Although majority of plasticizers are used in flexible PVC applications, a significant amount of plasticizers are used for elastomer applications. Plasticizers can be added to elastomers for various reasons: increasing softness or flexibility, lowering the glass transition temperature, reducing crystallization, increasing dispersion, or lowering the cost of the compound. Common plasticizers used in elastomer compounds are mineral oils and esters such as phthalates, sebacates, and adipates. However, plasticizer selection is largely dependent on which elastomer(s) is used and what the desired outcome is.
Below is some helpful information to consider when choosing a plasticizer for your specific elastomer application:
Acrylonitrile butadiene rubber (NBR)
Plasticizers can be added to NBR as an extender, mainly for soft roll compounds. Addition of plasticizer reduces the mixing time. A wide range of ester plasticizers are compatible with NBR, including adipates, phthalates, trimellitates, and epoxidized soybean oil (ESO).
Chloroprene (neoprene) rubber (CR)
Plasticizers are added to Polychloroprene Rubber to lower the glass transition temperature, reduce crystallization, and lower the cost. Mineral oils and organic esters are compatible with polychloroprene rubber. Aromatic mineral oils are used when reduction in crystallization rate is required, although their compatibility may be limited. Other recommended choices include Dioctyl Sebacate, Dioctyl Adipate, Dioctyl Phthalate, Diisononyl Phthalate. These choices may be good options for situations when low-temperature flexibility is required. Flame resistance can be improved with a plasticizer such as TBEP.
Chlorinated polyethylene (CPE)
CPE is compatible with a variety of plasticizers, which can be added as a filler and to increase flexibility. The amount and type of plasticizers used in CPE formulations are similar to that of PVC, including adipates, phthalates, and trimellitates. Common choices include general plasticizers such as DINP, DOP, and DOTP. Specialty plasticizers such as DOA, DINA, DBS, DOS, TOTM, and TINTM can be used as well.
Chlorosulfonated polyethylene (CSM)
Unplasticized CSM is very flexible already, so plasticizers selection for CSM should be done with the properties of the end use part in mind. For example, if low temperature flexibility is required an ester plasticizer such as DOS or DUP might be considered. TOTM might be a good choice is both low temperature properties and high heat applications are desired.
Epichlorohydrin rubber (ECO)
Plasticizers can be used to improve properties in ECO. ECO already has good low-temperature flexibility; however, it can be further improved by addition of plasticizers such as DOA or DBP. Ester plasticizers are compatible with ECO where the plasticizer has a similar polarity to that of the polymer. DOP, DIDP, and, TOTM are common choices.
Fluorocarbon rubber (FKM)
Most ester plasticizers cannot withstand the post-cure cycles and temperatures typically sued with FKM. This makes plasticizer selection difficult as very few plasticizers can be used. TBEP is one such plasticizer that is compatible with FKM.
Polyacrylate rubber (ACM)
Plasticizer use with ACM is limited dues to the high operating temperatures used. Polymeric plasticizers, TOTM and TBEP can be used in some cases.
Ethylene acrylic (AEM)
Both monomeric and polymeric ester plasticizers are compatible with AEM. DOS and DOP can be used to impart low-temperature flexibility, but can only be used in temperatures up to 125°C. Polymeric plasticizers are recommended for better permanence and higher continuous use temperature applications. Trimellitates such as 810TM and also TBEP can also be used.
Ethylene-propylene diene rubber (terpolymer) (EPDM)
EPDM is usually processed without plasticizers, however plasticizers can be added in for specific applications, such as correcting problems in pressure sensitive tapes. Polyisobutylene, paraffin oil, DBP, DOP, and vulcanized vegetable oil can be used.
Natural rubber (NR)
Plasticizers are added to NR to increase softness, improve dispersion of fillers, and aid in the breakdown of the elastomer. It is compatible with a variety of oil plasticizers including paraffinic, naphthenic and aromatic oil plasticizers.
Polyisoprene (IR)
IR is compatible with a broad range of esters (phthalates, adipates, sebacates) as well as aromatic, naphthenic, and paraffinic oils. Plasticizers are added to IR to change the rheological properties during processing, as well as to effect vibration damping and the elastic properties of the cured rubber.
Polybutadiene rubber (BR)
Plasticizers in BR serve many functions including increasing the elasticity, lowering the processing temperature, improving dispersion of the blend, and enhancing tackifying action. DOS, DBP, DOP are compatible with BR, as are some paraffinic, aromatic, or naphthenic mineral oils.
Styrene butadiene rubber (SBR)
SBR is compatible with most mineral oils, but has limited compatibility with paraffinic oils. Synthetic ester plasticizers are recommended for us in SBR as well.