Poly P-phenylene Terephthalamide Research Articles

Implication of Freeze-Thaw Erosion and Mechanism Analysis of High-Performance Aromatic Liquid Crystal Fibers.

According to the demand for high-performance fibers for high-latitude ocean exploration and development, this paper selects representative products of high-performance liquid crystal fibers: thermotropic liquid crystal polymer fibers (TLCP) and poly p-phenylene terephthalamide (PPTA) fibers. Through a series of freeze-thaw (F-T) experiments for simulating a real, cold marine environment, we then measure the retention of mechanical properties of these two kinds of fibers. Before that, due to the difference in their chemical structures, we tested their Yang-Laplace contact angle (YLCA) and water absorption; the results suggested that PPTA fibers would absorb more moisture. Surprisingly, then, compared with thermotropic liquid crystal polymer (TLCP) fibers, the retention of the mechanical properties of poly p-phenylene terephthalamide (PPTA) fibers decreased by around 25% after the F-T experiments. The Fourier-transformed infrared (FT-IR) analysis, the attenuated total reflection (ATR) accessory analysis and the degree of crystal orientation measured by two-dimensional wide-angle X-ray diffraction (2D-WAXD) confirm that no changes in the chemical and the orientation structure of the crystal region of the fibers occurred after they underwent the F-T cycles. However, as observed by scanning electron microscopy (SEM), there are microcracks of various extents on the surface of the PPTA fibers, but they do not appear on the surface of TLCP fibers. It is obvious that these microcracks will lead to the loss of mechanical properties; we infer that the moisture absorbed by the PPTA fibers freezes below the freezing point, and the volume expansion of the ice causes the collapse of the microfibrillar structure. The two sorts of fibers subjected to the F-T experiments are immersed in a sodium chloride solution, and the amount of water infiltrated into the PPTA microfibrillar structure is evaluated according to the content of sodium ions in the fiber surface and subsurface layers through X-ray spectroscopy (EDS) elemental analysis. From the above analysis, we found that TLCP fibers can more effectively meet the operating standards of the severe and cold marine environment.

Polarity, thermal stability, and hydrophilicity of three-layer crosslinked PPTA/cellulose composite insulation system: Molecular dynamics simulations

Preparing a novel insulating paper with relatively low dielectric constant, enhanced thermal stability, and low hydrophilicity has always been the research hotspot of the transformer insulation industry. This paper constructed a three-layer cross-linked poly-p-phenylene terephthalamide (PPTA)/Cellulose composite structure and explored its polarity, thermal stability, and hydrophilicity by molecular dynamics simulation. Results showed that the introduction of PPTA and constructing crosslinking network between the molecules could reduce the polar group density and molecular polarizability of the cellulose system; The three-layer crosslinked system has a 34.1% lower dielectric constant than the pure cellulose system. And the tensile modulus of the three-layer crosslinked structure is up to 92.1% of that of the pure cellulose system; The three-layer crosslinked system has a higher glass transition temperature (Tg) and a lower molecular chain mean square displacement (MSD), compared to the pure cellulose system. The results of the water diffusing from the outside into the fiber system and moving in the fiber system indicated that the three-layer crosslinked PPTA/Cellulose composite system had lower hydrophilicity than the pure cellulose system. This study provides a design basis for the development of the novel high-performance composite insulating paper.

Development of PPTA/cellulose three‐layer composite insulating paper with low dielectric constant and good mechanical strength based on molecular dynamics simulation

AbstractReducing the dielectric constant of insulating paper to improve the dielectric coordination performance of the oil‐paper systems has always been the research hotspot in the transformer insulation material industry. This paper prepares a novel poly‐p‐phenylene terephthalamide (PPTA)/cellulose composite paper with low dielectric constant and good mechanical properties. Various PPTA/cellulose mixing structures were established and the dielectric and mechanical properties were simulated via molecular dynamics simulation. Results showed that the PPTA/cellulose composite system had a lower dielectric constant than the cellulose system, for adding PPTA molecular could reduce the free volume of the system and limit the steering polarization of the dipole, as well as decrease the system polarization intensity. Constructing a three‐layer structure that contains continuous cellulose middle layer could improve the mechanical properties of the composite system greatly. Experimental results verified the simulation results. The dielectric constant of the three‐layer PPTA/cellulose composite paper decreased from 3.98 to 3.49 at 50 Hz, compared to the conventional cellulose paper. Moreover, the tensile strength of the novel three‐layer PPTA/cellulose composite paper (thickness: 130 μm) has reached 9.02 kN/m, increased by 27.6% than the directly mixed composite paper. Molecular dynamics simulation proves to be a promising method for guiding paper modification. Constructing three‐layer PPTA/cellulose structure represents an effective way to prepare a low dielectric constant composite insulating paper with good mechanical properties.

Direct Carbonization of High-performance Aromatic Polymers and the Production of Activated Carbon Fibers

For expanding the utilization of several high-performance aromatic polymeric fibers, e.g., poly p-phenylene benzobisoxazole (PBO, Zylon®), poly p-phenylene terephthalamide (PTA, Kevlar 29®), and polyarylate (PA, Vectran®), direct carbonizing and graphitizing behaviors have been investigated. The PBO-based carbon fiber showed a typical radial texture on its fracture surface, and the graphitization degree (P1) reached 0.35 and crystallite sizes of Lc(002), La(110) after graphitization exceeded 30 nm. On the other hand, the P1 indices of the graphitized carbon fibers from PTA and PA were no more than 0.15. However, a low P1 value is preferable for the production of activated carbon fibers (ACF). In addition, on the surface of the PA-based carbon fibers produced at 900°C, some fine mesh-like morphologies were observed indicating the formation of a porous carbon structure. In contrast, for the PTA-based carbon fibers the development of radial texture could be seen only partially on the fracture surface, and porous morphologies were not recognizable. It was confirmed that the direct carbonization was enough to convert PA fibers into ACF. The BET surface area of the PA-based carbon fibers increased up to 900~1,000 m2/g after the direct carbonization at 900 oC, and exceeded 1,000 m2/g easily when activated.

The thermal degradation behavior of meta- and para- hetero-amide fibers by TGA-FTIR

Abstract The thermal degradation behaviors of poly-p-phenylene-benzimidazole-terephthalamide (PBIA), poly-m-phenylene isophthalamide (PMIA) and poly-p-phenylene terephthalamide (PPTA) fibers are investigated by thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy (TGA-FTIR). The results demonstrate that PBIA fiber exhibits better thermal- and thermo-oxidative stability than that of the other two polymers. PBIA shows the highest onset degradation temperature, both in nitrogen and air. TGA-FTIR provides information on compositions of pyrolyzates and their relationship with the structures of polyamides. Analysis of the compositions and distributions of all pyrolyzates, at different temperatures, indicates that a hydrolytic mechanism plays a leading role at lower temperature, and a homolytic mechanism is dominant at higher temperature.

Thermal Decomposition Behavior of a Heterocyclic Aramid Fiber

Heterocyclic aramid fibers are one of the high-performance fibers with excellent mechanical and thermal properties. In this article, the thermal decomposition behaviors of a type of the fibers were studied in nitrogen and air by pyrolysis/gas chromatography–mass spectrometry (Py/GC-MS), thermal gravimetric analysis–differential thermal analysis/Fourier transform infrared spectroscopy (TGA-DTA/FTIR), and thermal gravimetric analysis–differential thermal analysis/mass spectrometry (TGA-DTA/MS). The results showed that under nitrogen atmosphere, the thermal decomposition mainly happened between 520°C and 580°C, the temperature of the maximum weight loss rate was 550°C, and the weight remaining at 800°C was 58%. HCN, NH3, NO2, NO, CO2, CO, H2O, and some other compounds containing benzene rings were detected by the TGA-DTA/FTIR. Among these released chemicals, the intensity of the absorption peak assigned to CO2 was the strongest. These chemicals were also identified by the TGA-DTA/MS. The Py-GC/MS analysis revealed that the number of chromatographic peaks increased with the increase of temperature. Most of the pyrolysis products were produced between 550°C and 600°C, which represented the major pyrolysis process. Moreover, the detection of benzene ring containing compound fragments reflected the process of the molecular chain scission. In air atmosphere, the thermal decomposition mainly happened between 500°C and 680°C. The maximum weight loss rate was observed at 600°C, and almost 100% weight was lost at 900°C. NH3, NO2, CO2, and H2O were detected by the TGA-DTA/MS, and the ion current intensity of CO2 was again the strongest with a strong oxidation reaction at around 670°C. It was speculated that the thermal decomposition began with the breaking of the bonds between PPTA (poly-p-phenylene terephthalamide) blocks and heterocyclic blocks at high temperature. Then, with the increase of temperature, the chemical bonds inside the PPTA blocks and heterocyclic blocks were broken. In this process, free radicals that led to restructuring and new breakages to produce micromolecular products were introduced.

Study of the Properties of Poly-P-Phenylene-Benzimidazole-Terephthalamide Fiber Material

The properties of the fiber material, which prepared from the high-performance heterocyclic polymer poly-p-phenylene-benzimidazole-terephthalamide (PBIA), were investigated. Poly-m-phenylene isophthalamide (PMIA) and poly-p-phenylene terephthalamide (PPTA) fibers were also studied, for comparison, under the same experimental conditions. Thermogravimetry(TG) and thermogravimetry coupled to Fourier transform infrared spectroscopy(TG-FTIR) were used to study the properties of these fibers. The results show that PBIA fiber has better tensile properties, thermal stability than that of PMIA and PPTA fibers. The onset degradation temperature of PBIA is the highest, namely 421°C in nitrogen. TG-FTIR provides information on the compositions of the pyrolyzates as well as their relationship to the structures of the polyamides. Analysis of the results indicates that a hydrolytic mechanism plays a leading role at lower temperature, and a homolytic mechanism is dominant at higher temperature.

Experimental Verification of the End-Effect Weibull Model as a Predictor of the Tensile Strength of Kevlar-29 (Poly p-Phenyleneterephthalamide) Fibres at Different Gauge Lengths

This paper describes the first application of the four-parameter end-effect Weibull model as a predictor of tensile failure frequency at a gauge length different from that used to generate the model parameters. As-received Kevlar-29 fibres were tensile tested at gauge lengths of 10, 25 and 40 mm. The resulting failure data were used to determine four empirical constants using a maximum-likelihood regression. The model and parameters were used to predict failure frequency at a gauge length outside the initial range (5 mm). The results show that the end-effect Weibull model accurately represents the data from which its parameters are evaluated and that the model may be applied as an effective predictor for gauge lengths beyond the original testing range.

Decreasing the combustibility of polycaproamide and polyethylene terephthalate by incorporation of microencapsulated fire retardants with a polymer shell

The possibility of decreasing the combustibility of polycaproamide (PCA) and polyethylene terephthalate (PETP) by incorporation of microencapsulated T-2 fireproofing compound in the polymer melt using a shell based on poly-m-phenylene isophthalamide (PMPIA) and poly-p-phenylene terephthalamide (PPTA) was investigated. A synergistic increase in the effectiveness of the fireproofing effect of microencapsulated fire retardants (ME FR) was observed with a shell concentration of 6–10%. The basic characteristics of thermooxidative decomposition of PETP and PCA containing ME FR were investigated.

Miscibility studies of poly-p-phenylene terephthalamide/polyamide molecular composites

Abstract Miscibility characteristics of poly-p-phenylene terephthalamide (PPTA) with nylon 6, nylon 66, nylon 11, and nylon 12 have been examined by means of differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Mixtures of PPTA/nylon 6, 66, 11, and 12 and amorphous nylon were prepared by coagulation in water from isotropic sulfuric acid solutions. The WAXD investigation shows the presence of small amounts of disordered crystals in the regenerated pure PPTA and to a lesser amount in the blends of PPTA/amorphous nylon or PPTA/aliphatic crystalline nylons. DSC studies show the melting point depression of nylon crystals. At low PPTA contents, a small melting point elevation occurs in nylon 6, presumably due to nucleation. The Flory-Huggins interaction parameter (χ) was subsequently calculated from the melting point depression of the nylons.

Miscibility in poly‐p‐phenylene terephthalamide/nylon 6 and nylon 66 molecular composites

AbstractMiscibility and crystallization of poly‐p‐phenylene terephthalamide (PPTA)/nylon 6 and nylon 66 composites prepared by coagulation of isotropic ternary sulfuric acid solutions were studied. The apparent crystallinity of nylon 6 and nylon 66 in molecular composites was investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy. The solvation of nylon 6 crystals in PPTA matrix was observed when the PPTA content exceeds 70 wt%. Cross‐hydrogen bonding seems to be responsible for the virtual disappearance of nylon 6 crystals. Specific interaction between PPTA and nylon 6 macromolecules and phase separation during thermal treatment has been discussed.

“Dynamics of Phase Segrewation in Poly-P-Phenylene Terephtualamide and Amorphous Nylon Molfcular Composites”

ABSTRACTTime-resolved light scattering has been employed to elucidate the dynamics of phase segregation of poly-p-phenylene terephthalamide (PPTA)/ amorphous nylon (AN) molecular composites. Miscible PPTA/AN blends can be prepared from sulfuric acid solution by rapidly coagulating the solution in distilled water. The composites, however, undergo phase segregation upon thermal treatment and exhibit a miscibility window reminiscent of a lower critical solution temperature (LCST). Several temperature-jump experiments were undertaken from ambient to a two-phase temperature region of 240, 250 and 260°C. Time-evolution of scattering profiles are analyzed in accordance with non-linear and dynamical scaling theories.

Structure and thermomechanical properties of high-modulus aramide copolymers. (I). An annealing effect on the structure.

The X-ray diffraction and infrared spectra have been measured for the aramide copolymer fibers (M50) produced by the condensation polymerization between p-phenylenediamine/3, 4′-diaminodiphenylether equimolar mixture and terephthalic chloride. The X-ray diagram of the unannealed fiber is diffuse and apparently assumed to be an overlap of the patterns of the homopolymers of each component 1 and 2 with poor crystallinity. After annealing at 400°C, where the large weight loss was observed, the X-ray and infrared patterns were found to coincide essentially with those of the homopolymer 1 i.e., poly-p-phenylene terephthalamide (PPTA). The X-ray and infrared spectra of the homopolymer 2 (M100) was found to change into the structureless broad pattern after annealed at 400°C. These experimental results indicate that (1) some crystalline domains consisting only of one component (1 or 2) are existent in the original copolymer sample and (2) the heat treatment above 400°C degrades chemically the component 2 and then only the component 1 remains left, giving a relatively high-crystalline pattern of PPTA. The sample was found to change into the carbon fiber by annealing above 500°C.

Aramid Fiber Composites for General Engineering

This paper focuses on the para-aramid, poly p-phenyleneterephthalamide, its basic structure/property relationships, its engineering properties, and applications in fiber-reinforced composites. Para-aramid technology will continue to advance toward achieving fiber tensile properties closer to theoretical. New systems engineering design options will be possible in the future spectrum of composite applications. In aircraft, composite design will emphasize p-aramid damage tolerance and crashworthiness for primary structures. The knowledge base will broaden for hybrides of p-aramid and carbon fiber. As aircraft composite technology advances, it will be applied to the redesign of automotive parts. In communications, p-aramids will provide lightweight flexible support structures for fiber optical cables and help meet high circuit density needs for printed wiring board composites. Para-aramid engineered short fibers will continue to replace asbestos composites in a range of applications.

Future of aramid fiber composites as a general engineering material.

The discovery of liquid crystalline solutions of extended chain aromatic polyamides led to a new family of high performance organic fibers with a unique combination of engineering properties. This paper focuses on the para-aramid, poly p-phenyleneterephthalamide, its basic structure/property relationships, its engineering properties, and applications in fiber-reinforced composites. Para-aramid tech-nology will continue to advance toward achieving fiber tensile properties closer to theoretical. New systems engineering design options will be possible in the future spectrum of composite applications. In aircraft, composite design will become more sophisticated and emphasize para-aramid damage tolerance and crashworthiness for primary structures in addition to strength and stiffness. Hence, the knowledge base will broaden for hybrids of para-aramid and carbon fiber. As aircraft composite technology advances, it will be applied to redesign of automotive parts. In communications, para-aramids will provide lightweight flexible support structures for fiber optical cables and help meet high circuit density needs for printed wiring board composites. Para-aramid engineered short fibers will continue to replace asbestos composites in a range of applications. As the world moves to more lightweight, energy efficient structures and devices, the possibilities are large for the future of aramid fiber composites as a general engineering material.

Change in the supermolecular structure of highly oriented fibres under the action of epoxy binders or their components

The effect of the epoxy binders EDT-10 and EKhD, and of their components, on the structure of highly oriented amorphous poly-p-amidobenzimidazole (PABI) and of amorphous-crystalline poly-p-phenylene terephthalamide (PPTA) fibres has been examined; it was investigated by the large-angle x-ray diffraction method.

Transitions in anisotropic solutions of poly- p-phenyleneterephthalamide

X-ray and differential thermal analysis, penetrometry, viscometry and polarized light microscopy have been used to study transitions in solutions in sulphuric acid of poly- p-phenyleneterephthalamide (PPhTA) with various molecular masses, M. On the basis of these data, a section of the phase diagram of the system has been constructed: this contains 3 phases, namely, an isotropic and an anisotropic liquid phase and an anisotropic solid phase, a transition zone existing between them. The use of a reduced concentration factor Mc (where c is the concentration) enabled the boundaries of the transition from the isotropic to the anisotropic liquid state to be reduced to a single curve for the PPhTA specimens of various M. Solvated crystals of PPhTA with H 2SO 4 are formed in the region of the anisotropic solid compositions, a fact which also explains the exclusion of this transition from the scheme of liquid crystal equilibrium. It is suggested that the observed sequence of transitons from the solvated crystal to the liquid crystal to the isotropic liquid (along the temperature scale) may be common to polymers that form lyotropic liquid crystals.