Serinol and serinol derivatives are used in place of diphenyl guanidine as secondary accelerators for the vulcanization of compounds based on diene elastomers and silica as the filler. Kinetics of crosslinking are investigated and confirmed by performing vulcanization of an NR based compound in the absence of any filler. Serinol can be obtained glycerol transformed, by means of sustainable technologies into molecules suitable for the rubber world.
Serinol derivatives for the sustainable vulcanization of diene elastomers
V. Barbera, L. Rubino, S. Musto, G. Infortuna, V. Cipolletti, A. Citterio, M. Galimberti
RFP Rubber Fibres Plastics 02|2019
Natural sources are definitely relevant for rubbers. NR is the most important rubber, accounting for about 40 % of the total rubber consumption. In 2004, the first of two reports on the research needs for biobased products was published by the US Department of Energy (DOE). Though the report is known as the “Top 10” report, a group of 15 target structures that could be produced from biorefinery was identified. In the author’s research group, focus was on the C-3 chemical platform alternative to the oil based one. Glycerol was identified as the starting building block for such a platform. Glycerol belongs to the DOE list, is easily available and cheap as it is the main by-product of bio-diesel production: basically, it is an industrial waste. It is not toxic, it is biodegradable and gives rise to many reaction pathways which lead to a multitude of derivatives. Among them, 2-amino-1,3-propanediol, also known as serinol, reveals great potential. It is an odorless, non-toxic, biodegradable substance, which can be also obtained from natural feedstocks and allows to build further synthetic pathways for preparing innovative chemicals. Serinol has hydroxyl and amino functional groups, hence it belongs to the class of amino alcohols and is a chemoselective prochiral molecule. It is indeed worth underlining the improvement of chemoselectivity with respect to glycerol.
Serinol and serinol derivatives were used as secondary accelerators for the vulcanization of composites based on diene elastomers and silica as the filler. They were used in place of diphenyl guanidine, in the same molar amount. With most serinol based accelerators, MH value was very similar to the one obtained with DPG. Differences between the serinol derivatives were observed in the kinetics of crosslinking: serinol gave the lowest induction time and 2-((Z)-((1S,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)amino)propane-1,3-diol (SCam) the highest, at temperatures typical of vulcanization and processing, such as 170 °C and 127 °C, respectively. These findings were confirmed by performing vulcanization of an NR based compound in the absence of any filler: the largest activation energy for the induction of polymerization was calculated (with both IIP and Arrhenius methods) for the composites with SCam as the secondary accelerators.
These results can be explained with the protection of the primary amine by an imino bond: the larger vulcanization induction time is used for the hydrolysis of the iminobond. Aldehydes and ketones play thus essentially the role of amine protective groups. Serinol does not present problems for the impact on health and environment and remains absorbed on silica. Synthesis of serinol derivatives with carbonyl compounds were performed in the absence of solvents and catalysts, in the frame of a sustainable process. This work demonstrates that a molecule such as serinol which can be obtained from an easily available industrial product such as glycerol, can be transformed, by means of sustainable technologies, into molecules suitable for the rubber world, obtaining the target compound properties and replacing critical ingredients.
V. Barbera, L. Rubino, S. Musto, G. Infortuna, V. Cipolletti, A. Citterio, M. Galimberti, RFP Rubber Fibres Plastics, 02|2019, 92-102