Durable graphite oxide nanocoating for high performing flame retarded foams

Recent developments in the design of water-based coatings encompassing platelet-like nanoparticles have clearly demonstrated the flame retardant potential of this approach for open cell flexible foams. However, the relatively high number of deposition steps required and the limited reports on the durability of the deposited coatings to multiple compression cycles currently represent the main constraints to this approach. This paper addresses these limitations by exploiting a few steps deposition procedure to produce coatings with durable flame retardant properties. Graphite oxide, sodium alginate and sodium hexametaphosphate were combined in a continuous protective coating that extends to the complex three-dimensional structure of the foam. The flame retardant properties of the coatings were evaluated before and after 1000 compression cycles. Even after such multiple deformations, the coated foams showed no melt dripping and self-extinguishment during flammability tests, as well as a highly reduced heat release rates (-70%) and total smoke release (-70%) during cone calorimetry tests. Furthermore, the ability to withstand the penetration of an impinging flame focused on one side of the coated foam for more than 5 min was also maintained. These results clearly demonstrate the durability of the coated foams, opening to real life application fields such as transports seats where high levels of flame retardancy must be maintained for long time under frequent mechanical stress

Green and Fire Resistant Nanocellulose/Hemicellulose/Clay Foams

Lightweight polymer foams from synthetic polymers are commonly used in a wide-spread spectrum of application fields. Their intrinsic flammability coupled with restrictions on flame retardant chemicals poses a severe threat to safety. Here, fire resistant foams comprising biobased components capable of replacing petroleum-based foams are investigated. Cellulose nanofibers are combined with 2D montmorillonite nanoplatelets and a native xyloglucan hemicellulose binder, using a water-based freeze casting approach. Due to the silicate nanoplatelets, these lightweight foams self-extinguish the flame during flammability tests. The limiting oxygen index is as high as 31.5% and in the same range as the best fire-retardant synthetic foams available. In cone calorimetry, the foams display extremely low combustion rates. Smoke release is near the detection limit of the instrument. In addition, the foams are withstanding the penetration of a flame torch focused on one side of the specimen (T on surface 800 °C) and structural integrity is maintained. At the same time, the unexposed side is insulated, as demonstrated by a through-thickness temperature drop of 680 °C cm−1. The results represent a tremendous opportunity for the development of fire-safe foams combining excellent sustainability with multifunctional performance

Linear Polyamidoamines as Novel Biocompatible Intumescent Flame Retardants for Cotton

Since the middle of the last century, many industrial and academic researchers have devoted a lot of effort to the development of safe and effective flame- retardants (FR). As regards cotton, phosphorylated compounds were the predominant FR for several decades [1] despite many of them had been shown to be bioaccumulative.[1] Recently, biomolecules including proteins have been proposed as FR.[2] Many linear polyamidoamines (PAAs), a family of synthetic polymers with exceptional structural versatility,[3] have high thermal stability coupled with chain structure and side substituents reminding those of proteins.[4] These features suggested that PAAs could act as FR. This presentation reports on the results obtained with a library of eight PAAs applied as coatings on cotton fabrics from aqueous solutions. All tested PAAs warrant remarkable potential as surface-confined intumescent FR. In ignitability tests, six of them exposed to direct flame for 10 s do not burn, but produce carbonaceous crusts sheltering the underneath sample. Thermogravimetric analyses show that at T 65 400 \ub0C all PAAs leave in air substantial char residues that oxidize at T > 500 \ub0C. At 450 \ub0C they form porous carbonaceous structures indicating the tendency to intumesce. In horizontal flame spread tests, cotton stripes impregnated with most PAAs extinguish flame at add-ons ranging from 4 to 20%, whereas untreated cotton vigorously burns without leaving residues. Upon 35 kW/m2 heat flux, all PAA-treated samples significantly reduce the main combustion parameters. References [1] R. A. Horrocks, Polym. Degrad. Stab. 2011, 96, 377. [2] L. Costes, F. Laoutid, S. Brohez, P. Dubois, Mater. Sci. Eng. Report, R. 2017, 117, 1. [3] P. Ferruti, J. Polym. Sci, Part A: Polym. Chem. 2013, 51, 2319. [4] F. Danusso, P. Ferruti, Polymer 1970, 11, 88

CFD Modeling of a Laboratory-Scale Setup for Thermochemical Materials Performance Analysis

The search for energy saving is nowadays mandatory because of the constant growth of CO2 emissions caused by an inefficient energy management. Thermal Energy Storage (TES) has an important role in designing of energy efficient systems, including solar energy storage (daily or seasonal) and waste heat from industrial batch processes. Different solutions are possible for thermal storage, based on sensible heat (e.g. water tanks), latent heat (phase change materials) or reaction enthalpy (thermochemical systems). In Thermochemical TES, a material is chosen so that it shows a high-enthalpy reversible chemical reaction at a desired temperature. In particular, water sorption in some inorganic salt hydrates is pointed out as one of the most suitable reactions for low temperature energy storage (60-120 °C). The reaction products, water and salt in a less hydrated form, are kept separated and consequently the heat is stored. Energy release is obtained with salt hydration. The main advantages are an energy storage capacity higher than other TES technologies and the possibility to control the energy release. On the other hand, one of the main issues is the difficulty to test materials performance, because standard characterization techniques use small amount of samples and their properties change dramatically when the system is scaled up to large reactors. The aim of this work is to realize a laboratory scale setup to test the performance of salt hydrate composites. A scheme of the system is reported in the attached figure (above). The active material is kept in an evaporator at a temperature sufficient to generate the dehydration reaction. Extracted water mass is measured in time in a condenser at 0°C. Air flow, temperature and humidity are measured with sensors in the system. The system was simulated using COMSOL® software. In particular the simulation was inspired by two models from the Application Library, Degradation of DNA in Plasma and Protein Adsorption. At first, a zero dimensional component was created with the Reaction Engineering module with two reactions to evaluate both the dehydration and condensation steps: H2Ocry->H2Ovap H2Ovap->H2Oliq Where H2Ocry is the crystallization water in the salt hydrate, H2Ovap is the air humidity and H2Oliq is the condensed water. Using a Parameter Estimation module, experimental data about dehydration were imported in the software and used to estimate the reactions kinetics constants. After that, using a Generate Space Dependent Model module we obtained a 3D component with a realistic system geometry (see attached figure below) including the modules Chemistry, Transport of Diluted Species, Surface Reactions, Heat transfer in Fluids and Single Phase Laminar Flow. Rate constants calculated in the zero-dimension model were used as first guess for the 3D model reactions. We verified that the model is able to evaluate temperature, flow and water concentration as well as the evolution of the two reactions in time. We expect that this model will allow us to classify different Thermochemical TES materials about their efficiency in heat and mass exchange, as well as to refine the design of the thermal storage system

Sulfur-based copolymeric polyamidoamines as efficient flame-retardants for cotton

The polyamidoamine derived from N,N'-methylenebisacrylamide (M) and glycine (G), M-G, has been shown to be an effective flame-retardant (FR) for cotton in horizontal flame spread tests (HFST), extinguishing the flame at 5% add-on. Its activity was attributed to its intrinsic intumescence. In vertical flame spread tests (VFST), M-G failed to extinguish the flame even at 30% add-on. Conversely, in VFST, the polyamidoamine derived from M and cystine (C), M-C, inhibited cotton combustion at 16% add-on, but in HFST failed to extinguish the flame below 12% add-on. Its activity was ascribed to the release of sulfur-containing volatiles acting as radical scavengers. In this work, the FR effectiveness of M-Gm-Cn copolymers with different G/C ratio was compared with that of the M-G and M-C homopolymers and of M-G/M-C blends of the same compositions. In HFST, both copolymers and blends extinguished the flame. In particular, M-G50-C50 and (M-G/M-C)50/50 extinguished the flame, even at 7% add-on. In VFST, the copolymers with 6550% M-C units, similar to M-C, inhibited cotton combustion at 16% add-on. At the same add-on, the M-G/M-C blends failed to extinguish the flame. It may be concluded that, in contrast to blends, copolymers combined the merits of both homopolymers in all tests

Flame retardant multilayered coatings on acrylic fabrics prepared by one-step deposition of chitosan/montmorillonite complexes

Multilayered coatings deposited using the layer-by-layer (LbL) assembly technique have attracted great interest in recent years as a sustainable and efficient solution for conferring flame retardant properties to fabrics. The unique structure and interaction established upon the coating assembly are the key factors for successful flame retardant properties. In this study we aimed at the deposition of multilayered coatings comprising chitosan and montmorillonite with a LbL-like structure and interactions by the simple processing of compacted chitosan/montmorillonite complexes obtained by the direct mixing of an oppositely charged solution/suspension. Upon drying, the prepared complex yielded a continuous coating characterized by a brick-and-mortar multi-layered structure, in which oriented clay nanoplatelets were held together by a continuous chitosan matrix. When deposited on acrylic fabrics these coatings were able to suppress the melt-dripping phenomenon, and at 10 and 20% add-ons achieved self-extinguishing behavior within a few seconds after ignition. Cone calorimetry testing revealed an increase in time to ignition (up to +46%) and considerable reductions of the rates at which heat is released (up to -62 and -49% for peak of heat release rate and total heat release, respectively). A reduction in the total smoke release (up to -49%) was also observed

Polyamidoamines derived from natural α-amino acids as effective flame retardants for cotton

In this paper, bioinspired polyamidoamines (PAAs) were synthesized from N,N′-methylene bisacrylamide 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

Polyelectrolyte-coated mesoporous bioactive glasses via layer-by-layer deposition for sustained co-delivery of therapeutic ions and drugs

In the field of bone regeneration, considerable attention has been addressed towards the use of mesoporous bioactive glasses (MBGs), as multifunctional therapeutic platforms for advanced medical devices. In fact, their extremely high exposed surface area and pore volume allow to load and the release of several drugs, while their framework can be enriched with specific therapeutic ions allowing to boost the tissue regeneration. However, due to the open and easily accessible mesopore structure of MBG, the release of the incorporated therapeutic molecules shows an initial burst effect leading to unsuitable release kinetics. Hence, a still open challenge in the design of drug delivery systems based on MBGs is the control of their release behavior. In this work, Layer-by-layer (LbL) deposition of polyelectrolyte multi-layers was exploited as a powerful and versatile technique for coating the surface of Cu-substituted MBG nanoparticles with innovative multifunctional drug delivery systems for co-releasing of therapeutic copper ions (exerting pro-angiogenic and anti-bacterial effects) and an anti-inflammatory drug (ibuprofen). Two different routes were investigated: in the first strategy, chitosan and alginate were assembled by forming the multi-layered surface, and, successively, ibuprofen was loaded by incipient wetness impregnation, while in the second approach, alginate was replaced by ibuprofen, introduced as polyelectrolyte layer. Zeta-potential, TGA and FT-IR spectroscopy were measured after the addition of each polyelectrolyte layer, confirming the occurrence of the stepwise deposition. In addition, the in vitro bioactivity and the ability to modulate the release of the cargo were evaluated. The polyelectrolyte coated-MBGs were proved to retain the peculiar ability to induce hydroxyapatite formation after 7 days of soaking in Simulated Body Fluid. Both copper ions and ibuprofen were co-released over time, showing a sustained release profile up to 14 days and 24 h, respectively, with a significantly lower burst release compared to the bare MBG particles

Superior flame retardancy of cotton by synergetic effect of cellulose-derived nano-graphene oxide carbon dots and disulphide-containing polyamidoamines

Linear polyamidoamines containing disulphide groups (SS-PAAs) were prepared by polyaddition of L-cystine with 2,2-bisacrylamidoacetic acid (B-CYSS), N,N\u2032-methylenebisacrylamide (M-CYSS) and 1,4-bisacryloylpiperazine (BP-CYSS). They were evaluated as flame retardants for cotton, alone or with cellulose-derived nano-graphene oxide (nGO) carbon dots, to assess whether, due to their potential as radical scavengers, the latter would improve the already good performance of SS-PAAs. In vertical flame spread tests (VFST), cotton treated with 1% nGO burned as quickly as cotton, whereas B-CYSS, M-CYSS and BP-CYSS extinguished the flame at add-ons 65 12, 16 and 20%, respectively. Probably, the gaseous products of SS-PAA thermal degradation quenched the radicals involved in oxidation. Cotton treated with 8, 12 and 15%, respectively, of B-CYSS, M-CYSS and BP-CYSS burned completely, but further addition of 1% nGO either inhibited ignition or shortly extinguished the flame, demonstrating synergism between the two components. Synergism was confirmed by assessing the synergism effectiveness parameter for the residual mass fraction (RMF) and by comparing the calculated and experimental TG curves in air for the cotton/SS-PAA-nGO systems. In cone calorimetry tests, the presence of nGO did not improve the already good performances of SS-PAAs, supporting the hypothesis that the action of both takes place in the gas phase

The thermo-oxidative behavior of cotton coated with an intumescent flame retardant glycine-derived polyamidoamine: A multi-technique study

Linear polyamidoamines (PAAs) derived from the polyaddition of natural α-amino acids and N,N′-methylene bis(acrylamide) are intumescent flame retardants for cotton. Among them, the glycine-derived M-GLY extinguished the flame in horizontal flame spread tests at 4% by weight add-on. This paper reports on an extensive study aimed at understanding the molecular-level transformations of M-GLY-treated cotton upon heating in air at 300◦C, 350◦C and 420◦C. Thermogravimetric analysis (TGA) identified different thermal-oxidative decomposition stages and, coupled to Fourier transform infrared spectroscopy, allowed the volatile species released upon heating to be determined, revealing differences in the decomposition pattern of treated and untreated cotton. XPS analysis of the char residues of M-GLY-treated cotton revealed the formation of aromatic nanographitic char at lower temperature with respect to untreated cotton. Raman spectroscopy of the char residues provided indications on the degree of graphitization of treated and untreated cotton at the three reference temperatures. Solid state13C nuclear magnetic resonance spectroscopy (NMR) provided information on the char structure as a function of the treatment temperature, clearly indicating that M-GLY favors the carbonization of cotton with the formation of more highly condensed aromatic structures