Flame-retardant Waterborne Polyurethane Research Articles

Preparation and performance of waterborne polyurethane coatings based on the intumescent flame retardant of boron, phosphorus, and nitrogen

AbstractPNB organic flame retardant was synthesized using 4‐formylphenylboronic acid, 4‐aminophenylthiophenol, 9,10‐dihydro‐9‐oxa‐10‐phos‐phaphenanthrene‐10‐oxide (DOPO), and then introduced into the hydroxyl‐terminated polybutadiene acrylonitrile (HTBN) molecular chain to successfully prepare a macromolecular flame retardant, which was used to prepare flame retardant waterborne polyurethane. The mechanical properties, thermal properties, and flame retardancy of waterborne polyurethane (FR‐WPU) were studied using thermogravimetic analysis (TGA), limiting oxygen index (LOI), scanning electron microscope (SEM), cone calorimeter, and universal testing machine, respectively, and the flame retardant mechanism of macromolecular flame retardants was explored. An LOI value of 29.76% and a UL‐94 V‐0 rating could be realized when the APFBH conjugation is 7.5 wt%, showing a significant improvement of melt dripping behavior and flame retardancy. It indicated that the fire resistance of FR‐WPU remarkably improved and displayed both gas and condensed phase mechanism. As the content of APBDH increased, the tensile strength and the elongation at break of FR‐WPU increased firstly and then decreased.

Flame-retardant waterborne polyurethane based on the synergistic effect of HGB and DOPO derivatives

Flame-retardant waterborne polyurethane based on the synergistic effect of HGB and DOPO derivatives

The impact of DOPO‐derived phosphoramides containing triazine moieties on the flame retardancy and smoke suppression properties of waterborne polyurethane

AbstractWaterborne polyurethane (WPU), which is a novel and environmentally friendly variety of polyurethane, replaces organic solvents with water. It has been extensively utilized in diverse fields encompassing coatings, textile finishing, building decoration, adhesives, plastic chemistry, and others. However, WPU is inherently flammable and releases a significant amount of smoke production during the combustion process. This research presents an original fire‐resistant Waterborne Polyurethane (WPU) with a newly‐integrated flame‐retardant component comprising a triazine phosphoramidate segment derived from 9,10‐dihydro‐9‐oxo‐10‐phosphaphenanthrene‐10‐oxide (DOPO) within its primary structure. In comparison to pure WPU, the limiting oxygen index (LOI) of flame‐retardant WPU (FRWPU) increased from 19.6% to 29.2%. In UL‐94 testing, the FRWPU film achieved a V‐0 rating with only 6% retarding component. Additionally, in cone calorimetry tests, Total Heat Release (THR), peak Heat Release Rate (pHRR), Total Smoke Production (TSP), Smoke Production Rate (SPR), and peak Carbon Monoxide Production Rate (pCOP) are decreased by 27.7%, 16.2%, 64.6%, 61.3%, and 77.8%, respectively. The greater degree of graphitization observed in the residual carbon substantially impeded heat exchange and the emission of smoke during combustion. Flame‐retardant intermediate segments greatly improved the FRWPUs' ability to suppress smoke and remain flame‐retardant. The creation and formulation of aqueous polyurethanes that are flame‐retardant can benefit greatly from the insights and references offered by this research.

Preparation of a flame-retardant waterborne polyurethane with core–shell structure and its application in a fire-resistant microfiber synthetic leather

Flame retardant waterborne polyurethane with core-shell structure was synthesized by encapsulating hexaphenoxycyclophosphazene with WPU, and applied to the preparation of flame retardant ultrafine fiber synthetic leather using a two-step method.

Synthesis and characterization of non-ionic flame-retardant waterborne polyurethane.

Waterborne polyurethane (WPU) offers many advantages and is widely used in coatings, leathers, adhesives, biomaterials, and other consumer products. However, WPU is highly flammable. Many reactive flame retardants have been developed, but their char formation efficiency is still unsatisfactory, and the melt dripping during combustion has not been effectively suppressed. In this paper, a novel phosphorus-containing flame retardant with dihydroxy groups, (6-((4-hydroxyphenyl)((4-hydroxyphenyl)amino)methyl) dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (PHAD), was successfully synthesized and incorporated into WPU molecular chain as a chain extender, thereby synthesizing a series of non-ionic flame-retardant waterborne polyurethane (NFRWPU) emulsions. The chemical structure of NFRWPU was successfully characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. With the help of a thermogravimetric analyzer, scanning electron microscope and other instruments, some key performance parameters of NFRWPU in applications were investigated, including: physical, mechanical, and thermal stability and flammability. Some important experimental results include: both the particle size and viscosity of the emulsion increase gradually with increasing PHAD content, and when the PHAD content reaches 12%, the average particle size of emulsion increases to 106.6 nm with a viscosity of 89 mPa s; with the addition of PHAD, the tensile strength of NFRWPU initially increased and then decreased, while the elongation at break showed a continuous downward trend. The maximum tensile strength reached 22.63 MPa, and the minimum elongation at break dropped to 1060%; the addition of PHAD improved the thermal stability and flame retardancy of the film, with the highest limiting oxygen index value reaching 25.6% and the maximum carbon residue increasing to 6.5%. All these results indicate that NFRWPU is a promising flame retardant WPU considering the comprehensive performance.

Synthesis of P-N-S elemental flame-retardant waterborne polyurethane and its application in polyamide fabric

A new type of flame-retardant polyether diols containing phosphorus, nitrogen, and sulfur (SPAE) was first synthesized by using phosphoryl chloride, 2-aminobenzothiazole and ethylene glycol. The SPAE as the soft segment was then utilized to prepare a series of flame-retardant waterborne polyurethanes (SPAE-WPU) through emulsion polymerization. Subsequently, SFR-WPU as a finishing agent was coated on polyamide fabric. When the content of SPAE-WPU was 18 wt%, the coated fabric exhibited a limiting oxygen index (LOI) of 28.2 %, afterflame time of 4.6 s, afterglow time of 0 s and damaged length of 11.2 cm, respectively. After 10 washes, the coated fabric retained its good flame-retardancy and anti-dripping properties. Furthermore, the flame-retardant mechanism of SPAE-WPU was investigated using various spectral analyses, which revealed that the P, N and S elements worked together to create non-combustible gas compounds, release free radicals, and promote dehydration and carbonization, leading to synergistic flame-retardant effects in both gas- and condensed-phase.

Preparation and performance investigation of high solid content flame retardant waterborne polyurethane

AbstractTo improve the flame retardancy and solid content of waterborne polyurethane (WPU), AOT, and AOD series of WPU were synthesized and characterized. Carboxylic acid/nonionic composite units were used as hydrophilic groups, and OP550/THPO and OP550/DOPO‐HQ combinations were used as flame retardant modifiers, respectively. The results revealed that the flame retardant‐modified WPU emulsions still had excellent dispersion, stability, and fluidity. The UL‐94 rating of modified WPU could reach V‐0, and the AOD series samples had better flame retardancy than the AOT series, where AO10D3‐WPU containing 3% DOPO‐HQ had an limiting oxygen index value up to 30.5%. Besides, the peak heat release rate and total heat release of AO10D3‐WPU were respectively decreased by 32% and 34%, compared with the control sample in the conical calorimetric test. The TGA, TG‐IR, and SEM‐EDS exhibited that the flame retardants functioned in the condensed phase by promoting carbon formation. The tensile strength of AOT series samples was excellent with a range of 15.84–27.47 MPa, while the elongation at break of AOD series samples was relatively high with a distribution of 850.8%–913.11%, which could be selected to suit the needs of different application scenarios.

A phosphorus- and nitrogen-containing aromatic Schiff base derivative in waterborne polyurethane backbone for excellent flame retardant, UV-shielding and mechanical properties

Waterborne polyurethane (WPU) is widely used in the fields of coatings, adhesives and treatment agents. However, the WPU is highly flammable and has a high demand for UV-shielding property in practical application. To date, it remains a challenge to effectively improve the flame retardant and UV-shielding properties without compromising the inherent mechanical property. Here, we report a novel flame retardant WPU (FRWPU) with 9, 10-dihydro-9-oxo-10-phosphophenanthrene-10 oxide (DOPO)-based aromatic Schiff base derivative containing phenolic hydroxyl (DOPO-HAMB) in the backbone. Compared to the pristine WPU, the FRWPU reaches the limiting oxygen index (LOI) value of 27.9 %, and achieves a V-0 rating in the UL-94 test with only 3 % of DOPO-HAMB. Meanwhile, in the cone calorimetry test, the peak heat release rate (pHRR) and total heat release (THR) of FRWPU are reduced by 37.7 and 29.3 %, respectively. In addition, the FRWPU can suppress melt dripping and smoke release during combustion effectively. These enhancements are attributed to the cooperation between DOPO and aromatic Schiff base derivatives with both gas-phase and condensed-phase flame retardant mechanisms. More interestingly, the FRWPU exhibits excellent UV shielding property while maintaining the inherent mechanical property of polyurethane, which provides a useful reference for the design and fabrication of flame retardant waterborne polyurethane.

Flame Retardant Waterborne Polyurethanes: Related Analytical Measurements

Flame-retardant waterborne polyurethane has long been studied as a flame-retardant, non-flammable, adhesive material for wood, for example. Since there are already many good review articles and specialized books, this chapter will review only the major studies of new flame-retardant aqueous polyurethanes reported in the last few years. In many cases, there is the synthesis of polymer materials, thermal analysis that proves flame retardancy alone or in combination with other materials, as well as FTIR, NMR, MS for structural confirmation, and SEM for aggregate state confirmation. The study may be carried out by several measurements such as EDX analysis. On the other hand, material flammability tests may include limiting oxygen index, vertical combustion, and cone calorimeter tests. This chapter focuses on methods of analytical measurement of flammability, the purpose of these methods, the correlation between flame retardancy and other structures/physical properties, and related experiments and discussions including composite/special measurements such as TGA-FTIR, and in situ FTIR. Additionally, the authors would like to summarize the relationship between analytical measurements such as thermal measurement with other applications such as macromolecules for photochromic and fluorescence.

Synthesis of P, N and Si-containing waterborne polyurethane with excellent flame retardant, alkali resistance and flexibility via one-step synthetic approach

To endow pristine waterborne polyurethane with excellent flame retardation without reducing the mechanical properties, a flame retardant waterborne polyurethane with phosphorus, nitrogen and silicon units (P-N-Si-WPU) with excellent alkaline resistance was successfully synthesized by one-step synthetic approach, which it is conducive to realizing industrialization and avoiding many unnecessary side-reactions. In contrast to pure waterborne polyurethane, the limiting oxygen index value of P-N-Si-WPU is demonstrated to be increased from 18 % to 27.5 %. The peak heat release rate of P-N-Si-WPU is decreased from 648 W/g to 262.4 W/g. All results demonstrate that the possible flame retardant mechanism of P-N-Si-WPU is gas phase flame retardant and condensed phase flame retardant. During the decomposition of P-N-Si-WPU, a thermally stable char layer consisting P (=O)-O-Si- structure is formed to endow the P-N-Si-WPU with better thermal insulation ability in the combustion process. At the same time, due to the flexibility of Si-O-Si bond, the flame retardant and mechanical properties of the film can be balanced in the process of synthesis of waterborne polyurethane, which provides a strategy for the preparation of outstanding flame retardant waterborne polyurethane.

Synthesis and characterization of bio-based "three sources in one" intumescent flame retardant monomer and the intrinsic flame retardant waterborne polyurethane

Synthesis and characterization of bio-based "three sources in one" intumescent flame retardant monomer and the intrinsic flame retardant waterborne polyurethane

Synthesis and characterization of flame‐retardant polyurethane based on new chain extenders

AbstractA series of novel flame‐retardant waterborne polyurethanes (FWPU) were synthesized with tris(hydroxymethyl)phosphine (THPO) obtained from the reaction of tetrakis(hydroxymethyl)phosphonium sulfate and bis(2‐hydroxyethyl)terephthalate from the alcoholysis of waste poly(ethylene terephthalate) as flame‐retardant chain extenders. Influences of THPO on flame retardancy and bonding properties of FWPU were investigated using limiting oxygen index (LOI) measurement, vertical burning test, cone calorimeter test (CCT), thermogravimetric analysis and shear tensile test. The results of LOI, vertical burning test and CCT indicated that flame retardancy of FWPU was improved with the introduction of THPO. The peak of heat release rate of FWPU with 1.5 wt% THPO was 401 kW m−2. After hard segment flame‐retardant modification, the initial bonding strength of FWPU adhesive increased by 150%, and the final bonding strength decreased slightly. A new way is provided for the design of novel reactive FWPU which maintained better flame retardancy and adhesive properties after hard segment flame‐retardant modification. © 2022 Society of Industrial Chemistry.

Halogen-free instinct flame-retardant waterborne polyurethanes: composition, performance, and application.

Ideal halogen-free instinct flame-retardant waterborne polyurethanes have high flame-retardant efficiency, environmental friendliness, fine compatibility, and good thermostability. Phosphorus flame-retardants are currently widely used in halogen-free instinct flame-retardant waterborne polyurethanes (HIFWPU), especially those with phosphorous–nitrogen co-structures. Phosphorous–nitrogen HIFWPU have become a hotspot because their co-structures provide higher flame-retardance as compared to waterborne polyurethanes. This review introduces three main types of HIFWPU based on composition, performance and application. HIFWPU not only have improved flame-retardance but also satisfy the various requirements for functionality. HIFWPU have been widely developed in textile, furniture, automobile, and aerospace applications.

Flame Retardant Waterborne Polyurethanes: Synthesis, Characterization, and Evaluation of Different Properties

A series of flame retardant waterborne polyurethanes (WBPUs) with varying NCO:OH mole ratio, i.e., isocyanate:hydroxyl groups, was synthesized using phosphorus-based polyester polyol and isophorone diisocyanate (IPDI). The phosphorus moiety was kept in the polymeric chain, which improves flame retardancy of the WBPU films. The prepolymer mixing process was adopted for the synthesis route of WBPU systems. The presence of structural-functional groups was confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The thermal stability and percentage char yield were observed by TGA analysis. As a consequence of the existence of phosphorous moiety, these WBPUs also exhibit flame retardancy, which was examined by limiting oxygen index (LOI) and UL-94 test. All the samples show an increment in thermal stability with an increase in NCO:OH ratio. Maximum flame retardancy was obtained in FWP5 and FWP6 systems with LOI value of 32%.

Fabrication of high transparent, mechanical strong, and flame retardant waterborne polyurethane composites by incorporating phosphorus‐silicon functionalized cellulose nanocrystals

AbstractTo manufacture transparent waterborne polyurethane composite coatings that possess desirable mechanical and flame retardancy properties is still a challenge. Herein, we first synthesized phosphorus‐silicon functionalized cellulose nanocrystals (FCNC) filler, and further introduced it into waterborne polyurethane (WPU) matrix to prepare composite. The phosphorus‐silicon‐containing components were grafted covalently on the surface of FCNC, and the FCNC showed good dispersion level in water and WPU matrix. Moreover, the inserted FCNC could not only maintain the high transparency of WPU‐FCNCs composites, but also remarkably enhancing the mechanical and flame retardancy performances. Noticeably, the WPU‐FCNC3 composite containing 3 wt% of FCNC showed balanced mechanical (σb = 16.7 MPa, εb = 557.5%), limiting oxygen index (22.9%), and a UL‐94 rating of V‐2 among prepared films. Additionally, WPU‐FCNC3 composite exhibited significantly reductions in heat release during combustion, and also showed a high transmittance of 92.2%. The present research supplies promising way for developing transparent, toughness, and flame retardant composite coatings.

Development of flame-retardant waterborne polyurethane dispersions (WPUDs) from sulfonated phosphorus-based reactive water-dispersible agents

The current study presents an attempt to develop two molecules, namely sulfonated aromatic diol (SAD) and sulfonated aromatic diamine (SADAM), to induce flame retardancy, thermal stability, and dispersion ability for water-based polyurethane dispersions (WPUDs). The previously reported itaconic acid-based polyester polyol was used for prepolymer synthesis as well as for chain extension. Pre- and post-sulfonated compounds were subjected to characterization tests such as FTIR, 13C-NMR, 1H-NMR, and CHNS for confirmation of their structures. The standard dispersant used for the basis of comparison was commercially available dimethyl propionic acid (DMPA). WPUDs were synthesized in different molar concentrations of DMPA, SAD, and SADAM, and the covalent incorporation of all three molecules in the polymer backbone was confirmed by FTIR. The WPUD films were subjected to various thermal tests like TGA and DSC as well as mechanical tests like flexibility and pencil hardness. WPUD films obtained from SADAM showed a remarkable increase in Tg as well as char content. The THRI values for SAD- and SADAM-based films were better than DMPA-based films. SAD- and SADAM-based WPUD films also showed an increase in LOI value and UL-94 ratings with the maximum LOI value of 26. Dispersions based on DMPA showed better stability as compared to dispersions based on SAD and SADAM.

Green fluorescent waterborne polyurethane polyols

In this paper, we reported a series of green fluorescent flame-retardant waterborne polyurethane polyols. The polyurethane polyols were uniformly sized and possessed decent colloidal stability. Comparing to other reported products, our aqueous dispersions showed much stronger fluorescence intensity and greatly improved long-term stability, which were desired for practical applications. Small molecule conjugation units were gated into polyurethane chains via reaction between −OH of naphthalene and −NCO of diisocyanate, which restricts intramolecular rotation of naphthalene chromophores and non-radiative transition to enhance fluorescence intensity. The non-radiative transition and chromophore aggregation are weakened to hinder aggregation-caused quenching of chromophores to improve fluorescence by weak collision. This study has demonstrated a facile method to prepare waterborne polyurethane polyols, providing detailed explanation and guidance for related work in the future.

Eco-friendly functional two-component flame-retardant waterborne polyurethane coatings: a review

Green functional two-component flame-retardant waterborne polyurethane (2K-FWPU) coatings possess outstanding green traits, such as providing eco-friendly protection, having low toxicity, and generating no pollution.

Intumescent flame retardant behavior of triazine group and ammonium polyphosphate in waterborne polyurethane

In this work, a novel triazine-based flame retardant, namely (4,6-dimethoxy-1,3,5- triazine)-2-methyl-propane-1,3-diol (TMPD) was synthesized and used as a chain extender to prepare flame retardant waterborne polyurethane (FRWPU). The structure of TMPD was characterized by fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR) and mass spectrometry (MS). To enhance the flame retardancy, ammonium polyphosphate (APP) was simultaneously introduced into FRWPU, and the synergistic flame retardant effects of both TMPD and APP were investigated in detail via the limited oxygen index (LOI), vertical burning test, cone calorimetry, and thermogravimetric analysis (TG). Compared with pure waterborne polyurethane (WPU), the flame retardancy of FRWPU with different TMPD loadings were all found to be increased, and LOI an value of 27 % and a UL-94 V-0 rating were attained when 5 wt% APP and 6 wt% TMPD were employed (APP/FRWPU-6). Moreover, the peak heat release rate (pk-HRR), total heat release (THR), and peak of smoke production rate (pk-SPR) of APP/FRWPU-6 were respectively found to be decreased by 43 %, 10 %, and 24 % compared with APP/WPU (with 5 wt% APP), respectively, thereby exhibiting an obvious synergistic flame retardant effect. In addition, the char residues of TMPD and APP in WPU after the cone calorimetry test were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), laser Raman spectroscopy (LRS), and x-ray photoelectron spectroscopy (XPS), and the results indicate that the combination of TMPD and APP can form a more compact and graphitized char layer and a nitrogen-containing gas isolation layer. Moreover, it can produce PO• radicals in the flame that combine with H• and OH• radicals. These factors are all believed to shield the underlying polyurethane from the further influence of heat flux. Therefore, this work presents a novel and efficient method by which to form FRWPU.

A highly-effective ionic liquid flame retardant towards fire-safety waterborne polyurethane (WPU) with excellent comprehensive performance

The flame-retardant waterborne polyurethane (WPU) has attracted more and more attentions from academia and industry. However, the addition of conventional flame retardants into WPU will damage the emulsion stability and introduce the potential further risk to demulsification and preparation failure. In this work, a novel flame-retardant approach is proposed, demonstrating outstanding efficiency, excellent compatibility and minimized side effect. A water-soluble ionic liquid 1-methyl-3-((6-oxidodibenzo[c,e] (Akindoyo et al., 2016; Chattopadhyay and Raju, 2007) [1,2]oxaphosphinin-6-yl)methyl)-1-H-imidazol-3-ium-4-methylbenzenesulfonate ([Dmim]Tos) is applied as the additive flame retardant for the WPU dispersions. The resulting WPUs (WPU/[Dmim]Toses) display excellent flame retardancy via a low loading content (max 6.0 wt%) and potential adhesion applicable to industries, while maintaining the major comprehensive performance, including storage stability, mechanical property, thermal stability, transparency, hydrophobicity, etc. Effort from this work, besides of overcoming the explicit drawback, also serves as reference of novel methodologies to solve the compatibility issue between additive agents and WPU.