Inverse evaluation of the integral ordering of the structure and defectiveness of fibres and yarns for technical applications based on normalized values of the mechanical properties

Methods are proposed for an integral (generalized) evaluation of the degree of ordering of the structure and defectiveness of fibres based on the inverse use of indexes of their mechanical properties — modulus of elasticity and strength — normalized with respect to their maximum attainable values. These maximum attainable values are determined in defined temperature-time conditions for a defect-free polymer crystal by several methods, obtaining values in relatively good agreement. The coefficients characterizing the overall ordering and imperfection of the structure, and the defectiveness of different types of fibres based on linear (aliphatic and aromatic), laminar (carbon), and three-dimensional (silicate) polymers were estimated. Different types of fibres, including fibres of the same type, were compared with respect to the level of structural organization and defectiveness. This could serve as a measure of the perfection of the fabrication processes.St. Petersburg State University of Technology and Design. Translated from Khimicheskie Volokana, No. 5, pp. 34–41 September–October, 1996.     

Struktur und mechanische eigenschaften von hochorientierten polymeren

Correlations between the structure and main mechanical properties of highly oriented linear and laminar polymer structures (fibres, films, needle crystals) are considered. To discuss structural conditionality of mechanical properties, different typical linear polymers having different molecular structure and values of intermolecular interactions are taken as, for example, polyethylene, polypropylene, polyvinyl alcohol, polyacrylonitrile, polyamides, polyesters, cellulose, aromatic polymers and laminar structures as, for example, graphite, boron nitride, silicon carbide. A number of physical and mechanical characteristics of fibres from the above polymers is compared with their structure. Calculation methods of strength and elastic properties of highly oriented polymer materials on the basis of their structural characteristics are given. Extreme mechanical properties of oriented polymer systems are fairly high. Theoretical strength values (at absolute zero temperature) for various polymers are from 600 to 13 000 kp/mm². On the basis of the data of temperature-time dependence of oriented polymers the ultimate strength values have been estimated, i. e. strength values of samples with the ideal structure a t a given temperature and time of destruction. These values are approximately from 1/3 to 4/5 of theoretical strength values (at room temperature and the time of destruction of 10 see). The values of ultimate elastic moduli of oriented linear polymers are up to 25 000 kp/mm², and more than 100 000 kp/mm² for laminar structures. The article summarizes experimental data about physical and mechanical properties of polymer monocrystals and practically obtained mechanical properties of man-made fibres. Relations between strength and elastic properties of oriented polymer substances have been also considered. Data on anisotropy of mechanical properties of oriented polymers as a function of anisotropy of their structure and heterodynamics of energy interactions are reported. Principal conditions determining the applicability of various polymers for preparing high modulus and super strong fibrous polymer materials have been analyzed.     

Change in the Mechanical Properties of Liquid-Crystalline Thermoplastic Polymers at High Temperatures

The change in the modulus of elasticity and tensile strength of initial and heat-treated liquid-crystalline polyester fibres after annealing at a temperature 20-40°C higher than the melting point of the crystallites in the polymers was investigated. It was shown that from 50 to 90% of the initial values of the strength characteristics were preserved. In heating above the melting point of the crystallites, LC polyester fibres can melt into a monolith with preservation of elevated mechanical properties, which permits production of self-reinforced composites. The fibres melt as a result of cooperative molecular movement, and preservation of the strength indexes is ensured by the cross-links formed at high temperatures. Selection of the temperature—time conditions of heat treatment and molding is especially important for production of high-strength self-reinforced composites by melting of LC polyester fibres into a monolith.     

The preparation of ultra-high modulus polypropylene films and fibres

Following the discovery that linear polyethylene can be drawn to very high draw ratios to produce oriented fibres and films with ultra-high initial moduli, a similar study has been undertaken for polypropylene. In particular, the modulus/draw ratio relationship has been obtained for a range of polymers of different molecular weight and molecular weight distribution. The effects of thermal history and draw temperature were studied, and it was shown that under optimum conditions material with an initial modulus at room temperature of 1.9 × 10¹⁰ Nm^?2 (205 gdtex, 3 × 10⁶ psi) can be obtained. This value is at least 50 percent greater than those previously recorded for drawn fibres and about one half of the theoretical modulus.     

Plasticizing polylactide—the effect of different plasticizers on the mechanical properties

Poly(lactide) (PLA), a biodegradable aliphatic polyester with excellent property profiles for different polymer applications, will play a major role in future markets for biodegradable polymers from renewable resources. PLA is a very brittle and stiff polymer with a glass transition temperature of around 58°C. The mechanical properties of PLA are comparable to those of polystyrene, with an elasticity modulus of 3500 MPa, a maximum tensile strength of 50 MPa, and an elongation at break of 4%. To introduce PLA into other applications requiring other mechanical property profiles, especially higher flexibility and higher impact resistance, it is necessary to use plasticizers. In this study the influence of several biocompatible plasticizer systems on the mechanical properties of PLA is determined. Poly(ethylene glycol), glucosemonoesters and partial fatty acid esters are introduced at 2.5, 5, and 10 wt% into polylactide. The mechanical properties, such as impact strength and the stress-strain-interrelationship of tensile tests, show changes, which are discussed.     

Thermoreversible Gels as Precursors of Polyacrylonitrile Fibres

Quantitative estimations of the kinetic parameters of phase transformations resulting in the formation and melting of thermoreversible gels in the high-molecular-weight PAN—PCT (propylene carbonate) system were obtained. Correlations were established between the conditions of production of the gels (xerogels) and their structure and mechanical properties. The selection of conditions ensuring production of highly oriented samples characterized by a modulus of elasticity of 19 GPa and breaking strength of 0.7 GPa was substantiated for the PAN—PCT system.     

Physicomechanical Properties of Carbon-Containing Film Composite Materials

Addition of 5 to 20% carbon filler to film composite material (FCM) decreases its strength and mechanical modulus of elasticity. Addition of porous carbon fillers (Aktilen fibre, industrial carbon, activated carbon) decreases the physicomechanical properties of FCM even at a low content, under 5%. FCM made from a liquid composition and containing carbon fibres exhibit anisotropy of the mechanical properties due to orientation of the filler; the strength and modulus of elasticity are higher in the longitudinal than in the transverse direction. A hypothesis is advanced concerning the presence of defective regions on the polymer—filler interface and stress concentration on the ends of the fibres, which probably also causes the decrease in the mechanical properties of the FCM. Acoustic studies suggested the existence of contacts between the carbon fibres at a content in FCM of 10% and higher. __________ Translated from Khimicheskie Volokna, No. 4, pp. 52–55, July–August, 2005.     

Development of high‐strength fibers from aliphatic polyketones by melt spinning and drawing

We have investigated the formation of high‐strength, high‐modulus fibers from four aliphatic polyketone resins. One resin was a perfectly alternating copolymer of ethylene and carbon monoxide, while the other three were terpolymers containing up to 6 mol % propylene. The mechanical properties were measured as a function of processing conditions, and the structures of the filaments were characterized using birefringence, WAXS, SAXS, SEM, and thermal analysis. Fibers formed from all resins develop very high molecular orientations and a microfibrillar structure. Fibers having room temperature tenacities as high as 10 gpd (～1.1 GPa) were obtained. Tensile moduli reached values as high as 120 gpd (～13 GPa). The melting point of the fibers was primarily dependent on the composition of the resin, while the maximum strength and modulus were largely determined by the maximum draw ratio achieved. The maximum draw ratio achieved in the present experiments was greater for the terpolymers than for the copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1794–1815, 2001     

Macroscopic effective moduli and tensile strength of saturated concrete

Many concrete structures such as dams, abutment piers of bridges, offshore platforms, costal and port structures, etc., are often submerged in water. The water within concrete pores or cracks has a great influence on the macroscopic mechanical properties of concrete, especially its global modulus of elasticity and strength. The present study investigates the quantitative influence of water content, i.e. concrete porosity, on the global mechanical properties of saturated concrete. By a three-phase spherical model and a hollow cylindrical rod model, the effect of porosity on the effective bulk and shear moduli of saturated concrete is studied in a quantitative manner. Based on the assumption that the pore-water has no shear capacity, the effective elastic modulus and Poisson's ratio of the saturated concrete are obtained using the theory of elasticity subsequently. Furthermore, according to the maximum tensile stress failure criterion, the quantitative relationships between the porosity and the global tensile strengths as well as their corresponding tensile peak strains of concrete in dry and saturated states are established. Finally, a comparison between the theoretical results and experimental data is made to verify the rationality and the accuracy of the present approach. The present results are comparable to the experimental observations of Yaman et al. [4,23], indicating that the present approach is applicable to predict the effective mechanical properties of concrete in both dry and saturated states. Moreover, it is found that compared with dry concrete, the water within saturated pores limits the surrounding concrete matrix deforming into pores, causing the enhancement of the global elastic modulus and Poisson's ratio of concrete. The effect of pore-water on concrete tensile strength is significant and should not be neglected in design.     

Mechanical properties of LDPE/granular starch composites

The mechanical properties of composites of granular starch and low density polyethylene (PE) have been studied as functions of starch volume fraction ?, granule size, and presence of compatibilizer. Property–volume fraction relationships were interpreted using various theories of composite properties. The dependence of elongation (? ～ ?^1/3) and tensile strength (σ ～ ?^2/3) agree with theoretical predictions, although the proportionality constants are less negative than theoretical values. The addition of compatibilzer (ethylene-co-acrylic acid copolymer, EAA) did not significantly affect the elongation or tensile strength, but significantly increased the composite tensile modulus. The cornstarch/PE moduli could be described by the Kerner or Halpin-Tsai equations. Analysis of the composite moduli data using the Halpin-Tsai equation allowed the estimation of the modulus of granular starch. The value obtained, 15 GPa, is considerably greater than most unfilled synthetic polymers of commercial importance, but significantly lower than the modulus of cellulose. It is also greater than a previously reported value of 2.7 GPa. © 1994 John Wiley & Sons, Inc.     

Effects of simulated clinical fabrication heat treatment and artificial weathering on the tensile testing of prosthetics/orthotics polymers

The tensile behavior was compared for five prosthetics/orthotics polymers: Durr-Plex (co-polyester), Polypropylene (polypropylene), Subortholen (polyethylene), Surlyn (ionomer), and Uvex (and cellulose acetate butyrate). Tensile properties, yield strength, and modulus of elasticity are related to a number of factors including composition and condition of polymers. The polymers were examined in the as-received and simulated clinical fabrication heat-treated conditions. The simulated clinical fabrication heat-treated specimens were subsequently treated to 2 weeks, 4 weeks, and 8 weeks of artificial weathering conditions, consisting of exposure to cycles of ultraviolet light and heated condensation. Tensile testing was performed on an Instron mechanical testing system, until fracture occurred. The ranges and respective rankings of yield strength and modulus of elasticity in tension were determined. Analysis of Variance (ANOVA) and post hoc Scheffé statistical analyses were performed for different polymers of the same treatment condition, and different treatment conditions of the same polymer. The analysis of variance (ANOVA) showed significant yield strength and modulus differences for the five polymers. The choice of material significantly influences the tensile properties for prosthetics/orthotics polymers. The Uvex polymer had the highest yield strength and elastic modulus, and the Surlyn polymer had the lowest yield strength and elastic modulus. The ranking trend was Uvex > Durr-Plex > polypropylene > Subortholen > Surlyn. © 1996 John Wiley & Sons, Inc.     

A novel,efficient route for the crosslinking and creep improvement of high modulus and high strength polyethylene fibres

A new route is presented for the chemical crosslinking of solution‐spun, ultra‐drawn Ultra‐High‐Molecular‐Weight Polyethylene (UHMW‐PE) fibres. UHMW‐PE fibres with a range of draw ratio's, Young's moduli and tensile strengths were impregnated with a radical initiator using supercritical carbon dioxide as a carrier. After impregnation, the drawn fibres were crosslinked with ultra‐violet light and fibres with a high gel content (> 90%) were obtained. It was found that the chemical crosslinking strongly reduces the plateau creep rate of the fibres and that the threshold stress for irreversible creep is enhanced. Simultaneously, the high Young's modulus and the high tensile strength of the drawn fibres are preserved which illustrates that the long term properties of the fibres (i. e. creep) are improved without a large sacrifice short term mechanical properties such as Young's modulus.     

Developments in oriented polymers, 1970–2004

Abstract

The discovery of methods to make highly oriented polymers has given tremendous stimulus to both basic polymer science and industrial developments in the period 1970 to the present. High modulus, high strength fibres for aramids and polyethylene, are based on very different methodologies but the ultimate result is similar in producing fully extended polymer chains. For polymers in solid sections, the enhancement of properties is less dramatic but still very worthwhile. In this case, three methods are described: hydrostatic extrusion, die-drawing and hot compaction of oriented fibres and tapes. Hot compaction is a new technique with many possibilities for which a wide range of applications has already been identified.     

Possible use of volcanic ash as a filler in polyphenylene sulfide composites: Thermal,mechanical, and erosive wear properties

It is a common practice to use particle materials as fillers to improve engineering properties of polymer composites and to lower the cost of final products. There is an obvious cost advantage of compounding volcanic ash (VA) in polymers, either to replace traditional fillers. This study is concerned with thermal, mechanical, and erosive properties of VA‐filled polyphenylene sulfide (PPS) composites. Composite samples containing VA particles at various concentrations (0, 2.5, 5, 10, 15, and 20 wt%) were manufactured by twin screw extruder and injection molding machine. Thermal properties were investigated by thermogravimetric and dynamic mechanical analysis methods. Erosive wear properties were investigated by performing solid particle erosion tests at 30º and 90º impingement angles. The mechanical properties such as flexural strength and modulus of uneroded samples and residual flexural strength and modulus of eroded composite samples were determined by three‐point bending tests. Results show that thermal, mechanical, and residual mechanical properties of the PPS composite were significantly improved by adding VA, although erosion resistance was decreased markedly. It was concluded that VA can be used as a reinforcement in PPS composites to improve thermal and mechanical properties and to reduce the cost of the PPS composites. POLYM. COMPOS., 35:1826–1833, 2014. © 2014 Society of Plastics Engineers     

Mechanical and thermal properties of polycarbonate. II. Influence of titanium dioxide content and quenching on pigmented polycarbonate

The effects of quenching temperature including different thermal histories on mechanical, physical, and thermal properties of pigmented polycarbonate (PC/TiO₂) were investigated. Tensile test, Izod impact strength and heat distortion temperature (HDT) were performed on specimens of 3 mm thickness. Pigment content and quenching temperature are two key factors that affect the properties of the materials. A higher content of pigments results in an increase of modulus of elasticity and a decrease of unotched and notched Izod impact strength, as well as elongation at break. A maximum of yield stress and HDT is obtained at 3% of TiO₂, which was considered as the optimum level of pigment. An additional second quenching at 40°C has allowed to improve Izod impact strength and elongation at break of specimens with 3% of TiO₂; whereas modulus of elasticity, density, yield stress, and HDT were minimum at this quenching temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Analysis and modeling of the mechanical properties of novel thermotropic polymer biomaterials

A series of random aromatic-aliphatic thermotropic copolyesters comprising p-hydroxybenzoic acid (HBA), vanillic acid (VA), 4,4′-sulfonyl bis(2-methylphenol) (dBPS) and three aliphatic diacids (Spacer), developed for potential applications in orthopaedic medicine, have been characterized in the context of their structure and mechanical properties. Each of the three polymers comprised the following molar percentages of monomer units 50/25/12.5/12.5 (HBA/VA/dBPS/Spacer). Oriented fibres prepared from the materials via melt-spinning have been analyzed using X-ray diffraction to evaluate order parameters describing the degree of molecular orientation and mechanical measurements to determine their tensile properties. In addition, measurements of the bulk isotropic and shear moduli of one polymer composition have also been performed. To obtain an understanding of the material properties the aggregate model due to Ward has been applied to the orientation dependence of the measured elastic moduli and the development of mechanical anisotropy.     

The effect of fibre diameter on the drawing behaviour of gel-spun ultra-high molecular weight polyethylene fibres

Summary In the continuous drawing of gel-spun UHMWPE fibres, the diameter of the undrawn fibre appears to have a pronounced effect on its drawing behaviour and on the mechanical properties of the resulting hot-drawn fibres. A highly oriented structure is developed more efficiently upon drawing of thinner fibres, which may be attributed to differences in the deformation mechanism between as-spun fibres of various diameters. By drawing of thin fibres, UHMWPE filaments having a strength of 6.0 GPa and a Young's modulus of 222 GPa can be obtained at a relatively low draw ratio of =70.     

Heat-Resistant Coreless Silicon Carbide Fibres for Composite Materials with Ceramic and Metallic Matrices

An original method of synthesis of fibre-forming polycarbosilane was developed. A study of the physicochemical properties of samples of Japanese and our polycarbosilane demonstrated their identity. Manufacture of coreless silicon carbide fibres was investigated. The conditions were developed and samples of fibres with a strength of up to 2.5 and a modulus of elasticity of 180 GPa were made. It was found that the physicomechanical properties of our fibres are on the level of mass-produced Japanese fibres and their structural and thermal characteristics are identical. Translated fromKhimicheskie Volokna, No. 4, pp. 9–14, July–August, 2000.     

Realization of the strength of carbon fibres in microplastics

Based on the model of fracture of carbon-filled plastics by breakage of fibres in stretching, the strength of CF realized in a microplastic was examined as part of the strength of fibres at their critical length. Based on an analysis of the experimental and calculated data for ENFB epoxy—phenol binders, the empirical dependence of the coefficient of realization of the strength of CF in a microplastic on the modulus of elasticity of the fibres and parameter B of the scale effect of the strength of CF was established. It was shown that the parameters of the strength scale effect and modulus of elasticity of CF have the determining effect on the strength of the microplastic.Translated from Khimicheskie Volokna, No. 1, pp. 42–45, January–February, 1995.     

Reinforcement of waste hemp fibres in aromatic diamine-based benzoxazine thermosets for the enhancement of mechanical and thermomechanical properties

Natural fibres (NFs) have been successfully reinforced in polymer matrices to strengthen the properties of the polymers. The polybenzoxazine thermosets are facing instable mechanical properties due to the high brittleness, herein, waste hemp fibres (WHF) reinforced polybenzoxazine composites are prepared. Effects of WHF volume % loading on curing, thermomechanical, mechanical, and thermal properties are studied. FTIR results confirmed that WHF rich in ?OH groups increased the ring-opening of oxazines and reduced curing temperature. In addition, an increase of 223%, 111%, 64%, and 253% in impact, tensile strength, flexural and Young's modulus, respectively, were recorded after loading optimum concentration (30 vol. %) in composites. Considerable enhancements were also seen in the thermomechanical properties on optimum loading, double stiffness and 26°C increase was recorded in the glass transition temperature. Nonetheless, the decline was observed in thermal stabilities, T_5% and Y_c were 24°C and 1.4 % lower, respectively, than neat poly(P-ddm).