Effect of Barium Titanate Reinforcement on Tensile Strength and Dielectric Response of Electrospun Polyvinylidene Fluoride Fibers

In this study, we used electrospinning to obtain polyvinylidene fluoride (PVDF) fibers reinforced with barium titanate (BaTiO3) and investigated the influence of BaTiO3 concentration on the tensile strength and dielectric behavior of PVDF fibers. X-ray diffraction (XRD) study and infrared spectroscopy revealed that PVDF fibers filled with BaTiO3 possessed higher fraction of ferroelectric β-crystals compared to neat PVDF fibers. Further, incorporation of 40 wt% BaTiO3 within the fibers increased their stiffness and strength by 95 and 38%, respectively. These improvements in tensile properties of BaTiO3 filled PVDF fibers arose from the reinforcement effect of BaTiO3. Also, the dielectric response of the BaTiO3/PVDF fibers was characterized. The effective dielectric constants of PVDF fibers reinforced with BaTiO3 were found to increase consistently with BaTiO3 content at all frequencies. The dielectric loss of the fibers did not show any significant change for all concentrations of BaTiO3 within the fibers

Hyperbaric laser chemical vapor deposition of high-strength aluminum- silicon-carbide nanocomposite fibers for aerospace and transportation applications

For over 25 years, hyperbaric pressure laser chemical vapor deposition (HP-LCVD) has been studied by various authors as a mean for growing three-dimensional structures and fibers [1-2]. Novel normally-immiscible materials (NIMs) [3], amorphous/glassy ceramics [4], and high-strength fibers have been grown [5]. However, the highest experimental pressures to date have only reached beyond the critical point of certain alkanes (\u3c60 bar) [6]. Our group has found it useful to synthesize materials from high pressure fluids, where the ensuing cooling rates after deposition can exceed 106 K/s. This has enabled the growth of (metastable) amorphous and nanostructured materials, including diamond-like carbon and boron carbides [7-8]. For this work, freestanding nanocomposite fibers were grown from mixtures of Bis(trimethylsilyl)methane and various organometallic and halide aluminum precursors. A chopped, cw fiber laser at 1064nm and diode lasers at 808nm were used for this work. The 1/e2 laser beam waists were approximately 10-15 microns across. The resulting Al-Si-C fibers could be grown continuously—and were nanostructured due to the precursor pressures and laser powers employed. A variety of phases were found to be present, including aluminum carbide, silicon carbide, carbon, and silicon-rich phases. Scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to characterize the composition and structure of the resulting materials. A map of the ternary phase diagram under these non-equilibrium conditions will be provided and discussed in detail. These fibers will find utility in reinforcements for ceramic- and metal-matrix composites for aerospace and transportation applications. References: [1]F. T. Wallenberger, P. C. Nordine, M. Boman, Composites Science and Technology, 1994, 51, 192. [2]J. L. Maxwell, US Patent #5,786,023, 1996. [3]J. L. Maxwell, M. R. Black, C. A. Chavez, K. R. Maskaly, M. Espinoza, M. Boman, Applied Physics A-Materials Science and Engineering, 2008, 91, 507. [4]F. T. Wallenberger, P. C. Nordine, Journal of Materials Research, 1994, 9, 527. [5]M. Boman, D. Bauerle, Journal of the Chinese Chemical Society, 1995, 42, 405. [6] J. Maxwell, Unpublished Results. [7]J. Maxwell, M. Boman, W. Springer, J. Narayan, S. Gnanavelu, Journal of the American Chemical Society, 2006, 128, 4405. [8]J. Maxwell, C. Chavez, W. Springer, K. Maskaly, D. Goodin, Diamond and Related Materials, 2007, 16, 1557

Use of facile mechanochemical method to functionalize carbon nanofibers with nanostructured polyaniline and their electrochemical capacitance

A facile approach to functionalize carbon nanofibers [CNFs] with nanostructured polyaniline was developed via in situ mechanochemical polymerization of polyaniline in the presence of chemically treated CNFs. The nanostructured polyaniline grafting on the CNF was mainly in a form of branched nanofibers as well as rough nanolayers. The good dispersibility and processability of the hybrid nanocomposite could be attributed to its overall nanostructure which enhanced its accessibility to the electrolyte. The mechanochemical oxidation polymerization was believed to be related to the strong Lewis acid characteristic of FeCl3 and the Lewis base characteristic of aniline. The growth mechanism of the hierarchical structured nanofibers was also discussed. After functionalization with the nanostructured polyaniline, the hybrid polyaniline/CNF composite showed an enhanced specific capacitance, which might be related to its hierarchical nanostructure and the interaction between the aromatic polyaniline molecules and the CNFs

Inner Profile Measurement for Pipes Using Penetration Testing

Penetration testing has been used to measure material properties for over fifty years. Currently, it is under-utilised as a contemporary scientific and engineering tool for investigating the condition of pipes whose inner surface has been exposed to chemical attack. We describe the design, development and calibration of a portable probe which uses a penetrative strain gauge load cell to measure where the semi-solid surface starts and stops within a pipe. We also describe the results of field tests of the probe in concrete sewers, affected by internal corrosion, where the probe proved to be a fast and reliable method for collecting pipe profile information. The results indicate significant benefit in the use of penetrometers to perform concrete sewer condition assessment

Fracture Behavior of Hydroxyapatite-Filled Polycaprolactone

This paper reports some fracture characterization results of hydroxyapatite (HAP)-filled poly(ε-caprolactone) (PCL). For the fracture toughness tests, the HAP concentration was steadily increased. The effect of HAP phase in PCL on the fracture and tearing toughnesses was investigated. The techniques of essential work of fracture (EWF) and tear strength were attempted. T-peel test was also used to evaluate the adhesive bond strength between HAP and PCL components using compression molded PCL-HAP-PCL laminates. Little is reported on the interfacial adhesion properties between bioactive components in scaffold development. The influence of PCL layer thickness (1.25, 2.5 and 3.5 mm) on adhesive strength between HAP and PCL was investigated. The adhesion between HAP and PCL components was found to be relatively strong; however, the thickness of PCL layers did not significantly influence the adhesive strength

Fracture Strength and Adhesive Strength of Hydroxyapatite-Filled Polycaprolactone

Fracture toughness and tear strength of hydroxyapatite (HAP)-filled poly(epsilon-caprolactone) (PCL) with increasing HAP concentration were studied. The toughness was assessed in terms of essential work of fracture (EWF). Adhesive strength between HAP and PCL interfaces was evaluated using T-peel testing. The adhesion between the two components was found to be relatively strong. Double edge notched tension (DENT) and trousers test specimens were used for the EWF tests. The effect of HAP phase in PCL on the fracture and tearing toughness was investigated. The results obtained from the EWF tests for the HAP-filled PCL complied with the validity criteria of the EWF concept, namely, (1) geometric similarity for all ligament lengths; (2) fully yielded ligament and (3) plane-stress fracture condition. Values for specific essential work of fracture (w ( e )) and specific plastic work of fracture (betaw ( p )) were found to decrease with increase in HAP concentration. The testing procedure showed promise in quantifying the tearing resistance and rising R-curve behavior common in natural materials and it can be extended to other biomaterials that exhibit post-yield deformation. A quantitative assessment based on fracture mechanics of the adhesive strength between the bioactive interfaces plays an important role for continued development of tissue replacement and tissue regeneration materials

Interfacial Adhesion between Hydroxyapatite and poly(E-caprolactone) and their Electrospun Composite Toughness

The interfacial adhesive strength between hydroxyapatite (HAP) and poly(?-caprolactone) (PCL) were determined using T-peel tests. Their composite fracture toughness was determined using essential work of fracture concept. Electrospinning techniques were employed to obtain nanometer scale PCL fibers with and without HAP reinforcements which also create micrometer-scale porosity in the structure. The effects of HAP morphology and HAP content on mechanical properties were evaluated

Effect of Fiber Diameter on Tensile Properties of Electrospun Poly(ɛ-Caprolactone)

The tensile properties of electrospun fibers have not been widely investigated due to the difficulties in handling nanofibers and measuring low load for deformation. In this study, the effect of dimensional confinement on free standing biodegradable poly(ɛ-caprolactone) (PCL) is investigated using electrospinning-enabled techniques and a nanoforce tensile tester. The structural properties such as crystallinity and molecular orientation of the spun fibers are examined using wide angle X-ray diffraction (WAXD). The degree of crystallinity and molecular orientation of fibers are enhanced when the diameter of spun fibers is reduced, resulting in improved mechanical strength and stiffness. It is evident that PCL fibers with decreasing fiber diameter exhibit an abrupt shift in tensile performance in comparison to those derived from non-spun systems. The abrupt shift in tensile strength and stiffness of electrospun PCL fibers occurs at around 700 nm in diameter and illustrates the importance of studying the mechanical behavior of the nanofibers, for the first time, systematically with the aid from electrospinning techniques. This shift cannot be otherwise explained by a noticeable change in Tg, and the gradual increase in crystallinity and molecular orientation

Hyperelastic Modeling of Enhanced Mechanical Properties of Electrospun Poly(-caprolactone) Fibers

Little is understood on the deformation of electrospun nanofibers. This study aims to evaluate the electrospun nanofiber deformation in both macroscopic and nanometer length scales using the classical hyperelastic models. The Mooney-Rivlin models are used to evaluate the tensile properties of poly(?-caprolactone) (PCL) made by the electrospinning technique. The stress-strain relationships of single fibers are reported. This study also provides comparative analyses among Mooney-Rivlin models. Analytical calculations illustrate the importance of understanding crystallinity and molecular orientations of nanofibers