Abstract
The solubility parameter of a series of methyl esters of fatty acids, the components of biodiesel, was calculated using the group incremental method proposed by Van Krevelen. The solubility parameter of biodiesel was compared with that of a series of rubbers like EPDM, butyl rubber, polyisoprene, polybutadiene, SBR (with different content of styrene), and nitrile rubber (with different content of acrylonitrile) showing that biodiesel is an effective solvent of all the above mentioned rubbers with the exclusion of nitrile rubber. Indeed, it was experimentally verified that polyisoprene, polybutadiene and SBR are easily soluble in biodiesel while polystyrene gives a cloudy solution. Considerations on the solubility parameter of the biodiesel and of a series of rubbers have led to the conclusion that biodiesel behaves essentially as an internal lubricant in a diene rubber matrix, the same situation occurs with the common aromatic mineral oil plasticizer known as T-RAE. The experimental evaluation of biodiesel as plasticizer in an SBR-based rubber compound in comparison to an aromatic mineral oil have led to the primary conclusion that biodiesel is reactive with the sulphur curing agent subtracting sulphur to the crosslinking polymer chains and leading to a vulcanizatewith lower moduli, tensile and hardness and higher elongationsin comparison to a reference compound fully plasticized with an aromatic mineral oil. However, biodiesel seems a good low temperature plasticizer because the low elastic modulus observed is desired in a winter tire tread for a good grip on snow and ice. The present work is only an exploratory work, and the tire tread formulation with biodiesel was not optimized.
Highlights
Typical plasticizers of rubber compounds are aromatic, naphthenic or paraffinic oils
The molecular weight of an aromatic plasticizer is about 550 Dalton followed by the molecular weight of a naphthenic plasticizer which is reported at about 440 Dalton and the lightest “average” molecule is represented by the paraffinic plasticizer at about 350 Dalton
We will introduce a new “green” plasticizer consisting in a mixture of methyl esters of fatty acids derived from rapeseed oil and commonly known as biodiesel, and we will test such a plasticizer in a standard rubber compound for a tire tread application
Summary
Typical plasticizers of rubber compounds are aromatic, naphthenic or paraffinic oils. These plasticizers are obtained from the processing of petroleum fractions, and they have not an univocal chemical structure but are mixtures of complex molecules of relatively high molecular weight. A naphthenic plasticizer is predominantly composed by cycloaliphatic rings of various types with some aromatic and aliphatic substituent In this case the core of the molecule is represented by the cycloaliphatic moiety. We will introduce a new “green” plasticizer consisting in a mixture of methyl esters of fatty acids derived from rapeseed oil and commonly known as biodiesel, and we will test such a plasticizer in a standard rubber compound for a tire tread application. It is worth mentioning here that castor oil is used in the formulation of butyl rubber compounds, epoxidized linseed oil is widely used in plastics and rubber as plasticizer and heat stabilizer, and vulcanized vegetable oils (known as factices) are used for long time in elastomers to ensure low temperature flexibility and low hardness [2]
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