Síntesis y caracterización de nanocompuestos de poliolefinas e hidróxidos dobles laminares

Con esta tesis se ha pretendido establecer las bases para la preparación y caracterización de compuestos nanoestructurados formados por laminillas de espesor nanométrico a partir de la exfoliación de un hidróxido doble laminar (LDH) organofílico y poliolefinas mediante proceso de mezclado en fundido. En una primera fase de la investigación se estableció una metodología sencilla para preparar un LDH híbrido con aniones dodecilsulfato a partir de LDH precursor del tipo hidrotalcita. Para ello se probaron cuatro rutas: reconstitución en dos pasos y directa del LDH precursor calcinado con aniones dodecilsulfato e intercambio iónico en dos pasos y directo de los carbonatos del LDH precursor por los aniones orgánicos. Las tres primeras rutas resultaron en la formación de un híbrido, tal como se confirmó por medidas de Difracción de rayos X (DRX) y Espectroscopia infrarroja de transformada de Fourier (FTIR). La formación de dicho híbrido provocó una expansión del espacio interlaminar, que pasó de 7.7 Å a unos 30 Å, conduciendo a una disminución de la densidad. El mayor grado de intercambio resultó para la ruta de intercambio en dos pasos. La ruta de reconstitución en dos pasos permitió obtener un LDH híbrido libre de óxidos sin reconstituir, mientras que el híbrido obtenido por la ruta de reconstitución directa resultó con impurezas de dichos óxidos. Además, el método de reconstitución en dos pasos condujo a un híbrido con mayor estabilidad termooxidativa. En segundo lugar, se prepararon una serie de materiales compuestos, tanto con el LDH precursor como con el híbrido, y tres polímeros de naturaleza olefínica: polipropileno, polietileno de alta densidad y un ionómero de etileno y ácido metacrílico parcialmente neutralizado con sodio. Algunas de las formulaciones también se prepararon con compatibilizantes. En los materiales con polipropileno se utilizó copolímero de polipropileno con injertos de anhídrido maléico (PP-g-MAH) y un copolímero tribloque de estireno-etileno/butileno-estireno con injertos de anhídrido maléico (SEBS-g-MAH) mientras que en los materiales con polietileno, se utilizó el ionómero de etileno y ácido metacrílico parcialmente neutralizado con sodio. La estructura de los nanocompuestos resultantes consistió en agregados cristalinos intercalados (tactoides) con laminillas individuales y grupos de unos pocas laminillas procedentes de la exfoliación, tal como confirmaron las medidas de DRX y Microscopia Electrónica de Transmisión (TEM). El empleo de los copolímeros favoreció la formación de la estructura exfoliada. La cristalización del polipropileno desde el estado fundido resultó afectada por el híbrido, acelerándose su nucleación, incrementándose la velocidad de cristalización y formándose una población cristalina más uniforme. La incorporación de las partículas contribuyó a incrementar ligeramente la rigidez de los polímeros sin una disminución acusada de la resistencia máxima. El análisis mecánico-dinámico confirmó como el módulo de almacenamiento se incremento ligeramente en los nanocompuestos, siendo este incremento de mayor o menor grado función de la composición. En los compuestos con el ionómero las altas fuerzas de interacción que se generan entre las laminillas del LDH y los grupos iónicos, tuvieron un efecto acusado sobre el comportamiento reológico, contribuyendo a una importante aumento de la viscosidad de los compuestos. Dichas partículas también contribuyeron a la formación de agregados iónicos más estables térmicamente. Las laminillas de LDH contribuyeron a una mejora de la degradación termooxidativa de los nanocompuestos una vez iniciada la descomposición. La combustibilidad de los compuestos se vio fuertemente afectada por las partículas, incrementándose el tiempo que transcurre desde que se inicia la combustión hasta que cae la primera gota considerablemente.Postprint (published version

ITMA Barcelona 2019: tendencias en tisaje de calada

En este artículo se presentan las principales tendencias en tisaje de calada vistas en la ITMA 2019 celebrada en Barcelona el pasado junio. Se revisan de forma general las innovaciones observadas en maquinaria de tejeduría tanto de lizos como Jacquard, así como maquinaria auxiliar, destacando las novedades presentadas por las principales marcas presentes en el mercadoPostprint (published version

Evolution of interfacial shear strength and mean intrinsic single strength in biobased composites from bio-polyethylene and thermo-mechanical pulp- corn stover fibers

In this article, with the aim of promoting sustainability, contributing to the circular economy and the fight against climate change, the production of composite materials from Bio-polyethylene reinforced with corn stover fibers has been studied. The behavior of the materials obtained has been studied experimentally and by mathematical models of micromechanics. The composite materials were produced by extrusion and then injection with from 10 to 50 wt.% of fibers. The creation of a good fiber-matrix interface was studied by the incorporation of coupling agent between (0–8 wt.%). Increase of 131.2% on tensile strength for 40wt.% reinforcement was achieved by adding 6 wt.% of coupling agent. The correct interface was demonstrated by a correlation of 0.99 between the experimental results and the results of the mathematical models usedPeer ReviewedPostprint (published version

Assessment of the natural fiber reinforced bio-polyethylene composites flexural macro and micromechanical properties

One of the most common load modes is flexure. The paper measures and models the flexural strength and modulus of a bio-polyethylene reinforced with thermos-mechanical fibers from corn stover. Moreover, the authors use modified rules of mixtures to evaluate the contribution of the reinforcements to the properties of the composite. It was found a high impact of coupling agent content on the strength of the composites, and materials with a 6% of such agent and 50% of reinforcement increased 181% the strength of the matrix, and 464% its modulus. The obtained values are noticeable higher than polypropylene and some of its composites. Micromechanics analysis shows that the effect of natural fiber reinforcement on the flexural properties of a bio-based PE is similar to the effects on a polyolefin. Thus, the use of fully bio-based composites can be proposed as a substitute for some oil-based polymers, partially bio-based materials, and their compositesPostprint (author's final draft

Abrasive elements and abrasion resistance tests for car seat upholstery

The weight of textile components in automobiles is expected to rise to 35 kg by 2020, and the average lifetime of a vehicle is about 12 years. Car seats are the most important part of the interior decoration, and polyester is the most widely used material in car seat covering. Abrasion resistance tests are used to quantify the duration of car seat upholstery in normal usage, and this is one of the most important requirements. Several testing methods, standards, and car producer specifications have been developed to define the abrasion resistance of specified materials, and pre-tests have been taken to identify parameters for this research. The objective of this study was to compare three abrasion tests with different abrasive elements using car seat upholstery structures. Comparison among abrasion testers and abrasive papers shows statistically significant differences. The relationship between weight loss and abrasion cycles can be modelled by regression equationsPostprint (published version

Assessment of chemical and mechanical behavior of bamboo pulp and nanofibrillated cellulose exposed to alkaline environments

This study was performed to study the effects of the cement paste composition (calcium aluminate cement—CAC and a geopolymer in comparison to Portland cement—OPC) on bamboo pulp and nanofibrillated cellulose (NFC). The changes in the composition and chemical structure of the fibers were analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The changes in the mechanical strength were evaluated through tensile tests on the fibers after immersion on the cement pastes, in the form of sheets. The XPS results showed that the immersion of the pulp and NFC in the different pastes (CAC, geopolymer and OPC) modified the chemical surface of these fibers: it was found removal of lignin and extractives and some degradation of hemicellulose and cellulose. The FTIR analysis indicated modifications in the hydrogen bonds energy. The tensile strength of pulp sheets decreased in 70% and 34% after immersion in OPC and geopolymer, respectively. The tensile strength of the NFC sheets decreased 36%, 68% and 54% after immersion in OPC, CAC and geopolymer, respectively. Thus, the response of the bamboo pulp and NFC immersed in different cement pastes was different due the inherent characteristics of such fibers, and not only the Portland cement should be considered as harmful to lignocellulosic fibers. Although CAC and geopolymer are free of calcium hydroxide, the high alkalinity of these pastes also accelerated the degradation process of lignocellulosic fibersPostprint (author's final draft

Towards more sustainable material formulations: a comparative assessment of PA11-SGW flexural performance versus oil-based composites

The replacement of commodity polyolefin, reinforced with glass fiber (GF), by greener alternatives has been a topic of research in recent years. Cellulose fibers have shown, under certain conditions, enough tensile capacities to replace GF, achieving competitive mechanical properties. However, if the objective is the production of environmentally friendlier composites, it is necessary to replace oil-derived polymer matrices by bio-based or biodegradable ones, depending on the application. Polyamide 11 (PA11) is a totally bio-based polyamide that can be reinforced with cellulosic fibers. Composites based on this polymer have demonstrated enough tensile strength, as well as stiffness, to replace GF-reinforced polypropylene (PP). However, flexural properties are of high interest for engineering applications. Due to the specific character of short-fiber-reinforced composites, significant differences are expected between the tensile and flexural properties. These differences encourage the study of the flexural properties of a material prior to the design or development of a new product. Despite the importance of the flexural strength, there are few works devoted to its study in the case of PA11-based composites. In this work, an in-depth study of the flexural strength of PA11 composites, reinforced with Stoneground wood (SGW) from softwood, is presented. Additionally, the results are compared with those of PP-based composites. The results showed that the SGW fibers had lower strengthening capacity reinforcing PA11 than PP. Moreover, the flexural strength of PA11-SGW composites was similar to that of PP-GF compositesPostprint (published version

Effect of chain extender and water-quenching on the properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) foams for its production by extrusion foaming

Bacterial polyesters such as polyhydroxyalkanoates (PHAs) are of great interest for a large number of applications both because of their properties and because they come from renewable resources, despite having a higher cost than commodity polymers. Their foaming—although it presents some difficulties—could be an option to increase their competitiveness. In this work, two strategies have been studied to enhance the poly(3-hydoxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) foamability by extrusion foaming. The effect of the cooling system (water-quenching or air-cooling), chain extender (CE) addition and chemical blowing agent (CBA) amount were evaluated. Density, cellular morphology, mechanical and thermal properties were studied. Optimal density reduction was achieved with use of CE and 3–4 wt.% of CBA masterbatch. The most effective strategy on density reduction was the addition of CE, while the water quenching had only a slight influence on the samples in which CE was not present. CE addition decreased the viscosity and the degradation rate of the polymer, thus leading to lighter foams with larger cells but with equal or even slightly better resistance to compressive and tensile stress, in general termsPostprint (author's final draft

Kinetics of low temperature polyester dyeing with high molecular weight disperse dyes by solvent microemulsion and agrosourced auxiliaries

This work focused on the evaluation of the kinetics of dyeing polyester fabrics with high molecular weight disperse dyes, at low temperature by solvent microemulsion. This study also compared the effect of two non-toxic agro-sourced auxiliaries (o-vanillin and coumarin) using a non-toxic organic solvent. A dyeing bath consisting of a micro-emulsion system involving a small proportion of n-butyl acetate was used, and the kinetics of dyeing were analysed at four temperatures (83, 90, 95 and 100 °C). Moreover, the dyeing rate constants, correlation coefficient and activation energies were proposed for this system. It was found that o-vanillin yielded higher dye absorption levels than coumarin, leading to exhaustions of 88% and 87% for Disperse Red 167 and Disperse Blue 79, respectively. K/S values of dyed polyester were also found to be higher for dye baths containing o-vanillin with respect to the ones with coumarin. In terms of hot pressing fastness and wash fastness, generally no adverse influence on fastness properties was reported, while o-vanillin showed slightly better results compared to coumarinPostprint (published version

Migration of calcium hydroxide particles from the matrix to the cellulosic fibres in cement mortar based composites

Postprint (published version