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
Synergistic effect between expandable graphite and ammonium polyphosphate on flame retarded polylactide
Abstract Synergistic effect was observed between expandable graphite (EG) and ammonium polyphosphate (APP) on flame retarded polylactide (PLA) in this paper using limiting oxygen index (LOI), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray spectroscopy (XPS) and cone calorimeter tests etc. In the experiments, PLA composites with 15 wt% of APP/EG(1:3) combinations showed a LOI value of 36.5 and V-0 rating in UL-94 tests, greatly improved flame retardant properties from composites with APP or EG alone. Results from TGA and cone calorimeter demonstrated that APP/EG combination could retard the degradation of polymeric materials above the temperature of 520 °C by promoting the formation of a compact char layer. This char layer protects the matrix effectively from heat penetrating inside and prevents its further degradation, resulting in lower weight loss rate and better flame retarded performance.
Copper Phthalocyanine Improving Nonaqueous Catalysis of Pseudomonas cepacia Lipase for Ester Synthesis
The nonaqueous catalysis of lipases is significant for synthesis of high pure esters, but they usually behave low catalytic activity due to denaturation and aggregation of enzyme protein in organic phases. To improve the nonaqueous catalysis, the inexpensive copper phthalocyanine was taken as a new carrier on which Pseudomonas cepacia lipase was immobilized by physical absorption, and used for synthesis of hexyl acetate, an important flavor, via transesterification of hexanol and vinyl acetate. Results showed that the desired loading was 10 mg lipase immobilized on 10 mg copper phthalocyanine powder. When the immobilized lipase was employed in the reaction system consisted of 1.5 mL hexanol and 1.5 mL vinyl acetate at 37℃ and 160 rpm, the conversion was five fold of that catalyzed by native lipase after 1 h, and reached 99.0% after 8 h. Undergoing six times of 8-h reuses, the immobilized lipase had an activity attenuation rate 1.22% h− 1, lower than 1.77% h− 1 of native lipase, which meant that the immobilized lipase was more stable. Even at the room temperature and the static state without shaking or stirring, the immobilized lipase could bring conversion 42.8% after 10 h and the native lipase gave 20.1%. Obviously, the immobilized lipase is an available biocatalyst in organic phase and has great potential in food industry.