Caracterización por espectroscopía IR de cambios estructurales del poli(ácido láctico) en presencia de agua. Efecto de la incorporación de arcillas

En los últimos años ha aumentado de forma significativa el interés en el poli(ácido láctico) (PLA) debido, entre otros factores, a que es un polímero obtenido de fuentes renovables que se degrada en productos no tóxicos, como el ácido láctico, y a que es biocompatible. Estas características hacen que este polímero tenga aplicaciones importantes en biomedicina y en otros campos como, por ejemplo, en el de la fabricación de envases para contener alimentos. En las aplicaciones citadas, el PLA está en contacto con el agua presente en los fluidos corporales o en los alimentos. Por ello, es de gran importancia conocer cómo la interacción entre PLA y agua puede afectar a la estructura del polímero, ya que variaciones en dicha estructura pueden suponer cambios importantes en las propiedades mecánicas y ópticas del material. Por otra parte, se han desarrollado materiales nanoestructurados, de PLA con diferentes nanoarcillas en los últimos años que han conducido a una mejora de algunas propiedades, como la resistencia mecánica, la protección frente a la luz UV y las propiedades de barrera. Estas mejoras incrementan las prestaciones de estos nanocomposites en el envasado de alimentos. La cuestión es, ahora, cómo estas nanoparticulas pueden afectar al comportamiento del material en presencia de agua. El objetivo de la presente investigación es, por tanto, estudiar los cambios estructurales experimentados por PLA en presencia de agua y el efecto de las arcillas en dichos cambios

Efecto del reciclado mecánico simulado en las propiedades de nanocompuestos poli(ácido láctico) - haloisita destinados a aplicaciones de envasado

El incremento previsto en el consumo de poli(ácido láctico) (PLA) en los próximos años, especialmente en aplicaciones de envasado, justifica el interés de estudiar el reciclado mecánico como alternativa para el manejo de los residuos de PLA, reduciendo así el consumo de materias primas y energía. El objetivo de este trabajo es estudiar el efecto del reciclado mecánico en las propiedades y estructura de un nanocompuesto de PLA y haloisita. Para ello se ha sometido un nanocompuesto con 2% m/m de haloisita a un proceso de reciclado que incluye un envejecimiento acelerado y un reprocesado. Los resultados de viscosidad intrínseca indican que el reciclado causa una ligera degradación del PLA; sin embargo, el efecto negativo de dicho descenso del peso molecular en la estructura y propiedades del material es limitado, lo que sugiere que los nanocompuestos PLA-haloisita reciclados podrían ser utilizados en aplicaciones de envasado

Effect of Iignocellulosic Nanoparticles Extracted from Yerba Mate (Ilex paraguariensis) on the Structural, Thermal, Optical and Barrier Properties of Mechanically Recycled Poly(lactic acid)

In this work, yerba mate nanoparticles (YMNs) were extracted from Ilex paraguairiencis yerba mate wastes and further used to improve the overall performance of mechanically recycled PLA (PLAR). Recycled PLA was obtained by melt reprocessing PLA subjected to an accelerated ageing process, which involved photochemical, thermal and hydrothermal ageing steps, as well as a final demanding washing step. YMNs (1 and 3 wt. %) were added to the PLAR during the melt reprocessing step and further processed into films. The main goal of the development of PLAR-YMNs bionanocomposites was to increase the barrier properties of recycled PLA, while showing good overall performance for food packaging applications. Thus, optical, structural, thermal, mechanical and barrier properties were evaluated. The incorporation of YMNs led to transparent greenish PLAR-based films with an effective blockage of harmful UV radiation. From the backbone FTIR stretching region (bands at 955 and 920 cm−1), it seems that YMNs favor the formation of crystalline domains acting as nucleating agents for PLAR. The morphological investigations revealed the good dispersion of YMNs in PLAR when they are used in the lowest amount of 1 wt. %, leading to bionanocomposites with improved mechanical performance. Although the addition of high hydrophilic YMNs increased the water vapor transmission, the addition of 1 wt. % of YMNs enhanced the oxygen barrier performance of the produced bionanocomposite films. These results show that the synergistic revalorization of post-consumer PLA and nanoparticles obtained from agri-food waste is a potential way for the production of promising packaging materials that meet with the principles of the circular econom

Effect of simulated mechanical recycling processes on the structure and properties of poly(lactic acid)

The aim of this work is to study the effects of different simulated mechanical recycling processes on the structure and properties of PLA. A commercial grade of PLA was melt compounded and compression molded, then subjected to two different recycling processes. The first recycling process consisted of an accelerated ageing and a second melt processing step, while the other recycling process included an accelerated ageing, a demanding washing process and a second melt processing step. The intrinsic viscosity measurements indicate that both recycling processes produce a degradation in PLA, which is more pronounced in the sample subjected to the washing process. DSC results suggest an increase in the mobility of the polymer chains in the recycled materials; however the degree of crystallinity of PLA seems unchanged. The optical, mechanical and gas barrier properties of PLA do not seem to be largely affected by the degradation suffered during the different recycling processes. These results suggest that, despite the degradation of PLA, the impact of the different simulated mechanical recycling processes on the final properties is limited. Thus, the potential use of recycled PLA in packaging applications is not jeopardized

Effects of Aging and Different Mechanical Recycling Processes on the Structure and Properties of Poly(lactic acid)-clay Nanocomposites

The growing use of poly(lactic acid) (PLA) and PLA-based nanocomposites in packaging has raised the interest of studying the mechanical recycling of the wastes and the properties of the recycled materials. The main objective of this work was to study the effect of two different mechanical recycling processes on the structure and properties of a PLA-montmorillonite nanocomposite. The two recycling processes included accelerated thermal and photochemical aging steps to simulate the degradation experienced by post-consumer plastics during their service life. One of them also included a demanding washing process prior to the reprocessing. A decrease in the molecular weight of PLA was observed in the recycled materials, especially in those subjected to the washing step, which explained the small decrease in microhardness and the increased water uptake at long immersion times. Water absorption at short immersion times was similar in virgin and recycled materials and was accurately described using a Fickian model. The recycled materials showed increased thermal, optical and gas barrier properties due to the improved clay dispersion that was observed by XRD and TEM analysis. The results suggest that recycled PLA-clay nanocomposites can be used in demanding applications

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

Estudio de la viabilidad del reciclado mecánico del poli(ácido láctico) y sus nanocomposites

El poli(ácido láctico) (PLA) es un bioplástico producido a partir de fuentes renovables que, debido a sus buenas prestaciones, ha ganado interés como candidato para reemplazar a los plásticos producidos a partir de combustibles fósiles en aplicaciones como el envasado de alimentos. Sin embargo, el uso creciente de este bioplástico podría traer problemas ambientales y sociales, relacionados con la gestión adecuada de la gran cantidad de residuos que podrían generarse y con la superficie necesaria para cultivar la materia prima empleada en la producción del PLA. Por este motivo, es interesante evaluar alternativas que permitan la valorización adecuada de los residuos de PLA y la reducción del consumo de materias primas. Por ello, uno de los objetivos principales de este trabajo es el estudio de la viabilidad del reciclado mecánico del PLA y sus nanocomposites con arcillas, analizando el efecto de este proceso en las propiedades de los plásticos reciclados. Para cumplir este objetivo se ha sometido al PLA, y sus nanocomposites con montmorillonita y haloisita, a diferentes procesos de reciclado, que pueden incluir: una etapa de extrusión y moldeo por compresión; un envejecimiento acelerado (utilizado para simular la degradación durante la vida útil) que consta de etapas de degradación fotoquímica, térmica e hidrolítica; un proceso de lavado intenso y, finalmente, una etapa de reprocesado por extrusión y moldeo por compresión. Los materiales resultantes han sido caracterizados mediante diferentes técnicas experimentales, incluyendo viscosimetría, espectroscopía infrarroja y UVvisible, calorimetría diferencial de barrido, termogravimetría, microscopía electrónica (barrido y trasnmisión) y difracción de rayos X. El reciclado mecánico ocasiona la degradación del PLA. Los resultados obtenidos indican que la magnitud de esta degradación depende de las condiciones del proceso, ya que, por ejemplo, la inclusión de una etapa de lavado enérgico produce descensos del 20 % en la viscosidad intrínseca, lo que complica la procesabilidad del plástico reciclado. Esta reducción de la viscosidad del PLA se traduce además en una mayor habilidad para cristalizar, una menor estabilidad térmica y un ligero descenso en las propiedades de barrera frente a gases del plástico reciclado. No obstante, el descenso de las propiedades debido al reciclado mecánico es en general pequeño, lo que sugiere que el plástico reciclado podría tener una segunda vida. En los nanocomposites con las diferentes arcillas, se observa también la degradación del PLA después de los diferentes procesos de reciclado. Sin embargo, el reprocesado ocasiona una mejor dispersión de las arcillas en la matriz polimérica, lo que conlleva en este caso incluso mejores propiedades mecánicas, térmicas y de barrera en los nanocomposites reciclados. El descenso de la viscosidad intrínseca, y de algunas propiedades, del PLA podría afectar negativamente al interés comercial por el plástico reciclado y, por tanto, a la reciclabilidad del material. Por ello, el otro objetivo de esta tesis es el estudio de alternativas para mejorar las prestaciones del PLA reciclado, sin encarecer excesivamente el coste del proceso. Para ello, se ha sometido un grado comercial de PLA a un proceso de reciclado que incluye una etapa de procesado en fundido, un envejecimiento acelerado, una etapa de lavado y un segundo procesado en fundido. Es en esta segunda etapa de procesado cuando se añaden diferentes aditivos (como peróxido de dicumilo y un extensor de cadena), o diferentes arcillas (montmorillonita y haloisita) para mejorar las propiedades del material reciclado. Los resultados indican que tanto adición del peróxido y del extensor de cadena, como la adición de las diferentes arcillas, ocasionan un incremento de la viscosidad intrínseca del material, así como una mejora de las propiedades mecánicas y térmicas del PLA reciclado. En resumen, se puede decir que el reciclado mecánico ocasiona la degradación del PLA, y un pequeño descenso en sus propiedades. Este descenso es pequeño en general, y el material reciclado podría ser utilizado nuevamente, incluso en aplicaciones de envasado. Sin embargo, es posible obtener PLA reciclado con mejores prestaciones sin aumentar de forma importante el coste del proceso, lo que debería mejorar la reciclabilidad de este bioplástico. ----------ABSTRACT---------- Poly(lactic acid) (PLA) is a bioplastic produced from renewable resources. Due to its good properties, PLA has attracted interest as an alternative to fossil-fuel based polymers in several applications, such as food packaging. However, the increasing use of this bioplastic might generate some environmental and social problems, related to the large amount of wastes and to the cropland needed to produce the raw materials used in PLA production. Therefore, is interesting to evaluate alternatives that allow the valorization of PLA wastes and the reduction of the consumption of raw materials. Consequently, one of the main aims of this work is to study the feasibility of mechanical recycling of PLA and its nanocomposites with clays, analyzing the effect of this process on the properties of the recycled plastics. To achieve this objective, PLA and its nanocomposites were subjected to different recycling processes, which might include: an extrusion and compression molding stage; an accelerated aging step (to simulate the degradation during service life), which consisted of photochemical, thermal and hygrothermal aging processes; a demanding washing step and, finally, a second reprocessing by extrusion and compression molding. The resulting materials were then characterized by viscosimetry, UV-Vis and infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, transmission and scanning electron microscopies and X-ray diffraction. Mechanical recycling causes the degradation of PLA. The results point out that the intensity of this degradation depends on the process conditions, since the inclusion of a washing step led to a 20 % decrease of the intrinsic viscosity. This degradation results in an increased crystallization ability and reduced thermal stability and gas barrier properties. However, the decrease of the properties due to the mechanical recycling processes is small, which suggests that PLA can be subjected to mechanical recycling. Regarding the nanocomposites with different clays, the degradation of PLA upon recycling was also noticeable. However, the reprocessing step caused a better dispersion of the clays in the polymer matrix, leading in this case to improved mechanical, thermal and gas barrier properties in the recycled material. The decrease of the intrinsic viscosity, and some properties, of recycled PLA might compromise the recyclability of the plastic. Therefore, other objective of this work is the study of different methods to improve the performance of recycled PLA, without significantly increasing the costs of the process. For this, a commercial grade of PLA was subjected to a recycling process including a melt processing step, an accelerated aging, a washing step and a second melt reprocessing step. It is in this second processing step in which different additives (such dicumyl peroxide and a chain extender), or different clays, are used to improve the performance of recycled PLA. The results indicate that both the addition of the peroxide and the chain extender, and the addition of the different clays, led to increased intrinsic viscosity, along with better mechanical and thermal properties of recycled PLA. Summarizing, mechanical recycling causes the degradation of PLA, and a decrease on its performance. This decrease is relatively small, and the recycled material could be used, even in demanding applications such as packaging. Moreover, there are cost-effective ways for obtaining mechanically recycled PLA with improved properties, which should improve the recyclability of this material

Amino-Modified Halloysite Nanotubes to Reduce Polymer Degradation and Improve the Performance of Mechanically Recycled Poly(lactic acid)

From an environmental point of view, mechanical recycling is, in general, a good end-of-life option for poly(lactic acid) (PLA), one of the most important biobased polymers. However, the degradation of PLA during the service life and, especially, during the mechanical recycling process, leads to a decrease in the properties of PLA, thus reducing the applications of the recycled plastic. The main aim of this work was to study the addition of small amounts of halloysite nanotubes, during the recycling step, as the basis of a cost-effective method for improving the properties of the recycled PLA. Raw halloysite was modified with an aminosilane, and 2% by weight of both raw and modified halloysite were melt compounded with PLA previously subjected to accelerated ageing. The addition of the nanotubes led to recycled materials with improved properties because halloysite reduces the degradation of PLA by blocking the carboxyl groups, generated during the ageing and washing steps, which catalyze the degradation during the recycling process. This effect was more intense in the silanized nanotubes, because the carboxyl groups were effectively blocked by acid–base interactions with the amino groups of the chemical modification. The properties of the recycled plastic with only 2 wt% of silanized halloysite were very close to those of the virgin plastic

Effect of simulated mechanical recycling processes on the properties of poly (lactic acid)

The aim of this work is to study the effects of different simulated mechanical recycling processes on the structure and properties of PLA. A commercial grade of PLA was melt compounded and compression molded, then subjected to two different recycling processes, one of them comprising an accelerated aging and a second melt compounding and compression molding step, and other which included a demanding washing step after the accelerated aging process. The intrinsic viscosity measurements indicate that both recycling processes produce a degradation in PLA, which is more pronounced in the sample subjected to the washing process. DSC results suggest an increase in the mobility of the polymer chains in the recycled materials, however the degree of crystallinity of PLA seems unchanged. The optical, mechanical and gas barrier properties of PLA do not seem to be largely affected by the degradation suffered during the different recycling processes. These results suggest that, despite the degradation of PLA, the impact of the different simulated mechanical recycling processes on the final properties is limited. Thus, the potential use of recycled PLA in packaging applications is not jeopardized

Investigation of mechanical recycling effect on structural, thermal, mechanical and electromagnetic properties of polylactic acid (PLA) – nanoclay nanocomposites: Towards a valorization of recycled PLA nanocomposites

Virgin and recycled poly(lactic acid) (PLA) based nanocomposite materials were obtained and subjected to microstructural, thermal and mechanical analysis in view of fabricating efficient microwave absorbers. PLA was first exposed to artificial accelerated aging, next was mechanically recycled through grinding followed by reprocessing using melt extrusion and compression molding, resulting in recycled PLA samples (rPLA). Addition of organically modified montmorillonite (OMMT) as nanoclay was performed in a second melt extrusion process in order to obtain virgin and recycled PLA-OMMT nanocomposites. The impact of recycling process and presence of OMMT nanoclay in the host PLA matrix has been studied by FTIR, TGA and DSC, while the mechanical performance has been investigated by micro-hardness test. The dielectric properties were measured in the 26–40 GHz frequency range using a Vector Network Analyzer to assess the performance of virgin and recycled PLA and OMMT-PLA material as microwave absorbers. The FTIR results show that the recycling process generated more C = O groups in the polymer. These polar groups tend to orient themselves in the direction of the applied field and increase the dielectric constant (ε’). Measured electromagnetic absorption index revealed that rPLA-4OMMT with a thickness of 400 μm is able to absorb 20.3% on average of the spectrum with a peak of 36%, while 200 μm-thick films of rPLA-4 wt.% OMMT has a mean absorption index of 14.5%. The overall results show that mechanically recycled polymer can replace virgin polymer in this kind of applications