Theoretical justification for the fire-protection modification of textiles through the action of laser radiation

Abstract

A theoretical justification and the conditions of use for multi-photon laser radiation in fire-protection of textiles were presented. A radical mechanism of chemical bond dissociation under the effects of multi-photon laser quanta was demonstrated. The reaction of polymer fibre radicals and fire retardant made the fire-protection treatment resistant to laundering whereas the formation of additional intermolecular bonds increased the structural ordering and the strength of the textiles.A promising direction for improved modification of textiles is the use of physical methods such as the treatment of materials with a gaseous corona discharge, high-frequency plasma, photochemical UV radiation, and irradiation by a beam of fast electrons, etc. [1][2][3]. Laser radiation is of special interest for the modification of polymeric fibres. It can be used to control chemical processes and to increase the reaction rate, mass yield, and purity of the products compared with traditional modification methods [4][5][6]. Its application to fire-protection of textiles also seemed interesting.IR radiation generated by a CO 2 -laser with wavelength 10.6 μm is widely used to modify polymers. These instruments currently have high efficiencies, are available and ecologically safe, and are convenient and simple to service. This makes them attractive for use in creating innovative technologies for fire-protection of textiles [7].The proposed theoretical justification of the physicochemical processes for modifying natural and chemical fibres and textiles with the phosphorus-containing fire retardants (FRs) dimethylmethylphosphonate (DMMP), phosdiol (PD), and methylphosphonamide (T-2) through the action of CO 2 -laser radiation was based on tenets of the theory of multi-photon excitation of their chemical bonds [8,9]. This theory has already been used to describe and confirm in practice many reactions that are initiated by CO 2 -laser radiation.Polymers are known to absorb selectively laser radiation (LR), the frequency of which coincides with the vibrational frequency of their bonds, i.e., through a resonance effect. Selective absorption of LR opens possibilities for targeted structural modification of fibre-forming polymers. Considering that CO 2 -laser radiation falls in the frequency range 900-1100 cm -1 , ···C-O-, ···C=O, and ···N-H bonds occurring in the structures of fibre-forming polymers and FRs absorb most of the radiation and are excited.Laser radiation incident on the material surface (E tot ) is distributed as follows. A part of the energy is absorbed (E a ); a part is reflected (E r ), and a part passes through the porous textile structure (E p ):The absorption coefficient of incident energy depends on the thermophysical properties and surface state of the treated material. Therefore, the greater the porosity of the textile cloth and the fibre reflection coefficient are, the more exposure energy (E exp ) the cloth can retain. The greater the thermal conductivity coefficient of the cloth (K t ) is, the greater the rate and dept...