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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Chemically Recyclable Polyester Thermosets from Activated Adipic Acid and Renewable Polyols

This study outlines a method for producing chemically recyclable crosslinked polyesters using renewable polyols-glycerol and sorbitol-combined with adipic acid (AA), which is transformed/activated into a polyanhydride mixture prior to use. A three-step procedure has been designed: 1) an acid-catalyzed reaction of AA with nontoxic isopropenyl acetate or acetic anhydride to form a crosslinking mixture (CLM) made of adipic-acetic mixed polyanhydrides; 2) a solvent- and additive-free process where glycerol or sorbitol, or a combination thereof, is reacted with the CLM to achieve a prepolymer, and 3) a casting/molding of the liquid viscous prepolymer to yield a thermoset as the end product. Different thermosets (eight examples) are prepared by changing the reagents ratio. These solids are thoroughly characterized by tensile tests, DMA, high-resolution magic angle spinning and solid-state NMR, thermal gravimetric analysis, DSC, and fourier transformed infra red (FT-IR) spectroscopy. The formation of cross-linked polyesters is confirmed in all cases, but mechanical properties varied significantly from one specimen to another. Interestingly, a tensile strength up to 18 MPa-approximately an order of magnitude higher than similar polymers-is achieved when sorbitol and the CLM are used in a 1:1 wt% ratio. The chemical recycle of the resulting polymers is achieved via methanolysis with quantitative recovery of the monomeric units.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Alkylamine Incorporation in Amidoxime Functionalized Polymers of Intrinsic Microporosity for Gas Capture and Separation

Amidoxime functionalized polymers of intrinsic microporosity (PIMs) are synthesized from postsynthetic functionalization of PIM‐1 with hydroxylamine and processed into chemisorbents with alkylamine incorporation. Strong interaction between functionalized PIM‐1 and primary amines is characterized in detail by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study. As‐prepared sorbents not only show the highest CO 2 uptake capacity (37.9 cm 3 g −1 at 0.15 bar and 298 K) recorded in reported PIMs, but they also demonstrate tunable, processable, and stable polymeric sorbent design, which can be nanoengineered for other gas capture and separation applications.

Miles, Ashley↗
DOE OSTI2022

Impact of specimen preparation method on photovoltaic backsheet degradation during accelerated aging test

In this study, we highlight some important factors in the specimen preparation methods for evaluating photovoltaic backsheet properties after accelerated aging. Two different sequences are considered: Method (I) cut-then-age: cut into 1-cm wide strips and then expose to stress, and Method (II) age-then-cut: expose a larger sheet to stress and then cut into 1-cm widths for mechanical property measurements. We also compare the effect of three cutting methods, (a) tensile specimen punch, (b) paper cutter, and (c) fresh razor blade. Several commercial backsheets were evaluated, with stress exposures including (a) pressure cooker test (PCT), (b) dry ultraviolet (UV) radiation exposure, and (c) UV combined damp heat tests. Fourier transform infrared spectrometer (FTIR) and intrinsic viscosity (IV) were used to analyze the materials on unstressed materials and samples exposed to PCT. The results show that both the cutting method and the time of cutting have an impact on the backsheet mechanical properties. Additionally, under UV exposure, Method II, age-then-cut, generally resulted in a higher average value, with more variation than Method I; however, if the side strips from Method II were excluded, the variation dropped to the same level. This is because the specimens at the sides of the sheet get additional damage from UV light from the exposed sides of the sample. In contrast to UV exposure, PCT specimens prepared by Method II result in lower average values and higher variability. This is attributed to embrittlement through the bulk of the sample where the cutting of embrittled specimens appears to result in more edge defects which can then initiate a break at smaller strains. The data suggest that for UV exposures, the specimens should be cut after aging and the exposed side specimens discarded, and that for PCT exposures, the specimens should be cut before the exposure.

14 SOLAR ENERGY↗
DOE OSTI2023

Corn stover‐derived porous carbon for asymmetric supercapacitors

In this investigation, hydrothermal liquefaction‐derived hydrochar from pulverized corn stover (avg. particle size 1.12 mm and ash content 6.75 wt%) is chemically activated with aqueous KOH in the presence of Pluronic F127 surfactant and thermally treated further up to 800°C to generate porous carbon (POC) with higher specific surface area and porosity. POC obtained under different processing conditions is thoroughly characterized by Brunauer‐Emmett‐Teller surface area analyzer, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Metallic impurity present in POC is characterized by inductively coupled plasma mass spectrometry. Higher specific surface area POC is observed with the use of the surfactant during the activation process. Fully characterized POC is used with (Mn, Ti)‐mixed oxide electrode to fabricate asymmetric supercapacitor (ASC). Specific capacitance of ASC is measured by cyclic voltammetry (CV) technique using Gamry G‐300 potentiostat/galvanostat/ZRA. CV plots are obtained with different voltage scan rates whereas galvanostatic charge‐discharge plots are studied by varying the current density. Renewable corn stover‐derived POC prepared using Pluronic F127/KOH activation method is found to be highly suitable as an electrode material because of higher capacitance and electrochemical stability over 100 charging‐discharging cycles.

25 ENERGY STORAGE↗
DOE OSTI2023

Fabrication of hybrid tin oxide‐cellulose nanocomposite as the flexible and thin supercapacitor

Abstract Microfibrillated cellulose (MFC) with reinforcing effects is a useful building block in the fabrication of flexible and thin supercapacitors. Herein, a hybrid tin oxide‐cellulose nanocomposite was hydrothermally produced and coated on MFC thin films to form a supercapacitor. The hybrid tin oxide‐cellulose thin films were structurally analyzed using scanning electrode microscopy, Fourier transform infrared spectroscopy and x‐ray diffraction. The cellulose thin film with the highest loading of hybrid tin oxide‐cellulose nanocomposite exhibited a specific capacitance of 225.88 F g −1 at 100 mV s −1 and 486.38 F g −1 at 20 mV s −1 in the three‐electrode electrochemical system. In addition, it revealed good cyclic stability up to 40 cycles run continuously with 95% cyclic retention. The high specific capacitance and superior cyclic stability could be related to the enhanced charge mobility and ion diffusion between the solid and electrolyte interface. The cellulose thin film coated with flower‐like hybrid nanocomposite showed great potential in energy storage.

Letchumanan, Iswary↗
DOE OSTI2020

Osteoporosis Treatments Affect Bone Matrix Maturation in a Rat Model of Induced Cortical Remodeling

ABSTRACT To test how osteoporosis drugs affect bone matrix maturation during cortical bone remodeling, 72 pregnant rats were switched from a 0.4% to a 0.01% calcium diet at parturition for a 23‐day lactation period. At weaning, eight dams were sacrificed to establish baseline values, while the remaining dams were returned to 0.4% calcium and treated with vehicle (saline), sodium fluoride (NaF), zoledronic acid (ZA), or sclerostin antibody (Scl‐Ab) for either 7 or 28 days (eight animals per group per time point). Femora were examined by μCT, dynamic histomorphometry, Fourier transform infrared imaging, and three‐point bending of notched specimens. Cortical porosity decreased in all groups from baseline to day 28. Intracortical mineralizing surface (MS/BS) and mineral apposition rate (MAR), as well as the mineral‐to‐matrix ratio were unaffected by treatment, but intracortical crystallinity was increased in the ZA group at day 10 compared with vehicle. Cortical area increased in all groups over 28 days mainly because of an addition of bone at the endocortical surface. Endocortical MS/BS did not vary among the groups, but endocortical MAR was suppressed in the NaF group at day 2 and elevated in the Scl‐Ab group at day 4 compared with vehicle. Endocortical mineral‐to‐matrix ratio was increased at days 5 and 10 following NaF treatment and endocortical crystallinity was increased at day 5 following ZA treatment compared with vehicle. Fracture toughness did not differ among the groups. Thus, the treatments affected matrix maturation more strongly at the endocortical then intracortical envelope. In this model of induced remodeling, the bone formation phase is synchronized at multiple sites, facilitating study of the effects of drugs or other bone‐targeting agents on matrix maturation independent of their effects on the initiation of remodeling. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Fabrication and characterization of dextran/zein hybrid electrospun fibers with tailored properties for controlled release of curcumin

Abstract BACKGROUND In recent years, there has been considerable interest in the use of biopolymer electrospun nanofibers for various food applications due to the biocompatibility, biodegradability, and high loading capacity. Herein, we fabricated and characterized novel hybrid electrospun fibers from dextran (50%, w/v ) and zein (0–30%, w/v ) solutions, and the effects of various zein concentrations on the properties of the hybrid electrospun fibers were investigated. RESULTS When zein was added at low concentrations (5% and 10%), dextran and zein showed poor miscibility, as reflected by significantly decreased viscosity of the solutions, and the poor mechanical properties of the derived fiber membranes. When zein was added at medium concentrations (15–25%), hydrogen bonds were formed between dextran and zein molecules, as indicated by the red shift of Fourier‐transform infrared bands and β‐sheet to α‐helix structural transformations. The fiber membranes electrospun from a solution with 25% zein showed the most hydrophobic surface, with a water contact angle of 116.9°. The homogenous dispersion of dextran and zein resulted in improved mechanical properties for fibers electrospun from a solution with 30% zein. Curcumin encapsulating dextran/zein electrospun fibers exhibited effective radical scavenging activity and ferric reducing power, along with the desired controlled release behavior for curcumin delivery. CONCLUSION Food grade dextran/zein hybrid electrospun fibers demonstrated tunable properties, and appear to be promising as delivery systems for bioactive and edible antimicrobial food packaging. © 2021 Society of Chemical Industry.

Luo, Shiyuan↗
DOE OSTI2022

Improving the bioaccessibility of lipophilic ingredient in its oral intestinal delivery by ultrasound and biological cross‐linker

Abstract BACKGROUND Great efforts have been made to improve the oral bioaccessibility of lipophilic ingredients with multi‐functionalities. Achieving intestinal delivery of lipophilic ingredients and their encapsulation in micelles composed of bile salts and lipid hydrolysates (i.e. fatty acids) is critical for improving oral bioaccessibility. Therefore, oil‐core microcapsules are considered ideal carriers of lipophilic ingredients. Previous studies have reported oil‐core/zein‐shell microcapsules constructed by a one‐step anti‐solvent process. Still, its efficacy as an intestinal delivery system was limited because if the porous shell structure. RESULTS Zein solution was pretreated with ultrasound and tannic acid (TA) cross‐linking. Composite oil‐core microcapsule (COM) with a compact shell structure was successfully prepared by using modified zein solution in the anti‐solvent process. Fourier‐transform infrared spectroscopy and circular dichroism analyses indicated that ultrasound and TA synergistically promote the conformational transition of zein from α‐helix to β‐sheet and enhance the hydrophobic interactions among protein chains. The above changes contribute to the strengthen of shell zein network. Correspondingly, COM presents superior encapsulation efficiency and environmental stability over the simple oil‐core microcapsule (SOM) prepared without the use of ultrasound and TA. Furthermore, antioxidant activity of β‐carotene was well retained during the encapsulation process. In vitro studies indicated that COM was more resistant to digestibility and acid‐induced swelling. More than 87% of β‐carotene could be released in the intestine in a sustainable way. The controllable release behavior thus promoted a significant increase in bioaccessibility of β‐carotene encapsulated in COM compared to SOM (85.9% versus 48.5%). CONCLUSION The COM generated here shows potential for bioaccessibility improvement of lipophilic ingredients. © 2022 Society of Chemical Industry.

Wei, Yun‐Shan↗
DOE OSTI2024

Investigating the impacts of solid phase extraction on dissolved organic matter optical signatures and the pairing with high‐resolution mass spectrometry data across a freshwater stream network

Abstract Advancing our understanding of dissolved organic matter (DOM) chemistry in aquatic systems necessitates the integration of data streams from multiple analytical platforms. Some measurements require pretreatment with solid phase extraction (SPE), while others are performed directly on whole water samples. Evidence has suggested that SPE will be biased against select DOM fractions, leading to concerns over the ability to establish data linkages across platforms with variable needs for SPE pretreatment, such as those from optical measurements and those that provide high‐resolution molecular information. Here, we directly addressed this concern by assessing the impact of SPE on DOM optical properties through excitation–emission matrices with parallel factor analysis (PARAFAC) for 47 samples across a stream network within a single watershed reflective of variable DOM sources. PARAFAC data was further paired with molecular information obtained by Fourier transform ion cyclotron resonance mass spectrometry (FTICR‐MS). A comparison of PARAFAC models first revealed no systematic qualitative differences in major components between whole water DOM and DOM isolated by SPE (SPE‐DOM); however, quantitative biases against select components were observed. Further linkages with FTICR‐MS data revealed that the molecular fingerprint associated with each PARAFAC component was consistent between the whole water DOM and SPE‐DOM. Our results suggest that bulk scale linkages across these analytical platforms could be inferred irrespective of the observed quantitative biases resulting from SPE for samples within this example watershed. This work represents a key step toward the systematic evaluation of linkages between optical and high‐resolution mass spectrometry datasets in freshwater lotic environments.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Observation of Quadratic (Charge-2) Weyl Point Splitting in Near-Infrared Photonic Crystals

Weyl points are point degeneracies that occur in momentum space of 3D periodic materials and are associated with a quantized topological charge. Here, the splitting of a quadratic (charge-2) Weyl point into two linear (charge-1) Weyl points in a 3D micro-printed photonic crystal is observed experimentally via Fourier-transform infrared spectroscopy. Using a theoretical analysis rooted in symmetry arguments, it is shown that this splitting occurs along high-symmetry directions in the Brillouin zone. This micro-scale observation and control of Weyl points is important for realizing robust topological devices in the near-infrared.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Design of High Efficient Mid-Wavelength Infrared Polarizer on ORMOCHALC Polymer

While an organically modified chalcogenide (ORMOCHALC) can be used to fabricate a polymeric mid-wavelength infrared (MWIR) polarizer with competitive extinction ratio compared to the commercial wire-grid polarizers, which are composed of fragile inorganic materials, there is still a knowledge gap regarding the systematic design process to obtain high transmission efficiency and extinction ratio. As such, a computational parameter study for design optimization is conducted with the geometric parameters of the bilayer grating ORMOCHALC polarizer. The computational study shows that the Fabry–Pérot cavity is the primary mechanism that determines the transmission behaviors and the extinction ratio. A bilayer grating design, guided by the parameter study, is realized through the thermal nanoimprint and metal deposition processes. The extinction ratios measured with the Fourier-transform infrared are 245, 304, and 351 at the wavelength of 3, 4, and 5 μm, respectively. Compared to the state-of-the-art of the polymeric MWIR linear polarizers, the extinction ratio is improved by 1.4 times, and the transmission efficiency is increased by 2.5 times. Theoretical analysis with the multiple-layer model based on the transfer matrix method predicts a matched transmission behavior with the experiment and a full-wave electromagnetic simulation.

42 ENGINEERING↗
DOE OSTI2023

Impact of carbamate formation on the surface tension of epoxy‐amine curing systems

Abstract Epoxy‐amine reactive systems, including their surface tension, have been studied due to their use and importance in composites and adhesives in laboratory and industrial applications. Understanding how the system's surface tension changes during curing could help target applications for tailored composites. Using the Wilhelmy plate method, surface tensions for epoxy‐curing agent systems were investigated under different environments. While the epoxy exhibited an expected negative temperature coefficient of −0.096 mN/m/°C, the curing agent exhibited a positive temperature coefficient of 0.073 mN/m/°C, which is due to the curing agent reacting with atmospheric CO 2 to form carbamate through a zwitterion pathway and functional groups accumulating at the surface of the reacting systems. Carbamate formation results in a surface tension below that of the individual constituents in the epoxy‐amine curing agent system. Fourier transform infrared (FTIR) spectroscopy was used to verify in situ formation of carbamate, and by reducing the system's temperature, it was demonstrated that the system surface tension profiles displayed micellar surfactant‐like characteristics. FTIR was used to explore the difference in composition between the surface and the bulk, in particular carbamate formation at the surface, resulting in a lowering of the surface tension of reacting systems.

Shenk, Timothy M.↗
DOE OSTI2024

Synthesis and characterization of biobased copolyesters based on pentanediol: (1) Poly(pentylene dodecanoate–co–furandicarboxylate)

A series of biobased aliphatic-aromatic copolyesters, poly(pentylene dodecanoate-co-furandicarboxylates) (PPeDFs) were synthesized via an esterification and polycondensation melt process. The copolyesters were characterized using gel permeation chromatography, Fourier transform infrared spectroscopy, 1 H NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, wide angle x-ray scattering, and tensile testing. The thermal transition behavior was strongly dependent on composition, with the melting and glass transition temperatures reaching a minimum at approximately equimolar ratio of D to F. All copolyesters were stable below 300°C with their R 600 (the weight of material remaining at 600°C) values increasing with F fraction. PPeD to PPeDF30 (e.g., mole ratio D/F = 7:3) show sharp PPeD crystalline reflections only while broad PPeF reflections are shown in PPeF and PPeDF90. PPeDF40 to PPeDF80 showed both crystal structures. The fractional crystallinity for the PPeD was much higher than PPeF and the fractional crystallinity of the copolymers showed a minimum at D/F ratios closer to the latter. Here, the stress at break and modulus both exhibited maxima at D/F ratios that were either high or low, but somewhat surprisingly a strong maximum in percent elongation at break of over 600% occurs at PPeDF40. For this composition, a typical plastic behavior curve was found including a yield point, high elongation at break, and strain hardening.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Microstructure changes during failure of PVDF-based photovoltaic backsheets

The backsheet layer of a solar module provides a safety and environmental barrier to the high voltages running through the photovoltaic (PV) cells and electrical contacts within the core of the module. However, in the past decade, backsheet cracking has become one of the most observed failure modes in PV module field surveys. In this work, the degradation of polyvinylidene fluoride (PVDF)-based backsheets is explored. Backsheet samples are either exposed to accelerated laboratory aging (UV light, heat, and moisture) or collected from the field. Fourier transform infrared and Raman spectroscopy, fragmentation testing, atomic force and scanning electron microscopy, and small-angle neutron scattering are combined to develop an understanding of how chemistry and microstructure evolve during aging. Chemical degradation, surface pitting, polymer phase changes, and anisotropic polymer domains are all observed in aged backsheet samples. The results provide insight into the degradation mechanisms that lead to cracking and field failure of PVDF-based backsheets. The comparison of aged PVDF-based backsheets helps to lay the groundwork for limiting polymer-based failure modes in PV modules.

PVDF↗
DOE OSTI2024

The melt memory effects in polymer crystallization

This paper presents a systematic review of the literature on the melt memory effects observed in polymers, an area that has engendered considerable debate for over 50 years. Recent advances in experimental techniques have provided fresh insights into how a polymer's thermal history influences its recrystallization behavior. It has been observed that given other conditions unchanged, the crystallization temperature during recrystallization decreases with an increase in the melt temperature T s above the melting point T m until a critical melt temperature is attained. This phenomenon also extends to the half-time of crystallization and the secondary structures, such as lamellar thickness, of semi-crystalline polymers. Despite these findings, a comprehensive constitutive model that encapsulates polymer melt memory effects remains elusive. Cutting-edge instrumentation, including in situ small and wide-angle X-ray scattering, temperature-controlled Fourier transform infrared spectroscopy, and flash differential scanning calorimetry, have posed significant challenges to the traditional nucleation and growth models established in the 1970s. These models are foundational to our understanding of polymer crystallization, which is an integral part of polymer processing and production. In this review, the historical contours of this discourse are traced, with an examination of both the recent experimental breakthroughs and theoretical advancements pertinent to polymer melt memory effects. In conclusion, this paper delves into the prevailing theories of polymer nucleation and crystallization and engages with theoretical discussions and numerical simulations that attempt to elucidate and rationalize these melt memory phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Energetic Copolymers From LLM-105 and Aliphatic Isocyanates

Energetic polymers typically feature fuel-rich backbones with pendant oxidizing explosophores, which are used to modify pressure and temperature characteristics in energetic formulations. However, these pendant explosophores generally increase sensitivity and decrease the thermal stability of the polymer in the condensed phase. Direct polymerization of insensitive high explosives (IHEs) bearing polymerizable functionalities, such as amines, provides a synthetic platform for deriving tunable energetic materials. Here, this work demonstrates the first direct polymerization of the IHE 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) with aliphatic isocyanate comonomers to yield an energetic copolyurea (PUa1) and an energetic copolyurea network (PUa2). 1 H and 13 C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) confirm copolyurea synthesis. PUa1 exhibited branching reactions commonly found in polyurea syntheses, and these side reactions were suppressed in PUa2 through use of a polyfunctional isocyanate. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) demonstrate the energetic IHE based polyurea preserves the energetic decomposition of the parent monomer LLM-105 in PUa1 (1203 J g −1 ) and PUa2 (687 J g −1 ), albeit with reduced thermal stability with peak decomposition temperatures of 235°C and 233°C, respectively. This work presents a new approach for generating energetic polymers from IHE cores with tunable energetic, thermal, and structural characteristics.

Chemistry↗
DOE OSTI2021

Depyrogenation using plasmas: A novel approach for endotoxin deactivation using a dielectric barrier discharge at atmospheric pressure

Developing a low-cost depyrogenation process is vital in extending the medical applicability of polymers that can be used in medicine. We present an overview of the plasma-based depyrogenation literature and address the need to develop a nonthermal plasma-based depyrogenation process for delicate materials such as chitosan. We present a low-cost plasma apparatus to treat chitosan powder in hermetically sealed bags. We decouple the experiments into two parts: depyrogenation experiments for dried standard endotoxin on glass slides and analysis of chitosan modifications through Fourier-transform infrared spectroscopy. We demonstrate depyrogenation efficacy with up to a 4-log reduction in endotoxin levels and discuss minor changes observed in plasma-treated chitosan.

atmospheric pressure plasmas↗
DOE OSTI2023

Evidence of plasma‐driven decomposition of common plastics exposed to an atmospheric nonthermal discharge

Abstract A nonthermal, pulsed spark discharge is applied to three polymer powders in Ar and Ar– gas mixtures. Hydrogen is introduced to assess plasma‐driven decomposition. Gaseous decomposition products, including methane, acetylene, and ethylene, are observed with Fourier‐transform infrared (FTIR). Surface modifications are observed on the residual polymer via attenuated total internal reflection‐FTIR. Time‐averaged rotational, vibrational, and excitation temperatures are characterized in the discharge. The plasma density is found to be around , with rotational and vibrational temperatures ranging from 1500 to 2200 K and an excitation temperature of 1–2 eV. While spark properties did not change with either gas composition or polymer composition, it was determined that the addition of hydrogen promoted higher concentrations of gaseous phase products (promoting hydrogenolysis).

36 MATERIALS SCIENCE↗