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27 records · Page 2

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DOE OSTI2019

Lignin-Based Polyurethanes from Unmodified Kraft Lignin Fractionated by Sequential Precipitation

In this work, lignin-based polyurethanes were synthesized from three unmodified softwood Kraft lignin fractions as the primary hydroxyl group providers which constituted >40% of the polymeric materials. High-, medium-, and low-molecular-weight Kraft lignin fractions were prepared by sequential precipitation from the acetone–methanol cosolvent by adding hexane as an antisolvent. A polyether, poly(ethylene glycol), and a polyester, poly(trimethylene glutarate), were selected as secondary polyols to form the soft segments in the lignin-based network. At a fixed NCO/OH ratio (1:1), the effects of lignin macromolecular features and their intermolecular interactions with the secondary polyols on mechanical and thermal properties of the lignin-based polyurethanes were investigated by tensile tests, DMA, SEM, and TGA. Because of the unique association behavior of macromolecular lignin, the sequential precipitation method was able to produce Kraft lignin fractions possessing very high molecular weights. The morphological study showed that the polyurethane network was assembled by cross-linking nanosized lignin complexes through urethane links. It was discovered that the mechanical properties of the lignin-based polyurethanes can be tuned by lignin molecular weight and the incorporation of a secondary polyol. Compared to poly(trimethylene glutarate), poly(ethylene glycol) interacts strongly with associated lignin complexes through hydrogen bonding. It promoted dissociation of the lignin complexes and consequently improved reactivity between lignin and diisocyanate. Moreover, at PEG/lignin = 1:4 (w/w), the soft segments formed by PEG enhanced the stiffness of the lignin-based polyurethanes; when the PEG content was increased to PEG/lignin = 2:3 (w/w), plastic deformation can be observed for the stress–strain curves of all corresponding lignin-based polyurethanes.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Process depending morphology and resulting physical properties of TPU

Thermoplastic polyurethane (TPU) is a rubber like material with outstanding properties, e.g. for seal applications. TPU basically provides high strength, low frictional behavior and excellent wear resistance. Though, due to segmented structure of TPU, which is composed of hard segments (HSs) and soft segments (SSs), physical properties depend strongly on the morphological arrangement of the phase separated HSs at a certain ratio of HSs to SSs. It is obvious that the TPU deforms differently depending on its bulk morphology. Basically, the morphology can either consist of HSs segregated into small domains, which are well dispersed in the SS matrix or of few strongly phase separated large size HS domains embedded in the SS matrix. The morphology development is hardly ruled by the melt processing conditions of the TPU. Depending on the morphology, TPU provides quite different physical properties with respect to strength, deformation behavior, thermal stability, creep resistance and tribological performance. The paper deals with the influence of important melt processing parameters, such as temperature, pressure and shear conditions, on the resulting physical properties tested by tensile and relaxation experiments. Furthermore the morphology is studied employing differential scanning calorimeter (DSC), transmission light microscopy (TLM), scanning electron beam microscopy (SEM) and transmission electron beam microscopy (TEM) investigations. Correlations between processing conditions and resulting TPU material properties are elaborated. Flow and shear simulations contribute to the understanding of thermal and flow induced morphology development.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Synthesis of Biodegradable and Blood-Compatible Polyurethane Based on Poly(vinylpyrrolidone)

Three kinds of degradable and blood-compatible polyurethane (PU) were synthesized by coupling hydroxyl-terminated poly(vinylpyrrolidone) (PVP) with diisocyanate-terminated PU. The chemical structure and molecular weight of the synthesized copolymer were systematically characterized by nuclear magnetic resonance spectrum ({sup 1}HNMR), Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The hydrophilicity and water absorption of the synthesized PU was increased by introducing PVP segment. To evaluate the hemocompatibility and degradability of the modified PU films, the extent of platelet adsorption, plasma recalcification time, hemolysis and degradation were measured. All results indicated that the blood compatibility and degradability of the PU films were improved significantly after introduction PVP segment into PU.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Investigation of Thermoplastic Polyurethanes Synthesized via Two Different Prepolymers

The man aim of this work was to investigate the effect of the molecular weight of polyols, mixture of prepolymers, and [NCO]/[OH] molar ratio used during the prepolymer chain extending step on the chemical structure, thermomechanical and mechanical properties, and thermal stability of thermoplastic poly(ether-urethane)s In this work thermoplastic poly(ether-urethane)s were synthesized by using polyols with a various molecular weight, 4,4′-diphenylmethane diisocyanate and bio-based glycol. Materials were obtained by a two-step method. The tests were carried out for polyurethanes obtained from a mixture of prepolymers and for reference samples. In the case of materials obtained with using mixture of prepolymers, the ratio of both prepolymers was determined on 50/50 weight percent. Soft segments of materials prepared with using mixture consist of two different polyols. The chemical structure was analyzed using FTIR spectroscopy. The Gaussian deconvolution technique was used to study the hydrogen bonding as well as to decompose carbonyl region of three peaks in various TPUs. The thermal degradation behavior was investigated by using thermogravimetric analysis at heating rates of 10 °C/min. It was confirmed that the mixture of prepolymers has an effect of the degree of phase separation, thermal stability and selected properties of synthesized thermoplastic poly(ether-urethane)s.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Damage progression and failure of SiC/SiC composite tubes under hard-contact radial expansion

The response of silicon carbide (SiC) fiber-reinforced SiC matrix (SiC/SiC) composite cladding to mechanical interaction with fissile fuel is a knowledge gap that must be overcome to design and assess SiC-based cladding systems for advanced nuclear applications. This study developed the relevant mechanical testing capability and identified the failure behavior and the critical microstructural features and processing defects. Sections of SiC composite tube were subjected to a modified expansion-due-to-compression (EDC) test in an X-ray computed tomography microscope: a polyurethane plug pressed surrogate Al 2 O 3 into the inner walls of the SiC/SiC composite tubes to achieve hard contact. A pure EDC test with just a polyurethane plug was also performed as a reference. Through the use of displacement fields, digital volume correlation revealed inhomogeneous deformation fields in the tubes, even for pure EDC, which was related to the inherent defects in the structure. Deep learning–aided segmentation and systematic data analysis revealed that the presence of inhomogeneous deformation applied by the hard contact was exaggerated by the presence of inner surface imperfections left behind from the matrix densification process. In conclusion, the findings provide insights into the applications, highlighting the necessity for improvements in inner surface roughness and the incorporation of localized contacts in pellet–cladding mechanical interaction computational models.

Composites↗

DOE OSTI2024

Renewable and Biodegradable Polyurethane Foams with Aliphatic Diisocyanates

The transition to renewable plastics will require the development of substitutes with existing industrial standards and manufacturing processes. Polyurethanes (PU), versatile plastics, are traditionally dominated by aromatic diisocyanates, which are challenging to derive from renewable sources. However, for higher biocontent, it is crucial to utilize aliphatic diisocyanates, which can be sourced from renewable plant or algae waste streams. Historically, PU foams relied on aromatic diisocyanates for essential hard segments, resulting in desired physical properties. Here, we report the generation of high-performance renewable and biodegradable PU foams utilizing aliphatic diisocyanates and aromatic polyols, translating hard segments into the polyester polyol component using biosourced furan dicarboxylic acid (FDCA) monomers. We demonstrate that an FDCA-based PU is suitable for foams with performance characteristics that meet commercial tolerances and can biodegrade under backyard compost conditions. Here, this demonstrates steps toward redesigning traditional petrochemical-based polymers to accommodate new biological monomers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Quantifying the cooperative evolution of microphase segregation and nanostructural order in annealed polyurethanes of MDI-BDO-PTHF

Here, we quantify the relationship between microphase segregation and local structure development in thermoplastic polyurethanes. Samples were prepared with varying ratios of 4,40 -methylene diphenyl diisocyanate (MDI) and 1,4-butanediol (BDO) to polytetrahydrofuran (PTHF) and annealed at temperatures T a between RT–140 °C for 20 h each. Distinct populations of smaller and larger ordered domains are distinguished by pair distribution func tion analysis. The intermediate-range order of nanoscale hard domains in the paracrystalline state (form I) is directly extracted and characterized. The results suggest that form I of the MDI-BDO:PTHF system presents a conformational and packing order similar to the form III structure, typically obtained from stretching/annealing, but with limited spatial coherence of 3–7 nm. Heating above T g of the hard segments is necessary to achieve a substantial structural response from the annealing treatment. Increasing T a promotes purification of the soft phase via microphase segregation, coalescence of the hard blocks, and growth of paracrystalline phase, while a minority fraction of longer-range ordered domains left over from production remains relatively constant. We observe a composition-dependent decrease in the average nearest-neighbor dis tance that can be correlated with the greater number of C C, C N, and C O bonds with increased hard segment content. A non-linear deviation in the trend is observed to correlate with sample densification. The mechanical and thermal behavior of the samples is intimately tied to the segregation state.

processing-structure-properties↗

DOE OSTI2022

Renewable low viscosity polyester-polyols for biodegradable thermoplastic polyurethanes

In the transition to renewably sourced, biodegradable polymers, the preparation of low viscosity polyester-polyols has posed a challenge for renewable polyurethane (PU) development. Low viscosity polyols not only reduce the requirement for high process temperatures but also decrease manufacturing time. In our efforts to incorporate increasing ratios of bio-based monomers into renewable PUs, we mixed diacids such as even carbon sebacic acid and odd carbon azelaic acid along with a renewable diol. This provided library of 2000 g/mol molecular weight polyester-polyols, and structures were established by 1 H and 13 C NMR analysis. The prepared polyester-polyols offered lower viscosity and enable lower fabrication temperatures to make TPUs, and their structure and material metrics were evaluated. The formation of TPUs is ascertained from FTIR and NMR analysis. The final TPUs displayed good physical and mechanical properties. Further, these TPUs exhibited T g in the range of -56.5 to -39.7°C, corresponding to TPU soft block structure, and T m between 98.3 and 105.1°C originating from the hard segment. Prepared TPUs exhibit excellent biodegradation under compost environmental conditions. These TPUs showed up to 57% decrease in molecular weight by GPC analysis after 9 weeks of biodegradation, and respirometer analysis displayed up to 97% biodegradation over 120 days.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Degradation of Polyester Polyurethane by Aspergillus sp. Strain S45 Isolated from Soil

A polyurethane (PU)-degrading fungus designated as strain S45 was isolated from a solid waste-dumping site in Islamabad, Pakistan. Strain S45 was identified as Aspergillus sp. through microscopic, morphologic as well as 18S rRNA sequencing (99% similarity with Aspergillus fumigatus). The degradation ability of strain S45, was analyzed through measurement of weight loss and evolution of CO{sub 2} as a result of breakdown of PU film. The degradation was confirmed through scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). Surface changes like pits, cracks and holes were observed in scanning electron micrographs upon degradation of PU film by strain S45. FTIR spectra were carefully examined, changes were observed in various peaks at different wavelength ranges that also correspond to degradation of PU film. Differential scanning calorimetric technique was used to measure the melting temperature of PU film pieces before and after incubation with strain S45. DSC curve indicated an increase in melting temperature of PU from 191 to 196 °C that might be due to increase in crystallinity of the exposed PU after degradation of amorphous soft segment. A gradual increase in specific activity of esterase was observed up to the maximum of 15th day of incubation with PU film in mineral salt medium. Enzyme activity was further confirmed by tween 20 agar plates, demonstrated by formation of calcium complex. It is concluded from the results that Aspergillus sp. strain S45 might be applied for the treatment of plastics-contaminated environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗