Hybrid Silica-Phytic Acid Coatings: Effect on the Thermal Stability and Flame Retardancy of Cotton

Abstract

New hybrid sol–gel coatings based on tetraethoxysilane (TEOS) and phytic acid (PA) were designed and applied to cotton; the flame-retardant properties of the treated fabrics were thoroughly investigated by means of flame-spread and forced-combustion tests. The first goal was to identify the TEOS:PA weight ratio that allowed the achievement of the best flame-retardant properties, with the lowest final dry add-on on the fabrics. Therefore, different TEOS:PA sols were prepared and applied to cotton, and the resulting coated fabrics were thoroughly investigated. In particular, solid-state NMR spectroscopy was exploited for assessing the condensation degree during the sol–gel process, even for evaluating the occurrence of possible reactions between phytic acid and the cellulosic substrate or the alkoxy precursor. It was found that a total dry add-on of 16 wt % together with 70:30 TEOS:PA weight ratio provided cotton with self-extinction, as clearly indicated by flame-spread tests. This formulation was further investigated in forced-combustion tests: a significant reduction of heat release rate (HRR), of the peak of HRR, and of total heat release (THR) was found, together with a remarkable increase of the residues after the test. Unfortunately, the treated fabrics were not resistant to washing cycles, as they significantly lost their flame-retardant properties, consequently to the partial removal of the deposited hybrid coatings.

Phytic Acid and Biochar: An Effective All Bio-Sourced Flame Retardant Formulation for Cotton Fabrics

“…The elemental analysis carried out by energy dispersive X-ray spectroscopy on some areas where BC particles appear ( Figure 4) confirms the presence of C, O and P elements (i.e., the main phytic acid and BC constituents, obviously not excluding the C and O contribution from the cellulosic substrate). It is noteworthy that PA, as already observed in sol-gel systems containing this bio-sourced product [27], is likely to coat the fibers with a homogeneous layer; BC micro-sized particles are quite well distributed on the fiber surface.…”

“…The scientific literature already reports some interesting works dealing with the application of phytic acid-based flame retardants to different types of textile materials. In particular, this eco-friendly, biocompatible and nontoxic organic polyphosphoric acid has been successfully utilized as flame retardant for wool [22], silk [23], poly(lactic acid) nonwoven fabrics [24] and, more recently, cotton fabrics [25][26][27][28].…”

Sol-Gel and Layer-by-Layer Coatings for Flame-Retardant Cotton Fabrics: Recent Advances

“…Very recently, TEOS was combined in a sol-gel recipe with phytic acid in order to combine the effect of the ceramic (silica phase) created by the alkoxy precursor with the char-forming character of phytic acid: its molecule, in fact, contains six phosphate groups that, upon exposure to a heat flux or a flame, decompose, giving rise to dehydration reactions on the cellulosic substrate, hence favoring the formation of char and limiting the generation of volatile combustible gases [47]. In particular, the treated fabrics with a total dry add-on of 16 wt.%, together with a 70:30 TEOS:phytic acid weight ratio were self-extinguishing in vertical flame-spread tests.…”

Construction of a Phytic Acid–Silica System in Wood for Highly Efficient Flame Retardancy and Smoke Suppression

“…PA can catalyze the protonation and polymerization processes of Si-O − anions in silica sol because of its strong acidity, and it can bond to silica when temperatures exceed 450 °C [ 31 , 32 ]. Flame-retardant and smoke-suppressed effects of combinations of PA with silica sol on other cellulosic materials, such as wool and cotton, were positive and strong [ 33 , 34 , 35 , 36 ]. Fabrics prepared with PA/silica hybrid sol improved in mechanical strength as well [ 37 ].…”