From fossil to renewable: The use of bio-based oils in a tire tread compound

The usage of fossil raw materials is one of the main problems in the rubber industry at the moment. On the one hand, burning fossil materials to obtain energy results in the release of CO2 emissions: the primary cause of the climate crisis. On the other hand, fossil materials are limited and non-renewable. Therefore, it is needed to replace fossil raw materials with sustainable alternatives.
In the tire industry, Treated Distilled Aromatic Extract (TDAE) is often used as a plasticizer. This oil is petroleum-based and obtained from fossil resources. To create a more sustainable tire tread compound, TDAE needs to be replaced with bio-based plasticizers obtained from renewable sources. However, the selection of suitable alternatives is challenging because the exact chemical structure of TDAE is unknown. In this study, different bio-based plasticizers are used to replace TDAE in a silica-filled SBR/BR compound. The selection of the alternatives was, amongst others, based on the Hansen Solubility Parameter, to get insight into the compatibility of the plasticizer with the used polymers.
The processing, curing, and testing results of the different plasticizers were evaluated. It was observed that the plasticizer does influence the curing process. Further research on this influence showed that the plasticizer can interact with the sulfur-curing agent. This influences not only the curing behavior, but also the crosslink network, and with that the mechanical properties of the compounds.
Besides, the plasticizer influences the dynamic mechanical behavior of the rubber compound. Using different types of plasticizers resulted in a clear shift in the tan δ peak, which is related to the glass transition temperature of the compound. These findings were in line with the free volume theory. This theory explains that the plasticizer migrates to free volume between the polymer chains, increasing these volumes, and creating more space for the polymer to move. This increase in polymer mobility and decrease in internal friction results in a decrease in glass transition temperature.
Although it was observed that the plasticizer does impact the material properties of the compound, it can also be concluded that TDAE can successfully be replaced with bio-based alternatives.