheets of fully recycled pp/opaque pet blends: Mechanical and fracture behaviour

This work presents the experimental results of the mechanical and fracture behaviour of three polymeric blends prepared from two recycled plastics, namely polypropylene and opaque poly (ethylene terephthalate), where the second one acted as a reinforcement phase. The raw materials were two commercial degrees of recycled post-consumer waste, i.e., rPP and rPET-O. Sheets were manufactured by a semi-industrial extrusion-calendering process. The mechanical and fracture behaviours of manufactured sheets were analyzed via tensile tests and the essential work of fracture approach. SEM micrographics of cryofractured sheets revelated the development of in situ rPP/rPET-O microfibrillar composites when 30 wt.% of rPET-O was added. It was observed that the yield stress was not affected with the addition of rPET-O. However, the microfibrillar structure increased the Young’s modulus by more than a third compared with rPP, fulfilling the longitudinal value predicted by the additive rule of mixtures. Regarding the EWF analysis, the resistance to crack initiation was highly influenced by the resistance to its propagation owing to morphology-related instabilities during tearing. To analyze the initiation stage, a partition energy method was successfully applied by splitting the total work of fracture into two specific energetic contributions, namely initiation and propagation. The results revelated that the specific essential initiation-related work of fracture was mainly affected by rPET-O phase. Remarkably, its value was significantly improved by a factor of three with the microfibrillar structure of rPET-O phase. The results allowed the exploration of the potential ability of manufacturing in situ MFCs without a “precursor” morphology, providing an economical way to promote the recycling rate of PET-O, as this material is being discarded from current recycling processes.Peer ReviewedPostprint (published version

Effect of the viscosity ratio on the PLA/PA10.10 bioblends morphology and mechanical properties

PLA bio-blends with a predominantly biosourced PA10.10 in the composition range 10-50wt.% were prepared by melt blending in order to overcome the advanced brittleness of PLA. Due to the inherent immiscibility of the blends, 30 wt.% of PA was needed to achieve a brittle-to-ductile transition and a co-continuous morphology was predicted at 58 wt.% of PA. The initial enhancement of the PLA rheological behaviour through the environmentally friendly reactive extrusion process yielded a finer and more homogeneous microstructure and hence enhanced the mechanical properties of the bio-blends at much lower PA contents. The brittle-to-ductile transition could be achieved with only 10 wt.% and co-continuity was observed already at 44 wt.% of PA. Results indicate the significant potential of modifying PLA flow behaviour as a promising green manufacturing method toward expanding PLA-based bio-blends applications.Peer ReviewedPostprint (published version

PLA/PA bio-blends: induced morphology by extrusion

The effect of processing conditions on the final morphology of Poly(Lactic Acid) (PLA) with bio-based Polyamide 10.10 (PA) 70/30 blends is analyzed in this paper. Two types of PLA were used: Commercial (neat PLA) and a rheologically modified PLA (PLAREx), with higher melt elasticity produced by reactive extrusion. To evaluate the ability of in situ micro-fibrillation (µf) of PA phase during blend compounding by twin-screw extrusion, two processing parameters were varied: (i) Screw speed rotation (rpm); and (ii) take-up velocity, to induce a hot stretching with different Draw Ratios (DR). The potential ability of PA-µf in both bio-blends was evaluated by the viscosity (p) and elasticity (k’) ratios determined from the rheological tests of pristine polymers. When PLAREx was used, the requirements for PA-µf was fulfilled in the shear rate range observed at the extrusion die. Scanning electron microscopy (SEM) observations revealed that, unlike neat PLA, PLAREx promoted PA-µf without hot stretching and the aspect ratio increased as DR increased. For neat PLA-based blends, PA-µf was promoted during the hot stretching stage. DMTA analysis revealed that the use of PLAREx PLAREx resulted in a better mechanical performance in the rubbery region (T > Tg PLA-phase) due to the PA-µf morphology obtained.Peer ReviewedPostprint (published version

EcoBlends'up:

En ciertas mezclas de polímeros una morfología microfibrilar de la fase dispersa debidamente orientada durante la etapa de procesamiento, puede generar un efecto reforzante aumentando la tenacidad a la fractura, sobre todo en la etapa de propagación de grieta. Este tipo de materiales se denominan “compuestos microfibrilados in situ” (MFCs). Su obtención viene condicionada por las propiedades reológicos de la mezcla y los parámetros del proceso de conformado. En este contexto, cobra interés la fabricación aditiva, especialmente la fabricación por filamento en fundido (FFF) con aporte de granza en vez de filamento. En este trabajo, se propone el estudio de la viabilidad de fabricación MFCs induciendo la microfibrilación de una BioPA en las “ecoblends” PLA/BioPA. Se evalúan las condiciones óptimas de procesamiento del proceso FFF para su generación, el comportamiento a tracción uniaxial y el comportamiento a fractura (mediante técnicas de impacto instrumentado en probetas SENB) de las probetas resultantes. Las evidencias obtenidas muestran que el uso de una matriz de PLA modificada reológicamente mediante extrusión reactiva (PLAREx) promueve la obtención de MFCs con un mejor balance de propiedades mecánicas en términos de módulo elasticidad (E) y ductilidad, y una mejora en la tenacidad aparente de la estructura fabricada.Postprint (published version