Modification of mesoporous silica with phosphotungstic acid and its effects on the combustion and thermal behavior of polylactic acid composites

High Value Utilization of Waste Wood toward Porous and Lightweight Carbon Monolith with EMI Shielding, Heat Insulation and Mechanical Properties

With the increasing pollution of electromagnetic (EM) radiation, it is necessary to develop low-cost, renewable electromagnetic interference (EMI) shielding materials. Herein, wood-derived carbon (WC) materials for EMI shielding are prepared by one-step carbonization of renewable wood. With the increase in carbonization temperature, the conductivity and EMI performance of WC increase gradually. At the same carbonization temperature, the denser WC has better conductivity and higher EMI performance. In addition, due to the layered superimposed conductive channel structure, the WC in the vertical-section shows better EMI shielding performance than that in the cross-section. After excluding the influence of thickness and density, the specific EMI shielding effectiveness (SSE/t) value can be calculated to further optimize tree species. We further discuss the mechanism of the influence of the microstructure of WC on its EMI shielding properties. In addition, the lightweight WC EMI material also has good hydrophobicity and heat insulation properties, as well as good mechanical properties.

Synergistic effect of poly(ionic liquid) and phosphoramide on flame retardancy and crystallization of poly(lactic acid)

Crystallinity and flame retardancy are two key properties for poly(lactic acid)(PLA) in applications. In this paper, a quaternary phosphonium salt poly(ionic liquid) (PIL) and a phosphamide (POFA) were prepared. The PIL, POFA and their blend were used to regulate the flame retardancy and crystallization behaviors of PLA using the limiting oxygen index, UL-94 vertical burning, and thermogravimetric analysis, and differential scanning calorimetry etc. The results showed that a synergistic effect exists between PIL and POFA on flame retardancy. When 6 wt% PIL/POFA (2/1) was added into PLA, its LOI value is 28.0 vol%, and achieves the UL-94 V-0 rating while the PLA composites containing 6 wt% PIL or POFA just achieve the UL-94 V2. The PIL/POFA improves the flame retardancy of PLA by melting-away mode. In addition, the crystallization rate of PLA containing PIL/POFA is faster than that of PLA/PIL and PLA/POFA. The degradation of PLA induced by PIL/POFA produces some small molecular oligomers, which enhances the molecular chain mobility and rearrangement, thus contributes to better flame retardancy and faster crystallization.

Roles of phosphoramide derivatives in flame retardancy, thermal degradation and crystallization behaviors of polylactic acid

Two kinds of phosphoramide derivatives containing one (POFA) or two (BPOFA) phosphoramide bonds were synthesized using diphenylphosphinic chloride, phenylphosphonic dichloride and furfurylamine, respectively. The flame retardancy, thermal degradation and crystallization behaviors of polylactic acid (PLA)/POFA and PLA/BPOFA blends were investigated using the limiting oxygen index (LOI), UL-94 vertical burning tests, cone calorimeter tests, thermogravimetric analysis and differential scanning calorimetry. A small amount of 1.0 wt% BPOFA increases the LOI of PLA from 20.4 vol% to 28.0 vol% and achieves the UL-94 V0 rating, while 7.0 wt% POFA is needed to achieve the UL-94 V0 rating indicating that the PLA/BPOFA has better flame retardancy than that of PLA/POFA. Both POFA and BPOFA decrease the amount of flammable gaseous compounds and play positive roles in transesterification of PLA. More importantly, BPOFA is easier to catalyze the degradation of PLA and improve UL-94 rating by melting-away mode. Moreover, the BPOFA accelerates the crystallization rate and thus improves the crystallinity of PLA, while POFA does not show a positive effect on crystallization behaviors of PLA.

Mesoporous silica via self-assembly of nano zinc amino-tris-(methylenephosphonate) exhibiting reduced fire hazards and improved impact toughness in epoxy resin

Mesoporous silica@nano-zinc amino-tris-(methylenephosphonate) (m-SiO₂@Zn-AMP) spheres were synthesized via a self-assembly process to integrate the outstanding flame retardancy, thermal stability, and mechanical properties of these materials. The results indicated that nano Zn-AMP particles were successfully deposited on the surface of m-SiO₂ through electrostatic interactions. The prepared m-SiO₂@Zn-AMP was utilized to improve the flame retardancy, smoke suppression, and mechanical properties of epoxy resin (EP). The storage modulus, impact, and tensile strengths of the EP with 1% m-SiO₂@Zn-AMP (sample EP/1m-SiO₂@Zn-AMP) were increased by 29.9, 50.0, and 23.5 %, respectively, relative to the values for untreated EP. The presence of multiple flame retardant elements (i.e. Si, P, N, and Zn) in the mesoporous spheres led to the formation of high yields of compact char residues and the release of inert substance during combustion, for high flame retardancy and efficient smoke suppression in the condensed and gaseous phase. The EP/5m-SiO₂@Zn-AMP sample achieved a V0 rating in a vertical UL-94 test. Compared to untreated EP, the amount of total smoke released and the peak CO production rate of EP/5m-SiO₂@Zn-AMP were reduced by 53.1 and 61.5 %, respectively. Additionally, the total heat release and peak heat release rate of EP/5m-SiO₂@Zn-AMP were decreased by 45.2 and 57.8 %, respectively.

Composite Sulfonated Polyether-Ether Ketone Membranes with SBA-15 for Electrochemical Energy Systems

The aim of this work is the evaluation of a Sulfonated Poly Ether-Ether Ketone (S-PEEK) polymer modified by the addition of pure Santa Barbara Amorphous-15 (SBA-15, mesoporous silica) and SBA-15 previously impregnated with phosphotungstic acid (PWA) fillers (PWA/SBA-15) in order to prepare composite membranes as an alternative to conventional Nafion^® membranes. This component is intended to be used as an electrolyte in electrochemical energy systems such as hydrogen and methanol Proton Exchange Membrane Fuel Cell (PEMFC) and Electrochemical Hydrogen Pumping (EHP). The common requirements for all the applications are high proton conductivity, thermomechanical stability, and fuel and oxidant impermeability. The morphology of the composite membranes was investigated by Scanning Electron Microscopy- Energy Dispersive X-ray Spectroscopy (SEM-EDS) analysis. Water Uptake (Wup), Ion Exchange Capacity (IEC), proton conductivity, methanol permeability and other physicochemical properties were evaluated. In PEMFC tests, the S-PEEK membrane with a 10 wt.% SBA-15 loading showed the highest performance. For EHP, the inclusion of inorganic materials led to a back-diffusion, limiting the compression capacity. Concerning methanol permeability, the lowest methanol crossover corresponded to the composites containing 5 wt.% and 10 wt.% SBA-15.