Research Article Burst Diaphragms Based on Carbon Black/Silica Hybrid Filler Reinforced Nitrile Rubber Compounds Ali Asghar Davoodi, 1 Tal’at Khalkhali, 1 Mohammad Mahdi Salehi, 1 and Soheil Sarioletlagh Fard 2 1 Polymer Science & Technology Division, Research Institute of Petroleum Industry, P.O. Box 14115-143, Tehran, Iran 2 Process Development Department, Research Institute of Petroleum Industry, P.O. Box 14115-143, Tehran, Iran Correspondence should be addressed to Ali Asghar Davoodi; davoodiaa@ripi.ir Received 23 June 2014; Revised 25 August 2014; Accepted 25 August 2014; Published 2 September 2014 Academic Editor: Eri Yoshida Copyright © 2014 Ali Asghar Davoodi et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Nitrile rubber (NBR) based elastomer compounds containing diferent carbon black/silica composition ratios were prepared using laboratory-scale two roll mill. According the cure characterization results, addition of the reinforcing fller, either carbon black or silica, shortened the optimum cure time and also scorch time of samples compared to that of pure NBR gum where the optimum cure time and scorch time both decreased with increasing the silica content of hybrid fller. Analysis of mechanical properties showed that burst strength of carbon black-rich NBR compounds was higher compared to the samples containing silica. Tis is presumably due to the higher elongation at break observed in NBR/silica compounds revealing lower crosslink density. In fact, adsorption of curing agents onto the functional groups present at the silica surface would be responsible for the lower crosslink density. According to the Barlow’s formula, despite the higher tensile strength of NBR/silica compounds, higher elongation at break leads to the lower burst strength of NBR/silica/carbon black diaphragms. 1. Introduction Many industries, such as petrochemical, chemical, phar- maceutical, food processing, and oilfeld applications, rely on pressurized equipments and assemblies such as pressure vessels and propellant subsystems. Burst diaphragms, also referred to as bursting discs and rupture discs, as pressure relief devices, sacrifcially protect mission-critical systems from predetermined diferential pressure, either positive or negative, that is, overpressurization and potentially damaging vacuum conditions. Major advantages of the use of rupture discs compared to pressure relief valves would be leak- tightness, no maintenance and cost. Burst discs usually have steel or aluminum housings enveloping a one-time-use membrane commonly made of cold-rolled steel, nickel alloys, aluminum, or any other material with yield strength close to its ultimate strength. Nitrile rubber and hydrogenated Nitrile Butadiene Rubber, as a family of unsaturated copolymers of acrylonitrile (ACN), are commonly used to produce such diaphragms operating up to 120 ∘ C. NBR is resistant to aliphatic hydrocarbons, oil, and fuel and hence is selected for this study contemplated for oilfeld applications. Te choice of the elastomer compound additives is closely linked to the type of properties to be achieved. Carbon blacks, presenting excellent properties such as heat, chemical, and weathering resistance, lightweight, electroconductivity, and low thermal expansion [1], are commonly used with both polar and nonpolar rubbers to enhance elongation, modulus, tear strength, tensile strength, and resilience. On the other hand, Silica ofers a unique combination of tear strength, abrasion resistance, and aging resistance compared to carbon black [2]. Besides, at elevated temperatures, such as those encountered during compound mixing process, the silanol groups present on the surface of silicas may attach to a number of chemical groups present in rubber compounds. It is worth noting that among rubbers (e.g., SBR, NR, BR, EPDM, and IIR), NBR has the strongest interactions with silica surface through hydrogen bonding according to inverse gas chromatography results [3–5]. Accordingly, since both Hindawi Publishing Corporation Journal of So Matter Volume 2014, Article ID 498563, 6 pages http://dx.doi.org/10.1155/2014/498563