Outgassing of Polymer Resins - A343
| Outgassing of Polymer Resins | |
|---|---|
| Foundational knowledge article | |
| |
| Document Type | Article |
| Document Identifier | 343 |
| Tags | |
Overview[edit | edit source]
The purpose of this document is to provide a general introduction and overview on outgassing of composites in the environment of outer space.
Background[edit | edit source]
Outgassing is an important phenomenon that needs to be considered when designing composite spacecraft components that will operate in low Earth orbit or beyond. Outgassing occurs due to the release of moisture and volatile gases in the vacuum of space, as well as decomposition of the material due to the effects of atomic oxygen erosion and ultraviolet radiation exposure. Shin et al. found that the primary outgassed products from an autoclave-cured graphite/epoxy composite were water \(H_2 O\), nitrogen gas \(N_2\), and hydrocarbon \(C_6H_5\)[1].
Due to the low pressure of space, escaped gas particles travel in a straight line until they collide with a spacecraft surface or escape into space. Approximately 1 in 10,000 to 1 in 100,000 molecules will collide with another molecule and return to the spacecraft [2]. When outgassed molecules hit the spacecraft they may bounce off, or stick to the surface forming a molecular layer. This contamination can degrade the performance of critical systems including thermal control systems, solar cells, optical lenses, and infrared sensors. Additionally, products from outgassing may lead to the formation of a particle cloud that results in light scattering and further degrades the performance of optical sensors.
Unknowns and Uncertainty[edit | edit source]
Outgassing can result in dimensional instability of a structure that can be critical in certain applications, such as optical benches in satellites. An experiment on the Long Duration Exposure Facility (LDEF) showed that a variety of carbon/epoxy composites took between 80 to 100 days to finish outgassing [3]. The time to finish outgassing depended on factors such as initial moisture concentration, volatile gas content, laminate thickness, ambient temperature, and constituent material diffusion properties. The experiment also demonstrated that outgassing resulted in significant strain for matrix dominated composite laminates (such as 90 degree laminates), but no significant strain was measured for unidirectional fibre dominated laminates. Although the outgassing created residual stresses in both laminates, the high stiffness of the fibres resulted in smaller strains in the fibre direction. Tennyson and Matthews developed an analytical model to predict the dimensional changes caused by outgassing [3]. The model was dependent on the initial moisture content, the temperature, laminate thickness, and diffusion coefficient of the material. Their model and experimental findings demonstrated that initial moisture content is critical for determining dimensional instability due to outgassing.
Practice[edit | edit source]
ASTM E595 outgassing testing can be performed to measure the mass of material outgassed under an elevated temperature in a vacuum environment. The ASTM E595 test equipment is shown in the figure below.
Total mass loss (TML) is calculated by comparing the original specimen mass to the total mass of the material outgassed after 24 hours. Collected volatile condensable material (CVCM) is calculated by dividing the mass of the outgassed matter that condenses on a cooled collector plate by the original specimen mass. ASTM E595 states that historically, TML of 1.00% and CVCM of 0.10% have been used as screening levels for rejection of spacecraft materials. NASA has a database of outgassing properties [4]. Most of the laminates included in the database have TML values between 0.1 and 0.5%, and CVCM levels of approximately 0.01%. It should be noted that there is not a direct relationship between void content and outgassing performance at low void content levels.
Fourier transform infrared spectroscopy can be used to identify the condensed outgassed materials. For carbon/epoxy laminates the most common products that condense on the collector plates are epoxy oligomers.
After the specimen is weighed to determine TML, it is conditioned for 24 hours at 23°C and 50% relative humidity. The specimen mass is measured once again after this exposure. This value is compared to the specimen mass determined after the vacuum exposure to calculate the water vapor regained (WVR) percentage. The WVR is an indicator of how much of the mass loss is attributable to moisture. Typically, more than half of the total mass loss can be attributed to moisture, and in many cases, the percentage is much higher. Moisture content is a primary driver in the outgassing of composite laminates, with the moisture originating from saturation after manufacturing is completed.
Conclusion and Further Information[edit | edit source]
Outgassing performance is an important consideration when a composite is deployed in the space environment. Neglecting its effect on the performance of the laminate can result in the degradation of sensitive instruments onboard the spacecraft. Material selection and manufacturing processes should be selected carefully to minimize these effects.
Return to Polymer properties[edit | edit source]
Related pages
| Page type | Links |
|---|---|
| Introduction to Composites Articles | |
| Foundational Knowledge Articles | |
| Foundational Knowledge Method Documents | |
| Foundational Knowledge Worked Examples | |
| Systems Knowledge Articles | |
| Systems Knowledge Method Documents | |
| Systems Knowledge Worked Examples | |
| Systems Catalogue Articles | |
| Systems Catalogue Objects – Material | |
| Systems Catalogue Objects – Shape | |
| Systems Catalogue Objects – Tooling and consumables | |
| Systems Catalogue Objects – Equipment | |
| Practice Documents | |
| Case Studies | |
| Perspectives Articles |
References
- ↑ [Ref] Shin, Kwang-Bok et al. (2000). "Prediction of failure thermal cycles in graphite/epoxy composite materials under simulated low earth orbit environments". 31 (3). doi:10.1016/S1359-8368(99)00073-6. ISSN 1359-8368. Cite journal requires
|journal=(help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link) - ↑ [Ref] Rawal, Suraj P.; Goodman, John W. (2000). Composites for Spacecraft. Elsevier. doi:10.1016/B0-08-042993-9/00216-3.CS1 maint: uses authors parameter (link) CS1 maint: date and year (link)
- ↑ 3.0 3.1 [Ref] Tennyson, R. C.; Matthews, R. (1995). "Thermal-vacuum response of polymer matrix composites in space". 32 (4). doi:10.2514/3.26672. ISSN 0022-4650. Cite journal requires
|journal=(help)CS1 maint: uses authors parameter (link) - ↑ [Ref] NASA (2016). "Outgassing Data for Selecting Spacecraft Materials". Retrieved 11 September 2023.CS1 maint: uses authors parameter (link) CS1 maint: date and year (link)
 |
 |
| About | Help |
Welcome
Welcome to the CKN Knowledge in Practice Centre (KPC). The KPC is a resource for learning and applying scientific knowledge to the practice of composites manufacturing. As you navigate around the KPC, refer back to the information on this right-hand pane as a resource for understanding the intricacies of composites processing and why the KPC is laid out in the way that it is. The following video explains the KPC approach:
Understanding Composites Processing
The Knowledge in Practice Centre (KPC) is centered around a structured method of thinking about composite material manufacturing. From the top down, the heirarchy consists of:
- The factory
- Factory cells and/or the factory layout
- Process steps (embodied in the factory process flow) consisting of:
The way that the material, shape, tooling & consumables and equipment (abbreviated as MSTE) interact with each other during a process step is critical to the outcome of the manufacturing step, and ultimately critical to the quality of the finished part. The interactions between MSTE during a process step can be numerous and complex, but the Knowledge in Practice Centre aims to make you aware of these interactions, understand how one parameter affects another, and understand how to analyze the problem using a systems based approach. Using this approach, the factory can then be developed with a complete understanding and control of all interactions.
Interrelationship of Function, Shape, Material & Process
Design for manufacturing is critical to ensuring the producibility of a part. Trouble arises when it is considered too late or not at all in the design process. Conversely, process design (controlling the interactions between shape, material, tooling & consumables and equipment to achieve a desired outcome) must always consider the shape and material of the part. Ashby has developed and popularized the approach linking design (function) to the choice of material and shape, which influence the process selected and vice versa, as shown below:
Within the Knowledge in Practice Centre the same methodology is applied but the process is more fully defined by also explicitly calling out the equipment and tooling & consumables. Note that in common usage, a process which consists of many steps can be arbitrarily defined by just one step, e.g. "spray-up". Though convenient, this can be misleading.
Workflows
The KPC's Practice and Case Study volumes consist of three types of workflows:
- Development - Analyzing the interactions between MSTE in the process steps to make decisions on processing parameters and understanding how the process steps and factory cells fit within the factory.
- Troubleshooting - Guiding you to possible causes of processing issues affecting either cost, rate or quality and directing you to the most appropriate development workflow to improve the process
- Optimization - An expansion on the development workflows where a larger number of options are considered to achieve the best mixture of cost, rate & quality for your application.
