BIOINSPIRED POLYAMIDOAMINES AS INNOVATIVE FLAME RETARDANTS FOR CELLULOSIC FABRICS

In the three years of my PhD course, I focused my attention and efforts onto 5 research lines: 1. Polyamidoamines derived from natural a-amino acids as effective flame retardants for cotton fabrics; 2. Study of the polyamidoamine decomposition products upon heating; 3. Phosphorous-sulphur-based polyamidoamines as flame retardants for cotton fabrics; 4. Study of the synergism between a-aminoacid derived-polyamidoamines and sodium montmorillonite for enhancing the flame retardancy of cotton fabrics; 5. Study of a novel approach for investigating the flame retardancy of upholstery materials. 1. This project was carried out in collaboration with Prof. Federico Carosio of Politecnico di Torino In this work, bioinspired polyamidoamines (PAAs) were synthesized by Michael-type polyaddition from N,N’-methylenebisacrylamide, M, and nine natural α-amino acids, namely 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 (M-GLN), L-aspartic acid (M-ASP) and L-glutamic acid (M-GLU) and their performance as flame retardants (FRs) for cotton determined. The aim of this work was to establish if the ability to protect cotton from fire by intumescing mechanism, previously observed for the glycine-derived, M-GLY, was a general feature of α-amino acid-derived PAAs. The intumescence is the ability of a material to swell when it is subjected to heating; a thermally stable carbonaceous structure (char) is formed on the surface, and it behaves as a physical barrier reducing the heat, mass and oxygen transfer to the substrate below. 2. This project was carried out in collaboration with Dr. Claudia Forte of CNR of Pisa, Istituto di Chimica dei Compositi Organometallici The aim of this research is to study the decomposition products of polyamidoamines upon heating, when PAAs are used as flame retardants. This work is divided in two different parts, the first one is focused on studying the release of volatile species using a TGA microbalance coupled with infrared spectroscopy (TG-IR), while the second one regards the study of PAA condensed phase using different analytical techniques, X-ray Photoelectron (XPS), Raman spectroscopies and Solid-State Nuclear Magnetic Resonance (SS-NMR). 3. This project was carried out in collaboration with Prof. Domenico Albanese of Università degli Studi di Milano. In a previous work, cystine-derived PAAs synthesized by N,N’-methylenebisacrylamide, M, and L-cystine, CYSS, coded as M-CYSS, was found to impart flame retardant properties to cotton fabrics in HFSTs thanks to its ability to act as radical scavenger in the gas phase, interrupting cotton self-sustained combustion. Phosphorous compounds were widely used to substitute some bromine derivatives; in fact, they can work in the condensed phase, increasing the amount of the char residue formed at elevated temperatures. In this context, a new monomer containing both sulphur and phosphorus, coded as PCASS, was used as monomer in a synthesis with the N,N’-methylenebisacrylamide and the resulting polymers, coded as M-PCASS, were tested in HFSTs. 4. This project was carried out in collaboration with Prof. Federico Carosio of Politecnico di Torino Previous research found PAAs derived from α-amino acids effective in extinguishing cotton combustion, but they struggled with vertical flame spread tests. To address this limitation, researchers explored combining PAAs with inorganic nanoparticles like sodium montmorillonite (NaMMT) to enhance flame retardancy. The study aimed to investigate the interaction between PAAs derived from glycine, arginine, and glutamic acid and NaMMT on cotton fabric's thermal-oxidative stability and flame retardancy. In fact, NaMMT can easily interact with PAAs due to their amphoteric nature, as already demonstrated for tissue-engineering applications. 5. This work was carried out during my 6-month abroad stage in the National Institute of Standards and Technology (USA) under the supervision of Dr. Mauro Zammarano. In this work, some bioinspired PAAs, which have already shown their flame retardant (FR) abilities, were selected for being evaluated in a new cutting-edge test, named Cube test. In detail, six different PAAs were chosen, formed by N,N’-methylenebisacrylamide, M, and 6 different α-amino acids, namely L-glycine (M-GLY), L-arginine (M-ARG), L-glutamine (M-GLN) and L-glutamic acid (M-GLU). Furthermore, also the polymer synthesized from M and L-cystine (M-CYSS) and the copolymer M-GLY50-CYSS50 were identified for the work. The Cube test is a bench-scale test based on the oxygen-consumption cone calorimeter that has been developed at the NIST to capture the mass and heat transfer phenomena in a representative cross-section of a multi-component product including a flammable core, formed by a flexible polyurethane foam (FPUF) cube and superficial layers (i.e. cotton fabrics) that may act as fire barriers. This type of test wants to mimic a full-scale chair mock-up test, obtaining some important parameters without the building of a real armchair.