Synergistic effect of nanoflaky manganese phosphate on thermal degradation and flame retardant properties of intumescent flame retardant polypropylene system

Fire retardant polyethylene terephthalate containing 4,4′-(hexafluoroisopropylidene)diphenol-substituted cyclotriphosphazene microspheres

Polyphosphazene derivatives are gaining popularity due to their eco-friendly character and high content of flame-retardant components. Herein, a polyphosphazene derivative (PZAF) microsphere was successfully synthesized utilizing an in-situ template approach, which was then employed as an additive flame retardant in polyethylene terephthalate (PET) to improve the fire safety. Thermogravimetric analysis revealed that PZAF promoted the pyrolysis of PET in advance to generate a stable char layer that protects the matrix from heat, consequently increasing char residues. With addition of 10 wt% PZAF, the PET nanocomposites obtained a V-0 grade in vertical combustion test and its LOI value increased from 24.2 vol% to 32.1 vol%. Moreover, the peak heat release and carbon monoxide production decreased by 46.6% and 50.6%, respectively. This was because the phosphonic acid fragments and pyridine ring compounds produced by the PZAF pyrolysis encouraged the development of a robust char layer. Meanwhile, the •PO radicals generated by the pyrolysis of PZAF could capture free radicals in the gas phase, ultimately ending the chain reaction of combustion. Also, mechanical properties of the PET nanocomposites were noticeably enhanced by the addition of 3 or 5 wt% PZAF.

Preparation of Mn2+ Doped Piperazine Phosphate as a Char-Forming Agent for Improving the Fire Safety of Polypropylene/Ammonium Polyphosphate Composites

A piperazine phosphate doped with Mn2+ (HP-Mn), as a new char-forming agent for intumescent flame retardant systems (IFR), was designed and synthesized using 1-hydroxy ethylidene-1,1-diphosphonic acid, piperazine, and manganese acetate tetrahydrate as raw materials. The effect of HP-Mn and ammonium polyphosphate (APP) on the fire safety and thermal stability of polypropylene (PP) was investigated. The results showed that the combined incorporation of 25 wt.% APP/HP-Mn at a ratio of 1:1 endowed the flame retardant PP (PP6) composite with the limiting oxygen index (LOI) of 30.7% and UL-94 V-0 rating. In comparison with the pure PP, the peak heat release rate (PHRR), the total heat release (THR), and the smoke production rate (PSPR) of the PP6 were reduced by 74%, 30%, and 70%, respectively. SEM and Raman analysis of the char residues demonstrated that the Mn2+ displayed a catalytic cross-linking charring ability to form a continuous and compact carbon layer with a high degree of graphitization, which can effectively improve the flame retardancy of PP/APP composites. A possible flame-retardant mechanism was proposed to reveal the synergistic effect between APP and HP-Mn.

Synergetic integration of thermal conductivity and flame resistance in nacre-like nanocellulose composites

Highly thermally conductive and flame resistant nanocellulose-based composites can synchronously achieve efficient thermal dissipation and low fire hazards of electronic devices, which shows great promise in next-generation green and flexible electronics. However, it has long been intractable to optimize the high thermal conductivity (TC) and flame resistance simultaneously. Herein, synergetic integration of high TC and flame resistance in nacre-like nanocellulose composites has been successfully achieved by the vacuum-assisted filtration of cellulose nanofibers (CNFs) and functionalized boron nitride nanosheets (BNNS-p-APP). Benefiting from the highly oriented hierarchical microstructure, strong hydrogen-bonding interaction, and successful immobilization of ammonium polyphosphate (APP), the as-obtained CNFs/BNNS-p-APP composite film achieves a high in-plane TC of 9.1 W m^-1 K^-1 and outstanding flame resistance. Meantime, this eco-friendly nanocellulose-based composite also exhibits remarkable flexibility, folding endurance, and mechanical robustness, robustness, which may open up a new opportunity for the thermal management of flexible electronics.

A Flame-Retardant Phytic-Acid-Based LbL-Coating for Cotton Using Polyvinylamine

Phytic acid (PA), as a natural source of phosphorus, was immobilized on cotton (CO) in a layer-by-layer (LbL) approach with polyvinylamine (PVAm) as the oppositely charged electrolyte to create a partly bio-based flame-retardant finish. PVAm was employed as a synthetic nitrogen source with the highest density of amine groups of all polymers. Vertical flame tests revealed a flame-retardant behavior with no afterflame and afterglow time for a coating of 15 bilayers (BL) containing 2% phosphorus and 1.4% nitrogen. The coating achieved a molar P:N ratio of 3:5. Microscale combustion calorimetry (MCC) analyses affirmed the flame test findings by a decrease in peak heat release rate (pkHRR) by more than 60% relative to unfinished CO. Thermogravimetric analyses (TGA) and MCC measurements exhibited a shifted CO peak to lower temperatures indicating proceeding reactions to form an isolating char on the surface. Fourier transform infrared spectroscopy (FTIR) coupled online with a TGA system, allowed the identification of a decreased amount of acrolein, methanol, carbon monoxide and formaldehyde during sample pyrolysis and a higher amount of released water. Thereby the toxicity of released volatiles was reduced. Our results prove that PA enables a different reaction by catalyzing cellulosic dehydration, which results in the formation of a protective char on the surface of the burned fabric.

Ammonium Polyphosphate with High Specific Surface Area by Assembling Zeolite Imidazole Framework in EVA Resin: Significant Mechanical Properties, Migration Resistance, and Flame Retardancy

A zeolite imidazole framework (ZIF-67) was assembled onto the surface of ammonium polyphosphate (APP) for preparing a series multifunctional flame-retardant APP-ZIFs. The assembly mechanism, chemical structure, chemical compositions, morphology, and specific surface area of APP-ZIFs were characterized. The typical APPZ1 and APPZ4 were selected as intumescent flame retardants with dipentaerythritol (DPER) because of their superior unit catalytic efficiency of cobalt by thermogravimetric analysis. APPZ1 and APPZ4 possessed 6.8 and 92.1 times the specific surface area of untreated APP, which could significantly enhance the interfacial interaction, mechanical properties, and migration resistance when using in ethylene-vinyl acetate (EVA). With 25% loading, 25% APPZ4/DPER achieved a limiting oxygen index value of 29.4% and a UL 94 V-0 rating, whereas 25% APP/DPER achieved a limiting oxygen index value of only 26.2% and a V-2 rating, respectively. The peak of the heat release rate, smoke production rate, and CO production rate respectively decreased by 34.7%, 39.0%, and 40.1%, while the char residue increased by 91.7%. These significant improvements were attributed to the catalytic graphitization by nano cobalt phosphate and the formation of a more protective char barrier comprised of graphite-like carbon.

Functionalized allylamine polyphosphate as a novel multifunctional highly efficient fire retardant for polypropylene

In this study, an efficient novel allylamine polyphosphate (AAPP) as a flame retardant (FR) crosslinker is used to improve the thermal stability of flame retarded polypropylene (PP) composites under electron beam treatment.

Bio-inspired formation of nanostructured arrays on flexible substrates with superoleophobicity

A bio-inspired synthesis of nanoarrays on a flexible substrate using Mn₃(PO₄)₂·3H₂O as a model is demonstrated and achieves superoleophobicity.

Thermal stability and combustion behavior of flame-retardant polypropylene with thermoplastic polyurethane-microencapsulated ammonium polyphosphate

In this article, thermoplastic polyurethane-microencapsulated ammonium polyphosphate (MTAPP) is prepared and well characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis (TGA). MTAPP and APP are added onto polypropylene (PP) as a novel intumescent flame-retardant system to improve the flame retardancy of PP. The flammability, thermal stability, and mechanical properties of the flame-retardant PP composites are investigated by limiting oxygen index (LOI), UL-94 vertical burning test, cone calorimeter test (CCT), TGA, and mechanical properties tests. The results show that MTAPP exhibits better flame retardancy and thermal stability than that of the APP in the flame-retardant PP composites. The LOI value of the PP/MTAPP composite at the same loading level is higher than that of PP/APP composite. The dripping of MTAPP system disappears compared with APP system from UL-94 test. The results of the CCT also indicate that MTAPP is an effective flame retardant in PP. The improvement may be attributed to the better charring capacity of MTAPP from TGA. Additionally, the mechanical properties of MTAPP are better than those of APP in PP.