The limitation in fossil resources, their negative impact on the environment, waste disposal problems and price volatility are some of the main reasons have recently driven industrial attention towards the production of plastics from renewable resources. This thesis project belongs to the research line of the Laboratory of Chemistry and Characterization of Innovative Polymers (ChIP Lab) of Politecnico di Milano. It was focused on the preparation and testing of fully bio-based unsaturated polyester resins to be applied in the field of composites. Its main aims were i) the synthesis of a suitable bio-based polyester, ii) the substitution of the commonly used styrene with a green and safer alternative reactive diluent for the resin preparation, with attention to the rheological characterization of the mixtures, and iii) the thermo-mechanical testing of the crosslinked materials and an example of glass fiber reinforced composite. The major problems to be faced were the poor commercial availability of bio-based monomers able to provide good thermal properties (in terms of glass transition temperature, Tg) to the synthetized polyester, together with the negative effect of styrene alternatives which further reduced the resin Tg. Nowadays, furandicarboxylic acid (FDCA) is identified as one of the few possible solution: FDCA containing polyester features an higher Tg, which can further increase the transition temperature of the resin to acceptable values, compensating the effect of low performing reactive diluents employed in its formulation. Firstly, unsaturated polyesters, based on different ratios of bio-based FDCA, itaconic acid (IA), 1,2-propandiol (1,2-PD) and 1,3-propandiol (1,3-PD), were synthetized and tested. The results of the synthesis sessions were evaluated in terms of residual acid value (AV), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). Data obtained confirmed the effect of FDCA in enhancing polymer Tg, especially when combined with 1,2-PD. In particular, values of Tg between 12 and 14 °C were registered, together with average number molecular weights between 1300 and 1500 g/mol. The polyesters were also characterized by means of FT-IR and NMR Spectroscopy. Secondly, the possibility to find a green and safer alternative to styrene was faced, moving attention towards monomers of proven reactivity via free radical polymerization. Three bio-based reactive diluents were tested: diethyl itaconate (DEI), dimethyl itaconate (DMI) and butanediol dimethacrylate (BDM). Their influence on prepared resin viscosity was investigated via rheological analyses, firstly performed keeping the sample polymer to solvent ratio constant (70/30), and then varying it. Finally, a comprehensive study of the crosslinking process was performed to determine the best combination of catalysts to be added and curing sequence to be applied. Thermal properties of the crosslinked samples were examined via DSC analyses, while the crosslinking efficiency was tested by gel content evaluation. In particular, values of Tg between 35 and 43 °C were registered, and a gel content between 86 and 98%gel was achieved. The most promising bio-based resin was tested in a possible final application by using it as a matrix for the preparation of glass fiber reinforced composites. Specimens were prepared with short chopped glass fibers (featuring a diameter of 15 µm and a length of 200 µm), and the so obtained samples were characterized via tensile tests and dynamic mechanical analyses (DMA). Tensile moduli in between 2.8 and 4.8 GPa were measured. Moreover, life cycle assessment (LCA) was conducted on the chosen unsaturated polyester resin: a comparison between the calculated category indicator results for the formulated resin and those of a reference fossil based resin were performed, confirming the lower environmental impact of the first one.
Nel corso degli ultimi anni, la limitata disponibilità delle risorse fossili, il loro impatto negativo sull’ambiente e i problemi relativi al loro smaltimento hanno spostato l interesse del settore industriale verso la produzione di plastiche provenienti da fonti rinnovabili. Questo progetto di tesi fa arte di una linea di ricerca già affrontata dal Laboratorio di chimica e caratterizzazione di polimeri innovativi (ChIP Lab) del Politecnico di Milano, ed è incentrato sulla sintetizzazione di un poliestere insaturo, completamente bio, utilizzato per la preparazione di resine termoindurenti da applicare nel campo dei materiali compositi. Esso si prefigge gli obbiettivi di i) indentificare un’adeguata formulazione del polimero, ii) di trovare una alternativa green all’uso dello stirene come diluente reattivo per la preparazione della resina con particolare attenzione alla sua caratterizzazione reologica. I principali problemi che sono stati affrontati durante questo percorso di tesi sono relativi alla mancanza di monomeri bio-based che inducano buone proprietà termiche al poliestere sintetizzato, e all’indesiderato effetto delle alternative allo stirene che tendono a deprimere ulteriormente il valore della temperatura di transizione vetrosa (Tg) della resina. Al momento l’acido furandicarbossilico (FDCA) rappresenta una delle poche soluzioni disponibili: polyester contenenti FDCA presentano una Tg più elevata, che può innalzare sufficientemente la temperatura di transizione della resina, compensando l’utilizzo di diluenti reattivi poco performanti. Nella prima parte del progetto, diversi poliesteri insaturi sono stati sintetizzati, variando il rapporto stechiometrico tra FDCA, l’acido itaconico (IA), 1,2-propandiolo (1,2-PD) e 1,3-propandiolo (1,3-PD), e testati. I polimeri ottenuti sono stati caratterizzati in termini di numero d’acido residuo (AV), calorimetria differenziata in scansione (DSC) e cromatografia a permeazione di gel (GPC). Dai dati ricavati è risultata evidente l’influenza dell’FDCA e dell’1,2-PD sull’innalzamento della temperatura di transizione vetrosa del polimero. In particolare, una Tg tra i 12 e i 14°C e un peso molecolare medio tra 1300 e 1500 g/mol sono stati raggiunti. L’attenzione del progetto di tesi si è poi spostata sulla necessità di trovare un’alternativa green e più sicura all’utilizzo dello stirene, prendendo in considerazione monomeri reattivi alla polimerizzazione radicalica. Tre diversi diluenti sono stati analizzati: il dietilitaconato (DEI), il dimetilitaconato (DMI) e il butandiolo dimetacrilato (BDM). La loro influenza sulla viscosità della resina insatura è stata studiata tramite analisi reologica . Uno studio dettagliato sul processo di reticolazione è stato poi condotto per individuare la migliore combinazione di catalizzatori e trattamento termico da impiegare. Le proprietà termiche dei campioni reticolati sono state esaminate attraverso analisi DSC, mentre l’efficacia della reticolazione valutata con il calcolo del percento gel. In particolare, valori di Tg tra 35 e 43°C sono stati misurati, insieme ad un valore di gel percento tra 86 e 98%gel. La resina più performante e potenzialmente bio-based, è stata utilizzata come matrice per la produzione di un composito a fibra corta. I provini sono stati preparati aggiungendo fibre corte di vetro aventi 15 µm di diametro e 200 µm di lunghezza, e sottoposti a test tensili e analisi di caratterizzazione meccanica dinamica(DMA). Moduli elastici tra 2.8 e 4.8 GPa sono stati misurati. Le formulazioni finali sono state oggetto di un life cycle assessment (LCA) e i risultati ottenuti confrontati con i valori di una resina fossile presa come riferimento: il confronto condotto ha confermato l’inferiore impatto ambientale delle resine bio sotto analisi.
Development and characterization of new unsaturated polyester from renewable resources
BOLIANDI, ALESSIA
2017/2018
Abstract
The limitation in fossil resources, their negative impact on the environment, waste disposal problems and price volatility are some of the main reasons have recently driven industrial attention towards the production of plastics from renewable resources. This thesis project belongs to the research line of the Laboratory of Chemistry and Characterization of Innovative Polymers (ChIP Lab) of Politecnico di Milano. It was focused on the preparation and testing of fully bio-based unsaturated polyester resins to be applied in the field of composites. Its main aims were i) the synthesis of a suitable bio-based polyester, ii) the substitution of the commonly used styrene with a green and safer alternative reactive diluent for the resin preparation, with attention to the rheological characterization of the mixtures, and iii) the thermo-mechanical testing of the crosslinked materials and an example of glass fiber reinforced composite. The major problems to be faced were the poor commercial availability of bio-based monomers able to provide good thermal properties (in terms of glass transition temperature, Tg) to the synthetized polyester, together with the negative effect of styrene alternatives which further reduced the resin Tg. Nowadays, furandicarboxylic acid (FDCA) is identified as one of the few possible solution: FDCA containing polyester features an higher Tg, which can further increase the transition temperature of the resin to acceptable values, compensating the effect of low performing reactive diluents employed in its formulation. Firstly, unsaturated polyesters, based on different ratios of bio-based FDCA, itaconic acid (IA), 1,2-propandiol (1,2-PD) and 1,3-propandiol (1,3-PD), were synthetized and tested. The results of the synthesis sessions were evaluated in terms of residual acid value (AV), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). Data obtained confirmed the effect of FDCA in enhancing polymer Tg, especially when combined with 1,2-PD. In particular, values of Tg between 12 and 14 °C were registered, together with average number molecular weights between 1300 and 1500 g/mol. The polyesters were also characterized by means of FT-IR and NMR Spectroscopy. Secondly, the possibility to find a green and safer alternative to styrene was faced, moving attention towards monomers of proven reactivity via free radical polymerization. Three bio-based reactive diluents were tested: diethyl itaconate (DEI), dimethyl itaconate (DMI) and butanediol dimethacrylate (BDM). Their influence on prepared resin viscosity was investigated via rheological analyses, firstly performed keeping the sample polymer to solvent ratio constant (70/30), and then varying it. Finally, a comprehensive study of the crosslinking process was performed to determine the best combination of catalysts to be added and curing sequence to be applied. Thermal properties of the crosslinked samples were examined via DSC analyses, while the crosslinking efficiency was tested by gel content evaluation. In particular, values of Tg between 35 and 43 °C were registered, and a gel content between 86 and 98%gel was achieved. The most promising bio-based resin was tested in a possible final application by using it as a matrix for the preparation of glass fiber reinforced composites. Specimens were prepared with short chopped glass fibers (featuring a diameter of 15 µm and a length of 200 µm), and the so obtained samples were characterized via tensile tests and dynamic mechanical analyses (DMA). Tensile moduli in between 2.8 and 4.8 GPa were measured. Moreover, life cycle assessment (LCA) was conducted on the chosen unsaturated polyester resin: a comparison between the calculated category indicator results for the formulated resin and those of a reference fossil based resin were performed, confirming the lower environmental impact of the first one.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/147335