The post-ageing mechanical response of specialised elastomers
The effects of material composition on the post-ageing mechanical response of elastomers are examined in this thesis. A series of experimental tests was carried out on two types of elastomer, namely Hydrogenated Nitrile Butadiene Rubber (HNBR) and the fluorocarbon (FKM). Both HNBR and FKM are widely used for various sealing applications in the automobile and the oil and gas industries. The experimental tests included uniaxial tension and compression; Shore A hardness; compression set and tear. These tests were conducted on the elastomers at room temperature after ageing for 3, 14 and 28 days at 50°, 100° and 150°, and at the elevated test temperatures of 50°C, 100° and 150°. Additional specimens were also tested as received. HNBR and FKM compound formulations differed in terms of elastomer base type, filler type (carbon black grade; FEF or SRF) and filler loading (10 to 50 parts of filler per hundred parts rubber (phr) by weight). This allowed the investigation into the effects of the composition on the mechanical properties of HNBR reinforced with SRF carbon black, HNBR reinforced with FEF carbon black, FKM reinforced with SRF carbon black and FKM reinforced with FEF carbon black. The results indicate that the amount of filler and type, the type of base polymer and the test conditions greatly influence the material properties of these elastomers. In some cases, the increase in filler loading not only results in an increase in the elastomer's overall cost and poor processing properties, but also impairs some of the mechanical properties. E.g. a maximum tensile strength is noted at filler loading of 40 phr for HNBR and at 30 phr for FKM irrespective of carbon black grade. The main observations are conveniently summarised in a tabular form. The implications of the experimental results for the design of oil well packers and bridge plugs are also discussed. Design charts are presented to aid the selection of elastomeric materials for various high temperature applications. The charts are shown to work for a simplified sealing packer problem.