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Síntese e caracterização de poliuretanos produzidos com monómeros resultantes da despolimerização de polihidroxialcanoatos (PHB)
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O elevado consumo de plásticos petroquímicos e a acumulação de resíduos impulsionam soluções alinhadas com a economia circular, nomeadamente através da utilização de biopolímeros, como o poli(3-hidroxibutirato) (PHB). Embora seja uma alternativa promissora aos plásticos convencionais, pelas suas propriedades comparáveis às do polipropileno, a sua baixa estabilidade térmica limita a reciclagem mecânica. Este trabalho focou-se na valorização química de monómeros e oligómeros de origem biológica obtidos por despolimerização do PHB, como polióis na síntese de novos poliuretanos sustentáveis. A metodologia iniciou-se com a determinação do índice de hidroxilo por titulação para estabelecer as proporções estequiométricas. Realizou-se uma triagem preliminar por polimerização em massa (bulk) de quatro monómeros com diisocianatos aromáticos (MDI) e alifáticos (HDI), selecionando-se os sistemas promissores por testes de solubilidade em dimetilformamida (DMF). Posteriormente, a síntese em solução foi otimizada em uma e duas etapas, e os materiais foram caracterizados quanto à sua estrutura química e massa molecular através de Espetroscopia de Infravermelho por Transformada de Fourier (FTIR-ATR) e Cromatografia de Permeação em Gel (GPC), respetivamente. Os resultados confirmaram a formação das ligações uretano e o forte impacto das condições reacionais e da estrutura dos monómeros no crescimento das cadeias. Na síntese de uma etapa, a comparação com o oligómero mostrou que o seu elevado volume e impedimento de tamanho limitam as massas moleculares finais com os monómeros obtidos por despolimerização do PHB, apenas o etilenoglicol, por ser pequeno e linear, conseguiu ultrapassar estas limitações. Verificou-se que o monómero 4HB-3HB originou poliuretanos com massas moleculares superiores, com uma massa molecular média em massa (𝑀𝑤) entre 8,7×103 e 1,5×104 g/mol, embora com uma distribuição mais heterogénea, enquanto o monómero 2HE-3HB originou um crescimento molecular mais moderado, 𝑀𝑤 entre 7,4×103 e 7,9×103 g/mol, mas com uma distribuição mais uniforme e controlada. Nas sínteses em duas etapas, a rota com DBTDL promoveu uma conversão inicial do oligómero altamente eficiente logo nas primeiras 24 horas. Como perspetiva futura, as amostras foram enviadas para análise por RMN de 1H na Hanze University of Applied Sciences, para validação estrutural.
The high consumption of petrochemical plastics and the accumulation of waste are driving solutions aligned with the circular economy, particularly through the use of biopolymers such as poly(3-hydroxybutyrate) (PHB). Although it is a promising alternative to conventional plastics, due to its properties comparable to those of polypropylene, its low thermal stability limits mechanical recycling. This work focused on the chemical valorisation of bio-based monomers and oligomers obtained through PHB depolymerisation, as polyols in the synthesis of new sustainable polyurethanes. The methodology began with the determination of the hydroxyl value by titration to establish stoichiometric ratios. A preliminary screening was carried out via bulk polymerisation of four monomers with aromatic (MDI) and aliphatic (HDI) diisocyanates, with promising systems being selected through solubility tests in dimethylformamide (DMF). Subsequently, solution synthesis was optimised in one and two steps, and the materials were characterised in terms of their chemical structure and molecular weight using Fourier Transform Infrared Spectroscopy (FTIR-ATR) and Gel Permeation Chromatography (GPC), respectively. The results confirmed the formation of urethane linkages and the strong impact of reaction conditions and monomer structure on chain growth. In the one-step synthesis, comparison with the oligomer showed that its high volume and steric hindrance limit the final molecular weights; among the monomers obtained from PHB depolymerisation, only ethylene glycol, due to its small size and linearity, was able to overcome these limitations. It was found that the 4HB-3HB monomer produced polyurethanes with higher molecular weights, with a weight-average molecular weight (𝑀𝑤) between 8.7×103 and 1.5×104 g/mol, although with a more heterogeneous distribution, while the 2HE-3HB monomer led to a more moderate molecular weight growth, 𝑀𝑤 between 7.4×103 and 7.9×103 g/mol, but with a more uniform and controlled distribution. In the two-step syntheses, the DBTDL route promoted a highly efficient initial conversion of the oligomer within the first 24 hours. As a future perspective, the samples were submitted for 1H-NMR analysis at Hanze University of Applied Sciences for structural validation.
The high consumption of petrochemical plastics and the accumulation of waste are driving solutions aligned with the circular economy, particularly through the use of biopolymers such as poly(3-hydroxybutyrate) (PHB). Although it is a promising alternative to conventional plastics, due to its properties comparable to those of polypropylene, its low thermal stability limits mechanical recycling. This work focused on the chemical valorisation of bio-based monomers and oligomers obtained through PHB depolymerisation, as polyols in the synthesis of new sustainable polyurethanes. The methodology began with the determination of the hydroxyl value by titration to establish stoichiometric ratios. A preliminary screening was carried out via bulk polymerisation of four monomers with aromatic (MDI) and aliphatic (HDI) diisocyanates, with promising systems being selected through solubility tests in dimethylformamide (DMF). Subsequently, solution synthesis was optimised in one and two steps, and the materials were characterised in terms of their chemical structure and molecular weight using Fourier Transform Infrared Spectroscopy (FTIR-ATR) and Gel Permeation Chromatography (GPC), respectively. The results confirmed the formation of urethane linkages and the strong impact of reaction conditions and monomer structure on chain growth. In the one-step synthesis, comparison with the oligomer showed that its high volume and steric hindrance limit the final molecular weights; among the monomers obtained from PHB depolymerisation, only ethylene glycol, due to its small size and linearity, was able to overcome these limitations. It was found that the 4HB-3HB monomer produced polyurethanes with higher molecular weights, with a weight-average molecular weight (𝑀𝑤) between 8.7×103 and 1.5×104 g/mol, although with a more heterogeneous distribution, while the 2HE-3HB monomer led to a more moderate molecular weight growth, 𝑀𝑤 between 7.4×103 and 7.9×103 g/mol, but with a more uniform and controlled distribution. In the two-step syntheses, the DBTDL route promoted a highly efficient initial conversion of the oligomer within the first 24 hours. As a future perspective, the samples were submitted for 1H-NMR analysis at Hanze University of Applied Sciences for structural validation.
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Economia circular Biopolímeros Poli(3-hidroxibutirato) (PHB) Valorização química Poliuretanos sustentáveis