Utilização de triglicerídeos nas sínteses de monômeros e materiais poliméricos renováveis
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2022-08-19
Autores
Gaglieri, Caroline
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Universidade Estadual Paulista (Unesp)
Resumo
O elevado consumo de materiais poliméricos oriundos de origem fóssil, associado aos seus baixos valores de reciclagem (5%) e de vida útil (1 ano), vêm demandando pesquisas em uma nova classe de polímeros, os biopolímeros. No entanto, ainda há a necessidade de aprimoramento/entendimento das propriedades mecânicas e térmicas para a expansão de suas aplicações. A partir desta necessidade, o presente trabalho mostra a utilização do óleo de uva, um subproduto da indústria alimentícia (de suco e de vinho) como precursor na síntese de dois monômeros. O primeiro foi sintetizado via reação de epoxidação, para obter-se o óleo de uva epoxidado; enquanto o segundo monômero foi obtido por reação de maleinização, para obtenção do óleo de uva maleinizado. Ambas as sínteses foram executadas de forma eficiente e consideradas limpas, sendo que os parâmetros de conversão, rendimento e seletividade na reação de epoxidação foram maiores do que aqueles reportados pela literatura para a epoxidação de outros óleos vegetais. Ambos monômeros foram caracterizados por técnicas espectroscópicas e térmicas todas as propriedades foram comparadas e relacionadas com as modificações realizadas na estrutura do triglicerídeo. O óleo de uva apresentou estabilidade térmica superior à de outros óleos vegetais com quantidades similares ou menores de insaturações. Tal propriedade pôde ser associada à presença de tocoferol na amostra, o qual foi sugerido por Análise Térmica. Embora a incorporação dos grupos epóxidos e anidridos à estrutura triglicerídica proporcionaram a diminuição da estabilidade térmica de ambos os monômeros obtidos em relação ao precursor; ambos foram termicamente estáveis acima de 200 ºC. Os valores de densidade e viscosidade aumentaram após as reações de modificações. Após a caracterização, dos dois monômeros, realizou-se a polimerização entre os dois, produzindo-se polímeros completamente renováveis. Até o presente momento, não se encontrou na literatura nenhum trabalho demonstrando utilização de apenas monômeros derivados de óleos vegetais na síntese de polímeros, caracterizando-se como um material inédito. A temperatura e o tempo de polimerização foram determinados pelos resultados das técnicas Calorimetria Exploratória Diferencial e Espectroscopia de Absorção na Região do Infravermelho Médio, respectivamente. Embora a polimerização tenha ocorrido de forma eficiente a 170 ºC por 3 h, a utilização da molécula 1-metilimidazol como catalisador proporcionou maiores valores de conversões monoméricas em menores temperaturas. Este catalisador também foi mais seletivo que os outros catalisadores imidazólicos (imidazol e 2-metilimidazol) testados. Foi demonstrado que o aumento do 1-metilimidazol na polimerização proporcionou o favorecimento da reação de esterificação, diminuindo a extensão da reação de eterificação, considerada uma reação paralela neste sistema. Além disso, os polímeros obtidos na presença deste catalisador apresentaram valores superiores de densidade de intercruzamento (aproximadamente 10x maior). Consequentemente, estes polímeros apresentaram melhores propriedades térmicas e mecânicas em relação ao polímero obtido sem catalisador. A partir da combinação dos resultados das caracterizações dos polímeros renováveis, foram avaliadas possíveis aplicações. Dentre elas, como revestimento de superfícies, considerando que o polímero renovável apresentou propriedades hidrofóbicas interessantes e também evitou a oxidação de superfícies metálicas em testes qualitativos.
The elevated consumption of polymeric materials from non-renewable sources, associated with their low recycling (5%) and life cycle (1 year), have demanded the research for a new polymer class, the biopolymers. However, it is necessary the improvement/comprehension of their thermal and mechanical properties to expand their application. Thus, this work showed the utilization of grapeseed oil, a byproduct of the food industry (juice and wine) as raw material for two monomers. The first one, epoxidized grapeseed oil, was obtained by epoxidation reaction; while the other, maleinized grapeseed oil, was obtained by maleinization reaction. Both syntheses were considered more efficient and cleaner compared with those reported in the literature for other vegetable oils. In addition, the epoxidation reaction was performed using a heterogeneous catalyst and achieved higher values of conversion, yield, and selectivity than those in the literature. Both monomers were characterized by spectroscopic and thermal techniques. The results obtained for each monomer were compared and they were associated with each modification performed on triglyceride structure. Grapeseed oil presented higher thermal stability compared to other vegetable oils that have similar or lower unsaturation degree. This result can be associated with the presence of tocopherol in the sample, which was also identified by Thermal Analysis. Although the incorporation of epoxides and anhydrides provided the decrease of thermal stability compared to grapeseed oil, both monomers exhibited thermal stability higher than 200 ºC, which can be considered as a good result. In addition, the values of density and viscosity increased after the chemical modifications of triglyceride structure. After monomers characterization, they were mixed and heated to provide renewable polymers. Until the moment, any paper reporting the synthesis of a polymer using all monomers derivatives from vegetable oils was found in the literature. Thus, the materials obtained in the present work can be considered unprecedented materials. The synthetic parameters time and temperature were respectively determined by Differential Scanning Calorimetry and Middle-infrared Analysis. Although the polymerization occurred in a good way at 170 ºC for 3 h, using 1-methylimidazole as a catalyst provided higher monomers conversion in lower values of time and temperature. This catalyst was also more selective than imidazole and 2-methylimidazole, which were also tested as catalysts for the polymerization reaction. Moreover, increasing the 1-methylimidazole amount in polymerization, the esterification reaction was favored over the etherification reaction, which is considered a parallel reaction. The crosslink density of polymers obtained using the catalyst was near to 10x higher than that obtained from the polymer without a catalyst. As a result, they presented higher thermal and mechanical properties; however, the polymers obtained using catalyst did not present significant changes in these properties among them. Thereafter, possible applications for these renewable polymers were evaluated, such as using them as coating materials. This was based on the hydrophobic properties exhibited by the polymer, as well as the non-oxidation of a metallic surface that was covered with it.
The elevated consumption of polymeric materials from non-renewable sources, associated with their low recycling (5%) and life cycle (1 year), have demanded the research for a new polymer class, the biopolymers. However, it is necessary the improvement/comprehension of their thermal and mechanical properties to expand their application. Thus, this work showed the utilization of grapeseed oil, a byproduct of the food industry (juice and wine) as raw material for two monomers. The first one, epoxidized grapeseed oil, was obtained by epoxidation reaction; while the other, maleinized grapeseed oil, was obtained by maleinization reaction. Both syntheses were considered more efficient and cleaner compared with those reported in the literature for other vegetable oils. In addition, the epoxidation reaction was performed using a heterogeneous catalyst and achieved higher values of conversion, yield, and selectivity than those in the literature. Both monomers were characterized by spectroscopic and thermal techniques. The results obtained for each monomer were compared and they were associated with each modification performed on triglyceride structure. Grapeseed oil presented higher thermal stability compared to other vegetable oils that have similar or lower unsaturation degree. This result can be associated with the presence of tocopherol in the sample, which was also identified by Thermal Analysis. Although the incorporation of epoxides and anhydrides provided the decrease of thermal stability compared to grapeseed oil, both monomers exhibited thermal stability higher than 200 ºC, which can be considered as a good result. In addition, the values of density and viscosity increased after the chemical modifications of triglyceride structure. After monomers characterization, they were mixed and heated to provide renewable polymers. Until the moment, any paper reporting the synthesis of a polymer using all monomers derivatives from vegetable oils was found in the literature. Thus, the materials obtained in the present work can be considered unprecedented materials. The synthetic parameters time and temperature were respectively determined by Differential Scanning Calorimetry and Middle-infrared Analysis. Although the polymerization occurred in a good way at 170 ºC for 3 h, using 1-methylimidazole as a catalyst provided higher monomers conversion in lower values of time and temperature. This catalyst was also more selective than imidazole and 2-methylimidazole, which were also tested as catalysts for the polymerization reaction. Moreover, increasing the 1-methylimidazole amount in polymerization, the esterification reaction was favored over the etherification reaction, which is considered a parallel reaction. The crosslink density of polymers obtained using the catalyst was near to 10x higher than that obtained from the polymer without a catalyst. As a result, they presented higher thermal and mechanical properties; however, the polymers obtained using catalyst did not present significant changes in these properties among them. Thereafter, possible applications for these renewable polymers were evaluated, such as using them as coating materials. This was based on the hydrophobic properties exhibited by the polymer, as well as the non-oxidation of a metallic surface that was covered with it.
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Palavras-chave
Óleo de semente de uva, Óleos vegetais modificados, Polímeros renováveis, Catalisadores imidazólicos, Grapeseed oil, Modified vegetable oils, Renewable polymers, Catalysts Imidazole