Optimización de la hidrólisis ácida de taninos hidrolizables de pinus Radiata para su uso en resinas adhesivas biobasadas.
No Thumbnail Available
Date
2024
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Universidad de Concepción
Abstract
El interés por los adhesivos de base biológica ha aumentado debido al aumento de los precios de los productos petroquímicos, las regulaciones ambientales más estrictas y la conciencia ambiental. Las actuales resinas adhesivas a base de formaldehído presentan riesgos para la salud y el medio ambiente. Se han realizado investigaciones para sustituir los adhesivos actuales por adhesivos de origen biológico, mediante la búsqueda de materias primas adecuadas como lo son los taninos. Los taninos son macromoléculas polifenólicas naturales que pueden reemplazar a los fenoles en las resinas. La hidrólisis ácida puede mejorar la síntesis de adhesivos a base de tanino al acortar la cadena de tanino y exponer grupos funcionales. Por esta razón, el objetivo central de esta investigación fue optimizar la reacción de hidrólisis ácida de los taninos hidrolizables de pino Radiata para su uso en resinas adhesivas de base biológica mediante un diseño experimental. Considerando lo anterior, se realiza un barrido de diferentes condiciones de temperatura y concentración del ácido sulfúrico para una hidrólisis ácida de 2 horas de reacción según un diseño experimental factorial y un análisis estadístico posterior. También, se sintetizó una resina en base a ácido sebácico, etilenglicol y taninos hidrolizados de bajo peso molecular. Se utilizaron diversas técnicas de caracterización física, química y térmica para caracterizar y comparar los taninos hidrolizables e hidrolizados de Pinus radiata, las más relevantes son la espectroscopia Infrarroja Transformada de Fourier (FTIR) y la cromatografía de permeación en gel (GPC).
Los taninos hidrolizables tienen un porcentaje de humedad bajo (9%), tienen una estructura compacta y homogénea, presentan una gran cantidad de grupos hidroxilos, de anillos fenólicos aromáticos, de enlaces éster, se presentan más como galotaninos que como elagitaninos y son compuesto con un alto peso molecular. Mientras que los taninos hidrolizados presentan una estructura disgregada y heterogénea, una composición química similar al tanino hidrolizable relacionado con la presencia de anillos fenólicos, pero tienen una mayor cantidad de grupos hidroxilos, menor presencia de enlaces C-O-C éter/éster y mayor presencia de ácido gálico libre y son compuestos de bajo peso molecular. Se determinó la influencia de las variables de la hidrólisis ácida (temperatura y concentración del ácido sulfúrico) sobre la respuesta (área en reemplazo del peso molecular) mediante un análisis estadístico de varianza. La temperatura, la concentración del ácido sulfúrico y el cuadrado de la concentración del ácido sulfúrico, son las variables que tienen un efecto estadísticamente significativo en el valor del área a niveles lineales y cuadráticos. La interacción entre temperatura y concentración del ácido y el cuadrado de la temperatura si influyen en el área, pero en menor medida. Se planteó una ecuación polinómica de segundo orden del modelo ajustado para el área en función de la temperatura y la concentración del ácido sulfúrico, validada por un alto valor del estadístico R-Cuadrada. Los experimentos que tengan menor valor del área se asocian con condiciones de reacción de hidrólisis ácida suaves (baja temperatura y concentración del ácido), que no logran romper los enlaces para disminuir el peso molecular del tanino. Los valores de las variables que maximizan el área, dentro de la región experimental, son: temperatura de 115°C y concentración del ácido del 10% p/p. Aunque no se obtuvo el óptimo de la ecuación del modelo ajustado, sigue siendo un resultado útil, ya que se busca obtener taninos que no estén completamente hidrolizados en sus monómeros, sino que se busca obtener oligómeros que tienen un peso molecular menor que el tanino original. Por lo tanto, es razonable concluir que las condiciones de la hidrólisis ácida que logren obtener como resultado valores cercanos de área al máximo encontrado, deberían ser suficientes para lograr el objetivo que plantea esta investigación. Se logró sintetizar una resina poliéster biobasada que representa una alternativa respetuosa con el medio ambiente y con la salud de las personas en comparación con las resinas comerciales y se evaluaron sus propiedades fisicoquímicas. Se concluye que la resina comienza a fundirse a una temperatura de 100°C, que presenta el grupo carbonilo del enlace éster debido a la reacción de polimerización (esterificación), no tiene capacidad de absorción de agua, tiene valores de viscosidad similares a los utilizados comercialmente y un comportamiento newtoniano. Por lo tanto, presenta características fisicoquímicas favorables para su uso posterior en tableros de madera. Es recomendable que a futuro se estudie el proceso de síntesis de la resina con diferentes porcentajes de taninos hidrolizados, sus propiedades mecánicas y su uso en tableros de madera.
Interest in bio-based adhesives has increased due to rising petrochemical prices, stricter environmental regulations, and environmental awareness. Current formaldehyde-based adhesive resins present health and environmental risks. Researchers studied to replace current adhesives with bio-based adhesives by searching for suitable raw materials such as tannins. Tannins are natural polyphenolic macromolecules that can replace phenols in resins. Acid hydrolysis may improve the synthesis of tannin-based adhesives by shortening the tannin chain and exposing functional groups. For this reason, the central objective of this research is to optimize the acid hydrolysis reaction of hydrolysable tannins from Radiata pine for their use in bio-based adhesive resins through an experimental design. Considering the above, a sweep of different temperature and sulfuric acid concentration values for a 2-hour acid hydrolysis reaction was carried out according to a factorial experimental design and a subsequent statistical analysis. Also, a resin based on sebacic acid, ethylene glycol, and low molecular weight hydrolyzed tannins was synthesized. Fourier Transform Infrared Spectroscopy (FTIR) and gel permeation chromatography (GPC) were the most relevant physical, chemical, and thermal characterization techniques. The hydrolyzable tannins have a low moisture content (9%), a compact and homogeneous structure, many hydroxyl groups, aromatic phenolic rings, and ester bonds. They are more commonly found as gallotannins than ellagitannins and are compounds with a high molecular weight. On the other hand, the hydrolyzed tannins have a disaggregated and heterogeneous structure, a chemical composition similar to hydrolyzable tannins related to the presence of phenolic rings. However, they have a more significant number of hydroxyl groups, a lower presence of C-O-C ether/ester bonds, and a more significant presence of free gallic acid. They are compounds with a low molecular weight. The influence of the acid hydrolysis variables (temperature and sulfuric acid concentration) on the response (area replacing molecular weight) was determined using a statistical analysis of variance. Temperature, sulfuric acid concentration, and the square of the sulfuric acid concentration are the variables that statistically affect the area value at linear and quadratic levels. The interaction between temperature and acid concentration and the square of the temperature does influence the area but to a lesser extent. A second-order polynomial equation adjusted the area as a function of temperature and sulfuric acid concentration, validated by a high value of the R-squared statistic. The experiments with a lower area value are associated with mild acid hydrolysis reaction conditions (low temperature and acid concentration), which fail to break the bonds to reduce the molecular weight of the tannin. The variables that maximize the area within the experimental region are 115°C and an acid concentration of 10% w/w. Although the optimum of the adjusted model equation was not obtained, it is still a helpful result since the aim is to obtain tannins that are not entirely hydrolyzed into their monomers but rather to obtain oligomers that have a lower molecular weight than the original tannin. Therefore, it is reasonable to conclude that the conditions of acid hydrolysis that manage to obtain area values close to the maximum found should be sufficient to achieve the objective set by this research. A bio-based polyester resin was successfully synthesized, representing an environmentally friendly and health-conscious alternative to commercial resins, and its physicochemical properties were evaluated. It is concluded that the resin begins to melt at a temperature of 100°C, that it presents the carbonyl group of the ester bond due to the polymerization reaction (esterification), it has no water absorption capacity, has viscosity values similar to those used commercially and exhibits Newtonian behavior. Therefore, it presents favorable physicochemical characteristics for later use in wood panels. It is advisable to study the synthesis process of the resin with different percentages of hydrolyzed tannins, its mechanical properties, and its future use in wood panels.
Interest in bio-based adhesives has increased due to rising petrochemical prices, stricter environmental regulations, and environmental awareness. Current formaldehyde-based adhesive resins present health and environmental risks. Researchers studied to replace current adhesives with bio-based adhesives by searching for suitable raw materials such as tannins. Tannins are natural polyphenolic macromolecules that can replace phenols in resins. Acid hydrolysis may improve the synthesis of tannin-based adhesives by shortening the tannin chain and exposing functional groups. For this reason, the central objective of this research is to optimize the acid hydrolysis reaction of hydrolysable tannins from Radiata pine for their use in bio-based adhesive resins through an experimental design. Considering the above, a sweep of different temperature and sulfuric acid concentration values for a 2-hour acid hydrolysis reaction was carried out according to a factorial experimental design and a subsequent statistical analysis. Also, a resin based on sebacic acid, ethylene glycol, and low molecular weight hydrolyzed tannins was synthesized. Fourier Transform Infrared Spectroscopy (FTIR) and gel permeation chromatography (GPC) were the most relevant physical, chemical, and thermal characterization techniques. The hydrolyzable tannins have a low moisture content (9%), a compact and homogeneous structure, many hydroxyl groups, aromatic phenolic rings, and ester bonds. They are more commonly found as gallotannins than ellagitannins and are compounds with a high molecular weight. On the other hand, the hydrolyzed tannins have a disaggregated and heterogeneous structure, a chemical composition similar to hydrolyzable tannins related to the presence of phenolic rings. However, they have a more significant number of hydroxyl groups, a lower presence of C-O-C ether/ester bonds, and a more significant presence of free gallic acid. They are compounds with a low molecular weight. The influence of the acid hydrolysis variables (temperature and sulfuric acid concentration) on the response (area replacing molecular weight) was determined using a statistical analysis of variance. Temperature, sulfuric acid concentration, and the square of the sulfuric acid concentration are the variables that statistically affect the area value at linear and quadratic levels. The interaction between temperature and acid concentration and the square of the temperature does influence the area but to a lesser extent. A second-order polynomial equation adjusted the area as a function of temperature and sulfuric acid concentration, validated by a high value of the R-squared statistic. The experiments with a lower area value are associated with mild acid hydrolysis reaction conditions (low temperature and acid concentration), which fail to break the bonds to reduce the molecular weight of the tannin. The variables that maximize the area within the experimental region are 115°C and an acid concentration of 10% w/w. Although the optimum of the adjusted model equation was not obtained, it is still a helpful result since the aim is to obtain tannins that are not entirely hydrolyzed into their monomers but rather to obtain oligomers that have a lower molecular weight than the original tannin. Therefore, it is reasonable to conclude that the conditions of acid hydrolysis that manage to obtain area values close to the maximum found should be sufficient to achieve the objective set by this research. A bio-based polyester resin was successfully synthesized, representing an environmentally friendly and health-conscious alternative to commercial resins, and its physicochemical properties were evaluated. It is concluded that the resin begins to melt at a temperature of 100°C, that it presents the carbonyl group of the ester bond due to the polymerization reaction (esterification), it has no water absorption capacity, has viscosity values similar to those used commercially and exhibits Newtonian behavior. Therefore, it presents favorable physicochemical characteristics for later use in wood panels. It is advisable to study the synthesis process of the resin with different percentages of hydrolyzed tannins, its mechanical properties, and its future use in wood panels.
Description
Tesis presentada para optar al título de Ingeniero/a Civil Químico/a.
Keywords
Hidrólisis, Taninos, Pinus radiata