Acrylic fibers [polyacrylonitrile (PAN) fibers] have excellent flame-retardant properties after they are modified by hydrazine hydrate and metal ions; however, their widespread applications are restricted because of poor mechanical properties. To improve the mechanical properties of these modified PAN fibers, poly(vinyl alcohol) (PVA) was added to the spinning solution of PAN as an effective reinforcing agent. The structure of the fibers before and after modification was studied by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy, and wide-angle X-ray diffraction. The mechanical properties and flame resistance of the fibers after treatment were also tested by a single-fiber tensile tester and a limiting oxygen index (LOI) analyzer, respectively. We found that the LOI of the modified fibers was reduced from 54.7 to 29.1 after the introduction of 50 wt % PVA; however, the tensile strength was dramatically improved from about 1.50 cN/dtex to more than 4.00 cN/dtex. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43006.

Octa-ammonium chloride salt of polyhedral oligomeric silsesquioxane (POSS) was synthesized by a hydrolysis reaction and introduced into poly(p-phenylene-1,3,4-oxadiazole) (p-POD) and poly(p-phenylene terephthalamide) (PPTA) fibers by a finishing method to enhance the UV resistance. The effects of the POSS concentration, treatment temperature, and time on the tensile strength of the fibers were investigated. The surface morphology, mechanical properties, crystallinity, degree of orientation of fibers, and intrinsic viscosity of the polymer solution were characterized in detail. The results indicate that the tensile strength retention and intrinsic viscosity retention of the fibers treated with POSS were much higher than those of the untreated fibers after the same accelerated irradiation time; this demonstrated that this treatment method was feasible. We also found that the efficacy of the protection provided by POSS was more beneficial to p-POD than PPTA because of the different structure. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42643.

The sodium ions were introduced into the acrylic fibers by post-treating the fibers with hydrazine hydrate and aqueous sodium hydroxide to improve the flame resistance of the fibers. The molecular structure of the modified acrylic fibers was characterized by FTIR spectra. The flame resistance of the acrylic fibers was significantly increased after post-treatment and was relied mostly on the content of sodium ions. The flame-retardant mechanism of the modified fiber was studied in details. The micro calorimeter tests showed that the total heat release and the peak heat release rate were largely reduced after post-treatment. Photographs of the char residues and the results of TGA and TG-IR technique revealed that the flame retardance of the modified acrylic fiber was provided through the combination effect of the gas phase and condensed phase. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41996.

To improve the paper properties of the poly(1,3,4-oxadiazoles) (POD), the POD pulps were prepared by prechemical and mechanical methods to increase their polarity, contact area, and interaction. The fibrillated degree of the staple fibers was evaluated by the Canadian Standard Freeness and the specific surface area, while the surface free energy was calculated by the Micro–wilhelmy method. Meanwhile, the functional groups and compositions on the surface of the POD fibers were confirmed by the FTIR–ATR and the X-ray photoelectron spectroscopy, and the surface morphological structure and the crystalline structure of the POD fibers were observed by the fiber analyzer, scanning electron microscope, and Wide-angle X-ray diffraction, respectively. It was found that the pronounced abrasive and distinctive grooves were formed on the surface of the POD fibers after prechemical and mechanical treatment. The surface free energy of POD fibers increased 8.41%, and the polar part increased by 32.10% after treatment. It was confirmed that the polar functional groups and fibril were formed after chemical and mechanical treatment, so the interaction of the POD fibers was highly enhanced, and as a result the apparent density, tensile strength, fold endurance, and tear strength of the paper formed by those treated fibers were all improved apparently. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39818.

A series of composite fibers based on poly(ether ether ketone)s (PEEK) and a novel thermotropic liquid crystalline polyetherarylates (PEAR) with the aryl-ether linkages, have been prepared by melt spinning. The impact of PEAR on PEEK is investigated by rheological measurements, differential scanning calorimetry, thermal gravimetric analysis, wide angle X-ray diffraction and scanning electron microscope, orientation degree test and mechanical properties test, etc. The results show that the flowing curves of the blends can be divided into three regions: the first shear thinning region, the shear thickening region, and the second shear thinning region; meanwhile, the PEAR can function as a processing aid by reducing the viscosity of PEEK, thus the processing can be carried out at relatively low temperatures. Although, they are partially compatible, the mechanical properties of the post-treatment fibers have been improved by 14% after adding 2% PEAR to PEEK. The crystallinity of the as-spun fibers increases from 22.47 to 42.10%, suggesting that PEAR can act as nucleating agent. Regretfully, both of the initial degradation temperatures and the maximal degradation temperatures decrease with the increase of the PEAR content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A series of polyarylates containing phosphorus (pho-PARs) were synthesized from bisphenol A with different molar ratios of bis-(4-carboxyphenyl) phenyl phosphine oxide (BCPPO) to terephthalic acid (TPA). When the contents of BCPPO are in the range of 0.4–1.0, the pho-PARs are readily soluble in a wide range of organic solvents and have the glass transition temperatures of 243.0–260.4°C. The initial degradation temperatures of these pho-PARs are all above 450°C and their char yields at 800°C under nitrogen atmosphere are in the range of 28.7–33.0%, suggesting they have excellent thermal stability. The results of TG-FTIR and FT-IR show the introduction of BCPPO change the decomposition model of the pho-PARs. The limiting oxygen indexes are at a range of 30.7–34.5%, which suggests that the pho-PARs are a kind of excellent inherent flame retardant materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3521–3529, 2013

To improve the processability of the poly(p-hydroxybenzoic acid), copolyarylates containing m-aryl ether units were synthesized using p-acetoxybenzoic acid, 1,4-diacetoxybenzene and 1,3-bis(4'-carboxyphenoxy)benzene by melt transesterification reaction. The structure and properties of these polyarylates were characterized using infrared spectra, differential scanning calorimetry, thermogravimetric analyses, wide-angle X-ray diffraction and polarized optical microscopy etc. The results showed that all polyarylates were semicrystalline materials and could form a thermotropic liquid crystalline intermediate state. As the content of aryl ether units increased, the crystallization and melting temperatures of the polyarylate decreased; meanwhile, the crystalline ability became lower. The introduction of the aryl ether could restrain the formation of a liquid crystalline structure and reduce the thermal stability to some extent. After solid state polymerization (SSP), the intrinsic viscosity, melting temperature, crystallinity and thermal stability of the polyarylate increased while the melting range narrowed. However, the SSP reaction might be accompanied by degradation and crosslinking.

High-molecular weight (HMW) poly(vinyl alcohol) (PVA) was prepared via an emulsifier-free emulsion polymerization of vinyl acetate (VAc) using a redox initiation system in low temperatures, and the subsequent saponification with potassium hydroxide in methanol. The effect of the polymerization conditions on the conversion, molecular weight, and branching degree was investigated. PVA with maximum viscosity-average degree of polymerization (DP) of 8270 could be prepared by saponification of poly(vinyl acetate) (PVAc), with DP of 10,660 obtained at temperature of 10°C, monomer concentration of 30%, potassium persulfate molar ratio to monomer of 1/2000, agitation speed of 160 rpm. The conversion was above 90%. From the emulsifier-free emulsion polymerization of VAc in low temperature, PVAc with HMW and high linearity was effectively prepared, which might be useful for the preparation of high-strength and high-modulus PVA fiber. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Poly(vinyl alcohol) (PVA) is an important water-soluble polymer. In this study, a novel method has been developed for preparing water-soluble PVA fiber with narrowly dissolving temperature range via wet spinning of partly acetalized PVA. The structures and properties of the fiber were characterized by IR, ¹H-NMR, DSC, WAXD, tensile strength tester, etc. IR and NMR spectra showed that acetal groups were successfully generated on the lateral chains of PVA with the catalysis of acid. As a small quantity of CH₂O was added, the introduction of the acetal group could reduce both the hydrophilicity of amorphous region and the crystallinity of PVA water-soluble fiber, and hence narrowed the dissolving temperature range of fiber. However, the dissolving temperature range was broadened with a further increase of CH₂O amount, because of the large decrease of crystallinity and crystallite perfection. When the CH₂O added amount reached up to 20%, the acetalized PVA was completely insoluble, so that the spinning process could not be carried out. The breaking strengths of most acetalized fibers were beyond 4 cN/dtex, which satisfied the ordinary use of industrial and domestic field. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

In order to obtain poly(ether ether ketone)s having enhanced solubility and processability without extreme loss of other properties, a series of copoly(ether ether ketone)s (Co-PEEKs) with pendant phenyl groups were synthesized from 1,1-bi(4-hydroxyphenyl)-1-phenylethane (ph-BPA), hydroquinone and 4,4′-difluorobenzophenone via aromatic nucleophilic substitution reaction. The structures and properties of the Co-PEEKs were characterized using Fourier transform infrared and ¹H NMR spectroscopies, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffraction and solubility testing. These Co-PEEKs have inherent viscosities in the range 0.14–1.09 dL g⁻¹, and their number-average and weight-average molecular weights reach 72 659 and 163 400 g mol⁻¹, respectively. The Co-PEEK with the lowest content of ph-BPA has a semi-crystalline nature and is only soluble in 98% sulfuric acid. However, with an increase of ph-BPA in the Co-PEEKs, they become amorphous and readily soluble in a wide range of organic solvents and can afford tough films. These Co-PEEKs have glass transition temperatures of 137–180 °C depending on the content of ph-BPA. All the Co-PEEKs have initial degradation temperatures above 480 °C in nitrogen atmosphere. Thus, these Co-PEEKs with excellent thermal stability, good solubility and processability have potential for use in high-performance films, coatings, hollow fiber membranes, etc. Copyright © 2011 Society of Chemical Industry

A series easily soluble polyarylates were synthesized from either 1,1-bis(4-hydroxyphenyl)-1-phenylethane or tetramethylbisphenol A with various aromatic diacid chlorides by the two-phase interfacial polycondensation. These polyarylates have the inherent viscositiesin the range of 0.36–0.97 dL/g, and their number-average and weight-average molecular weights determined by gel permeation chromatography are 14,200–43,200 and 31,900–102,500, respectively. All these polyarylates are readily soluble in a wide range of organic solvents, thus these polymers can be convenient to process into heat resistance films by cast, spin- or dip-coating. The polyarylates have the glass transition temperatures in the range of 165.0–201.6°C. The pendent phenyl-containing polyarylates reveal excellent thermal stability, and their initial degradation temperatures are all above 480°C and char yields at 700°C are 37.97–40.53% in nitrogen atmosphere. However, the polymers prepared from tetramethylbisphenol A have a large decrease in thermal stability, and their initial degradation temperatures in nitrogen are only about 440°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The nonisothermal crystallization kinetics of linear Poly(phenylene sulfide) (PPS) was studied with differential scanning calorimetry. Ozawa theory, Jeziorny model, and Mo equation were applied to describe the crystallization kinetics and to determine the crystallization parameters and mechanism of the linear PPS resin. The crystallization activation energies were also calculated using Kissinger formula and Flynn-Wall-Ozawa equation, respectively. According to the Ozawa model, it is found that instantaneous nucleation takes place during crystallization of PPS; the Ozawa exponent m is 3 in initial stage of crystallization; as the crystallization temperature decreases, the value of m reduces, and the growth rate of crystal almost keeps a constant. The Avrami exponent n obtained from Jeziorny model fluctuate around 1.84. Based on the Jeziorny model, the crystallization rate increases with increasing the cooling rate, but it does not change any longer when the cooling rate rise to a certain value. Mo equation also exhibits great advantages in treating the nonisothermal crystallization kinetics of PPS. The activation energy E of nonisothermal crystallization process of PPS is calculated to be −162.73 kJ/mol by the Kissinger formula, and the mean value of E determined by Flynn-Wall-Ozawa equation is −152.40 kJ/mol. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Poly(p-phenylene-1,3,4-oxadiazoles) (p-PODs) spinning solution was prepared by one-step polycondensation, and p-POD fibers were obtained by wet spinning method using dilute sulfuric acid as coagulation bath. The morphology and mechanical properties of p-POD fibers under different coagulating conditions, such as bath concentration and temperature, were qualitatively and quantitatively studied by microscopes, ultrasonic orientation measurement, WAXD, and other traditional methods. The microscopic observation indicated that the p-POD fibers were of three-layer structure which consisted of outer skin, inner skin, and the core. The skin-core structure and surface feature of the fibers were greatly affected by the coagulating conditions. At the same time, the results of WAXD and ultrasonic orientation measurement demonstrated that the crystallinity and orientation of the fibers also varied with the change of bath conditions. The tests of mechanical properties showed that the tensile strength, elongation at break, and maximum draw ratio of the p-POD fibers were determined by their solid-phase structures, which were largely influenced by coagulation conditions. According to the structure analysis and the mechanical tests, the optimal coagulation parameters were chosen to obtain p-POD fibers with denser and more regular structure and better mechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009