Effect of Surface Fluorination of Poly (p-Phenylene Terephthalamide) Fiber

Direct fluorination is one of the most important and effective method to modify the polymer surface. It isa simple and fast method that allows the simultaneous treatment of outer and inner surfaces of complex shapedpolymeric materials. Poly-p-phenylene terephthalamide fibers which are a very important class of material wassurface modified by direct fluorinaton. An extensive characterization of both the virgin and the fluorinated materialswere performed by various techniques (XRD, FT-IR, Surface energy and DSC, TGA). From these data, possibleeffects of fluorination are discussed.Defence Science Journal, Vol. 64, No. 3, May 2014, pp. 230-235, DOI: http://dx.doi.org/10.14429/dsj.64.732

Application of In Situ Fiberization for fabrication of improved strain isolation pads and graphite epoxy composites

The feasibility of applying the in situ fiberization process to the fabrication of strain isolation pads (SIP) for the Space Shuttle and to the fabrication of graphite-epoxy composites was evaluated. The ISF process involves the formation of interconnected polymer fiber networks by agitation of dilute polymer solutions under controlled conditions. High temperature polymers suitable for SIP use were fiberized and a successful fiberization of polychloro trifluoroethylene, a relatively high melting polymer, was achieved. Attempts to fiberize polymers with greater thermal stability were unsuccessful, apparently due to characteristics caused by the presence of aromaticity in the backbone of such materials. Graphite-epoxy composites were fabricated by interconnecting two dimensional arrays of graphite fiber with polypropylene IS fibers with subsequent epoxy resin impregnation. Mechanical property tests were performed on laminated panels of this material to evaluate intralaminar and interlaminar shear strength, and thus fracture toughness. Test results were generally unpromising

Degradation of high performance polymeric fibers: Effects of sonication, humidity and temperature on poly (p-phenylene terephthalamide) fibers

High performance fibers are characterized by properties such as high strength and resistance to chemicals and heat. Due to their outstanding properties, they are used on applications under harsh environments that can degrade and decrease their performance. Fiber degradation due to different chemical and mechanical factors, is a process that begins at a microstructural level. Changes in the polymer’s chemical or physical structure can alter their mechanical properties. Knowledge of the structure-properties relationship and the effects of environmental chemical and physical factors over time, is crucial for the improvement and development of high performance fibers. In this study ballistic fibers of poly(p-phenylene terephthalamide) (PPTA) were studied. Methods of accelerated degradation were used to mimic the wearness of the fibers over long periods of time at a smaller time range. Fibers were subjected to ultrasonication in aqueous solution at pH 7 for up to six hours in order to produce surface damage. Once degraded, properties like the creep behavior of these fibers were studied under a humidity range of 0-80% and temperatures of 30°C and 60°C. Characterization of the chemical and mechanical properties of degraded PPTA fibers were characterized by thermogravimetrical analysis (TGA), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and tensile testing to failure. Sonication produces small but significant changes in the crystalline structure of the fibers that allows the formation of layers of water and consequently affecting mechanical properties like the elastic modulus and peak load. These small changes can be related to the early stages of degradation. Moreover, this study shows the efficiency of techniques such as the DMA for the detection of early signs of degradation by measuring the amount of creep the material undergoes as humidity changes

Manufacturing and properties of aramid-reinforced composites

The functional properties of the aramid-reinforced polymer composites depend primarily on the properties of the aramid reinforcing fibers, since the fraction of the fiber constituent in FRP is quite high, usually well above 30% by volume. The properties of the aramid fibers, in turn, depend on their chemical composition and manufacturing conditions: both of these determine the fibers physical structure and mechanical properties. The chapter will focus on these issues. Some specific problems related to the fiber-matrix nteraction.in aramid-containing FRP will also be addressed.Fundação para a Ciência e Tecnologia (FCT) - post-doctiral grant SFRH/BPD/45252/2008 (to Nadya Dencheva)Fundação para a Ciência e Tecnologia (FCT) - bolsa licença sabatica SFRH/BSAB/812/2008 (to Zlatan Denchev

Failure analysis of high performance ballistic fibers

High performance fibers have a high tensile strength and modulus, good wear resistance, and a low density, making them ideal for applications in ballistic impact resistance, such as body armor. However, the observed ballistic performance of these fibers is much lower than the predicted values. Since the predictions assume only tensile stress failure, it is safe to assume that the stress state is affecting fiber performance. The purpose of this research was to determine if there are failure mode changes in the fiber fracture when transversely loaded by indenters of different shapes. An experimental design mimicking transverse impact was used to determine any such effects. Three different indenters were used: round, FSP, and razor blade. The indenter height was changed to change the angle of failure tested. Five high performance fibers were examined: Kevlar® KM2, Spectra® 130d, Dyneema® SK-62 and SK-76, and Zylon® 555. Failed fibers were analyzed using an SEM to determine failure mechanisms. The results show that the round and razor blade indenters produced a constant failure strain, as well as failure mechanisms independent of testing angle. The FSP indenter produced a decrease in failure strain as the angle increased. Fibrillation was the dominant failure mechanism at all angles for the round indenter, while through thickness shearing was the failure mechanism for the razor blade. The FSP indenter showed a transition from fibrillation at low angles to through thickness shearing at high angles, indicating that the round and razor blade indenters are extreme cases of the FSP indenter. The failure mechanisms observed with the FSP indenter at various angles correlated with the experimental strain data obtained during fiber testing. This indicates that geometry of the indenter tip in compression is a contributing factor in lowering the failure strain of the high performance fibers. TEM analysis of the fiber failure mechanisms was also attempted, though without success

The effect of coagulants on the microstructure and mechanical properties of lyotropic fiber-forming polymers/

The effect of coagulant on the mechanical properties and microstructure of three lyotropic fiber-forming polymers, poly(p-phenylene benzobisthiazole) (PBZT), poly(p-phenylene terephthalamide) (PPTA) and poly(p-phenylene benzobisoxazole) (PBO) was studied. Previous research found that the imbalance between tensile and compressive/shear properties in these high-modulus fibers is due to a low degree of lateral interaction between microfibrillar elements. In this work, coagulants were chosen which could have strong specific molecular interactions with some portion of the polymer chain; the goal of this research was to increase compressive and shear properties by creating lateral physical crosslinks among the polymer chains. Results from these coagulation studies show that macroscopic properties such as compressive strength and torsion modulus are dependent on the coagulant; these interactions are strong enough to significantly affect mechanical and structural properties of the fiber. For oxygen-containing lyotropic polymers, the cations present in the coagulant may be important in determining the occurrence of specific interactions. As-spun PBZT fiber coagulated in iodine/ethanol solution with a spin/draw of 3 had a shear modulus of 1.14 GPa and tensile strength of 2.2 GPa; fiber coagulated in ethanol had respective values of 0.63 GPa and 1.8 GPa. Wide-angle X-ray scattering (WAXS) studies showed that I\sb3\sp- and I\sb5\sp- anions were present within the fiber, and that there was some disruption of the standard PBZT unit cell. PPTA fiber was coagulated into water, ethanol, iodine/ethanol and aqueous solutions of alkali salts. Coagulation in water produced PPTA fiber with the highest tensile, shear and compressive properties. The shear and/or compressive properties of PPTA fibers could be decreased without a corresponding change in crystal structure; these properties seem to be based on an element of microstructure above that of the unit cell. PBO fibers were coagulated in many of the same coagulants; mechanical properties were unaffected. Coagulation in aqueous potassium iodide produced fiber containing oriented potassium iodide crystals within the fiber

A study of all-polymer composites: all-poly(ethylene terephthalate) and all-poly(p-phenylene terephthalamide)

PhDComposites are normally composed of two distinct phases: reinforcement and matrix. In recent years, a new class of “self-reinforced” polymer composites or “all-polymer” composites, which are based on similar or identical materials for both reinforcement and matrix have generated increasing interests in both academia and industries due to their advantages in terms of processing, interfacial properties and recyclability. Current research trend in this field is to investigate the potential possibilities of all-polymer composites based on high-performance polymer fibres. In this thesis, all-poly(ethylene terephthalate) composites (Part 1) and all-aramid composites (Part 2) were prepared. In Part 1, Chapter 3 describes the melt spinning and drawing of poly(ethylene terephthalate) (PET) into highly oriented fibres, with moduli of 20GPa and tensile strengths of 925MPa. The effects of spinning and drawing conditions on the mechanical properties of PET fibres were studied. In the following Chapters 4 and 5, all-PET composites were prepared from 1) hot compaction of bi-component multifilament PET yarns; and 2) a film stacking technique, i.e. combining PET tapes unidirectionally with copolyester adhesive films in an alternating “brick-wall” layer-by-layer structure. The effects of processing conditions on mechanical properties were investigated. In Part 2 Chapter 7, all-aramid composites were prepared by a selective surface dissolution method where aramid fibres were partially dissolved to form a matrix phase to bond remaining fibres together into composites. The structure, morphology and mechanical properties were characterized by X-ray diffraction, scanning electronic microscopy, dynamic mechanical analysis and tensile testing. Compared to traditional aramid/epoxy composites, these all-aramid composites show significantly high mechanical properties, even at elevated temperatures. In Chapter 8, the effects of processing conditions on various properties of all-aramid composites were studied and an optimum condition was found. By replacing high concentration sulphuric acid as a solvent, a mild mixed solvent was used to dissolve aramid fibre surfaces in Chapter 9. In this way, all-aramid composites with prolonged immersion times were prepared and characterized. Potential future work including all-PET composites from post-consumer PET waste, microstructural characterization of all-aramid composites and woven all-aramid composites are discussed in Chapter 10