Aprovechamiento de deshechos lignocelulósicos derivados de la producción industrial de aceite de palma en el desarrollo de materiales compuestos
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2024
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El trabajo doctoral se enfocó en la valorización de residuos de raquis de palma africana
(variedad INIAP-Tenera) provenientes de la industria ecuatoriana, en el desarrollo de
materiales compuestos de matrices poliméricas termoplásticas. En una primera etapa se
acondicionaron los residuos por medio de procesos de secado, molienda y tamizado. La
clasificación por tamaños provocó que las mayores proporciones de masa retenida se
encuentren en los tamices intermedios (mallas N° 20, 30 y 40) del sistema, por lo que se
decidió emplear las fibras retenidas en estas mallas para el posterior desarrollo de los
materiales compuestos. En virtud de que las fibras que fueron retenidas, así como aquellas
que atravesaron la separación libre del tamiz pudieron contener longitudes mayores o
menores a su correspondiente abertura, se procedió a evaluar la longitud de las fibras
contenidas en cada retenido. Con el objetivo de disponer de suficiente data para un estudio
estadístico riguroso, se planteó una metodología que permita obtener un volumen de datos
de longitud de fibra significativamente superior al sugerido en bibliografía. En este sentido,
se considera que la metodología desarrollada tiene amplio potencial para ser aplicada en la
medición de cualquier fibra natural. El comportamiento de los datos obtenidos para las
longitudes de fibra tamizada no estuvo descrito por los supuestos de normalidad estadística
como se reporta en bibliografía, sino que se ajustan satisfactoriamente a una distribución
exponencial para las fibras sin tamizar y distribución gamma para las retenidas en las mallas
N° 20, 30 y 40.
En una siguiente fase, se realizó la caracterización de las fibras provenientes de las fracciones
pedunculares del tallo y espiguillas. En virtud de que las diferencias entre todas las
características evaluadas del tallo en comparación con las de las espiguillas no fueron
significativas, se decidió trabajar con la fibra del tallo y de las espiguillas en conjunto para el
posterior desarrollo de la investigación experimental. Posteriormente, se elaboraron y
caracterizaron materiales compuestos a partir de las fibras acondicionadas en cuatro matrices
poliméricas (acrílica, vinil-acrílica, poliolefínica e híbrida). En términos generales se estudió la
influencia del tipo de matriz, parámetros de procesamiento y longitud de fibra (sin tamizar,
mallas N° 20, 30 y 40) en las propiedades de los materiales obtenidos, dentro del siguiente
contexto: (i) Composites a partir de resinas base acuosa acrílicas y vinil-acrílicas, por separado,
y a través del embebido de las fibras en los polímeros contenidos en las resinas. Durante el
procesamiento, se estudiaron cinco temperaturas de modelo por compresión. (ii) Composites
con matriz de polietileno de alta densidad reciclado, procesados por extrusión, a tres
contenidos de fibra y con dos mecanismos de compatibilización. (iii) Composites de matriz
híbrida (acrílica–polietileno de alta densidad reciclado) por medio de un proceso de
transformación combinado entre los mecanismos propuestos en los ítems i y ii.
Para todos los casos, los composites obtenidos fueron caracterizados en términos de sus
propiedades mecánicas a tracción, espectrofotométricas, morfológicas y estabilidad térmica.
Los resultados de esta caracterización evidenciaron diferencias significativas en cuanto a su
Aprovechamiento de desechos lignocelulósicos derivados de la producción industrial de aceite de palma en el desarrollo de materiales
compuestos
4
comportamiento mecánico a tracción, así como también en la estabilidad térmica de cada
una de las formulaciones. Este comportamiento está asociado principalmente al tipo de
matriz empleada y en menor término al método de procesamiento. La distribución de
tamaños de fibra de las fracciones sin tamizar, malla 20, 30 y 40 influyeron fundamentalmente
en el comportamiento mecánico de los composites elaborados, con diferentes tendencias
para cada caso.
Posterior a la elaboración y caracterización de composites, las formulaciones que presentaron
balance positivo de propiedades fueron sometidas a ensayos de envejecimiento acelerado en
atmósfera salina permanente, atmósfera salina cíclica, radiación ultravioleta cíclica, y la
combinación de atmósfera salina cíclica y radiación ultravioleta cíclica. Los resultados de
envejecimiento acelerado demostraron que las condiciones de la atmósfera salina
permanente favorecieron el biodeterioro fúngico. Desde la perspectiva de las características
mecánicas, térmicas y espectrofotométricas, todos los composites presentaron tendencias de
comportamiento relativamente similares bajo la influencia de los ensayos de envejecimiento.
Respecto a la caracterización complementaria, se presentaron cambios importantes en la
capacidad de absorción de agua. Para este caso, los composites de matriz vinil-acrílica
exhibieron las tasas más elevadas de absorción e hinchamiento. Debido a la naturaleza de las
materias primas empleadas en la presente investigación, los composites presentaron tasas
bajas de conductividad eléctrica y térmica. Por otra parte, los materiales compuestos
obtenidos exhibieron potencial para ser empleados como elementos constructivos;
específicamente, los de matriz acrílica para placas y mobiliario en tanto que, los de matriz de
polietileno e híbrida para mobiliario y perfiles.
Como un aporte complementario a la investigación realizada, se exploró el uso de materiales
biodegradables como el polivinil acetato, almidón de oca (Oxalis tuberosa) y harina de
amaranto (Amaranthus hypochondriacus) para ser empleados como matrices poliméricas; sin
embargo, la naturaleza higroscópica de los composites obtenidos limita su aplicación como
elementos constructivos.
The doctoral thesis was focused on the valorization of oil palm empty fruit bunch wastes (INIAP-Tenera variety), from Ecuadorian industry, on the thermoplastic-matrix composites development. First of all, wastes were conditioned in terms of drying, milling and sieving. Sieve analysis determined that greatest weight was retained among mesh N° 20, 30 and 40; therefore, fibers retained in those meshes were selected to later composite fabrication. Since retained fibers, as well as those passing through the nominal size of aperture, could include lengths greater or less than their corresponding aperture, length fibers of each retained fiber mesh were evaluated. In order to perform rigorous statistical study, it was proposed a methodology for obtaining significantly higher fiber length data than those suggested in literature. It is considered that the method has wide potential to be applied on measurement of any natural fiber. In addition, data coming from fiber lengths did not follow a normal distribution as reported in bibliography; but rather, they satisfactorily adjusted to exponential distribution in case of unsieved fibers, and gamma distribution for fibers retained in mesh N° 20, 30 and 40. Afterwards, peduncles (stalk and spikelet) of oil palm empty fruit bunch were separately characterized. On the whole, no differences between stalk and spikelet were identified; hence, it was not necessary to separate those fractions to overcome the following experimental stages. Subsequently, composites were elaborated based on conditioned fibers and four matrices (acrylic, vinyl-acrylic, polyolefin and hybrid). In broad terms, the influence of matrix, processing parameters and length fiber (unsieved, mesh N° 20, 30 and 40) over materials properties, was studied. As such, it was prepared (i) waterborne acrylic and vinyl acrylic based composites by means of fibers imbibition in resins. (ii) recycled high density polyethylene composites processed by extrusion with three reinforcement content and two compatibilization mechanisms. (iii) hybrid composites (acrylic–recycled high density polyethylene) by a combination between processes i and ii. All composites were evaluated in terms of tensile, spectrophotometric, morphologic and thermal properties. Characterization results showed differences in mechanical behavior as well as thermal stability of each formulation, which are associated to the matrix rather than processing method. Length distribution of fibers unsieved, mesh 20, 30 and 40 affected tensile characteristics of composites with different patterns in each case. After elaboration and characterization of composites, formulations exhibiting positive balance of properties were subjected to accelerated aging test i.e. permanent salt fog testing, cyclic salt fog testing, cyclic ultraviolet testing and the combination cyclic salt fog-cyclic ultraviolet testing. It should be noted that saline conditions favored fungal degradation. From the perspective of mechanical, thermal and spectrophotometric characteristics, all composites exhibited similar tendency under accelerated aging tests. Regarding complementary characterization, it was observed significative changes in water absorption tests. It is worth noting that vinyl-acrylic composites showed the highest absorption and swelling. Due to origin and nature of raw materials, the composites presented low electrical and thermal conductivity rates. On the other hand, the materials obtained Aprovechamiento de desechos lignocelulósicos derivados de la producción industrial de aceite de palma en el desarrollo de materiales compuestos showed potential to be used as construction elements; specifically, those of acrylic matrix for panels, while those of polyethylene and hybrid matrix for furniture and profiles. As a complementary contribution to the research, biodegradable materials such as polyvinyl acetate, oca starch (Oxalis tuberosa) and amaranth flour (Amaranthus hypochondriacus) were incorporated as polymeric matrices; however, the hygroscopic nature limited their application as construction elements.
The doctoral thesis was focused on the valorization of oil palm empty fruit bunch wastes (INIAP-Tenera variety), from Ecuadorian industry, on the thermoplastic-matrix composites development. First of all, wastes were conditioned in terms of drying, milling and sieving. Sieve analysis determined that greatest weight was retained among mesh N° 20, 30 and 40; therefore, fibers retained in those meshes were selected to later composite fabrication. Since retained fibers, as well as those passing through the nominal size of aperture, could include lengths greater or less than their corresponding aperture, length fibers of each retained fiber mesh were evaluated. In order to perform rigorous statistical study, it was proposed a methodology for obtaining significantly higher fiber length data than those suggested in literature. It is considered that the method has wide potential to be applied on measurement of any natural fiber. In addition, data coming from fiber lengths did not follow a normal distribution as reported in bibliography; but rather, they satisfactorily adjusted to exponential distribution in case of unsieved fibers, and gamma distribution for fibers retained in mesh N° 20, 30 and 40. Afterwards, peduncles (stalk and spikelet) of oil palm empty fruit bunch were separately characterized. On the whole, no differences between stalk and spikelet were identified; hence, it was not necessary to separate those fractions to overcome the following experimental stages. Subsequently, composites were elaborated based on conditioned fibers and four matrices (acrylic, vinyl-acrylic, polyolefin and hybrid). In broad terms, the influence of matrix, processing parameters and length fiber (unsieved, mesh N° 20, 30 and 40) over materials properties, was studied. As such, it was prepared (i) waterborne acrylic and vinyl acrylic based composites by means of fibers imbibition in resins. (ii) recycled high density polyethylene composites processed by extrusion with three reinforcement content and two compatibilization mechanisms. (iii) hybrid composites (acrylic–recycled high density polyethylene) by a combination between processes i and ii. All composites were evaluated in terms of tensile, spectrophotometric, morphologic and thermal properties. Characterization results showed differences in mechanical behavior as well as thermal stability of each formulation, which are associated to the matrix rather than processing method. Length distribution of fibers unsieved, mesh 20, 30 and 40 affected tensile characteristics of composites with different patterns in each case. After elaboration and characterization of composites, formulations exhibiting positive balance of properties were subjected to accelerated aging test i.e. permanent salt fog testing, cyclic salt fog testing, cyclic ultraviolet testing and the combination cyclic salt fog-cyclic ultraviolet testing. It should be noted that saline conditions favored fungal degradation. From the perspective of mechanical, thermal and spectrophotometric characteristics, all composites exhibited similar tendency under accelerated aging tests. Regarding complementary characterization, it was observed significative changes in water absorption tests. It is worth noting that vinyl-acrylic composites showed the highest absorption and swelling. Due to origin and nature of raw materials, the composites presented low electrical and thermal conductivity rates. On the other hand, the materials obtained Aprovechamiento de desechos lignocelulósicos derivados de la producción industrial de aceite de palma en el desarrollo de materiales compuestos showed potential to be used as construction elements; specifically, those of acrylic matrix for panels, while those of polyethylene and hybrid matrix for furniture and profiles. As a complementary contribution to the research, biodegradable materials such as polyvinyl acetate, oca starch (Oxalis tuberosa) and amaranth flour (Amaranthus hypochondriacus) were incorporated as polymeric matrices; however, the hygroscopic nature limited their application as construction elements.
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Composites, Polímeros acrìlicos/vinil acrílicos, Polietileno reciclado, Raquis de palma africana, Elementos constructivos
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