Bio-Based Pyrrole Compounds Containing Sulfur Atoms as Coupling Agents of Carbon Black with Unsaturated Elastomers

Abstract

In this work, the hysteresis of elastomer composites suitable for tire compounds was reduced by using CB functionalized with pyrrole compounds containing sulfur-based functional groups reactive with the elastomer chains. CB was functionalized with bio-based pyrrole compounds: 2-(2,5-dimethyl-1H-pyrrol-1-yl)ethane-1-thiol (SHP) and 1,2-bis(2-(2,5-dimethyl-1H-pyr-rol-1-yl)ethyl)disulfide (SSP), bearing an -SH and an -SS- functional group, respectively. SHP and SSP were synthesized via a one-pot two-step synthesis, with yields higher than 70%, starting from biosourced chemicals as follows: 2,5-hexanedione from 2,5-dimethylfuran, cysteine and cysteamine. The functionalization of CB was carried out by mixing the CB with PyC and heating, with quantitative yields ranging from 92 to 97%. Thus, the whole functionalization process was characterized by a high carbon efficiency. The formation of the covalent bond between SHP, SSP and CB, in line with the prior art of such a functionalization technology, was proven by means of extraction and TGA analyses. The reactivity of the sulfur-based functional groups with unsaturated polymer chains was demonstrated by using squalene as the model compound. Poly(styrene-co-butadiene) from solution anionic polymerization and poly(1,4-cis-isoprene) from Hevea Brasiliensis were the elastomers employed for the preparation of the composites, which were crosslinked with a sulfur-based system. Pristine CB was partially replaced with CB/SHP (33%) and CB/SSP (33% and 66%). The PyC resulted in better curing efficiency, an increase in the dynamic rigidity of approximately 20% and a reduction in the hysteresis of approximately 10% at 70 °C, as well as similar/better ultimate tensile properties. The best results were achieved with a 66% replacement of CB with CB/SSP. This new family of reactive carbon blacks paves the way for a new generation of ‘green tires’, reinforced by a CB reactive with the polymer chains, which provides high mechanical properties and low rolling resistance. Such a reactive CB eliminates the use of silica, and thus the ethanol emission resulting from the condensation of silane is used as a coupling agent. In addition, CB-based tires are characterized by a higher mileage, at a moment in which the reduction in tire wear has become a primary concern.

Pyrrole Compounds from the Two-Step One-Pot Conversion of 2,5-Dimethylfuran for Elastomer Composites with Low Dissipation of Energy

“…The objective of this study was to replace silica with a functionalized carbon black, CB/SHP, in an elastomer matrix based on S-SBR, whose vinyl groups were reported to react with CB/SHP. The preparation and characterization of the CB/SHP adduct used in this work has been recently reported [ 46 ]. Silica was used as the reinforcing filler in the reference composite.…”

“…The -SH and -SS- functional groups were reported to react with the unsaturated elastomers [ 46 ]. The functionalization of silica and of sp 2 carbon allotropes, mainly carbon black, with the two mentioned families of PyCs improved the properties of elastomeric composites for a large-scale application such as that in tire compounds [ 46 , 47 ]. The development on an industrial scale was announced by a major player in the tire field [ 48 ].…”

“…The pyrrole compound selected for the functionalization of CB was SHP, obtained from cysteamine as the primary amine. The procedure used for the functionalization of CBN234 was already reported [ 46 ]. The aim was to reproduce the dynamic mechanical properties of the silica-based composite.…”

“…The ultrafast thiol-ene reaction based on cysteine has been reported [ 57 , 58 ] and the reaction of thiol groups with internal double bonds has been documented [ 59 ]. In a recent paper [ 46 ], some of the authors showed the ability of SHP to react with squalene, used as a model compound of the unsaturated elastomer. The increase in the dynamic rigidity of the elastomer composite, by using CB/SHP in place of CB [ 46 ], was attributed to the chemical bond between CB and the elastomer chains.…”

“…In a recent paper [ 46 ], some of the authors showed the ability of SHP to react with squalene, used as a model compound of the unsaturated elastomer. The increase in the dynamic rigidity of the elastomer composite, by using CB/SHP in place of CB [ 46 ], was attributed to the chemical bond between CB and the elastomer chains. In this work, for the first time, CB/SHP was used in place of silica with the aim to prepare an elastomer composite for low dissipation of energy.…”