In this work, a pioneering study on the electrical properties of composite carbon nanofibres (CNFs) using current-sensitive atomic force microscopy (CS-AFM) has been demonstrated.
In the present study, DOPO-based alkoxysilane (DOPO-ETES) and amido alkoxysilane (DOPO-AmdPTES) were synthesized by one-step and without by-products as halogen-free flame retardants. The flame retardants were applied on cotton fabric utilizing sol–gel method and pad-dry-cure finishing process. The flame retardancy, the thermal stability and the combustion ehaviour of treated cotton were evaluated by surface and bottom edge ignition flame test (according to EN ISO 15025), thermogravimetric analysis (TGA) and micro-scale combustion calorimeter (MCC). Unlike CO/DOPO-ETES sample, cotton treated with DOPO-AmdPTES nanosols exhibits self-extinguishing ehaviour with high char residue, an improvement of the LOI value and a significant reduction of the PHRR, HRC and THR compared to pristine cotton. Cotton finished with DOPO-AmdPTES reveals a semi-durability after ten laundering cycles keeping the flame-retardant properties unchanged. According to the results obtained from TGA-FTIR, Py-GC/MS and XPS, the major activity of flame retardant occurs in the condensed phase via catalytic induced char formation as physical barrier along with the activity in the gas phase derived mainly from the dilution effect. The early degradation of CO/DOPO-AmdPTES compared to CO/DOPO-ETES, triggered by the cleavage of the weak bond between P and C=O, as the DFT study indicated, provides the beneficial effect of this flame retardant on the fire resistance of cellulose.
Graphical abstract
Nylon-cotton textile blends (Nyco) are known to be challenging
substrates regarding their flame-retardant functionalization and its
durability. In this study, two different water-soluble flame retardants
based on cyclophosphazene together with glycerol (GlyCPZ) and thioglycerol
(ThioGlyCPZ) were synthesized enabling a waterborne finishing for
Nyco. An extensive investigation of the flame-retardant performance
and mechanism as well as the washing fastness was conducted. Thermogravimetric
analysis (TGA) indicated changed degradation mechanisms for treated
samples, which resulted in a reduced heat release capacity in microscale
combustion calorimetry (MCC) measurements and an increased char yield.
As a consequence, the limiting oxygen index (LOI) was enhanced from
20% for pure Nyco to 23% and 27.5% for GlyCPZ and ThioGlyCPZ, respectively.
Also, the standardized flammability test according to ISO 15025 was
passed. In addition, self-extinguishing characteristics were observed
even after 10 washing cycles at 80 °C confirming the durability
of the finishing. Sulfur was found to be gas phase active, as recombined
sulfur compounds were identified in pyrolysis gas chromatography mass
spectrometry (Py-GC/MS). Phosphorus was mainly active in the condensed
phase, which was verified by analyses of digested burned textile samples
using inductively coupled optical emission spectroscopy (ICP-OES).
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