Application And Prospect of Nanotechnology in Flame Retardant Materials

Application and Prospect of Nanotechnology in Flame Retardant Materials

Currently, polymers such as plastics, rubbers and fibers are widely used, but their flammability has caused some impact on their use and promotion. Although flame retardant materials play a positive role in blocking combustion, slowing down the spread of fire, and fighting for escape and rescue time to a certain extent, they are also deficient in mechanical properties, cost-effectiveness, environmental pollution, and so on. 

With the application of nanomaterials in many fields such as mechanics, electromagnetism, thermology, optics, etc., nanotechnology and nanomaterials show a broad development prospect. The research and development of nano-flame retardant materials is conducive to overcoming and improving the shortcomings of traditional materials, which implies great social effects and economic benefits.

1. Introduction to Nanomaterials

Nanomaterials refers to materials with nanometer scale in structure and its corresponding functional characteristics, 1 nanometer is one billionth of a meter, and the nanometer scale generally refers to 1~100 nm. when the structure and particle size of materials enter into the range of the nanometer scale, they show a variety of special effects, such as surface effect, small-size effect, quantum-size effect, and macroscopic quantum tunneling effect, which make the materials show a variety of peculiar functions.

Nanomaterials can be categorized into nano-metallic materials, nano-nonmetallic materials, nano-polymer materials and nanomaterials according to their materials. The combination of nanotechnology and a variety of materials greatly changes the comprehensive characteristics of materials and provides powerful technical support to further optimize the function of materials.

2. Classification and requirements of flame retardant materials

Flame retardant materials can be divided into inorganic and organic, halogenated and halogen-free and other types. Inorganic mainly refers to aluminum hydroxide, magnesium hydroxide, silicon, antimony trioxide and other flame-retardant material systems, organic mainly halogen, nitrogen and phosphorus-based system, which through compounding or reaction to form an additive or reactive composite materials, which in turn play a flame retardant role.

Comparatively speaking, inorganic flame retardant materials have the advantages of low cost, good thermal properties, less toxic gases during combustion, but they also have poor mechanical properties, large filler and poor compatibility with the substrate and other defects.

Organic flame retardant materials have good flame retardant properties, good compatibility with the substrate, small filler, etc., but has a large amount of smoke and toxic gases during combustion and other defects. Therefore, the development of low-smoke, low-toxicity, halogen-free, superior physical and mechanical properties of environmentally friendly flame retardant materials has been an important research topic, the emergence and development of nanotechnology to solve the existing defects of the flame retardant materials provides a possible.

Research shows that nano-flame retardant materials should meet the following requirements: first, the materials should meet the requirements of environmental protection, and produce less toxic gases during combustion. Secondly, the materials should be characterized by strong functionality and high flame retardant efficiency, and at the same time, they should overcome the existing defects in the mechanical and physical properties of the traditional flame retardant materials and expand the scope of application of the materials. Thirdly, the comprehensive cost should be reduced to enhance the cost-effectiveness of the materials.

3. Types of nano-flame retardant materials

Nano flame retardant materials can be obtained by refining traditional flame retardant particles to nanometer level and applying them to related materials. The application of nanotechnology, the acquisition of nanoscale particles and the unique multiple effects of nanoscale greatly enhance the compatibility between flame retardants and materials, reducing the amount of flame retardant application to a certain extent, but also improve the flame retardant properties and enhance the cost-effectiveness of flame retardant materials. At present, the commonly used nano-flame-retardant composites that have been developed are roughly as follows.

3.1 Polymeric clay nanomaterials

Clay nano flame retardant materials involve raw materials such as cationic clay mineral montmorillonite, anionic clay mineral layered bimetallic hydroxide, and nonionic clay mineral kaolinite, etc., which are modified with the help of intercalation method to obtain composite flame retardant materials that are effective for polymethylmethacrylate (PMMA) and polypropylene (PP).

The layered silicate of clay flame retardant contains carbonized layer, which can capture some free radicals at high temperature, which improves the flame retardant property of the material while changing the mechanical property of the material, and avoids the defects such as large amount of smoke, corrosive and toxic gases during combustion with the addition of halogenated flame retardant. In case of fire, the silicate carbonization layer slows down the rate of volatiles escaping from the material during combustion thus making the clay nanomaterials in the condensed phase decomposition process of volatiles with a low overflow rate.

3.2 Nano magnesium hydroxide flame retardant materials

Nanoscale magnesium hydroxide flame retardant materials, flame retardancy, smoke generation and compatibility with the substrate and other properties are better than the corresponding properties of micron-sized magnesium hydroxide flame retardant materials. Under a certain dosage, nanoscale magnesium hydroxide flame retardant body can reach UL94 standard V-0 level.

The advantages of metal hydroxide itself is obvious, the key is to add a relatively large amount, usually more than 60%, and high filler volume on the physical and mechanical properties of flame retardant materials have a greater impact, and nanotechnology is just a good solution to the dispersion and compatibility between the flame retardant and the matrix, the combination of the two technologies has greatly enhanced the application of magnesium hydroxide flame retardant and flame retardant materials after the flame retardant properties. Nano-magnesium hydroxide flame retardant materials have a wide range of excellent properties such as non-halogen, low smoke, non-toxic, non-dripping, acid-resistant, good stability, high decomposition temperature, non-corrosive equipment, etc., which has a broad application prospect.

3.3 Calcium carbonate nanocomposites

With zinc stannate coated calcium carbonate nanopowder and applied to polyvinyl chloride (PVC), the product particle size of 40~60nm is obtained, which reduces the amount of plasticizer in PVC and improves the processing performance of the product, coupled with the high chlorine content and high flame retardant of rigid PVC itself, the limiting oxygen index (LOI) can reach 45%, and excellent flame-retardant composites are obtained.

The methacrylic acid-treated calcium carbonate nanoparticles/polystyrene (PS) in-situ composites also have a particle size of 100 nm or less, and also have good flame retardant properties. In addition can also be applied to fatty acids, titanate coupling agent and nano-calcium carbonate after surface treatment to get polypropylene / nano-calcium carbonate composites, after experimentation and application, are to maintain better flame retardant properties on the basis of the mechanical properties of the material has been greatly improved, the impact strength of the material has also been improved.

3.4 Nanoscale antimony oxide flame retardant materials

Nanoscale antimony oxide flame retardant PVC materials have high flame retardant properties, low smoke, its performance is better than the corresponding performance of traditional PVC materials, and is suitable for use in textiles. Nano-scale antimony oxide particles are used in small quantities and will not block the machine's spinneret holes, making the textiles flame retardant.

In addition, nanoscale antimony oxide material has a large specific surface area, the penetration performance of some textiles is good, has a strong adhesion, the resulting textile material also has good fastness to washing, not easy to fade. Antimony oxide nanoparticles have the advantages of low cost, small average particle size, uniform dispersion in polyester materials, and good compatibility.

3.5 EVA/silica nanocomposites

Silica nanomodified polymers have gained wide application due to the fact that the nanocomposites obtained after nanosizing and modification have a variety of advantages such as light weight, high strength, and high toughness.

The nano-filler layer in EVA-type nanocomposites forms an isolation layer outside the inner polymer layer, which strengthens the charring process, prolongs the degradation process of the material, produces a very low peak heat release rate as measured by a conical calorimeter, and substantially improves the flame retardant properties compared to traditional flame retardant materials.

In terms of mechanical properties, it is shown that the volume filling fraction in EVA/silica composites is 4%, the composite material has the highest tensile strength, which is about twice of that of the matrix, which also fully reveals the important role of nanotechnology in enhancing the physical and mechanical properties of composites.

4. Progress in the preparation process of nano flame retardant materials

The preparation methods of nanomaterials are mainly as follows:

① Sol-gel method. Sol-gel method is a more common preparation method for preparing nanomaterials. The process is: dissolve metal oxides or metal salts in water, through the hydrolysis reaction, the formation of sol-like nanoscale particles, and then evaporate the solvent, after which a gel object is formed. This results in the formation of organic polymers and inorganic molecules interpenetrated with multilayer ordered structure of flame retardant materials. The method of chemical reaction is mild, inorganic components and organic components are mixed with each other, and the structure is close, but there are also shortcomings such as easy material shrinkage and brittleness when gel drying.

② Co-precipitation method. Co-precipitation method refers to the prior formation of inorganic nanoparticles and organic polymers mixed with the method of precipitation to form flame retardant materials. In this method, nanoparticles and material synthesis are produced separately, the size and structure of nanoparticles can be well controlled, while nanoparticles are uniformly distributed in the polymer, with good comprehensive performance. However, the nanoparticles are easy to agglomerate in this method, and uniformly dispersing the nanoparticles is the biggest problem. Co-precipitation method can be divided into solution co-precipitation method, emulsion co-precipitation method and melt co-precipitation method and other ways.

③ Interpolation method. The process of intercalation method is to make nanoparticles into layers, and then inserted into the organic polymer layer, resulting in the two to achieve nanoscale composite. There are various types of these methods such as polymerization intercalation method, melt intercalation method and solution intercalation method.

④ In-situ copolymerization method. In-situ copolymerization method refers to the uniform dispersion of nanoparticles in solution, and then with the help of heating, radiation and other means, so that the polymer and nanoparticles polymerization and a series of other reactions, and finally get the nanoscale dispersion of flame retardant materials. The flame retardant materials obtained by this method have the advantages of good particle nanoparticle characteristics and low enthalpy-entropy barrier between layers.⑤ In-situ self-assembly method. In-situ self-assembly method refers to the use of polymer molecules and nanoparticles between the intermolecular force, interlayer electrostatic force, etc., in-situ self-assembly, the generation of inorganic main crystal nuclei, and finally the polymer will be generated by the crystal surrounded. This method of synthesizing bis-hydroxy nanocomplexes is more favorable and the nanophase can be distributed in an orderly manner.

5. Prospect of nano-flame retardant materials

In the field of flame retardants, inorganic additive flame retardants have the earliest application and the largest amount. Such as antimony system, aluminum system, phosphorus system, boron system flame retardants and so on. However, at present, there are mainly problems such as poor compatibility of flame retardants and base materials and large impact on physical and mechanical properties. Research shows that the use of nanotechnology can improve the flame retardancy and mechanical properties of plastic products, strengthen the flame retardancy and antistatic ability of fiber products, strengthen the flame retardancy of rubber products and reduce the release of toxic gases and the amount of smoke during combustion. Nano-flame-retardant materials can greatly improve the comprehensive performance of inorganic flame-retardant materials with the help of nanotechnology on the basis of the advantages of inorganic flame-retardant materials such as low-halogen or non-halogen, low smoke and low corrosion.

In addition, nano-flame-retardant materials will also be further developed in terms of improving the thermal stability of the materials, reducing the agglomeration of the materials in use, enhancing the optimization of the dosage, particle size, lamellar structure and compounding between the flame retardants and the materials, optimizing the storage and transportation of the materials and the process of adding them, enhancing the flame-retardant effect of the materials, and promoting the multifunctionality of the materials, and so on. Strengthening research in the microstructure and formation mechanism of nano-flame-retardant composite materials, details of flame-retardant mechanism of materials and other basic theories, and continuously accelerating the development of nano-flame-retardant materials business in the sunrise, are conducive to the smooth realization and expansion of industrialization of related products.

In summary, nano-flame retardant materials have good flame retardant performance, good environmental protection effect, and less toxic gases released during combustion, less filling dosage, and the products tend to be multi-functional development characteristics, which can be widely used in automotive, aviation, electronic home appliances and other industries, and has a lot of space for development.

However, the development of nano-flame retardant materials, there are still many practical problems that need to be solved, such as the control of nanoparticle morphology, nanoparticle distribution process and the unity of multifunctionalization. It is believed that with the continuous progress of polymer materials science and engineering technology, and with the emergence, application and rapid development of nanotechnology, the research on nano-flame-retardant materials will certainly make great progress, and provide a solid material and technological guarantee for the better protection of people's lives and properties.