Parker is a manufacturer of PPO-based hollow fiber membrane products which are used for air separation applications in aerospace and industrial areas. The objective of the project is to develop a new potting technology for one of our largest products to allow expanding its operating conditions.
A new epoxy adhesive formulation and potting process needs to be found that allows the manufacturing of hollow fiber gas separation modules with a housing of at least 150 mm diameter. The final tube sheet needs to have sufficient mechanical strength and glass transition temperature to allow operation at 65oC and 13 barg. The fibers need to be potted using a centrifuge to prevent wicking effects which typically cause fiber breakages upon pressurization of the module.
The challenge
Typically, epoxy adhesive mixtures with high Tg react strongly exothermic when a certain temperature is achieved (so-called kick-off). The exotherm becomes larger when larger amounts of adhesive mixture are used. This exotherm needs to be properly controlled to prevent defects in the tube sheet.
The main challenge of this work is to select the right combination of adhesive components that fulfill the technical requirements of the final tube sheet, can be used with products up to 150 mm OD (specific mass), can be potted using a centrifuge, does not kick-off at room temperature but does not overheat due to the exotherm and a curing schedule that allows large-scale manufacturing. A cure schedule needs to be defined with low peak exotherm that results in an epoxy fully cured all through and fully stress relieved.
Having access to a large scale R&D centrifuge helped us to do tests we could not do in our production facility.
Hylke Sijbesma
Senior Membrane Scientist – Gas Separation and Filtration Division
Results
Various suppliers were approached for suitable epoxy adhesive systems based on the defined specification, but only a few responded and could offer a suitable system. Especially the high Tg required made the selection difficult for suppliers (without having to develop something new). Despite these difficulties, the IMCEPO project did result in a selection of systems that based on their datasheet fulfil most of the requirements.
The systems that were obtained were screened for their reactivity (exotherm), thermal and mechanical properties. A method was developed to analyze the reaction kinetics using DSC. Furthermore, a silicone-based mould was developed to prepare sample bars for testing the mechanical properties of the various epoxies using an Instron tensile tester.
Based on the results, the most suitable epoxy system was selected for further trials with hollow fiber membranes. A potting fixture was designed and built and mounted to the existing centrifuge to allow potting first 6”scale prototypes with the selected epoxy adhesive system. The module consisted of 3D-printed potting caps, that were glued to a straight thin-walled stainless steel tube.
