The hydrogen bond and its effect on spontaneous orientation during the heating of aromatic polyamides

A heterocyclic meta-aramid fiber containing benzimidazole structure was prepared by the low-temperature polycondensation of m-phenylenediamine, 2-(4-aminophenyl)-5-benzimidazole, and isophthaloyl dichloride, followed by dry-jet wet spinning. The structure and properties of the heterocyclic modified meta-aramid (h-aramid for short) were explored and compared with poly(isophthaloylmetaphenylene diamine) (m-aramid for short). H-aramid exhibits excellent spinnability. The surface of the fiber is smooth and even, with a partially ordered structure. Mechanical properties, thermal resistance, and flame retardant of h-aramid are significantly enhanced as the introduction of benzimidazole can not only increase the rigidity of molecular chains but also strengthen hydrogen bonds and act as physical crosslinking points. The strength and modulus of h-aramid are up to 0.84 GPa and 16.66 GPa, respectively, with an elongation at break of 20%. The glass transition temperature and melting temperature of h-aramid reach 302°C and 356°C, respectively, about 30°C and 40°C higher than that of m-aramid. Temperature of 10 wt% weight loss under nitrogen and air atmosphere is 17°C and 39°C higher than those of m-aramid. Besides, the thermal degradation behavior of h-aramid was studied, and its degradation process and mechanism was proposed.

Section: Mechanical Propertiesmentioning

confidence: 94%

The preparation and characterization of a heterocyclic meta-aramid fiber with outstanding thermal stability

Cao

Liu²,

Yang³

et al. 2020

“…Our results are in line with previous observations that hydrogen bonds play an important role in strengthening supramolecular interactions, dictating the orientation between the macromolecular chains, promoting the intermolecular 'self-orientation', and enhancing the mechanical properties of fibres. [34][35][36][37] Thermal stability A high thermal stability is a critical characteristic for industrial applications. Thus, the thermal degradation behaviour in both nitrogen and air atmospheres was explored by TGA.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

Preparation and properties of an aromatic polyamide fibre derived from a bio-based furan acid chloride

Cao

Liu²,

Feng³

et al. 2021

A high-molecular-weight aromatic polyamide resin incorporating furan-rings (f-resin) was prepared by low-temperature solution polycondensation of bio-based 2,5-furandiformyl chloride and 3,4′-diaminodiphenyl ether, in N,N-dimethylacetamide. Further, an aromatic polyamide fibre containing furan-rings (f-fibre) was obtained from the fresin by dry-jet wet spinning, and its structure and properties were investigated. The prepared f-resin showed good solubility and possessed good spinnability in solution. The mechanical, heat-resistance, and flame-retardant properties of the f-fibre were found to be excellent – comparable to or exceeding those of meta-aramid fibre (m-fibre). In addition, the furan acid chloride monomer is bio-based and is derived from abundant resources, unlike petroleum-based monomers. Therefore, f-fibre has good potential and broad application prospects as an environment-friendly and sustainable high-performance material.

“…In addition, in order to study the effect of heat treatment on orientation, polarized FTIR spectra of unheated CPA films are shown in Figure 5, and the R values are also shown in Table 1. When the films were heated, the R values decrease more at 3300 and 1650 cm À1 band and increase more at 1515, 1490, and 1320 cm À1 relative to the unheated CPA samples with the same draw ratio, which clearly indicates that the macromolecular orientation is enhanced after heating at 380 C. This phenomenon of improvement of orientation after heat treatment is called spontaneous orientation, which was found in many rigid-rod polymers on exposure to heat, such as PI, 28 cellulose, 29 and polyamide, 30 resulting in the improvement of mechanical properties. What's more, when cold-drawing ratio is 0%, the R value of unheated CPA-0 and CPA-0 films are the same (R ¼ 1).…”

Section: The Orientation In the Filmsmentioning

confidence: 86%

Ultrahigh strength and modulus copolyamide films with uniaxially cold-drawing induced molecular orientation

Luo

Huang

Yan

et al. 2016

The tensile strength of polymer films is generally lower than 200 MPa. Copolyamide (CPA) films with ultrahigh strength (approximately 317-865 MPa) and high modulus (approximately 3.96-11.76 GPa) were obtained by uniaxial cold-drawing and heat treatment. The relationship between structures and properties in the orientation state was also investigated. The results of Fourier transform infrared (FTIR) spectroscopy indicate that hydrogen bonding interactions change a little with drawing. Wide-angle X-ray diffraction patterns show orientational stretch induces -ordered packing after drawing 100%. The tensile strength and modulus of the drawn CPA films are improved approximately 41%-173% and 9%-197% compared to undrawn films. Dichroic ratios obtained under polarized FTIR spectroscopy represent overall orientation factors. The decrease of dichroic ratios at about 3300 cm À1 and 1650 cm À1 and the increase of dichroic ratios at 1515 cm À1 prove that the orientation of macromolecular chains is improved along stretch direction. What's more, the degree of orientation is further increased after heat treatment, which is the phenomenon of spontaneous orientation. The degree of spontaneous orientation increases with the increase of cold-drawing ratio. Thus, the initial orientation in colddrawing and spontaneous orientation during heat treatment leads to ultrahigh modulus and high strength.