Bio-Based Alkali Lignin Cooperative Systems for Improving the Flame Retardant and Mechanical Properties of Rigid Polyurethane Foam

Lignin was utilized as an environmentally friendly synergistic agent to augment the fire resistance and mechanical characteristics of rigid polyurethane foam (PUF)/melamine-formaldehyde resin ammonium polyphosphate (MFAPP). The incorporation of lignin significantly enhanced the charring capability and flame retardancy of PUF/MFAPP. Specifically, PUF/MFAPP12/A-lignin3 exhibited a charring residue of 23.1% at 800 °C, accompanied by an increase in the limiting oxygen index (LOI) to 23.1%, resulting in a UL-94 V-0 rating. The cone calorimeter test (CCT) revealed that the peak heat release rate (PHRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) values of PUF/MFAPP12/A-lignin3 were all lower than for pure PUF. MFAPP and alkali lignin exerted a noticeable influence on the physical and mechanical properties, leading to increases in density (35.4 kg/m3), thermal conductivity (32.68 mW/(m·K)), and compressive strength (160.5 kPa). Observations of the morphology and elemental composition of char residues after combustion indicated the formation of an intact, thick, and continuous char layer enriched with nitrogen and phosphorus elements, which acted as a protective shield for the underlying foam.

Surface Flame-Retardant Systems of Rigid Polyurethane Foams: An Overview

Rigid polyurethane foam (RPUF) is one of the best thermal insulation materials available, but its flammability makes it a potential fire hazard. Due to its porous nature, the large specific surface area is the key factor for easy ignition and rapid fires spread when exposed to heat sources. The burning process of RPUF mainly takes place on the surface. Therefore, if a flame-retardant coating can be formed on the surface of RPUF, it can effectively reduce or stop the flame propagation on the surface of RPUF, further improving the fire safety. Compared with the bulk flame retardant of RPUF, the flame-retardant coating on its surface has a higher efficiency in improving fire safety. This paper aims to review the preparations, properties, and working mechanisms of RPUF surface flame-retardant systems. Flame-retardant coatings are divided into non-intumescent flame-retardant coatings (NIFRCs) and intumescent flame-retardant coatings (IFRCs), depending on whether the flame-retardant coating expands when heated. After discussion, the development trends for surface flame-retardant systems are considered to be high-performance, biological, biomimetic, multifunctional flame-retardant coatings.

Synergistic Function between Phosphorus-Containing Flame Retardant and Multi-Walled Carbon Nanotubes towards Fire Safe Polystyrene Composites with Enhanced Electromagnetic Interference Shielding

As a universal polymer material, polystyrene (PS) is widely applied in electrical devices and construction. Thus, it is necessary to improve the flame retardancy and electromagnetic shielding properties of PS material. In this work, PS/silicon-wrapped ammonium polyphosphate/Inorganic acid-treated multi-walled carbon nanotubes composites (PS/SiAPP/aMWCNT, abbreviated as PAC) were prepared via methods of filtration-induced assembly and hot-pressing. Morphology and structure characterization demonstrated that SiAPP and aMWCNT had good dispersion in PS and excellent compatibility with the PS matrix. Thermogravimetric analysis revealed that the addition of aMWCNT to PS improved its thermal stability and carbon-forming characteristics. The peak heat release rate, the peak carbon monoxide production rate, and the peak smoke production rate of the PAC10 composite decreased by 53.7%, 41.9%, and 45.5%, respectively, while its electromagnetic shielding effectiveness reached 12 dB. These enhancements were attributed to the reason that SiAPP and aMWCNT synergistically catalyzed the char generation and SiAPP produced free radical scavengers and numbers of incombustible gases, which could decrease the oxygen concentration and retard the combustion reaction. Therefore, the assembled PS/SiAPP/aMWCNT system provides a new pathway to improve the flame retardant and electromagnetic shielding properties of PS.

Constructing segregated polystyrene composites for excellent fire resistance and electromagnetic wave shielding

Electroconductive polystyrene (PS) composites with ideal flame-retardant properties are considered as potential electromagnetic interference (EMI) shielding materials. In this work, PS/silicon wrapped ammonium polyphosphate/multi-wall carbon nanotubes (PS/SiAPP/MWCNT) composites with segregated structure were synthesized via the methods of balling mill and hot-pressing. The obtained results revealed that the SiAPP and MWCNT were successfully introduced onto PS spheres and showed uniform distribution on the PS surface. The thermogravimetric analysis showed that PS/SiAPP/MWCNT containing 7 wt% MWCNT exhibited excellent thermal stability. Furthermore, the results of cone calorimeter test indicated that the heat release rate and total heat release of the PS/SiAPP/MWCNT containing a loading of 7 wt% MWCNT were reduced by 60.5% and 33.9%, respectively. In addition, the EMI shielding performance could reach 11 dB. Above results implied that the synergistic effect between the MWCNT and SiAPP effectively enhanced the flame retardant performance of the PS by promoting the generation of dense and continuous char layer to protect the PS from burning. The multiple reflection and adsorption are responsible for improved EMI shielding effectiveness. Therefore, segregated PS/SiAPP/MWCNT hybrid is an up-and-coming candidate for satisfactory EMI shielding materials with exceptional fire retardancy for electronic devices.

Influence of Titanium Dioxide Modified Expandable Graphite and Ammonium Polyphosphate on Combustion Behavior and Physicomechanical Properties of Rigid Polyurethane Foam

In this research, the individual influence and synergistic behavior between titanium dioxide modified expendable graphite and ammonium polyphosphate on combustion behavior and physicomechanical properties of rigid polyurethane foam (RPUF) were investigated. Combustion behavior was evaluated by limiting oxygen index, and vertical-combustion tests. Thermal stability was studied via thermogravimetric/differential thermal gravimetric (TG/DTG) analysis. Results showed that the modified expendable graphite presented better thermal stability and flame retardancy for RPUF than the normal expandable graphite. Furthermore, the combination of the modified expendable graphite and ammonium polyphosphate with the mass ratio of 1 : 1 caused the RPUF to exhibit better flame retardancy, compression strength and high temperature thermal stability. Especially, the compression strength of this polymer composite sharply increased by 52.4 % over RPUF.

The pyrolysis behaviors of phosphorus-containing organosilicon compound modified ammonium polyphosphate with different phosphorus-containing groups, and their different flame-retardant mechanisms in polyurethane foam

Two phosphorus-containing organosilicon compounds (PCOCs) with similar structure but different phosphorus-containing groups (phenyl phosphate group, PCOC1; phenylphosphoryl group, PCOC2) were synthesized. They were used to modify ammonium polyphosphate (APP), and the products obtained were coded as MAPP1 and MAPP2. Then MAPP1 and MAPP2 were respectively incorporated into low-density rigid polyurethane foam (LD-RPUF). The pyrolysis behavior of these two kinds of MAPP was investigated. Results showed that PCOC2, with the phenylphosphoryl group, induced the decomposition of APP, leading to early and rapid decomposition of MAPP2 with the release of NH₃ in a short time and the formation of crosslinked structure quickly. Simultaneously, the phosphorus of MAPP2 was all retained in the condensed phase. In contrast, PCOC1, with the phenyl phosphate group, also induced the decomposition of APP. However, not all the phosphorus-containing groups of MAPP1 were retained in the condensed phase; some of the phosphorus was released into the gas phase in the form of PO₂· and PO· free radicals. Evaluation of the flame-retardant effect by means of the cone calorimeter test demonstrated that MAPP2 had better flame-retardant properties in the LD-RPUF system, including the reduction of peak heat release rate, total heat release, and total smoke release. Moreover, the char yield of LD-RPUF/MAPP2 was more than that of LD-RPUF/MAPP1. Macro and micro photographs showed that MAPP2 can promote the LD-RPUF matrix to form an intumescent char layer with more complete and stable foam during the combustion process compared with MAPP1. Finally, a possible flame-retardant mechanism of MAPP1 and MAPP2 in LD-RPUF is proposed.

The centralized release of nonflammable gas and quick formation of crosslinked structure increase the flame retardant properties of polyurethane foams.

Preparation and Flame Retardance of Polyurethane Composites Containing Microencapsulated Melamine Polyphosphate

A new microencapsulated flame retardant containing melamine polyphosphate (MPP) and 4,4'-oxydianiline-formaldehyde (OF) resin as the core and shell materials, respectively, was synthesized by in situ polymerization. ²⁹Si NMR was used to measure the condensation density of polyurethane containing silicon compound (Si-PU). The structures and properties of the microencapsulated melamine polyphosphate (OFMPP) were characterized using X-ray photoelectron spectroscopy, scanning electron microscopy and water solubility. Thermal behavior of the OFMPP was systematically analyzed through thermogravimetric analysis. Flame retardance tests such as the limiting oxygen index and UL-94 were employed to evaluate the effect of composition variation on the MPP and OFMPP in polyurethane composites. The results indicated that the microencapsulation of MPP with the OF resin improved hydrophobicity and that the flame retardance of the Si-PU/OFMPP composite (limiting oxygen index, LOI = 32%) was higher than that of the Si-PU/MPP composite (LOI = 27%) at the same additive loading (30 wt %).

Surface microencapsulation modification of aluminum hypophosphite and improved flame retardancy and mechanical properties of flame-retardant acrylonitrile–butadiene–styrene composites

Silicone-microencapsulated aluminum hypophosphite (SiAHP) improved effectively the flame retardancy and significantly enhanced the notched impact strength of ABS/SiAHP composites.

Environmentally Friendly Flame-Retardant and Its Application in Rigid Polyurethane Foam

A novel Flame-Retardant N-(P,P′-diphenyl) phosphorus-based-(3-triethoxysilicon) propylamine (DPTP) was synthesized in this study. The impact of DPTP on the mechanical properties, thermal stability, and flame retardancy of rigid polyurethane foam (RPUF) was studied. The addition of DPTP to RPUF can significantly reduce the undesirable thermal effects and smoke density during combustion, as well as increasing the limiting oxygen index. Compared with pure RPUF, the peak heat release rate of RPUF containing 10 phr of DPTP decreased by 39.4%, while its peak smoke production rate decreased by 49.9%. However, it was also found that the addition of DPTP reduced the compressive strength of RPUF.