Search

In order to improve the flame retardance of aromatic polyoxadiazole (p-POD) fiber, a series of phosphorus-containing PODs (pho-POD) were synthesized by introducing triaryl phosphine oxide (TPO) units into the main chains of p-POD using hydrazine sulfate, terephthalic acid and bis(p-carboxy)phenyl phosphine oxide (BCPPO) as monomers, and then halogen-free flame resistant pho-POD fibers were obtained from wet spinning. The structure and properties of the pho-POD fibers were characterized and measured in detail using the methods of wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), the limiting oxygen index (LOI), oxygen bomb calorimeter, Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) etc. The results show that the introduction of TPO units resulted in the weakening of the crystallization ability, the formation of the poriferous and lax interior structure, the slight decrease in the thermal stability and mechanical properties of the POD fibers. However, the value of LOI obviously increased from 28% to 35%, and the gross heat of combustion (GHC) decreased from 19.72 MJ kg−1 to 17.84 MJ kg−1 with the increase in the content of the BCPPO. Moreover, the combustion residue of pho-POD fiber revealed a smooth, dense and non-porous carbon layer, which could effectively play a role of oxygen barrier and enhance the flame resistance. From the above results, it can be concluded that the flame resistance of the POD fiber could be improved significantly after introducing the TPO unit. The results of Py-GC/MS illustrate that the TPO unit of pho-POD could inhibit the production of volatile products, which could be confirmed that the mechanism of enhancing the flame retardancy by introducing TPO units was mainly the flame retardation of the condensed phase.

The interfacial strength between reinforced fiber and a polymeric matrix is a critical factor for determining the mechanical properties of composites. Here, grafting multi-walled carbon nanotubes (MWCNTs) onto plain weave glass fabric (PWGF) is introduced to improve the interfacial strength of PWGF reinforced polyphenylene sulfide (PPS) composites. Firstly, MWCNTs-g-PWGF is prepared by grafting oxidized MWCNTs onto functionalized PWGF, and then the MWCNTs-g-PWGF/PPS composite laminates are fabricated by an opening hot pressing process. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirm that the MWCNTs are successfully grafted onto PWGF by chemical linkage. The interfacial morphologies are characterized by scanning electron microscopy (SEM), which reveals a good interfacial compatibility in MWCNTs-g-PWGF/PPS composites. The mechanical properties of MWCNTs-g-PWGF/PPS composites are also characterized by dynamic mechanical analysis (DMA) and universal tensile or bending testing. According to the results, the present method of manufacturing MWCNTs-g-PWGF/PPS composites produces an increase of almost 126% in tensile strength and a significant enhancement of nearly 155% in the bending strength compared with PWGF/PPS composites. The notable increase in the glass transition temperature of MWCNTs-g-PWGF/PPS composites also reflects the remarkable improvement in interfacial strength of the composites.

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.