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Modificação química sustentável da celulose em condições homogéneas
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Sendo a celulose uma matéria-prima biodegradável praticamente inesgotável, tem sido
alvo de diversos estudos, de modo a encontrar aplicações alternativas a matérias-primas
convencionais. A sua derivatização à escala industrial ocorre maioritariamente de modo
heterogéneo, o que dificulta o controlo da reação. Esta limitação pode ser suprimida
utilizando condições homogéneas. No entanto, a solubilização da celulose não é um processo
trivial, devido à sua estrutura supramolecular que impede a sua solubilização em
solventes convencionais.
Neste trabalho, foi estudada a solubilidade e síntese homogénea de um éter de celulose,
dicarboximetilcelulose (DCMC) com bromalonato de sódio (NaBMA), em diferentes
tipos de solventes: aquoso (NaOH/Ureia/H2O), e não aquosos (AMIMCl, formato
de trietilmetilamónio, [EMIM]Ac, DMAc/LiCl) e comparado com o DCMC sintetizado
heterogeneamente. Os polímeros sintetizados foram caracterizados por técnicas de espectroscopia
de infravermelho (FTIR) e emissão atómica (ICP-AES), e a sua estrutura
cristalina foi avaliada por difração de raio-X. Neste estudo, verificou-se que ocorreu uma
menor substituição dos DCMCs sintetizados homogeneamente, com DS entre 0.043-0.247,
em comparação com um polímero obtido em condições heterogéneas, com DS de 0.482.
Dos polímeros sintetizados homogeneamente, verificou-se uma maior substituição no
DCMC obtido no solvente aquoso. Observou-se ainda potencial na utilização de LIs como
solvente. Verificou-se, no entanto, indícios de interações entre o solvente e a celulose que
podem perturbar a funcionalização da celulose.
Foi também testada a síntese de um análogo de DCMC, em condições homogéneas,
com 2-metilenomalonato de dietilo, obtendo-se rendimentos muitos baixos, o que indica
que esta metodologia da síntese deverá ser repensada.
A tosilação da celulose em formato de trietilmetilamónio resultou no produto pretendido
com um DS de 1, sendo, no entanto, este inferior aos valores obtidos para a tosilação
homogénea numa solução concentrada de NaOH, e DMAc/LiCl, com de DS de 1.4 e 2
respetivamente, documentados na literatura.
As cellulose is a biodegradable raw material that is practically inexhaustible, it has been the target of several studies to find alternative applications to conventional raw materials. Its derivatization on an industrial scale occurs mostly heterogeneously, which makes it difficult to control the reaction. This limitation can be overcome by using homogeneous conditions. However, solubilization of cellulose is not a trivial process, due to its supramolecular structure that prevents its solubilization in conventional solvents. In this work, the solubility and homogeneous synthesis of a cellulose ether, dicarboxymethyl cellulose (DCMC) with sodium bromalonate (NaBMA), was studied in different types of solvents: aqueous (NaOH/Urea/H2O), and non-aqueous (AMIMCl, triethylmethylammonium formate, [EMIM]Ac, DMAc/LiCl) and compared with heterogeneously synthesized DCMC. The synthesized polymers were characterized by infrared (FTIR) and atomic emission (ICP-AES) spectroscopy techniques, and their crystal structure was evaluated by X-ray diffraction. In this study, it was found that less substitution occurred in the homogeneously synthesized DCMCs, with DS between 0.043-0.247, compared to a polymer obtained under heterogeneous conditions, with DS of 0.482. Of the homogeneously synthesized polymers, there was a higher substitution in the DCMC obtained in the aqueous solvent. Potential was also observed in the use of LIs as a solvent. There was, however, evidence of interactions between the solvent and the cellulose that may disrupt the functionalization of the cellulose. The synthesis of an analog of DCMC under homogeneous conditions with diethyl 2-methylenomalonate was also tested, obtaining very low yields, indicating that this synthesis methodology should be rethought. Cellulose tosylation in triethylmethylammonium formate resulted in the desired product with a DS of 1, which is, however, lower than the values obtained for homogeneous tosylation in a concentrated NaOH solution, and DMAc/LiCl, with DS of 1.4 and 2 respectively, documented in the literature.
As cellulose is a biodegradable raw material that is practically inexhaustible, it has been the target of several studies to find alternative applications to conventional raw materials. Its derivatization on an industrial scale occurs mostly heterogeneously, which makes it difficult to control the reaction. This limitation can be overcome by using homogeneous conditions. However, solubilization of cellulose is not a trivial process, due to its supramolecular structure that prevents its solubilization in conventional solvents. In this work, the solubility and homogeneous synthesis of a cellulose ether, dicarboxymethyl cellulose (DCMC) with sodium bromalonate (NaBMA), was studied in different types of solvents: aqueous (NaOH/Urea/H2O), and non-aqueous (AMIMCl, triethylmethylammonium formate, [EMIM]Ac, DMAc/LiCl) and compared with heterogeneously synthesized DCMC. The synthesized polymers were characterized by infrared (FTIR) and atomic emission (ICP-AES) spectroscopy techniques, and their crystal structure was evaluated by X-ray diffraction. In this study, it was found that less substitution occurred in the homogeneously synthesized DCMCs, with DS between 0.043-0.247, compared to a polymer obtained under heterogeneous conditions, with DS of 0.482. Of the homogeneously synthesized polymers, there was a higher substitution in the DCMC obtained in the aqueous solvent. Potential was also observed in the use of LIs as a solvent. There was, however, evidence of interactions between the solvent and the cellulose that may disrupt the functionalization of the cellulose. The synthesis of an analog of DCMC under homogeneous conditions with diethyl 2-methylenomalonate was also tested, obtaining very low yields, indicating that this synthesis methodology should be rethought. Cellulose tosylation in triethylmethylammonium formate resulted in the desired product with a DS of 1, which is, however, lower than the values obtained for homogeneous tosylation in a concentrated NaOH solution, and DMAc/LiCl, with DS of 1.4 and 2 respectively, documented in the literature.
Descrição
Palavras-chave
Dicarboximetil celulose (DCMC) dissolução de celulose líquidos iónicos