Rubber materials are nowadays used for many applications, ranging from shoes, adhesives, and gloves. Since most rubber is used to produce tires, both sulfur vulcanization and reinforcing fillers such as silica nanoparticles (SiO2 NPs) are used to obtain highly performant tires. To enhance the rate of the curing process, activators (ZnO), accelerators (sulfenamides) and co-activators (fatty acids) are usually used. Zinc single site-based activator, previously developed and based on Zn (II) ions anchored on the SiO2 NPs through the formation of a metal complex, demonstrated to be more efficient than ZnO and to reduce the leaching phenomenon of Zn2+ ions, thus reducing the environmental impact. The aim of this research project was to achieve a complete knowledge of its catalytic activity, to tune and control the vulcanization efficiency and the mechanical behaviour of the final rubber nanocomposite (NC). To reach this objective the chemical nature of the zinc single site-based activator has been changed by following three strategies: ● change the ligand of the metal complex to study the activator’s vulcanization efficiency arising from the different coordination sphere of the metal centre; ● exploit a different localization of the metal centre on the filler surface or a different distribution of the activator in the polymer matrix to study the effect on the mechanical behaviour of the NC; ● change the metal of the complex, with the aim to reduce the zinc content in the rubber vulcanization process. In the first part of the research, the catalytic activity of the zinc single site-based activator has been investigated by changing the coordination sphere of the metal using different organic ligands. Depending on the stability of the metal complex formed, a different vulcanization efficiency was observed: a too high stability of the complex, like the one observed using sulphur ligands, hinders the participation of Zn2+ ions to the curing reaction. Instead, stable bonds but reactive towards the curing reactions, such as in the case of amino and carboxyl ligands, promote higher catalytic activity of the activator. Later on, the research focused on the study of the influence that the localization of the metal centre has on the mechanical behaviour of rubber NCs, underlying a strong relationship between the localization of Zn2+ ions and the density and distribution of crosslinks inside the polymer matrix. In order to study the influence on the NC mechanical behaviour, a different localization of the metal centre was achieved by using longer hydrocarbon chains-based ligands, and the different distribution of the activator in the polymer matrix was reached by assembling the activators NPs in supraparticles (SPs). Finally, the approach of localizing the metal centre on the filler surface was used to develop a new activator based on Fe (III) ions anchored on SiO2 NPs. Its vulcanization efficiency was tested, and promising results were obtained, since higher efficiency than ZnO was observed, making the iron single site-based activator a possible substitute of ZnO in the rubber production.

I materiali elastomerici vengono utilizzati in molti ambiti, come ad esempio nella produzione di pneumatici. La loro performance dipende dal processo di vulcanizzazione e dall'impiego di filler di rinforzo, come le nanoparticelle di silice. Per aumentare la velocità del processo di vulcanizzazione, vengono utilizzati acceleranti e attivatori. L'attivatore maggiormente impiegato, in virtù delle sue caratteristiche, è l'ossido di zinco, che tuttavia presenta anche degli svantaggi, come ad esempio il fatto di essere tossico ed inquinante. Lo scopo di questa tesi è sviluppare nuovi attivatori efficienti e più sicuri dell'ossido di zinco. Sono stati sviluppati nuovi materiali basati sulla presenza di un centro metallico ( ioni Zn(II))ancorato sulla superficie della particella di silice, mediante la formazione di un complesso metallo-legante, L'efficienza catalitica di questo materiale dipende dalla natura chimica del complesso metallico, che può essere variata seguendo tre strategie: 1) variare il legante del complesso; 2) variare la localizzazione del centro catalitico; 3) cambiare centro metallico. In questo studio sono stati testati vari leganti organici, aventi gruppi funzionali diversi che coordinano gli ioni Zn(II) ed è stato dimostrato che l'efficienza catalitica dell'attivatore dipende dalla stabilità del complesso che si forma. Complessi troppo stabili infatti, impediscono la partecipazione degli ioni Zn(II) alle reazioni di vulcanizzazione, mentre complessi stabili ma non troppo, aumentano l'efficienza di vulcanizzazione. Una localizzazione diversa del centro catalitico può essere ottenuta mediante l'impiego di leganti aventi catena idrocarburica più lunga, così da influenzare la distribuzione dei crosslinks nella matrice polimerica e quindi le proprietà meccaniche del nanocomposito. Infine, centri metallici di Fe(III) sono stati ancorati alla superficie della silice in sostituzione di ioni zinco, comportando la formazione di un attivatore di vulcanizzazione molto performante e più sicuro dell'ossido di zinco.

(2022). Single-site metal activator for enhancing curing efficiency and substituting zinc in rubber vulcanization process. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2022).

Single-site metal activator for enhancing curing efficiency and substituting zinc in rubber vulcanization process

MILANA, PAOLA
2022

Abstract

Rubber materials are nowadays used for many applications, ranging from shoes, adhesives, and gloves. Since most rubber is used to produce tires, both sulfur vulcanization and reinforcing fillers such as silica nanoparticles (SiO2 NPs) are used to obtain highly performant tires. To enhance the rate of the curing process, activators (ZnO), accelerators (sulfenamides) and co-activators (fatty acids) are usually used. Zinc single site-based activator, previously developed and based on Zn (II) ions anchored on the SiO2 NPs through the formation of a metal complex, demonstrated to be more efficient than ZnO and to reduce the leaching phenomenon of Zn2+ ions, thus reducing the environmental impact. The aim of this research project was to achieve a complete knowledge of its catalytic activity, to tune and control the vulcanization efficiency and the mechanical behaviour of the final rubber nanocomposite (NC). To reach this objective the chemical nature of the zinc single site-based activator has been changed by following three strategies: ● change the ligand of the metal complex to study the activator’s vulcanization efficiency arising from the different coordination sphere of the metal centre; ● exploit a different localization of the metal centre on the filler surface or a different distribution of the activator in the polymer matrix to study the effect on the mechanical behaviour of the NC; ● change the metal of the complex, with the aim to reduce the zinc content in the rubber vulcanization process. In the first part of the research, the catalytic activity of the zinc single site-based activator has been investigated by changing the coordination sphere of the metal using different organic ligands. Depending on the stability of the metal complex formed, a different vulcanization efficiency was observed: a too high stability of the complex, like the one observed using sulphur ligands, hinders the participation of Zn2+ ions to the curing reaction. Instead, stable bonds but reactive towards the curing reactions, such as in the case of amino and carboxyl ligands, promote higher catalytic activity of the activator. Later on, the research focused on the study of the influence that the localization of the metal centre has on the mechanical behaviour of rubber NCs, underlying a strong relationship between the localization of Zn2+ ions and the density and distribution of crosslinks inside the polymer matrix. In order to study the influence on the NC mechanical behaviour, a different localization of the metal centre was achieved by using longer hydrocarbon chains-based ligands, and the different distribution of the activator in the polymer matrix was reached by assembling the activators NPs in supraparticles (SPs). Finally, the approach of localizing the metal centre on the filler surface was used to develop a new activator based on Fe (III) ions anchored on SiO2 NPs. Its vulcanization efficiency was tested, and promising results were obtained, since higher efficiency than ZnO was observed, making the iron single site-based activator a possible substitute of ZnO in the rubber production.
SCOTTI, ROBERTO
elastomero; vulcanizzazione; ossido di zinco; attivatore; ferro
nanocomposite; silica; nanoparticle; efficiency; ferro
CHIM/05 - SCIENZA E TECNOLOGIA DEI MATERIALI POLIMERICI
English
30-mag-2022
SCIENZA E NANOTECNOLOGIA DEI MATERIALI
34
2020/2021
embargoed_20250530
(2022). Single-site metal activator for enhancing curing efficiency and substituting zinc in rubber vulcanization process. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2022).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/381164
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