Water-blown Rigid Polyurethane Foams Research Articles

Improved thermal and mechanical properties of water-blown rigid polyurethane foams synthesized with renewable castor oil and toluene diisocyanate-based trifunctional polyols

In this work, glycerol was chemically modified into novel toluene diisocyanate (TDI) based trifunctional polyol (NTP) by a two step process, involving the reaction of TDI with glycerol to form an isocyanate-terminated pre-polymer, followed by the reaction with glycol. A thermal and mechanical property of water-blown rigid polyurethane foam (WB-PUF) was enhanced by the partial substitution (30 & 50 wt%) of castor oil with glycerol or synthesized NTP. The effects of glycerol content and NTP on the WB-PUF properties were investigated using various characterization techniques including ATR-FTIR, TGA, SEM, compression test, and Shore-A hardness test. Notably, the introduction of NTP substitution into the formulation of WB-PUF foams had beneficial impact on the structure of materials enhancing foam density from 77 kg/m3 to 117 kg/m3 and also exhibited superior thermal and mechanical properties compared to those with glycerol and unmodified foams. Shore A hardness and compression strength of those foams ranged from 50 to 69.5 °Sh A and 1.88-3.28 MPa, respectively. These findings suggest potential applications of the modified WB-PUF in areas such as rigid tissue engineering.

Acoustic Performance and Flame Retardancy of Ammonium Polyphosphate/Diethyl Ethylphosphonate Rigid Polyurethane Foams.

Flame-retardant water-blown rigid polyurethane foams (RPUFs) modified by ammonium polyphosphate (APP) and diethyl ethylphosphonate (DEEP) were synthesized by a one-pot free-rising method. We performed scanning electron microscopy (SEM), compression strength tests, acoustic absorption measurements and thermogravimetric analysis, as well as limited oxygen index, vertical burning and cone calorimeter tests to investigate the mechanical properties, acoustic performance and flame retardancy of the foams. SEM confirmed that the open-cell structures of the foams were successfully constructed with the introduction of a cell-opening agent. Upon using 20 php APP, the average acoustic absorption coefficient of the foam reached 0.535 in an acoustic frequency range of 1500–5000 Hz. The results of thermogravimetric analysis demonstrated that the incorporation of APP and DEEP can effectively restrain mass loss of RPUFs during pyrolysis. In particular, the compressive strength of a foam composite containing 5 php APP and 15 php DEEP increased to 188.77 kPa and the LOI value reached 24.9%. In a vertical burning test and a cone calorimeter test, the joint use of APP and DEEP endowed RPUFs with a V-0 rating and they attained a THR value of 23.43 MJ/m2. Moreover, the addition of APP improved the acoustic absorption performance of the foam, verified by acoustic absorption measurements. Considering potential applications, the formulation containing 15 php APP and 5 php DEEP could be used in the preparation of a new flame-retardant acoustic absorption rigid polyurethane foam.

Characterization and Properties of Water-Blown Rigid Polyurethane Foams Reinforced with Silane-Modified Nanosepiolites Functionalized with Graphite.

In the present study, a promising flame retardant consisting of 80 wt% silane-modified nanosepiolites functionalized with 20 wt% graphite (SFG) is used to obtain a synergistic effect principally focussed on the thermal stability of water-blown rigid polyurethane (RPU) foams. Density, microcellular structure, thermal stability and thermal conductivity are examined for RPU foams reinforced with different contents of SFG (0, as reference material, 2, 4 and 6 wt%). The sample with 6 wt% SFG presents a slightly thermal stability improvement, although its cellular structure is deteriorated in comparison with the reference material. Furthermore, the influence of SFG particles on chemical reactions during the foaming process is studied by FTIR spectroscopy. The information obtained from the chemical reactions and from isocyanate consumption is used to optimize the formulation of the foam with 6 wt% SFG. Additionally, in order to determine the effects of functionalization on SFG, foams containing only silane-modified nanosepiolites, only graphite, or silane-modified nanosepiolites and graphite added separately are studied here as well. In conclusion, the inclusion of SFG in RPU foams allows the best performance to be achieved.

Preparation of a catalyst-free and water-blown rigid polyurethane foam from malic-co-citric acid-based polyols

Bio-based polyols (MCPs) were synthesized from 1,6-hexanediol, malic acid, and citric acid by a series of one-pot esterification reactions. Subsequently, water-blown rigid polyurethane foams (RPUF) were prepared using the MCPs and polyisocyanates by a catalyst-free method. The effect of the molar ratios of malic acid to citric acid on the foaming process, physicomechanical performance, and thermal stability were investigated. Moreover, the thermal degradation behavior of the MCP-based RPUFs was also investigated. The various MCPs exhibited high hydroxyl values (450–515 mg KOH/g) and low viscosities (1550–2150 mPa∙s). In addition, citric acid had a positive influence on the compressive strength and thermal stability of the MCP-based RPUFs. When the ratio of malic acid:citric acid was 95:5, the corresponding RPUF had a density of 42.6 kg/m3, a high compressive strength of ∼191 kPa, a low thermal conductivity of 0.0365 W/(m K), and a high initial thermal degradation temperature (> 280°C). Compared to commercial polyether polyols, the MCP-based, water-blown RPUFs demonstrated lower apparent densities, lower thermal conductivities, and higher normalized compressive strengths. These results demonstrated that malic-co-citric acid-based polyols could be an adequate substitute for petrochemical-based polyols for providing water-blown RPUFs with excellent comprehensive properties.

Long‐term thermal conductivity of cyclopentane–water blown rigid polyurethane foams reinforced with different types of fillers

AbstractAn understanding of the long‐term thermal conductivity of rigid polyurethane (RPU) foams presents great interest in the building field considering the conservation of energy efficiency. In this study, the effect of different types of particles (talc, diatomaceous earth and non‐porous silica) on the thermal conductivity of RPU foams blown with cyclopentane and water as blowing agents was investigated during 3 years of aging. The characterization of the cellular structure shows how the addition of particles causes a cell size reduction of the foams, and consequently an enhancement of the thermal properties just after production. However, this initial reduction is not maintained, because each foam shows a different thermal conductivity evolution with time. We have found, for the first time, a relationship between the slope of the thermal conductivity versus time at the first measurements and the internal temperature reached during the foaming process. The evolution of the RPU foams in which higher internal temperatures were reached is more pronounced than in those RPU foams where lower foaming temperatures were observed. This effect is related to the kinetics of the diffusion of the gas occluded inside the cells and imposes a new criterion for the selection of particles to reduce the thermal conductivity of RPU foams; these additives should ideally decrease the temperature reached during the foaming process. Moreover, the effect of aging on the thermal conductivity is explained by using theoretical models. © 2019 Society of Chemical Industry

Threshold cell diameter for high thermal insulation of water-blown rigid polyurethane foams

Water-blown rigid polyurethane foams manufactured in eco-friendly manners attract great attentions for applications in various industrial products. Especially, the polyurethane foams are widely applicable as thermal insulation materials for LNG carrier, electronic appliances, pipes, and building. Heat transfer mechanisms in foamed materials have strong relationships with gaseous molecules in cells, solid parts, and cellular morphologies. In this study, thermal conductivity of the water-blown rigid polyurethane foams was investigated by controlling the cellular morphologies using different types of surfactant molecules and gelling catalysts. The cell sizes were controlled from 551 μm to 153 μm by varying surfactants and gelling catalysts. The small cell sizes showed low radiative thermal conductivity due to the high number of thick cell walls and struts to obstruct the photon transport process. More importantly, there was a clear cell threshold size (230 μm) in variations of the overall thermal conductivity value (about 24.3 mW/m K) of polyurethane foams, and the delayed slowly weaken thermal insulation property was also noted in the cell sizes less than 230 μm.

The effects of functional nanofillers on the reaction kinetics, microstructure, thermal and mechanical properties of water blown rigid polyurethane foams

The use of functional nanofillers to improve the properties of rigid polyurethane (PU) foams has caused the need for a better understanding of how these nanofillers modify the reaction kinetic of the PU system. In this study, different nanoclays and nanosilicas are used as functional nanofillers. Analysis of the kinetic data obtained by in-situ FTIR spectroscopy monitoring allows to correlate the isocyanate consumption with the type of nanoparticles. The quantification of urethane and urea, obtained by deconvolution of the carbonyl region absorptions, enables to follow the blowing and gelling reactions during the foaming process. These reactions are correlated to the nature of the chemical groups present on the surface of the nanoparticles added. In addition, the effect of the modification of the reaction kinetics on the density, cellular structure, thermal conductivity and mechanical properties is herein discussed.

나노기포 적용 수발포 경질 폴리우레탄 폼의 물성 연구

나노기포 적용 수발포 경질 폴리우레탄 폼의 물성 연구

Bi-phase flame-retardant actions of water-blown rigid polyurethane foam containing diethyl-N,N-bis(2-hydroxyethyl) phosphoramide and expandable graphite

Flame-retardant water-blown rigid polyurethane foams (RPUFs) with a reactive-type phosphoramidate named diethyl-N,N-bis(2-hydroxyethyl) phosphoramide (DEPA) and expandable graphite (EG) were fabricated through free foaming technique. The flame retardancy and fire behaviors of RPUFs were characterized using limiting oxygen index (LOI), microscale combustion calorimeter (MCC) and cone calorimetric tests. Compared to the effects of individual flame retardant agent (DEPA or EG), the complex system (EG/DEPA) endowed RPUFs enhanced LOI values (28.8%–30.4%), higher protective char yields, lower heat release and smoke production. EG and DEPA jointly acted to remarkably inhibit the combustion intensity and smoke production through their addition or synergistic flame-retardant effects. To further validate the flame-retardant mechanism of EG/DEPA in RPUF, thermogravimetric analysis connected with Fourier transform infrared spectrometry (TG–FTIR), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) tests were conducted. These results demonstrated that DEPA decomposed potential free radical scavenger (PO) and promoted generating more H2O and CO2 in gaseous phase. Furthermore, DEPA facilitated the formation of phosphorus-rich residue, which was combined with worm-like expanded graphite to constitute protective char layers. On the basis of these results, a bi-phase flame-retardant mechanism of EG/DEPA in RPUF was proposed.

The influence of rapeseed oil-based polyols on the foaming process of rigid polyurethane foams

The foaming process of water-blown rigid polyurethane foams with different contents of a rapeseed oil-based polyol was analyzed. The present work reports for an analysis of the foaming process using foam qualification system FOAMAT—which allows recording characteristic parameters such as the dielectric polarization, rise height of a sample, pressure, temperature during a foaming process. A replacement of a petrochemical polyol by a rapeseed oil-based polyol (ROP) affects the foaming process of rigid polyurethane foams by reducing the reactivity of the system. Increasing the content of ROP resulted in a smaller decrease in the dielectric polarization which reflects slower gelling and foaming reactions.

Bio-Based Polyols from Seed Oils for Water-Blown Rigid Polyurethane Foam Preparation

The preparation of water-blown rigid polyurethane (RPUR) foams using bio-based polyols from sesame seed oil and pumpkin seed oil has been reported. Polyols synthesis involved two steps, namely, hydroxylation and alcoholysis reaction. FTIR, NMR, and ESI-MS were used to monitor the process of the synthesized polyols and their physicochemical properties were determined. The resulting polyols have OH number in the range of 340–351 mg KOH/g. RPUR foams blown with water were produced from the reaction of biopolyols with commercial polymeric methylene diphenyl diisocyanate (PMDI). The proper PUR formulations can be manipulated to produce the desired material applications. These seed oil-based RPUR foams exhibited relatively high compressive strength (237.7–240.2 kPa) with the density in the range of 40–45 kg/m3. Additionally, the cell foam morphology investigated by scanning electron microscope indicated that their cellular structure presented mostly polygonal closed cells. The experimental results demonstrate that these bio-based polyols can be used as an alternative starting material for RPUR production.

Evaluation of forming mixture composition impact on properties of water blown rigid polyurethane (PUR) foam from rapeseed oil polyol

Rapeseed oil based water blown rigid polyurethane foam was prepared by two shot method. Water was used as a blowing agent on purpose to increase the green nature of the foams. In order to reduce the temperature and shrinkage, acetone and glycerine were added. The influence of these additives on foaming characteristics, density, closed cell content, compressive strength and water absorption was described. It was found that reduction in shrinkage using glycerine leads to greater open cell content and water absorption, lower compressive strength (by almost 72% and 53%), density (by almost 64% and 74%) for moulded and free rise specimens, respectively, and delayed cream time of foaming mixture. The use of acetone reduced foam formation temperature by 15°C, increased moulded and free rise densities by approximately 8%, as well as compressive strength by 22%, and by 10% for moulded and free rise water blown polyurethane specimens.

Effects of Different Graphite Particle Sizes on the Properties of Rigid Polyurethane Foam

By Using Two Different Kinds of the Graphite Particles 80 Mesh and 325 Mesh on the Whole Water-blown Rigid Polyurethane Foam, its Properties Will Be Modified and Improved. the Result Shows that both of them Can Improve the Compressive Strength of Matrix when the Graphite Content Is Low. the 80 Mesh Graphite Destroys the Pore Structure of the Matrix, Resulting in the Increase of the Thermal Conductivity. in Addition, the Tensile Properties Are Reduced. in Contrast, the 325 Mesh Graphite Reduces the Thermal Conductivity of the Matrix, and the Tensile Properties Get Improved. Meanwhile, the Thermal Stability Enhancement of 325 Mesh Graphite Is Better than 80 Mesh Graphite.

The influence of expandable polystyrene fillers on properties of water-blown rigid polyurethane foams

This work presents the results of study of fillers addition influence on selected properties of polyurethane/polystyrene porous composite. The porous materials based on water blown rigid polyurethane foam (RPURF) matrix containing thermoplastic expandable polystyrene (EPS) beads as the fillers were obtained. In RPURF-EPS composites, the EPS beads were expanded after heating above the glass transition temperature of EPS and vaporing EPS gas incorporated inside, by using the heat of exothermic reaction of polyol with isocyanate. The thermal conductivity, compressive strength, core apparent density and dimensional stability of new materials were investigated.

Halogen-free flame retardant PUF: Effect of melamine compounds on mechanical, thermal and flame retardant properties

Water blown rigid polyurethane foam (PUF) was prepared with melamine polyphosphate (MPP) and melamine cyanurate (MC) as fire retardant (FR) additives. The effect of these additives on the properties of rigid PUF such as physico-mechanical, morphological, thermo-oxidative stability, flame retardancy and smoke density properties were studied. The mechanical and thermo-oxidative stability of PUF filled with MC was found to be better than those of MPP filled PUF. The insulation property of both MPP and MC filled PUF was improved with respect to the neat PUF. The FR properties of these filled PUF were evaluated by cone calorimeter, limiting oxygen index (LOI), smoke density, rate of burning and char residue estimation. The FR property of MPP filled PUF was better than that of the MC filled PUF.

Effect of a Nanoclay on the Mechanical, Thermal and Flame Retardant Properties of Rigid Polyurethane Foam

Water blown rigid polyurethane foams (PUF) with organoclay/organically modified nanoclay (ONC) were prepared and their properties such as density, mechanical, morphological, insulation, thermal and flame retardant properties were studied. In this investigation, the ONC content was varied from 1 to 10 parts per hundred of polyol (php) by weight. It was observed that the compressive strength of ONC filled PUF increased up to 3 php of ONC loading and then it decreased. Wide angle X-ray diffraction and transmission electron microscopy studies indicated the exfoliated dispersion of ONC in PUF. The thermal conductivity of ONC filled PUF decreases up to 5 php and then increases. The glass transition temperature (Tg) of PUF decreases on loading of ONC. The TGA analysis shows that there is slight increase in degradation temperature with increase in ONC loading. The flame retardant properties (LOI and flame spread rate) are improved slightly on addition (3 php) of ONC filled PUF.

Properties of water blown rigid polyurethane foams with different functionality

Water blown rigid polyurethane foams with different functionality were prepared. The physical properties of rigid foams were measured with rotational viscometer (NDJ-1), universal testing machine (Instron3365), scanning electron microscope (SEM) and differential scanning calorimeter (DSC). The results show that the viscosity of polyether polyol increases exponentially from 62 mPa s to 6 000 mPa s with the increase of functionality from 2 to 5.6, respectively. The overall density of foam increases slightly from 31.7 kg/m(3) to 37.4 kg/m(3) with increasing functionality while core density exhibited little difference. Compressive strength of foam shows the similar behavior wit h density except for 2-functional sample. At the same time, dimensional stability becomes better with increasing functionality except for 5.6-functional foam that has worse stability than 4.8-functional foam. From the SEM results, the functionality is not an important factor in determining distribution of cell size of foam. According to the results of thermal analysis, the glass transition temperature (T-g) shifts to a higher temperature from 128.9 degrees C to 166.3 degrees C for the 2 to 5.6 functional foam, respectively.

Effect of foam density on the properties of water blown rigid polyurethane foam

AbstractDensity is an important parameter that influences the properties and performances of rigid polyurethane foam (PUF). Rigid PUF with different densities were prepared by varying the amount of distilled water as blowing agent. This investigation reports the mechanical, morphological, water absorption, thermal conductivity, and thermal behavior of rigid PUF varying with the density, which controls the foam architecture. The density of the PUF decreased from 116 to 42 kg/m3 with an increase in the amount of water from 0.1 to 3.0 parts per hundred polyol by weight (phr), respectively. It was found that the mechanical properties of the PUFs changed with the foam density. The results of water absorption of the PUFs showed that water absorption increased with decrease in density, due to increase in the cell size and decrease in the cell‐wall thickness. The thermal conductivity measurements showed that the thermal conductivity decreased with increase in density. It was due to the decrease in cell size. The thermal analysis of the PUFs shows that the glass transition temperature increases with the decrease in foam density, but the thermal stability decreases with the decrease in foam density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Structure and properties of polyurethane foams obtained from rapeseed oil polyols

By transesterifying rapeseed oil with tr iethanolamine or glycerol, polyols with a hydroxyl number of 290-310 mg KOH/g were synthesized. Water-blown rigid polyurethane foams (PUFs) with an isocyanate index of 150-250 were obtained from rapeseed oil polyols. Studies on the effect of the concentration of potassium oleate, the cyclotrimerization catalyst of isocyanate groups, on the conversion degree of isocyanate groups were carried out using FTIR spectroscopy. The optimal physical and mechanical properties of the obtained PUFs were achieved at an isocyanate index of 150-200. Water-blown PUFs from rapeseed polyols, in contrast to water-blown PUFs from petrochemical polyols, are characterized by quite high hydrophobicity.

Regulation of Cell Structure in Water Blown Rigid Polyurethane Foam

AbstractRigid polyurethane foams are generally “closed celled” with a gas entrapped in each cell. The properties of such foams are significantly affected by the cell size distribution and morphology of the cells. For example, in thermal insulation foams, small cells lead to lower thermal conductivity and in foams for buoyancy applications, stronger cell windows are resistant to ingress of water until higher hydraulic pressures. The effect of formulation parameters on the size and structure of rigid polyurethane foams was investigated. Foams were made with different surfactants, with variation of surfactant concentration at different blowing agent concentration, with variation of nucleating agent concentration and with variation of catalyst concentration. Micron sized silica particles were used as nucleating agent. The densities of the foams were in the range of 140 to 165 kg/m3. The cell window areas of different foams have been measured. The bubble size in the polyol depends on the surface tension lowering ability of a surfactant, and the entrainment of a large number of small bubbles during mixing leads to a foam with a small cell size and a narrow cell size distribution. Increasing the concentration of the surfactant reduces the cell size and narrows the distribution. Increasing the proportion of organometallic catalyst in the amount of total catalyst used, results in smaller cell sizes, which are narrowly distributed. Hydraulic resistance of the foams was monitored by measuring buoyancy losses at different hydraulic pressures. Hydraulic resistance of the foams can be improved by decreasing the area and increasing the thickness of the cell windows.