Advanced Flame Retardant Materials

Recent disasters caused by the spread of fire in buildings and in transportations remind us of the importance of fire protection. Using flame-retardant materials is one important element of the firefighting strategy, which aims to prevent fire development and propagation. These materials are used in different applications, such as in textiles, coatings, foams, furniture, and cables. The development of more efficient and environmentally friendly flame-retardant additives is an active multidisciplinary approach that has attracted a great deal of interest. Studies have aimed at the development of new, sustainable, and flame-retardant additives/materials, providing high performance and low toxicity. Also studied were their properties during ageing and recycling, as well as modeling physical and chemical processes occuring before ignition and during their combustion. The development of sustainable flame retardants and understanding their modes of action provide a strong link between these topics and cover many fields from organic chemistry, materials engineering, and toxicology, to physics and mathematics

Lignin Nanoparticles as A Promising Way for Enhancing Lignin Flame Retardant Effect in Polylactide

International audienceThe present study investigates the effect of using lignin at nanoscale as new flame-retardant additive for polylactide (PLA). Lignin nanoparticles (LNP) were prepared from Kraft lignin microparticles (LMP) through a dissolution-precipitation process. Both micro and nano lignins were functionalized using diethyl chlorophosphate (LMP-diEtP and LNP-diEtP, respectively) and diethyl (2-(triethoxysilyl)ethyl) phosphonate (LMP-SiP and LNP-SiP, respectively) to enhance their flame-retardant effect in PLA. From the use of inductively coupled plasma (ICP) spectrometry, it can be considered that a large amount of phosphorus has been grafted onto the nanoparticles. It has been previously shown that blending lignin with PLA induces degradation of the polymer matrix. However, phosphorylated lignin nanoparticles seem to limit PLA degradation during melt processing and the nanocomposites were shown to be relatively thermally stable. Cone calorimeter tests revealed that the incorporation of untreated lignin, whatever its particle size, induced an increase in pHRR. Using phosphorylated lignin nanoparticles, especially those treated with diethyl (2-(triethoxysilyl)ethyl) phosphonate allows this negative effect to be overcome. Moreover, the pHRR is significantly reduced, even when only 5 wt% LNP-SiP is used

Recycled tire rubber in additive manufacturing: selective laser sintering for polymer-ground rubber composites

peer reviewe

Lignin as a flame retardant for biopolymers

peer reviewedVery recently, China and India as the game changers of the world producing million tons of greenhouse gases have promised to invest up to 35% of their gross domestic product on global climate change before 2030. In line with such green policies, but starting more than 3 decades ago, research centers active in the field of materials sciences and engineering and those working on the development of flame retardants for polymers have been advised by the governments to switch from halogen-based to sustainable flame retardants. Bio-based flame retardants rapidly proved obvious candidates for this purpose, but to display adequate flame retardancy, they require physical and/or chemical modification. Lignin is a versatile biodegradable polymer, which has been widely applied as a part of flame retardant systems in polymers. There is a plethoric number of works on lignin-based flame retardants and flame retardancy of lignin-incorporated polymer systems. This chapter aims at reporting and classifying these works on flame retardancy of unmodified and modified lignin and its "sister", i.e., nanolignin, as flame retardant additives for polymer systems

Engineering Polypropylene-Calcium Sulfate (Anhydrite II) Composites: The Key Role of Zinc Ionomers via Reactive Extrusion.

peer reviewedPolypropylene (PP) is one of the most versatile polymers widely used in packaging, textiles, automotive, and electrical applications. Melt blending of PP with micro- and/or nano-fillers is a common approach for obtaining specific end-use characteristics and major enhancements of properties. The study aims to develop high-performance composites by filling PP with CaSO4 β-anhydrite II (AII) issued from natural gypsum. The effects of the addition of up to 40 wt.% AII into PP matrix have been deeply evaluated in terms of morphology, mechanical and thermal properties. The PP-AII composites (without any modifier) as produced with internal mixers showed enhanced thermal stability and stiffness. At high filler loadings (40% AII), there was a significant decrease in tensile strength and impact resistance; therefore, custom formulations with special reactive modifiers/compatibilizers (PP functionalized/grafted with maleic anhydride (PP-g-MA) and zinc diacrylate (ZnDA)) were developed. The study revealed that the addition of only 2% ZnDA (able to induce ionomeric character) leads to PP-AII composites characterized by improved kinetics of crystallization, remarkable thermal stability, and enhanced mechanical properties, i.e., high tensile strength, rigidity, and even rise in impact resistance. The formation of Zn ionomers and dynamic ionic crosslinks, finer dispersion of AII microparticles, and better compatibility within the polyolefinic matrix allow us to explain the recorded increase in properties. Interestingly, the PP-AII composites also exhibited significant improvements in the elastic behavior under dynamic mechanical stress and of the heat deflection temperature (HDT), thus paving the way for engineering applications. Larger experimental trials have been conducted to produce the most promising composite materials by reactive extrusion (REx) on twin-screw extruders, while evaluating their performances through various methods of analysis and processing

Natural Cellulose from Ziziphus jujuba Fibers: Extraction and Characterization.

peer reviewedNowadays, due to their natural availability, renewability, biodegradability, nontoxicity, light weight and relatively low cost, natural fibers, especially lignocellulosic fibers, present attractive potential to substitute non-eco-friendly synthetic fibers. In this study, Ziziphus jujuba fibers were used, thanks to their low lignin content, as an alternative of renewable resource for the production of cellulosic fibers with suitable characteristics and minimal time and energy consumption. In fact, due to their valuable chemical composition, it was possible to remove the amorphous fractions and impurities from the fiber surface by applying ultrasounds coupled with alkaline treatment (80 °C, 5 wt.% NaOH), followed by a bleaching step. The efficient dissolution of the noncellulosic compounds was confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The resulted increase in the crystallinity index (from 35.7% to 57.5%), occurred without impacting the crystalline structure of the fibers. The morphological analysis of the fibers evidences the higher surface area of the obtained fibers. Based on the obtained results, Ziziphus jujuba fibers were found to present a suitable sustainable source for the production of cellulosic fibers

Fire retardant behaviour of halogen-free calcium-based hydrated minerals

peer reviewe

Recent Advances in Production of Ecofriendly Polylactide (PLA)-Calcium Sulfate (Anhydrite II) Composites: From the Evidence of Filler Stability to the Effects of PLA Matrix and Filling on Key Properties.

peer reviewedThe melt-mixing of polylactide (PLA) with micro- and/or nanofillers is a key method used to obtain specific end-use characteristics and improvements of properties. So-called "insoluble" CaSO4 (CS) β-anhydrite II (AII) is a mineral filler recently considered for the industry of polymer composites. First, the study proves that AII made from natural gypsum by a specifically thermal treatment is highly stable compared to other CS forms. Then, PLAs of different isomer purity and molecular weights (for injection molding (IM) and extrusion), have been used to produce "green" composites filled with 20-40 wt.% AII. The composites show good thermal and mechanical properties, accounting for the excellent filler dispersion and stability. The stiffness of composites increases with the amount of filler, whereas their tensile strength is found to be dependent on PLA molecular weights. Interestingly, the impact resistance is improved by adding 20% AII into all investigated PLAs. Due to advanced kinetics of crystallization ascribed to the effects of AII and use of a PLA grade of high L-lactic acid isomer purity, the composites show after IM an impressive degree of crystallinity (DC), i.e., as high as 50%, while their Vicat softening temperature is remarkably increased to 160 °C, which are thermal properties of great interest for applications requiring elevated rigidity and heat resistance

Tailoring and Long-Term Preservation of the Properties of PLA Composites with "Green" Plasticizers.

peer reviewedConcerning new polylactide (PLA) applications, the study investigates the toughening of PLA-CaSO4 β-anhydrite II (AII) composites with bio-sourced tributyl citrate (TBC). The effects of 5-20 wt.% TBC were evaluated in terms of morphology, mechanical and thermal properties, focusing on the enhancement of PLA crystallization and modification of glass transition temperature (Tg). Due to the strong plasticizing effects of TBC (even at 10%), the plasticized composites are characterized by significant decrease of Tg and rigidity, increase of ductility and impact resistance. Correlated with the amounts of plasticizer, a dramatic drop in melt viscosity is also revealed. Therefore, for applications requiring increased viscosity and enhanced melt strength (extrusion, thermoforming), the reactive modification, with up to 1% epoxy functional styrene-acrylic oligomers, was explored to enhance their rheology. Moreover, larger quantities of products were obtained by reactive extrusion (REX) and characterized to evidence their lower stiffness, enhanced ductility, and toughness. In current prospects, selected samples were tested for the extrusion of tubes (straws) and films. The migration of plasticizer was not noted (at 10% TBC), whereas the mechanical and thermal characterizations of films after two years of aging evidenced a surprising preservation of properties