21. March 2019

EPDM rubber plasticized with polymeric soybean oil of different molecular weights

Due to environmental and sustainability concerns, it is desirable to replace mineral oil with vegetable oils as processing aids and plasticizers in rubbers. In this paper the effect of four polymerized soybean oils of high viscosity on processing and physical properties of EPDM rubber in a standard sulfur-cured formulation is evaluated.

Bleed-out of soybean oil from cured tensile pad molded from EPDM-6

Bleed-out of soybean oil from cured tensile pad molded from EPDM-6

EPDM rubber plasticized with polymeric soybean oil of different molecular weights
Z. S. Petrović, M. Ionescu, J. Milic, J. R. Halladay
RFP Rubber Fibres Plastics 01|2019

The most widely used plasticizers for EPDM are naphthenic oils, but paraffinic oils are recommended for higher temperature applications or for peroxide cures. EPDM compounds often use very high levels of plasticizer and some commercial polymers are supplied in oil extended grades with up to 100 phr oil. Without plasticizer, EPDM is dry and very difficult to mix and process. Due to environmental and sustainability concerns, it is desirable to replace some petrochemical components with renewable materials. Following this trend, attempts have been made to replace mineral oil with vegetable oils as processing aids and plasticizers in rubbers. In this paper the effect of four polymerized soybean oils of high viscosity on processing and physical properties of EPDM rubber in a standard sulfur-cured formulation has been tested. The rational for using high molecular weight oil is based on the assumption that although compatibility may decrease with increasing molecular weight, the chance of oil being chemically bonded to rubber increases with molecular weight and diffusion (sweating out) would be less likely.

Four polymerized soybean oils of different molecular weights showed good compatibility with EPDM rubber but due to the presence of double bonds and copolymerization with EPDM, decreased the cross-linking density when compared with paraffinic extender oil. As a consequence, polymeric soybean oils reduced tensile strength and modulus but increased elongation, tear strength and compression set. Higher molecular weight plasticizers are expected to reduce sweating out of oils. Pure soybean oil was not completely compatible at the concentration tested but it showed strong plasticizing effect, dramatically lowered tensile strength, tear strength and modulus and increased elongation at break and compression set. No clear effect of molecular weight of polymerized soybean oils on properties was observed, but increasing sulfur content was found to be beneficial. Using polymeric vegetable oils instead of petrochemical extenders in EPDM rubbers is economical and environmentally desirable but the curing system requires optimization to accommodate loss of cross-linking density.

Citation:
Z. S. Petrović, M. Ionescu, J. Milic, J. R. Halladay, RFP Rubber Fibres Plastics, 01|2019, 40-47.

www.gupta-verlag.com/magazines/rfp-rubber-fibres-plastics-international/01-2019

URL: https://www.gupta-verlag.com/news/technology/22694/epdm-rubber-plasticized-with-polymeric-soybean-oil-of-different-molecular-weights