Fiber Defects Research Articles

Defects in natural fibres: their origin, characteristics and implications for natural fibre-reinforced composites

This article reviews defects in natural fibres and how, ultimately, they affect the properties of composite materials reinforced with such fibres. Under ideal circumstances, certain natural fibre like flax and hemp can display excellent tensile mechanical properties. However, the potential of the fibre is generally not realised in natural fibre-reinforced composites. Partly, this poor performance can be explained by the presence of defects in the fibres known variously as dislocations, kinks or microcompressions. After briefly considering the chemistry and structure of plant fibres, the properties of selected natural fibres are reviewed. The origin of defects and the impact that processing has on their presence is then considered. The effect that defects have on the mechanical properties of bast fibre and their susceptibility to chemical degradation is also reviewed. Finally, the effect that dislocations have on the properties of composites reinforced with natural fibres is discussed and areas of potential further research needed are highlighted.

Fiber making directly from poly(tetrafluoroethylene) emulsion

Poly(tetrafluoroethylene) (PTFE) fiber with a superior mechanical property was prepared directly from its emulsion by the novel manufacturing process. The PTFE emulsion turned into a paste when a high shear flow was applied and the paste was extruded through a nozzle into a strand consisting of fine PTFE particles. The diameter of the strand was reduced stepwise by applying the die-drawing process through a conical die at a low temperature. The strand was further die-drawn down at elevated temperatures into fine PTFE fibers with a highly oriented crystalline structure. The crystalline orientation factor of the PTFE fiber reached very close to unity. Although the fibers obtained have a very high tensile modulus, the tensile strength was not as high as that expected from the crystalline orientation, suggesting that the presence of some defects in the PTFE fiber formed in the instantaneous deformation.

Influence of nanostructured defects in carbon fibers and ribbons on sensor properties

The present report describes the experimental studies of sensor (electrophysical) properties for carbon fibers and ribbons on the number and shapes of their nanostructured defects. The structural studies conducted allow one to determine the different structural components of carbon fibers and ribbons.

Advantages and limitations of the fiber‐optic probe hydrophone for characterization of shock waves in water.

The fiber‐optic probe hydrophone (FOPH) (RP Acoustics, Leutenbach, Germany) is the standard for shock wave measurement, as it is omnidirectional with a flat frequency response ranging from static pressure to several megahertz. The FOPH calibration is determined from the equation of state of water, the optical refractive index of the glass/water interface, and the dc level of reflected light. We tested the accuracy of this calibration by placing the sensitive tip of the FOPH under static pressure up to 140 MPa. The FOPH gave accurate readings of applied static pressures provided there were no defects in the fiber. Defects (cracks and chips) in the glass fiber were difficult to control and could occur during routine handling: stripping, cleaving, or mounting. Such defects led to spurious spikes in measured waveforms. Defects were also caused by cavitation damage to the fiber. In addition, cavitation bubbles on the fiber compressed the fiber and resulted in distorted waveform measurement. Thus, although the FOPH is omnidirectional and accurate from zero to tens of megahertz, it is also susceptible to minute defects in the fiber and to cavitation bubble collapse along the fiber. [This work was supported in part by NIH‐DK‐43881 and by Impulse ACPT Contract No. W9113M‐07‐C‐0178.]

Analysis on PLA Textile Fiber Production Technology and Properties

PLA fiber is a green eco-fiber of excellent properties and sustainable development, with adequate sources of raw materials, low energy consumption, good biodegradability, and excellent physical and mechanical properties, thus the development of this product not only has considerable economic benefits, and also has excellent social benefits. In this paper, through comprehensively testing the properties of PLA fiber, it carries out the systematical analysis and research on the Tests of PLA fiber length, fineness, over length, double length, and defects, combustion property, heat resistance, and hydrolysis property, etc. several aspects.

Myasthenic syndrome caused by plectinopathy

Plectin crosslinks intermediate filaments to their targets in different tissues. Defects in plectin cause epidermolysis bullosa simplex (EBS), muscular dystrophy (MD), and sometimes pyloric atresia. Association of EBS with a myasthenic syndrome (MyS) was documented in a single patient in 1999. To analyze the clinical, structural, and genetic aspects of a second and fatal case of EBS associated with a MyS and search for the genetic basis of the disease in a previously reported patient with EBS-MD-MyS. Clinical observations; histochemical, immunocytochemical, and electron microscopy studies of skeletal muscle and neuromuscular junction; and mutation analysis. An African American man had EBS since early infancy, and progressive muscle weakness, hyperCKemia, and myasthenic symptoms refractory to therapy since age 3 years. Eventually he became motionless and died at age 42 years. At age 15 years, he had a marked EMG decrement, and a reduced miniature endplate potential amplitude. The myopathy was associated with dislocated muscle fiber organelles, structurally abnormal nuclei, focal plasmalemmal defects, and focal calcium ingress into muscle fibers. The neuromuscular junctions showed destruction of the junctional folds, and remodeling. Mutation analysis demonstrated a known p.Arg2319X and a novel c.12043dupG mutation in PLEC1. The EBS-MD-MyS patient reported in 1999 also carried c.12043dupG and a novel p.Gln2057X mutation. The novel mutations were absent in 200 Caucasian and 100 African American subjects. The MyS in plectinopathy is attributed to destruction of the junctional folds and the myopathy to defective anchoring of muscle fiber organelles and defects in sarcolemmal integrity.

Scanning transmission electron microscope observations of defects in as-grown and pre-strained Mo alloy fibers

Compression testing of micro-pillars has recently been of great interest to the small-scale mechanics community. Previous compression tests on single crystal Mo alloy micro-pillars produced by directional solidification of eutectic alloys showed that as-grown pillars yield at strengths close to the theoretical strength while pre-strained pillars yield at considerably lower stresses. In addition, the flow behavior changes from stochastic to deterministic with increasing pre-strain. In order to gain a microstructural insight into this behavior, an aberration corrected scanning transmission electron microscope was used to study the defect structures in as-grown and pre-strained single crystal Mo alloy fibers. The as-grown fibers were found to be defect free over large lengths while the highly pre-strained (16%) fibers had high defect densities that were uniform throughout. Interestingly, the fibers with intermediate pre-strain (4%) exhibited an inhomogeneous defect distribution. The observed defect structures and their distributions are correlated with the previously reported stress–strain behavior. Some of the mechanistic interpretations of Bei et al. are examined in the light of new microstructural observations.

Influence of Ce codoping and H 2 pre-loading on Er/Yb-doped fiber: Radiation response characterized by Confocal Micro-Luminescence

Confocal microscopy luminescence measurements were applied to study the X-ray radiation response of Er/Yb-doped optical fibers in connection with H 2 pre-loading and with the addition of another lanthanide element (Cerium) in the core composition. Laser excitations at 488 nm and 325 nm allow deriving the emission and absorption pattern of Er 3+, the latter derived from the dips appearing in a wide luminescence band related to defects in silica. We found that the luminescence spectrum of the X-irradiated Er/Yb-doped core fiber evidences an increase in the emission intensity around 520 and 660 nm; in contrast, no changes are induced by radiation neither after H 2 pre-loading nor when the Cerium is added to the core composition. Both treatments reduce the generation of defects in the Er-doped fibers thus providing hardness in the radiative environment.

Luminescent Porous Silica Fibers as Drug Carriers

Luminescent and porous silica fibers have been successfully prepared by using the electrospinning process. The obtained multifunctional silica fibers, which possess a porous structure and display blue luminescence, can serve as a drug delivery host carrier, using ibuprofen (IBU) as a model drug, allowing the investigation of storage/release properties. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), N(2) adsorption/desorption, photoluminescence (PL) spectra, and kinetic decay were used to characterize the structural, morphological, and optical properties of the as-obtained samples. The results reveal that the multifunctional silica materials exhibit an irregular porous structure, and display a fiberlike morphology with dimensions of several hundred nanometers in width and several millimeters in length. The obtained silica fibers exhibit an intense broad bluish emission, which might be attributed to impurities and/or defects in the silica fibers. The IBU-loaded silica fiber system shows blue luminescence under UV irradiation and controlled release behavior for IBU. In addition, the emission intensities of silica fibers in the drug carrier system vary with the released amount of IBU, thus allowing the drug release to be easily tracked and monitored by the change of the luminescence intensity.

Isolated thoracic aortitis: clinicopathological and immunohistochemical study of 11 cases

Isolated thoracic aortitis (ITA) is diagnosed in a variable proportion of patients operated on for dilation/aneurysm of ascending aorta. The etiopathogenesis of ITA remains unclear. We studied 11 cases of ITA in order to determine the role of IgG4-mediated immune responses in its pathogenesis. The series included nine women and two men aged 52-79 years. All patients developed aortic incompetence due to dilation/aneurysm of ascending aorta. None of the patients had a history of IgG4-related disease neither did they develop features of such disease during the follow-up period. The microscopic findings included the presence of lymphoplasmacellular fibrosing infiltrate of varied intensity involving the adventitia and media of aorta. This inflammation was associated with severe medial elastic fiber defects. Obliterative phlebitis of the vasa vasorum was absent. Immunohistochemically, the inflammatory infiltrate comprised T- and B-lymphocytes as well as plasma cells. The plasma cell population was polyclonal with a predominance of IgG-producing cells. In all the cases, IgG4-producing plasma cells were detected. In five cases, the count exceeded 20 cells per high-power field. The IgG4/IgG ratio ranged from 0.07 to 0.98 (median 0.55). In six cases with the ratio >0.50, severe adventitial fibrosis was present. To the best of our knowledge, ours is the first study focused on investigating the role of IgG4-positive plasma cells in the development of ITA. Our results suggest that a subset of ITA may represent aortic manifestation of IgG4-related disease. Further research is necessary in order to clarify this issue.

Comparison of gunshot injuries caused from Tokarev, Makarov and Glock 19 pistols at firing distances of 1, 3 and 5 cm

Test shots at cloth and at human skin from autopsy material were performed with 7.62 mm Tokarev (TT), 9 mm Makarov (PM) and 9 × 19 mm Glock 19 pistols, using common ammunition. The largest central material defects, with fibre deformation in cotton, the largest burn holes in polyester, and also many fibre defects caused by the perforation of powder, were produced in shots from the TT at all distances. Tears in the cloth were longest in the case of the TT at 1 cm and were present at 3 cm, whereas the shots from the PM and the Glock 19 did not leave tears. There were small tears of the edges of the skin defect from shots fired from the TT at 1 and 3 cm. On cloth-soot deposits at 3 and 5 cm, the radial structures of soot resembled a cobweb (the TT), and radial branching structures (the PM) of soot were seen. Some shots from the PM left four shafts of rays of soot and formed the bullet wipe with four narrow and four wide sections, indicating the form of rifling. In the soot deposit from the Glock 19 with hexagonal rifling, hexagonal or polygonal or petal-like areas were visible. On skin, the soot zones were less distinct. The Glock 19 (at 3 and 5 cm) left a lot of gunpowder particles densely around the cloth and skin defect. The least powder left on the cloth and skin was by the PM. On histological tissue sections, in shots from the TT, a lot of soot and gunpowder residue particles in the epidermis and in both layers of the dermis, and intraepithelial tears and recesses containing soot, were seen. The PM left fine soot and only a few gunpowder particles in the epidermis and in the papillary layer of the dermis. The Glock 19 produced the least soot and a lot of gunpowder particles. The soot and most of the gunpowder particles were present on the tissue sections, which originated from the central area around the skin defect and were detected in the epidermis and in both layers of the dermis. Some tears and recesses in the epidermis were also seen. The further the distance from the centre of skin defect to the periphery, the depth of the penetration of the powder into the skin decreased.

Increased Calcium Response to Depolarization in Voltage Clamped Skeletal Muscle Cells of a Transgenic Model of Amyotrophic Lateral Sclerosis

Mitochondrial Ca uptake is believed to help regulate mitochondrial metabolism and synthesis of ATP to meet the demands of muscle contraction. Whether mitochondrial Ca uptake modifies Ca signaling during EC-coupling remains an open question. While studies show that mitochondria in skeletal muscle may take up Ca during contraction, it is not known whether altered mitochondrial Ca uptake can play a role in pathophysiological conditions. Our study on ALS mouse model G93A shows that ALS muscle fibers display defective mitochondria with loss of their inner membrane potential in fiber segments. The finding of localized mitochondrial defects in ALS fibers presents a unique opportunity to test whether changes in mitochondrial function can affect intracellular Ca signaling, as Ca release activity can be compared in regions with or without depolarized mitochondria in the same muscle fiber. By loading muscle fibers with TMRE (a probe of mitochondrial membrane potential) and fluo-4 (a Ca indicator) we characterized simultaneously mitochondrial function and Ca release activity in living muscle fibers. The fiber segment with depolarized mitochondria shows greater osmotic stress-induced Ca release activity. Abolishing mitochondrial inner membrane potential by FCCP or blocking mitochondrial uniporter by Ru360 exacerbates the osmotic stress-induced hyperactive Ca release. Furthermore, we evaluated the voltage-induced Ca transient by patch-clamping ALS fibers and found that fiber segments with depolarized mitochondria displayed 5∼25% greater Ca transients. Our study constitutes a direct demonstration of the importance of mitochondria in shaping cytosolic Ca signaling in skeletal muscle. Malfunction of mitochondrial Ca uptake may play an important role in muscle degeneration of ALS. Supported by MDA/NIH.

Functional Characterization of Poplar Wood-Associated NAC Domain Transcription Factors

Wood is the most abundant biomass produced by land plants. Dissection of the molecular mechanisms underlying the transcriptional regulation of wood formation is a fundamental issue in plant biology and has important implications in tree biotechnology. Although a number of transcription factors in tree species have been shown to be associated with wood formation and some of them are implicated in lignin biosynthesis, none of them have been demonstrated to be key regulators of the biosynthesis of all three major components of wood. In this report, we have identified a group of NAC domain transcription factors, PtrWNDs, that are preferentially expressed in developing wood of poplar (Populus trichocarpa). Expression of PtrWNDs in the Arabidopsis (Arabidopsis thaliana) snd1 nst1 double mutant effectively complemented the secondary wall defects in fibers, indicating that PtrWNDs are capable of activating the entire secondary wall biosynthetic program. Overexpression of PtrWND2B and PtrWND6B in Arabidopsis induced the expression of secondary wall-associated transcription factors and secondary wall biosynthetic genes and, concomitantly, the ectopic deposition of cellulose, xylan, and lignin. Furthermore, PtrWND2B and PtrWND6B were able to activate the promoter activities of a number of poplar wood-associated transcription factors and wood biosynthetic genes. Together, these results demonstrate that PtrWNDs are functional orthologs of SND1 and suggest that PtrWNDs together with their downstream transcription factors form a transcriptional network involved in the regulation of wood formation in poplar.

Sensitivity Analysis of the Pressure-Based Direct Integrity Test for Membranes Used in Drinking Water Treatment

We conducted a sensitivity analysis of the commonly employed pressure-based direct integrity test (DIT), the most sensitive test for defects in low-pressure hollow fiber (LPHF) microfiltration and ultrafiltration systems used in drinking water treatment. Incorporating uncertainty to assess the practice of DIT, we find the resolution in some tests may be insufficient to verify the presence of a barrier to oocysts of Cryptosporidium. Applying distributions and boundaries derived from literature and practice, we solved for the defect size resolution (DSR) using Monte Carlo and Probability Bounds Analysis for five commercial membrane designs. Surface tension was modeled using annual temperature profiles from three rivers. Contact angle measurement error and variability were derived from literature, respectively, as a standard deviation of 5.7 degrees and +/- 9.6 degrees median change due to natural organic matter (NOM) fouling. These measures of contact angle uncertainty and variability were combined in a normal distribution with the discrete values currently applied. Additionally we considered model uncertainty, applying the maximum bubble pressure method, an established method of surface tension measurement in liquids in which the maximum air pressure in a submerged capillary is developed after the contact angle becomes zero prior to bubble formation. Where the DSR exceeds 3 microm the test design is not compliant with applicable drinking water regulations. Implications include uncertain and variable log-removal values (LRV) as determined by DIT due to the possible emergence of defects large enough to allow oocysts to pass without detection by the DIT. Specifically, we found the DSR may exceed 3 microm and may be as large as 8 microm. With the variable contact angle model, all lower bound possibilities are compliant, whereas the upper bound is over 80% noncompliant for three of five commercial designs. Using the Maximum Bubble Pressure Method, the lower bounds in three designs start to exceed 3 microm for between 50 and 100% of the produced water, whereas the upper bounds of the DSR completely exceed 3 microm for four of five commercial designs examined.

Identification method of structural defects in glass fiber fabric/epoxy resin laminate

We present the experimental methods proposed for the identification of structural defects of the laminate constituted of 12 layers of glass fiber fabric/epoxy resin. Two techniques of control were used to analyze the principal structural defects (local or global disorientation). The first technique provides a superficial observation (macroscopic analysis) of the superior and lower surfaces of each layer, while the second one ensures internal observation (microscopic analysis) of different layers after pyrolysis of the matrix (delamination of the laminate).

Effects of commercial cellobiohydrolase treatment on fiber strength and morphology of bleached hardwood pulp 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Abstract Development of fiber strength properties and morphological changes on the surface of bleached hardwood kraft pulp after treatment with commercial cellobiohydrolase (CBH) was evaluated. Tensile and tear indices showed no significant effect of the treatment. The treatment resulted in reduction of wet zero-span strength, while the dry zero-span values increased. The decrease in wet zero-span values was most likely caused by preferential action of CBH on structurally irregular zones in the fiber wall coupled with greater sensitivity of wet zero-span testing towards the localized fiber defects. The fracture zone of the wet zero-span tested samples was imaged by scanning electron microscopy (SEM). Visual observation revealed differences in fiber fracture between treated and control samples. The straighter and cleaner fractures of the treated sample could be attributed to the localized hydrolytic action of CBH. Visual analysis of the treated fiber surface morphology by SEM showed an increase of more visible fiber wall dislocations, particularly on fibers of smaller diameter. The increased presence of the fiber dislocation correlates with the decrease in the wet zero-span values of treated samples.

Fibulin-5, an integrin-binding matricellular protein: its function in development and disease.

Interactions between the extracellular matrix (ECM) and cells are critical in embryonic development, tissue homeostasis, physiological remodeling, and tumorigenesis. Matricellular proteins, a group of ECM components, mediate cell-ECM interactions. One such molecule, Fibulin-5 is a 66-kDa glycoprotein secreted by various cell types, including vascular smooth muscle cells (SMCs), fibroblasts, and endothelial cells. Fibulin-5 contributes to the formation of elastic fibers by binding to structural components including tropoelastin and fibrillin-1, and to cross-linking enzymes, aiding elastic fiber assembly. Mice deficient in the fibulin-5 gene (Fbln5) exhibit systemic elastic fiber defects with manifestations of loose skin, tortuous aorta, emphysematous lung and genital prolapse. Although Fbln5 expression is down-regulated after birth, following the completion of elastic fiber formation, expression is reactivated upon tissue injury, affecting diverse cellular functions independent of its elastogenic function. Fibulin-5 contains an evolutionally conserved arginine-glycine-aspartic acid (RGD) motif in the N-terminal region, which mediates binding to a subset of integrins, including α5β1, αvβ3, and αvβ5. Fibulin-5 enhances substrate attachment of endothelial cells, while inhibiting migration and proliferation in a cell type- and context-dependent manner. The antagonistic function of fibulin-5 in angiogenesis has been demonstrated in vitro and in vivo; fibulin-5 may block angiogenesis by inducing the anti-angiogenic molecule thrompospondin-1, by antagonizing VEGF165-mediated signaling, and/or by antagonizing fibronectin-mediated signaling through directly binding and blocking the α5β1 fibronectin receptor. The overall effect of fibulin-5 on tumor growth depends on the balance between the inhibitory property of fibulin-5 on angiogenesis and the direct effect of fibulin-5 on proliferation and migration of tumor cells. However, the effect of tumor-derived versus host microenvironment-derived fibulin-5 remains to be evaluated.

High temperature does not alter fatigability in intact mouse skeletal muscle fibres

Intense activation of skeletal muscle results in fatigue development, which involves impaired function of the muscle cells resulting in weaker and slower contractions. Intense muscle activity also results in increased heat production and muscle temperature may rise by up to 6 degrees C. Hyperthermia is associated with impaired exercise performance in vivo and recent studies have shown contractile dysfunction and premature fatigue development in easily fatigued muscle fibres stimulated at high temperatures and these defects were attributed to oxidative stress. Here we studied whether fatigue-resistant soleus fibres stimulated at increased temperature show premature fatigue development and whether increasing the level of oxidative stress accelerates fatigue development. Intact single fibres or small bundles of soleus fibres were fatigued by 600 ms tetani given at 2 s intervals at 37 degrees C and 43 degrees C, which is the highest temperature the muscle would experience in vivo. Tetanic force in the unfatigued state was not significantly different at the two temperatures. With 100 fatiguing tetani, force decreased by approximately 15% at both temperatures; the free cytosolic [Ca(2+)] (assessed with indo-1) showed a similar approximately 10% decrease at both temperatures. The oxidative stress during fatigue at 43 degrees C was increased by application of 10 microM hydrogen peroxide or tert-butyl hydroperoxide and this did not cause premature fatigue development. In summary, fatigue-resistant muscle fibres do not display impaired contractility and fatigue resistance at the highest temperature that mammals, including humans, would experience in vivo. Thus, intrinsic defects in fatigue-resistant muscle fibres cannot explain the decreased physical performance at high temperatures.

Radiation-induced defects in fluorine-doped silica-based optical fibers: Influence of a pre-loading with H2

We investigated the effects of 10-keV X-ray radiation on the transmission properties of F-doped optical fibers in the 200–850 nm range of wavelengths (1.5–6 eV). We also studied the influence of pre-loading this kind of fibers with hydrogen on its radiation sensitivity. Our results showed that, for our experimental conditions (pre-treatment with H2 several months before irradiation with diffusion of all the H2 out the fiber core and cladding before X-ray exposure), this pre-treatment increases the radiation-induced attenuation in the ultraviolet part (200–300 nm) of the spectrum. A previous H2-loading has no influence at greater wavelengths. The nature of the radiation-induced point defects is discussed from the decomposition analysis of the attenuation spectra with Gaussian bands.

Paramagnetic germanium-related centers induced by energetic radiation in optical fibers and preforms

We investigated the creation processes of Ge-related paramagnetic point defects in silica fibers and preforms, doped with different amounts of germanium, and X-ray irradiated at several radiation doses. Different paramagnetic defect species, like GeE′, Ge(1) and Ge(2), were revealed by electron paramagnetic resonance measurements and their concentration was studied as a function of the irradiation dose. The comparison with the optical absorption spectra points out the main role of Ge(1) on the optical transmission loss of fibers in the UV region.