An Investigation on Synergistic Effect of EG with IFR in Polyethylene
Great concerns with environmental pollutions caused by halogen elements and heavy metals have been driving the development of eco-friendly wire and cable compounds, among which halogen-free low-smoke flame-retardant polyolefins are of great importance. Intumescent flame retardants (IFR) show better efficiency in flame retardant polyolefins (PO) than metal hydroxides, such as magnesium hydroxide and aluminum hydroxide, but the flame retardancy of IFR/PO is still limited. Recently, expandable graphite (EG), a promising eco-friendly flame retardant, has attracted much attention. In the paper, the synergistic effect of expandable graphite (EG) with intumescent flame retardants (IFR) on flame retardant polyethylene (PE) was investigated by limited oxygen index (LOI) and the investigations on the synergistic mechanism were performed by thermogravimetric (TG) and scanning electron microscope (SEM). The results showed that the flame retardant properties of PE/EG/IFR were greatly improved by the synergistic effect of EG with IFR. Compared with the cracking barrier on the combustion surface of PE/EG or PE/IFR, a very thick and compact char layer forming on the combustion surface of PE/EG/IFR was more in favor of preventing the transfer of oxygen and heat, thus leading to lower thermal degradation rate and more char left
Thermal properties of polyethylene flame retarded with expandable graphite and intumescent fire retardant additives
Low‐density polyethylene was flame retarded by combinations of expandable graphite with either ethylenediamine phosphate or 3,5‐diaminobenzoic acid phosphate. Cone calorimeter, laser pyrolysis, and open flame exposure tests (supported by video and infrared camera data capture and analysis) were conducted to assess ignition and burn behavior. Cone calorimeter results indicated substantial reductions in the peak heat release rates for all flame‐retarded samples but with reduced ignition times and increased flame out times. Smoke generation was suppressed in the presence of expandable graphite. Infrared and video data from open flame fire tests indicated cohesive bonding of expanded strings and thermal shielding properties in all binary systems. All binary systems delivered fire retardation exceeding any of the single fire retardant compounds. They were also able to withstand higher temperatures before ignition, burn through, or sag occurred. All ethylenediamine phosphate‐containing binary systems prevented sample burn through, maintaining structural integrity of samples until eventual melting of the polymer media occurred. Thermogravimetric analysis laser pyrolysis results confirmed the good thermal shielding imparted by the intumescent additives. Copyright © 2016 John Wiley & Sons, Ltd.
Thermal degradation of chlorinated polystyrenes
Abstract p-Chlorostyrene was polymerized using a radical initiator, α,α′-azobis(isobutyronitrile). Polystyrene was chlorinated in the liquid phase using an SbCl3, catalyst combined with 10-trifluoroacetylphenothiazine. The chlorinated polymers were characterized spectroscopically and molecular weight measurements were carried out. The polymers were pyrolysed at 600°C, the pyrolysis products identified by means of gas chromatography/mass spectrometry and their relative percentages calculated. The differences in the products distributions gave helpful indications about the structure and the mechanism of degradation of the chlorinated polymers.