Electrospun nanofibers from copolymers and terpolymers of acrylonitrile, vinyl acetate and vinylphosphonic acid

Polymer materials are active in every area of human life. They are preferred because they are lighter than ceramics and metals and are easy to process and have high mechanical properties. Depending on the area to be used, a number of improvements can be made using physical or chemical methods to improve the properties of polymer materials. Particularly fillers and additives are frequently used with the aim of enhancing the polymer properties. The structure of each filler and additive to be used varies depending on the polymer structure. Additives such as flame retardants, stabilizers, antioxidants and plasticizers are frequently used to improve the properties of the materials. Nanofibers are found in many applications as high function materials with diameters below 100 nm, high surface area and porosity. These applications include areas such as scaffolds in tissue engineering, drug delivery, enzyme immobilization, filtration, wound healing, biosensors. Acrylic fibers are the most commonly used fiber type in the textile industry. Acrylic fibers found in the works to meet the increasing wool need in the world are preferred because of their natural feel like wool, easy washability, resistance to sunlight and chemical resistance. The first acrylic fiber produced as homopolymer with 100% acrylonitrile polymerization, marketed by Orlon patent name, is hard and brittle and difficult to paint. In order to solve this difficulty, it was mixed with a second monomer and converted into copolymers to make the use in textile. Acrylic fiber, which is made up of acrylonitrile monomer and comonomer, usually produced by wet and dry spinning systems, can be produced as a nanofiber. In this study, it is aimed to produce nanofibers of acrylonitrile copolymers and terpolymers. For this purpose, the polymerization reaction of acrylonitrile monomers and comonomers was carried out and the nanofiber production was carried out using electrospinning technique. At the same time, acrylonitrile copolymers and terpolymers were produced in different formulations with different water/monomer ratios and nanofiber of each formulation was produced. In the first step, the acrylonitrile monomer and the vinyl acetate comonomer are polymerized with an ammonium persulfate initiator at a temperature of 70 °C. Copolymers have been produced in different compositions with the water/monomer ratios: 3,5 and 10. The same method was used for the terpolymer production. In addition to acrylonitrile and vinyl acetate monomer, vinylphosphonic acid monomer is used for the terpolymer. Environmentally friendly, halogen-free flame retardant species, phosphorus-containing flame retardants are widely used. In the condensed phase mechanism, flame retardant phosphoric acid contributes to the formation of coal by altering the thermal degradation of the polymer. In the second step, solutions were prepared from the polymers formed using dimethylformamide (DMF) solvent. While the copolymer solutions were prepared at 10%, the terpolymer solutions were prepared at 5%. These solutions were produced to use in electrospinning method which is a nanofiber production method. Nanofibers and polymers are characterized by FTIR-ATR (Fourier Transform Infrared Spectrophotometer), SEM (Scanning Electron Microscope), TGA (Temperature Mass Analyzer), DSC (Differential Scanning Calorimetry), Ostwald viscometer, ICP (Inductively Coupled Plasma) analysis. Nanofiber formation was carried out from copolymer solutions prepared with different water / monomer ratios. In the case of the terpolymer solutions prepared at the same ratios, the nanofiber formation of the terpolymer solution having a water / monomer ratio of 10 can be carried out, whereas the nanofiber formation of the terpolymer solutions having a water / monomer ratio of 3 and 5 can not be achieved. This is due to the high viscosity values of the terpolymer solutions with a water / monomer ratio of 3 and 5. These polymers with a high viscosity values appear to release solvent when fiber production is needed, during the fiber production stage. It is known that glass transition temperatures and melting temperatures of semicrystalline polymers decrease with comonomer addition. The results of differential scanning calorimetry (DSC) show that the glass transition temperatures of the terpolymer and copolymers are increased when compared to the glass transition temperature of the acrylonitrile homopolymer. The increase in glass transition temperatures is due to the influence of the hydrogen bond formed by the electronegative atoms in the vinyl acetate monomer and the vinylphosphonic acid monomer. In addition, the increase in glass transition temperatures of terpolymers is greater than that of the copolymers. The Char layer enhances the formation of water vapor which reduces flammable volatile substances. At the same time, it reduces heat transfer from the heat source to the polymeric material. The increase in the amount of residues in the polymer means that the formation of carbon layer is increased. In the sample CP-2 with a residual amount of about 52%, the most carbon layer formation occurs. Among the terpolymers, TP-1 with a residual amount of 47% shows the maximum amount of residues and maximum carbon layer formation. In addition, carbon layer formation in the terpolymers decrease with increasing the amount of water. It has been found that the contribution of the synthesized copolymers and terpolymers to carbon layer formation is less than the contribution of homopolymer and commercial P (AN-co-VAc) to the formation of carbon layer. According to the water absorption test results, it appears that the water absorption percentage of the synthesized copolymers and terpolymer increases with respect to homopolymer. If we compare the water absorption percentages of the copolymers and terpolymers, it is seen that the water absorption percentages of the copolymers are almost equal to or even greater than the terpolymers. The reason for this is that the phosphonic acid groups present in the terpolymers form hydrogen bonds between themselves and therefore the rate of hydrogen bonding with water is reduced. Low water absorption values of terpolymers may be useful for use in different areas of nanofibers. These polymers can be used to produce a water-resistant nanofiber.