Baojun Qu

Flammability characterization and synergistic effects of expandable graphite with magnesium hydroxide in halogen-free flame-retardant EVA blends

Abstract The flammability characterization and synergistic effects of different types of expandable graphite (EG) with magnesium hydroxide (MH) in halogen-free flame-retardant (HFFR) ethylene vinyl acetate (EVA) blends have been studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and UL-94 test. The results show that the particle size and expansion ratio of EG have a great effect on the flammability of the HFFR EVA/MH/EG blends. The EG with bigger particle size and higher expansion ratio can apparently increase the LOI value and improve the UL-94 flammability properties of EVA blends. The data obtained from the CCT indicate that the heat release rate (HRR), the effective heat of combustion (EHC), and the mass loss rate (MLR) of EVA/MH/EG blends decrease remarkably with increasing the particle size and expansion ratio of EG. However, the specific extinction area (SEA) data show that the addition of EG can apparently increase the smoke emission of EVA/MH/EG blends. The TGA results show that the thermal stability of EVA/MH/EG blends increase with increasing the EG particle size and expansion ratio.

Synergistic effects of silicotungistic acid on intumescent flame-retardant polypropylene

Abstract The synergistic effects of silicotungistic acid (SiW12) as a catalyst in polypropylene (PP) flame-retarded by the intumescent flame-retarder (IFR) based on the NP28 phosphorus-nitrogen compound were studied using the limiting oxygen index (LOI), the UL-94 test, thermogravimetric analysis (TGA), real time Fourier transform infrared (FTIR), laser Raman spectroscopy (LRS), and scanning electron microscopy (SEM). The LOI data show that SiW12 added to PP/IFR systems has a synergistic FR effect with NP28. The TGA data show that SiW12 increases the thermal stability of the PP/IFR systems at high temperature (T>500xa0°C). The FTIR results provide positive evidence that IFR can improve the thermal stability of PP and SiW12 and can efficiently promote the formation of charred layers with phosphocarbonaceous structures. The LRS measurements provide useful information on the carbonaceous microstructures. The morphological structures observed by SEM have demonstrated that SiW12 can promote formation of compact intumescent charred layers. Thus, a suitable amount of SiW12 plays a synergistic effects with the IFR in increasing the LOI value and the thermal stability at high temperature and promoting the formation of charred structures in the PP blends.

Synergistic effects of expandable graphite with some halogen-free flame retardants in polyolefin blends

The synergistic effects of expandable graphite (EG) with some halogen-free flame retardant (HFFR) additives in the polyolefin (PO) blends have been studied by cone calorimeter test (CCT), thermal analysis (TGA and DTA), limiting oxygen index (LOI), and mechanical properties measurements etc. The results in this work show that EG combined with some HFFR additives, such as ammonium polyphosphate, zincborate, phosphorus-nitrogen containing compound NP28, and microcapsulated red phosphorus, can apparently increase the LOI values and improve the flammability properties of PO blends. The data obtained from the CCT indicate that the heat release rate (HRR) and effective heat of combustion (EHC) decrease and the residues of carbonaceous chars increase remarkably with addition of EG and/or the other HFFR additives. The TGA and DTA data give the positive evidence that the decreases of HRR and EHC values of the retarded PO materials are due to the increase of oxidative degradation temperature and the decrease of oxidization heat. By optimizing the formulation system and using ethylene vinylacetate copolymer as a compatilizer, the PO/EG/HFFR blends with good flame-retardant and mechanical properties have been obtained in this study.

Dynamic FTIR studies of thermo-oxidation of expandable graphite-based halogen-free flame retardant LLDPE blends

Abstract The dynamic thermo-oxidative degradation of expandable graphite (EG)-based intumescent halogen-free flame retardant (HFFR) LLDPE blends in the condensed phase at 300 or 400°C has been studied in situ by real time Fourier transform infrared spectroscopy. The kinetic characteristics and dynamic changes of various kinds of pyrolysis products during the thermo-oxidative degradation were examined extensively for several LLDPE/EG blends with different HFFR additives, such as the phosphorus–nitrogen compound NP28, ammonium polyphosphate (APP), red phosphorus (RP), and zinc borate (ZB). It has been found (i) that the dynamic monitoring of the LLDPE/EG/HFFR blends during the pyrolysis shows that the breakdown of LLDPE main chains and formation of various kinds of carbonyl products increase with increasing thermo-oxidation time and temperature; the latter have been identified as carboxylic acids, ketone, lactone and cyclic anhydrides; (ii) that the fast formation rate and high initial concentrations of P–O–P and P–O–C products in the phosphorus-containing HFFR systems have a crucial importance for decreasing the thermo-oxidative degradation rate of LLDPE efficiently (the NP28 system is the most efficient in the present study); and (iii) that the pyrolysis temperature has a significant effect on the efficiency of flame retardants, which requires the LLDPE/EG/HFFR formulation should be optimized at certain temperature range in order to form compact intumescent charred layers immediately at the beginning of the thermo-oxidative degradation of the LLDPE blends.

Thermo-oxidative degradation behaviors of expandable graphite-based intumescent halogen-free flame retardant LLDPE blends

Abstract The thermo-oxidative degradation behaviors of expandable graphite (EG)-based intumescent halogen-free flame retardant LLDPE blends under different thermo-oxidation conditions have been studied by real time Fourier transform infrared (FTIR) spectroscopy or FTIR photoacoustic spectroscopy (FTIR–PAS), X-ray photoelectron spectroscopy (XPS), and wide-angle X-ray diffraction (WAXD). The real time FTIR results show that the pyrolysis of LLDPE at high temperature leads to the breakdown of PE chains and the formation of various kinds of thermal oxidation products. The addition of EG can improve the stability of thermo-oxidative degradation effectively. The FTIR–PAS and XPS data show that the thermo-oxidative degradation of LLDPE decreases remarkably with the increase of EG concentration and/or its synergists and increases dramatically with the increases of pyrolytic temperature and thermal degradation time. The thermo-oxidative degradation products have been identified as various kinds of carbonyl compounds, such as ethers, esters, ketone or carboxyl products. The WAXD measurements demonstrate that the crystalline structures of LLDPE/EG or LLDPE/EG/HFFR blends after the thermo-oxidation degradation have been destroyed partly or totally dependent on the pyrolytic temperature and thermal degradation time. The changes of crystalline structure in the LLDPE/EG/HFFR blends are due to the breakdown of LLDPE chains and a series of reaction products with FR additives.

Surface photo-oxidation and photostabilization of photocross-linked polyethylene

Abstract The surface photo-oxidation and photostabilization of photocross-linked polyethylene (XLPE) have been studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The FTIR and XPS data gave the evidence that the surface photo-oxidation of XLPE increases, apparently, with increasing UV-irradiation time. The main photo-oxidation products have been identified as hydroperoxides and various carbonyl compounds. The photostabilization of XLPE can be carried out by suitable pre-irradiation of low-pressure mercury (LPM) lamp and by addition of hinder amine light stabilizers (HALS). The FTIR and XPS data also show that the optimum time of pre-irradiation of LPM lamp is 10 s under the experimental conditions of the present study. The addition of HALS into PE resin can protect the XLPE efficiently from surface photo-oxidation in the photocross-linking process of PE.

Photo- and thermo-oxidative degradation of photocrosslinked ethylene–propylene–diene terpolymer☆

Abstract Photocrosslinking of ethylene–propylene–diene terpolymer (EPDM), and photo- and thermo-oxidative degradation of photocrosslinked EPDM have been studied by photoacoustic Fourier transform infrared spectroscopy (PAS-FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The relative ratios of degradation to crosslinking for photocrosslinked EPDM by swelling measurement were estimated by Charlesbys random crosslinking theory to be 0.06 for EPDM 4770 and 0.1 for EPDM 4045. The PAS-FTIR and XPS data gave the evidence that the surface photo- and thermo-oxidation degradation of photocrosslinked EPDM samples with a given UV irradiation time apparently increase with aging time. The main photo-oxidation products were identified as hydroperoxides and various carbonyl compounds. The SEM measurements show that the photo-oxidative degradation of photocrosslinked EPDM has a crucial effect compared with thermo-oxidative degradation.

Effects of PE-g-DBM as a compatiblizer on mechanical properties and crystallization behaviors of magnesium hydroxide-based LLDPE blends

A linear low density polyethylene (LLDPE) grafted with dibutyl maleate (DBM) (PE-g-DBM) was prepared in the presence of dicumyl peroxide (DCP) and characterized by FTIR, melt index, and contact angle. The effects of PE-g-DBM as a compatiblizer on the mechanical properties, morphological structure and crystallization behaviors of magnesium hydroxide (MH)-based halogen-free flame retardant (HFFR) LLDPE blends have been investigated using scanning electron microscope (SEM), differential scanning calorimetry, and mechanical properties measurements. The results show that a suitable amount of PE-g-DBM compatiblizer can increase the adhesion between MH and polyethylene and thus improve the mechanical properties of LLDPE/MH/PE-g-DBM blends. The crystallinity degree of the blends decreases with increasing PE-g-DBM content.