New Generation Boron-Doped Nanomaterials and Their Applicability as Flame Retardants

ABSTRACT

With humanity's development, increasing industrialization and the rapidly advancing technology that follows have led to a growing search for environmentally friendly, non-toxic materials that do not burn at high temperatures. Boron, one of indispensable mineral resources, is among strategically important sources capable of meeting this material search. Boron compounds, generally produced using high-technology methods, hold commercial significance worldwide. Each of the special boron compounds produced is used for many purposes in different sectors. One of the most important reasons for preferring special boron compounds is their flame-retardant structure. Substances known as flame retardants help prevent the ignition and progression of combustion, minimize loss of life and property, and contribute to environmental protection. The addition of flame-retardant additives increases the ignition time of combustible materials while reducing the duration of combustion progression. Boron-containing compounds used as flame retardants have widespread application areas. Boron compounds added to wood, cellulosic insulation, PVC and textile materials impart flame resistance properties to these materials. In this study, investigations into non-flammability were conducted and attention was drawn to the flame-retardant effects of next-generation nanomaterials.

1. Introduction

Boron, used in many important fields, is extremely significant for Turkey and contains approximately 73.5% of the world's reserves. Boron, which can also be used in fuel cells and similar applications, possesses important properties such as high combustion temperature, easy transfer of products following combustion, and non-emission of pollutants that would harm the environment. Due to its flame-delaying effect, boron has played an effective role in many working areas. The special boron compounds showing boron's flame-retardant properties most prominently are zinc borate and fluoroborates. The aforementioned boron compounds also demonstrate an additional advantage in showing high-temperature resistant pigment properties. The addition of non-flammable and smoke-suppressing minerals into products such as epoxy resin, used widely in various sectors (plastics, wood products, textiles, paper, adhesives, coatings, aviation and electronics) to prevent loss of life and property in fires, is increasingly common today, with boron and similar flame retardants coming to the fore and becoming necessary [1-19]. It is of great importance that the flame retardants we use do not alter or damage the processing properties of the material to which they are added. Flame retardants added to materials in certain proportions not only dilute the combustible material but also reduce the minimum amount of oxygen needed for continued burning. For a used flame retardant to be considered an effective flame retardant, it must have low ignition properties. Additionally, it should be able to reduce the intensity of flammability during the reaction, cause smoke at low rates and amounts, and must not be toxic. Flame retardants have different mechanisms. As a polymer burns, the vapor phase developing in the combustion process creates free radicals. Added additives, either alone or through chain reactions with other materials in the compound, provide flame retardancy by preventing the formation of released free radicals. Brominated and chlorinated flame retardants operate through this mechanism [3-12]. Flame retardants work through a physical dilution mechanism by reducing fuel content below the lower flammability limit of the material and increasing the heat capacity of the product. Glass fibers and certain minerals can be cited as examples of this mechanism. Some flame retardants produce large amounts of non-flammable gases when the product decomposes during combustion. The gases dilute the oxygen source for flaming or fuel concentration below the ignition limit. Metal hydroxides and metal carbonates, known as flame retardants, operate in this manner. Recently, particularly with the development of nanotechnology, boron-containing nanomaterials are increasingly being sought for use as combustion-inhibiting materials. Generally, nanotechnology deals with the production, examination, development, and application of materials with nanostructures. Nanomaterials serve as a transition between molecules and infinitely large systems. As one moves from macroscopic scale to nano-scale, the physical and chemical properties of materials show changes. The variation of material properties according to size enables the production of new technologies and new tools. All these studies and developments have brought together electronics, chemistry, physics, materials science, aerospace and even health sciences at a multidisciplinary common point. Nanomaterials are generally classified in literature by dimensionality as: a) 0-D nanomaterials (nanoparticles) b) 1-D nanomaterials (nanofibers, nanotubes, nanowires) c) 2-D nanomaterials (nanofilms) These nanostructures can be produced using different methods, with drawing method, chemical reduction, phase separation, chemical vapor deposition (CVD), melt spraying, nano-templating and electrospinning methods being frequently used techniques in nanomaterial production. Generally, these methods make it possible to produce nanomaterials in the 10–500 nm diameter range and control particle size. Besides these, boron-based nanomaterials have many application areas due to their very high resistance to chemical reactions, low density, high thermal stability, high hardness, high neutron capture capacity and excellent thermoelectric properties. Some of these application areas include the production of abrasive wear-resistant materials and ceramic armor. Additionally, there is potential for use in neutron moderators of nuclear reactors and in power generators for space flight applications. Boron nitride nanotubes, which can be cited as examples of boron-containing nanomaterials, are semiconductor materials with a wide band gap (Eg = 5.5 eV) and can only absorb UV light; through these properties, they can be modified with dyes and used as an energy source. Moreover, due to their excellent mechanical and thermal properties and particularly their high resistance to oxidation, they can be used as reinforcing elements in high-temperature composite materials. The fact that chemicals used in boron-containing nanomaterial production are highly toxic and costly, and that the equipment used in nanomaterial production is complex and expensive, necessitates the use of new starting materials and investigation of production methods for boron-containing nanomaterial production. The production of high-value-added boron products using advanced technologies to effectively utilize our country's rich boron resources is a very important requirement.

2. Results and Discussion

For the reasons mentioned, this study aimed at producing boron-containing nanomaterials using the electrospinning technique, one of the economical production methods for use in many applications such as non-flammability. In this context, the effects of solution preparation parameters such as viscosity and pH, production parameters such as applied voltage, solution flow rate and distance between substrate and needle tip, and different starting materials on results were examined, and appropriate starting materials and optimum production conditions were determined. Since the physical and chemical properties of materials differ as material size decreases to the nanometer level, the structural properties of the produced nanomaterials were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and similar methods. Additionally, a differential thermal analysis/thermogravimetry (DTA-TG) device was used to determine the thermal treatment regime applied during production and the final product yield obtained, and the material was patented due to its superior properties. Generally, when boron-containing nanomaterials are used as flame retardants, they are environmentally friendly, do not cause toxic gas emissions, and have low volatility values. They suppress combustion by coating the burning material to cut off contact with oxygen. In conclusion, boron-containing nanomaterials prepared using the electrospinning technique hold a very strong position among flame retardants, one of their application areas, and through the studies conducted, they are finding increasing application with each passing day.

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Prof. Fatih Şen / Dumlupınar Üniversitesi / Faculty of Science and Letters / Department of Biochemistry Betül Şen / Dumlupınar Üniversitesi / Faculty of Science and Letters / Department of Biochemistry Aysun Şavk / Dumlupınar Üniversitesi / Faculty of Science and Letters / Department of Biochemistry