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At least 163 records · Page 9

All sources NASA NTRS DOE OSTI

NASA NTRS2010

High Temperature VARTM of Phenylethynyl Terminated Imides (PETI) Resins

Fabrication of composite structures using vacuum assisted resin transfer molding (VARTM) is generally more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications a void fraction of less than 2% is desired. In the current study, two PETI resins, LARCTM PETI-330 and LARCTM PETI-8 have been used to fabricate test specimens using HT-VARTM. The resins were infused into carbon fiber preforms at 260 C and cured between 316 C and 371 C. Modifications to the thermal cycle used in the laminate fabrication have reduced the void content significantly (typically < 3%) for carbon fiber biaxially woven fabric. Photomicrographs of the panels were taken and void contents were determined by acid digestion. For carbon fiber uniaxial fabric, void contents of less than 2% have been obtained using both PETI-8 and PETI-330. Mechanical properties of the panels were determined at both room and elevated temperatures. These include short beam shear and flexure tests. The results of this work are presented herein.

Ghose, Sayata↗

NASA NTRS2011

Polyimide Composites Properties of RTM370 Fabricated by Vacuum Assisted Resins Transfer Molding (VARTM)

RTM370 imide resin based on 2,3,3 ,4 -biphenyl dianhydride ( a-BPDA), 3,4 -oxydianinline (3,4 -ODA) with 4-phenylethynylphthalic (PEPA) endcap has shown to exhibit high Tg (370 C) and low melt viscosity (10-30 poise) at 280 C with a pot-life of 1-2 h. Previously, RTM370 resin has been fabricated into composites with T650-35 carbon fabrics by resin transfer molding (RTM) successfully. RTM370 composites exhibit excellent mechanical properties up to 327 C (620 F), and outstanding property retention after aging at 288 C (550 F) for 1000 hrs. In this presentation, RTM 370 composites will be fabricated by vacuum assisted resins transfer molding (VARTM), using vacuum bags without mold. The mechanical properties of RTM370 composites fabricated by VARTM will be compared to those of RTM370 made by RTM.

Chuang, Kathy C.↗

NASA NTRS2011

Effects of Hygrothermal Cycling on the Chemical, Thermal, and Mechanical Properties of 862/W Epoxy Resin

The hygrothermal aging characteristics of an epoxy resin were characterized over 1 year, which included 908 temperature and humidity cycles. The epoxy resin quickly showed evidence of aging through color change and increased brittleness. The influence of aging on the material s glass transition temperature (Tg) was evaluated by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). The Tg remained relatively constant throughout the year long cyclic aging profile. The chemical composition was monitored by Fourier Transform Infrared Spectroscopy (FTIR) where evidence of chemical aging and advancement of cure was noted. The tensile strength of the resin was tested as it aged. This property was severely affected by the aging process in the form of reduced ductility and embrittlement. Detailed chemical evaluation suggests many aging mechanisms are taking place during exposure to hygrothermal conditions. This paper details the influence of processes such as: advancement of cure, chemical degradation, and physical aging on the chemical and physical properties of the epoxy resin.

Miller, Sandi G.↗

NASA NTRS2011

Composite Properties of RTM370 Polyimide Fabricated by Vacuum Assisted Resin Transfer Molding (VARTM)

RTM370 imide resin based on 2,3,3?,4?-biphenyl dianhydride (a-BPDA), 3,4'-oxydianinline (3,4'-ODA) with the 4-phenylethynylphthalic (PEPA) endcap has been shown to exhibit a high cured T(sub g) (370 C) and low melt viscosity (10-30 poise) at 280 C with a pot-life of 1-2 h. Previously, RTM370 resin has been successfully fabricated into composites reinforced with T650-35 carbon fabrics by resin transfer molding (RTM). RTM370 composites exhibit excellent mechanical properties up to 327?C (620?F), and outstanding property retention after aging at 288?C (550?F) for 1000 h. In this work, RTM370 composites were fabricated by vacuum assisted resin transfer molding (VARTM), using vacuum bags on a steel plate. The mechanical properties of RTM370 composites fabricated by VARTM are compared to those prepared by RTM.

Chuang, Kathy C.↗

NASA NTRS2013

Process Optimization of Bismaleimide (BMI) Resin Infused Carbon Fiber Composite

Engineers today are presented with the opportunity to design and build the next generation of space vehicles out of the lightest, strongest, and most durable materials available. Composites offer excellent structural characteristics and outstanding reliability in many forms that will be utilized in future aerospace applications including the Commercial Crew and Cargo Program and the Orion space capsule. NASA's Composites for Exploration (CoEx) project researches the various methods of manufacturing composite materials of different fiber characteristics while using proven infusion methods of different resin compositions. Development and testing on these different material combinations will provide engineers the opportunity to produce optimal material compounds for multidisciplinary applications. Through the CoEx project, engineers pursue the opportunity to research and develop repair patch procedures for damaged spacecraft. Working in conjunction with Raptor Resins Inc., NASA engineers are utilizing high flow liquid infusion molding practices to manufacture high-temperature composite parts comprised of intermediate modulus 7 (IM7) carbon fiber material. IM7 is a continuous, high-tensile strength composite with outstanding structural qualities such as high shear strength, tensile strength and modulus as well as excellent corrosion, creep, and fatigue resistance. IM7 carbon fiber, combined with existing thermoset and thermoplastic resin systems, can provide improvements in material strength reinforcement and deformation-resistant properties for high-temperature applications. Void analysis of the different layups of the IM7 material discovered the largest total void composition within the [ +45 , 90 , 90 , -45 ] composite panel. Tensile and compressional testing proved the highest mechanical strength was found in the [0 4] layup. This paper further investigates the infusion procedure of a low-cost/high-performance BMI resin into an IM7 carbon fiber material and the optical, chemical, and mechanical analyses performed.

Ehrlich, Joshua W.↗

NASA NTRS2013

Assessment of Service Life for Regenerative ECLSS Resin Beds

The International Space Station (ISS) Water Processor Assembly (WPA) and Oxygen Generation Assembly (OGA) manage and process water at various levels of cleanliness for multiple purposes. The effluent of theWPA and the influent of the OGA require water at very high levels of purity. The bulk of the water purification that occurs in both systems is performed by consumable activated carbon and ion exchange resin beds. Replacement beds must be available on orbit in order to continue the ISS critical processes of water purification and oxygen generation. Various hurdles exist in order to ensure viable spare resin beds. These include the characteristics of resin beds such as: storage environment, shelf life requirements, microbial growth, and variations in the levels and species of contaminants the beds are required to remove. Careful consideration has been given to match water models, bed capacities and spares traffic models to ensure that spares are always viable. The results of these studies and considerations, in particular, how shelf life requirements affect resin bed life management, are documented in this paper.

Cloud, Dale L.↗

NASA NTRS2019

Characterization of New TPS Resins

Ablative thermal protection systems are commonly used as protection from the intense heat during re-entry of a space vehicle and have been used successfully on many missions including Stardust and Mars Science Laboratory both of which used PICA a phenolic based ablator. Historically, phenolic resin has served as the ablative polymer for many TPS systems. However, it has limitations in both processing and properties such as char yield, glass transition temperature and char stability. Therefore alternative high performance polymers are being considered such as: cyanate ester resin, polyimide, polybenzoxazine (PBZ), and polyimidazole (PBI).Thermal and mechanical properties of these four resin systems were characterized and compared with phenolic resin.

Boghozian, T.↗

NASA NTRS2021

Latent Cure Epoxy Resins for Reliable Joints in Secondary-Bonded Composite Structures

In high-performance polymer matrix composite assemblies, adhesive bonding is generally superior to mechanical fastening in structural performance and manufacturing efficiency. However, adhesive bonds are susceptible to minute levels of contamination accumulated during assembly that can lead to unpredictable, weak bonds. Current methods of measuring bond strength are all destructive mechanical tests. To overcome these challenges, redundant load paths (e.g., mechanical fasteners) are often implemented in secondary-bonded, primary-structures, which can greatly reduce structural performance. This study investigated reformulated aerospace epoxy matrix resins with stoichiometric offset to inhibit cure of the matrix resin prior to assembly. Inhibited resins can reflow and mix across the joint interface, which eliminates the material discontinuity and forms a homogenous joint with reliable fracture properties. The goal of this study was to develop and demonstrate secondary composite assemblies that are mechanically and microscopically indistinguishable from a co-cured composite joint. This article describes the development of latent epoxy resins, the fabrication of test articles, and the mechanical properties measured from experimental joints compared with conventional, co-cured laminates. Methods of in-line quality control using and infrared spectroscopy and post-assembly forensics are also described. The final mode-II fracture toughness measured from precracked AERoBOND specimens was similar to that measured from co-cured laminates indicating that later cure epoxy materials could be a suitable replacement for secondary bonding.

Polymer-matrix composites (PMCs)↗

NASA NTRSDate not supplied

Predicting Char Yield of High-Temperature Resins

A simulation protocol is developed to predict the char yield of organic resins during high-temperature processing. Such in silico methods can help screen promising new formulations for advanced materials, but previously no chemistry-sensitive technique existed to predict the important experimental value of char yield. The method utilizes a reactive force field (ReaxFF) to model the chemical transformation of precursor monomers into carbonized structures during three processing stages: ramp-up to processing temperatures (~3000 K), pyrolysis, and quenching. Achieving good agreement with experimental char yields requires continuous removal of small byproduct molecules to mimic outgassing, and the application of high pressure to eliminate porosity and encourage graphitization. More than ten different resin chemistries are investigated, including arylacetylenes, cyanate esters, phthalonitriles, and polyimides, representing a diverse group of precursors with respect to initial cyclic content, heteroatoms and reactive groups. The protocol correctly predicts the relative char yield between the investigated chemistries and provides quantitative agreement with experimental values, especially for high char yield resins. The properties of the resins during processing are compared, including outgassing products, morphology of the final chemical configurations, cyclic content and mechanical properties.

polymer simulations, molecular dynamics↗

NASA NTRS2023

Dynamic Crush Performance of Thermoplastic and Resin Infused Thermoset Triaxially Braided Composite Structures

Dynamic crush tests were conducted on triaxially braided composite tubes and C-channel structural elements to measure their relative energy absorbing characteristics. The elements were manufactured from triaxially braided [0/+60/-60] T700 fiber preforms with two different resin systems, a PR520 thermoset resin and a LM-PAEK thermoplastic resin. T700/PR520 composite tubes and C-channel elements were manufactured using a resin infusion process. T700GC/LMPAEK composite tubes were manufactured by braiding slit tape prepreg onto cylindrical mandrels. Consolidation pressure was applied through thermally activated shrink tape in an oven. The energy absorbing characteristics of the composite elements were measured using a pneumatically actuated sled with a flat-faced impacting mass, which provided several independent measurements of force, displacement, and energy absorption. The parameter primarily used for comparison between the systems was the specific energy absorption (SEA), a measure of energy absorbed per unit crushed length. The T700/LMPAEK tubes performed slightly better than T700/PR520 tubes, with an approximately 9% higher SEA. T700/PR520 tubes had over 20% higher SEA than C-channels made from the same material. Additional tests were conducted on tubes using a tapered-conical impactor to force the tubes to fail in circumferential tension. This type of impact significantly reduced the energy absorption.

Composite Materials↗

NASA NTRSDate not supplied

Predicting Char Yield of High-Temperature Resins

A simulation protocol is developed to predict the char yield of organic resins during high-temperature processing. Simulation protocol in silico methods can help screen promising new formulations for advanced materials, but previously no chemistry-sensitive technique existed to predict the important experimental value of char yield. The method utilizes a reactive force field (ReaxFF) to model the chemical transformation of precursor monomers into carbonized structures during three processing stages: ramp-up to processing temperatures (~3000 K), pyrolysis, and quenching. Achieving good agreement with experimental char yields requires continuous removal of small byproduct molecules to mimic outgassing, and the application of high pressure to eliminate porosity and encourage graphitization. More than ten different resin chemistries are investigated, including arylacetylenes, cyanate esters, phthalonitriles, and polyimides, representing a diverse group of precursors with respect to initial cyclic content, heteroatoms and reactive groups. The protocol correctly predicts the relative char yield between the investigated chemistries and provides quantitative agreement with experimental values, especially for high char yield resins. The properties of the resins during processing are compared, including outgassing products, morphology of the final chemical configurations, cyclic content and mechanical properties.

polymer simulations, molecular dynamics↗

NASA NTRS2023

Dynamic Crush Performance of Thermoplastic and Resin Infused Thermoset Triaxially Braided Composite Structures

Composite Materials↗

DOE OSTI2025

Exploring the Functional Performance of a Commercial High-Temperature Photopolymer Resin for Vat Photopolymerized Injection Molding Tools

Additive manufacturing (AM) presents a promising approach for rapid tooling, offering significant reductions in production costs and lead times compared to that of conventional moldmaking processes. This work examines the fabrication of molds for injection molding through vat photopolymerization (VPP) AM, using a commercially available photopolymer resin intended for high temperature applications (High Temp V2 resin). The photorheological behavior of the resin is examined to evaluate its curing kinetics and mechanical development during polymerization, ensuring suitability for mold fabrication. The thermal and mechanical properties of the printed photopolymer resin are characterized, alongside assessments of dimensional accuracy and surface finish, which are critical factors influencing the performance and quality of injection molded parts. Additionally, specimens produced using VPP-fabricated molds are evaluated and benchmarked against those molded with traditional metal molds.

Jones, Haley W. [Savannah River National Laborator↗

DOE OSTI2024

Enhanced CO 2 Adsorption Capacity in Highly Porous Carbon Materials Derived from Melamine-Formaldehyde Resin

Here, the present study explores the synthesis of N-doped carbon materials with large surface porosity using commercial melamine-formaldehyde resin as the precursor and KOH as the activator. The resin was carbonized first and then activated by KOH with varying KOH amount and activation temperature. Notably, the as-obtained sorbents display advanced porosity with the highest surface area and pore volume of 1591 m 2 /g and 0.74 cm 3 /g, respectively, along with high N content ranging from 6.43 to 18.34 wt %. Remarkably, maximum CO 2 capture amounts of 5.42 and 3.52 mmol/g were accomplished at 0 and 25 degrees C, 1 bar for as-synthesized carbons. Systematic studies point out that narrow microporosity is the major factor determining the CO 2 uptake of these carbons under ambient pressure. Furthermore, these sorbents display notable CO 2 selectivity, rapid adsorption kinetics, moderate heat of adsorption, substantial dynamic CO 2 capture capacity, and stable recyclability. These results underscore the potential of melamine-formaldehyde resin-derived N-doped porous carbon as an efficient and versatile adsorbent for CO 2 capture.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Extraction and separation of rare earth elements using LN resins in hydrochloric acid

The separation of the rare earth elements is essential for numerous scientific applications but remains a significant challenge due to the nearly identical chemical properties of the adjacent lanthanide elements. Eichrom’s LN series of extraction chromatographic resins feature organophosphorus extractants and are widely used to achieve adjacent lanthanide separations. While extensive characterization of these resins has been completed for nitric acid matrices, the use of hydrochloric acid is preferred for a variety of applications. Further, the extraction of the rare earth elements, La–Lu and Y, has been characterized on LN and LN2 resins in hydrochloric acid via batch uptake and column chromatographic studies.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

DOE OSTI2024

Mapping Structure and Rheology of pH-Responsive Resins for Low-VOC Coatings

In recent years, the paint and coatings industry has shifted away from traditional resin formulations that require high concentrations of volatile organic compounds (VOCs) to achieve the desired rheological performance and sustainability targets. One approach to eliminate or reduce VOCs in paint and coating formulations while maintaining the final performance is to disperse stimuli-responsive polymer latex particles in water. The chemistry and architecture of these particles have been engineered such that the suspension rheology changes in response to the pH changes. The particles can also be swollen with organic solvents to illicit similar rheological changes. To understand how the particle microstructure influences the observed macroscopic properties, we use small-angle neutron scattering and dynamic light scattering to determine that these particles consist of a cross-linked core with long polymer tails that extend into the dispersing medium. Carboxylic acid groups present on the tails deprotonate with increasing pH, and the extension of the polymer chain due to charge repulsion increases the hydrodynamic drag on the particle. Here we find that adjusting the pH alone has a much more significant effect on the shear dependence of the viscosity of the studied resin than adding organic solvent alone. We also find that this resin architecture is more responsive per mole of pH-responsive group than other architectures of pH-responsive latex particles in the literature.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Enhancing Resource Recovery through Electro-Assisted Regeneration of an Ammonia-Selective Cation Exchange Resin

Ammonia-selective adsorbents can manage reactive nitrogen in the environment and promote a circular nutrient economy. Weak acid cation exchangers loaded with zinc exhibit high ammonia selectivity but face two implementation barriers: the stability of the zinc–carboxylate bond in complex wastewaters and energy- and logistics-intensive adsorbent regeneration with acidic solutions. In this paper, we examined the stability of zinc–carboxylate bonds in varying solutions (pure ammonium solution, synthetic urine, and real urine) and during electro-assisted regeneration. For electrochemical regeneration, both electrolyte concentration and current density influenced the trade-off between ammonia regeneration and zinc elution. Using 10 mM K 2 SO 4 anolyte at a 0.08 mA/cm 2 current density, we achieved 4% zinc elution and 61% ammonia regeneration. In contrast, using 100 mM K 2 SO 4 at 4.96 mA/cm 2 improved the regeneration efficiency to 97% but eluted 60% of zinc. We found that electrolyte concentration was the key factor influencing the regeneration efficiency of the NH 3 -selective adsorbents. Due to prevalent zinc elution, we designed an in situ procedure for reforming the zinc–carboxylate bond and achieved similar adsorption densities between pre- and post-regenerated resins, thus enabling multiple cycle resin use. Ultimately, this study advances understanding of ammonia-selective resins that can facilitate high-purity, selective, and durable recovery of nutrients from waste streams.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

A Mechanism-Based Reaction–Diffusion Model for Accelerated Discovery of Thermoset Resins Frontally Polymerized by Olefin Metathesis

Frontal ring-opening metathesis polymerization (FROMP) involves a self-perpetuating exothermic reaction, which enables the rapid and energy-efficient manufacturing of thermoset polymers and composites. Current state-of-the-art reaction–diffusion FROMP models rely on a phenomenological description of the olefin metathesis kinetics, limiting their ability to model the governing thermo-chemical FROMP processes. Furthermore, the existing models are unable to predict the variations in FROMP kinetics with changes in the resin composition and as a result are of limited utility toward accelerated discovery of new resin formulations. In this work, we formulate a chemically meaningful model grounded in the established mechanism of ring-opening metathesis polymerization (ROMP). Our study aims to validate the hypothesis that the ROMP mechanism, applicable to monomer-initiator solutions below 100 °C, remains valid under the nonideal conditions encountered in FROMP, including ambient to >200 °C temperatures, sharp temperature gradients, and neat monomer environments. Through extensive simulations, we demonstrate that our mechanism-based model accurately predicts the FROMP behavior across various resin compositions, including polymerization front velocities and thermal characteristics (e.g., T max ). Additionally, we introduce a semi-inverse workflow that predicts FROMP behavior from a single experimental data point. Notably, the physiochemical parameters utilized in our model can be obtained through DFT calculations and minimal experiments, highlighting the model’s potential for rapid screening of new FROMP chemistries in pursuit of thermoset polymers with superior thermo-chemo-mechanical properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗