Hongqiang Qu

Zinc Hydroxystannate- or Zinc Stannate-coated Calcium Carbonate as Flame Retardant for Semirigid Poly(vinyl chloride)

The flame retardant and smoke suppressant properties of semirigid PVC treated with CaCO3, zinc hydroxystannate, zinc stannate, zinc hydroxystannate-coated calcium carbonate, and zinc stannate-coated calcium carbonate have been studied through the limiting oxygen index, anaerobic char yield, and smoke density rating (SDR) methods. The thermal degradation in air of the treated semirigid PVC is studied by thermogravimetry (TG) and differential thermal analysis (DTA) from ambient temperature to 1073 K. The morphologies of the additives and the unaerobic char formation are studied through SEM. The mechanical property is also studied. The results show that the semirigid PVC treated with zinc hydroxystannate-coated calcium carbonate or zinc stannate-coated calcium carbonate has a higher limiting oxygen index and anaerobic char yield, lower SDR and starting decomposition temperature, a more compact structure of char formation and reduced tensile strength and elongation, and improved impact strength than the semirigid PVC without flame retardant.

Using TG-FTIR and XPS to understand thermal degradation and flame-retardant mechanism of flexible poly(vinyl chloride) filled with metallic ferrites

The effect of three metallic ferrites, LaFeO3, ZnFe2O4, and BiFeO3, on the thermal degradation and flame retardancy of flexible poly(vinyl chloride) (PVC) was investigated using thermogravimetric analysis (TG), differential thermal analysis, and TG coupled with Fourier transform infrared spectrometry. In combination with X-ray photoelectron spectroscopy techniques, the charring and flame-retardant mechanism has been obtained. The results show that compared with LaFeO3 and ZnFe2O4, BiFeO3 promoted the dehydrochlorination reaction of PVC more effectively and generated a large amount of stable char residue in a condensed phase. In the char residue of PVC/BiFeO3, the Fe2p spectra are assigned to FeCl2 and FeOCl, which acts as effective catalysts for the ionic dehydrochlorination of PVC owing to their strong Lewis acidity. Bi exists as BiOCl, which has a lower melting point and boiling point and can more easily decompose to form BiCl3 gas at the flame temperature. The results demonstrated that BiFeO3 can not only effectively inhibit the production of smoke from PVC during combustion, but it also has an effect similar to that of Sb2O3 in flame-retardant PVC.

Using TG–FTIR and TG–MS to study thermal degradation of metal hypophosphites

Three typical metal hypophosphite flame retardants La(H2PO2)3·H2O (LHP), Ce(H2PO2)3·H2O (CHP), and Al(H2PO2)3 (AHP) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis (TG), derivative thermogravimetric analysis, and differential thermal analysis. The thermal degradation products from the synthesized metal hypophosphites were also investigated using thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR) and thermogravimetry coupled with mass spectrometry (TG–MS). The synthesized metal hypophosphites were also used as flame retardants for poly (1,4-butylene terephthalate) (PBT), and the combustion properties of flame-retarded PBT were evaluated using the limiting oxygen index and UL-94 tests. The results showed that the metal hypophosphites LHP, CHP, and AHP can be used as effective flame retardants for PBT, and these compounds can be obtained through a simple precipitation method. TG–FTIR and TG–MS results showed that the degradation process of AHP involves two steps, corresponding to the removal PH3 reaction and the further dehydration reaction of the hydrogen phosphate aluminum. While LHP and CHP have three degradation steps, the additional step is due to that LHP and CHP which will loss the crystal water at lower temperature.

Flame-Retarding and Mechanical Properties of Flexible Polyvinyl Chloride with Surface-Treated Lamellar Magnesium Hydroxide

abstract The effects of hydrophobic magnesium hydroxide (Mg(OH)2) particles, prepared by a surface modification method with oleic acid, on the flame-retarding and mechanical properties of polyvinyl chloride (PVC) were investigated. Comparison between the use of modified and unmodified Mg(OH)2 in the preparation of PVC composites showed that the former could provide excellent optical and flame-retarding properties. The dispersion of the modified Mg(OH)2 particles in the PVC matrix was investigated through scanning electron microscopy. Compared with a composite containing unmodified Mg(OH)2, the rheological and impact strength properties of that containing the modified Mg(OH)2 filler were found to be significantly improved. These improvements were mostly attributed to the better dispersion of the modified Mg(OH)2 particles and the strong adhesion between the filler and matrix.

Synergistic effect of silica sol and K2CO3 on flame-retardant and thermal properties of wood

In this study, silica sol (SiO2 sol) and K2CO3 were used as flame retardants for wood. The synergistic effect of SiO2 sol and K2CO3 on the flame retardancy, leaching resistance, and thermal properties of wood was investigated. The limiting oxygen index results revealed a significant improvement in the flame retardancy and leaching resistance of the wood sample treated with K2CO3 and SiO2 sol using the double bath technique. The thermal analysis results showed that the synergistic effect of K2CO3 and the SiO2 sol effectively prolonged the degradation of the wood sample during the charring stage and improved the stability of the char residue. The thermogravimetry–mass spectrometry analysis and scanning electron microscopy results showed that K2CO3 catalyzed the degradation reaction of the wood sample at lower temperatures resulting in an increase in the water and carbon dioxide output, and the SiO2 sol formed a compact and melted barrier on the surface of the char residue, which hindered the transfer of heat and combustible gases in the condensed phase. Thus, the combination of K2CO3 and SiO2 sol proves to be a promising flame-retardant system for wood.

Two kinds of activated carbon spheres-supported metal oxides for reducing smoke release volume and fire hazard in flexible poly(vinyl chloride)

Two kinds of activated carbon spheres (ACS)-supported metal oxides, ACS-supported Fe3O4 (ACS@Fe3O4) and ACS-supported NiO (ACS@NiO), were synthesized and used as flame retardants for reducing smoke release volume and fire hazard in flexible poly(vinyl chloride) (PVC). Scanning electron microscope measurement, Fourier transform infrared spectrum, X-ray diffraction and thermogravimetric analysis (TGA) were utilized to investigate the morphology, chemical structure and stability of the flame retardants. The TGA coupled with mass spectrometry (TG-MS) results of PVC composites showed that ACS could retard the heat and oxygen transfer between gas and polymers. Under the same condition, ACS@Fe3O4 could promote the dehydrochlorination reaction of PVC in lower temperature, while the ACS@NiO could make the dehydrochlorination reaction faster. Therefore, both ACS@Fe3O4 and ACS@NiO effectively promoted the cross-linked carbonization reaction of PVC and then generated a large amount of stable char residues. Limiting oxygen index (LOI) and cone calorimeter test results of the PVC composites showed that ACS@Fe3O4 and ACS@NiO were much more efficient than ACS alone to improve the flame retardancy and smoke suppression of PVC. The incorporation of ACS@Fe3O4 and ACS@NiO increased the LOI from 24.9 to 27.4% and 26.9% and reduced the peak of heat release rate by 47.2 and 30.8%, respectively, compared with pure PVC.

The synergism of MgCO3 and 2ZnCO3·3ZnO·4H2O as flame retardants and smoke suppressants for flexible poly(vinyl chloride) (PVC)

Abstract MgCO3 and 2ZnCO3·3ZnO·4H2O (AZC) as flame-retardants and smoke suppressants for flexible poly(vinyl chloride) (PVC) was evaluated using limiting oxygen index (LOI), smoke density rating (SDR) tests, scanning electron microscopy (SEM) and thermogravimetry analysis (TGA). The activation energy (Ea) of the original and flame retardant PVCs’ degradation processes was calculated by the Vyazovkin method. The results showed that the AZC can be used as a synergistic agent for MgCO3 as flame retardants agent of flexible PVC. The composites of MgCO3 and AZC cannot only decrease the initial decomposition temperature and increase the weight loss rate in the first stage, but also can promote the char formation in the second stage. The AZC decreased the Ea of the degradation reaction of PVC in the first stage and MgCO3 increased the Ea in the second stage, which means that the AZC combined with MgCO3, catalyzed the dehydrochlorination, promoted the early crosslinking for the PVC compound and improve the stability of the char residue. The SEM results also show that the char residue of MgCO3/AZC treated sample has a continuous and denser structure, which can be used as a barrier for the PVC bulk.