A review on flame retardant technology in China. Part II: flame retardant polymeric nanocomposites and coatings

Development of a UiO-66 Based Waterborne Flame-Retardant Coating for PC/ABS Material

The flame-retardancy of polymeric materials has garnered great interest. Most of the flame retardants used in copolymers are functionalized additives, which can deteriorate the intrinsic properties of these materials. As a new type of flame retardant, functionalized metal-organic frameworks (MOFs) can be used in surface coatings of polymers. To reduce the flammability, a mixture of phytic acid, multi-wall carbon nanotubes, zirconium-based MOFs, and UiO-66 was coated on a PC/ABS substrate. The structure of the UiO-66-based flame retardant was established by FT-IR, XRD, XPS, and SEM. The flammable properties of coated PC/ABS materials were assessed by LOI, a vertical combustion test, TGA, CCT, and Raman spectroscopy. The presence of a UiO-66-based coating on the PC/ABS surface resulted in a good flame-retardant performance. Heat release and smoke generation were significantly reduced. Importantly, the structure and mechanical properties of PC/ABS were less impacted by the presence of the flame-retardant coating. Hence, this work presents a new strategy for the development of high-performance PC/ABC materials with both excellent flame-retardancy and good mechanical properties.

Effects of Additives on the Mechanical and Fire Resistance Properties of Pultruded Composites

Under high temperatures, fiber-reinforced polymers are destroyed, releasing heat, smoke, and harmful volatile substances. Therefore, composite structural elements must have sufficient fire resistance to meet the requirements established by building codes and regulations. Fire resistance of composite materials can be improved by using mineral fillers as flame-retardant additives in resin compositions. This article analyzes the effect of fire-retardant additives on mechanical properties and fire behavior of pultruded composite profiles. Five resin mixtures based on vinyl ester epoxy and on brominated vinyl ester epoxy modified with alumina trihydrate and triphenyl phosphate were prepared for pultrusion of strip profiles of 150 mm × 3.5 mm. A series of tests have been conducted to determine mechanical properties (tensile, flexural, compression, and interlaminar shear) and fire behavior (ignitability, flammability, combustibility, toxicity, smoke generation, and flame spread) of composites. It was found that additives impair mechanical properties of materials, as they the take place of reinforcing fibers and reduce the volume fraction of reinforcing fibers. Profiles based on non-brominated vinyl ester epoxy have higher tensile, compressive, and flexural properties than those based on brominated vinyl ester epoxy by 7%, 30%, and 36%, respectively. Profiles based on non-brominated epoxy resin emit less smoke compared to those based on brominated epoxy resin. Brominated epoxy-based profiles have a flue gas temperature which is seven times lower compared to those based on the non-brominated epoxy. Mineral fillers retard the spread of flame over the composite material surface by as much as 4 times and reduce smoke generation by 30%.

Rapid Preparation of Flame-Retardant Coatings Using Polyurethane Emulsion Mixed with Inorganic Fillers

The traditional aqueous flame-retardant coating faces the problem of slow solvent evaporation rate in the preparation process. It is an urgent problem to ensure that the function of the membrane is not destroyed while accelerating the solvent volatilization. Herein, we fabricated films on the metal substrate surface by a totally novel method: demulsification-induced fast solidification to rapidly obtain the flame-retardant coating. The environmentally friendly flame retardants aluminum hydroxide and red phosphorus were mixed with the commercial water-based polyurethane 906 emulsion to explore the optimal mixing ratio, where the adhesion of the flame-retardant reached the Grade 3 standard, the sample remained intact after the 100 cm drop hammer test and the limiting oxygen index value reached 30.4%. In addition, compared with the traditional process, this method, with the advantages of rapidly drying, environmentally friendly, uniformly prepared coatings on the surface of any shape substrates, as well as accurate and controllable coating thickness, can be widely applied in the flame-retardant field.

Advanced Flame-Retardant Methods for Polymeric Materials

Most organic polymeric materials have high flammability, for which the large amounts of smoke, toxic gases, heat, and melt drips produced during their burning cause immeasurable damages to human life and property every year. Despite some desirable results having been achieved by conventional flame-retardant methods, their application is encountering more and more difficulties with the ever-increasing high flame-retardant requirements such as high flame-retardant efficiency, great persistence, low release of heat, smoke, and toxic gases, and more importantly not deteriorating or even enhancing the overall properties of polymers. Under such condition, some advanced flame-retardant methods have been developed in the past years based on "all-in-one" intumescence, nanotechnology, in situ reinforcement, intrinsic char formation, plasma treatment, biomimetic coatings, etc., which have provided potential solutions to the dilemma of conventional flame-retardant methods. This review briefly outlines the development, application, and problems of conventional flame-retardant methods, including bulk-additive, bulk-copolymerization, and surface treatment, and focuses on the raise, development, and potential application of advanced flame-retardant methods. The future development of flame-retardant methods is further discussed.

Barrier Effects of Cellulosic Fibers with Hybrid Coating Based on Zirconium Metal-Organic Framework

Metal-organic frameworks (MOFs) have great potential for the development of fire barriers for flammable materials. Accordingly, zirconium-based metal-organic framework (Zr-MOF), branched polyethyleneimine (BPEI), and vinyltriethoxysilane (VTES) were deposited to produce composites assembled on cellulosic fibers to investigate their barrier effects. The structure, morphology, and thermal properties of the cellulosic fibers were characterized using FTIR spectroscopy, SEM, and TGA. Compared with the untreated cotton sample, the temperature of the maximum rate of weight loss (T_max) of C-Zr-MOF/BPEI/VTES increased from 479 to 523.3 °C and the maximum weight loss rate (R_max) at T_max decreased from 37.6 to 17.2 wt%/min. At 800 °C, the pristine cotton was burned out without residues whereas the residual char content of the C-Zr-MOF/BPEI/VTES sample was 7.2355 wt%. From the vertical burning tests, the results suggested that the C-Zr-MOF/BPEI/VTES sample had better barrier effects by reducing the flame-spread speed and generating more protective char layers.

Poly(ethyl methacrylate) Composite Coatings Containing Halogen-Free Inorganic Additives with Flame-Retardant Properties

This investigation is motivated by the need for the development of polymer coatings containing inorganic flame-retardant materials (FRMs) and the replacement of toxic halogenated FRMs. A green strategy is reported for the fabrication of poly(ethyl methacrylate) (PEMA)-FRM composite coatings using a dip-coating method. The use of water-isopropanol co-solvent allows the replacement of regular toxic solvents for PEMA. The abilities to form concentrated solutions of high-molecular-mass PEMA and to disperse FRM particles in such solutions are the main factors in the fabrication of coatings using a dip-coating technique. Huntite, halloysite, and hydrotalcite are used as advanced FRMs for the fabrication of PEMA-FRM coatings. FTIR, XRD, SEM, and TGA data are used for the analysis of the microstructure and composition of PEMA-FRM coatings. PEMA and PEMA-FRM coatings provide corrosion protection of stainless steel. The ability to form laminates with different layers using a dip-coating method facilitates the fabrication of composite coatings with enhanced properties.

The Evolution of Intumescent Char in Flame-Retardant Coatings Based on Amino Resin

Intumescent flame-retardant (IFR) coatings have been gaining more attention. The behaviors of intumescent char in IFR coatings play the most important role in its flame-retardant properties. However, the evolution of intumescent char throughout the whole process of protection is still unclear. In this study, both the formation and shrinkage of char were studied. The formulation of IFR includes melamine modified urea-formaldehyde resin (MUF), ammonium polyphosphate (APP) and pentaerythritol (PER). The flame-retardant properties of the coating were measured by the cone calorimeter (CONE). The evolution of the volume and the pore size distribution of char were monitored. The morphological and chemical structures were characterized by the scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results show that the evolution of intumescent char could be divided into three stages. More than 50% shrinkage of char occurs in the second stage. There are obvious transformations of the morphological and chemical structures of char between the different stages.

A Dual Active-Passive Coating with Intumescent and Fire-Retardant Properties Based on High Molecular Weight Tannins

In this study, the tannins extracted from the Pinus radiata bark were used to develop an active–passive dual paint scheme with intumescent (IN) and fire-resistant (FR) behaviors. The properties of the coating were observed to depend on the concentration of high-molecular-weight tannins (H-MWT) incorporated into the formulation. At high concentrations (13% w/w), the coating exhibits fire-retardant properties due to the generation of a carbonaceous layer; however, at low concentrations (2.5% w/w), it generates an intumescent effect due to the formation of a carbonaceous foam layer. The dual IN–FR scheme was evaluated against fire by flame advance tests, carbonization index, mass loss, and intumescent effect, and was also compared to a commercial coating. The dual scheme presented good mechanical properties with a pull-off adhesion value of 0.76 MPa and an abrasion index of 54.7% at 1000 cycles, when using a coating with a high solid content (>60%) and the same thickness as those of the commercial coatings. The results of the fire resistance test indicate that the dual scheme generates a protective effect for wood and metal, with an excellent performance that is comparable to that of a commercial intumescent coating.

A simple approach with scale-up potential towards intrinsically flame-retardant bio-based co-plasticizer for PVC artificial materials

Abstract

As an imitation of genuine leather, polyvinyl chloride (PVC) artificial materials are versatile, but suffers from being flammable due to the presence of large amounts of combustible plasticizers. Under such circumstance, intrinsically flame-retardant plasticizers displaying dual functions have been a subject of intensive research interest. However, previous strategies attempting to covalently attach flame-retardant moiety to plasticizers invariably required either expensive starting materials or laborious and tedious procedures, ultimately limiting their scale-up application in industry. In addition, driven by escalating demand of halogen-free flame retardants worldwide from an environmental health perspective, previously reported intrinsically flame-retardant plasticizers were mainly halogen-free, less attractive in PVC artificial material industry simply because PVC itself is a halogen-containing polymer. Here, we report an approach to introduce chlorine moieties into unsaturated fatty acid methyl ester by a simple addition reaction occurring on carbon-carbon double bonds, yielding a chlorine-containing, intrinsically flame-retardant bio-plasticizer. When combined with di-(2-ethylhexyl) phthalate (DOP) in PVC formulations, the chlorinated fatty acid methyl ester is qualified as a co-plasticizer while conferring flame retardancy upon the PVC coatings. This approach involves only a one-step procedure that employs renewable fatty acid methyl esters and cheap chlorine gas as raw materials, thus being of great potential to enable intrinsically flame-retardant bio-plasticizers on a large scale to manufacture functional PVC artificial materials for application in fire-prone scenarios.

Graphical abstract

Synergistic Charring Flame-Retardant Behavior of Polyimide and Melamine Polyphosphate in Glass Fiber-Reinforced Polyamide 66

The synergistic charring, flame-retardant behavior of the macromolecular charring agents polyimide (PI) and melamine polyphosphate (MPP) were studied in glass fiber-reinforced polyamide 66 (PA66). This kind of synergistic charring effect is explained by the fact that PI performed better char-forming ability while working with phosphorus content. The research results showed that, compared with the incorporation of individual MPP, MPP/PI with an appropriate ratio exhibited better flame retardancy and better charring ability. A blend of 11.9%MPP/5.1%PI/PA66 possessed an increased LOI (limiting oxygen index) value of 33.9% and passed the UL94 V-0 rating, obtained a lower peak heat release rate value (pk-HRR), a lower total heat release (THR) value, a lower total smoke release (TSR) value, and a higher residue yield. The results verified the synergistic flame-retardant effect between MPP and PI in the PA66 composite. Melamine polyphosphate and PI jointly interacted with PA66 matrix and locked more carbonaceous compositions in residue and formed a more compact char layer, resulting in a reduced burning intensity and a reduction in the release of fuels. Therefore, the enhanced flame-retardant effect of the MPP/PI system is attributed to the higher charring ability and stronger barrier effect of the char layer in PA66 in the condensed phase.

Effects of Size of Zinc Borate on the Flame Retardant Properties of Intumescent Coatings

This paper is aimed at assessing the fire retardancy and thermal stability of intumescent flame retardant (IFR) containing ammonium polyphosphate (APP), pentaerythritol (PER), and melamine (MEL). Zinc borate (ZB) was added at the loading of 2%, 4%, 6%, 8%, 10%, and 12% by weight of IFR. The sizes of investigated ZB fall in 3 ranges: 1-2 μm, 2-5 μm, and 5-10 μm. The performance of APP/PER/MEL was investigated by using thermogravimetry analysis (TGA), cone calorimeter test, Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy, and energy-dispersive spectrometry. The results obtained from the above experiments show that the incorporation of ZB can improve the fire protection performance. A 77% decrease in total smoke production and 84.6% decrease in total heat release were achieved for the addition of 2 wt% ZB (2-5 μm) in the IFR coating. TGA results indicate an increased amount of char residue. Compared to the control IFR coating, the char residue of IFR containing 2 wt% ZB (2-5 μm) has increased approximately 1.5-fold, 10-fold, and 25-fold, at 600°C, 700°C, and 800°C, respectively. The effective char formation results in excellent smoke suppression. Regarding smoke suppression performance, the order for smoke density is IFR/ZB (2-5 μm) < IFR/ZB (5-10 μm) < IFR/ZB (1-2 μm), regardless of investigated loading levels. The decline of smoke suppression performance for IFR/ZB (5-10 μm) and IFR/ZB (1-2 μm) is believed to be due to the poor char formation, as a result of a weak interaction of APP, PER, MEL, and ZB. This weak interaction is caused by the decrease in the specific surface area and agglomeration of ZB particles for IFR/ZB (5-10 μm) and IFR/ZB (1-2 μm), respectively.

Ultrathin Nanosheets of Organic-Modified β-Ni(OH)2 with Excellent Thermal Stability: Fabrication and Its Reinforcement Application in Polymers

β-Nickel hydroxide (β-Ni(OH)2), which combines two-dimensional (2D) structure and the catalytic property of nickel-containing compounds, has shown great potential for the application in polymer nanocomposites. However, conventional β-Ni(OH)2 exhibits large thickness, poor thermal stability, and irreversible aggregation in polymer matrices, which limits its application. Here, we use a novel phosphorus-containing organosilane to modify the β-Ni(OH)2 nanosheet, obtaining a new β-Ni(OH)2 ultrathin nanosheet with excellent thermal stability. When compared to pristine β-Ni(OH)2, the organic-modified β-Ni(OH)2 (M-Ni(OH)2) maintains nanosheet-like structure, and also presents a small thickness of around 4.6 nm and an increased maximum degradation temperature by 41 °C. Owing to surface organic-modification, the interfacial property of M-Ni(OH)2 nanosheets is enhanced, which results in the exfoliation and good distribution of the nanosheets in a PMMA matrix. The addition of M-Ni(OH)2 significantly improves the mechanical performance, thermal stability, and flame retardancy of PMMA/M-Ni(OH)2 nanocomposites, including increased storage modulus by 38.6%, onset thermal degradation temperature by 42 °C, half thermal degradation temperature by 65 °C, and decreased peak heat release rate (PHRR) by 25.3%. Moreover, it is found that M-Ni(OH)2 alone can catalyze the formation of carbon nanotubes (CNTs) during the PMMA/M-Ni(OH)2 nanocomposite combustion, which is a very helpful factor for the flame retardancy enhancement and has not been reported before. This work not only provides a new 2D ultrathin nanomaterial with good thermal stability for polymer nanocomposites, but also will trigger more scientific interest in the development and application of new types of 2D ultrathin nanomaterials.

Solid acid-reduced graphene oxide nanohybrid for enhancing thermal stability, mechanical property and flame retardancy of polypropylene

PMoA enhances the radical trapping effect of graphene.

Simultaneously enhancing the flame retardancy and toughness of epoxy by lamellar dodecyl-ammonium dihydrogen phosphate

Lamellar dodecyl-ammonium dihydrogen phosphate flame retardant was synthesized in one-pot. Its incorporation into epoxy leads to the simultaneous enhancement of flame retardancy and impact toughness for the resulting epoxy composites.

Ordered exfoliated silicate platelets architecture: hydrogen bonded poly(acrylic acid)–poly(ethylene oxide)/Na–montmorillonite complex nanofibrous membranes prepared by electrospinning technique

Well-ordered/dispersed exfoliated clay platelets aligned along as-electrospun PAA–PEO/Na–MMT composite nanofibrous membranes were synthesized successfully for the first time.

A convenient method for preparation of polystyrene-single-walled carbon nanotubes by metal-catalyzed living radical polymerization method

In this research, a new direction for functionalizing of single-walled carbon nanotubes (SWCNTs) via the atom transfer radical polymerization (ATRP) method was utilized. SWCNTs were grafted with polystyrene (PSt) by the in situ ATRP method, in the presence of α-phenyl chloro acetylated SWCNT. This functional SWCNT was synthesized by the reaction between α-phenyl chloro acetyl chloride and a hydroxylated SWCNT that was obtained by reduction of a carboxylated SWCNT by lithium aluminum hydride (LiAlH4). Oxidation, reduction and coupling reactions of SWCNTs were confirmed by Fourier transform infrared (FTIR) spectroscopy and polymerization of styrene from SWCNTs surfaces was illustrated by transfer electron microscopy (TEM). Thermal properties of attached polymers onto SWCNTs surfaces were investigated by thermogravimetry analysis (TGA), and differential scanning calorimetry (DSC) analysis.