BiosourcedJanusMolecules as Silica Coupling Agents in Elastomer Composites for Tires with Lower Environmental Impact

Abstract

A biosourced Janus molecule was used as a coupling agent between silica and unsaturated polymer chains in an elastomeric composite suitable for tire compounds with low energy dissipation, with potential important reduction of the environmental impact of the tire. 2-(2,5-Dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (serinol pyrrole, SP) was synthesized through the neat reaction of serinol and 2,5-hexanedione, with a high atom efficiency (ca. 85%). Adducts of SP with silica were prepared (SP ≈ 9% by mass), with very high yield. In the whole process, from reagents to adducts, only substances from natural sources could be used, and the only co-product was water and the carbon efficiency was close to 100%. The silica/SP adduct was used in an elastomeric composite based on diene elastomers such as poly(styrene-cobutadiene) and poly(1,4-cis-isoprene) from Hevea brasiliensis. Comparison was made with a composite containing silica and a traditional coupling agent, a sulfur-based silane, bis(triethoxysilylpropyl)tetrasulfide (TESPT). SP appears to behave as a coupling agent for silica. To have similar properties for the SP and TESPT-based composites, tuning of the formulation of the composite with silica/SP has to be performed. Model reactions revealed the condensation of the OH of SP with the SiOR groups of an alkoxysilane, the reaction of the pyrrole ring with sulfur and a thiyl radical and the reaction of the sulfurated pyrrole ring with the unsaturation of squalene. SP appears thus able to establish covalent bonds with both silica and the unsaturated elastomer. With SP, the release of ethanol, which occurs from the silanization of silica with TESPT and is usually burned in industrial plants to give CO 2 , is avoided. This work paves the way for the development at the industrial scale of elastomeric composites which allow remarkable reduction of the carbon footprint of the tire technology.

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

“…In previous works by some of the authors, pyrrole compounds were prepared by using oil-derived HD. The yields were worse in the case of 1-hexyl-2,5-dimethyl- 1H -pyrrole (73%) [ 40 ] and 1,2,5-Trimethylpyrrole (86.9%) [ 42 ] and better in the case of 2-(2,5-dimethyl-1 H -pyrrol-1-yl)propane-1,3-diol (96%) [ 40 ] (the water in the serinol sample used in the present work affected the yield). Hence, the process here reported at least does not make the reaction yield worse.…”

“…With the aim of scaling up the process, some of the authors developed the neat Paal–Knorr reaction by simply mixing and heating primary amines and HD in the absence of solvent(s) and catalysts, achieving high atom efficiency [ 39 , 40 , 41 ]. The PyCs were used for the neat functionalization of sp 2 carbon allotropes [ 41 , 42 ] and inorganic oxy-hydroxides such as silica [ 43 ].…”

“…The most studied PyC, with hydroxy functional groups in the substituent of the nitrogen atom, was 2-(2,5-dimethyl-1 H -pyrrol-1-yl)-1,3-propanediol (serinol pyrrole, SP), whose chemical structure is reported below in the text [ 39 , 41 ]. The hydroxy groups promote the condensation reaction of SP with silica with excellent/quantitative yield without the need for solvents or catalysts [ 42 ]. The most investigated PyCs with sulfur-based functional groups were 2-(2,5-dimethyl-1 H -pyrrol-1-yl)ethane-1-thiol (SHP) and 1,2-bis(2-(2,5-dimethyl-1 H -pyrrol-1-yl)ethyl)disulfide (SSP).…”

“…A further objective of this work was to use a pyrrole compound prepared through the one-pot two-step process in an elastomeric composite characterized by low dissipation of energy and also suitable for large-scale tire application. As mentioned above, SP was used as a coupling agent for silica in composites suitable for tire compounds [ 42 ]. It is well-known that silica is the filler of choice [ 52 , 53 , 54 , 55 ] for the preparation of low-dissipation-energy tires because silica elastomer composites are characterized by low hysteresis.…”

Hexagonal Boron Nitride as Filler for Silica-Based Elastomer Nanocomposites

“…Tire compounds must be designed in order to reduce their hysteresis and thus the rolling resistance. Nowadays, in tire compounds, precipitated silica [ 39 , 40 ] is the preferred filler for preparing materials with low hysteresis [ 39 , 40 , 41 ]. The silanol groups on its surface allow reactions to occur with sulfur-containing silanes, which act as coupling agents with the elastomer matrix through crosslinking reactions [ 42 ].…”