Pengqing Liu

Preparation, flame retardancy and thermal degradation behaviors of polyacrylonitrile fibers modified with diethylenetriamine and zinc ions

A kind of flame-retardant polyacrylonitrile fiber was prepared successfully by the modification with diethylenetriamine and zinc ions (Zn2+). The chemical, aggregation and morphological structures of the aminated fibers were studied by Fourier transform infrared (FTIR) spectra, X-ray diffraction and scanning electron microscope (SEM). Meanwhile, mechanical and adsorption properties were investigated by a tensile tester and atomic absorption spectrometry. The flame retardancy of the modified fibers was significantly improved after modification. And the thermal degradation behaviors and flame retardancy mechanisms were studied in detail. The microscale combustion calorimeter and TG-FTIR results showed that the modified fibers decomposed less combustible gases and more non-combustible gases comparing the original fibers. And thermogravimetric analysis and SEM tests revealed that Zn2+ would stabilize the main chains and promote formation of compact char layers. And differential scanning calorimetry tests indicated that Zn2+ would inhibit the cyclization exothermic process. Results showed that the combination of gas phase and condensed phase mechanisms optimized the flame retardancy performance.

Hydrogen bond and crystalline structure of the junction network in polyvinyl alcohol/dimethysulfoxide gels

The hydrogen bond and aggregation structures of polyvinyl alcohol (PVA) gels prepared with dimethylsulfoxide (DMSO) were investigated as were the the rheological properties. The variable temperature Fourier Transform Infrared (FTIR) and X-ray results of PVA-DMSO gels show that the hydrogen bond and crystalline structure are destroyed as temperature increases. In the Tanaka model, the value of ζ (the number of sequential units per chain in the junction) is 1.45 and s (the number of polymer chains in a single junction), which reveals the ability of solution to form gel, varied as a function of gel melting temperature Tgm. The results of dynamic rheology show that the elastic modulus G′ is proportional to the gel concentration and inversely proportional to the temperature. It was found that gels formed from solutions with same viscosities showed different properties. This is because a gel with a higher polymerization degree has a lower value of s.

A novel method to prepare a flame-retardant polyvinyl alcohol fiber with modified acrylonitrile coatings

To improve the flame resistance of polyvinyl alcohol (PVA) fibers, the well-designed permanent flame-retardant coatings were introduced on the surface of PVA fibers. Acrylonitrile (AN) was firstly grafted on the PVA fiber surface and then the grafted fibers (PVA-g-AN fibers) were reacted with hydrazine hydrate and copper sulfate solution to form the coatings with flame retardant performance. The structure of the fibers was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The flame-retardant performance of the fibers was evaluated by limiting oxygen index (LOI) and micro calorimeter (MCC) tests. It was found that the coatings were effective in improving the flame resistance of PVA fibers. SEM photos of char residues and the results of the TG-IR technique revealed that flame retardance is mainly provided through the barrier action of the coatings with the partial effect of gaseous phase.

Rheological Behavior of Blends of Poly(Phenylene Sulfide) with a Thermotropic Liquid Crystalline Aromatic Poly(Ether Ester)

A new type of thermotropic liquid crystalline aromatic poly(ether ester) (PEE) was prepared from 1,3-bis(4′-carboxyphenoxy)benzene, 1,4-diacetoxybenzene, and p-acetoxybenzoic acid through a melt transesterification process. The rheological behavior of blends of poly(phenylene sulfide) (PPS) with PEE was studied using a high-pressure capillary rheometer with the shear rate range of 50 s−1 to 3000 s−1. The results show that according to the range of shear rate, the flow curves of PEE/PPS blends can be divided into three zones: a first shear-thinning zone (n < 1, “n” represents non-Newtonian indexes), a shear-thickening zone (n > 1), and a second shear-thinning zone (n < 1), and the former two zones are more obvious with the increase of PEE content or elevated temperature. In the second shear-thinning zone, the PPS melt is close to a Newtonian fluid at high temperature and high shear rate; meanwhile the non-Newtonian behavior of the PPS melt at high temperature is enhanced with the addition of PEE. The apparent viscosity of PPS melts sharply dropped after adding PEE, especially at relatively low temperature and low shear rate. The curve of apparent viscosity vs. shear rate starts to flatten out after adding PEE, suggesting that the addition of PEE lowers the sensitivity of PPS to shear rate. As the content of PEE increases, the activation energy of the viscous flow, ΔEη, of PPS decreases, which means that adding PEE weakens the temperature sensitivity of the apparent viscosity of the PPS melt. It can clearly be seen that the addition of PEE is beneficial to the processing of PPS.

Nonisothermal Degradation Kinetics and Life Prediction of the Pendent Phenyl-Containing Polyarylate

ABSTRACT The nonisothermal degradation kinetics of a pendent phenyl-containing polyarylate (PAR-P)were studied using different kinetic models, including the Kissinger method, Flynn–Wall–Ozawa (FWO) method, and Coats–Redfern (CR) method. The “three kinetic factors” of degradation, namely, activation energy (E), pre-exponential factor (A), and the reaction mechanism function (f(α)) were determined by these methods. Moreover, the lifetime equations of PAR-P were deduced, and its lifetime was predicted. The Kissinger method could be used to describe the nonisothermal degradation of PAR-P, and the results indicated that PAR-P could be degraded more easily in air than in nitrogen. The FWO method was expected to give more reliable values of the activation energy (209.71 kJ·mol−1 in nitrogen and 176.22 kJ·mol−1 in air) due to not having to introduce the reaction mechanism function during the calculation. According to the results of the CR method, the thermal degradation reaction mechanism was probably the R1 model in nitrogen, while it was likely to be the F2 model in air. The long-term and short-term use temperatures of PAR-P in air were 260°C and 300°C, respectively. The lifetime of PAR-P in nitrogen was much longer than that in air at low temperature, but had little difference when the use temperature exceeded 260°C. Although the lifetime of PAR-P obtained from the present work was unrealistic due to probable contributions from other unconsidered factors and being determined by a single factor method, it still could play a guiding role for designing the structure and determining the use conditions of the material.

Study of the thermal decomposition and flame-retardant mechanism of sulfonated polyoxadiazole fibers

Various proportions of 4,4′-oxybisbenzoic acid (OBBA) were incorporated to obtain the spinning solution of sulfonated polyoxadiazole (SPOD) copolymer through copolymerization in oleum. And the sulfonated fibers were prepared from the solution by using wet spinning approaches. The chemical structures of the fibers were characterized using Fourier transform infrared spectroscopy (FTIR) and elemental analyzer. The results indicated that sulfo groups were successfully introduced into the macromolecular chain. And the flame retardancy of the SPOD fibers was evaluated by limiting oxygen index, UL-94 and microscale combustion calorimeter tests, showing that flame-retardant properties could be significantly enhanced. And the thermal decomposition and flame-retardant mechanism were studied through various analytical methods. And thermogravimetric (TG) analyzer and scanning electron microscope results showed that the incorporation of OBBA would help fibers form more compact carbon residue. X-ray photoelectron spectroscopy and TG-FTIR results revealed that sulfur element increased carbon residue rate in the condensed phase and some converted into SO2 in the gas phase. Py-GC/MS results showed that thermal decomposition happened at oxadiazole rings and the introduction of OBBA did not alter the decomposition mechanism of POD essentially.

Influences of solution state on the formation of polyvinyl alcohol as-spun fiber during dry-wet gel spinning

The polyvinyl alcohol (PVA) as-spun fibers were prepared by dry-wet gel spinning, with dimethylsulfoxide (DMSO) as solvent and methanol as the cooling medium. The rheological properties of spinning solutions, matter exchanges, sonic orientation factor and entanglement of PVA as-spun fibers were investigated. Solution with lower PVA content at lower temperature has a same viscosity with the more concentrated solution at higher temperature. Solution with lower concentration has a higher G′ and a lower Tan δ, which leads to a lower sonic orientation factor for the fiber. The calculating results from the optical microscope show that solution with lower PVA content loses less DMSO due to the weaker gel ability and the possible phase separation during the coagulation. Moreover, solution more closed to the gel point bounds more DMSO, which makes the DMSO exchange difficult to process. The entanglement in the as-spun fiber decreases with the decreasing PVA content in the solution. Suitable crystallization and entanglement can obtain fibers with higher strength.