Publicação
Degradation of polyhydroxyalkanoates for the development of sustainable polyurethanes
| Resumo: | Polyhydroxyalkanoates (PHAs) are biodegradable, biocompatible polyesters produced by microorganisms and considered promising alternatives to petrochemical plastics. Within this family, poly(3-hydroxybutyfrate) (PHB) stands out for its high crystallinity and bio-origin, but its inherent brittleness and processing window limit advanced applications. This work explores a route to value added PHB-based polyurethanes by first generating hydroxyl terminated PHB oligomers via acid-catalyzed alcoholysis and then using these oligomers as soft segments in polyurethane synthesis. PHB was depolymerized with ethylene glycol (EG) in chloroform using p-toluenesulfonic acid (p-TsOH) (24–72h), and the evolution of molar mass was tracked by Size Exclusion Chromatography (SEC) with RI/RALS/LALS detection, which showed progressive peak shifts to higher elution volumes, indicating chain scission and formation of oligomers. Fourier Transform Infrared Spectroscopy (FTIR) of the oligomers confirmed preservation of ester carbonyls and the emergence of terminal O–H groups. Polyurethanes were then synthesized using either Hexamethylene Diisocyanate (HDI) (aliphatic) or Methylene Diphenyl Diisocyanate (MDI) (Aromatic) with triethylamine (TEA) as catalyst, from both ethylene glycol (EG) and PHB- oligomers polyols, with and without chloroform. FTIR of the polymers consistently showed diagnostic urethane bands (N–H, C=O, C–N/C–O–C); HDI-based systems exhibited no residual –NCO, whereas some MDI/PHB-oligomers formulations retained a weak –NCO band, indicating incomplete conversion. Size Exclusion Chromatography (SEC) confirmed the formation of high-molecular-weight fractions with minor low-MW by-products, the latter more evident for PHB-oligomer/MDI systems. Overall, the results demonstrate the feasibility of PHB-oligomers soft segments for polyurethane formation, clarify the impact of diisocyanate type (HDI vs MDI), polyol intensity (EG vs PHB-oligomers), and solvent, and suggests process adjustments (catalyst load, stoichiometry, drying) to minimize residual isocyanate and narrow dispersity. |
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| Autores principais: | Elajimi, Mahdi |
| Assunto: | Polyhydroxyalkanoates Poly(3-hydroxybutirate Alcoholysis Hydroxyl-terminated oligomers Polyurethane FTIR Size exclusion chromatography |
| Ano: | 2025 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Instituto Politécnico de Bragança |
| Idioma: | inglês |
| Origem: | Biblioteca Digital do IPB |
| Resumo: | Polyhydroxyalkanoates (PHAs) are biodegradable, biocompatible polyesters produced by microorganisms and considered promising alternatives to petrochemical plastics. Within this family, poly(3-hydroxybutyfrate) (PHB) stands out for its high crystallinity and bio-origin, but its inherent brittleness and processing window limit advanced applications. This work explores a route to value added PHB-based polyurethanes by first generating hydroxyl terminated PHB oligomers via acid-catalyzed alcoholysis and then using these oligomers as soft segments in polyurethane synthesis. PHB was depolymerized with ethylene glycol (EG) in chloroform using p-toluenesulfonic acid (p-TsOH) (24–72h), and the evolution of molar mass was tracked by Size Exclusion Chromatography (SEC) with RI/RALS/LALS detection, which showed progressive peak shifts to higher elution volumes, indicating chain scission and formation of oligomers. Fourier Transform Infrared Spectroscopy (FTIR) of the oligomers confirmed preservation of ester carbonyls and the emergence of terminal O–H groups. Polyurethanes were then synthesized using either Hexamethylene Diisocyanate (HDI) (aliphatic) or Methylene Diphenyl Diisocyanate (MDI) (Aromatic) with triethylamine (TEA) as catalyst, from both ethylene glycol (EG) and PHB- oligomers polyols, with and without chloroform. FTIR of the polymers consistently showed diagnostic urethane bands (N–H, C=O, C–N/C–O–C); HDI-based systems exhibited no residual –NCO, whereas some MDI/PHB-oligomers formulations retained a weak –NCO band, indicating incomplete conversion. Size Exclusion Chromatography (SEC) confirmed the formation of high-molecular-weight fractions with minor low-MW by-products, the latter more evident for PHB-oligomer/MDI systems. Overall, the results demonstrate the feasibility of PHB-oligomers soft segments for polyurethane formation, clarify the impact of diisocyanate type (HDI vs MDI), polyol intensity (EG vs PHB-oligomers), and solvent, and suggests process adjustments (catalyst load, stoichiometry, drying) to minimize residual isocyanate and narrow dispersity. |
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