Self-Healing Materials to Reduce Unintended Methane Release

Pneumatic actuators in oil and gas operations often utilize pressurized natural gas as a compressed gas source for operation. This approach is convenient as the pipeline systems can directly supply the compressed gas needed for the operation of control systems. However, if the actuator is damaged, methane gas can be unintentionally released into the environment. Methane is a powerful and abundant greenhouse gas and therefore the environmental impact of this leakage is significant. The operation of these actuators is controlled by gas pressure acting on a flexible or elastomeric diaphragm. The diaphragms tend to fail due to either environmental or mechanical damage. In this work, we present a self-healing material that is compatible with a commercial device. This material is based on a microvascular network embedded within the diaphragm material and healing is triggered by damage to these materials, rupturing a channel, and releasing a healing agent. The healing agent polymerizes, sealing the damage and preventing the release of methane from the system. This study analyzes self-healing characteristics of polymer-based diaphragm materials using both experimental and numerical approaches.<br/>The microvascular network was created by sampling various interdigitated designs. The healing chemistries were held within close proximity to each other, as the interaction of the healing chemistries is needed for any healing to occur. The channels have a diameter of 1 mm with 1 mm spacing in between them. The MicroVasc approach, developed by Esser-Khan et al [1], was employed to leave behind hollow channels within the material. This involves 3D printing a microvascular network out of doped poly(lactic acid). These poly(lactic acid) channels create the positive scaffold within a mold. A two-part elastomeric matrix material was poured into the mold to create the diaphragm with the channels suspended within it. The diaphragms were then placed within a vacuum oven to depolymerize the doped poly(lactic acid) into gaseous monomers leaving behind hollow channels. A resin and an initiator, referred to as healing chemistries, of the same matrix material were held within the interdigitated microvascular network. Upon rupture of the diaphragm, the healing chemistries interacted to repair the damage. Through an initial round of testing using elastomeric poly(dimethylsiloxane) membrane samples, full and partial healing of elastomeric materials was shown. The samples were all injected with healing chemistries, prescribed various lengths and shapes through thickness cuts, and given 24 hours to cure and reseal the damage. Pressure differential tests were conducted up to 50 psi for the fabricated lab-scale membrane materials incorporated with self-healing microvascular channels and their ability to reseal the damage was observed and recorded. All samples displayed full healing up to 30psi and at least partial healing up to 50psi. The healing was also observed visually as when bent and flexed by hand, the membrane's integrity was held and no damage was observed where they had been previously cut. These self-healing capabilities vary with the orientation of the damage relative to the channels. To understand how channels influence the stress distribution through these materials, FEA was performed. The incorporation of channels within the membrane did not significantly impact internal stresses.<br/>[1] A. P. Esser-Kahn, P. R. Thakre, H. Dong, J. F. Patrick, V. K. Vlasko-Vlasov, N. R. Sottos, J. S. Moore, and S. R. White, “Three-dimensional microvascular fiber-reinforced composites,” Advanced Materials, vol. 23, no. 32, pp. 3654–3658, 2011.