One-pot synthesis of a novel s-triazine-based hyperbranched charring foaming agent and its enhancement on flame retardancy and water resistance of polypropylene

Enhanced flame retardancy and toughness of eco-friendly polyhydroxyalkanoate/bentonite composites based on in situ intercalation of P-N-containing hyperbranched macromolecules

Polyhydroxyalkanoates (PHA) is a biodegradable polyester, and its application range is limited by the poor flame retardancy and low modulus. Bentonite (BNT) as a green inorganic filler can improve the modulus and flame retardancy of PHA to a certain extent. An in situ polymerization method was designed to intercalate P-N-containing hyperbranched macromolecules (HBM) among BNT layers (HBM-B) and to improve the flame retardancy while improving the dispersion of BNT in the PHA matrix. The layer spacing of BNT was increased from 1.2 nm to 4.5 nm. The effect law of the joint action of in situ intercalation of BNT and the HBM on flame retardancy and mechanical properties of PHA was systematically studied. The HBM-B showed stronger flame retardancy when the mass ratio of HBM to BNT was 75/25. The limiting oxygen index (LOI) of the PHA/HBM-B composite was increased to 27.6 % while maintaining good toughness. Compared to the physical blend of HBM and BNT (HBM/B), the elongation at break of PHA/HBM-B₂₅ composites can be increased by up to 10 times. When the content of HBM-B is up to 15 wt%, the LOI of PHA-Based composites can reach 29.6 % and the UL-94 rating reaches V-0, which meets the standard of flame-retardant material. Therefore, the present work is expected to expand the application of PHA-based composites in the field of flame retardancy.

A rational design of functionalized black phosphorus cooperates with piperazine pyrophosphate to significantly suppress the fire hazards of polypropylene

The flammability of polypropylene (PP) not only has negative effects on human health but also causes environmental pollution. Herein, from the molecular polarity point of view, rationally designed hyperbranched charring foaming agents (HCFA) modified black phosphorus nanosheets by in situ polymerization to solve the fire hazards of PP. Based on the UL-94 test V-0 rating, the conventional flame retardant of piperazine pyrophosphate (PAPP) is substituted partly by the BP@PPC. Surprisingly, compared with 27 wt% of PAPP/PP, composites consisting of only 2 wt% of BP@PPC and 20 wt% PAPP/PP also passes the V-0 rating. The results of the cone calorimeter test confirmed that adding BP@PPC decreases the total heat release (THR) and peak heat release (PHRR) by a large amount, which are decreased by 23.4%, 85.8% respectively compared with PP. Moreover, it is uncommon for the fire growth index of BP@PPC composites to be 66.7% lower than that of PAPP/PP composites. In addition, the incorporation of BP@PPC has almost no impact on the mechanical characteristics of PP composites. This study offers a reference for combining established flame retardants with novel compounds to modify the burning behaviors of PP.

Mechanical Properties of Polypropylene-Based Flame Retardant Composites by Surface Modification of Flame Retardants

A flame retardant refers to a substance that can be added to a material having the property of being efficiently combusted to improve the material physically and chemically. It should not affect the physical properties required for the final product. Halogen-based compounds are representative flame retardants with excellent flame retardancy. However, their use is limited due to restrictions on the use of chemicals introduced due to human safety. Magnesium hydroxide, one alternative material of halogen flame retardants, is widely used as an eco-friendly flame retardant. However, the most significant disadvantage is high load. To find a solution to this problem, many studies have been conducted by mixing magnesium hydroxide with other additives to create a synergistic effect. In this study, flame retardancy and mechanical properties of polypropylene-based flame retardant composites as a function of mixing surface-modified magnesium hydroxide with phosphorus-based flame retardants were investigated. All materials including PP, additives, and flame retardants were mixed using an extrusion process. Specimens were prepared by an injection process of the compound made after mixing. As a result of the evaluation of the mechanical properties by the modified flame retardant, the relational expression of the mechanical performance degradation as a function of the amount of addition was obtained, and the tensile (CBATS) and bending strength (CBABS) were performed on the amount of flame retardant added. The relational expression obtained in this study is considered to be a formula for predicting the strength reduction according to the addition amount of the modified flame retardant and can be used in industry. In addition, it was found that the addition amount of the modified flame retardant had a greater effect on the lowering of the bending strength.

Synthesis of New S-Triazine Bishydrazino and Bishydrazido-Based Polymers and Their Application in Flame-Retardant Polypropylene Composites

In this study six new s-triazine bishydrazino and bishydrazido-based polymers were synthesized via condensation of bishydrazino s-triazine derivatives with terephthaldehyde or via nucleophilic substitution of dichloro-s-triazine derivatives with terephthalic acid hydrazide. The synthesized polymers were characterized by different techniques. The new polymers displayed good thermal behavior with great values in terms of limited oxygen indexed (LOI) 27.50%, 30.12% for polymers 5b,c (bishydrazino-s-triazine based polymers) and 27.23%, 29.86%, 30.85% for polymers 7a–c (bishydrazido-s-triazine based polymers) at 800 °C. Based on the LOI values, these polymers could be classified as flame retardant and self-extinguishing materials. The thermal results also revealed that the type of substituent groups on the triazine core has a considerable impact on their thermal behavior. Accordingly, the prepared polymers were mixed with ammonium polyphosphate (APP) in different proportions to form an intumescent flame-retardant (IFRs) system and were introduced into polypropylene (PP) to improve the flame-retardancy of the composites. The best results were obtained with a mass ratio of APP: 5a–c or 7a–c of 2:1, according to the vertical burning study (UL-94). In addition, the presence of 25% “weight ratio” of IFR in the composite showed great impact and passed UL-94 V-0 and V-1 tests.

Investigation on the effect of supported synergistic catalyst with intumescent flame retardant in polypropylene

In this paper, cerium nitrate supported silica was prepared as a new type of catalytic synergist to improve the flame retardancy in polypropylene. When 1% of Ce(NO3)2 supported SiO2 was added, the vertical combustion performance of UL-94 of polypropylene composites was improved to V-0, the limiting oxygen index (LOI) was increased to 33.5. From the thermogravimetric analysis (TGA), the residual carbon of C and D was increased by about 6% at high temperature compared with B. When adding supported catalyst, the heat release rate (HRR) and total heat release (THR) were significantly reduced according to the microscale combustion calorimetry (MCC), the HRR of sample E with 2% synergist was the lowest. The combustion behaviors of intumescent flame retardant sample B and sample D were analyzed by cone calorimeter test (CCT), the HRR of sample D with supported synergist was significantly reduced, and the PHRR decreased from 323 kW/m2 to 264 kW/m2. The morphologies of the residue chars after vertical combustion of polypropylene composites observed by scanning electron microscopy (SEM) gave positive evidence that the supported synergist could catalyze the decomposition of intumescent flame retardants into carbon, which was the main reason for improving the flame retardancy of materials.

Flame Retardant Polypropylenes: A Review

Polypropylene (PP) is a commodity plastic known for high rigidity and crystallinity, which is suitable for a wide range of applications. However, high flammability of PP has always been noticed by users as a constraint; therefore, a variety of additives has been examined to make PP flame-retardant. In this work, research papers on the flame retardancy of PP have been comprehensively reviewed, classified in terms of flame retardancy, and evaluated based on the universal dimensionless criterion of Flame Retardancy Index (FRI). The classification of additives of well-known families, i.e., phosphorus-based, nitrogen-based, mineral, carbon-based, bio-based, and hybrid flame retardants composed of two or more additives, was reflected in FRI mirror calculated from cone calorimetry data, whatever heat flux and sample thickness in a given series of samples. PP composites were categorized in terms of flame retardancy performance as Poor, Good, or Excellent cases. It also attempted to correlate other criteria like UL-94 and limiting oxygen index (LOI) with FRI values, giving a broad view of flame retardancy performance of PP composites. The collected data and the conclusions presented in this survey should help researchers working in the field to select the best additives among possibilities for making the PP sufficiently flame-retardant for advanced applications.

Synthesis of a Novel Phosphorous-Nitrogen Based Charring Agent and Its Application in Flame-retardant HDPE/IFR Composites

In this work, a novel phosphorous-nitrogen based charring agent named poly(1,3-diaminopropane-1,3,5-triazine-o-bicyclic pentaerythritol phosphate) (PDTBP) was synthesized and used to improve the flame retardancy of high-density polyethylene (HDPE) together with ammonium polyphosphate (APP). The results of Fourier transform infrared spectroscopy (FTIR) and ¹³C solid-state nuclear magnetic resonance (NMR) showed that PDTBP was successfully synthesized. Compared with the traditional intumescent flame retardant (IFR) system contained APP and pentaerythritol (PER), the novel IFR system (APP/PDTBP, weight ratio of 2:1) could significantly promote the flame retardancy, water resistance, and thermal stability of HDPE. The HDPE/APP/PDTBP composites (PE3) could achieve a UL-94 V-0 rating with LOI value of 30.8%, and had a lower migration percentage (2.2%). However, the HDPE/APP/PER composites (PE5) had the highest migration percentage (4.7%), lower LOI value of 23.9%, and could only achieve a UL-94 V-1 rating. Besides, the peak of heat release rate (PHRR), total heat release (THR), and fire hazard value of PE3 were markedly decreased compared to PE5. PE3 had higher tensile strength and flexural strength of 16.27 ± 0.42 MPa and 32.03 ± 0.59 MPa, respectively. Furthermore, the possible flame-retardant mechanism of the APP/PDTBP IFR system indicated that compact and continuous intumescent char layer would be formed during burning, thus inhibiting the degradation of substrate material and improving the thermal stability of HDPE.

The Effects of a Macromolecular Charring Agent with Gas Phase and Condense Phase Synergistic Flame Retardant Capability on the Properties of PP/IFR Composites

In order to improve the efficiency of intumescent flame retardants (IFRs), a novel macromolecular charring agent named poly(ethanediamine-1,3,5-triazine-p-4-amino-2,2,6,6-tetramethylpiperidine) (PETAT) with gas phase and condense phase synergistic flame-retardant capability was synthesized and subsequently dispersed into polypropylene (PP) in combination with ammonium polyphosphate (APP) via a melt blending method. The chemical structure of PETAT was investigated by Fourier transform infrared spectroscopy (FTIR), and ¹H nuclear magnetic resonance (NMR) spectroscopy. Thermal properties of the PETAT and IFR systems were tested by thermogravimetric-derivative thermogravimetric analysis (TGA-DTG) and thermogravimetry–Fourier transform infrared spectroscopy (TG-FTIR). The mechanical properties, thermal stability, flame-retardant properties, water resistance, and structures of char residue in flame-retardant composites were characterized using tensile and flexural strength property tests, TGA, limiting oxygen index (LOI) values before and after soaking, underwritten laboratory-94 (UL-94) vertical burning test, cone calorimetric test (CCT), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDXS), and FTIR. The results indicated that PETAT was successfully synthesized, and when the ratio of APP to PETAT was 2:1 with 25 wt % loading, the novel IFR system could reduce the deterioration of tensile strength and enhance the flexural strength of composites. Meanwhile, the flame-retardant composite was able to pass the UL-94 V-0 rating with an LOI value of 30.3%, and the peak of heat release rate (PHRR), total heat release (THR), and material fire hazard values were considerably decreased compared with others. In addition, composites also exhibited excellent water resistance properties compared with traditional IFR composites. SEM-EDXS and FTIR analyses of the char residues, as well as TG-FTIR analyses of IFR were used to investigate the flame-retardant mechanism of the APP/PETAT IFR system. The results indicated that the efficient flame retardancy of PP/IFR composites could be attributed to the synergism of the free radical-quenching and char layer-protecting mechanisms in the gas phase and condense phase, respectively.

Scalable Preparation of Multifunctional Fire-Retardant Ultralight Graphene Foams

Traditional flame-retardant materials often show poor tolerance to oxidants, strong acidic/alkaline reagents, organic solvents, along with toxicity problems. Herein, highly fire-retardant ultralight graphene foam has been developed, which possesses not only ultralight and compressible characteristics but also efficient flame-retardant properties, outperforming those traditional polymer, metallic oxide, and metal hydroxide based flame retardant materials and their composites. The newly developed unconventional refractory materials are promising for specific applications as demonstrated by the observed high temperature resistant microwave absorption capability.