The synthesis of meltable and highly thermostable triazine‐DOPO flame retardant and its application in PA66

Flame Retardancy and Mechanical Properties of Melt-Spun PA66 Fibers Prepared by End-Group Blocking Technology

Preparing flame-retardant polyamide 66 (PA66) fibers through melt spinning remains one of the biggest challenges nowadays. In this work, dipentaerythritol (Di-PE), an eco-friendly flame retardant, was blended into PA66 to prepare PA66/Di-PE composites and fibers. It was confirmed that Di-PE could significantly improve the flame-retardant properties of PA66 by blocking the terminal carboxyl groups, which was conducive to the formation of a continuous and compact char layer and the reduced production of combustible gas. The combustion results of the composites showed that the limiting oxygen index (LOI) increased from 23.5% to 29.4%, and underwriter laboratories 94 (UL-94) passed the V-0 grade. The peak of heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) decreased by 47.3%, 47.8%, and 44.8%, respectively, for the PA66/6 wt% Di-PE composite compared to those recorded for pure PA66. More importantly, the PA66/Di-PE composites possessed excellent spinnability. The prepared fibers still had good mechanical properties (tensile strength: 5.7 ± 0.2 cN/dtex), while maintaining good flame-retardant properties (LOI: 28.6%). This study provides an outstanding industrial production strategy for fabricating flame-retardant PA66 plastics and fibers.

Thermal Stabilities and Flame Retardancy of Polyamide 66 Prepared by In Situ Loading of Amino-Functionalized Polyphosphazene Microspheres

The flame-retardant polyamide 66 composites (FR-PA66) were prepared by in situ loading of amino-functionalized polyphosphazene microspheres (HCNP), which were synthesized in the laboratory and confirmed by a Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), and transmission electron microscope (TEM). The thermal stabilities and flame retardancy of FR-PA66 were measured using thermogravimetric analysis (TGA), a thermogravimetric infrared instrument (TG-IR), the limiting oxygen index (LOI), the horizontal and vertical combustion method (UL-94), and a cone calorimeter. The results illustrate that the volatile matter of FR-PA66 mainly contains carbon dioxide, methane₄, and water vapor under heating, accompanied by the char residue raising to 14.1 wt% at 600 °C and the value of the LOI and UL-94 rating reaching 30% and V-0, respectively. Moreover, the addition of HCNP decreases the peak of the heat release rate (pHRR), total heat release (THR), mass loss (ML), and total smoke release (TSR) of FR-PA66 to 373.7 kW/m², 106.7 MJ/m², 92.5 wt%, and 944.8 m²/m², respectively, verifying a significant improvement in the flame retardancy of PA66.

An Efficient Composite Modifier Prepared for Enhancing the Crystallization and Flame-Retardancy of Poly(m-xylylene adipamide)

Poly(m-xylylene adipamide) (MXD6) has good gas barrier properties and high mechanical strength. However, in nature, this resin has a low rate of crystallization. In order to overcome this obstacle in its applications, this study prepares a new, efficient modifier for MXD6 by combining the synthesized DOPO derivative (DT) and P22. It is found that the use of the binary modifier exhibits obvious effects on the crystallization of MXD6. When 11.0 wt.% DT is added together with 0.1 wt.% P22 (DT/P22), the crystallization temperature of MXD6 shifts to a higher temperature of 19.7 °C, and the crystallinity degree of MXD6 is significantly increased by 60%. Meanwhile, this modifier exhibits obviously intumescent flame-retardancy on MXD6 by increasing the limited oxygen index (LOI) from 26.4% to 33.4%. The results of the cone calorimeter test (CCT) reveal that the peak heat release rate (PHRR), total heat release (THR) and average effective heat release (av-EHC) are obviously suppressed due to the use of this modifier. Moreover, the influences of this modifier on the crystal structures, mechanical and rheological properties of MXD6 are analyzed in detail. This study can provide an efficient modifier for MXD6.

Unsaturated polyester resin modified with a novel reactive flame retardant: effects on thermal stability and flammability

A new reactive flame retardant (DTA), containing phosphaphenanthrene and triazine-trione groups was synthesized and applied to improve the flame retardancy of unsaturated polyester resin. The thermal stability, flame retardancy and combustion behaviors of UP/DTA thermosets were detected by thermogravimeric analysis (TG), limited oxygen index (LOI), vertical burning (UL94) test and cone calorimeter test. According to the research results, the addition of DTA contributed to improving the flame retardancy of UP. After adding 20 wt% DTA, the LOI of UP composite increased from 19.0% of the neat UP to 26.6%, and UL94 rating reached V-0. In addition, compared with pure UP, the peak heat release rate (pk-HRR), average heat release rate (av-HRR) and total heat release rate (THR) of UP/DTA-20 thermosetting material decreased by 44.0, 26.2 and 29.5%, respectively. In the gaseous phase, DTA decomposed to generate nitrogen-containing fragments with diluting effect and phosphorus-containing free radicals with quenching effect to inhibit the combustion. In the condensed phase, phosphaphenanthrene group of DTA decomposed to generate phosphorus-based compounds, which promoted the carbonization of the UP matrix and cooperated with triazine-trione group to increase the char yield. Therefore, DTA plays an important role in flame retardancy in the gas and condensed phases.

Synthesis, Structures, and Properties of a New Pentaerythritol-Derived Flame Retardant Used in Polyamide 66

A melting phosphorous-based flame retardant (FR) named as diphenyl phosphoryl (DPP)-PEPA is synthesized from 2,6,7-trioxa-1-phosphabicyclo-(2.2.2)-octane-4-methanol (PEPA) and diphenyl phosphoryl chloride. The melting DPP-PEPA FR possesses high thermostability with T _5wt% at 344 °C, which can match the melt-spinning of engineering plastics at high temperatures. The structure of DPP-PEPA is defined by nuclear magnetic resonance and infrared spectrometry. The influences of DPP-PEPA on polyamide 6,6 (PA66) are assessed in terms of rheology parameters and crystallinity. It is observed that the flame retardancy of PA66 is greatly improved when DPP-PEPA is added to the PA66 resin. The results show that the modified PA66 has limited oxygen index as high as 29.4%, and the compact char layers are obviously formed on top of the burned samples. As compared to the pure PA66, the peak heat release rate and the average effective heat of combustion are decreased by 26.5 and 19.3%, respectively. It is obtained that the value of flame retardancy index is 1.4, indicating high efficiency of the entire flame retardancy. Moreover, pyrolysis of DPP-PEPA is carried out at different temperatures for identifying gaseous products and types of flame retardancy.