Water-blown Polyurethane Foams Research Articles

Antibacterial Properties of Polyurethane Foams Additivated with Terpenes from a Bio-Based Polyol.

Water-blown polyurethane (PU) foams were prepared by bio-polyols from epoxidized linseed oils and caprylic acid in combination with toluene diisocianate (TDI). A series of terpenes (menthol, geraniol, terpineol, and borneol), natural compounds with recognized antibacterial properties, were included in the starting formulations to confer bactericidal properties to the final material. Foams additivated with Irgasan®, a broad-spectrum antimicrobial molecule, were prepared as reference. The bactericidal activity of foams against planktonic and sessile E. coli (ATCC 11229) and S. aureus (ATCC 6538) was evaluated following a modified AATCC 100-2012 static method. Menthol-additivated foams showed broad-spectrum antibacterial activity, reducing Gram+ and Gram- viability by more than 60%. Foams prepared with borneol and terpineol showed selective antibacterial activity against E. coli and S. aureus, respectively. NMR analysis of foams leaking in water supported a bactericidal mechanism mediated by contact killing rather than molecule release. The results represent the proof of concept of the possibility to develop bio-based PU foams with intrinsic bactericidal properties through a simple and innovative synthetic approach.

Role of Air Bubble Inclusion on Polyurethane Reaction Kinetics.

In this study, we investigated the influence of mixing conditions on the foaming process of water blown polyurethane (PU) foams obtained at different mixing speeds (50, 500, 1000 and 2000 rpm). In particular, the morphological evolution during the foaming process, in terms of the bubble size and bubble density, was studied via optical observations, while the effects on the reaction kinetics were monitored using in situ FTIR spectroscopy. At the slow mixing speed (50 rpm), no air bubbles were included and the early foaming process was characterized by the formation of new bubbles (CO2 nucleation), provided by the blowing reaction. Later on, it was observed that the coalescence affected the overall foaming process, caused by the gelling reaction, which was inhibited by the indigent mixing conditions and could not withstand the bubbles expansion. As a result, a PU foam with a coarse cellular structure and an average bubble size of 173 µm was obtained. In this case, the bubbles degeneration rate, dN/dt, was −3095 bubble·cm−3·s−1. On the contrary, at 500 rpm, air bubbles were included into the PU reaction system (aeration) and no formation of new bubbles was observed during the foaming process. After this, the air bubbles underwent growth caused by diffusion of the CO2 provided by the blowing reaction. As the gelling reaction was not strongly depleted as in the case at 50 rpm, the coalescence less affected the bubble growth (dN/dt = −2654 bubble·cm−3·s−1), leading to a PU foam with an average bubble size of 94 µm. For the foams obtained at 1000 and 2000 rpm, the bubble degeneration was first affected by coalescence and then by Ostwald ripening, and a finer cellular structure was observed (with average bubble sizes of 62 µm and 63 µm for 1000 rpm and 2000 rpm, respectively). During the first foaming stage, the coalescence was less predominant in the bubble growth (with dN/dt values of −1838 bubble·cm−3·s−1 and −1601 bubble·cm−3·s−1, respectively) compared to 50 rpm and 500 rpm. This occurrence was ascribed to the more balanced process between the bubble expansion and the PU polymerization caused by the more suitable mixing conditions. During the late foaming stage, the Ostwald ripening was only responsible for the further bubble degeneration (with dN/dt values of −89 bubble·cm−3·s−1 and −69 bubble·cm−3·s−1, respectively).

Fire retardancy, thermal, and physico-mechanical properties of semi-rigid water-blown polyurethane foam from palm oil-based polyol

This paper presents the experimental work undertaken to assess rigid palm oil-based polyurethane (PU) foam. The bio-composite foam was characterized to determine its foaming kinetics and morphology, as well as fire retardancy, thermal, and mechanical responses, which was later compared with its petrochemical-based counterpart. The palm oil-based foam displayed poor fire-retardancy performance based on Limiting Oxygen Index (LOI) and UL-94 Vertical Combustion Test. Although less char residue was produced, the palm oil-based PU foam exhibited higher onset degradation temperatures, indicating improved thermal stability. The Scanning Electron Microscopy (SEM) revealed finer cell sizes for the bio-based foam and a higher fraction of open cell structures, which affected its density and compressive properties. As a conclusion, the palm oil-based PU foam is a viable alternative to be utilized in low load-bearing and thermal environment applications.

Flexible Polyurethane Foams from Epoxidized Vegetable Oils and a Bio-Based Diisocyanate.

Bio-polyols from epoxidized soybean and linseed oils and caprylic acid or 3-phenyl butyric acid were prepared using an environmentally friendly, solvent-free method evaluating the presence of triethylamine as catalyst. Side reactions, leading to a cross-linking structure with high density, were reduced, introducing the catalyst and properly tuning the reaction conditions. A medium functionality value of around 3 along with a hydroxyl number up to around 90 mg KOH/g, narrow polydispersity index, and relatively low molecular mass up to 2400 g/mol were the experimental targets. From selected bio-polyols and an aliphatic partially bio-based isocyanate, a series of water blown polyurethane (PU) foams was produced, estimating the effect of the chemical nature of substituents in the polyol backbone on the PU properties. The apparent density of the foams was in the range of 79–113 kg/m3, with higher values for foams from the aromatic acid. Flexible polyurethane foams with open cell structure from bio-based polyols were obtained, with higher cavity size and lower pore sizes for foams from caprylic acid. The bio-based flexible PU foams showed comparable Young’s moduli (14–18 kPa) and compression deflection values (4.6–5.5 kPa) and exhibited an almost complete recovery of their initial size.

Numerical simulation of mold filling water blown polyurethane foams: Effects of sequential pour

Batch molding of polyurethane foams is a widely used processing technique to produce crosslinked cellular structures which form to the shape of the mold. For water-blown polyurethane foams, water is reacted to form gaseous carbon dioxide resulting in a foam which expands to fill the mold completely. Batch molding typically requires an operator to coat the surface of a mold, introducing a significant lag time during the filling stage where significant asymmetric volume change can occur. The purpose of this work is to show, through simulations, that this lag time is significant when predicting flow profiles and part quality. When the mold geometry is complex enough to force bifurcation of the flow, simulations incorporating various filling lag times predicted significantly different locations of knit or weld lines where the flow fronts meet. Current simulation techniques, which assume the filling stage occurs instantaneously, are unable to predict variations in weld line locations. The introduction of a lag time, referred to herein as sequential pour, was achieved through user-defined modules incorporated into Ansys Fluent software.

From Cells to Residues: Flame-Retarded Rigid Polyurethane Foams

ABSTRACT Rigid polyurethane foams (RPUFs) exhibit short times to ignition as well as rapid flame spread and are therefore considered to be hazardous materials. This paper focuses on the fire phenomena of RPUFs, which were investigated through a multimethodological approach. Water-blown polyurethane (PUR) foams without flame retardants (FRs) as well as water-blown PUR foams containing triethyl phosphate as a gas phase-active FR were examined. The aim of this study is to clarify the influence of the FR on the fire phenomena during combustion of the foams. Additionally, materials’ densities were varied to range from 30 to 100 kg/m3. Thermophysical properties were studied by means of thermogravimetry; fire behavior and flammability were investigated via cone calorimeter and limiting oxygen index, respectively. During the cone calorimeter test, the temperature development inside the burning specimens was monitored with thermocouples, and cross sections of quenched specimens were examined visually, giving insight into the morphological changes during combustion. The present paper delivers a comprehensive study, illuminating phenomena occurring during foam combustion and the influence of a FR active in the gas phase. The superior fire performance of flame-retarded PUR foams was found to be based on flame inhibition, and on increased char yield leading to a more effective protective layer. It was proven that in-depth absorption of radiation is a significant factor for estimation of time to ignition. Cross sections investigated with the electron scanning microscope exhibited a pyrolysis front with an intact foam structure underneath. The measurement of temperature development inside burning specimens implied a shift of burning behavior towards that of non-cellular materials with rising foam density.

Effect of propylene glycol, rapeseed glycerine, and corn starch modified polyol blends parameters on the properties of thermal insulating polyurethane foams

Water-blown polyurethane foams have some drawbacks such as intensive shrinkage, relatively high density, skin peeling phenomena post blowing, and longer demold time. These drawbacks can be partiall...

A Study of Rapeseed Oil-Based Polyol Substitution with Bio-based Products to Obtain Dimensionally and Structurally Stable Rigid Polyurethane Foam

Water-blown polyurethane foams from low functionality polyols are characterized by intensive shrinkage, high density, post blowing, and longer demold time. These drawbacks can be partially, or fully, eliminated by varying chemical parameters of the main components. Therefore, an aliphatic polyester rapeseed oil-based polyol was modified with bio-based glycerin (RGL) and propylene glycol (RPG). The impact of the molecular weight and hydroxyl value of the blends were evaluated by testing obtained bio-based polyurethane foams. Compared to RGL-based foams, RPG-modified foams had the strictest standard (EN 13165) requirements regarding dimensional stability. These foams demonstrated a reduced apparent density from 12.6 to 20.8%, a faster foam curing capability by 47%, and the shortest demold time due to the open cell structure. The RGL modified foams had better cross-linking capability, slower ageing of thermal conductivity, and an increased compressive strength of 82.7% compared to the non-modified foam.

Analysis of thermal properties and heat transfer mechanisms for polyurethane foams blown with water

Rigid polyurethane foam (PUF) is one of the outstanding insulation materials and has been widely used in freezers and cryogenic facilities. Among the various blowing agents used in the manufacturing PUF, water-blown PUF is attracting much attention as environmentally friendly PUF as prominent replacements for the environmentally hazardous CFCs and HCFCs due to their significant ozone depletion potential. We investigated the effective thermal conductivity of PUF blown with different amounts of water, on the basis of the heat transfer mechanisms in terms of thermal conduction of solids and gases and the thermal conductivity of radiation in the cells. A predictive model for the effective thermal conductivity of PUFs with different densities is presented. The predictive model was validated by comparing the predicted values with the experimentally measured ones. The result showed that the effective thermal conductivity increased from 0.023 to 0.027 W m−1 K−1 as the PUF density increased from 48 to 120 kg m−3: increased by 158% from 0.0034 to 0.0089 W m−1 K−1 for the thermal conductivity of solid PUF and decreased by 50% from 0.0037 to 0.0018 for the thermal conductivity of radiation.

Manufacturing of micro-scale polyurethane foams by reactive inkjet printing

Reactive inkjet printing (RIJ) was used as an additive manufacturing (AM) tool. Combined with polyurethane (PU) chemistry, it is shown that RIJ can be used to build micro-scale foams. Waterblown polyurethane foams (PUF) based on polyethylene glycol 200 (PEG200), glycerol ethoxylate (Star-PEG) and 1,6-hexamethylene diisocyanate (HDI) were used to prepare the foams. The system was catalyzed using iron(III) chloride, dibutyltin dilaurate (DBTL), diazabicyclo octane (DABCO) and bis(2-dimethylaminoethyl) ether. The influence of iron(III) chloride and DBTL were investigated by means of temperature profile measurements. The stability of the catalyst system was tested for 32 hours within the ink formulation. The ink formulations were then printed with a Dimatix DMP3000 (Fujifilm, USA) printer using a 16 nozzle printhead with a nominal 10 pL drop volume. The reaction of the inks and the building of PUF after printing were investigated by light microscopy and SEM. It seems favorable to use high amounts of catalyst in order to obtain a more porous structure.

Water-Blown Polyurethane Foams Showing a Reversible Shape-Memory Effect.

Water-blown polyurethane (PU) foams are of enormous technological interest as they are widely applied in various fields, i.e., consumer goods, medicine, automotive or aerospace industries. The discovery of the one-way shape-memory effect in PU foams provided a fresh impetus for extensive investigations on porous polymeric actuators over the past decades. High expansion ratios during the shape-recovery are of special interest when big volume changes are required, for example to fill an aneurysm during micro-invasive surgery or save space during transportation. However, the need to program the foams before each operation cycle could be a drawback impeding the entry of shape-memory polymeric (SMP) foams to our daily life. Here, we showed that a reversible shape-memory effect (rSME) is achievable for polyurethane water-blown semicrystalline foams. We selected commercially available crystallizable poly(ε-caprolactone)-diols of different molecular weight for foams synthesis, followed by investigations of morphology, thermal, thermomechanical and shape-memory properties of obtained compositions. Densities of synthesized foams varied from 110 to 180 kg∙m−3, while peak melting temperatures were composition-dependent and changed from 36 to 47 °C, while the melting temperature interval was around 15 K. All semicrystalline foams exhibited excellent one-way SME with shape-fixity ratios slightly above 100% and shape-recovery ratios from the second cycle of 99%. The composition with broad distribution of molecular weights of poly(ε-caprolactone)-diols exhibited an rSME of about 12% upon cyclic heating and cooling from Tlow = 10 °C and Thigh = 47 °C. We anticipate that our experimental study opens a field of systematic investigation of rSMEs in porous polymeric materials on macro and micro scale and extend the application of water-blown polyurethane foams to, e.g., protective covers with zero thermal expansion or even cushions adjustable to a certain body shape.

Strategy for Obtaining Bimodal Bubble Size Distribution in Water Blown Polyurethane Foams

Polyurethane foams with multimodal cell distribution exhibit superior mechanical and thermal properties. A technique for generating bimodal bubble size distribution exists in the literature, but it uses supercritical conditions. In the present work, an alternative based on milder operating conditions is proposed. It is a modification of reaction injection molding (RIM), using reactants already seeded with bubbles. The number density of the seeds determines if two nucleating events can occur. A bimodal bubble size distribution is obtained when this happens. A mathematical model is used to test this hypothesis by simulating water blown free rise polyurethane foams. The effects of initial concentration of bubbles, temperature of the reactants, and the weight fraction of water are studied. The study reveals that for certain concentrations of initial number of bubbles, when initial temperature and weight fraction of water are high, it is possible to obtain a second nucleation event, leading to bimodal bubble s...

Design and formulation of soybean oil derived flexible polyurethane foams and their underlying polymer structure/property relationships

A series of water blown polyurethane foams was produced in which polyether polyol content was progressively reduced by the addition of a designed soybean oil derived polyol (SBOP). A sample from each foam was tested for a variety of standard properties and a sample from the same foam was also compression molded into plaques which were tested for elastomer properties. The morphology of the foams and their underlying elastomers was probed by SEM, AFM, DMA, X-ray, FTIR, tensile properties and cyclic stress/strain (hysteresis) experiments. The properties of the polyether control and SBOP containing foams are representative of their underlying polymers. However, foams containing SBOP do not have well developed hard segment organization relative to that of polyether soft segment control foams. Similarly, the SBOP foams do not have as good hard segment organization as the elastomers derived by compression molding the same foams. This suggests that hard segments of SBOP containing foams do not reach thermodynamic equilibrium prior to vitrification during the foaming process. It is possible that this is an artifact of the low equivalent weight (ca. 670 gr/eq) of SBOP which promotes gelation ahead of phase separation. The fact that the elevated temperature modulus is independent of the amount of added SBOP suggests that tensile properties of the foam are not a function of the soft segment crosslink density, but rather the hard segment phase separation. Other foam properties such as airflow and tear strength are shown to be related to the same factors. Improvements in foam properties are achieved by designing the foam formulation to increase phase separation.

Development of Water Blown Bio-Based Thermoplastic Polyurethane Foams

Water blown biobased thermoplastic polyurethane (TPU) foams were prepared using synthetic and biobased chain extender. The concentration of chain extender, blowing agent (BA) and surfactant were varied and their effects on physical, mechanical and morphological properties of foams were investigated. Density, compressive strength and modulus of foams decreases with an increase in BA content and increased with chain extender concentration, but do not change significantly with change in surfactant concentration. The glass-transition temperatures of the foam samples increases with an increase in BA and chain extender concentration. The cell size of the foam sample increases slightly with an increase in BA whereas chain extender concentration has no effect on cell size.

Diethanolamides of Castor Oil as Polyols for the Development of Water-Blown Polyurethane Foam

Castor oil was chemically modified into a diethanolamide by a two step process. The first step was the hydroxylation of double bonds in castor oil and second step was the transamidation using diethanolamine to increase the hydroxyl value. Water blown polyurethane foams were developed with this castor oil based polyol using polypropylene glycol of molecular weight 1,000 as the copolyol and polymeric MDI. The density and mechanical properties namely compression and flexural strength depended on the composition of the foam formulation. The hydroxyamide content and molecular weight of commercial polyol had significant effect on the micro structure as observed by optical microscopy.

Nanoclay Modified Water-Blown Polyurethane Foams Derived from Bifunctional Soybean Oil-Based Polyol

In this brief communication, we report on the modification of polyurethane (PU) foams based on bifunctional soy bean oil-based polyol by nanoclay. Presence of clay at small loading has been observed to make the foam system more rigid. Modification has been analyzed by measurements on density and compressive strength. In addition, differential scanning calorimetry and thermogravimetric analysis have been used to explain changes in properties of the foams. Scanning electron microscopy have been used to verify the foam rigidity in presence of nanoclay. We conclude that nanoclays are capable of strengthening PU foams derived from bifunctional soy polyol.

Characterization of Local Structures in Flexible Polyurethane Foams by Solid-state NMR and FTIR Spectroscopy

The article examines the characterization of local structures in water-blown flexible polyurethane foams with various amine catalysts. In this study, the authors have applied solid-state nuclear magnetic resonance (NMR) relaxation, nuclear spin diffusion, and Fourier transform infrared (FTIR) microscope analysis on flexible polyurethane foams. Quantitative knowledge of the polymer structure and dynamics by these methods provides a significant insight on understanding the microphase separation and the domain structure of urethane and urea hard segments and polyether soft segments in foam. Furthermore, the authors analyze the influence of hydrothermal degradation on the microphase structure of the foams. A detailed comparison of the fundamental results with conventional foam durability tests (e.g., humid aged compression sets) is described, and the hydrothermal degradation mechanism and the influence of catalysts on the foam stability are discussed.

Application of Ethoxylated Inulin in Water-Blown Polyurethane Foams

Inulin, a polydisperse reserve polysaccharide from chicory, was chemically modified via alkoxylation using ethylene oxide, in a water free medium. The reaction resulted in a range of products with very distinct properties, such as a highly increased water solubility, moderate surface-active properties and high cloud points in electrolyte media. Because of the unique characteristics of inulin, such as its molecular weight range, and because of the high water solubility of the ethoxylates, the products were evaluated as additive in water-blown polyurethane foams. The addition of inulin ethoxylates resulted in an increased foam hardness and density, the latter in fact being unwanted. The foam properties were evaluated based on the indentation test, the foam density, the SAG factor, and the hysteresis curves of standard cubes. Based on these parameters inulin ethoxylates were shown to have a beneficial effect on the foam properties. The inulin ethoxylate with a theoretical degree of substitution of 0.5 proved to be the best derivative, since the increase in hardness was the highest, while the increase in density was negligible.

Relevant factors in scorch generation in fire retarded flexible polyurethane foams: I. Amino group reactivity

Use of water instead of chlorofluorocarbons in foaming processes results in increased slabstock temperature and concomitant scorching which often occur more easily in the fire retardant foams. However, not all fire retardants aggravate scorch. Interaction of a number of fire retardants with aniline, which was chosen as a model compound simulating the –NH 2 groups always present in water-blown polyurethane foams, has been examined by several experimental techniques. The reported results highlight that this interaction leads to alkylation of the amine and to the formation of phosphoric acid or alkyl phosphoric acids or hydrogen chloride in the case of chloroalkyl phosphates. As this interaction occurs the scorch phenomenon occurs as well in the fire retardant foams, therefore the scorch could be possibly connected with this interaction. It is likely that N-alkyl anilines or HCl or phosphoric acids can promote scorch.

Relevant factors in scorch generation in fire retarded flexible polyurethane foams: II Reactivity of isocyanate, urea and urethane groups

Water-blown polyurethane foams contain an essential amount of amino groups, urea and urethane bridges as well as residual isocyanates. In order to understand the appearance of scorch in some flame retardant polyurethane systems, the reactivity of isocyanates, urea and urethane bridges with flame retardants has been investigated using model compounds. Both IR and UV analyses showed the lack of chemical interaction of isocyanates, ureas and urethanes with aromatic phosphates, brominated diphenylethers, halogenated-aliphatic and aliphatic phosphates at the temperature and in the timescale of a typical foaming process. Only a physical interaction between these groups and the fire retardant which involved disruption of the H bonding network in the original systems was observed. The ability of the flame retardant to break the hydrogen bonds was controlled by the viscosity of the flame retardant. It was concluded that scorching is not linked to the reactions with urea, urethane or isocyanate groups.