Change in the mechanical properties of para-aramid fibres in thermal aging

The change in the mechanical properties of high-strength, high-modulus carbocyclic and heterocyclic para-aramids exposed to high (250, 275, 300°C) temperatures for up to 100 h was investigated. It was found that the change in the strength characteristics and elongation at break after prolonged thermal effects is diminishing in character. A small increase in the elongation, probably caused by predominance of the effect of structural transformations over degradation processes, was only observed in the fibres based on CpPABI in the initial period at 250 and 275°C. The data on the change in the strength and elongation at break as a function of the duration of the thermal effect are described by exponential dependences: second order for the elongation at break of Rusar and Armos fibres at 250 and 275°C and first-order in the other cases. The values of the coefficients in these dependences were found. The data obtained and curves approximating them describe the change in the strength and elongation at break of para-aramid fibres in the time range of up to 100 h and can be used to approximately predict the change in them over a longer period. The results of the study of the effect of high temperatures on the mechanical properties of high-strength, high-modulus para-aramid fibres can be used to determine the temperature boundaries of use of articles made from them. It follows from the data obtained that these articles can be used for a long time at 250 and even 275°C and briefly up to 300°C. __________ Translated from Khimicheskie Volokna, No. 5, pp. 44–49, September–October, 2006.     

Effect of the structure of glass fibres on their physicomechanical properties

It was found that the critical twisting of glass fibres is within the limits of 250–300 turns/m. In fabrication of some types of glass cloth and thread-sewn cloth, it is expedient to use complex glass fibres with low twisting —within the limits of 0 to 30 turns/m. Moscow State Textile Academy. Translated fromKhimicheskie Volokna, No. 3, pp. 52–54, May–June, 1999.     

Effect of internal stresses on the structure and physical and mechanical properties of a complex glass fibre

The correlations of internal stresses arising in a complex glass fibre during with the shape of the fibre as a function of the surface properties of the lubricant and the tension of the fibre in the pack layers were obtained in differential and integral form. The results of the studies confirm the validity of the proposed analytical model of formation of internal stresses in a complex fibre during its drying. The conclusion that the different lengths of the monofilaments in the complex fibre is the basic cause of formation of the twisted structure of the complex fibre was experimentally confirmed.Fiberglass Plastics—Certificate AF, Moscow. Translated from Khimicheskie Volokna, No. 1, pp. 46–48, January–February, 1994.     

Change in the properties of polycaproamide fibres in treatment with metal complex salts

The modifying effect of chromium and aluminum salts on the properties of polyamide films was demonstrated. The possibility of increasing chemisorption of metal cations by polycaproamide fibres by treatment with UHF radiation was investigated. __________ Translated from Khimicheskie Volokna, No. 3, pp. 33–34, May–June, 2007.     

Change in mechanical properties,composition, and structure of hydrated polyurethaneurea

Relative to the extensive study on the relationship between the structure and properties of polyurethane (PU) and polyurethaneurea (PUU), basic information available on hydrated PUU is limited. In this study, PUU films were immersed in a saline solution (0.9 wt % NaCl, 37°C) for periods of up to 60 days and evaluated by the change in static and dynamic mechanical properties, composition, and hydrogen‐bonding structure. It was found that immersion in a saline solution could greatly increase the average molecular weight and degree of phase separation, which enhanced the mechanical strength and reduced the flexibility. The increase in the average molecular weight is believed to come from the chain extensions or crosslink reactions between intramolecules and/or between intermolecules and from the leaching out of poly(tetramethylene oxide) (PTMO) oligomers. FTIR analysis indicated that H₂O molecules did not obviously alter the hydrogen‐bonding structure of PUU. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 252–260, 2001     

Surface topography and mechanical properties of carbon fibres

Surface topography of polyacrylonitrile based carbon fibres preoxidized under a variety of conditions has been studied in detail. Only those carbon fibres processed under optimum conditions are found to possess defect free surface topography. Changes in surface topography and the tensile strength of carbon fibres with processing conditions have been discussed.     

Structure and mechanical properties of PGA crystals and fibres

The elastic constants of poly(glycolic acid) (PGA) crystals are reported on the basis of a commercial software package and the published crystal structure of the polymer. Due to the planar zigzag conformation of the molecular chains, very high elastic anisotropy is found with a tensile chain modulus of 294 GPa and a longitudinal shear modulus for a fibre of 6 GPa. A combination of small and wide angle X-ray scattering and differential scanning calorimetry are used to characterise the structure of highly oriented PGA fibres. The combination of long period data, crystal size and crystallinity measurements suggests a structure similar to the Prevorsek model, with alternating crystalline and amorphous regions along the fibre axis, and layers of amorphous material in parallel. A parallel-series Takayanagi model, using the theoretically calculated chain modulus, is shown to give good agreement with the experimental data in a wide temperature range.     

Defect content and nonuniformity in mechanical properties of polyacrylonitrile fibres

Conclusions Defect content and nonuniformity in mechanical properties of polyacrylonitrile fibres have been investigated in the cross section of tow and over the length of individual elementary fibres.For a generalized evaluation of defectiveness and nonuniformity in mechanical properties we have used the scale dependence of strength and histograms for strength distribution. Scale coefficients for the strength of polyacrylonitrile fibres have been determined.For rapid characterization of defectivity and nonuniformity of mechanical properties of fibres one can use the ratio of the mean strengths at two clamped lengths which differ significantly (by an order of magnitude or so).Translated from Khimicheskie Volokna, No. 1, pp. 33–34, January–February, 1989.     

Effect of the temperature on the structure and mechanical properties of poly(ethylene terephthalate) fibres and yarns

The load—elongation diagrams were obtained for PETP yarns and monofilaments at different deformation temperatures, demonstrating the dependence of the σ(ε) curves on the testing temperature and the thermomechanical history of the samples. The dependences of the basic strain characteristics determined from the σ(ε) curves on the temperature can be used to predict the change in the mechanical properties of PETP yarns and fibres at high temperatures. In addition to the fundamental relaxation transition, the σ(ε) curves can be used to find a new transition in the 180°C region which controls the behavior of PETP yarns and fibres above the transition temperature. The thermomechanical tests and structural studies of the fibres at different temperatures allow correlating the transition found with crystallites and assigning it to an α_c transition based on the characteristic set of properties. St. Petersburg State University of Technology and Design. Translated fromKhimicheskie Volokna, No. 1, pp. 32–35, January–February, 2000.     

Surface structure of silane-treated glass beads and its influence on the mechanical properties of filled composites

The surface treatment of glass beads, chosen as a model filler, was carried out using four different silane coupling agents with multilayer coverage. For this purpose, silanes having an aminopropyl or a methacryloxypropyl group as an organofunctional group with di- or tri-alkoxy structures were used. The amount of silane detected on the bead surface was four to six times that required for a monolayer coverage. The topography of the silane layer on the bead surface was observed using an atomic force microscope. The topography was strongly affected by the composition of the silane solution and the number of alkoxy groups in the silane. The effects of the organofunctional group and the number of alkoxy groups of the silanes on the mechanical properties of bead-filled poly(vinyl chloride), chosen as a typical ductile polymer, were investigated. A higher yield stress was observed for the silane with an aminopropyl group than for that with a methacryloxypropyl group. Furthermore, for each organofunctional group, the yield stress was higher for the silane with a dialkoxy structure than for that with a trialkoxy structure. However, their effects on the elongation-at-break were contrary to the above tendencies.     

Investigation of the structure and mechanical properties of a novel dental graded glass/zirconia ceramic

Constructing graded structure is a promising solution to reduce the occurrence of cracking and delamination of bilayered zirconia prosthesis. In this work, a novel graded glass/zirconia ceramic was developed by utilizing the interdiffusion between dense zirconia and a novel lithium disilicate glass in the SiO₂-Li₂O-Al₂O₃ system. Results demonstrated that a graded glass/zirconia structure with a depth of about 300 µm was constructed, which exhibited obviously gradient characteristics in microstructure, glass content and mechanical properties. The hardness (H) and elastic modulus (EM) values at the surface reduced significantly (64% for H and 79% for EM), and increased gradually with depth of graded layer. When the graded layer was subjected to loading force, the biaxial flexural strength increased. The mechanism of the evolution of graded structure and change of strength were also elucidated in detail. This study provides a promising strategy to improve the interface stability of bilayered zirconia restoration.     

Annealing effect on crystalline structure and mechanical properties in long glass fiber reinforced polyamide 66

Generally, annealing is one of the important post‐processing methods used to obtain injection molding products coupled with excellent comprehensive performance. Based on a series of experimental studies in this work, a systematic investigation was performed to research the annealing effect on crystalline structure and mechanical properties in long glass fiber reinforced polyamide 66 (LGF‐PA66) composite. The composite was prepared by injection molding, using LGF‐PA66 pellet with 50 wt % fiber content and 12 mm length. Composite samples were annealed in 120 °C to 200 °C range and then subjected to various tests at room temperature. Besides, the releasing strain during a specific temperature cycle was also investigated. Our results suggest that annealing treatment had a neglected impact on the crystallinity and crystal morphology of LGF‐PA66 composite. However, with the increasing of processing temperature, annealing could strikingly promote the phase transition from γ to α and the further growth of α₂ crystal in (010)/(110). In addition, annealing of LGF‐PA66 composite resulted in a drastic increase in tensile and flexural properties and a reduction in impact strength, along with the transition of failure mode. The changes in mechanical properties were attributed to the crystal transition, strengthening of matrix performance, and the release of residual stress. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44832.     

Compounding of glass fiber-reinforced polypropylene and investigation of its mechanical properties under simple and complex loading

Polypropylene is one of the important thermoplastics that has been reinforced with glass fibers to give a reasonably good engineering plastic. Because of its inert nature, it does not easily adhere to the glass surface and hence some improvement in mechanical properties. In the present study a vinyltriethoxysilane coupling agent in polymeric form has been tried and seen to improve the properties. Tests have been carried out at (a) constant strain rate (in the Instron testing machine), and (b)constant stress rate (water loading on a biaxial testing machine). Under constant strain rate only tensile properties have been studied while under constant stress rate, the tensile, torsional and combined tensile-torsional tests have been carried out. In each of the above cases, a considerable improvement in elastic modulus has been observed. The Tensile strength is improved to the extent of about 25 percent. There is only a slight improvement in torsional strength. Different fiber volume contents were used and their effect studied on modulus and strength. The mechanical data for reinforced-polypropylene samples have been discussed in terms of the fiber-length distribution in the composite. Detailed analysis of tensile data suggests that at low strains, when the critical length is relatively low, the fibers contribute to a high modulus. With increasing strain the critical length increases and the load carrying capacity of the fibers is reduced. Consequently the gain in strength is relatively less. The effect of fiber length distribution in torsion and combined tension-torsion tests would be expected to be similar and the results seem to confirm this.