Sustainable materials for tyres. 3. Biobased secondary accelerators for silica based compounds

It is well known the sentence by Charles Goodyear: “There is probably no other inert substance the properties of which excite in the human mind an equal amount of curiosity, surprise and admiration”. He was referring to entropic elasticity. To have such a property, a rubber has to be crosslinked. Compounds for tyre application are crosslinked with sulphur base system. In particular, when silica is the reinforcing filler, the sulphur vulcanization package is composed by orthorhombic sulphur, at least a sulphenamide and a secondary accelerator, such as guanidines, thiurames, mercaptobenzothiazoles and others, in order to boost the reaction. In this work, innovative chemicals were developed as secondary accelerators for silica based rubber compounds, starting from 2-amino-1,3-propanediol (known as serinol), which was used as such or as the starting building block for the preparation of imines. Imines, also known as Schiff bases, are traditionally synthesized from the reaction of primary amines with aldehydes or ketones, in the presence of an acid catalyst. This work had the aim to develop synthetic strategy to perform reactions for the synthesis of imines, by adopting reaction conditions inspired to the basic principles of green chemistry, in the absence of any solvent and catalyst, with aldehydes and ketones such as: acetone, cinnamaldehyde and camphor. Serinol and serinol derivatives were thus used as secondary accelerators for the vulcanization of compounds based on silica and diene elastomers. Their behaviour was compared with that of diphenyl guanidine. Kinetics of crosslinking was studied, in the presence and in the absence of fillers. Dynamic-mechanical properties of the compound were determined. Extractability of vulcanizers from the compound was as well investigated.