High Tensile Strength (high + tensile_strength)

Distribution by Scientific Domains

Selected Abstracts

Disc structure function and its potential for repair

J. Melrose
The intervertebral disc (IVD) is the largest predominantly avascular, aneural, alymphatic structure of the human body. It provides articulation between adjoining vertebral bodies and also acts as a weight-bearing cushion dissipating axially applied spinal loads. The IVD is composed of an outer collagen-rich annulus fibrosus (AF) and a central proteoglycan (PG)-rich nucleus pulposus (NP). Superior and inferior cartilaginous endplates (CEPs), thin layers of hyaline-like cartilage, cover the ends of the vertebral bodies. The AF is composed of concentric layers (lamellae) which contain variable proportions of type I and II collagen, this tissue has high tensile strength. The NP in contrast is a gelatinous PG-rich tissue which provides weight-bearing properties to the composite disc structure. With the onset of age, cells in the NP progressively die as this tissue becomes depleted of PGs, less hydrated and more fibrous as the disc undergoes an age-dependent fibrocartilaginous transformation. Such age-dependent cellular and matrix changes can decrease the discs' biomechanical competence and trauma can further lead to failure of structural components of the disc. Annular defects are fairly common and include vertebral rim-lesions, concentric (circumferential) annular tears (separation of adjacent annular lamellae) and radial annular tears (clefts which initiate within the NP). While vascular in-growth around annular tears has been noted, evidence from human post-mortem studies indicate they have a limited ability to undergo repair. Several experimental approaches are currently under evaluation for their ability to promote the repair of such annular lesions. These include growth of AF fibrochondrocytes on a resorbable polycaprolactone (PCL) bio-membrane.1 Sheets of fibrochondrocytes lay down type-I collagen and actin stress fibres on PCL. These matrix components are important for the spatial assembly of the collagenous lamella during annular development and correct phenotypic expression of cells in biomatrices.1 An alternative approach employs preparation of tissue engineered IVDs where AF and NP cells are separately cultured in polyglycolic acid and sodium alginate biomatrices, either separately or within a manifold designed to reproduce the required IVD dimensions for its use as a prospective implant device.2 AF and NP cells have also been grown on tissue culture inserts after their recovery from alginate bead culture to form plugs of tissue engineered cartilage.3 A key component in this latter strategy was the stimulation of the high density disc cell cultures with osteogenic protein-1 (OP-1) 200 ng/mL.3 This resulted in the production of tissue engineered AF and NP plugs with compositions, histochemical characteristics and biomechanical properties approaching those of the native disc tissues.2,3 Such materials hold reat promise in future applications as disc or annular implants. The introduction of appropriate genes into disc cells by gene transduction methodology using adenoviral vectors or ,gene-gun' delivery systems also holds considerable promise for the promotion of disc repair processes.4 Such an approach with the OP-1 gene is particularly appealing.5 The anchoring of discal implants to vertebral bodies has also been evaluated by several approaches. A 3D fabric based polyethylene biocomposite holds much promise as one such anchorage device6 while biological glues used to seal fibrocartilaginous structures such as the AF and meniscus8 following surgical intervention, also hold promise in this area. Several very promising new experimental approaches and strategies are therefore currently under evaluation for the improvement of discal repair. The aforementioned IVD defects are a common cause of disc failure and sites of increased nerve in-growth in symptomatic IVDs in man and are thus often sources of sciatic-type pain. Annular defects such as those described above have formerly been considered incapable of undergoing spontaneous repair thus a clear need exists for interventions which might improve on their repair. Based on the rapid rate of progress and the examples outlined above one may optimistically suggest that a successful remedy to this troublesome clinical entity will be developed in the not so distant future. References 1JohnsonWEBet al. (2001) Directed cytoskeletal orientation and intervertebral disc cell growth: towards the development of annular repair techniques. Trans Orthop Res Soc26, 894. 2MizunoHet al. (2001) Tissue engineering of a composite intervertebral disc. Trans Orthop Res Soc26, 78. 3MatsumotoTet al. (2001) Formation of transplantable disc shaped tissues by nucleus pulposus and annulus fibrosus cells: biochemical and biomechanical properties. Trans Orthop Res Soc26, 897. 4NishidaKet al. (2000) Potential applications of gene therapy to the treatment of intervertebral disc disorders. Clin Orthop Rel Res379 (Suppl), S234,S241. 5MatsumotoTet al. (2001) Transfer of osteogenic protein-1 gene by gene gun system promotes matrix synthesis in bovine intervertebral disc and articular cartilage cells. Trans Orthop Res Soc26, 30. 6ShikinamiY , Kawarada (1998) Potential application of a triaxial three-dimensional fabric (3-DF) as an implant. Biomaterials19, 617,35. [source]

Polyamide 66 binary and ternary nanocomposites: Mechanical and morphological properties

Miray Mert
Abstract Polyamide 66 (PA 66)/impact modifier blends and polyamide/organoclay binary and PA 66/organoclay/impact modifier ternary nanocomposites were prepared by the melt-compounding method, and the effects of the mixing sequences on the morphology and mechanical and flow properties were investigated. Lotader AX8840 and Lotader AX8900 were used as impact modifiers. The concentrations of the impact modifiers and the organoclay (Cloisite 25A) were maintained at 2 and 5 wt %, respectively. Both the binary and ternary nanocomposites displayed high tensile strength and Young's modulus values compared to the PA 66/impact modifier blends. Decreases occurred in the strength and stiffness of the binary nanocomposites upon incorporation of the elastomeric materials into the polymeric matrix. In general, the mixing sequence in which all three ingredients were added simultaneously and extruded twice (the All-S mixing sequence) exhibited the most enhanced mechanical properties in comparison with the mixing sequences in which two of the components were extruded in the first extrusion step and the third ingredient was added in the second extrusion step. The mechanical test results were in accordance with the organoclay dispersion. The impact strength was highly affected by the elastomeric domain sizes, interdomain distances, interfacial interactions, and organoclay delamination. The smallest elastomeric domain size was obtained for the All-S mixing sequence, whereas the elastomeric domain sizes of the other mixing sequences were quite close to each other. Drastic variations were not observed between the melt viscosities of the ternary nanocomposites prepared with different mixing sequences. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Novel organosoluble and colorless poly(ether imide)s based on 3,3-bis[4-(3,4-dicarboxyphenoxy)phenyl]phthalide dianhydride and aromatic bis(ether amine)s bearing pendent trifluoromethyl groups

Chin-Ping Yang
Abstract A novel series of colorless and highly organosoluble poly(ether imide)s were prepared from 3,3-bis[4-(3,4-dicarboxyphenoxy)phenyl]phthalide dianhydride with various fluorinated aromatic bis(ether amine)s via a conventional two-stage process that included ring-opening polyaddition to form the poly(amic acid)s followed by cyclodehydration to produce the polymer films. The poly(ether imide)s showed excellent solubility, with most of them dissoluble at a concentration of 10 wt % in amide polar solvents, in ether-type solvents, and even in chlorinated solvents. Their films had a cutoff wavelength between 358 and 373 nm, and the yellowness index ranged from 3.1 to 9.5. The glass-transition temperatures of the poly(ether imide) series were recorded between 237 and 297 C, the decomposition temperatures at 10% weight loss were all above 494 C, and the residue was more than 54% at 800 C in nitrogen. These films showed high tensile strength and also were characterized by higher solubility, lighter color, and lower dielectric constants and moisture absorption than an analogous nonfluorinated polyimide series. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3140,3152, 2006 [source]

Thermoplastic Acrylic Rubber Physically Crosslinked by Tiny Poly(vinylidene fluoride) Crystals

Yongjin Li
Abstract Summary: Acrylic rubber showed greatly improved mechanical properties and very nice elasticity when blended with small amount of PVDF. PVDF crystallized into very sparse and loose spherulites in the blends with ACM molecular chains incorporated into the PVDF lamellae. These micro-crystals were precisely dispersed in the ACM matrix and acted as the physical crosslink points for the matrix upon stretching. Therefore, the ACM/PVDF blends containing small amounts of PVDF display the typical properties of thermoplastic elastomers with large elongation at break, high tensile strength, and excellent strain recovery from the highly deformed state. Schematic diagram of physically crosslinked ACM by the tiny PVDF crystals in ACM-rich PVDF/ACM blends. [source]

Processing of a Strong Biodegradable Poly[(R)-3-hydroxybutyrate] Fiber and a New Fiber Structure Revealed by Micro-Beam X-Ray Diffraction with Synchrotron Radiation

Tadahisa Iwata
Abstract Summary: Biodegradable poly[(R)-3-hydroxybutyrate] (P(3HB)) fibers with high tensile strength of 1.32 GPa were processed from ultra-high-molecular-weight P(3HB) by a method combining cold-drawing and two-step-drawing procedures at room temperature. The distribution of molecular structures in a mono-filament was analyzed by micro-beam X-ray diffraction with synchrotron radiation. It was revealed that the P(3HB) fiber has a new core-sheath structure consistent with two types of molecular conformations: a 21 helix conformation in the sheath region and a planar zigzag conformation in the core region. P(3HB) fiber processed by cold-drawing in ice water and two-step drawing at room temperature, and subsequently annealing at 50,C. [source]

Production of leather-like composites using short leather fibers.


Leather-like composites were prepared by addition of chemically modified short leather fibers (SLF) into a plasticized polyvinyl chloride (pPVC) matrix. The fibers were subjected to chemical modification by emulsion polymerization to achieve good interfacial adhesion between SLF and the pPVC matrix. The SLF with chemical modification were obtained from three different reaction conditions where these SLF have different percentages of grafted and deposited PMMA polymer onto the fiber surface. The incorporation of the SLF into the thermoplastic matrix was carried out using a torque-rheometer and the composites obtained were molded by compression. Tensile and tear mechanical tests were performed on composite samples, and the morphology of the fractured surfaces was analyzed using scanning electron microscopy (SEM). The results show that the incorporation by grafting of polymethyl metacrylate (PMMA) onto the fibers produced a significant improvement of their interfacial adhesion to pPVC, promoting the compatibilization between the fiber surface and matrix. The findings are discussed and interpreted in terms of enhanced adhesion at phase boundaries. Overall, the results confirm that it is possible to produce modified leather composites based on a pPVC matrix, which exhibit relatively high tensile strength, tear resistance and flexibility. These composites are very suitable candidate materials for applications in the footwear industry. [source]

The rotational molding of a thermotropic liquid crystalline polymer

Eric Scribben
Thermotropic liquid crystalline polymers (TLCPs) exhibit a number of mechanical and physical properties such as excellent chemical resistance, low permeability, low coefficient of thermal expansion, high tensile strength and modulus, and good impact resistance, which make them desirable as a rotationally molded storage vessel. However, there are no reports in the technical literature of the successful rotational molding of TLCPs. In this article, conditions are identified that lead to the successful rotational molding of a TLCP, Vectra B 950. First, a technique was developed to produce particles suitable for rotational molding because TLCPs cannot be ground into a free-flowing powder. Second, because the viscosity at low shear rates can be detrimental to the sintering process, coalescence experiments with isolated particles were carried out to determine the thermal and environmental conditions at which sintering should occur. These conditions were then applied to static sintering experiments to determine whether coalescence and densification of the bulk powder would occur. Finally, the powders were successfully rotationally molded into tubular structures in a single axis, lab-scale device. The density of the molded structure was essentially equivalent to the material density and the tensile strength and modulus were approximately 18 MPa and 2 GPa, respectively. POLYM. ENG. SCI., 45:410,423, 2005. 2005 Society of Plastics Engineers [source]

Mesoscopic Structure and Properties of Liquid Crystalline Mesophase Pitch and Its Transformation into Carbon Fiber

Isao Mochida
Abstract The history and present state of the art in the chemistry of mesophase pitch, which is an important precursor for carbon fiber and other high-performance industrial carbons, are reviewed relative to their structural properties. The structural concepts in both microscopic and macroscopic views are summarized in terms of the sp2 carbon hexagonal plane as a basic unit common to graphitic materials, its planar stacking in clusters, and cluster assembly into microdomains and domains, the latter of which reflect the isochromatic unit of optical anisotropy. Such a series of structural units is described in a semiquantitative manner corresponding to the same units of graphitic materials, although the size and stacking height of the hexagonal planes (graphitic sheets) are very different. Mesophase pitch is a liquid crystal material whose basic structural concepts are maintained in the temperature range of 250 to 350,C. The melt flow and thermal properties are related to its micro- and mesoscopic structure. The structure of mesophase-pitch,based carbon fiber of high tensile strength, modulus, and thermal conductivity has been formed through spinning, and has inherited the same structural concepts of mesophase pitch. Stabilization settles the structure in successive heat treatments up to 3000,C. Carbonization and graphitization enable growth of the hexagonal planes and their stacking into units of graphite. Such growth is governed and controlled by the alignment of micro- and mesoscopic structures in the mesophase pitch, which define the derived carbon materials as nanostructural materials. Their properties are controlled by the nanoscopic units that are expected to behave as nanomaterials when appropriately isolated or handled. 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2:81,101, 2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10016 [source]

Synthesis and Characterization of Poly(butylene adipate- co - terephthalate) Catalyzed by Rare Earth Stearates

Abstract Rare earth (Nd, Y, La, Dy) stearates have been synthesized and used as single component catalysts for the polycondensation of dimethyl terephthalate, adipic acid and 1,4-butanediol for the first time preparing biodegradable poly(butylene adipate- co -terephthalate) (PBAT) with high molecular weight. The microstructures of PBAT were characterized by 1H NMR spectra. The PBAT exhibits good mechanical properties such as high tensile strength (ca. 20 MPa) and long break elongation (>700%). [source]