Effect of expansion temperature on the properties of expanded graphite and modified linear low density polyethylene

To study the influence of expansion temperature on the properties of expanded graphite (EBG), EBG300, EBG600, and EBG900 were prepared by heating expandable graphite (EG) at 300, 600, and 900 °C, respectively. Furthermore, the influence of these EBGs on the combustion performance and physical-mechanical properties of linear low density polyethylene (LLDPE) were investigated. The expansion volumes of EBG300, EBG600, and EBG900 increase with the rise of temperature, and a four-stage ordered structure of “graphite worm” gradually forms. The thermal stability increases gradually for EBG300, EBG600, and EBG900. On the contrary, the thermal conductivity decreases in sequence. However, the incorporation of EBG900 promotes the formation of a continuous network structure and makes the modified LLDPE to present the best heat transmission. The addition of 30 wt% of these EBGs significantly improves LLDPE’s flame retardancy and high-temperature thermal stability. The total heat release, the peak value of heat release rate, and the fire growth index of 70LLDPE/30EBG300 reduce by 69, 91, and 87% respectively, while the effective fire performance index improves seven times. The addition of these additives reduces the tensile strength and elongation at break, the larger the EBG size, the more obvious the effect.

Recovering chemical sludge from the zero liquid discharge system of flue gas desulfurization wastewater as flame retardants by a stepwise precipitation process

In this study, a five-stage stepwise precipitation process, including pre-sedimentation, magnesium removal, gypsum precipitation, ettringite precipitation and calcium removal, was proposed as a softening pretreatment for zero liquid discharge system for flue gas desulfurization wastewater. Batch tests and long-term bench-scale experiment showed that magnesium, sulfate and calcium were efficiently removed with efficiencies all above 98.0%, leaving a clean effluent majorly containing NaCl and NaOH. The precipitated CaSO₄, CaCO₃, Mg(OH)₂ and ettringite were completely separated by stepwise precipitation, and the purity of Mg(OH)₂ and ettringite were further enhanced by washing and soaking treatment. CaSO₄ and CaCO₃ can be directly recycled as gypsum product and desulfurizing agent within the power plant, while Mg(OH)₂ and ettringite presented proper particle size and excellent thermal properties as a synergistic flame retardant. The flame retardancy of ethylene vinyl acetate copolymer were greatly improved when blended with recovered Mg(OH)₂ and ettringite, and possessed better performance by blending them together because ettringite could act as a dispersing and compatible agent of Mg(OH)₂, and relieve the intensity of smoke releasing. Chemical sludge recovery compensates the total cost of the five-stage process by 45.0%, and makes the process technically versatile, economically beneficial and environmentally friendly without solid waste production.

The Effect of Ultraviolet Ageing on the Flame Retardancy, Thermal Stability and Mechanical Properties of LGFPP/IFR

In this work, long glass fibre reinforced polypropylene/intumescent flame retardants (LGFPP/IFR) composites are exposed to ultraviolet (UV) radiation with wavelength of 340 nm for 0–800 h. The effects of UV ageing on the flame retardancy, thermal stability and mechanical properties of LGFPP/IFR composites are investigated and discussed by limiting oxygen index (LOI), UL–94 test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), scanning electronic microscopy (SEM), mechanical properties and energy dispersive X-ray analysis (EDAX). A slight variation in LOI values and UL-94 levels are observed, and CCT results display a lower heat release rate for all aged samples. The TGA result also shows that aged samples have a higher degradation temperature with the prolongation of the aging time. EDAX showed higher content of the O, P and N elements on the surface of samples after 600 h ageing, which means partly gathering of IFR particles. The tensile, bending and impact strengths decrease after ageing, and the fracture morphology shows that interface debonding occurs.

Influence of Thermo-Oxidative Ageing on the Thermal and Dynamical Mechanical Properties of Long Glass Fibre-Reinforced Poly(Butylene Terephthalate) Composites Filled with DOPO

In this work, the long glass fibre-reinforced poly(butylene terephthalate) (PBT) composites filled with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were prepared by melt blending, and the influence of thermo-oxidative ageing on the static and dynamic mechanical properties, thermal behaviours and morphology of composites with different ageing time at 120 °C were investigated and analysed. The results showed that the mechanical properties decreased in the primary stage of ageing, while embrittlement occurs in the later period, and the crystallinity of PBT decreases first, and then recovers to some extent. The scanning electron microscopy (SEM) photos of the samples indicated that the obvious crack appeared on the sample surface and a deeper, broader crack occurred with a longer ageing time. The results of energy dispersive X-ray analysis (EDAX) proved the DOPO filler diffused to the sample surface by measuring the content of phosphorus. Thermal gravimetric analysis (TGA) curves showed that the thermal stabilities of composites increased with longer ageing time, as did the values of the limited oxygen index (LOI). Meanwhile, the results of dynamic mechanical analysis (DMA) indicated that the glass transition temperature shifted to a higher temperature after ageing due to the effect of crosslinking, and both the crosslinking and degradation of PBT molecular chains act as the main factors in the whole process of thermo-oxidative ageing.

Efficient organic–inorganic intumescent interfacial flame retardants to prepare flame retarded polypropylene with excellent performance

An efficient and simple approach for the preparation of organic–inorganic intumescent interfacial flame retardants, aiming at enhancing the flame-retardant efficiency and interfacial adhesion between matrix and flame retardants was presented.