Burst Diaphragms Based on Carbon Black/Silica Hybrid Filler Reinforced Nitrile Rubber Compounds

Nitrile rubber (NBR) based elastomer compounds containing different carbon black/silica composition ratios were prepared using laboratory-scale two roll mill. According the cure characterization results, addition of the reinforcing filler, 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 filler. Analysis of mechanical properties showed that burst strength of carbon black-rich NBR compounds was higher compared to the samples containing silica. This 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, pharmaceutical, food processing, and oilfield 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, sacrificially protect mission-critical systems from predetermined differential 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 oilfield applications. The 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