The use of hydrotreated vegetable oils (HVO) as an alternative to conventional mineral fuels and fluids has introduced distinct material requirements for rubber components used in sealing systems, flexible hoses, and extruded profiles. Although HVO are often considered chemically “benign,” their interaction with elastomers reveals different degradation mechanisms compared to those associated with conventional mineral oils.

The approach to formulating elastomeric materials for these applications requires a precise understanding of HVO composition and its effects on the polymer network.

Chemical characteristics of HVO relevant to elastomers

HVO are obtained through hydrogenation of vegetable oils, resulting in a mixture predominantly of saturated paraffinic hydrocarbons. Unlike FAME-type biodiesel (Fatty Acid Methyl Esters), HVO do not contain polar ester groups. This chemical difference modifies the mechanisms of rubber absorption and swelling.

However, the absence of polarity does not eliminate interaction with elastomers. The distribution of chain fractions and the content of additives in HVO can favor plasticizer migration or induce changes in elastic modulus over time.

Limitations of conventional elastomers

Elastomers frequently used in contact with mineral oils, such as NBR (Nitrile Butadiene Rubber) with medium acrylonitrile content, may exhibit atypical behavior in contact with HVO. In certain formulations, the following are observed:

• initially reduced swelling, followed by progressive stiffening;
• extraction of low molecular weight plasticizers;
• variations in sealing properties during repeated thermal cycles.

These effects indicate that direct extrapolation of performance from mineral oil applications to HVO is technically incorrect.

Formulation directions dedicated to HVO applications

Elastomeric materials intended for contact with HVO are formulated through simultaneous adjustment of several parameters:

• selection of the base polymer, with emphasis on modified EPDM (Ethylene Propylene Diene Monomer) or HNBR (Hydrogenated Nitrile Butadiene Rubber);
• use of plasticizers with high stability and low solubility in paraffinic media;
• optimization of the vulcanization system to limit network rearrangements over time.

In the case of EPDM, chemical resistance is favorable, but compatibility with applications involving high pressures or high temperatures must be evaluated separately. HNBR offers a better compromise between chemical resistance and mechanical performance, with higher technological costs.

Implications for extrusion and molding

Formulations optimized for HVO can modify processing behavior. In extrusion, the following may be observed:

• variations in shear viscosity;
• increased temperature sensitivity;
• need for adjustment of cooling profiles.

In molding, vulcanization cycles may require longer times or adjusted temperatures to obtain a stable network. Ignoring these effects leads to dimensionally compliant products that are unstable in operation.

Material validation: a critical stage

Standard tests in mineral oils are not sufficient for validation of materials intended for HVO. Proper evaluation requires:

• long-term immersion tests in HVO specific to the application;
• measurement of variations in volume, hardness, and mechanical properties;
• simulation of actual operating thermal cycles.

Without these stages, the risk of premature degradation remains high, regardless of the theoretical qualifications of the material.

Conclusion

Rubber materials formulated for applications in contact with hydrotreated vegetable oils represent a distinct category that cannot be addressed through minor adaptations of conventional formulations. Chemical compatibility, long-term stability, and processing behavior must be treated simultaneously. In the absence of dedicated formulation and rigorous validation, the use of elastomers in HVO applications remains a significant source of technical risk.