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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Thermoplastic coating of carbon fibers

A continuous powder coating system was developed for coating carbon fiber with LaRC-TPI (Langley Research Center-Thermoplastic Polyimide), a high-temperature thermoplastic polymide invented by NASA-Langley. The coating line developed used a pneumatic fiber spreader to separate the individual fibers. The polymer was applied within a recirculating powder coating chamber then melted using a combination of direct electrical resistance and convective heating to make it adhere to the fiber tow. The tension and speed of the line were controlled with a dancer arm and an electrically driven fiber wind-up and wind-off. The effects of heating during the coating process on the flexibility of the prepreg produced were investigated. The uniformity with which the fiber tow could be coated with polymer also was examined. Composite specimens were fabricated from the prepreg and tested to determine optimum process conditions. The study showed that a very uniform and flexible prepeg with up to 50 percent by volume polymer could be produced with this powder coating system. The coating line minimized powder loss and produced prepeg in lengths of up to 300 m. The fiber spreading was found to have a major effect on the coating uniformity and flexibility. Though test results showed low composite tensile strengths, analysis of fracture surfaces under scanning electron microscope indicated that fiber/matrix adhesion was adequate.

Edie, D. D.↗
DOE OSTI2022

Carbon fibers derived from commodity polymers: A review

Carbon fiber composites are prohibitively expensive for a wide array of applications that would greatly benefit from their superior specific strength and specific stiffness. Replacing the market-dominant carbon fiber precursor material, polyacrylonitrile, with a low-cost alternative would significantly reduce the cost of carbon fiber production. Commodity polymers may provide such an alternative thanks to their abundance and ease of production into fibers. Furthermore, this review presents state-of-the-art carbon fiber production from polyacrylonitrile, an overview of melt-spinnable alternative precursors broadly, and an in-depth review of the latest advances in the synthesis of carbon fibers from low-cost, commodity thermoplastics such as polyethylene, polyamide, polystyrene, polyester, and poly(vinyl chloride).

36 MATERIALS SCIENCE↗
NASA NTRS1986

Semi-interpenetrating networks of LARC-TPI

In a previous research project at NASA-Langley, a novel semi-2-interpenetrating polymer network (semi-2-IPN) was prepared from the linear, thermoplastic polyimidesulfone, and the more brittle, crosslinked, acetylene-terminated imidesulfone. Synergistic qualities such as improved thermooxidative stability and better processability were achieved from this combination. The novelty of the system lay in the fact that the structures of the linear and crosslinking components were nearly identical. This similarity in structure eliminates any phase separation problems common to many-IPNs. In a similar way, a semi-2-IPN was prepared from linear, thermoplastic LARC-TPI and acetylene-terminated LARC-TPI (ATLARC-TPI). The preparation and characterization of this system will be discussed as well as adhesive and composite data.

Egli, Annemarie H.↗
DOE OSTI2024

Testing Protocol Development for the Fracture Toughness of Parts Built with Big Area Additive Manufacturing

The mechanical testing of additively manufactured parts has largely relied on the existing standards developed for traditional manufacturing. While this approach leverages the investment made in current standards development, it inaccurately assumes that the mechanical response of additive manufacturing (AM) parts is identical to that of parts manufactured through traditional processes. When considering thermoplastic, material extrusion AM, the differences in response can be attributed to an AM part’s inherent inhomogeneity caused by porosity, interlayer zones, and surface texture. Additionally, the interlayer bonding of parts printed with large-scale AM is difficult to adequately assess, as much testing is performed such that stress is distributed across many layer interfaces; therefore, the lack of AM-specific standards to assess interlayer bonding is a significant research gap. To quantify interlayer bonding via fracture toughness, double cantilever beam (DCB) testing has been used for some AM materials, and DCB has been generally used for a variety of materials including metal, wood, and laminates. Mode I DCB testing was performed on thermoplastic matrix composites printed with Big Area Additive Manufacturing (BAAM). Of particular interest was the notch shape and deflection speed during testing. The results examine the differences when using two notch types and three deflection speeds. The testing method introduced by the following paper differentiates itself from the ones described in the standards used by modernizing the methodology. This was conducted with the introduction of Digital Image Correlation (DIC) to gather displacement and load data simultaneously without human intervention.

Polymer Science↗
NASA NTRS1998

Global Failure Modes in High Temperature Composite Structures

Composite materials have been considered for many years as the major advance in the construction of energy efficient aerospace structures. Notable advances have been made in understanding the special design considerations that set composites apart from the usual "isotropic" engineering materials such as the metals. As a result, a number of significant engineering designs have been accomplished. However, one shortcoming of the currently favored composites is their relatively unforgiving behavior with respect to failure (brittleness) under seemingly mild impact conditions and large efforts are underway to rectify that situation, much along the lines of introducing thermoplastic matrix materials. Because of their relatively more pronounced (thermo) viscoelastic behavior these materials respond with "toughness" in fracture situations. From the point of view of applications requiring material strength, this property is highly desirable. This feature impacts several important and distinct engineering problems which have been' considered under this grant and cover the 1) effect of impact damage on structural (buckling) stability of composite panels, the 2) effect of time dependence on the progression of buckling instabilities, and the 3) evolution of damage and fracture at generic thickness discontinuities in structures. The latter topic has serious implications for structural stability problems (buckling failure in reinforced shell structures) as well as failure progression in stringer-reinforced shell structures. This grant has dealt with these issues. Polymer "toughness" is usually associated with uncrosslinked or thermo-plastic polymers. But, by comparison with their thermoset counterparts they tend to exhibit more pronounced time dependent material behavior; also, that time dependence can occur at lower temperatures which places restriction in the high temperature use of these "newer and tougher" materials that are not quite so serious with the thermoset matrix materials. From a structural point of view the implications of this material behavior are potentially severe in that structural failure characteristics are no longer readily observed in short term qualification tests so characteristic for aerospace structures built from typical engineering metals.

Knauss, W. G.↗
DOE OSTI2026

Tunable PA6 Polymer System for Thermoplastic Reinforced Body Panels

Project Goal: Overall, a redesigned polyamide system will combine the ductility and processing of a PA6 matrix, the strength and modulus of CF, and the facile recyclability of esters. Approach: PEA can be synthesized under conventional, industrially relevant pathways. Material properties and processing will be analyzed and compared to commercial PA6 material. Results: Polycondensation, traditional for polyesters, was successful in synthesized a PEA. PEA exhibited fast crystallization and bimodal melting behavior suggesting beneficial crystallization kinetics. PEA exhibit reduced melting temperatures owed to the incorporation of ester units in the polymer structure.

42 ENGINEERING↗
DOE OSTI2025

Compatibilization Strategy and Mechanism for Co-stabilizing Commingled Plastics and Pyrolyzed Rubber in Asphalt

Hot mix asphalt mixture is considered the ideal approach to reuse waste plastics in high-value applications because of its very high amount of usage in highway construction. However, the differences in polarity and density between polymers and asphalt lead to polymer coalescence and therefore the poor storage stability of modified asphalt. These challenges are exalted when recycling commingled plastics. This study introduced an innovative compatibilization strategy and mechanism for co-stabilizing commingled plastics and pyrolyzed rubber in asphalt. Commingled plastics were first grafted with maleic anhydride for surface activation, followed by reactive kneading with pyrolyzed rubber and crosslinking agent to form an integrated thermoplastic elastomer (ITPE) for asphalt modification. The mechanical, thermal, and interfacial behaviors of the ITPE were evaluated through tensile testing, thermogravimetric analysis, and scanning electron microscopy. The storage stability and rheological properties of the modified binder blends were evaluated through the cigar tube test and dynamic shear rheometer testing. Results demonstrated a successful formation of imide bonds in the ITPE, which can improve the strength, ductility, and thermal stability of rubber–plastic composites. Appropriate utilization of crosslinking agents can improve both rutting and fatigue resistance of ITPE-modified asphalt with good storage stability because of the co-existence of rigid plastic and soft rubbery regimes and the formation of a crosslink network. Furthermore, excessive content of crosslinker led to severe phase separation and reduced storage stability of modified binder blends. Extra crosslinker tended to float in asphalt because of its low density and caused an excessive formation of the crosslink network in the top section of the asphalt.

asphalt binder modifiers↗
NASA NTRS1990

LARC-IA: A flexible backbone polyimide

A new linear, aromatic, thermoplastic polyimide, prepared from oxydiphthalic anhydride (ODPA) and 3,4'-oxydianiline (ODA) in diglyme and identified as LARC-IA, was synthesized and evaluated. The monomers are relatively inexpensive and physiologically safe. Molecular weight was controlled by use of a monofunctional anhydride, phthalic anhydride (PA), in order to promote controlled flow and wetting properties. The polymer is considered a safe alternative to commercially available LARC-TPI which is prepared with an expensive diamine of uncertain carcinogenicity. The evaluation was based primarily on the polymer's adhesive properties as determined by thermal and water boil exposure of lap shear specimens. Strengths were determined at room temperature, 177, 204 and 232 C before and after exposure to determine the adhesive system's durability to adverse environments over a period of time. Other properties (FWT, G(1c), film and composite properties) were examined which were determined to be typical of a high temperature polyimide. Results of the study show a favorable comparison to LARC-TPI, a commercially available polyimide.

Progar, Donald J.↗
DOE OSTI2025

Enabling Industrial Re-Use of Large-Format Additive Manufacturing Molding and Tooling

Large-format additive manufacturing (LFAM) is an enabling manufacturing technology capable of producing large parts with highly complex geometries for a wide variety of applications, including automotive, infrastructure/construction, and aerospace mold and tooling. In the past decade, the LFAM industry has seen widespread use of bio-based, glass, and/or carbon fiber reinforced thermoplastic composites which, when printed, serve as a lower-cost alternative to metallic parts. One of the highest-volume materials utilized by the industry is carbon fiber (CF)-filled polycarbonate (PC), which in out-of-autoclave applications can achieve comparable mechanical performance to metal at a significantly lower cost. Previous work has shown that if this material is recovered at various points throughout the manufacturing process for both the lab and pilot scale, it can be mechanically recycled with minimal impacts on the functional performance and printability of the material while significantly reducing the feedstock costs. End-of-life (EOL) CF-PC components were processed through industrial shredding, melt compounding, and LFAM equipment, followed by evaluation of the second-life material properties. Experimental assessments included quantitative analysis of fiber length attrition, polymer molecular weight degradation using gel permeation chromatography (GPC), density changes via pycnometry, thermal performance using dynamic mechanical analysis (DMA), and mechanical performance (tensile properties) in both the X- and Z-directions. Results demonstrated a 24.6% reduction in average fiber length compared to virgin prints, accompanied by a 21% decrease in X-direction tensile strength and a 39% reduction in tensile modulus. Despite these reductions, Z-direction tensile modulus improved by 4%, density increased by 6.8%, and heat deflection temperature (HDT) under high stress retained over 97% of its original value. These findings underscore the potential for integrating mechanically recycled CF-PC into industrial LFAM applications while highlighting the need for technological innovations to mitigate fiber degradation and enhance material performance for broader adoption. This critical step toward circular material practices in LFAM offers a pathway to reducing feedstock costs and environmental impact while maintaining functional performance in industrial applications.

additive manufacturing↗
DOE OSTI2026

Design, characterization and shape recovery behavior of 3D/4D printed shape memory polymers (SMPs)

Shape memory polymers (SMPs) represent a paradigm shift in material science, uniquely capable of undergoing reversible shape transformations triggered by external stimuli, positioning them as pivotal in developing next-generation biomedical devices, aerospace components, and adaptive structures. Extensive research has been done on SMPs with a major focus on high-temperature programming methods, which can limit energy efficiency and applicability with temperature-sensitive materials. Additionally, while various SMP blends have demonstrated great potential, limited work has been done on the suitability for 3D printing these materials, particularly under high-strain and ambient temperature programming conditions. In this study, a three-component optimized SMP composition was evaluated by 3D printing via the Material Extrusion (MEX) technique and investigating its ambient temperature-programming behavior at high strains. The SMP formulation studied was a tailored blend of thermoplastic polyurethane (TPU), polycaprolactone (PCL), and an octadecane diol-based copolymer (OBC) that exhibits robust shape memory behavior, high strain tolerance, and efficient force generation. Rigorous thermal, mechanical, and shape recovery analyses, along with optimized printing parameters and consistent shape recovery rates of up to 90%, were achieved under dynamic mechanical analysis (DMA), even under ambient programming conditions. This work demonstrates the SMP composition’s potential for adaptive, self-deployable systems with 4D printing characteristics ideal for bio-inspired structures and artificial muscle fibers.

Sudan, Kavish [University of Louisville, KY]↗
NASA NTRSDate not supplied

Evaluation of Hydrolytic Degradation of Poly(lactic acid) (PLA) Matrices in Compression Molded Flax/PLA Composites

Poly(lactic acid) (PLA) is a bio-based plastic that is an attractive alternative to its petroleum-based counterparts because of its high strength and ease of thermal processing. In an effort to reduce the carbon footprint of fossil-fuel based polymer matrix composites, PLA along with naturally-occurring fibers are being explored to produce entirely bio-based replacements. Challenges in producing these composites occur due to the water affinity of the natural fibers and the susceptibility of the PLA to hydrolytic degradation. Hydrolysis of PLA occurs at elevated processing temperatures and can further be accelerated by the presence of water contained in the natural fibers. This talk will discuss the challenges and considerations associated with processing PLA in the presence of water-absorbing flax fibers to produce composites via compression molding. The thermal, physical, and mechanical properties of PLA/flax composites will be characterized at various processing times in an effort to identify optimal manufacturing conditions.

Natural Materials↗
NASA NTRS1981

Flow properties of a series of experimental thermoplastic polymides

The softening temperature to degradation temperature range of the polymers was about 440 to 650 K. All of the polymers retained small amounts of solvent as indicated by an increase in T(sub g) as the polymers were dried. The flow properties showed that all three polymers had very high apparent viscosities and would require high pressures and/or high temperatures and/or long times to obtain adequate flow in prepregging and molding. Although none was intended for such application, two of the polymers were combined with carbon fibers by solution prepregging. The prepregs were molded into laminates at temperatures and times, the selection of which was guided by the results from the flow measurements. These laminates had room temperature short beam shear strength similar to that of carbon fiber laminates with a thermosetting polyimide matrix. However, the strength had considerable scatter, and given the difficult processing, these polymides probably would not be suitable for continuous fiber composites.

Burks, H. D.↗
DOE OSTI2020

Recent Advances in the Application of Functionalized Lignin in Value-Added Polymeric Materials

The quest for converting lignin into high-value products has been continuously pursued in the past few decades. In its native form, lignin is a group of heterogeneous polymers comprised of phenylpropanoids. The major commercial lignin streams, including Kraft lignin, lignosulfonates, soda lignin and organosolv lignin, are produced from industrial processes including the paper and pulping industry and emerging lignocellulosic biorefineries. Although lignin has been viewed as a low-cost and renewable feedstock to replace petroleum-based materials, its utilization in polymeric materials has been suppressed due to the low reactivity and inherent physicochemical properties of lignin. Hence, various lignin modification strategies have been developed to overcome these problems. Herein, we review recent progress made in the utilization of functionalized lignins in commodity polymers including thermoset resins, blends/composites, grafted functionalized copolymers and carbon fiber precursors. In the synthesis of thermoset resins such as polyurethane, phenol-formaldehyde and epoxy, they are covalently incorporated into the polymer matrix, and the discussion is focused on chemical modifications improving the reactivity of technical lignins. In blends/composites, functionalization of technical lignins is based upon tuning the intermolecular forces between polymer components. In addition, grafted functional polymers have expanded the utilization of lignin-based copolymers to biomedical materials and value-added additives. Different modification approaches have also been applied to facilitate the application of lignin as carbon fiber precursors, heavy metal adsorbents and nanoparticles. These emerging fields will create new opportunities in cost-effectively integrating the lignin valorization into lignocellulosic biorefineries.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of natural carbon filler on thermo-oxidative degradation of thermoplastic-based composites

Here thermo-oxidative degradation of thermoplastic-based composites filled with two types of carbon filler including bituminous (Pittsburgh No.8, P8) and sub-bituminous (Powder River Basin, PRB) coals were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. Oxidation induction time (OIT) and activation energy (AE) for coal plastic composites (CPCs), HDPE, and commercially available wood plastic composites (WPCs) were determined using isothermal and isoconversional kinetic methods. OIT values for CPC increased with coal content, indicating higher thermo-oxidative stability. AE values obtained using isothermal method were 52–116 kJ/mol for all CPC formulations, 32 kJ/mol for HDPE, and 33–114 kJ/mol for WPCs. AEs for CPCs obtained using isoconversional methods were not constant but rather dependent on the degree of degradation with CPC/ P8 coal possessing higher overall AE. Incorporating coal into HDPE increased thermo-oxidative stability of the resulting composite, indicating coal potentially acts as a natural primary and secondary antioxidant for polymer materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

Multiscale Modeling of Thermoplastics Using Atomistic-informed Micromechanics

A multiscale model was developed for predicting the thermoelastic behavior of semi-crystalline thermoplastic materials for composite aerospace applications. At the highest scale containing the semi-crystalline spherulite in an amorphous matrix, the generalized method of cells, or high fidelity method of cells, was used to perform the homogenization calculations to obtain the effective properties. Models were developed assuming a cubic, or spherical shape, for the spherulite to understand if the morphology of the spherulite affects the effective thermoelastic properties. The generalized method of cells was used to model at the repeating unit cells at the subscales of the microstructure including the lamellae stacks and granular crystal blocks. The scales are integrated using the multiscale micromechanics method in the NASA Multiscale Analysis Tool. Data from molecular dynamics simulations were used as inputs for the amorphous and crystalline constituents. Convergence studies were performed to determine the best level of discretization for the repeating unit cell at the highest scale. Effective Young’s modulus, shear modulus, Poisson’s ratio, coefficient of thermal expansion, and thermal conductivity were predicted for polyether ether ketone and polyether ketone ketone, and very good agreement between the model utilizing the cubic spherulite and the experimental data, where available, was observed for polyether ketone ketone. Normalization of the data for the bulk polyether ketone ketone, against amorphous data, improved the predictions as compared to experimental data. Overall, the high fidelity method of cells predicted a stiffer response then the generalized method of cells as the crystallinity was increased. The shape of the spherulite had a minimal effect on the predicted bulk properties of the polymers.

thermoplastics↗
DOE OSTI2025

One Step Block-like Copolymers from an Upcycled Monomer Using Ring-Opening Metathesis Polymerization

Block-like copolymers can be readily synthesized in one step using monomers with widely separated reactivity ratios. Here, we show that trans,trans,trans-1,5,9-cyclododecatriene (CDT), produced from polybutadiene via cyclodepolymerization (CDP), undergoes gradient copolymerization via ring-opening metathesis polymerization (ROMP) with a selected norbornene monomer to produce a block-like copolymer that exhibits bulk nanophase separation and excellent thermomechanical performance. These data highlight a new ROMP copolymerization system with a sharp compositional drift and introduce a simple pathway to convert waste plastic into a valuable building block for high-value thermoplastic materials.

block copolymer↗
NASA NTRS1986

Characterization of the relationship of the cure cycle chemistry to cure cycle processing properties

Dynamic Dielectric measurements made over a wide range of frequency provide a sensitive and convenient means for monitoring the cure process in thermosets and thermoplastics. The measurement of dielectric relaxation is one of only a few instrumental techniques available for studying molecular properties in both the liquid and solid states. Furthermore, it is probably the only convenient experimental technique for studying the polymerization process of going from a monomeric liquid of varying viscosity to a crosslinked, insoluble, high temperature solid. The objective of the research is to develop on-line dielectric instrumentation for quantitative nondestructive material evaluation and closed loop smart cure cycle control. The key is to relate the chemistry of the cure cycle process to the dielectric properties of the polymer system by correlating the time, temperature, and frequency dependent dielectric measurements with chemical characterization measurements. Measurement of the wide variation in magnitude of the complex permittivity with both frequency and state of cure, coupled with chemical characterization work, have been shown in the laboratory to have the potential to determine: resin quality, composition and age; cure cycle window boundaries; onset of flow and point of maximum flow; extent of and completion of reaction; evolution of volatiles; T sub g; and, crosslinking and molecular weight buildup.

Kranbuehl, D. E.↗
NASA NTRS1991

Emerging polyheterocyclic films, coatings and resins - Thermoplastic polyquinolines

The processing and performance characteristics of a soluble, thermoplastic polyquinoline suggest its utility in a variety of high performance applications. The polymer is characterized by excellent thermal and oxidative stability, very low moisture absorption, good mechanical properties, very low dielectric constant, and an unusually low thermal expansion coefficient. This polymer, designated PQ-100 (TM), can be cast into strong, transparent, free standing films from common solvents. Coatings of variable thickness can be spin-coated on to silicon and other surfaces. After processing into films, PQ-100 (TM) can be rendered insoluble in a wide range of solvents using a proprietary process. The low CTE contributes to very low residual stress when the polymer is spin-coated onto silicon wafers. PQ-100 (TM) is currently under evaluation for use as an interlayer dielectric substrate in high-density interconnect applications, including multichip modules. Many of the characteristics of the polymer also suggest its utility as a high-performance film and as a matrix resin for specialty composite applications.

Hendricks, Neil H.↗