SEARCH · Engineering Papers

Results for “molecular weight”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20

All sources NASA NTRS DOE OSTI

DOE OSTI2021

Coupling of Flavonoid Initiation Sites with Monolignols Studied by Density Functional Theory

Lignin recalcitrance presents a challenge for the development of a bioeconomy that employs lignocellulosic feedstocks. The efficiency of lignin deconstruction is improved by a reduction of molecular weight, and given the discovery that flavones serve as initiation sites in lignin biosynthesis, these molecular weight reductions could potentially be achieved with plant metabolic engineering to over-express flavonoids. Upon increasing the flavonoid content in lignin, the bond strengths and properties of flavonoid-monolignol linkages become increasingly important. To that end, the current work applies density functional theory calculations to elucidate the bond dissociation enthalpies (BDEs) of flavonoid-monolignol linkages, including dimers with oxidized monolignols. Specifically, the dimer bond strengths and monomer hydrogen abstraction energies for the flavonoids tricin, chrysoeriol, luteolin, apigenin, catechin, epicatechin, epigallocatechin, and epigallocatechin gallate are calculated, when coupled to seven natural and engineered monolignols. Results indicate that 4'-O-ß linkage strengths between flavonoids and monolignols are of comparable strength to inter-monolignol ß-O-4 linkages, with average flavonoid-monolignol BDEs of 70.7 kcal/mol relative to ~69.3 kcal/mol in analogous canonical monolignols. Epigallocatechin yielded the lowest 4'-O-ß bond strength of 52.3 kcal/mol when coupled to an oxidized monolignol, while the flavones overall produced lower average BDEs, relative to the flavanols. Substituents at the 3'-C and 5'-C positions on flavonoids affected the dimer linkage strengths to a greater extent than glycosylation or substituents further from the linkage. Erythro and threo stereochemistry across the flavonoid-monolignol linkage library exhibited only small energetic differences and no pronounced correlations. Taken together, the predictions from this work support the concept that higher concentrations of flavonoid initiation sites in lignin may afford linkage properties conducive to more facile lignin depolymerization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1974

Resin/graphite fiber composites

Techniques were developed that provided thermo-oxidatively stable A-type polyimide/graphite fiber composites using the approach of in situ polymerization of monomeric reactants directly on reinforcing fibers, rather than employing separately prepared prepolymer varnish. This was accomplished by simply mixing methylene dianiline and two ester-acids and applying this solution to the fibers for subsequent molding. Five different formulated molecular weight resins were examined, and an optimized die molding procedure established for the 1500 formulated molecular weight system. Extensive ultrasonic inspection of composites was successfully utilized as a technique for monitoring laminate quality. Composite mechanical property studies were conducted with this polyimide resin at room temperature and after various time exposures in a thermo-oxidative environment at 561 K (550 F), 589 K (600 F) and 617 K (650 F). It was determined that such composites have a long term life in the temperature range of 561 K to 589 K. The final phase involved the fabrication and evaluation of a series of demonstration airfoil specimens.

Cavano, P. J.↗

NASA NTRS1984

Relationship of isolated turbulent regions to the general turbulent background, part 4.4A

The atmosphere below 100 km is often referred to as the homosphere; the region above, the heterosphere. In the homosphere, constitutents are mixed, and average molecular weight is constant. In the heterosphere, diffusive separation occurs, and species tend to fractionate; average molecular weight decreases with height. Mixing in the homosphere has its source dynamical (wind) energy. Against this background turbulence, intermittent enhancements of turbulent intensity are observed. Some of these enhancements are long lived -- for example, a turbulent layer at approximately 86 km altitude seems to be almost a permanent feature of the (global) daytime D region, as oserved by partial reflection. This may well be a delineation of the mesopause level, since long-term radio meteor studies have shown approx. 85 km to be the breakpoint between thermospheric circulation above, and mesospheric circulation below. The use of stratosphere-troposphere (ST) radars in the lower atmosphere, and mesosphere-stratosphere-troposphere (MST) and partial-reflection radars in the mesosphere for height/time profiles of turbulent intensity is discussed.

Roper, R. G.↗

NASA NTRS1985

Polyfunctional epoxies. I - Rubber-toughened brominated and nonbrominated formulations for graphite composites. II - Nonrubber versus rubber-toughened brominated formulations for graphite composites

A new trifunctional epoxy resin, Tris-(hydroxyphenyl) methane triglycidyl ether, is compared to a state-of-the-art tetraglycidyl 4,4'-diaminodiphenyl methane (TGDDM), in graphite composites. Rubber-toughened brominated formulations of the epoxy resin are compared to nonbrominated ones in terms of their mechanical performance, environmental stability, thermochemical behavior, and flame retardancy. It is shown that the new resin performs almost the same way as the TGDDM does, but has improved glass transition temperature and environmental properties. Brominated polymeric additives (BPA) of different molecular weights are tested as a Br source to flame retardant graphite epoxy composites. The optimal molecular weight of the BPA and its polymeric backbone length are derived and compared with a 10 percent rubber-toughened formulation of the epoxy resin. Results indicate that when the Br content in the graphite composite is increased without the use of rubber, the mechanical properties improved. The use of BPAs as tougheners for graphite composites is also considered.

Nir, Z.↗

NASA NTRS1989

Characterization of a thermally imidized soluble polyimide film

A soluble aromatic poly(amic acid) film was converted to a soluble polyimide by staging at 25 deg intervals to 325 C and characterized at each interval by several analytical methods. The behavior observed was consistent with an interpretation that a reduction occurred in molecular weight of the poly(amic acid) during the initial stages of cure before the ultimate molecular weight was achieved as a polyimide. This interpretation was supported by the results of solution viscosity, gel permeation chromatography, low angle laser light scattering photometry and infrared spectroscopy analysis. The results serve to increase the fundamental understanding of how polyimides are thermally formed from poly(amic acids).

Young, Philip R.↗

NASA NTRS1990

Characterization of a thermally imidized soluble polyimide film

Young, Philip R.↗

DOE OSTI2020

Poly(N-isopropylacrylamide)-grafted gold nanoparticles at the vapor/water interface

Hypothesis: Grafting nanoparticles surfaces with water-soluble polymers modify interparticle interactions that are pivotal for assembling them into ordered phases. By manipulating salt concentrations of gold nanoparticles (AuNPs) that are grafted with poly(N-isopropylacrylamide) (PNIPAM-AuNPs), we hypothesize that various aggregated phases form at the suspension/vapor interface or in the bulk that depend on the molecular weight (MW) of PNIPAM and on salt concentrations. Experiments: AuNPs are grafted with thiolated PNIPAM of molecular weights of 3 or 6 kDa, and grafting is confirmed by dynamic light scattering. Liquid-surfaces X-ray reflectivity and grazing incidence small-angle X-ray scattering are used to determine the density profiles of the suspension/vapor interface and their inplane structure as salt is added to the suspensions. Findings: We observe that surface enrichment is induced by adding NaCl to the suspensions, and that at low salt concentrations, the monoparticle layer formed is dispersed, and above a threshold salt concentration, depending on MW of PNIPAM, the PNIPAM-AuNPs order in a hexagonal structure. We show that the lattice constant of the two-dimensional hexagonal structure varies with salt concentration, and more significantly with MW of PNIPAM.

36 MATERIALS SCIENCE↗

NASA NTRS1994

Phenylethynyl-Terminated Polyimides

Phenylethynyl-terminated polyimides exhibit properties suitable for films, moldings, adhesives, and composite-material matrices. Polyimides synthesized at various molecular weights, selected to obtain desirable properties for specific applications. Thermally cured to form cross-linked molecular structures typically increasing resistance to solvents, glass-transition temperatures, and moduli of elasticity. Also have low molecular weights and low melt viscosities for easier processing into composites and adhesive bonds.

Jensen, Brian J.↗

NASA NTRS2000

The Role of Electrolyte Upon the SEI Formation Characteristics and Low Temperature Performance of Lithium-Ion Cells With Graphite Anodes

Quarternary lithium-ion battery electrolyte solutions containing ester co-solvents in mixtures of carbonates have been demonstrated to have high conductivity at low temperatures (< -20C). However, in some cases the presence of such co-solvents does not directly translate into improved low temperature cell performance, presumably due to the formation of ionically resistive surface films on carbonaceous anodes. In order to understand this behavior, a number of lithium-graphite cells have been studied containing electrolytes with various ester co-solvents, including methyl acetate (MA), ethyl acetate (EA), ethyl propionate (EP), and ethyl butyrate (EB). The charge/discharge characterization of these cells indicates that the higher molecular weight esters result in electrolytes which possess superior low temperature performance in contrast to the lower molecular weight ester-containing solutions, even though these solutions display lower conductivity values.

Smart, M. C.↗

NASA NTRS2004

Reduced Gravity Studies of Soret Transport Effects in Liquid Fuel Combustion

Soret transport, which is mass transport driven by thermal gradients, can be important in practical flames as well as laboratory flames by influencing transport of low molecular weight species (e.g., monatomic and diatomic hydrogen). In addition, gas-phase Soret transport of high molecular weight fuel species that are present in practical liquid fuels (e.g., octane or methanol) can be significant in practical flames (Rosner et al., 2000; Dakhlia et al., 2002) and in high pressure droplet evaporation (Curtis and Farrell, 1992), and it has also been shown that Soret transport effects can be important in determining oxygen diffusion rates in certain classes of microgravity droplet combustion experiments (Aharon and Shaw, 1998). It is thus useful to obtain information on flames under conditions where Soret effects can be clearly observed. This research is concerned with investigating effects of Soret transport on combustion of liquid fuels, in particular liquid fuel droplets. Reduced-gravity is employed to provide an ideal (spherically-symmetrical) experimental model with which to investigate effects of Soret transport on combustion. The research will involve performing reduced-gravity experiments on combustion of liquid fuel droplets in environments where Soret effects significantly influence transport of fuel and oxygen to flame zones. Experiments will also be performed where Soret effects are not expected to be important. Droplets initially in the 0.5 to 1 mm size range will be burned. Data will be obtained on influences of Soret transport on combustion characteristics (e.g., droplet burning rates, droplet lifetimes, gas-phase extinction, and transient flame behaviors) under simplified geometrical conditions that are most amenable to theoretical modeling (i.e., spherical symmetry). The experiments will be compared with existing theoretical models as well as new models that will be developed. Normal gravity experiments will also be performed.

Shaw, Benjamin D.↗

DOE OSTI2024

Reversed dynamics of bottlebrush polymers with stiff backbone and flexible side chains

The segmental dynamics of bottlebrush polymers with a stiff backbone and flexible side chains has been studied. The segmental relaxation time of side chains attached to a flexible backbone follows the same trend as linear polymers, an increase with the increasing molecular weight, but is slowed down compared to their linear counterparts. Theoretical work predicts a reversal of the molecular weight dependence of the relaxation time for stiff backbones. As a model for a stiff-g-flexible system, bottlebrushes with poly(norbornene) backbone and poly(propylene oxide) side chains, PNB-g-PPO, at a uniform grafting density have been synthesized and characterized with quasi-elastic neutron scattering. Indeed, the anticipated reversed dynamics was found. Increasing the side chain length decreases the segmental relaxation time. This indicates the importance of the characteristics of the grafting site beyond a simplified picture of an attached side chain. The mean square displacement shows a similar trend with longer side chains exhibiting a larger displacement.

Chemistry↗

NASA NTRS1975

Liquid ethylene-propylene copolymers

Oligomers are prepared by heating solid ethylene-propylene rubber in container that retains solid and permits liquid product to flow out as it is formed. Molecular weight and viscosity of liquids can be predetermined by process temperature. Copolymers have low viscosity for given molecular weight.

Rhein, R. A.↗

NASA NTRS1986

Utilization of non-conventional systems for conversion of biomass to food components: Recovery optimization and characterizations of algal proteins and lipids

Protein isolate obtained from green algae (Scenedesmus obliquus) cultivated under controlled conditions was characterized. Molecular weight determination of fractionated algal proteins using SDS-polyacrylamide gel electrophoresis revealed a wide spectrum of molecular weights ranging from 15,000 to 220,000. Isoelectric points of dissociated proteins were in the range of 3.95 to 6.20. Amino acid composition of protein isolate compared favorably with FAO standards. High content of essential amino acids leucine, valine, phenylalanine and lysine makes algal protein isolate a high quality component of closed environment life support system (CELSS) diets. To optimize the removal of algal lipids and pigments supercritical carbon dioxide extraction (with and without ethanol as a co-solvent) was used. Addition of ethanol to supercritical CO2 resulted in more efficient removal of algal lipids and produced protein isolate with a good yield and protein recovery. The protein isolate extracted by the above mixture had an improved water solubility.

Karel, M.↗

NASA NTRS1987

Non-conventional approaches to food processing in CELSS, 1. Algal proteins: Characterization and process optimization

Protein isolate obtained from green algae cultivated under controlled conditions was characterized. Molecular weight determination of fractionated algal proteins using SDS-polyacrylamide gel electrophoresis revealed a wide spectrum of molecular weights ranging from 15,000 to 220,000. Isoelectric points of dissociated proteins were in the range of 3.95 to 6.20. Amino acid composition of protein isolate compared favorably with FAO standards. High content of essential amino acids leucine, valine, phenylalanine and lysine make algal protein isolate a high quality component of closed ecological life support system diets. To optimize the removal of algal lipids and pigments supercritical carbon dioxide extraction (with and without ethanol as a co-solvent) was used. Addition of ethanol to supercritical carbon dioxide resulted in more efficient removal of algal lipids and produced protein isolate with a good yield and protein recovery. The protein isolate extracted by the above mixture had an improved water solubility.

Nakhost, Z.↗

NASA NTRS1987

Non-conventional approaches to food processing in CELSS. I - Algal proteins: Characterization and process optimization

Protein isolate obtained from green algae (Scenedesmus obliquus) cultivated under controlled conditions was characterized. Molecular weight determination of fractionated algal proteins using SDS-polyacrylamide gel electrophoresis revealed a wide spectrum of molecular weights ranging from 15,000 to 220,000. Isoelectric points of dissociated proteins were in the range of 3.95 to 6.20. Amino acid composition of protein isolate compared favorably with FAO standards. High content of essential amino acids leucine, valine, phenylalanine and lysine makes algal protein isolate a high quality component of CELSS diets. To optimize the removal of algal lipids and pigments supercritical carbon dioxide extraction (with and without ethanol as a co-solvent) was used. Addition of ethanol to supercritical CO2 resulted in more efficient removal of algal lipids and produced protein isolate with a good yield and protein recovery. The protein isolate extracted by the above mixture had an improved water solubility.

Nakhost, Z.↗

DOE OSTI2022

Plant Oil-Based Acrylic Latexes towards Multisubstrate Bonding Adhesives Applications

To investigate the utility of acrylic monomers from various plant oils in adhesives manufacturing, 25–45 wt. % of high oleic soybean oil-based monomer (HOSBM) was copolymerized in a miniemulsion with commercially applied butyl acrylate (BA), methyl methacrylate (MMA), or styrene (St). The compositions of the resulting ternary latex copolymers were varied in terms of both “soft” (HOSBM, BA) and “rigid” (MMA or St) macromolecular fragments, while total monomer conversion and molecular weight of copolymers were determined after synthesis. For most latexes, results indicated the presence of lower and higher molecular weight fractions, which is beneficial for the material adhesive performance. To correlate surface properties and adhesive performance of HOSBM-based copolymer latexes, contact angle hysteresis (using water as a contact liquid) for each latex-substrate pair was first determined. The data showed that plant oil-based latexes exhibit a clear ability to spread and adhere once applied on the surface of materials differing by polarities, such as semicrystalline polyethylene terephthalate (PET), polypropylene (PP), bleached paperboard (uncoated), and tops coated with a clay mineral paperboard. The effectiveness of plant oil-based ternary latexes as adhesives was demonstrated on PET to PP and coated to uncoated paperboard substrates. As a result, the latexes with high biobased content developed in this study provide promising adhesive performance, causing substrate failure instead of cohesive/adhesive break in many experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Direct Measure of Electrode Spatial Heterogeneity: Influence of Processing Conditions on Anode Architecture and Performance

The spatial (in)homogeneity of aqueous processed silicon electrodes using standard poly(acrylic acid)-based binders and slurry preparation conditions is demonstrated in this work. X-ray nanotomography shows segregation of materials into submicron-thick layers depending on the mixing method and starting binder molecular weights. Using a dispersant, or in situ production of dispersant from the cleavage of the binder into smaller molecular weight species, increases the resulting lateral homogeneity while drastically decreasing the vertical homogeneity as a result of sedimentation and separation due to gravitational forces. This data explains some of the variability in the literature with respect to silicon electrode performance and demonstrates two potential ways to improve slurry-based electrode fabrications.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Olefin oligomerization by main group Ga 3+ and Zn 2+ single site catalysts on SiO 2

In heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni 2+ and Cr 3+ . Here we report that silica-supported, single site catalysts containing immobilized, main group Zn 2+ and Ga 3+ ion sites catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni 2+ . The molecular weight distribution of products formed on Zn 2+ is similar to Ni 2+ , while Ga 3+ forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250 °C where oligomerization is catalytically relevant. This work illuminates new chemistry for main group metal catalysts with potential for development of new oligomerization processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗