Degradation of a mechanically recycled polylactide/halloysite nanocomposite in an ethanolic food simulant

[EN] This work aims to study the effect of immersion in a ethanolic food simulant in mechanically recycled poly(lactic acid) (PLAR) and its nanocomposites reinforced with halloysite nanotubes (HNT). PLAR was obtained by subjecting PLA to an accelerated ageing process, which includes photochemical, thermal and hydrothermal ageing steps, followed by a final demanding washing step. PLAR was further reinforced with 4 %wt. HNT to improve the properties of the PLAR films. The materials were melt compounded by melt extrusion and processed into films by compression molding. The resulting films were exposed to food simulant D1 (50 %vol. ethanol solution) for 10 days at 40 °C. The intrinsic viscosity, crystallization behavior, thermal stability as well as the mechanical performance were analyzed before and after the contact with the food simulant. The swelling, plasticizing and hydrolyzing effect of the food simulant led to an important decrease of the intrinsic viscosity of all the samples, along with a significant increase of the crystallinity. Thermal stability was negatively affected by the decrease of the molecular weight, while the high crystallinity values resulted in materials with higher Vickers hardness values after the immersion in the food simulant.This work was supported by European Union’s Horizon 2020 research and innovation program [grant agreement No. 860407 BIO-PLASTICS EUROPE], by MINECO-Spain [project CTM2017-88989-P] as well as Universidad Politécnica de Madrid [project UPM RP 160543006].Beltrán, FR.; Arrieta, MP.; Hortal, Y.; Gaspar, G.; De La Orden, MU.; Martínez Urreaga, J. (2021). Degradation of a mechanically recycled polylactide/halloysite nanocomposite in an ethanolic food simulant. 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Efecto del Peso Molecular en la Formación del Polimorfo Beta en Polipropileno Isotáctico Metalocénico.

Existe un gran número de referencias relativas al efecto que la adición de agentes nucleantes, AN, en el polipropileno, iPP, supone en la generación de los distintos polimorfos, no existiendo estudios previos en el iPP metalocénico, m-iPP. Es objetivo de este trabajo llenar la laguna existente en dicha área, con el fin de mejorar la estabilidad térmica y la transparencia, acortar los ciclos de producción y optimizar las propiedades. Se han estudiado diferentes tipos de nucleantes de última generación que conllevan, en primer lugar, la formación de la celdilla monoclínica α y el aumento de la temperatura de cristalización, lo que acorta los ciclos de transformación. Para la evaluación exhaustiva5 de la forma β, objetivo de este trabajo, se ha utilizado como AN una mezcla de estearato cálcico y ácido pimélico (1:2), denominada a5. La competencia entre las formas α, β y γ en el m-iPP depende de la velocidad de cristalización y de la temperatura de cristalización isoterma5. Además, el contenido de AN β necesario para generar esta forma cristalina en el m-iPP es considerablemente superior en relación con el iPP sintetizado con catalizadores Ziegler-Natta, Z-N, debido a la coexistencia del polimorfo γ en el primero. La competencia entre las tres formas cristalinas en el m-iPP provoca que la generación de la forma β en función de la velocidad de enfriamiento sea, bajo ciertas condiciones, opuesta a la observada previamente en el iPP Z-N convencional. Estos resultados novedosos son de gran interés dado que han establecido las bases científicas sobre las que se cimenta el objetivo de la adición de AN β en los diferentes iPPs seleccionados, objeto de estudio en esta comunicación. Se han mezclado dos m-iPP con índices de fluidez, IF, de 15 y 30 g/min, suministrados por Basell, con un 0.3 % en peso de AN, en un mezclador interno a 190 ºC, 40 rpm y 10 min. Posteriormente, se han preparado filmes mediante moldeo por compresión en muestras sin y con AN. Las muestras se han enfriado desde el fundido a unos 100 ºC/min (entre platos de agua fría y presión), tratamiento Q y a 1.5 ºC/min (velocidad de enfriamiento de la prensa bajo presión), tratamiento S. La caracterización de la estructura y la competición entre las diferentes formas cristalinas se ha seguido mediante difracción de rayos X y DSC, mientras que el estudio de las propiedades mecánicas se ha realizado mediante DMTA y microdureza. En la figura se reproducen los difractogramas de RX para las muestras en estudio sin y con 0.3% de AN y tratamiento térmico S. Las muestras sin aditivar, sn, presentan polimorfismo, es decir, la coexistencia de las difracciones a 18.5 y 21.2º características de las celdillas cristalinas α y γ, respectivamente. Por otro lado, la presencia del AN a5 da lugar a una difracción adicional a 16.1º asociada a la fase trigonal β. La intensidad de dicha difracción es mayor para el polímero de menor peso molecular (mayor IF)

Caracterización del polimorfismo de un polirpopileno metalocénico por medio de espectroscopia FTIR

Se presentan resultados sobre al caracterización morfológica de PP's metalocénicos por medio de espectroscopía infrarroja

Technical Evaluation of Mechanical Recycling of PLA 3D Printing Wastes

The importance of 3D printing is growing rapidly. A recent example of this increasing importance involves the fight against the Covid-19 pandemic, in which 3D printing has helped to overcome the shortage of critical supplies. However, 3D printing generates large amounts of plastic waste that could pose an environmental problem, thus making it necessary to find methods for the correct management of such wastes. The combination of additive manufacturing and distributed mechanical recycling can contribute to the development of a more circular economy. The main goals of this work were to characterize the poly(lactic acid) (PLA) wastes generated in 3D printing processes and evaluate the effect of their heterogeneity on the technical feasibility of mechanical recycling. Two PLA 3D printing wastes were used: waste coming from a well-known PLA grade, and a mixture of PLA 3D printing residues coming from an association of coronamakers in Madrid. Recycled material obtained from the waste of a well-known PLA grade shows good properties, similar to those for non-used material. However, the recycled material obtained from mixed PLA waste shows lower viscosity values, higher crystallization ability and less transparency. These results highlight that special attention should be paid to the sorting and characterization of the 3D wastes, to obtain recycled materials with good properties