Abstract
In this paper, bioinspired polyamidoamines (PAAs) were synthesized from N,N′-methylenebisacrylamide and nine natural α-amino acids: L-alanine, L-valine, L-leucine (M-LEU), L-histidine, L-serine, L-asparagine, L-glutamine (M-GLN), L-aspartic acid and L-glutamic acid (M-GLU) and their performance as flame retardants (FRs) for cotton were determined. The aim was to ascertain if the ability to protect cotton from fire by the process of intumescing, previously found for the glycine-derived M-GLY, was a general feature of α-amino acid-derived PAAs. None of the PAAs ignited by flame impingement, apart from M-LEU, which burned for a few seconds leaving 93% of residue. All of them formed carbon- and oxygen-rich, porous chars with a graphitic structure in the air at 350 °C, as revealed by X-ray photoelectron spectroscopy. All samples were tested as FRs for cotton by horizontal flame spread tests. At a 5% add-on, M-GLU and M-GLN extinguished the flame. The same results were obtained with all the other PAAs at a 7% add-on. The α-amino acid residues influenced the FR performance. The most effective were those that, by heating, were most suitable for producing thermally stable cyclic aromatic structures. All PAA-treated cotton samples, even when burning, left significant residues, which, according to scanning electron microscopy analysis, maintained the original cotton texture.
Highlights
A library of nine PAAs was prepared by the aza-Michael polyaddition of N,N 0 methylenebisacrylamide (MBA) with L-alanine (M-ALA), L-valine (M-VAL), L-leucine (M-LEU), L-histidine (M-HIS), L-serine (M-SER), L-asparagine (M-ASN), L-glutamine (MGLN), L-aspartic acid (M-ASP), and L-glutamic acid (M-GLU), as previously reported [9]
All products were used with no further purification as, after having been purified by ultrafiltration, they showed no different flame retardants (FRs) performance compared to the raw products
The aim of this work was to ascertain whether the ability of intumescing under the effect of oxygen and heating, and to act as efficient flame retardant, were general features of the PAAs derived from α-amino acids or were limited to a few of them
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The aza-Michael polyaddition of prim- or bis-sec-amines with bisacrylamides leads to a family of multifunctional polymers named polyamidoamines (PAAs) [1,2,3,4]. The polymerization reaction is favored by protic solvents and is highly specific. A few chemical functions other than amines, such as thiols and phosphines, can interfere with the polymerization reaction. Many other chemical functions can be introduced in PAAs as side substituents and this whole class is highly versatile. PAAs can be designed to be biocompatible; they have been extensively studied for biotechnological applications [5,6]
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