Synthesis of polyacrylonitrile and mechanical properties of its electrospun nanofibers

AbstractPolyacrylonitrile (PAN) nanofibers are very important to achieve high performance carbon nanofibers. In this work, co-polyacrylonitriles (co-PANs) with different molecular weights were synthesized by a simple free-radical polymerization. The effect of the initiator amount on the molecular weight of co-PAN was investigated. The co-PANs with different molecular weight were electrospun into aligned nanofibers by adjusting the absolute viscosity of co-PAN solution into ~1.0 Pa·s. All the co-PAN nanofibers showed smooth surfaces and homogeneous fiber diameters of ~450 nm. Tensile tests were applied to evaluate the mechanical properties of electrospun aligned co-PAN nanofibers. The results indicated that higher molecular weight led to better mechanical performance of electrospun aligned co-PAN nanofibers. When the molecular weight was 2.3×105, the highest strength of 153 MPa, strain of 0.148, and toughness of 16.0 J/g were obtained. These electrospun aligned co-PAN nanofibers could be good candidates for the preparation of high performance carbon nanofibers.

Download Full-text

IM7/LARCTM-IA polyimide composites

High Performance Polymers ◽

10.1088/0954-0083/7/1/009 ◽

1995 ◽

Vol 7 (1) ◽

pp. 105-124 ◽

Cited By ~ 30

Author(s):

T H Hou ◽

N J Johnston ◽

T L St Clair

Keyword(s):

Mechanical Properties ◽

Molecular Weight ◽

High Performance ◽

Flexural Modulus ◽

Engineering Properties ◽

Solvent Resistance ◽

Polymer Backbone ◽

Molecular Weights ◽

Interlaminar Shear ◽

Langley Research Center

LARCTM-IA (Langley Research Center-Improved Adhesive) aromatic polyimide, based on oxydiphthalic anhydride and 3.4'-oxydianiline, was evaluated as a matrix for high-performance composites. Six poly(amide acid)solutions in N-methylpyrrolidone (NMP), end-capped with phthalic anhydride to various theoretical molecular weights, were synthesized and their molecular weights and molecular weight distributions determined, Importantly, high concentrations of low-molecular-weight species were found in all the offset compositions. Except for the 1% offset polymer, all fully imidized films failed a solvent resistance test which involved immersion in acetone, methyl ethyl ketone, toluene, dimethylacetamide and chloroform for 1 min followed by a fingernail crease. Unidirectional prepreg was fabricated from each of the six resins by both standard drum winding procedures and the LARC multipurpose prepreg machine. The consolidation cycle developed previously for IM7/LARCTM-ITPI composites was found to be equally applicable for IM7/LARCTM-IA composites since both materials are similar and were prepared in and prepregged from NMP. An optimal end-capped resin composition was identified (4% stoichiometric imbalance) by using, as a screening tool, initial composite mechanical properties (short-beam shear strength, longitudinal flexural strength and flexural modulus) at room temperature, 93, 150 and 177°C. Composite engineering properties for the 4% offset composition were obtained, including longitudinal tension, transverse flexural, longitudinal compression, interlaminar shear, short block compression, open hole compression and compression strength after impact. Notably, the CAI strength was 303.2 MPa (44 Ksi) showing that the LARCTM-IA composites have good damage tolerance. A minor modification of LARCTM-IA polymer backbone which did not alter the consolidation cycle, designated as LARCTM-IAX, improved solvent resistance measurably. Mechanical properties of IM7/LARCTM-IAX composites were shown to be comparable to those exhibited by the baseline IM7/LARCTM-IA composites.

Download Full-text

Effects of Molecular Weight of Functionalized Liquid Butadiene Rubber as a Processing Aid on the Properties of SSBR/Silica Compounds

Polymers ◽

10.3390/polym13060850 ◽

2021 ◽

Vol 13 (6) ◽

pp. 850

Author(s):

Donghyuk Kim ◽

Byungkyu Ahn ◽

Kihyun Kim ◽

JongYeop Lee ◽

Il Jin Kim ◽

...

Keyword(s):

Molecular Weight ◽

Anionic Polymerization ◽

High Performance ◽

Crosslink Density ◽

Functional Group ◽

Vital Role ◽

Butadiene Rubber ◽

Molecular Weights ◽

Mooney Viscosity ◽

Silica Dispersion

Liquid butadiene rubber (LqBR) which used as a processing aid play a vital role in the manufacturing of high-performance tire tread compounds. However, the studies on the effect of molecular weight, microstructure, and functionalization of LqBR on the properties of compounds are still insufficient. In this study, non-functionalized and center-functionalized liquid butadiene rubbers (N-LqBR and C-LqBR modified with ethoxysilyl group, respectively) were synthesized with low vinyl content and different molecular weights using anionic polymerization. In addition, LqBR was added to the silica-filled SSBR compounds as an alternative to treated distillate aromatic extract (TDAE) oil, and the effect of molecular weight and functionalization on the properties of the silica-filled SSBR compound was examined. C-LqBR showed a low Payne effect and Mooney viscosity because of improved silica dispersion due to the ethoxysilyl functional group. Furthermore, C-LqBR showed an increased crosslink density, improved mechanical properties, and reduced organic matter extraction compared to the N-LqBR compound. LqBR reduced the glass transition temperature (Tg) of the compound significantly, thereby improving snow traction and abrasion resistance compared to TDAE oil. Furthermore, the energy loss characteristics revealed that the hysteresis loss attributable to the free chain ends of LqBR was dominant.

Download Full-text

Semi-bio-based aromatic polyamides from 2,5-furandicarboxylic acid: toward high-performance polymers from renewable resources

RSC Advances ◽

10.1039/c6ra15797a ◽

2016 ◽

Vol 6 (90) ◽

pp. 87013-87020 ◽

Cited By ~ 22

Author(s):

Kaiju Luo ◽

Yan Wang ◽

Junrong Yu ◽

Jing Zhu ◽

Zuming Hu

Keyword(s):

Mechanical Properties ◽

Thermal Stability ◽

Molecular Weight ◽

High Molecular Weight ◽

Renewable Resources ◽

High Performance ◽

Good Thermal Stability ◽

Aromatic Polyamides ◽

High Performance Polymers ◽

Furandicarboxylic Acid

Aromatic furanic polyamides with relatively high molecular weight were synthesized, and good thermal stability and mechanical properties were demonstrated.

Download Full-text

Synthesis of Cyclic Polysulfides and their Properties as Curing Agents

Rubber Chemistry and Technology ◽

10.5254/1.3547830 ◽

2004 ◽

Vol 77 (2) ◽

pp. 380-390

Author(s):

Wonmun Choi ◽

Tomoyuki Matsumura

Keyword(s):

Mechanical Properties ◽

Molecular Weight ◽

Tensile Strength ◽

High Molecular Weight ◽

Mass Spectra ◽

Elongation At Break ◽

Molecular Weights ◽

Aging Properties ◽

Curing Agents ◽

Polysulfide Polymer

Abstract The reactions of dichloroalkanes and sodium tetra-sulfide (Na2S4) were carried out in a mixture of water and toluene to produce corresponding cyclic polysulfides and polysulfide polymer. The low molecular weights of cyclic sulfides were obtained by the reaction at 90 °C, while the high molecular weight of polysulfide polymer was obtained by the reaction at 50 °C. GPC chromatograms and Mass spectra revealed that the structures of cyclic polysulfide were 1:1, 2:2, and 3:3 adducts of dichloroalkane and sodium tetra-sulfide. The mechanical properties of vulcanized NR at 148 °C with cyclic sulfides were similar to that with sulfur. However, both tensile strength and elongation at break of vulcanized NR at 170 °C with cyclic sulfides are much higher than that with sulfur. The aging properties of vulcanized NR at 148 °C or 170 °C with cyclic polysulfides indicate better stability.

Download Full-text

Microstructural Characterization and Mechanical Properties of L-PBF Processed 316 L at Cryogenic Temperature

Materials ◽

10.3390/ma14195856 ◽

2021 ◽

Vol 14 (19) ◽

pp. 5856

Author(s):

Pragya Mishra ◽

Pia Åkerfeldt ◽

Farnoosh Forouzan ◽

Fredrik Svahn ◽

Yuan Zhong ◽

...

Keyword(s):

Mechanical Properties ◽

Cryogenic Temperature ◽

Room Temperature ◽

Mechanical Performance ◽

Microstructural Characterization ◽

Tensile Tests ◽

Phase Changes ◽

X Ray Diffraction ◽

Temperature Range ◽

Aerospace Applications

Laser powder bed fusion (L-PBF) has attracted great interest in the aerospace and medical sectors because it can produce complex and lightweight parts with high accuracy. Austenitic stainless steel alloy 316 L is widely used in many applications due to its good mechanical properties and high corrosion resistance over a wide temperature range. In this study, L-PBF-processed 316 L was investigated for its suitability in aerospace applications at cryogenic service temperatures and the behavior at cryogenic temperature was compared with room temperature to understand the properties and microstructural changes within this temperature range. Tensile tests were performed at room temperature and at −196 °C to study the mechanical performance and phase changes. The microstructure and fracture surfaces were characterized using scanning electron microscopy, and the phases were analyzed by X-ray diffraction. The results showed a significant increase in the strength of 316 L at −196 °C, while its ductility remained at an acceptable level. The results indicated the formation of ε and α martensite during cryogenic testing, which explained the increase in strength. Nanoindentation revealed different hardness values, indicating the different mechanical properties of austenite (γ), strained austenite, body-centered cubic martensite (α), and hexagonal close-packed martensite (ε) formed during the tensile tests due to mechanical deformation.

Download Full-text

Characterisation of a High-Performance Al–Zn–Mg–Cu Alloy Designed for Wire Arc Additive Manufacturing

Materials ◽

10.3390/ma13071610 ◽

2020 ◽

Vol 13 (7) ◽

pp. 1610 ◽

Cited By ~ 3

Author(s):

Paulo J. Morais ◽

Bianca Gomes ◽

Pedro Santos ◽

Manuel Gomes ◽

Rudolf Gradinger ◽

...

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Additive Manufacturing ◽

High Performance ◽

Mechanical Performance ◽

Fluorescence Analysis ◽

Cold Metal Transfer ◽

Direction Parallel ◽

X Ray ◽

Wire Arc Additive Manufacturing

Ever-increasing demands of industrial manufacturing regarding mechanical properties require the development of novel alloys designed towards the respective manufacturing process. Here, we consider wire arc additive manufacturing. To this end, Al alloys with additions of Zn, Mg and Cu have been designed considering the requirements of good mechanical properties and limited hot cracking susceptibility. The samples were produced using the cold metal transfer pulse advanced (CMT-PADV) technique, known for its ability to produce lower porosity parts with smaller grain size. After material simulations to determine the optimal heat treatment, the samples were solution heat treated, quenched and aged to enhance their mechanical performance. Chemical analysis, mechanical properties and microstructure evolution were evaluated using optical light microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray fluorescence analysis and X-ray radiography, as well as tensile, fatigue and hardness tests. The objective of this research was to evaluate in detail the mechanical properties and microstructure of the newly designed high-performance Al–Zn-based alloy before and after ageing heat treatment. The only defects found in the parts built under optimised conditions were small dispersed porosities, without any visible cracks or lack of fusion. Furthermore, the mechanical properties are superior to those of commercial 7xxx alloys and remarkably independent of the testing direction (parallel or perpendicular to the deposit beads). The presented analyses are very promising regarding additive manufacturing of high-strength aluminium alloys.

Download Full-text

Structure, Mechanical Performance, and Dimensional Stability of Radiata Pine (Pinus radiata D. Don) Scrimbers

Advances in Polymer Technology ◽

10.1155/2019/5209624 ◽

2019 ◽

Vol 2019 ◽

pp. 1-8

Author(s):

Jinguang Wei ◽

Fei Rao ◽

Yuxiang Huang ◽

Yahui Zhang ◽

Yue Qi ◽

...

Keyword(s):

Mechanical Properties ◽

Pinus Radiata ◽

Dimensional Stability ◽

High Performance ◽

Water Resistance ◽

Mechanical Performance ◽

Three Dimensional ◽

Radiata Pine ◽

Specific Strength ◽

Shearing Strength

Natural wood has certain advantages such as good processability and high specific strength and thus has been used for millennium as a structural material. But the mechanical performance and water resistance, particularly for fast-growing species, are unsatisfactory for high-end applications. In this study, the “new-type” scrimber technology was introduced to radiata pine (Pinus radiata D. Don) scrimbers. The structure, mechanical properties, and dimensional stability of the scrimber panels were investigated. Results showed that OWFMs as basic units of scrimber had been very even in size and superior permeability. The scrimbers exhibited a three-dimensional porous structure, and the porosity had a decrease with increasing density. Both OWFMs and densification contributed to the high performance in terms of mechanical properties and water resistance. The flexural, compressive, and short-beam shearing strength were significantly enhanced with increasing density. As the density was 0.80 g cm−3, the flexural strength (MOR) was approximately 120 MPa, much larger than many selected wood-based panels. Moreover, the water resistance and dimensional stability also were closely related to the density. At the density of 1.39 g cm−3, the water absorption rate and thinness swelling rate of the panels in boiled water were only 19% and 5.7%, respectively.

Download Full-text

Comparison of exopolysaccharides from mucoid and nonmucoid strains of Clavibacter michiganensis subspecies sepedonicus

Canadian Journal of Microbiology ◽

10.1139/m93-041 ◽

1993 ◽

Vol 39 (3) ◽

pp. 291-296 ◽

Cited By ~ 14

Author(s):

Paul J. Henningson ◽

Neil C. Gudmestad

Keyword(s):

Molecular Weight ◽

High Performance ◽

Size Exclusion ◽

Enzyme Linked Immunosorbent Assay ◽

Low Molecular Weight ◽

Neutral Sugar ◽

Clavibacter Michiganensis ◽

Serological Reaction ◽

Molecular Weights ◽

Exclusion Chromatography

The exopolysaccharides produced by six strains of Clavibacter michiganensis ssp. sepedonicus were isolated and purified by liquid chromatography. Neutral sugar composition and molecular weights were determined for each polysaccharide fraction, using gas chromatography and high-performance size-exclusion chromatography. The serological reaction of each fraction was tested using enzyme-linked immunosorbent assay. Exopolysaccharide from nonmucoid strains contained only low molecular weight polysaccharides (1.5 × 103 to 1.1 × 104). Exopolysaccharide from mucoid and intermediate strains could be separated into low (4.0 × 103 to 1.1 × 104) molecular weight and high (5.0 × 105 to 1.6 × 106) molecular weight fractions. High molecular weight polysaccharides were composed almost exclusively of galactose, glucose, and fucose. The ratios of these sugars were highly variable among strains. Low molecular weight polysaccharides were primarily composed of galactose with significant and varying amounts of glucose, rhamnose, mannose, and ribose. All polysaccharide fractions except one, produced by a nonmucoid strain, reacted in the immunoassay test.Key words: exopolysaccharide, polysaccharide, Clavibacter, michiganensis, sepedonicus.

Download Full-text

Effect of Zr Diffusion Barrier Properties on the Irradiation Performance of U-10Mo Monolithic Fuel Plate

ASME 2019 Power Conference ◽

10.1115/power2019-1870 ◽

2019 ◽

Author(s):

Walid Mohamed ◽

Hakan Ozaltun ◽

Hee Seok Roh

Keyword(s):

Mechanical Properties ◽

Diffusion Barrier ◽

High Performance ◽

Mechanical Performance ◽

Plate Thickness ◽

Barrier Properties ◽

Element Analysis ◽

Uranium Fuel ◽

High Enrichment ◽

Irradiation Performance

Abstract The most recent design of U-Mo monolithic fuel as adopted by the U.S. for the conversion of its High Performance Research Reactors (USHPRR) from high enrichment uranium (HEU) to low enrichment uranium fuel (LEU, < 20% U235) consists of a high density (LEU) U-10Mo fuel sandwiched between Zirconium (Zr) diffusion barriers and encapsulated in aluminum (AA6061) cladding. In this work, finite element analysis (FEA) was used to evaluate effect of Zr diffusion barrier properties on the thermal and mechanical performance of a U-10Mo monolithic fuel plate by considering possible variation in thermal and mechanical properties of the Zr diffusion barrier. Possible variation in thermo-mechanical properties of the Zr diffusion barrier were determined and a simulation matrix was designed accordingly. Analyses of simulation results included determination of global peak stresses in the fuel, Zr diffusion barrier, and cladding sections as well as the plate thickness profile at a transverse section toward the top side of the plate. Results showed that variation in yield stress, elastic modulus and thermal conductivity of the Zr diffusion barrier has negligible effect on the thermal and mechanical performance of the monolithic fuel plate. The effect of variation in these properties was found to be limited to the barrier section itself, which may be attributed to the relatively smaller thickness of that section compared to the fuel and cladding sections of the fuel plate.

Download Full-text

Quantifying High-Performance Material Microstructure Using Nanomechanical Tools with Visual and Frequency Analysis

Scanning ◽

10.1155/2018/4975317 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12 ◽

Cited By ~ 5

Author(s):

Emil Sandoz-Rosado ◽

Michael R. Roenbeck ◽

Kenneth E. Strawhecker

Keyword(s):

Mechanical Properties ◽

Frequency Analysis ◽

Visual Processing ◽

High Performance ◽

Mechanical Performance ◽

Structure Property ◽

Spatially Resolved ◽

Macro Scale ◽

Organization Strategy ◽

Stiffness Scanning

High-performance materials like ballistic fibers have remarkable mechanical properties owing to specific patterns of organization ranging from the molecular scale, to the micro scale and macro scale. Understanding these strategies for material organization is critical to improving the mechanical properties of these high-performance materials. In this work, atomic force microscopy (AFM) was used to detect changes in material composition at an extremely high resolution with transverse-stiffness scanning. New methods for direct quantification of material morphology were developed, and applied as an example to these AFM scans, although these methods can be applied to any spatially-resolved scans. These techniques were used to delineate between subtle morphological differences in commercial ultra-high-molecular-weight polyethylene (UHMWPE) fibers that have different processing conditions and mechanical properties as well as quantify morphology in commercial Kevlar®, a high-performance material with an entirely different organization strategy. Both frequency analysis and visual processing methods were used to systematically quantify the microstructure of the fiber samples in this study. These techniques are the first step in establishing structure-property relationships that can be used to inform synthesis and processing techniques to achieve desired morphologies, and thus superior mechanical performance.

Download Full-text