Abstract
In the present article, we report on the chemical modifications of some carbohydrate-based substrates, such as potato starch, dextran, β-cyclodextrin, agar agar and tamarind, by reacting with diethylchlorophosphate (DECP), in dispersions in dichloromethane (DCM), in the presence of triethylamine (TEA) as the base. The modified substrates, after recovery and purification, were analyzed for their chemical constitutions, thermal stabilities and calorimetric properties using a variety of analytical techniques. These included: solid-state 31P NMR, inductively coupled plasma-optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA) and pyrolysis combustion flow calorimetry (PCFC). The unmodified counterparts were also subjected to the same set of analyses with a view to serving as controls. Phosphorus analyses, primarily through ICP-OES on the recovered samples, showed different degrees of incorporation. Such observations were optionally 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 PCFC runs. Overall, the modified systems containing phosphorus were found to be less combustible than the parent substrates, and thus can be considered as promising matrices for environmentally benign fire-resistant coatings.
Highlights
Much attention has been paid to the development of bio-degradable, carbohydrate-based materials, mainly owing to rising environmental concerns spurred by an overdependence on petro-chemically derived raw materials and polymers [1,2,3]
Several studies have been carried out to improve the flame-retardant efficacies of these materials, including surface modification, impregnation, and chemical modification to functionalize the hydroxyl groups of the base glucose units [4,5,6]
The carbohydrate-based materials selected for the current study included potato starch, dextran, β-cyclodextrin and agar agar, which were obtained from Aldrich Chemical Company, Melbourne, Victoria, Australia, whereas tamarind kernel powder was sourced locally (Figure 1)
Summary
Much attention has been paid to the development of bio-degradable, carbohydrate-based materials, mainly owing to rising environmental concerns spurred by an overdependence on petro-chemically derived raw materials and polymers [1,2,3]. Several studies have been carried out to improve the flame-retardant efficacies of these materials, including surface modification, impregnation, and chemical modification to functionalize the hydroxyl groups of the base glucose units [4,5,6]. In this context, our long-term interest is to use Polymers 2020, 12, 588; doi:10.3390/polym12030588 www.mdpi.com/journal/polymers. Keglevich et al established that multiple phosphorylation reactions were possible with different propensities, and the amount of phosphorylation was found to occur predominantly in positions 6 and 3 [7,11]. Muhammad et al reported on the influence of pH on the degree and nature of phosphorylation of a starch substrate [10]
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