Crystallization of triethyl-citrate-plasticized poly(lactic acid) induced by chitin nanocrystals

The aim of this study was to gain a better understanding of the crystallization behavior of triethyl-citrate-plasticized poly(lactic acid) (PLA–TEC) in the presence of chitin nanocrystals (ChNCs). The isothermal crystallization behavior of PLA–TEC was studied by polarized optical microscopy, scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction (XRD). Interestingly, the addition of just 1 wt % ChNCs in PLA–TEC increased the crystallization rate in the temperature range of 135–125 °C. The microscopy studies confirmed the presence of at least three distinct types of spherulites: negative, neutral, and ring banded. The ChNCs also increased the degree of crystallinity up to 32%, even at a fast cooling rate of 25¿°C min-1. The XRD studies further revealed the nucleation effect induced by the addition of ChNCs and thus explained the faster crystallization rate. To conclude, the addition of a small amount (1 wt %) of ChNC to plasticized PLA significantly affected its nucleation, crystal size, and crystallization speed; therefore, the proposed route can be considered suitable for improving the crystallization behavior of PLA.Peer ReviewedPostprint (author's final draft

Estudio de la fractura de materiales compuestos por una matriz de plástico

Se estudia el comportamiento a fractura de materiales, compuestos por una matriz de plástico en la que se ha dispersado una segunda fase en forma de partículas elastoméricas. Como matriz se han utilizado dos materiales diferentes: una resina de poliéster insaturada y poliestireno. Se estudia la morfología de los materiales compuestos preparados, se determinan los parámetros de fractura y otras propiedades mecánicas, se realiza el estudio fractográfico y finalmente se analizan los resultados e identifican los mecanismos de refuerzo que han actuado en cada caso.Se demuestra que la modificación con partículas elastoméricas tanto del poliéster insaturado como del poliestireno produce una mejora de la tenacidad a la fractura.El mecanismo de refuerzo de la tenacidad para el caso de matriz termoestable es el de "crack pinning-bowing" y para el caso de matriz termoplástica es el de múltiple "crazing".Postprint (published version

Evaluación de las propiedades mecánicas en mezclas de Poliestireno/Polietileno de baja densidad reciclado y tamizado

En el presente trabajo se prepararon mezclas de poliestireno (PS) con residuo tamizado de Polietileno de baja densidad (LDPE) reciclado de cables eléctricos. Las mezclas se pr epararon utilizando una línea de extrusión mono-husillo a nivel planta piloto. Las mezclas, con concentraciones nominales de 5, 7.5, 15, 25 y 35 % en peso de residuo, fueron ensayadas bajo las configuraciones a tracción y a flexión. La evaluación mecánica se realizó en funció n del contenido de residuo y del número de pasos por extrusión mono-hus illo. En ambas configuracion es de ensayo se observó una disminución de la rigidez y la resistencia del PS al añadir el residuo de LDPE, aunque la ductilidad del PS se vio favorecida, lo cual se adjudicó a la naturaleza intrínseca de ambos materiales. Las obs ervaciones realizadas sobre la superficie de rotura de las mezclas permitieron apreciar la aglome ración del residuo dentro del PS, observ ándose dos fases distintas y muy bien definidas. Un segundo paso por extrusión mono-husillo perm itió mejorar la dispersión del residuo dentro del PS, aumentando la ductilidad de las mezclas reprocesad as sin afectar la rigidez y la resistencia.Peer ReviewedPostprint (published version

Enhancement of the thermal resistance of poly(lactic acid) obtained by reactive extrusion by adding nanoclays

In the present work, poly(lactic acid) sheets (with a nominal width of 1 mm) reinforced with organically modified montmorillonite (with a mass content of 2.5%) have been manufactured through a reactive extrusion process. A chain extensor (with a mass content of 0.5%) has been used in order to improve poly(lactic acid) properties. The kinetics of the thermal degradation has been analyzed by means of the general analytical equation. Various empirical and theoretical solid-state mechanisms have been tested to elucidate the best kinetic model. In order to reach this goal, master plots have been constructed by means of standardized conversion functions. Given that it is not always easy to visualize the best accordance between experimental and theoretical values of standardized conversion functions, a new index, based on integral mean errors, has been developed to quantitatively discern the best mechanism. By doing that, it has been possible to ascertain that random scission of macromolecular chains was the best kinetic model. The presence of nanoparticles has been beneficial, thus enhancing the thermal resistance of poly(lactic acid).Postprint (author's final draft

High added value rubber composites and thermoplastic elastomers as strategies to recycle wastes rubber

Reducing the environmental impact of the polymers production using bio-based plastics and rubber wastes valorization, are two essential ways of reversing the negative impact of the polymer industry on the environment [1]. The design of rubber composites and/or bio-based thermoplastics elastomers using wastes rubber can be proposed [2] but providing high values materials still requires investigation to deliver industrially suitable products. To this aim, we prepared rubber composites and thermoplastic elastomers using natural rubber (NR), wastes rubber (GTR) and Polylactic acid (PLA). First, we prepared vulcanized NR/GTR blends, where the GTR shows a nucleation ability on strain induced crystallization (SIC) in the NR, associated with a large strain reinforcement [3]. The latent heat due to crystallization/melting during cyclic tests performed in adiabatic conditions generates heating/cooling that was found superior in the NR/GTR blends as compared to neat NR [4]. Second, we aimed to improve the toughness of the biobased Polylactic acid (PLA) and take advantage of properties of the previously prepared NR/GTR blends. To do so, PLA/NR/GTR blends were dynamically vulcanized. The elastic modulus, the impact strength and the shape recovery in PLA/NR/GTR were maintained as compared to the PLA/NR blends that do not use wastes, that we attributed to the encapsulation of the GTR particles into the NR matrix forming a co-continuous PLA/rubber morphology. Moreover, PLA/NR/GTR blends exhibit a ten-fold increase of the impact strength as compared to the neat PLA. The NR/GTR and PLA/NR/GTR materials are promising candidates for applications such as heating/cooling technology or high impact pieces

Mechanical and barrier properties enhancement in film extruded bio-polyamides with modified nanoclay

The plastics industry is increasingly oriented towards the use of bio-based polymers replacing the fossil-based ones. Bio-based polyamides (PAs) in the film packaging application are not still used and need enhancement to overcome some drawbacks. In this scenario, fully (PA10.10) and partially (PA6.10) bio-based PAs were extruded in a laboratory sheet-casting machine. The materials used to obtain films were previously melt blended with modified clay in a twin-screw extruder. The resulting films were morphologically investigated through the scanning electron microscope. The magnifications show agglomerated particles and the packed layers are preferentially aligned in the extrusion machine direction. X-rays confirm that 5 wt% of clay content is difficult to exfoliate in such matrices. The crystallinity was studied by using X-ray diffraction (XRD) and differential scanning calorimetry. The XRD results show coexisting a and ¿ phases in the PA6.10 while the presence of only ¿ in the PA10.10. The presence of clay platelets constrains the crystallites formation, especially in the more polar PA6.10, resulting in changes in the type and the amount of crystals. The mechanical analysis data showed that 5 wt% of clay induced significant improvement in Young's modulus (+68 and + 14%), a slight increase in the tensile yield stress (+21 and + 5%) and only a surprisingly small decrease in the deformation at break (-15 and -24%) for PA10.10 and PA6.10, respectively. Furthermore, the addition of clay gave the best oxygen barrier properties reaching a value of 1.8 ± 0.2 cm3 × mm/m2 × day × atm comparable to a commercial PA6 film used in the packaging field.Peer ReviewedPostprint (published version

Elastocaloric waste/natural rubber materials with various crosslink densities

The characterization of the mechanical behavior of elastocaloric materials is essential to identify their viability in heating/cooling devices. Natural rubber (NR) is a promising elastocaloric (eC) polymer as it requires low external stress to induce a wide temperature span, ¿T. Nonetheless, solutions are needed to further improve DT, especially when targeting cooling applications. To this aim, we designed NR-based materials and optimized the specimen thickness, the density of their chemical crosslinks, and the quantity of ground tire rubber (GTR) used as reinforcing fillers. The eC properties under a single and cyclic loading conditions of the resulting vulcanized rubber composites were investigated via the measure of the heat exchange at the specimen surface using infrared thermography. The highest eC performance was found with the specimen geometry with the lowest thickness (0.6 mm) and a GTR content of 30 wt.%. The maximum temperature span under single interrupted cycle and multiple continuous cycles were equal to 12 °C and 4 °C, respectively. These results were assumed to be related to more homogeneous curing in these materials and to a higher crosslink density and GTR content which both act as nucleating elements for the strain-induced crystallization at the origin of the eC effect. This investigation would be of interest for the design of eC rubber-based composites in eco-friendly heating/cooling devices.Peer ReviewedPostprint (published version

Influence of injection molding parameters on the morphology, mechanical and surface properties of ABS foams

In this work, microcellular ABS foams were studied. A series of injection molding samples defined by a design of experiments was carried out to analyze the effect of shot volume, mold temperature, and injection velocity on the morphology, mechanical properties, and surface roughness of microcellular samples. A predominant influence of shot volume on the cell structure and tensile properties was evidenced. Higher cell densities and narrower cell size distributions were obtained at lower injection volume. However, elastic modulus and tensile strength were improved by increasing the shot size. The effect of mold temperature and injection velocity was secondary. Higher levels of mold temperature and injection rate provided finer cell morphologies, but their effects on the elastic modulus and tensile strength were negligible. The decrease in shot volume and increase in gas content led to poor surface quality, whereas it was greatly improved by raising both mold temperature and injection velocityPostprint (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

Mechanical recycling of plastic wastes. Case of study: high impact polystyrene for manufacturing TV components shelf

En este trabajo se presenta una introducción sobre la situación actual del reciclaje de los materiales plásticos a nivel mundial, con un especial interés en la situación en la que se encuentra el estado Europeo. A pesar de que existen numerosas técnicas de reciclado de plásticos, el método de reciclado mecánico ha llamado mucho la atención por parte de las industrias transformadoras del plástico debido a la capacidad de producción que puede llevarse a cabo mediante el uso de técnicas como la extrusión y la inyección de plásticos. La parte final de este trabajo se enfoca en un caso práctico que se llevó a cabo en el Centre Català del Plàstic (CCP) y la empresa SONY para la obtención de materiales plásticos reciclables para manufacturar carcasas de televisiones. El trabajo realizado en el CCP fue el estudio de la viabilidad de la sustitución de materiales vírgenes por materiales reciclados procedentes de residuos industriales. El estudio consistió en analizar la viabilidad de sustituir un poliestireno antichoque (HIPS) virgen por el mismo material de origen pero reciclado. De esta manera, se compararon las propiedades de cuatro materiales HIPS reciclados (HIPS-RA, -RB, -RC y -RD) así como un estudio de su morfología. Se observó que el índice de fluidez del HIPS aumentó con la proporción de material reciclado y con el número de procesos de transformación. La propiedad mecánica más afectada resultó ser la resistencia al impacto, y se observaron dos tipos de morfologías claramente diferentes. El material reciclado que mostró mejores propiedades fue el HIPS-RB, y fue escogido para sustituir al HIPS virgen en la producción de componentes de electrónica de consumo. Finalmente, el estudio realizado permitió analizar los factores que intervienen en el estudio de materiales reciclados, conocer las posibilidades de su aplicación en el caso concreto de componentes de electrónica de consumo y crear las bases para poder establecer una metodología para realizar futuros estudios de introducción de materiales reciclados en otras aplicaciones tecnológicas. Por lo anterior, el trabajo presenta una completa introducción en el área del reciclaje mecánico y las tendencias del mercado así como la viabilidad del reaprovechamiento de materiales de residuo para el desarrollo de componentes no estructurales y de elevada producción industrial.Postprint (published version