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NASA NTRS1972

Quantitation of buried contamination by use of solvents. Part 1: Solvent degradation of amine cured epoxy resins

The solubility and/or swelling of cured epoxy resins was studied using the solubility parameter method. Determination of solubility parameters were found in order to select solvents for solvent-assisted degradation of cured epoxy polymers used in spacecraft. A method for improving recovery of seeded spores is suggested for assay of buried contaminants. Three commercial epoxy resins were cured using four different alkyl amines. For each resin-amine combination, three levels of amine were used, corresponding to 1/3, 2/3, and all of the amine required to react with the oxirane groups of the resin. The solubility parameters of the 36 resulting model compounds were determined in poorly and moderately hydrogen-bonded solvents. No strongly hydrogen-bonded solvents caused dissolution or swelling. The tolerance of cured resins is discussed in terms of polymer structure.

Rheineck, A. E.↗

NASA NTRS2005

X-Ray Fluorescence Solvent Detection at the Substrate-Adhesive Interface

With environmental regulations limiting the use of volatile organic compounds, low-vapor pressure solvents have replaced traditional degreasing solvents for bond substrate preparation. When used to clean and prepare porous bond substrates such as phenolic composites, low vapor pressure solvents can penetrate deep into substrate pore networks and remain there for extended periods. Trapped solvents can interact with applied adhesives either prior to or during cure, potentially compromising bond properties. Currently, methods for characterizing solvent time-depth profiles in bond substrates are limited to bulk gravimetric or sectioning techniques. While sectioning techniques such as microtome allow construction of solvent depth profiles, their depth resolution and reliability are limited by substrate type. Sectioning techniques are particularly limited near the adhesive-substrate interface where depth resolution is further limited by adhesive-substrate hardness and, in the case of a partially cured adhesive, mechanical properties differences. Additionally, sectioning techniques cannot provide information about lateral solvent diffusion. Cross-section component mapping is an alternative method for measuring solvent migration in porous substrates that eliminates the issues associated with sectioning techniques. With cross-section mapping, the solvent-wiped substrate is sectioned perpendicular rather than parallel to the wiped surface, and the sectioned surface is analyzed for the solvent or solvent components of interest using a two-dimensional mapping or imaging technique. Solvent mapping can be performed using either direct or indirect methods. With a direct method, one or more solvent components are mapped using red or Raman spectroscopy together with a moveable sample stage and/or focal plane array detector. With an indirect method, an elemental "tag" not present in the substrate is added to the solvent before the substrate is wiped. Following cross sectioning, the tag element can then be mapped by its characteristic x-ray emission using either x-ray fluorescence, or electron-beam energy-and wavelength-dispersive x-ray spectrometry. The direct mapping techniques avoid issues of different diffusion or migration rates of solvents and elemental tags, while the indirect techniques avoid spectral resolution issues in cases where solvents and substrates have adjacent or overlapping peaks. In this study, cross-section component indirect mapping is being evaluated as a method for measuring migration of d-limonene based solvents in glass-cloth phenolic composite (GCP) prior to and during subsequent bonding and epoxy adhesive cure.

Wurth, Laura↗

NASA NTRS2001

ODC-Free Solvent Implementation Issues for Vulcanized Rubber and Bond Systems

Thiokol Propulsion has worked extensively to replace 1,1,1-trichloroethane (TCA) with ozone depleting chemicals (ODC)-free solvents for use in the manufacture of the Reusable Solid Rocket Motor (RSRM) for the Space Shuttle Program. As Thiokol has transitioned from sub-scale to full-scale testing and implementation of these new solvents, issues have been discovered which have required special attention. The original intent of Thiokol's solvent replacement strategy was to replace TCA with a single drop-in solvent for all equivalent applications. We have learned that a single candidate does not exist for replacing TCA. Solvent incompatibility with process materials has caused us to seek for niche solvents and/or processing changes that provide an ODC-free solution for special applications. This paper addresses some of the solvent incompatibilities, which have lead to processes changes and possible niche solvent usage. These incompatibilities were discovered during full-scale testing of ODC-free solvents and relate to vulcanized rubber and bond systems in the RSRM. Specifically, the following items are presented: (1) Cure effects of d-limonene based solvents on Silica Filled Ethylene Propylene Diene Monomer (SF-EPDM) rubber. During full-scale test operations, Thiokol discovered that d-limonene (terpene) based solvents inhibit the cure of EPDM rubber. Subsequent testing showed the same issue with Nitrile Butadiene Rubber (NBR). Also discussed are efforts to minimize uncured rubber exposure to solvents; and (2) Cured bond system sensitivity to ODC-free solvents. During full scale testing it was discovered that a natural rubber to steel vulcanized bond could degrade after prolonged exposure to ODC-free solvents. Follow on testing showed that low vapor pressure and residence time seemed to be most likely cause for failure.

Hodgson, James R.↗

NASA NTRS2016

An Improved Approach for Analyzing the Oxygen Compatibility of Solvents and other Oxygen-Flammable Materials for Use in Oxygen Systems

Solvents used to clean oxygen system components must be assessed for oxygen compatibility, as incompatible residue or fluid inadvertently left behind within an oxygen system can pose a flammability risk. The most recent approach focused on solvent ignition susceptibility to assess the flammability risk associated with these materials. Previous evaluations included Ambient Pressure Liquid Oxygen (LOX) Mechanical Impact Testing (ASTM G86) and Autogenous Ignition Temperature (AIT) Testing (ASTM G72). The goal in this approach was to identify a solvent material that was not flammable in oxygen. As environmental policies restrict the available options of acceptable solvents, it has proven difficult to identify one that is not flammable in oxygen. A more rigorous oxygen compatibility approach is needed in an effort to select a new solvent for NASA applications. NASA White Sands Test Facility proposed an approach that acknowledges oxygen flammability, yet selects solvent materials based on their relative oxygen compatibility ranking, similar to that described in ASTM G63-99. Solvents are selected based on their ranking with respect to minimal ignition susceptibility, damage and propagation potential, as well as their relative ranking when compared with other solvent materials that are successfully used in oxygen systems. Test methods used in this approach included ASTM G86 (Ambient Pressure LOX Mechanical Impact Testing and Pressurized Gaseous Oxygen (GOX) Mechanical Impact Testing), ASTM G72 (AIT Testing), and ASTM D240 (Heat of Combustion (HOC) Testing). Only four solvents were tested through the full battery of tests for evaluation of oxygen compatibility: AK-225G as a baseline comparison, Solstice PF, L-14780, and Vertrel MCA. Baseline solvent AK-225G exhibited the lowest HOC and highest AIT of solvents tested. Nonetheless, Solstice PF, L-14780, and Vertrel MCA HOCs all fell well within the range of properties that are associated with proven oxygen system materials. Tested AITs for these solvents fell only slightly lower than the AIT for the proven AK-225G solvent. Based on these comparisons in which solvents exhibited properties within those ranges seen with proven oxygen system materials, it is believed that Solstice PF, L-14780, and Vertrel MCA would perform well with respect to oxygen compatibility.

Harper, Susan A.↗

NASA NTRS1990

Mechanism of transport and distribution of organic solvents in blood

Little is known about the mechanism of transport and distribution of volatile organic compounds in blood. Studies were conducted on five typical organic solvents to investigate how these compounds are transported and distributed in blood. Groups of four to five rats were exposed for 2 hr to 500 ppm of n-hexane, toluene, chloroform, methyl isobutyl ketone (MIBK), or diethyl ether vapor; 94, 66, 90, 51, or 49%, respectively, of these solvents in the blood were found in the red blood cells (RBCs). Very similar results were obtained in vitro when aqueous solutions of these solvents were added to rat blood. In vitro studies were also conducted on human blood with these solvents; 66, 43, 65, 49, or 46%, respectively, of the added solvent was taken up by the RBCs. These results indicate that RBCs from humans and rats exhibited substantial differences in affinity for the three more hydrophobic solvents studied. When solutions of these solvents were added to human plasma and RBC samples, large fractions (51-96%) of the solvents were recovered from ammonium sulfate-precipitated plasma proteins and hemoglobin. Smaller fractions were recovered from plasma water and red cell water. Less than 10% of each of the added solvents in RBC samples was found in the red cell membrane ghosts. These results indicate that RBCs play an important role in the uptake and transport of these solvents. Proteins, chiefly hemoglobin, are the major carriers of these compounds in blood. It can be inferred from the results of the present study that volatile lipophilic organic solvents are probably taken up by the hydrophobic sites of blood proteins.

Solvents/administration & dosage/metabolism/pharma↗

NASA NTRS2001

Nonflammable, Nonaqueous, Low Atmospheric Impact, High Performance Cleaning Solvents

For many years, chlorofluorocarbon (CFC) and chlorocarbon solvents have played an important part in aerospace operations. These solvents found extensive use as cleaning and analysis (EPA) solvents in precision and critical cleaning. However, CFCs and chlorocarbon solvents have deleterious effects on the ozone layer, are relatively strong greenhouse gases, and some are suspect or known carcinogens. Because of their ozone-depletion potential (ODP), the Montreal Protocol and its amendments, as well as other environmental regulations, have resulted in the phaseout of CFC-113 and 1,1,1-trichloroethane (TCA). Although alternatives have been recommended, they do not perform as well as the original solvents. In addition, some analyses, such as the infrared analysis of extracted hydrocarbons, cannot be performed with the substitute solvents that contain C-H bonds. CFC-113 solvent has been used for many critical aerospace applications. CFC-113, also known as Freon (registered) TF, has been used extensively in NASA's cleaning facilities for precision and critical cleaning, in particular the final rinsing in Class 100 areas, with gas chromatography analysis of rinse residue. While some cleaning can be accomplished by other processes, there are certain critical applications where CFC-113 or a similar solvent is highly cost-effective and ensures safety. Oxygen system components are one example where a solvent compatible with oxygen and capable of removing fluorocarbon grease is needed. Electronic components and precision mechanical components can also be damaged by aggressive cleaning solvents.

Dhooge, P. M.↗

NASA NTRS2001

Issues Related to Cleaning Complex Geometry Surfaces with ODC-Free Solvents

Implementing ozone depleting chemicals (ODC)-free solvents into full-scale reusable solid rocket motor cleaning operations has presented problems due to the low vapor pressures of the solvents. Because of slow evaporation, solvent retention is a problem on porous substrates or on surfaces with irregular geometry, such as threaded boltholes, leak check ports, and nozzle backfill joints. The new solvents are being evaluated to replace 1,1,1-trichloroethane, which readily evaporates from these surfaces. Selection of the solvents to be evaluated on full-scale hardware was made based on results of subscale tests performed with flat surface coupons, which did not manifest the problem. Test efforts have been undertaken to address concerns with the slow-evaporating solvents. These concerns include effects on materials due to long-term exposure to solvent, potential migration from bolthole threads to seal surfaces, and effects on bolt loading due to solvent retention in threads. Tests performed to date have verified that retained solvent does not affect materials or hardware performance. Process modifications have also been developed to assist drying, and these can be implemented if additional drying becomes necessary.

Bradford, Blake F.↗

NASA NTRS1975

Diffusion in mixed solvents. II - The heat of mixing parameter

Correlation of second-order rate constants for many reactions involving electron transfer between organic molecules, solvated electron reactions, iodine diffusion coefficients, and triplet state electron transfer reactions has been made with the heat of mixing parameter (HMP) for the aqueous binary solvent systems. The aqueous binary solvents studied are those containing methanol or ethanol (type I solvent); 1-propanol or tert-butyl alcohol (type II solvent); or sucrose or glycerol (type III solvent). A plot of the HMP vs. the diffusion parameter for each reaction yields superimposable curves for these reactions in a particular solvent mixture over the entire solvent mixture range, irrespective of the value of the reaction's rate constant or diffusion coefficient in water.

Carapellucci, P. A.↗

NASA NTRS1999

Life of Pennzane and 815Z-Lubricated Instrument Bearings Cleaned with Non-CFC Solvents

This report takes the form of two papers: (1) "Life of Pennzane and 815Z-Lubricated Instrument Bearings cleaned with Non-CFC Solvents" and (2) a published paper, entitled "Instrument bearing life with NON-CFC cleaners". Abstract for paper # 1 : Bearings used in spacecraft mechanisms have historically been cleaned with chlorofluorocarbon CFC-1 13 (Freon) solvents and lubricated with a perfluorinated polyalkylether (PFPE) oils like 815-Z. Little full-scale bearing life test data exists to evaluate the effects of the newer class environmental-friendly bearing cleaners or improved synthetic hydrocarbon space oils like Pennzane. To address the lack of data, a cooperative, bearing life test program was initiated between NASA, Lockheed Martin and MPB. The objective was to obtain comparative long-term, life test data for flight-quality bearings, cleaned with non-CFC solvents versus CFC-1 13 under flight-like conditions with two space oils. A goal was to gain a better understanding of the lubricant surface chemistry effects with such solvents. A second objective was to obtain well-controlled, full-scale bearing life test data with a relatively new synthetic oil (Pennzane), touted as an improvement to Bray 815Z, an oil with considerable space flight history. The second paper, which serves as an attachment, is abstracted below: Bearings used in spacecraft mechanisms have historically been cleaned with chlorofluorocarbon CFC-113 (Freon) solvents and lubricated with a perfluorinated polyalkylether (PFPE) oils like 815-Z. Little full-scale bearing life test data exists to evaluate the effects of the newer class environmental-friendly bearing cleaners or improved synthetic hydrocarbon space oils like Pennzane. To address the lack of data, a cooperative, bearing life test program was initiated between NASA, Lockheed Martin and MPB. The objective was to obtain comparative long-term, life test data for flight-quality bearings, cleaned with non-CFC solvents versus CFC-1 13 under flight-like conditions with two space oils. A goal was to gain a better understanding of the lubricant surface chemistry effects with such solvents. A second objective was to obtain well-controlled, full-scale bearing life test data with a relatively new synthetic oil (Pennzane), touted as an improvement to Bray 815Z, an oil with considerable space flight history.

Loewenthal, Stuart↗

NASA NTRS2001

Improved Detection Technique for Solvent Rinse Cleanliness Verification

The NASA White Sands Test Facility (WSTF) has an ongoing effort to reduce or eliminate usage of cleaning solvents such as CFC-113 and its replacements. These solvents are used in the final clean and cleanliness verification processes for flight and ground support hardware, especially for oxygen systems where organic contaminants can pose an ignition hazard. For the final cleanliness verification in the standard process, the equivalent of one square foot of surface area of parts is rinsed with the solvent, and the final 100 mL of the rinse is captured. The amount of nonvolatile residue (NVR) in the solvent is determined by weight after the evaporation of the solvent. An improved process of sampling this rinse, developed at WSTF, requires evaporation of less than 2 mL of the solvent to make the cleanliness verification. Small amounts of the solvent are evaporated in a clean stainless steel cup, and the cleanliness of the stainless steel cup is measured using a commercially available surface quality monitor. The effectiveness of this new cleanliness verification technique was compared to the accepted NVR sampling procedures. Testing with known contaminants in solution, such as hydraulic fluid, fluorinated lubricants, and cutting and lubricating oils, was performed to establish a correlation between amount in solution and the process response. This report presents the approach and results and discusses the issues in establishing the surface quality monitor-based cleanliness verification.

Hornung, S. D.↗

NASA NTRS1995

Cleaning without chlorinated solvents

Because of health and environmental concerns, many regulations have been passed in recent years regarding the use of chlorinated solvents. The Oak Ridge Y-12 Plant has had an active program to find alternatives for these solvents used in cleaning applications for the past 7 years. During this time frame, the quantity of solvents purchased has been reduced by 92 percent. The program has been a twofold effort. Vapor degreasers used in batch cleaning operations have been replaced by ultrasonic cleaning with aqueous detergent, and other organic solvents have been identified for use in hand-wiping or specialty operations. In order to qualify these alternatives for use, experimentation was conducted on cleaning ability as well as effects on subsequent operations such as welding, painting, and bonding. Cleaning ability was determined using techniques such as x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) which are capable of examining monolayer levels of contamination on a surface. Solvents have been identified for removal of rust preventative oils, lapping oils, machining coolants, lubricants, greases, and mold releases. Solvents have also been evaluated for cleaning urethane foam spray guns, swelling of urethanes, and swelling of epoxies.

Thompson, L. M.↗

NASA NTRS2009

Microfluidic Extraction of Biomarkers using Water as Solvent

A proposed device, denoted a miniature microfluidic biomarker extractor (mu-EX), would extract trace amounts of chemicals of interest from samples, such as soils and rocks. Traditionally, such extractions are performed on a large scale with hazardous organic solvents; each solvent capable of dissolving only those molecules lying within narrow ranges of specific chemical and physical characteristics that notably include volatility, electric charge, and polarity. In contrast, in the mu-EX, extractions could be performed by use of small amounts (typically between 0.1 and 100 L) of water as a universal solvent. As a rule of thumb, in order to enable solvation and extraction of molecules, it is necessary to use solvents that have polarity sufficiently close to the polarity of the target molecules. The mu-EX would make selection of specific organic solvents unnecessary, because mu-EX would exploit a unique property of liquid water: the possibility of tuning its polarity to match the polarity of organic solvents appropriate for extraction of molecules of interest. The change of the permittivity of water would be achieved by exploiting interactions between the translational states of water molecules and an imposed electromagnetic field in the frequency range of 300 to 600 GHz. On a molecular level, these interactions would result in disruption of the three-dimensional hydrogen-bonding network among liquid-water molecules and subsequent solvation and hydrolysis of target molecules. The mu-EX is expected to be an efficient means of hydrolyzing chemical bonds in complex macromolecules as well and, thus, enabling analysis of the building blocks of these complex chemical systems. The mu-EX device would include a microfluidic channel, part of which would lie within a waveguide coupled to an electronically tuned source of broad-band electromagnetic radiation in the frequency range from 300 to 600 GHz (see figure). The part of the microfluidic channel lying in the waveguide would constitute an interaction volume. The dimensions of the interaction volume would be chosen in accordance with the anticipated amount of solid sample material needed to ensure extraction of sufficient amount of target molecules for detection and analysis. By means that were not specified at the time of reporting the information for this article, the solid sample material would be placed in the interaction volume. Then the electromagnetic field would be imposed within the waveguide and water would be pumped through the interaction volume to effect the extraction.

Amashukeli, Xenia↗

NASA NTRS2012

A New Method to Grow SiC: Solvent-Laser Heated Floating Zone

The solvent-laser heated floating zone (solvent-LHFZ) growth method is being developed to grow long single crystal SiC fibers. The technique combines the single crystal fiber growth ability of laser heated floating zone with solvent based growth techniques (e.g. traveling solvent method) ability to grow SiC from the liquid phase. Initial investigations reported in this paper show that the solvent-LHFZ method readily grows single crystal SiC (retains polytype and orientation), but has a significant amount of inhomogeneous strain and solvent rich inclusions.

Woodworth, Andrew A.↗

NASA NTRS2012

A New Method to Grow SiC: Solvent-Laser Heated Floating Zone

Woodworth, A. A.↗

NASA NTRS2017

Solvent Replacement for Hydrochlorofluorocarbon-225 for Cleaning Oxygen System Components

This Technical Memorandum is the result of a 2-year project funded by the Defense Logistics Agency-Aviation, Hazardous Minimization and Green Products Branch, to identify and test two candidate solvents to replace hydrochlorofluorocarbon-225 (HCFC-225) for cleaning oxygen systems. The solvents were also compared to a second solvent composed predominantly of perfluorobutyl iodide (PFBI), which had received limited approval by the United States Air Force (USAF) for hand wipe cleaning of components for aviators’ breathing oxygen systems. The tests performed for this study were based on those reported in AFRL-ML-WP-TR-2003-4040, “The Wipe Solvent Program,” the test program used to qualify Ikon® Solvent P for USAF applications.The study was completed in August 2014, prior to the completion of a more extensive study funded by the NASA Rocket Propulsion Test (RPT) program. The results of the RPT project are reported in NASA/TP-2015-18207, “Replacement of Hydrochlorofluorocarbon–225 Solvent for Cleaning and Verification Sampling of NASA Propulsion Oxygen Systems Hardware, Ground Support Equipment, and Associated Test Systems.” The test methods used in this study for nonvolatile residue (NVR) background, materials compatibility, and cleaning effectiveness were different than those used for the RPT project; a smaller set of materials and contaminants were tested. The tests for this study were complementary to and provided supplementary information for the down-selection process during the course of the test program reported in NASA/TP-2015-218207.

Mitchell, M. A.↗

NASA NTRS2018

Phenolic Polymer Interactions with Water and Ethylene Glycol Solvents

Interactions between pre-cured phenolic polymer chains and a solvent have a significant impact on the structure and properties of the final post-cured phenolic resin. Developing an understanding of the nature of these interactions is important and will aid in the selection of the proper solvent that will lead to the desired final product. Here, we investigate the role of the phenolic chain structure and the solvent type on the overall solvation performance of the system through ab initio techniques and molecular dynamics simulations. Two types of solvents are considered: ethylene glycol (EGL) and H2O. Three phenolic chain structures are considered, including two novolac-type chains with either an ortho-ortho (OON) or an ortho-para (OPN) backbone network and a resole-type (RES) chain with an ortho-ortho network. Each system is characterized through a structural analysis of the solvation shell and the hydrogen-bonding environment as well as through a quantification of the solvation free energy along with partitioned interaction energies between specific molecular species. The combination of simulations and the analyses indicate that EGL provides a higher solvation free energy than H2O due to more energetically favorable hydrophilic interactions as well as favorable hydrophobic interactions between CH element groups. In addition, the phenolic chain structure significantly affects the solvation performance, with OON having limited intermolecular hydrogen-bond formations, while OPN and RES interact more favorably with the solvent molecules. The results suggest that a resole-type phenolic chain with an ortho-para network should have the best solvation performance in EGL, H2O, and other similar solvents.

Haskins, Justin B.↗

NASA NTRS1975

Diffusion in mixed solvents - On the viscosity question

Linear plots of reaction rate vs reciprocal of solvent viscosity are generally used as the classifying criteria for diffusion controlled reactions in fluid solutions and to determine reaction mechanisms in mixed hydroxylic solvents like glycerol and water. This paper presents data which shows that the above-mentioned criteria are insufficient in many cases where nonideal mixed solvent systems are used to increase solvent viscosity. Data correlations suggest that the excess functions determine the variation in reaction rate constants. Kinetic parameters are presented for sucrose-water and methanol-water solvent systems for a reaction involving Fe(CN)6 and zinc uroporphyrin.

Carapellucci, P. A.↗

NASA NTRS1984

Thermoplastic composite matrices with improved solvent resistance

In order to improve solvent resistance of aromatic thermoplastic polymers, ethynyl-terminated aromatic sulfone polymers (ETS), sulfone/ester polymers (SEPE) containing pendent ethynyl groups, and phenoxy resin containing pendent ethynyl groups are synthesized. Cured polysulfones and phenoxy resins containing ethynyl groups on the ends or pendent on the molecules exhibited systematic behavior in solvent resistance, film flexibility, and toughness as a function of crosslink density. The film and composite properties of a cured solvent-resistant ETS were better than those of a commercially available solvent sensitive polysulfone. The study was part of a NASA program to better understand the trade-offs between solvent resistance, processability and mechanical properties which may be useful in designing composite structures for aerospace vehicles.

Hergenrother, P. M.↗