Among the different polymeric materials, thermosets, characterized by a permanent network made of covalent bonds, have excellent mechanical performance and chemical and thermal resistance but, once formed, they cannot be reprocessed and recycled. On the other hand, thermoplastic materials, thanks to their non-permanent chemical crosslinking, are reprocessable and recyclable, but exhibit lower mechanical properties and resistance to high temperatures with respect to thermosets. A new class of polymeric materials, i.e., vitrimers, are emerging in the last years as a bridge between thermosetting and thermoplastics world. Vitrimeric polymers are characterized by a lattice which is able to reorganize itself through dynamic bond exchange reactions between covalent bonds when an external stimulus is applied. The associative dynamism of the bonds guarantees the vitrimeric materials their reprocessability, self-healing and shape memory, while maintaining the dimensional stability typical of thermosets. In this work, new bioderived vitrimeric systems are synthesized and characterized exploiting crosslinking reaction between cardanol-based epoxy resins and several bioderived curing agents. The permanent network is achieved through epoxide-carboxylic acid or epoxide-anhydride reactions, which are essential to introduce ester bonds able to undergo transesterification reactions at sufficiently high temperatures when a suitable catalyst is added. Specifically, the resins used are denoted as Cardolite NC547 and NC514S and are both derived from the cashew nut. Regarding curing agents, hexahydro-4-methylphthalic anhydride, a product derived from non-renewable fossil sources, is taken as a reference to have a method of comparison with the materials completely obtained from fully bio-based chemicals. Therefore, glutaric and succinic anhydride, DFDCA, pristine Soda lignin and succinated Soda lignin are used as the bio-derived crosslinking reagents for the cardanol-based epoxy vitrimers here presented. A preliminary characterization of the samples is carried through Differential Scanning Calorimetry (DSC), Fourier-Transform Infrared Spectroscopy (FTIR) and gel content evaluations in order to check if a crosslinked network is obtained. For the compositions which show a gel content equal or higher than 85%, Dynamic Mechanical Analysis (DMA) and stress relaxation tests are performed to completely characterize their behaviour.
Tra i diversi materiali polimerici, i termoindurenti, caratterizzati da legami covalenti permanenti, presentano eccellenti proprietà meccaniche e resistenza termica e chimica, ma non possono essere riprocessati o riciclati. Viceversa, i polimeri termoplastici, caratterizzati da un reticolo chimico non permanente, risultano essere riprocessabili e riciclabili ma presentano proprietà meccaniche e resistenza alle alte temperature nettamente inferiori rispetto ai termoindurenti. Per questo motivo, una nuova classe di materiali polimerici, i vitrimeri, è stata sviluppata negli ultimi anni come ponte tra il mondo dei termoplastici e dei termoindurenti. I materiali vitrimerici sono caratterizzati da un reticolo polimerico in grado di riorganizzarsi attraverso reazioni dinamiche di scambio tra legami covalenti attraverso l’applicazione di stimoli esterni. Il dinamismo dei legami garantisce la riprocessabilità, l’autoriparazione e la memoria di forma dei materiali vitrimerici preservando la stabilità dimensionale tipica dei termoindurenti. In questo lavoro nuovi sistemi vitrimerici completamente bioderivati sono stati sintetizzati e caratterizzati tramite la reticolazione di resine epossidiche a base di cardanolo con diversi agenti reticolanti. I sistemi ottenuti si basano su reazioni epossido-acido carbossilico o epossido-anidride, fondamentali per introdurre legami estere che posso venire successivamente sfruttati per reazioni di transesterificazione a temperature sufficientemente elevate tramite l’introduzione di un adeguato catalizzatore. Nello specifico, le resine epossidiche utilizzate, indicate con i simboli Cardolite NC547 e NC514S, sono entrambe derivate dal frutto dell’anacardo. Per quanto riguarda gli agenti reticolanti, l’anidride ftalica, provenendo da fonti fossili non rinnovabili, è considerata come riferimento per la comparazione con i materiali vitrimerici ottenuti da reagenti completamente bioderivati quali l’anidride glutarica e succinica, il DFDCA, la lignina Soda e la lignina Soda succinata. Inizialmente, è stata effettuata una caratterizzazione preliminare tramite misure di calorimetria differenziale a scansione (DSC), analisi spettroscopiche (FTIR) e misure di gel content per valutare se un’accettabile reticolazione del sistema è stata ottenuta. Per le composizioni aventi una percentuale di gel uguale o maggiore a 85%, sono state effettuate analisi dinamico meccaniche (DMA) e di rilassamento degli sforzi per caratterizzare in modo completo il loro comportamento vitrimerico.
Synthesis and characterization of cardanol-based epoxy vitrimers
RICCI, MARTINA
2020/2021
Abstract
Among the different polymeric materials, thermosets, characterized by a permanent network made of covalent bonds, have excellent mechanical performance and chemical and thermal resistance but, once formed, they cannot be reprocessed and recycled. On the other hand, thermoplastic materials, thanks to their non-permanent chemical crosslinking, are reprocessable and recyclable, but exhibit lower mechanical properties and resistance to high temperatures with respect to thermosets. A new class of polymeric materials, i.e., vitrimers, are emerging in the last years as a bridge between thermosetting and thermoplastics world. Vitrimeric polymers are characterized by a lattice which is able to reorganize itself through dynamic bond exchange reactions between covalent bonds when an external stimulus is applied. The associative dynamism of the bonds guarantees the vitrimeric materials their reprocessability, self-healing and shape memory, while maintaining the dimensional stability typical of thermosets. In this work, new bioderived vitrimeric systems are synthesized and characterized exploiting crosslinking reaction between cardanol-based epoxy resins and several bioderived curing agents. The permanent network is achieved through epoxide-carboxylic acid or epoxide-anhydride reactions, which are essential to introduce ester bonds able to undergo transesterification reactions at sufficiently high temperatures when a suitable catalyst is added. Specifically, the resins used are denoted as Cardolite NC547 and NC514S and are both derived from the cashew nut. Regarding curing agents, hexahydro-4-methylphthalic anhydride, a product derived from non-renewable fossil sources, is taken as a reference to have a method of comparison with the materials completely obtained from fully bio-based chemicals. Therefore, glutaric and succinic anhydride, DFDCA, pristine Soda lignin and succinated Soda lignin are used as the bio-derived crosslinking reagents for the cardanol-based epoxy vitrimers here presented. A preliminary characterization of the samples is carried through Differential Scanning Calorimetry (DSC), Fourier-Transform Infrared Spectroscopy (FTIR) and gel content evaluations in order to check if a crosslinked network is obtained. For the compositions which show a gel content equal or higher than 85%, Dynamic Mechanical Analysis (DMA) and stress relaxation tests are performed to completely characterize their behaviour.| File | Dimensione | Formato | |
|---|---|---|---|
|
2021_12_Ricci.pdf
accessibile in internet solo dagli utenti autorizzati
Descrizione: Tesi Magistrale
Dimensione
5.18 MB
Formato
Adobe PDF
|
5.18 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/183466