Jia-Wei Long

Novel Multifunctional Organic–Inorganic Hybrid Curing Agent with High Flame-Retardant Efficiency for Epoxy Resin

A novel multifunctional organic-inorganic hybrid was designed and prepared based on ammonium polyphosphate (APP) by cation exchange with diethylenetriamine (DETA), abbreviated as DETA-APP. Then DETA-APP was used as flame-retardant curing agent for epoxy resin (EP). Curing behavior, including the curing kinetic parameters, was investigated by differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). The flame retardance and burning behavior of DETA-APP cured EP were also evaluated. The limiting oxygen index (LOI) value of DETA-APP/EP was enhanced to 30.5% with only 15 wt % of DETA-APP incorporated; and the UL-94 V-0 rating could be easily passed through with only 10 wt % of the hybrid. Compared with DETA/EP, the peak-heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and peak-smoke production release (SPR) of DETA-APP/EP (15 wt % addition), obtained from cone calorimetry, were dropped by 68.3, 79.3, 79.0, and 30.0%, respectively, suggesting excellent flame-retardant and smoke suppression efficiency. The flame-retardant mechanism of DETA-APP/EP has been investigated comprehensively. The results of all the aforementioned studies distinctly confirmed that DETA-APP was an effective flame-retardant curing agent for EP.

Piperazine-modified ammonium polyphosphate as monocomponent flame-retardant hardener for epoxy resin: flame retardance, curing behavior and mechanical property

To obtain highly fire-safe epoxy resin (EP), piperazine-modified ammonium polyphosphate (PAz-APP) with multiple active –NH– groups was prepared and utilized as a highly effective flame-retardant hardener. After curing by PAz-APP as a monocomponent hardener, cross-linked networks containing both tertiary amino and ether linkages were obtained, which resulted in two glass transitions. Thanks to the phosphorus-containing inorganic part, PAz-APP brought excellent flame retardance and smoke suppression efficiency to the EP system. The cured sample passed V-0 rating (UL-94) with only 7.5 wt% addition of PAz-APP. Cone calorimetric results suggested that, compared with PAz/EP (as a reference sample), both the peak-heat release rate (PHRR) and total smoke production (TSP) of PAz-APP 15/EP (15 wt% addition) sharply dropped by 81.5% and 80.0%, respectively. By analyzing the chemical constitution of the decomposing residues at different temperatures, it was noticed that PAz-APP mainly acted as a flame retardant in the condensed phase via the formation of phosphorus-rich char. Dynamic mechanical analysis (DMA) illustrated that the main glass transition temperature (Tg) of PAz-APP 15/EP was as high as 162.4 °C. Furthermore, the incorporation of PAz-APP did not worsen the mechanical properties, but contrarily, improved the impact strength.

A Novel Organophosphorus Hybrid with Excellent Thermal Stability: Core–Shell Structure, Hybridization Mechanism, and Application in Flame Retarding Semi-Aromatic Polyamide

An organophosphorous hybrid (BM@Al-PPi) with unique core-shell structure was prepared through hybridization reaction between boehmite (BM) as the inorganic substrate and phenylphosphinic acid (PPiA) as the organic modifier. Fourier transform infrared spectra (FTIR), solid state (31)P and (27)Al magic angle spinning nuclear magnetic resonance, X-ray diffraction, and element analysis were used to investigate the chemical structure of the hybrids, where the microrod-like core was confirmed as Al-PPi aggregates generated from the reaction between BM and PPiA, and those irregular nanoparticles in the shell belonged to residual BM. Compared with the traditional dissolution-precipitation process, a novel analogous suspension reaction mode was proposed to explain the hybridization process and the resulting product. Scanning electronic microscopy further proved the core-shell structure of the hybrids. BM exhibited much higher initial decomposition temperature than that of Al-PPi; therefore, the hybrid showed better thermal stability than Al-PPi, and it met the processing temperature of semi-aromatic polyamide (HTN, for instance) as an additive-type flame retardant. Limiting oxygen index and cone calorimetric analysis suggested the excellent flame-retardant performance and smoke suppressing activity by adding the resulting hybrid into HTN.

Carbon Fibers Decorated by Polyelectrolyte Complexes Toward Their Epoxy Resin Composites with High Fire Safety

The achievement of both robust fire-safety and mechanical properties is of vital requirement for carbon fiber (CF) composites. To this end, a facile interfacial strategy for fabricating flame-retardant carbon fibers decorated by bio-based polyelectrolyte complexes (PEC) consisting of chitosan (CH) and ammonium polyphosphate (APP) was developed, and its corresponding fire-retarded epoxy resin composites (EP/(PEC@CF)) without any other additional flame retardants were prepared. The decorated CFs were characterized by SEMEDX, XPS and XRD, indicating that the flame-retardant PEC coating was successfully constructed on the surface of CF. Thanks to the nitrogen- and phosphorous-containing PEC, the resulting composites exhibited excellent flame retardancy as the limiting oxygen index (LOI) increased from 31.0% of EP/CF to 40.5% and UL-94 V-0 rating was achieved with only 8.1 wt% PEC. EP/(PEC8.1@CF) also performed well in cone calorimetry with the decrease of peak-heat release rate (PHRR) and smoke production rate (SPR) by 50.0% and 30.4%, respectively, and the value of fire growth rate (FIGRA) was also reduced to 3.41 kW·m–2·s–1 from 4.84 kW·m–2·s–1, suggesting a considerably enhanced fire safety. Furthermore, SEM images of the burning residues revealed that the PEC coating exhibited the dominant flame-retardant activity in condensed phase via the formation of compact phosphorus-rich char. In addition, the impact strength of the composite was improved, together with no obvious deterioration of flexural properties and glass transition temperature. Taking advantage of the features, the PEC-decorated carbon fibers and the relevant composites fabricated by the cost-effective and facile strategy would bring more chances for widespread applications.