Flexible polyurethane foams reinforced with organic and inorganic nanofillers

The effect of three different types of cellulose nanofillers on the morphology, mechanical, and thermal properties of flexible polyurethane foam was studied. Cellulose nanocrystals (CNC), cellulose nanofibrils (CNF), and cellulose filaments (CelFil) were used as fillers at 0.1–0.8 wt% loading levels. The comparison of the results showed that smaller loading levels resulted in foams with better performance in almost all cases. In the next step, the properties of foams containing CNC, CNF, or CelFil at 0.025%–0.1% loading levels were compared with those made with inorganic nanofillers including nanosilica (nSi), reduced graphene oxide, and halloysite nanotubes (HNT). Among all the properties evaluated, the tensile modulus of the foams was improved up to 40% by adding HNT at 0.05 wt% loading level whereas the addition of CNF resulted in a 44% increase in the compressive modulus of the foams at 0.1 wt% loading level.     

Flame retardant polyurethane nanocomposite: Study of clay dispersion and its synergistic effect with dolomite

Polyurethane–clay nanocomposite adhesives were prepared by different synthetic routes and their microstructures were determined by X‐ray diffraction measurements and from transmission electron microscopy images. The preparation method of the polyurethane nanocomposite adhesives was systematically changed, that is, condensation either in the presence or absence of catalyst, concentration and type of nanoclay, premixing order of nanoclay (nanoclay was either premixed with the polyol or isocyanate part) and by using MDI surface treated nanoclays. Depending on the polymerization conditions cluster, intercalated, and exfoliated clay structures were obtained. The flame retardant properties of the manufactured nanocomposite adhesives and the synergistic effect of clay in combination with dolomite were investigated by cone calorimeter and UL 94 vertical burning tests. The results indicate that addition of nanoclay reduces burning time and the total heat evolved (THE) at flame out, and that the type of assembled clay structure (cluster, intercalated or exfoliated) had a significant effect on the flame retardant property. Nanocomposites with 3 wt % of clay loading gave the shortest burning time, the lowest THE and also UL 94 V‐2 ratings were reached, although the flame retardancy in terms of heat release rate and time to ignition was not improved. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A facile strategy to fabricate microencapsulated expandable graphite as a flame‐retardant for rigid polyurethane foams

A facile strategy is reported for one‐step preparation of reactive microencapsulated expandable graphite (EG) for flame‐retardant rigid polyurethane foams (RPUF), which is based on in situ emulsion polymerization and the use of poly(glycidyl methacrylate) (PGMA) as reactive polymer shell. FTIR and SEM observations well demonstrate the formation of PGMA microencapsulated EG (EG@PGMA) particles. The encapsulation of PGMA shell significantly improves the expandability of EG particles from 42 to 70 mL g^?1. RPUF/EG@PGMA composite with only 10 wt % EG@PGMA loading reaches the UL‐94 V‐0 rating. The limiting oxygen indexes increase remarkably from 21.0 to 27.5 vol %. Additionally, the improved chemical and physical interaction enhance the interfacial bonding between EG and matrix, thus resulting in improved mechanical properties of RPUF/EG@PGMA. These attractive features suggest that the strategy proposed here can serve as a promising means to prepare highly efficient, reactive microencapsulated EG and corresponding good flame‐retarding RPUF with high mechanical properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42364.     

Intumescent foams—A novel flame retardant system for flexible polyurethane foams

A combination of intumescent components was evaluated as a novel flame retardant system in a flexible polyurethane foam, and the incorporation of these components gave rise to a significant enhancement of the flame retardant properties of the foam. The heat release rate was lowered at an early stage as well as throughout the fire, the total heat production was decreased and the time to ignition was prolonged. Mechanical measurements of the foam revealed enhanced properties in terms of stiffness accompanied by a large decrease in elongation at break as compared with a reference foam. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of expandable graphite and dimethyl methylphosphonate on mechanical,thermal, and flame‐retardant properties of flexible polyurethane foams

Expandable graphite (EG) and dimethyl methylphosphonate (DMMP) were added to polyurethane to form flame‐retardant high‐resilience flexible polyurethane foam (FPUF) in one‐step. The effects of EG and DMMP on cell morphology, mechanical properties, dynamic mechanical properties, thermal degradation, and flame‐retardant properties of FPUF were studied. The results indicated that adding proper amount EG or/and DMMP would not seriously damage cell morphology and mechanical properties. Dynamic mechanical analysis (DMA) demonstrated that there were two tan δ peaks attributed to soft and hard segment seperately and 15 pbw EG or/and 15 pbw DMMP could enhance damping property of FPUF. Thermogravimetric analysis–Fourier transform infrared spectroscopy (TGA–FTIR) results indicated that 15 pbw EG or 15 pbw DMMP could improve the thermal stability of the second degradation step but there were no synergistic effect between the two. DMMP made FPUF composites produce more toxic gases such as CO, however, EG displayed an opposite effect. Both EG and DMMP could effectively improve the flame retardant properties of FPUF, and there was synergistic effect between the two. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 916‐926, 2013     

Layer double hydroxide and sodium montmorillonite multilayer coatings for the flammability reduction of flexible polyurethane foams

Flexible polyurethane foam (PUF) is coated by layer‐by‐layer (LbL) assembly using branched polyethyleneimine (BPEI), poly(acrylic acid) (PAA), and two different charged nanoparticles, such as sodium montmorillonite (Na‐MMT) and layered double hydroxide (LDH). Three different deposition strategies, that is, bilayer, trilayer, and quadlayer, exhibit different coating growth, morphology, and flammability properties. Changing the nanosheet from LDH to MMT dramatically alter the coating mass for the same number of layers. A five bilayer PAA/BPEI+LDH coating reduced the peak heat release rate by 40% and the average heat release rate by 70%, which is two times more effective than commercial fire retardants (FRs) and other LbL‐FR coatings for PUF. MMT and LDH mixed multilayers resulted in effective flame‐retardant coatings with less coating mass by manipulating the deposition strategy. This study manifests the flexibility of LbL to fine‐tune flammability reduction by switching the coating weight gains, which is significant to accelerate the development of other LbL coating regardless of the intended applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41767.     

Preparation and characterization of polyurethane/silica aerogel nanocomposite materials

In this investigation, silica aerogel (SA)/Rigid Polyurethane (PUR) foam composites and silica aerogel/Polyurethane (PU) composites were prepared by dry mixing of granular and grinded silica aerogels with polyol part. They were then combined with diisocyanate part. Three different types of PUR foams and an elastomeric coating grade of PU were studied as well. Results show that thermal conductivity of foams did not decrease by adding silica aerogel. It even increased for some grades which is assumed to be due to the change in cell configuration of these foams. It was also found that sound insulation performance of these cellular composites did not improve significantly. Unlike foam composites, addition of silica aerogel into elastomeric PU improved its thermal and acoustic insulation properties. Because of the more promising properties of elastomeric PU composites, further examinations including measurements of compression strength and water contact angle of silica aerogel/PU composites were also taken. Final results showed a significant improvement in general properties of PU coatings by adding little amounts of silica aerogel (1–4 wt %). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44521.     

Preparation and characterization of surface‐modified ammonium polyphosphate and its effect on the flame retardancy of rigid polyurethane foam

A functional surface‐modification agent was synthesized via a reaction between hexachlorocyclotriphosphazene and γ‐aminopropyl triethoxysilane. Ammonium polyphosphate (APP) was modified with this agent and then incorporated into a rigid polyurethane foam (RPUF). Fourier transform infrared spectroscopy, ¹H‐NMR, and X‐ray photoelectron spectroscopy were used to characterize the modified ammonium polyphosphate (M‐APP). The results show that the dispersibility was improved and the particle size decreased after the modification. The limiting oxygen index and cone calorimetry test results show that M‐APP enhanced the flame‐retardant properties of RPUF. The peak heat‐release rate of polyurethane (PU)/20% M‐APP decreased by 51.18% compared with that of PU–APP. The scanning electron microscopy results illustrate that M‐APP facilitated the formation of intumescent and compact char. The excellent flame‐retardant performance of M‐APP resulted from the flame‐inhibition and barrier effects, which were attributed to the phosphazene group and the intumescent char, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45369.     

In situ polymerization of polyurethane‐silver nanocomposite foams with intact thermal stability,improved mechanical performance,and induced antimicrobial properties

Silver nanoparticle‐reinforced thermoplastic polyurethane (PU/AgNP) nanocomposite foams were prepared using in situ polymerization techniques in accordance with DOW chemicals’ industrial standards. The foams exhibited improved mechanical performance, induced antimicrobial properties, and intact stability when subjected to a thermal degradation treatment. Scanning electron microscopy (SEM) indicated a homogeneous dispersion of the silver nanoparticle (AgNP) within the polymeric matrix at low filler loadings and a cluster formation at higher loadings. SEM also indicated the agglomeration of the silver nanofiller particles as a result of the thermal degradation treatment, which caused them to lose their nanoscopic characteristics and act as ordinary silver metal. Molecular modeling techniques were used to explain these observations and confirmed the higher repulsive interactions between the polymer chains and the silver nanoparticles with the increase in the nanofiller content. Stress relaxation of the nanocomposites showed optimum mechanical performance and lowest hysteresis for the 0.1% AgNP nanocomposites due to the confinement of the PU chains between the large number of the nanoparticles. Incubation with 0.1% foam inhibited the growth of Klebseilla spp. and Escherichia coli and to some extent Staphylococcus spp. This is very interesting as the same nanocomposite loaded with 0.1% AgNp has also shown the best mechanical performance highlighting the strong action of this “unclustered” low concentration on both the material and biomedical sides. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43125.     

Relationship between the thermal degradation chemistry and flammability of commercial flexible polyurethane foams

In this article, we report the use of a variety of analytical methods, in particular, solid‐state ¹H‐NMR and ¹³C‐NMR to characterize the relationship between the condensed‐phase chemistry and burning behavior as determined by a series of combustion tests for two commercially derived flexible polyurethane foams, one combustion‐modified. The combustion tests showed that the foams met several regulatory requirements in terms of their fire performance, whether or not they were combustion‐modified. Both foams passed the MV SS 302 and CAL 117 small‐flame tests. The nonmodified foam failed the Crib 5 test, but this test had a much larger ignition source. The particular problem with the nonmodified foam was melt drip into the flame zone. This led to a steady maintenance of the fuel feed and a rapid escalation of the fire. In contrast, the combustion‐modified foam showed little melt drip and self‐extinguished. Thermal analysis data for the two foams showed that melamine acted in part as an endothermic heat sink. This alone did not account for the much reduced melt flow and drip of the combustion‐modified foam, but the solid‐state ¹H‐NMR data clearly showed that the molecular mobility of the combustion char from combustion‐modified foam was lower than the unmodified foam char, which indicated that the flame‐retardant formulation in the combustion‐modified foam acted by a condensed‐phase mechanism. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3024–3033, 2006     

Synergistic effect of expandable graphite and aluminum hypophosphite on flame‐retardant properties of rigid polyurethane foam

A series of flame retarding rigid polyurethane foam (RPUF) composites based on expandable graphite (EG) and aluminum hypophosphite (AHP) were prepared by the one‐pot method. The properties were characterized by limiting oxygen index (LOI) test, cone calorimeter test, thermogravimetric analysis (TGA), real‐time Fourier transform‐infrared spectra (RT‐FT‐IR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), etc. The results indicate that both EG and AHP could enhance the flame retardency of RPUF composites. Besides, the flame retardant effect of EG was better than that of AHP. The results also show that partial substitution of EG with AHP could improve the flame retardency of RPUF, and EG and AHP presented an excellent synergistic effect on flame retardancy. What is more, compared with RPUF/20EG and RPUF/20AHP, the heat release rate (HRR) and total heat release (THR) of RPUF/15EG/5AHP were lower.TGA results indicate that partial substitution of EG with AHP could improve the char residue which provided better flame retardancy for RPUF composites. The thermal degradation process of RPUF composites and the chemical component of the char residue were investigated by RT‐FT‐IR and XPS. And the results prove that RPUF/15EG/5AHP had higher heat resistance in the later stage. Compared with the RPUF composites filled with EG, a better cell structure and mechanical properties were observed with the substitution of AHP for part of EG. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42842.     

Preparation and properties of Waterborne polyurethane/nanosilica composites: A diol as extender with triethoxysilane group

Waterborne polyurethane (WPU) was prepared from toluene diisocyanate, polypropylene glycol, 2,2‐bis(hydroxymethyl)propionic acid and a diol containing triethoxysilane group as the chain extender which was synthesized via Michael addition between 3‐triethoxysilylpropylamine and 2‐hydroxyethylacrylate. Different amounts of nanosilica were incorporated into the WPU to prepare WPU/nanosilica composites. The results showed that the particle size of the emulsions increased and their viscosity decreased first and then increased with increasing the amount of nanosilica. Incorporation of nanosilica into WPU enhanced the water contact angle and thermal stability of the composites films, meanwhile, their tensile strength and hardness increased first and then decreased. However, increasing the amount of nanosilica resulted in reduction in the elongation at break of the films. It suggested that nanosilca was anchored into the side chain of WPU due to the condensation process between the triethoxysilane group in the side chain of WPU molecular and the silanols group on the surface of nanosilica. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40526.     

Synergistic effect of aluminum hydroxide and expandable graphite on the flame retardancy of polyisocyanurate–polyurethane foams

For the first time, expandable graphite (EG) and aluminum hydroxide (ATH) was combined to improve the flame retardancy of polyisocyanurate–polyurethane (PIR–PUR) foam. The limited oxygen index increased from 26.5 for the PIR–PUR matrix to an incredible value of 92.8 when 24 phr (parts per 100 of matrix) EG and 60 phr ATH were incorporated into the matrix. Based on morphology observation and thermogravimetric analysis, it was speculated that two factors contributed to the improvement of flame retardancy primarily. First, ATH could effectively induce “villi” like particles, which was useful to form a dense char. The compact char layer could effectively impede the transport of bubbles and heat. Second, ATH and EG accelerated the initial degradation and fluffy char was quickly generated on the surface of the composites. Thus, the degradation of the composite was slowed down and the diffusion of volatile combustible fragments to flame zone was delayed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39936.     

Preparation of halogen-free flame-retardant expandable polystyrene foam by suspension polymerization

In this research, using hexaphenoxycyclotriphosphazene (HPCTP) as the halogen-free flame retardant, we prepared flame-retardant expandable polystyrene (EPS) beads by suspension polymerization. The effects of process parameters and the amount of flame retardant on polystyrene (PS)/HPCTP composite beads were investigated. The results show that the change in HPCTP content has little effect on the particle size distribution of composite beads. When the oil–water ratio is 1/4, TCP dosage is 3 wt %, stirring rate is 350 rpm, initiator dosage is 1.25 wt %, and HPCTP dosage is 15 wt %, the size of the composite beads is uniform, and the average particle size is 1.12 mm. HPCTP formed nanodispersed particles in the PS matrix with an average particle size of 44.86 nm. In addition, the thermogravimetric behavior and heat-release properties of composite beads were evaluated. The results showed that HPCTP mainly acted in the gaseous phase, which can effectively decrease the maximum mass-loss rate of the PS/HPTCP composite beads and significantly reduce the heat-release rate and heat-release capacity. The EPS foams were obtained by a prefoaming method. The average cell diameter was 62.15 μm, and the foaming ratio was 11 times. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47779.     

Reactive flame retardant with core‐shell structure and its flame retardancy in rigid polyurethane foam

With a shell of poly (methyl methacrylate‐co‐hydroxyl ethyl acrylate) (PMMA‐HA), microencapsulated ammonium polyphosphate (MHAPP) is prepared by in situ polymerization. The core‐shell structure of the reactive flame retardant (FR) is characterized by Fourier transform infrared (FTIR) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The results of water leaching rate and water contact angle measurements show that ammonium polyphosphate (APP) is well coated by a hydrophobic shell. Due to the presence of active groups (–OH) and hydrophobic groups (–CH₃) in shell, MHAPP exhibits better compatibility, flame retardancy, and water resistance compared with neat ammonium polyphosphate (APP) in rigid polyurethane foam (PU). Compression strength of PU/MHAPP with suitable loading is higher than that of PU/APP and PU, the reason is that the active groups in shell can improve the compatibility of MHAPP in PU composite. From thermal stability and residue analysis, it can be seen that the presence of reactive flame retardant shows positive effect on thermal stability of PU composite at high temperature, results also indicate that MHAPP can promote the carbonization formation efficiency of PU composite during combustion process compared with APP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42800.     

Effects of TiO2, ZnO,and Fe3O4 nanofillers on rheological behavior,microstructure, and reaction kinetics of rigid polyurethane foams

Effects of different types and shapes of titanium dioxide, zinc oxide, and magnetite nanofillers on the rheological behavior of polyol/nanofiller suspensions, on the rigid polyurethane foam formation reaction, and hence on the final microstructure were investigated. The rheological percolation threshold of polyol/nanofiller suspensions decreased as the aspect ratio of nonspherical nanoparticles (platelet or rod) increased, regardless of the nanofiller type. The results of reaction kinetics showed that above a critical surface area (≈30 m²), independently of nanofiller type, the reaction rate increased as the surface area increased. The introduction of oxide surfaces reduced the final cell size until a critical surface area (≈30 m²). However, above this critical value cell size distribution gets wider and the cell size can no longer be correlated with the surface area. In the latter case, an increase of the reaction rate and the polymerization reaction being exothermic may facilitate uncontrolled cell nucleation, growth, and hence coalescence which results in an uncontrolled foam structure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43658.     

Flame retardant polyurethane elastomer nanocomposite applied to coal mines as air‐leak sealant

Polyurethane elastomer (PUE) was firstly applied to mining coal roadway as air‐leak sealant. It is very important for air‐leak sealants to possess the super mechanical properties and good flame retardant performance when applied to the coal‐rock mass with cracks. The reinforced and toughened PUE nanocomposites were obtained by adding surface modified TiO₂ and SiO₂ nanoparticles. The modified PUE was characterized in terms of morphology, structure, and thermal stability by field‐emission scanning electron microscopy (FESEM), X‐ray diffraction (XRD), infrared spectroscopy (IR), and thermogravimetric analysis (TGA). Its flame‐retardant performance and mechanical properties were also tested. The results showed that the surface modified nanoparticles were uniformly dispersed in the PUE matrix and enhanced its thermal stability and flame retardant performance. The dual effects of uniform dispersion of nanoparticles and hydrogen bonding between nanoparticles and PUE improved the mechanical properties of the composites. The PUE modified by nanoparticles was successfully applied to coal mines and showed great air‐leak sealing effect. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Addition flame‐retardant effect of nonreactive phosphonate and expandable graphite in rigid polyurethane foams

A series of flame‐retardant rigid polyurethane foams (RPUFs) containing nonreactive phosphonate (5‐ethyl‐2‐methyl‐1,3,2‐dioxaphosphorinan‐5‐yl) methyl dimethyl phosphonate P‐oxide (EMD) and expandable graphite (EG) were prepared by water blown. The flame‐retardant properties and mechanism of EMD/EG on RPUFs were systematically investigated. The EMD/EG system effectively increased the limiting oxygen index (LOI) value and decreased the values of total heat release (THR), av‐effective heat of combustion (EHC), pk‐heat release rate (HRR), total smoke release (TSR) of RPUFs. The impact values of LOI, THR, and av‐EHC resulted by EMD/EG system are nearly equal to the sum of the impact values by EMD and EG individually in RPUFs, which implies the addition flame‐retardant effect from EMD and EG. EMD alone exerted excellent gas‐phase flame‐retardant effect by releasing PO fragments with quenching effect. The firm residue produced by EMD combined well with the loose and worm‐like expanded graphite from EG further to form compact and expanded char layer, which brought excellent barrier effect and filtration effect to matrix. That's why pk‐HRR and TSR values of RPUF reduced. Depending on the simultaneous actions of EMD/EG system in gas phase and condensed phase during combustion, the flame‐retardant effects from nonreactive phosphonate and EG on RPUFs were added together. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45960.     

Carbon nanoparticles/polyvinyl alcohol composites with enhanced optical,thermal, mechanical,and flame-retardant properties

In this work, polyvinyl alcohol (PVA) is chemically bonded to carbon nanoparticles (CNPs) by a very simple and versatile solution casting method. Five different kinds of CNPs/PVA composite films were prepared; 0.5, 1.0, 1.5, 2.0, and 3.0 wt% CNPs dispersed in PVA. The as-prepared samples were characterized using various characterization techniques. The resulting nanocomposites proved to possess homogeneity and better mechanical, thermal, optical, and flame-retardant properties than pure PVA. Most of the CNPs with average particle size ≤100 nm were homogeneously dispersed in the PVA matrix showing fluorescence in the violet color zone. The crystallinity of the nanocomposites show a decline in the diffraction intensity as compared to pure PVA which results from the dwelling of CNPs inside the gaps of stacked-layer chains of PVA. The mechanical properties of nanocomposites indicated enhancement in toughness, elastic modulus and tensile strength with an increase in CNPs contents. The assessment for flame-retardant properties was carried out through cone calorimetry. The results show a decrease in both total heat release rate (THRR) and peak heat release rate (pHRR) of the resulting nanocomposites as compared to pure PVA. The superior properties of the CNPs/PVA composites stemmed from the good interfacial bonding between the CNPs and PVA matrix.     

Preparation and application of phosphorous‐containing bio‐polyols in polyurethane foams

A bio‐polyol phosphonate acting as the polyol component in the preparation of polyurethane foam was synthesized from the liquefaction product of bagasse by the halogenation of the liquefaction product followed by the Michaelis–Arbuzov rearrangement. The FT‐IR spectra showed that phosphorus‐containing groups were introduced into the polyol chain. The data of the viscosity and the hydroxyl number suggested that the bio‐polyol phosphonate would be a good polyol component in the preparation of polyurethane foam. The limiting oxygen index of polyurethane foam containing bio‐polyol phosphonate varied in the range of 24–28, while that of polyurethane foam without bio‐polyol phosphonate was 23, demonstrating that the introduction of the phosphorus‐containing group into the polymer helped to improve the flame retardancy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40422.