Thermal and calorimetric evaluations of some bio-inspired fire-resistant coatings for ligno-cellulosic materials

Through the current project, we have investigated the passive fire protection efficiency of some bio-inspired substrates, which included: β-cyclodextrin, dextran, potato starch, agar agar, tamarind, chitosan, rice bran and fish gelatin. In an attempt to enhance the passive fire protection attributes of these substrates, we prepared formulations of these with both inorganic and organic compounds, the latter included some phosphorus-containing compounds with the phosphorus atom in different chemical environments and oxidation states. Here we have also explored both the reactive and additive strategies. The degrees of functionalization were primarily gauged from inductively-coupled plasma/optical emission spectroscopy (ICP-OES), 31P solid-state Nuclear Magnetic Resonance Spectroscopy (NMR). We also chose several thermal and calorimetric techniques for evaluating the efficacies of such formulations, such as: thermo-gravimetric analysis (TGA), pyrolysis combustion flow calorimetry (PCFC), a proprietary ignition propensity test and cone calorimetry. In addition, with a view to deciphering the elements of condensed phase mechanism, we carried out an estimation of the extents of phosphorus retention in the char residues (using ICP-OES) and chemical nature of the char residues (via solid-state NMR and Raman spectroscopies) that were obtained through the cone calorimetric runs. The unmodified counterparts were also subjected to the same set of analyses with a view to serving as controls. We also endeavoured to analyse the gaseous volatile fragments emanating from some of the additives using, either by employing gas chromatography/mass spectrometry (GC/MS), or pyrolysis-GC/MS, technique. Phosphorus analyses, primarily, through ICP-OES on the recovered samples showed different degrees of incorporation. Such observations were verified through solid-state 31P NMR spectroscopy. The thermograms of the modified substrates were noticeably different from the unmodified counterparts, both in terms of the general profiles and the amounts of char residues produced. Such observations correlated well with the relevant parameters obtained through the PCFC runs. Furthermore, we have carried out a detailed kinetic analyses of the thermograms of the unmodified substrates, obtained at different heating rates, using the Flynn Wall Ozawa (FWO) method, and through a proprietary software developed by our research group (SB method). We have also endeavoured to seek correlations, if any, among the various empirical parameters that were collated through the different test methods. Overall, the modified systems containing phosphorus were found to be less combustible than the parent substrates, and thus can be considered as promising base matrices for environmentally-benign fire resistant coatings. With a view to understanding the overall flammability profiles, optionally, in some of the formulations, initially we screened them through an ignitability propensity test that was developed in our laboratories. This was followed by cone calorimetric measurements on Radiata Pine plaques, particularly, coated with potato starch, chitosan, chitin, rice bran and fish gelatin. The results from the cone tests indicated that formulations based on fish gelatin endowed with the best fire protection property, followed by chitosan, whereas potato starch and rice bran seem to be ineffective as fire proofing agents.