Reinforcing fillers are the primary component of rubber compounds which are added to improve the properties of elastomers. Carbon black and silica are the most commonly used reinforcing fillers in the tire industry due to their outstanding reinforcing effects. Despite the high reinforcing effects, the production of carbon black from non-renewable fossil fuels and high densities of these two fillers make the density of final product relatively high and impart a negative effect on the fuel efficiency of automobiles. These challenges have triggered the increasing concerns for the development of low-density, eco-friendly, sustainable, and renewable materials. Lignocellulosic biomasses have been emerged as potential renewable resources due to their annual renewability and large biomass stock and can be fractionated into value-added products. The work presented in this thesis was started by setting up an integrated biorefinery process for the simultaneous recovery of lignin, hemicelluloses, silica, and cellulose nanocrystals (CNCs) from two lignocellulosic biomasses; Arundo donax and rice husk. The CNCs extracted from these lignocellulosic biomasses can be used as promising reinforcing filler due to their fascinating properties. The feasibility of using CNCs instead of or along with silica in the rubber compounds was studied by investigating the effect of CNCs incorporation on the final properties of the rubber compounds. The incorporation of CNCs in rubber compounds was carried out using three approaches. In the first approach, silica was partially replaced with CNCs in natural rubber compounds prepared through the dry-mixing process. An investigation of the dynamic and tensile mechanical properties of the prepared compounds demonstrated a decrease in the reinforcement of the rubber compounds with the increase of CNCs contents. The tendency of CNCs to form aggregates due to strong hydrogen bonding between hydroxyl groups of CNCs resulted in poor dispersion in the polymer matrix and the dry-mixing process was not strong enough to break down these aggregates, hence reduced mechanical properties were observed. In the second approach, to enhance the filler dispersion and interfacial interaction between CNCs and polymer, the surface of CNCs was functionalized with six different silane coupling agents and the rubber compounds were prepared through the co-precipitation method. The functionalization was carried out by two different strategies: pre-functionalization of CNCs in ethanol/water mixture before preparing the rubber compound and post-functionalization of CNCs by adding silane coupling agents during the compounding process in the internal mixer. The compounds filled with post-functionalized CNCs showed much higher reinforcement than the silica-filled compound. The mixing of CNCs suspension with natural rubber latex improved the dispersion of CNCs particles in matrix and silane coupling agents enhanced the interfacial interaction between the CNCs and the polymer, resulting in the improved reinforcing effect of CNCs. In the third approach, the CNC/Silica hybrid was prepared using CNCs as a template and decorating the surface of CNCs with a layer of silica. The hybrid material produced by combining organic and inorganic phases at nanoscale provided unique properties acquired by the synergistic combination of organic and inorganic components with complementary properties. The microscopic and surface area analyses confirmed the rod-like morphology and the core-shell structure of the prepared hybrid. The incorporation of CNC/Silica hybrid in natural rubber significantly improved the mechanical properties of the resulting compounds. The CNC/Silica hybrid demonstrated much higher reinforcement than silica-filled compounds, however much lower density of the final compound. Thus, the prepared hybrid can be used as potential reinforcing filler to replace traditional silica filler in the tire compounds.

Le cariche rinforzanti sono i componenti principali dei compositi elastomericie vengono aggiunti per migliorarne le proprietà meccaniche. Il nero di carbonio e la silice sono i filler rinforzanti più comunemente usati nell'industria degli pneumatici a causa dei loro effetti di rinforzo. Nonostante le ottime proprietà conferite, la produzione di nerofumo proviene da combustibili fossili non rinnovabili e l’alta densità della silice rende la densità del prodotto finale piuttosto elevata e influisce negativamente sull'efficienza energetica delle automobili. Questi problemi hanno provocato una crescente richiesta per lo sviluppo di materiali a bassa densità, eco-compatibili, sostenibili e rinnovabili. Le biomasse lignocellulosiche sono emerse come potenziali risorse rinnovabili a causa della loro elevata disponibilità annuale e possono essere frazionate in prodotti a valore aggiunto. Il lavoro presentato in questa tesi è iniziato con il set up di un processo integrato di biorefinery per il recupero simultaneo di lignina, emicellulosa, silice e nanocristalli di cellulosa (CNC) da due biomasse lignocellulosiche: Arundo donax e lolla di riso. I CNC estratti da queste biomasse lignocellulosiche possono essere utilizzati come agente rinforzante grazie alle loro proprietà come la rinnovabilità, la biodegradabilità, la bassa densità, l'elevato aspect ratio e le elevate proprietà meccaniche. È stata studiata la possibilità di utilizzare i CNC in totale o parziale sostituzione della silice nelle mescole di gomma. L'incorporazione di CNC in mescole di gomma è stata effettuata utilizzando tre approcci. Nel primo approccio, la silice è stata parzialmente sostituita con i CNC in composti di gomma naturale preparati mediante miscelazione a secco. Lo studio delle proprietà meccanico/dinamiche e di trazione dei composti preparati ha dimostrato una diminuzione del rinforzo all'aumento del contenuto di CNC. La tendenza dei CNC a formare aggregati a causa dei forti legamia idrogeno tra i gruppi ossidrili dei CNC ha portato a una scarsa dispersione nella matrice polimerica e il processo di miscelazione a secco non era in grado di rompere questi aggregati. Nel secondo approccio, per migliorare la dispersione del filler e l'interazione interfacciale tra CNC e polimero, la superficie dei CNC è stata funzionalizzata con sei diversi agenti di accoppiamento a base di silano ed i compositi sono stati preparati mediante il metodo di co-precipitazione. La funzionalizzazione è stata effettuata con due diverse strategie: la pre-funzionalizzazione dei CNC in miscela di etanolo/acqua prima di preparare il composito; e la post-funzionalizzazione dei CNC aggiungendo gli agenti di accoppiamento durante il processo di miscelazione nel miscelatore interno. I compositi con CNC post-funzionalizzati hanno mostrato un rinforzo molto più alto rispetto al composito di silice. La co-precipitazione di CNC con lattice di gomma naturale ha migliorato la dispersione delle particelle di CNC migliorando la reattività coi silani e quindi l'interazione interfacciale tra CNC e polimero, con conseguente miglioramento dell'effetto di rinforzo. Nel terzo approccio, un ibrido CNC/Silice è stato preparato utilizzando i CNC come templante e decorando la superficie dei CNC con uno strato di silice. Il materiale ibrido prodotto combinando fasi organiche e inorganiche su scala nanometrica fornisce proprietà uniche acquisite dalla combinazione sinergica deidue componenti. Le analisi microscopiche e di superficie hanno confermato la morfologia a bastoncello e la struttura nucleo-guscio dell'ibrido preparato. L'incorporazione di ibridi CNC/Silice in gomma naturale ha migliorato significativamente le proprietà meccaniche dei composti risultanti. L'ibrido CNC/Silice ha dimostrato un rinforzo molto più elevato rispetto ai composti di carica di silice ma una densità molto inferiore del composto finale.

(2018). BIOFILLERS FROM RENEWABLE LIGNOCELLULOSIC FEEDSTOCK FOR ELASTOMERS. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2018).

BIOFILLERS FROM RENEWABLE LIGNOCELLULOSIC FEEDSTOCK FOR ELASTOMERS

ALI, SYED DANISH
2018

Abstract

Reinforcing fillers are the primary component of rubber compounds which are added to improve the properties of elastomers. Carbon black and silica are the most commonly used reinforcing fillers in the tire industry due to their outstanding reinforcing effects. Despite the high reinforcing effects, the production of carbon black from non-renewable fossil fuels and high densities of these two fillers make the density of final product relatively high and impart a negative effect on the fuel efficiency of automobiles. These challenges have triggered the increasing concerns for the development of low-density, eco-friendly, sustainable, and renewable materials. Lignocellulosic biomasses have been emerged as potential renewable resources due to their annual renewability and large biomass stock and can be fractionated into value-added products. The work presented in this thesis was started by setting up an integrated biorefinery process for the simultaneous recovery of lignin, hemicelluloses, silica, and cellulose nanocrystals (CNCs) from two lignocellulosic biomasses; Arundo donax and rice husk. The CNCs extracted from these lignocellulosic biomasses can be used as promising reinforcing filler due to their fascinating properties. The feasibility of using CNCs instead of or along with silica in the rubber compounds was studied by investigating the effect of CNCs incorporation on the final properties of the rubber compounds. The incorporation of CNCs in rubber compounds was carried out using three approaches. In the first approach, silica was partially replaced with CNCs in natural rubber compounds prepared through the dry-mixing process. An investigation of the dynamic and tensile mechanical properties of the prepared compounds demonstrated a decrease in the reinforcement of the rubber compounds with the increase of CNCs contents. The tendency of CNCs to form aggregates due to strong hydrogen bonding between hydroxyl groups of CNCs resulted in poor dispersion in the polymer matrix and the dry-mixing process was not strong enough to break down these aggregates, hence reduced mechanical properties were observed. In the second approach, to enhance the filler dispersion and interfacial interaction between CNCs and polymer, the surface of CNCs was functionalized with six different silane coupling agents and the rubber compounds were prepared through the co-precipitation method. The functionalization was carried out by two different strategies: pre-functionalization of CNCs in ethanol/water mixture before preparing the rubber compound and post-functionalization of CNCs by adding silane coupling agents during the compounding process in the internal mixer. The compounds filled with post-functionalized CNCs showed much higher reinforcement than the silica-filled compound. The mixing of CNCs suspension with natural rubber latex improved the dispersion of CNCs particles in matrix and silane coupling agents enhanced the interfacial interaction between the CNCs and the polymer, resulting in the improved reinforcing effect of CNCs. In the third approach, the CNC/Silica hybrid was prepared using CNCs as a template and decorating the surface of CNCs with a layer of silica. The hybrid material produced by combining organic and inorganic phases at nanoscale provided unique properties acquired by the synergistic combination of organic and inorganic components with complementary properties. The microscopic and surface area analyses confirmed the rod-like morphology and the core-shell structure of the prepared hybrid. The incorporation of CNC/Silica hybrid in natural rubber significantly improved the mechanical properties of the resulting compounds. The CNC/Silica hybrid demonstrated much higher reinforcement than silica-filled compounds, however much lower density of the final compound. Thus, the prepared hybrid can be used as potential reinforcing filler to replace traditional silica filler in the tire compounds.
ORLANDI, MARCO EMILIO
CASTELLANI, LUCA
Biofillers,; Cellulose; Nanocrystals,; CNC/SilicaHybrid,; Elastomers
Biofillers,; Cellulose; Nanocrystals,; CNC/SilicaHybrid,; Elastomers
CHIM/06 - CHIMICA ORGANICA
English
21-mar-2018
SCIENZA E NANOTECNOLOGIA DEI MATERIALI - 79R
30
2016/2017
open
(2018). BIOFILLERS FROM RENEWABLE LIGNOCELLULOSIC FEEDSTOCK FOR ELASTOMERS. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2018).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/199113
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