Caracterització microestructural i mecànica de compòsits hdpe/fibres lignocel.lulòsiques

A partir de polietilè d'alta densitat i de fibres lignocel·lulòsiques provinents del trèmol (Populus tremula) s'han obtingut uns materials amb propietats úniques denominats compòsits. Aquests compòsits, amb un màxim de 40% de fibres lignocel·lulòsiques han estat tractats i modificats amb diferents agents (silà A-174 i epolè C-18) per millorar la compatibilitat entre la matriu de polietilè i el reforç fibrós. En una primera etapa les fibres lignocel·lulòsiques han estat pretractades amb cada un dels diferents tipus d'agents d'adhesió utilitzats i comentats prèviament, per seguidament barrejar aquestes fibres (en proporcions del 10, 20, 30 i 40%) amb la matriu d'HDPE. Una vegada els dos components s'han homogeneïtzat, es sotmeten a un procés de mòlta per aconseguir, mitjançant compressió, les provetes corresponents. Finalment, el conjunt de provetes ha estat exposat a condicions climàtiques dràstiques (baixa temperatura i fatiga tèrmica, dues característiques significatives de l'hivern canadenc) durant períodes variables de temps (0, 15, 30, 60 i 90 dies).Per tal d'avaluar tots i cada un dels paràmetres més significatius d'aquests compòsits, s'ha fet una caracterització orientada en dues vessants: estudi de la compatibilitat entre components del compòsit i estudi dels canvis estructurals que pateixen els compòsits degut a fenòmens d'envelliment provocats per exposició a les condicions climàtiques prèviament comentades.L'estudi de compatibilitat es fonamenta en les possibles interaccions que s'originen entre els dos components en funció del tipus de tractament al que ha estat sotmès el compòsit (silà i epolè). Per valorar aquestes interaccions, s'han estudiat diferents propietats mecàniques, com ara la resistència a la tracció, el mòdul d'elasticitat, la deformació a trencament, la resiliència i la tenacitat, mitjançant una màquina universal d'assaigs. Tanmateix també s'ha fet una caracterització espectrefotomètrica FT-ir per comprovar els diferents mecanismes d'adhesió que actuen en la interfase fibra- matriu en funció del tipus de tractament i una caracterització morfològica, utilitzant la tècnica de microscòpia electrònica de rastreig (SEM). Amb els resultats obtinguts de la caracterització espectrefotomètrica, també s'ha realitzat un seguiment de la influència que cada component fa en la modificació del grau de cristal·linitat de l'altre.L'estudi dels canvis estructurals que pateixen els compòsits degut a fenòmens d'envelliment s'ha fet partint de l'evolució de les propietats mecàniques bàsiques en funció dels diferents períodes d'exposició, on s'han caracteritzat els mateixos paràmetres definits anteriorment. Mitjançant valoració espectrefotomètrica s'han mesurat els canvis microestructurals (principalment de configuració), així com les modificacions en el grau de cristal·linitat que han tingut lloc sobre cada un dels diferents components del compòsit.Cal afegir que les possibilitats que ofereix la tècnica espectrefotomètrica FT-ir ha permès dur a terme la realització d'aquesta tesi. L'estudi dels canvis en la microestructura dels compòsits esdevinguts a partir dels fenòmens prèviament esmentats no hauria pogut fer-se sense la possibilitat d'un processament adequat dels espectres, així com d'una subtracció espectral que permet la detecció de moltes bandes complexes i difícils de detectar mitjançant altres tècniques d'anàlisi.Los materiales compuestos se han obtenido a partir de polietileno de alta densidad y fibras lignocelulósicas que provienen del alamo temblón. Estos materiales con un máximo del 40% de refuerzo lignocelulósico han sido tratadas y modificadas con distintos tipos de agentes de acoplamiento (Silano A-174 y epoleno C-18) para mejorar la compatibilidad entre la matriz y el refuerzo.Las fibras tratadas previamente con cada uno de los distintos tipos de agentes de adhesión utilizados, se mezclan en distintas proporciones de las mismas (10,20,30 y 40%) con la matriz de HDPE. Una vez ambos componentes se han homogenizado se someten a un proceso de molturación para obtener probetas tipo halterio mediante compresión. Estas probetas se han sometido durante distintos períodos de tiempo (hasta 90 días) a condiciones de exposición drásticas (baja temperatura y fatiga térmica, características significativas del invierno canadiense).Para evaluar los parámetros más significativos de estos materiales compuestos se ha caracterizado la compatibilidad entre la matriz y el refuerzo, asimismo también se han estudiado los cambios estructurales que sufren estos materiales debido a fenómenos de envejecimiento provocados por la exposición de los mismos a las condiciones climáticas previamente comentadas.Els estudio de compatibilidad se centra en las posibles interacciones que se originen entre ambos componentes en función del tipo de tratamiento al que se ha sometido dicho material compuesto (silano y epoleno). Para valorar las interacciones que se generen entre ambos componentes, se ha ensayado distintas propiedades mecánicas (resistencia a tracción, módulo de elasticidad, deformación a rotura, resilencia y tenaciadad, utilizando la máquina universal de ensayos. Asimismo, también se ha caracterizado mediante espectroscopia de infrarrojo (FTIR) los posibles mecanismos de adhesión que tienen lugar entre la matriz y el refuerzo en función del tipo de tratamiento, asi como la caracterización morfológica utilizando la técnica de microscopía electrónica de barrido (SEM). A partir de los resultados obtenidos se ha podido seguir la influencia que tiene cada componente en la modificación de los respectivos grados de cristalinidad. El estudio de los cambios estructurales a los que se han visto sometido los distintos materiales compuestos, debido a fenómenos de envejecimiento, se ha realizado mediante el seguimiento de la evolución de las propiedades mecánicas en función de los distintos períodos de exposición. Mediante valoración espectofotométrica se han medido los cambios micorestrucutrales (cambios de configuración), así como las modificaciones en el grado de cristalinidad sobre cada uno de los componentes de material compuesto.Composite materials have been obtained from high density polyethylene (HDPE) and lignocellulosic fibers from aspen wood. These materials with a maximum of 40% of lignocellulosic reinforcement have been treated and modified with different types of coupling agents (Silane A-174 and epolene C-18) to improve the compatibility between the matrix and the reinforcement.Four contents (10.20.30 and 40%) of fibers treated previously with each one of the different types of adhesion or coupling agents, are mixed with HDPE matrix. The above mixture was compression-molded into dog-bone shaped tensile test specimens. The molding temperature was slowly raised to 150ºC and samples were held at this temperature for 20 min. Then the samples were slowly cooled to room temperature keeping constant pressure during cooling. These test specimens have been submitted during different periods of time (up to 90 days) to drastic conditions of exposition (low temperature and thermal stress, main characteristics of the Canadian winter).In order to evaluate the most significant parameters of these composite materials, we have studied two ways: the compatibility between both components: matrix and reinforcement and the structural changes to composites due to phenomena of aging caused by the exposition of these materials to the drastic climatic conditions previously commented.The study of compatibility has been centered in the possible interactions that are originated between both components as a function of lignocellulosic fiber pretreatment. In order to evaluate the interactions that are generated between both components, different mechanical test has been tested (tensile strength, elasticity modulus, deformation at break, resilence and toughness) by mean an Instron Testing Machine. Moreover, the possible mechanisms of adhesion that take place between the matrix and the reinforcement as a function of different pretreatments has been characterized by means infrared spectroscopy (FTIR), and by the morphologic characterization using the scanning electronic microscopy (SEM). From the obtained results it has been possible to follow the influence that has each component in the modification of the respective degrees of crystallinity.The study of the structural changes of different composite materials, due to aging phenomena, has been analized by means of the pursuit of the evolution of the mechanical properties based on the different periods of exposure time. Furthermore the microstructural changes (basically configurational and crystallinity) has been evaluated by means of spectroscopy technique. The obtained results indicate that the macroscopic properties of the composite materials must depend on the lignocellulosic fiber content and whether or not a coupling agent is used. SEM micrographs of fracture surfaces show that the addition of coupling agents enhances their dispersion in the continuous HDPE phase. They also show that the silane coupling agent facilitates the direct contact between the lignocellulosic fibers and HDPE matrix more than untreated and epolene treated composites do. The tensile strength depends on both the lignocellulosic fiber content and the type of coupling agent used. The other mechanical properties (elasticity modulus, elongation at break and toughness) mainly depend on the lignocellulosic fiber content and, to a lesser extent, on the presence of a coupling agent. Silane-treated composites show the best mechanical performance as a consequence of significant interactions at the interface between the HDPE matrix and the lignocellulosic fibers.The differences observed between the various composites studied are explained by means of different adhesion mechanisms. Interdiffusion takes place in untreated composites; multiple mechanism of adsorption-wettability, interdiffusion and, to a lesser extent, chemical bonds take place in epolene treated composites, and finally, the adhesion in composites modified with silane is mainly a chemical mechanism of covalent bonds

Properties and optimal manufacturing conditions of chicken feathers thermoplastics biocomposites

The aim of this study was the analysis and characterization of composites based on thermoplastics (ethylene vinyl acetate, polypropilene and high-density polyethylene) and chicken feathers. Several composite samples with a content of 20% v/v of chicken feathers have been studied to determine the optimal manufacturing conditions of temperature, mixing time, and mixing speed to achieve the best tensile properties. The results have shown that the addition of micronized chicken feather (20% v/v) to thermoplastic matrices increases stiffness and provides a more brittle behavior. Ethylene vinyl acetate matrix also shows an ability to participate in second-order intermolecular interactions with chicken feathers, providing better tensile properties (tensile strength and toughness) than polypropilene and high-density polyethylene. Optimal manufacturing conditions were found for a mixing time of around 5min; a mixing speed of 50rmin 1 ; and temperature values of 160 C in case of high-density polyethylene, 120 C for ethylene vinyl acetate, and 170 C for polypropilene. Fourier transform infrared spectroscopy, differential scanning calorimetry and scanning electron microscopy analysis have been performed in order to provide further understanding of the compatibility and microstructural features that support the tensile properties of the materialsPostprint (author’s final draft

Processing and structure-property relationships of natural rubber/wheat bran biocomposites

In this work, wheat bran was used as cellulosic filler in biocomposites based on natural rubber. The impact of wheat bran content [ranging from 10 to 50 parts per hundred rubber (phr)] on processing, structure, dynamic mechanical properties, thermal properties, physico-mechanical properties and morphology of resulting biocomposites was investigated. For better characterization of interfacial interactions between natural rubber and wheat bran, achieved results were compared with properties of biocomposites filled with commercially available cellulosic fillers—wood flour and microcellulose. It was observed that wheat bran, unlike commercial cellulosic fillers, contains high amount of proteins, which act like plasticizers having profitable impact on processing, physical, thermo-mechanical and morphological properties of biocomposites. This is due to better dispersion and distribution of wheat bran particles in natural rubber, which results in reduction of stiffness and porosity of the biocomposites. Regardless of cellulosic filler type, Wolff activity coefficient was positive for all studied biocomposites implying reinforcing effect of the applied fillers, while tensile strength and elongation at break decreased with increasing filler content. This phenomenon is related to restricted strain-induced crystallization of NR matrix due to limited mobility of polymer chains in the biocomposites. Furthermore, this explains negligible impact of particle size distribution, chemical composition and crystallinity degree of applied cellulosic filler on static mechanical properties of highly-filled NR biocomposites. The conducted investigations show that wheat bran presents interesting alternative for commercially available cellulosic fillers and could be successfully applied as a low-cost filler in polymer compositesPostprint (author's final draft

FTIR spectroscopic and thermogravimetric characterization of ground tyre rubber devulcanized by microwave treatment

In this work the phenomena involved with the microwave devulcanization of ground tyre rubber (GTR) were investigated. During studies three types of GTR characterized by different content of organic compounds (elastomers, plasticizers, etc..), carbon black and ash have been analyzed. The chemical structure of GTR before and after microwave devulcanization process was studied by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Furthermore, efficiency of microwave devulcanization conducted at different time was evaluated based on the crosslinking density and sol content values. FTIR spectroscopy results shown that devulcanization of GTR causes a decrease in carbon black with generation of CO2 due to its thermo oxidation, a decrease in structural groups of elastomeric components (mainly methylene and methine) and a breaking of C-S groups and S-S bridges. The presented results indicate the strong correlation between content of SiO2 in GTR and its degree of devulcanization. It was observed that GTR with a high content of SiO2 are easier devulcanized than samples with low content of SiO2, which suggest the presence of silica fillers improve microwave devulcanization efficiencyPostprint (author's final draft

Preparation and characterization of natural rubber composites highly filled with brewers' spent grain/ground tire rubber hybrid reinforcement

Brewers' spent grain (BSG) and ground tire rubber (GTR) were applied as low-cost hybrid reinforcement natural rubber (NR). The impact of BSG/GTR ratio (in range: 100/0, 75/25, 50/50, 25/75 and 0/100 phr) on processing and performance properties of highly filled natural rubber composites was evaluated by oscillating disc rheometer, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, swelling behavior, tensile tests and impedance tube measurements. It was found that increasing content of GTR in NR/BSG/GTR composites accelerate cross-linking reactions during their preparation, which resulted in decrease of scorch time and optimal cure time. Simultaneously, higher content of GTR filler in NR/BSG/GTR composites significantly improved their physico-mechanical, thermal, morphological and acoustical properties. This indicates better compatibility between natural rubber matrix and GTR than with BSG, which is related to correlation between two factors. First factor is obvious differences in particles size and polarity of GTR and BSG, which affected physical interactions into phase boundary between NR matrix and BSG/GTR hybrid reinforcement. Second factor is possible migration of unreacted curing additives and carbon black particles from GTR filler to NR matrix, which played a significant role on processing and final properties of NR/BSG/GTR compositesPostprint (author's final draft

Análisis de los diferentes tipos de desvulcanizado en la caracterización de nuevos materiales elastoméricos formados por la mezcla de estireno butadieno-caucho natural y mezclados con neumáticos fuera de uso (GTR)

This article proposes the creation of a new material useful for the industry from the mixture with rolls of two 50% virgin elastomers, styrene-butadiene (SBR) and natural rubber (NR) with tires out of use (GTR). These tires have been previously devulcanized following a number of techniques, which will be analyzed in this article, and then mixed with the virgin elastomer SBR/NR and the corresponding additives, revulcanized this new material in order to reach the mechanical properties, thermal and of structure that allow its use in the industry. Specifically, three types of samples have been analyzed; a first one formed by the virgin elastomer (SBR/NR), a second adding to the SBR/NR, GTR in the proportion of 20 phr (parts per hundred rubber), and a third adding to the SBR/NR, GTR in the proportion of 40 phr (more percentages were used in the mechanical tests in order to provide greater validity in the results). The GTR received has been devulcanized using different techniques: without devulcanitation (dn); mechanically devulcanized (dm); chemically and mechanically devulcanized (dcm); and microwave devulcanized (dmw). All these compounds have been tested with different tests; Mechanical, Crisscrossing Density, Gravimetric Thermal Analysis and Microscopy TestPeer ReviewedPostprint (published version

Induction motor with spiral sheet rotor

mprovements in torque at low currents using a rotor with spiral sheets are analyzed. Several rotors and stators have been built combining different constructive and mechanical characteristics of the related elements : inertias, constructive materials, geometrical shapes of the sheets and geometrical disposition of the sheets . These different types of motors have been simulated using computer aided tools and then tested in the laboratory. Finally, four stators (1000, 1500, 1500-type A, and 3000 rpm) with the same constructive parameters, have been simulated and tested with the following rotors types: solid rotor, solid rotor with diamagnetic rings, drag cup, and simple and double squirrel cage rotor; the results have been compared to those obtained with the seven variants of spiral sheet rotor presented in this paper.Peer ReviewedPostprint (published version

Towards circular economy by the valorization of different waste subproducts through their incorporation in composite materials: ground tire rubber and chicken feathers

Incorporation of residua into polymeric composites can be a successful approach to creating materials suitable for specific applications promoting a circular economy approach. Elastomeric (Ground Tire Rubber or GTR) and biogenic (chicken feathers or CFs) wastes were used to prepare polymeric composites in order to evaluate the tensile, acoustic and structural differences between both reinforcements. High-density polyethylene (HDPE), polypropylene (PP) and ethylene vinyl acetate (EVA) polymeric matrices were used. EVA matrix defines better compatibility with both reinforcement materials (GTR and CFs) than polyolefin matrices (HDPE and PP) as it has been corroborated by Fourier transform infrared spectroscopy (FTIR), termogravimetric analysis (TGA) and scanning electron microscopy (SEM). In addition, composites reinforced with GTR showed better acoustic properties than composites reinforced with CFs, due to the morphology of the reinforcing particlesPostprint (published version

Structural and physico-mechanical properties of natural rubber/GTR composites devulcanized by microwaves: influence of GTR source and irradiation time

Ground tire rubber from car and truck was modified using microwave irradiation at variable time. The irradiated ground tire rubber was used as filler in composites based on natural rubber. The composites, with high content of ground tire rubber, were prepared using an internal batch mixer and subsequently cross-linked at 160¿. The influence of the ground tire rubber source (car/truck) and irradiation time on structure, physico-mechanical behaviour, thermal properties and morphology of natural rubber/ground tire rubber composites was studied. The interfacial interactions between ground tire rubber and natural rubber as function of ground tire rubber source and irradiation time were evaluated by Fourier transform infrared spectroscopy, thermogravimetric analysis, tensile tests, swelling measurements and scanning electron microscopy. The results showed that irradiation of ground tire rubber slightly enhanced tensile properties and cross-link density of natural rubber/ground tire rubber composites. This effect was more evident in the case of ground tire rubbertruck because of its higher content of natural rubber and was reflected in changes in the interfacial adhesion, which were confirmed by the results of Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy analysisPostprint (author's final draft

Investigating the impact of curing system on structure-property relationship of natural rubber modified with brewery by-product and ground tire rubber

The application of wastes as a filler/reinforcement phase in polymers is a new strategy to modify the performance properties and reduce the price of biocomposites. The use of these fillers, coming from agricultural waste (cellulose/lignocellulose-based fillers) and waste rubbers, constitutes a method for the management of post-consumer waste. In this paper, highly-filled biocomposites based on natural rubber (NR) and ground tire rubber (GTR)/brewers’ spent grain (BSG) hybrid reinforcements, were prepared using two different curing systems: (i) sulfur-based and (ii) dicumyl peroxide (DCP). The influence of the amount of fillers (in 100/0, 50/50, and 0/100 ratios in parts per hundred of rubber) and type of curing system on the final properties of biocomposites was evaluated by the oscillating disc rheometer, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, swelling behavior, tensile testing, and impedance tube measurements. The results show, that the scorch time and the optimum curing time values of sulfur cured biocomposites are affected by the change of the hybrid filler ratio while using the DCP curing system, and the obtained values do not show significant variations. The results conclude that the biocomposites cured with sulfur have better physico-mechanical and acoustic absorption, and that the type of curing system does not influence their thermal stability. The overall analysis indicates that the difference in final properties of highly filled biocomposites cured with two different systems is mainly affected by the: (i) cross-linking efficiency, (ii) partial absorption and reactions between fillers and used additives, and (iii) affinity of additives to applied fillersPostprint (published version