Synergistic Action of Montmorillonite with an Intumescent Formulation: The Impact of the Nature and the Strength of Acidic Sites on the Flame-Retardant Properties of Polypropylene Composites

A raw montmorillonite (Mt) was submitted to different acidic activation times in order to investigate the influence of the strength and the nature (Brønsted and Lewis) of acidic sites on the synergistic action with an intumescent formulation (IF) composed of ammonium polyphosphate (APP) and pentaerythritol (PER) when incorporated into a polypropylene (PP) matrix. The acidity of the Mt samples was quantified by ammonia temperature-programmed desorption (TPD-NH3) and Fourier transform infrared spectroscopy (FTIR) with pyridine adsorption. The mineral clays were also characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), nitrogen adsorption analysis and particle size distribution. Thermogravimetric analysis (TGA), limit oxygen index (LOI) and UL-94 were performed to evaluate the flame-retardant properties and the thermal stability. The TGA results show that the final residue increased 2 to 3 fold in comparison to the values predicted theoretically. The flammability properties achieved a maximum for the system containing an excess of moderate-strength Brønsted sites relative to the Lewis ones, reaching 38% in the LOI test. This result suggests that the presence of these Brønsted acidic sites is important, as they take part in the esterification reaction between APP and PER which gives rise to the char formation. The FTIR-Pyr adsorption and flammability results indicate that both the nature and strength of the acidic sites influence the flame-retardant properties.

Improving Mechanical Properties and Reaction to Fire of EVA/LLDPE Blends for Cable Applications with Melamine Triazine and Bentonite Clay

The high flame-retardant loading required for ethylene-vinyl acetate copolymer blends with polyethylene (EVA-PE) employed for insulation and sheathing of electric cables represents a significant limitation in processability and final mechanical properties. In this work, melamine triazine (TRZ) and modified bentonite clay have been investigated in combination with aluminum trihydroxide (ATH) for the production of EVA-PE composites with excellent fire safety and improved mechanical properties. Optimized formulations with only 120 parts per hundred resin (phr) of ATH can achieve self-extinguishing behavior according to the UL94 classification (V0 rating), as well as reduced combustion kinetics and smoke production. Mechanical property evaluation shows reduced stiffness and improved elongation at break with respect to commonly employed EVA-PE/ATH composites. The reduction in filler content also provides improved processability and cost reductions. The results presented here allow for a viable and halogen-free strategy for the preparation of high performing EVA-PE composites.

Interface decoration of exfoliated MXene ultra-thin nanosheets for fire and smoke suppressions of thermoplastic polyurethane elastomer

Thermoplastic polyurethane (TPU) has broad applications as lightweight materials due to its multiple advantages and unique properties. Nevertheless, toxicity emission under fire conditions remains a major concern, particularly in building fire scenarios. To circumvent the problem, it is imperative that an effective flame retardant is sought to suppress the flame and release of combustion/smoke products whilst maintaining the favorable material properties of TPU. In the current work, a simple method is proposed for the preparation and utilization of cetyltrimethyl ammonium bromide (CTAB) and tetrabutyl phosphine chloride (TBPC) modified Ti₃C₂ (MXene) ultra-thin nanosheets. During the cone calorimeter tests, significant reduction in peak heat release rate (51.2% and 52.2%), peak smoke production rate (57.1% and 57.4%), peak CO production (39.4% and 41.6%) and peak CO₂ production (49.7% and 51.7%) were recorded by the mere introduction of 2 wt.% CTAB-Ti₃C₂ and TBPC-Ti₃C₂ to TPU. These superior fire safety properties resulting from the significant reduction of the fire, smoke and toxicity hazards are attributed to the excellent dispersion, catalytic and barrier effect of Ti₃C₂ ultra-thin nanosheets in TPU. Future applications of exfoliated MXene nanosheets as flame retardant appear to be very promising.

Functionalization of MXene Nanosheets for Polystyrene towards High Thermal Stability and Flame Retardant Properties

Fabricating high-performance MXene-based polymer nanocomposites is a huge challenge because of the poor dispersion and interfacial interaction of MXene nanosheets in the polymer matrix. To address the issue, MXene nanosheets were successfully exfoliated and subsequently modified by long-chain cationic agents with different chain lengths, i.e., decyltrimethylammonium bromide (DTAB), octadecyltrimethylammonium bromide (OTAB), and dihexadecyldimethylammonium bromide (DDAB). With the long-chain groups on their surface, modified Ti3C2 (MXene) nanosheets were well dispersed in N,N-dimethylformamide (DMF), resulting in the formation of uniform dispersion and strong interfacial adhesion within a polystyrene (PS) matrix. The thermal stability properties of cationic modified Ti3C2/PS nanocomposites were improved considerably with the temperatures at 5% weight loss increasing by 20 °C for DTAB-Ti3C2/PS, 25 °C for OTAB-Ti3C2/PS and 23 °C for DDAB-Ti3C2/PS, respectively. The modified MXene nanosheets also enhanced the flame-retardant properties of PS. Compared to neat PS, the peak heat release rate (PHRR) was reduced by approximately 26.4%, 21.5% and 20.8% for PS/OTAB-Ti3C2, PS/DDAB-Ti3C2 and PS/DTAB-Ti3C2, respectively. Significant reductions in CO and CO2 productions were also obtained in the cone calorimeter test and generally lower pyrolysis volatile products were recorded by PS/OTAB-Ti3C2 compared to pristine PS. These property enhancements of PS nanocomposites are attributed to the superior dispersion, catalytic and barrier effects of Ti3C2 nanosheets.

Study on the Synergetic Fire-Retardant Effect of Nano-Sb₂O₃ in PBT Matrix

Nano-Sb₂O₃ has excellent synergistic flame-retardant effects. It can effectively improve the comprehensive physical and mechanical properties of composites, reduce the use of flame retardants, save resources, and protect the environment. In this work, nanocomposites specimens were prepared by the melt-blending method. The thermal stability, mechanical properties, and flame retardancy of a nano-Sb₂O₃–brominated epoxy resin (BEO)–poly(butylene terephthalate) (PBT) composite were analyzed, using TGA and differential scanning calorimetry (DSC), coupled with EDX analysis, tensile testing, cone calorimeter tests, as well as scanning electron microscopy (SEM) and flammability tests (limiting oxygen index (LOI), UL94). SEM observations showed that the nano-Sb₂O₃ particles were homogeneously distributed within the PBT matrix, and the thermal stability of PBT was improved. Moreover, the degree of crystallinity and the tensile strength were improved, as a result of the superior dispersion and interfacial interactions between nano-Sb₂O₃ and PBT. At the same time, the limiting oxygen index and flame-retardant grade were increased as the nano-Sb₂O₃ content increased. The results from the cone calorimeter test showed that the peak heat release rate (PHRR), total heat release rate (THR), peak carbon dioxide production (PCO₂P), and peak carbon monoxide production (PCOP) of the nanocomposites were obviously reduced, compared to those of the neat PBT matrix. Meanwhile, the SEM–energy dispersive spectrometry (EDX) analysis of the residues indicated that a higher amount of C element was left, thus the charring layer of the nanocomposites was compact. This showed that nano-Sb₂O₃ could promote the degradation and charring of the PBT matrix, improving thermal stability and flame retardation.

Comparative Studies on Thermal, Mechanical, and Flame Retardant Properties of PBT Nanocomposites via Different Oxidation State Phosphorus-Containing Agents Modified Amino-CNTs

High-performance poly(1,4-butylene terephthalate) (PBT) nanocomposites have been developed via the consideration of phosphorus-containing agents and amino-carbon nanotube (A-CNT). One-pot functionalization method has been adopted to prepare functionalized CNTs via the reaction between A-CNT and different oxidation state phosphorus-containing agents, including chlorodiphenylphosphine (DPP-Cl), diphenylphosphinic chloride (DPP(O)-Cl), and diphenyl phosphoryl chloride (DPP(O₃)-Cl). These functionalized CNTs, DPP(Ox)-A-CNTs (x = 0, 1, 3), were, respectively, mixed with PBT to obtain the CNT-based polymer nanocomposites through a melt blending method. Scanning electron microscope observations demonstrated that DPP(Ox)-A-CNT nanoadditives were homogeneously distributed within PBT matrix compared to A-CNT. The incorporation of DPP(Ox)-A-CNT improved the thermal stability of PBT. Moreover, PBT/DPP(O₃)-A-CNT showed the highest crystallization temperature and tensile strength, due to the superior dispersion and interfacial interactions between DPP(O₃)-A-CNT and PBT. PBT/DPP(O)-A-CNT exhibited the best flame retardancy resulting from the excellent carbonization effect. The radicals generated from decomposed polymer were effectively trapped by DPP(O)-A-CNT, leading to the reduction of heat release rate, smoke production rate, carbon dioxide and carbon monoxide release during cone calorimeter tests.

Fire hazard reduction of hollow glass microspheres in thermoplastic polyurethane composites

Nowadays, reducing the fire hazard of thermoplastic polyurethane (TPU) is an important research direction in the fields of fire safety materials. In this article, hollow glass microsphere (HGM) was used to reduce the fire hazard of TPU in combustion process. The fire characteristics including smoke and heat production of TPU composites were evaluated using smoke density test (SDT) and cone calorimeter test (CCT). And the thermal decomposition and flammable properties were further studied using thermogravimetric analysis/infrared spectrometry (TG-IR) and limiting oxygen index (LOI), etc. The SDT results showed that the luminous flux (LF) of TPU4 containing 2.00wt% HGM was up to 24% at the end of test without flame, which is much higher than that of TPU0 (5%). And, the CCT results indicated that 2.00wt% HGM could make the total smoke release (TSR) decrease from 1019m²/m² (TPU0) to 757m²/m² (TPU4), reduced by 26%. The TG-IR results confirmed that HGM could improve the thermal stability of composites and reduce the production of some toxic gases. The above results illustrated HGM had a good prospect in reducing the fire hazard for TPU.

Fire safety improvement of para-aramid fiber in thermoplastic polyurethane elastomer

This article mainly studied fire safety effects of para-aramid fiber (AF) in thermoplastic polyurethane (TPU). The TPU/AF composites were prepared by molten blending method, and then the fire safety effects of all TPU composites were tested using cone calorimeter test (CCT), microscale combustion colorimeter test (MCC), smoke density test (SDT), and thermogravimetric/fourier transform infrared spectroscopy (TG-IR). The CCT test showed that AF could improve the fire safety of TPU. Remarkably, the peak value of heat release rate (pHRR) and the peak value of smoke production rate (pSPR) for the sample with 1.0wt% content of AF were decreased by 52.0% and 40.5% compared with pure TPU, respectively. The MCC test showed that the HRR value of AF-2 decreased by 27.6% compared with pure TPU. TG test showed that AF promoted the char formation in the degradation process of TPU; as a result the residual carbon was increased. The TG-IR test revealed that AF had increased the thermal stability of TPU at the beginning and reduced the release of CO₂ with the decomposition going on. Through the analysis of the results of this experiment, it will make a great influence on the study of the para-aramid fiber in the aspect of fire safety of polymer.

Simultaneous enhancements in the mechanical, thermal stability, and flame retardant properties of poly(1,4-butylene terephthalate) nanocomposites with a novel phosphorus–nitrogen-containing polyhedral oligomeric silsesquioxane

A novel functionalized POSS greatly reinforced the mechanical, thermal stability, and flame retardant properties of PBT.

A novel triazine-rich polymer wrapped MMT: synthesis, characterization and its application in flame-retardant poly(butylene terephthalate)

A novel flame retardant (PTAC–MMT) was successfully prepared by wrapping montmorillonite (MMT) with poly(2,4,6-triallyloxy-1,3,5-triazine) (TAC) via in situ polymerization, and its structure and properties were systematically characterized.