Preparation, properties and characterizations of halogen-free nitrogen–phosphorous flame-retarded glass fiber reinforced polyamide 6 composite

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.

Effects of Zinc Borate on the Flame Retardancy Performance of Aluminum Diethylphosphinate in Polyamide-6 and its Composites

In this study, the flame retardancy contribution of zinc borate when used together with a traditional flame retardant (aluminum diethylphosphinate compound) was investigated for neat polyamide-6 and for 15 wt% short glass fiber reinforced composite. Melt mixing with twin-screw extrusion was the compounding method while injection and compression molding were the shaping methods of specimens. Three different flammability tests (limiting oxygen index, UL-94 vertical burning, mass loss calorimetry) indicated that many flame retardancy parameters could be improved significantly by replacing a certain amount of aluminum diethylphosphinate with zinc borate. For example, using aluminum diethylphosphinate alone resulted in only 32 % suppression in the value of the peak heat release rate for neat polyamide-6, while it was 82 % (more than two-fold) when used together with zinc borate. It was revealed by evolved gas analyses, char analyses, x-ray diffraction and thermogravimetry that the main contribution of zinc borate to aluminum diethylphosphinate was in terms of a barrier mechanism via formation of additional boron phosphate inorganic content in the barrier layer.

Ionic Liquid-Grafted Polyamide 6 by Radiation-Induced Grafting: New Strategy To Prepare Covalently Bonded Ion-Containing Polymers and their Application as Functional Fibers

Ion-containing polymers are of great importance for its unique structure and properties. An ion-containing polyamide 6 (PA6) was prepared by grafting an ionic liquid, 1-vinyl-3-butyl imidazole chloride [VBIM][Cl], onto the main chain of PA6 using radiation-induced grafting. The grafted ions on the PA6 main chain significantly influenced the structure and properties of the PA6 matrix. The ions form nanoscale aggregations without inducing further microphase separation. Acting as a physical "cross-linking point," each aggregation enhanced inter/intrachain interactions, which increased the viscosity, storage modulus, and relaxation time and reduced the ability of PA6 to crystallize. However, the bulky cations of the grafted ionic liquid can also be seen as "spacers," which enlarge the distance among chains and reduce the strength of the hydrogen bonds inherently existing in the PA6 matrix. The "cross-linking points" and "spacers" of ions as well as the hydrogen bonds of PA6 take effect collectively in the system. Moreover, the ion-containing PA6 retains good melt processability compared with PA6, despite increased viscosity, and can be easily melt-spun into fibers. Fibers prepared from ion-containing PA6 showed improved mechanical properties and antistatic performance and exhibited the expected antibacterial properties, especially with regard to Escherichia coli. Inspiringly, covalently bonding ions to the PA6 main chain offers a new strategy for fabricating functional fibers with permanent antistatic and antibacterial properties.

Flame Retardant Polypropylene Composites with Low Densities

Polypropylene (PP) is currently widely used in areas requiring lightweight materials because of its low density. Due to the intrinsic flammability, the application of PP is restricted in many conditions. Aluminum trihydroxide (ATH) is reported as a practical flame retardant for PP, but the addition of ATH often diminishes the lightweight advantage of PP. Therefore, in this work, glass bubbles (GB) and octacedylamine-modified zirconium phosphate (mZrP) are introduced into the PP/ATH composite in order to lower the material density and simultaneously maintain/enhance the flame retardancy. A series of PP composites have been prepared to explore the formulation which can endow the composite with balanced flame retardancy, good mechanical properties, and low density. The morphology, thermal stability, flame retardancy, and mechanical properties of the composites were characterized. The results indicated the addition of GB could reduce the density, but decreased the flame retardancy of PP composites at the same time. To overcome this defect, ATH and mZrP with synergetic effect of flame retardancy were added into the composite. The dosage of each additive was optimized for achieving a balance of flame retardancy, good mechanical properties, and density. With 47 wt % ATH, 10 wt % GB, and 3 wt % mZrP, the peak heat release rate (pHRR) and total smoke production (TSP) of the composite PP-4 were reduced by 91% and 78%, respectively. At the same time, increased impact strength was achieved compared with neat PP and the composite with ATH only. Maintaining the flame retardancy and mechanical properties, the density of composite PP-4 (1.27 g·cm-3) is lower than that with ATH only (PP-1, 1.46 g·cm-3). Through this research, we hope to provide an efficient approach to designing flame retardant polypropylene (PP) composites with low density.

The preparation and application of a graphene-based hybrid flame retardant containing a long-chain phosphaphenanthrene

A novel hybrid flame retardant combining graphene oxide (GO) with long-chain phosphaphenanthrene was fabricated via surface grafting reaction. Taking advantageous of the double barrier effects, including the physical shield contributed by graphene nanoplates during the initial stage and the chemical char contributed by phosphaphenanthrene during the later stage, greatly decreased the release rate of decomposed volatiles from the resin, as well as minimized the release of oxygen and combustion heat. Hence, such hybrid flame retardant can overcome the shortcomings of early acid catalyzed degradation effects caused by conventional flame retardants containing phosphorus. Satisfactory flame retardance was achieved (UL94 V-0 rating) with only 4% addition of the hybrid flame retardant to the epoxy resin laminate. Due to the long-chain and bulky phosphaphenanthrene groups, the interlayer attractive forces of the modified GO were effectively weakened, thus favoring the exfoliation and dispersion of graphene sheets. As a result, the incorporation of the flame retardant slightly enhanced the mechanical properties of the polymer composites, rather than deteriorating them, as occurs with traditional additive flame retardants. As a potential application for graphene, it is believed that the reported hybrid flame retardant has promising future prospect.

Effect of Brominated Epoxy Resins on the Thermal Stability and Flame Retardancy of Long-Glass-Fiber Reinforced Polyamide 6

In this work, the compounds of brominated epoxy resins and antimony trioxide (BER/Sb2O3) additives are analyzed and added into long-glass-fiber reinforced polyamide 6 (PA6/LGF) composites in order to solve the “candle-wick effect” caused by glass fibers. The thermal stability, flammability, and morphology of charred residues of the flame retardant PA6/LGF composites are investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), and scanning electronic microscopy (SEM). The results show the addition of BER/Sb2O3 provides improvements in flame retardancy by increasing the LOI values, enhancing UL-94 rating, and reducing the heat release rate, total heat release and effective heat of combustion due to the formation of consolidated and thick charred residual structures on the surfaces of the LGF reinforced PA6 composites. When the content of BER/Sb2O3 is increased to 12 wt%, the LOI value and UL-94 rating of BER/PA6/LGF composites reach 24.8 and V-0, respectively. The TGA results exhibit that the decomposition temperature of the PA6/LGF composites decreases with the addition of BER/Sb2O3 additive, resulting in forming some high quality residual char layer. A possible flame retardant mechanism is proposed to illustrate the effect of the gaseous and condensed phases on the flame retardancy of the PA6/LGF composites.

Key Role of Reinforcing Structures in the Flame Retardant Performance of Self-Reinforced Polypropylene Composites

The flame retardant synergism between highly stretched polymer fibres and intumescent flame retardant systems was investigated in self-reinforced polypropylene composites. It was found that the structure of reinforcement, such as degree of molecular orientation, fibre alignment and weave type, has a particular effect on the fire performance of the intumescent system. As little as 7.2 wt % additive content, one third of the amount needed in non-reinforced polypropylene matrix, was sufficient to reach a UL-94 V-0 rating. The best result was found in self-reinforced polypropylene composites reinforced with unidirectional fibres. In addition to the fire retardant performance, the mechanical properties were also evaluated. The maximum was found at optimal consolidation temperature, while the flame retardant additive in the matrix did not influence the mechanical performance up to the investigated 13 wt % concentration.

Understanding the crystallization behavior of polyamide 6/polyamide 66 alloys from the perspective of hydrogen bonds: projection moving-window 2D correlation FTIR spectroscopy and the enthalpy

In this study, the crystallization behavior of PA6/PA66 alloys was studied using in situ FTIR spectroscopy, combined with Proj-MW2D correlation analysis and Van't Hoff analysis.

Interfacial carbonation for efficient flame retardance of glass fiber-reinforced polyamide 6

The interfacial carbonation mode is introduced to solve the high flammability of GF-reinforced polymer composites through interfacial char produced.

Preparation and characterization of flame retardant polyurethane foams containing phosphorus–nitrogen-functionalized lignin

Lignin-based phosphate melamine was used as a partial substitute for polyols to synthesize rigid polyurethane foams which exhibit high mechanical strength and low flammability.