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
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.
Randi Weingarten, the American Federation of Teachers, and the Challenges of Policy Leadership in a Hostile Environment
Randi Weingarten is the president of the most vocal and influential teachers’ union, the American Federation of Teachers. Since rising through the ranks to AFT president in just two years, Weingarten is now a major, if not the most prominent, nongovernmental player in national education policy. She has earned deep respect from many educational policy actors. Likewise, Weingarten elicits withering criticism from others. This fascinating profile explains why, in such a brief period, she has proved to be a fierce, fearless, and effective leader under extraordinarily difficult circumstances. Her experience offers invaluable lessons applicable for others working in similarly intense policy arenas.