Halogen-free flame retardants for polymeric foams

Sunflower Oil as a Renewable Resource for Polyurethane Foams: Effects of Flame-Retardants

Currently, polyurethane (PU) manufacturers seek green alternatives for sustainable production. In this work, sunflower oil is studied as a replacement and converted to a reactive form through epoxidation and oxirane opening to produce rigid PU foams. Confirmatory tests such as Fourier-transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), and hydroxyl value among others were performed to characterize the synthesized polyol. Despite the versatility of rigid PU foams, they are highly flammable, which makes eco-friendly flame retardants (FRs) desired. Herein, expandable graphite (EG) and dimethyl methyl phosphonate (DMMP), both non-halogenated FR, were incorporated under different concentrations to prepare rigid PU foams. Their effects on the physio-mechanical and fire-quenching properties of the sunflower oil-based PU foams were elucidated. Thermogravimetric and compression analysis showed that these foams presented appreciable compressive strength along with good thermal stability. The closed-cell contents (CCC) were around 90% for the EG-containing foams and suffered a decrease at higher concentrations of DMMP to 72%. The burning test showed a decrease in the foam's flammability as the neat foam had a burning time of 80 s whereas after the addition of 13.6 wt.% of EG and DMMP, separately, there was a decrease to 6 and 2 s, respectively. Hence, our research suggested that EG and DMMP could be a more viable alternative to halogen-based FR for PU foams. Additionally, the adoption of sunflower polyol yielded foams with results comparable to commercial ones.

It Takes Two to Tango: Synergistic Expandable Graphite–Phosphorus Flame Retardant Combinations in Polyurethane Foams

Due to the high flammability and smoke toxicity of polyurethane foams (PUFs) during burning, distinct efficient combinations of flame retardants are demanded to improve the fire safety of PUFs in practical applications. This feature article focuses on one of the most impressive halogen-free combinations in PUFs: expandable graphite (EG) and phosphorus-based flame retardants (P-FRs). The synergistic effect of EG and P-FRs mainly superimposes the two modes of action, charring and maintaining a thermally insulating residue morphology, to bring effective flame retardancy to PUFs. Specific interactions between EG and P-FRs, including the agglutination of the fire residue consisting of expanded-graphite worms, yields an outstanding synergistic effect, making this approach the latest champion to fulfill the demanding requirements for flame-retarded PUFs. Current and future topics such as the increasing use of renewable feedstock are also discussed in this article.

Effects of Expanded Graphite, Aluminum Hydroxide, and Kaolin on Flame Retardancy and Smoke Suppression of Polyurethane Composites

Polyurethane is a widely used polymer that has good abrasion resistance and low-temperature resistance. However, polyurethane composite materials are highly inflammable and thus require the use of flame retardants. This study selected green and environment-friendly flame retardants such as expanded graphite, aluminum hydroxide, and kaolin to be used as individual or paired retardants to produce polyurethane composites. By analyzing the potential and mechanical properties of the polyurethane composites, it was found that the composite material with the flame retardant composed of graphite and modified kaolin had better flame retardancy, smoke suppression performance, and high thermal stability.

Composites of Semi-Rigid Polyurethane Foams with Keratin Fibers Derived from Poultry Feathers and Flame Retardant Additives

Semi-rigid composites of polyurethane foams (SRPUF) modified with the addition of keratin flour from poultry feathers and flame retardant additives were manufactured. Ten percent by mass of keratin fibers was added to the foams as well as halogen-free flame retardant additives such as Fyrol PNX, expandable graphite, metal oxides, in amounts such that their total mass did not exceed 15%. Thermal and mechanical properties were tested. Water absorption, dimensional stability, apparent density and flammability of produced foams were determined. It was found that the use of keratin fibers and flame retardant additives changes the foam synthesis process, changes their structure and properties as well as their combustion process. The addition of the filler made of keratin fibers significantly limits the amount of smoke generated during foam burning. The most favorable reduction of heat and smoke release rate was observed for foams with the addition of 10% keratin fibers and 10% expandable graphite. Systems of reducing combustibility of polyurethane foams using keratin fillers are a new solution on a global scale.

Flame Retardancy of Biobased Composites-Research Development

Due to the thermal and fire sensitivity of polymer bio-composite materials, especially in the case of plant-based fillers applied for them, next to intensive research on the better mechanical performance of composites, it is extremely important to improve their reaction to fire. This is necessary due to the current widespread practical use of bio-based composites. The first part of this work relates to an overview of the most commonly used techniques and different approaches towards the increasing the fire resistance of petrochemical-based polymeric materials. The next few sections present commonly used methods of reducing the flammability of polymers and characterize the most frequently used compounds. It is highlighted that despite adverse health effects in animals and humans, some of mentioned fire retardants (such as halogenated organic derivatives e.g., hexabromocyclododecane, polybrominated diphenyl ether) are unfortunately also still in use, even for bio-composite materials. The most recent studies related to the development of the flame retardation of polymeric materials are then summarized. Particular attention is paid to the issue of flame retardation of bio-based polymer composites and the specifics of reducing the flammability of these materials. Strategies for retarding composites are discussed on examples of particular bio-polymers (such as: polylactide, polyhydroxyalkanoates or polyamide-11), as well as polymers obtained on the basis of natural raw materials (e.g., bio-based polyurethanes or bio-based epoxies). The advantages and disadvantages of these strategies, as well as the flame retardants used in them, are highlighted.

Anti-flammability, mechanical and thermal properties of bio-based rigid polyurethane foams with the addition of flame retardants

Adding efficient and environmentally friendly flame retardants to polyurethane foams is the preferable way to improve their flame resistance ability. In this work, bio-based rigid polyurethane foams (RPUFs) were prepared with the addition of dicyclohexyl aluminium hypophosphate (DAH) or aluminium diethyl phosphinate (ADP) as the flame retardant. The mechanical properties, thermal degradation and flammability behavior of the obtained RPUFs were evaluated by means of compressive strength tests, thermogravimetry analysis, vertical burning test and scanning electron microscopes. The characterization results indicate that, with the same content of flame retardant, the compressive strength at the deformation of 10% for each RPUF prepared with the addition of DAH is higher than that of the foams with ADP addition, which fully meets the specifications for building insulation materials. Moreover, the average flame height of each RPUF with the addition of flame retardants is less than 250 mm, whereas the average burning time of RPUF with 15 wt% addition of DAH is only 4.4 s, far less than that (12.5 s) of the foam with the same addition amount of ADP. The RPUFs with DAH addition have the potential advantages for thermal insulation applications in various fields.

Rigid polyurethane foams modified with borate and oxamide groups – Preparation and properties

In this work the results of the research on modification of rigid polyurethane foams properties by new polyols with borate and oxamide groups have been presented. Propylene glycols — the products of hydroxyalkylation of N,N′-bis(2-hydroxypropyl)oxamide bis(dihydrogenborate) by excess of propylene carbonate (PC) was used as a polyol component. The new polyols have been foamed using polymeric 4,4′-diphenylmethane diisocyanate, water and triethylamine. The modification of the foam structure by oxamide and borate groups guarantees their low water uptake, very good heat-insulating properties, good dimension stability and decreases their flammability, and does not worsen their mechanical properties and thermal stability.

Preparation of Flame-Retardant Rigid Polyurethane Foams by Combining Modified Melamine-Formaldehyde Resin and Phosphorus Flame Retardants

In this work, ethylene glycol-modified melamine-formaldehyde resin (EMF) was synthesized from ethylene glycol, paraformaldehyde, and melamine, and then rigid polyurethane foams (RPUFs) were prepared using EMF, polyols and polyisocyanate. The effects of ammonium polyphosphate (APP) and dimethyl methylphosphonate (DMMP) on the flame retardancy, mechanical properties, thermal stability, and morphology of the prepared RPUFs were studied. It is shown that the flame-retardant performance of EMF-filled RPUFs can be enhanced by the addition of APP and DMMP. Thus, APP and DMMP can synergistically improve the flame retardancy of RPUFs. APP has good smoke suppression, while DMMP can increase the total smoke production and CO/CO2 weight ratio during the combustion of RPUFs.

Structure and Flame-Retardant Actions of Rigid Polyurethane Foams with Expandable Graphite

In this paper, rigid polyurethane foams that were filled with expandable graphite (RPUF/EG) composites were prepared by the liquid blending method, and then the structure and flame retardancy performance of materials were investigated through optical microscope, scanning electron microscope, limit oxygen index, cone calorimeter, thermogravimetric analysis coupled to fourier transform infrared spectrum, and X-ray photoelectron spectroscopy. The results showed that a large number of EG could be good to the exhibition of flame retardancy of RPUF, where the optimal material was found at loading 15 phr EG that showed an increased limit oxygen index value and a decreased calorific or fuming value. TGA coupled FTIR and XPS revealed that EG could disassembled before RPUF under heating treatment, and it could form a pyknotic and enahnced residual carbon layer on RPUF surface after the fire, which restricted the transfer of gas, like oxygen or heat into PU matrix, finally resulting in the promotion of flame retardancy of RPUF.

Influence of the Characteristics of Expandable Graphite on the Morphology, Thermal Properties, Fire Behaviour and Compression Performance of a Rigid Polyurethane Foam

Three types of expandable graphite (EG) differing in particle size and expansion volume, are compared as flame retardant additives to rigid polyurethane foams (RPUFs). In this paper we discuss microstructure, thermal stability, fire behavior, and compression performance. We find that ell size distributions were less homogeneous and cell size was reduced. Furthermore, thermal conductivity increased along with EG loading. Thermogravimetric analysis (TGA) showed that EG only increased residue yield differently. The results indicate that a higher expansion of EG increased the limiting oxygen index (LOI) value, whereas a bigger particle size EG improved the rating of the vertical burning test (UL94). Results from the cone calorimeter test showed that a bigger particle size EG effectively reduced peak of heat release rate (pHRR). Furthermore, a higher expansion, led to a decrease in smoke production (TSP). The combination of both characteristics gives extraordinary results. The physical–mechanical characterization of the EG/RPUF foams revealed that their compression performance decreased slightly, mostly due to the effect of a bigger size EG.

Polyurethane Foams: Past, Present, and Future

Polymeric foams can be found virtually everywhere due to their advantageous properties compared with counterparts materials. Possibly the most important class of polymeric foams are polyurethane foams (PUFs), as their low density and thermal conductivity combined with their interesting mechanical properties make them excellent thermal and sound insulators, as well as structural and comfort materials. Despite the broad range of applications, the production of PUFs is still highly petroleum-dependent, so this industry must adapt to ever more strict regulations and rigorous consumers. In that sense, the well-established raw materials and process technologies can face a turning point in the near future, due to the need of using renewable raw materials and new process technologies, such as three-dimensional (3D) printing. In this work, the fundamental aspects of the production of PUFs are reviewed, the new challenges that the PUFs industry are expected to confront regarding process methodologies in the near future are outlined, and some alternatives are also presented. Then, the strategies for the improvement of PUFs sustainability, including recycling, and the enhancement of their properties are discussed.

Molecular Firefighting-How Modern Phosphorus Chemistry Can Help Solve the Challenge of Flame Retardancy

The ubiquity of polymeric materials in daily life comes with an increased fire risk, and sustained research into efficient flame retardants is key to ensuring the safety of the populace and material goods from accidental fires. Phosphorus, a versatile and effective element for use in flame retardants, has the potential to supersede the halogenated variants that are still widely used today: current formulations employ a variety of modes of action and methods of implementation, as additives or as reactants, to solve the task of developing flame-retarding polymeric materials. Phosphorus-based flame retardants can act in both the gas and condensed phase during a fire. This Review investigates how current phosphorus chemistry helps in reducing the flammability of polymers, and addresses the future of sustainable, efficient, and safe phosphorus-based flame-retardants from renewable sources.

Fire retardant sol–gel coatings for flexible polyurethane foams

Untreated flexible polyurethane foams used in upholstered products are prone to rapid fire growth. Sol–gel process was evaluated to flame retard it. A successful intumescent formulation gave 60% reduction of the peak of heat release rate.

Novel flame retardant flexible polyurethane foam: plasma induced graft-polymerization of phosphonates

Flame retardancy of flexible polyurethane foams has become an issue due to very severe regulations.

Influence of ferrite yellow on combustion and smoke suppression properties in intumescent flame-retardant epoxy composites

A series of intumescent flame-retardant epoxy resins (IFREP) were prepared based on bisphenol A epoxy resin (EP) as matrix resin, ammonium polyphosphate (APP) and pentaerythritol as intumescent flame retardants (IFRs), and ferrite yellow (goethite) as smoke suppressant. Then, the synergistic flame-retardant and smoke suppression properties of α-FeOOH on IFR epoxy composites were intensively investigated using cone calorimeter test and scanning electron microscopy. The thermal degradation process of IFR epoxy composites were studied using thermogravimetric analysis–infrared spectrometry under nitrogen atmosphere. Then, the pyrolysis kinetics parameters were investigated using Kissinger and Flynn–Wall–Ozawa methods. The results showed that goethite can significantly reduce heat release rate, total heat release, smoke production rate, and total smoke release. There are obvious synergistic flame-retardant and smoke suppression effects between goethite and IFRs in epoxy composites.

Study of different-sized sulfur-free expandable graphite on morphology and properties of water-blown semi-rigid polyurethane foams

In this paper, EG with different nominal particle sizes (70 μm, 430 μm and 960 μm) and different loadings from 0 to 50 pphp were considered to investigate the effect of expandable graphite on the morphology and properties of water-blown semi-rigid polyurethane foams (SPFs).

Influence of Aluminum Hydroxide and Expandable Graphite on the Flammability of Polyisocyanurate-Polyurethane Foams

The aim of this work was to verify the influence of expandable graphite (EG) and aluminum hydroxide (ATH) fillers on the flammability of polyisocyanurate-polyurethane (PIR). Limited oxygen index increased to 72.5 with an incorporation of 16 phr (parts per hundred of matrix) EG and 50 phr ATH into the matrix (total weight percent was 39.76%). Cone calorimetry was employed to study the flammability properties of these PIR/ATH/EG composites. Scanning electron microscopy analysis was conducted to study the char characteristics of the composites after the cone calorimetry tests. It was found ATH could effectively induce villi like particles, which made the intumescent char denser, on the surface of EG. The compact char layer could effectively impede the transport of bubbles and heat. ATH and EG accelerated the initial degradation and fluffy char was quickly generated on the surface. Thus, degradation products of the composite were slowed down and the diffusion of volatile combustible fragments to flame zone was delayed.

Preparation of low initial expansion temperature expandable graphite and its flame retardancy for LLDPE

To get expandable graphite (EG) flame retardant for Liner Low-Density Polyethylene (LLDPE) with low initial expansion temperature and high dilatability, the effects of various factors on dilatability were investigated including the dosages of oxidant KMnO4, intercalating reagent H2SO4, assistant intercalating reagent acetic acid (HAc) and reaction temperature. Feasible conditions were obtained according to the results of L9 (34) experiments and single factor experiments. EG with an initial expansion temperature of 160°C and expansion volume of 460 mL g−1 could be prepared according to the mass ratio of material graphite C: KMnO4: 100% H2SO4: HAc = 1.0: 0.4: 5.0: 1.0 (H2SO4 should be diluted to the mass concentration of 75% before the intercalation reaction); the reaction time was 1.0 hour at 25°C. It was found that reaction temperature and H2SO4 dosage were the most important influence factors for dilatability. The limiting oxygen index could be improved to 28.1% by adding 30% of the prepared EG to LLDPE, and the synergistic anti-flame capability of 20% EG with 10% Ammonium polyphosphate (APP) (I) can reach to 33.9%. According to thermal gravimetric and differential thermal analysis results, 70% LLDPE /10% APP (I) /20% EG synergistic anti-flame system shows higher residual carbon and thermal stability.

Exceptionally Flame Retardant Sulfur-Based Multilayer Nanocoating for Polyurethane Prepared from Aqueous Polyelectrolyte Solutions

Many current flame retardant (FR) strategies for polymers contain environmentally harmful compounds and/or negatively impact processing and mechanical properties. In an effort to overcome these issues, a effective flame retardant nanocoating comprised of positively charged chitosan (CH) and anionic poly(vinyl sulfonic acid sodium salt) (PVS) was deposited onto flexible polyurethane foam using layer-by-layer (LbL) assembly. This coating system completely stops foam melt dripping upon exposure to the direct flame from a butane torch. Furthermore, 10 CH-PVS bilayers (∼30 nm thick) add only 5.5% to the foam's weight and completely stop flame propagating on the foam due to the fuel dilution effect from non flammable gases (e.g, water, sulfur oxides, and ammonia) released from the coating during degradation. Cone calorimetry reveals that this same coated foam has a 52% reduction in peak heat release rate relative to an uncoated control. This water-based, environmentally benign nanocoating provides an effective postprocess flame retardant treatment for a variety of complex substrates (foam, fabric, etc.).