Enhanced mechanical property and thermal insulation of modified rigid polyurethane foams by few surface-functional silica aerogel

The effect of perfluoroalkane (PFA) on the morphology, thermal conductivity, mechanical properties and thermal stability of rigid polyurethane (PU) foams was investigated under ambient and cryogenic conditions. The PU foams were blown with hydrofluorolefin. Morphological results showed that the minimum cell size (153 μm) was observed when the PFA content was 1.0 part per hundred polyols by weight (php). This was due to the lower surface tension of the mixed polyol solution when the PFA content was 1.0 php. The thermal conductivity of PU foams measured under ambient (0.0215 W/mK) and cryogenic (0.0179 W/mK at −100°C) conditions reached a minimum when the PFA content was 1.0 php. The low value of thermal conductivity was a result of the small cell size of the foams. The above results suggest that PFA acted as a nucleating agent to enhanced the thermal insulation properties of PU foams. The compressive and shear strengths of the PU foams did not appreciably change with PFA content at either −170°C or 20°C. However, it shows that the mechanical strengths at −170°C and 20°C for the PU foams meet the specification. Coefficient of thermal expansion, and thermal shock tests of the PU foams showed enough thermal stability for the LNG carrier’s operation temperature. Therefore, it is suggested that the PU foams blown by HFO with the PFA addition can be used as a thermal insulation material for a conventional LNG carrier.

Investigating the potential of dihydroxystearic acid as feedstock for rigid polyurethane foam

A reconstruction method is proposed for the polyurethane foam and then a complete numerical method is developed to predict the effective thermal conductivity of the polyurethane foam. The finite volume method is applied to solve the 2D heterogeneous pure conduction. The lattice Boltzmann method is adopted to solve the 1D homogenous radiative transfer equation rather than Rosseland approximation equation. The lattice Boltzmann method is then adopted to solve 1D homogeneous conduction-radiation energy transport equation considering the combined effect of conduction and radiation. To validate the accuracy of the present method, the hot disk method is adopted to measure the effective thermal conductivity of the polyurethane foams at different temperature. The numerical results agree well with the experimental data. Then, the influences of temperature, porosity and cell size on the effective thermal conductivity of the polyurethane foam are investigated. The results show that the effective thermal conductivity of the polyurethane foams increases with temperature; and the effective thermal conductivity of the polyurethane foams decreases with increasing porosity while increases with the cell size.

The enhancement of mechanical and thermal properties of rigid polyurethane foam (RPUF) achieved through a cost‐effective and sustainable approach remains an ongoing interest in both industry and academia. In this study, water‐blown rigid polyurethane (PU) foams based on crude glycerol (CG) polyol are developed and halloysite nanotubes (HN) and microcrystalline cellulose (MC) with different loadings of 1.0, 3.0, and 5.0% are incorporated to improve the performance of the foams, respectively. Effects of different loadings of HN or MC on the viscosity of CG polyols and the foaming process are investigated. CG‐based polyurethane (CGPU) foams and their foam composites (CG‐HN PU foams and CG‐MC PU foams) are characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results reveal that HN is easier to disperse uniformly in the CG polyol than MC and CGPU foams with 1.0% of HN and MC shows significantly improved performance. Their compressive strength increases by 3.8 and 12.5%, respectively, as the HN and MC loadings increases from 0 to 1.0%. The thermal conductivities of CG PU foams reinforced with 1.0% of HN and MC are 37.79 and 37.94 mWm−1K−1, which are lower than that (38.24 mWm−1K−1) of CGPU foams without the addition of fillers. Moreover, compared to CGPU foams, both CG‐HN PU foams and CG‐MC PU foams show improved thermal stabilities, and the latter is higher than the former.Practical Applications: Different fillers (HN and MC) are used to reinforce the CG‐based polyurethane, and water‐blown rigid PU biofoam composites with improved properties are prepared. The use of fillers (HN and MC) has the potential for the production of advanced CG‐based rigid PU foams.Water‐blown rigid crude glycerol‐based polyurethane foams (PU) reinforced with halloysite nanotubes (HN) and microcrystalline cellulose (MC). The results reveal that HN is easier to disperse uniformly in the CG polyol than MC and CGPU foams with 1.0% of HN and MC show significantly improved performance. The thermal conductivities of CG PU foams reinforced with 1.0% of HN and MC are 37.79 and 37.94 mWm−1K−1, which are lower than that of CGPU foams without the addition of fillers. Moreover, compared to CGPU foams, both CG‐HN PU foams and CG‐MC PU foams show improved thermal stabilities.

ABSTRACTRigid polyurethane (PU) foam is used as a thermal insulating and supporting material in domestic refrigerator/freezers and it is produced by reaction injection molding (RIM) process. There is a need to improve the thermal property of rigid PU foam but this is still a challenging problem. Accordingly, this work investigates the RIM process parameters to evaluate their effects on rigid PU foam's structure and hence property. It has been found that mold temperature is a key parameter whereas curing time has negligible effect on structure of PU foam. Cell size, strut thickness, and foam density have been found very critical in controlling the thermal and mechanical properties. Upper and lower values of 30 to 32 kg/m3 density are critical to observe contribution of radiation and solid conductivity separately. Finally, PU foam with 160 µm average cell size, 16 µm strut thickness, below 10% open cell content, and 30 to 32 kg/m3 density allow obtaining better thermal insulation without significant reducing in the compressive strength. The presented work provides a better understanding of processing‐structure‐property relationship to gain knowledge on producing high‐quality rigid PU foams with improved properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44870.

The green rigid polyurethane (PU) foam has been developed with 100 % soy polyol after optimization of formulation ingredients and lignin has been introduced and isocyanate content reduced in the green rigid PU foam. The cellulosic nanofibers have also been successfully incorporated and dispersed in green rigid PU foam to improve the rigidity. The influence of nano cellulose fiber modification (enzymatic treatment, hydrophobic modification with latex) on the foam density, open cell content, foam raise height, water vapor, and mechanical properties of rigid PU foam were studied. The foamed structures were examined using scanning electron microscopy to determine the cell size and shape due to the addition of cellulosic nanofibers. The odor test were performed to evaluate the odor concentration 100 % soyol based PU foam including lignin and nanofiber and compared to 100 % synthetic based polyol PU foam. The experimental results indicated that the compression and impact properties improved due to the modification of nano cellulosic fibers. The odor concentration level of nanofiber reinforced rigid PU foam reduced significantly compared to 100 % PU foam due to the replacing of isocyanate content. It can be said that with an appropriate combination of replacing isocyanate by lignin and addition of nanofiber, rigid PU foam properties could be improved.

Rosin‐based polyester polyols were synthesized from a rosin–maleic anhydride adduct, diethylene glycol, and ethylene glycol with and without adding adipic acid and phthelic anhydride, in the presence of catalyst. Rigid polyurethane (PU) foams were prepared with these rosin‐based polyols and compared with foam made with an industrial polyester Daltolac™ P744. The experimental results show that the foaming behavior for the foams prepared from such rosin‐based polyols is similar to that of industrial products, but their 10% compression strength, both parallel and vertical to foaming rise direction, is higher and the dimensional stability at 100 and −30°C is similar or somewhat better than that of a comparable system. Furthermore, the rosin‐modified PU foams exhibit even lower thermal conductivity and much higher activation energies during the pyrolysis process. All these unique physical properties of the rosin‐modified rigid PU foams were correlated to the structures of these PU foams. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 598–604, 2002; DOI 10.1002/app.10312

Bi-phase flame-retardant effect of hexa-phenoxy-cyclotriphosphazene on rigid polyurethane foams containing expandable graphite

In this study, clay minerals such as bentonite and dolomite were included to increase the compressive tensile strength and decrease the thermal conductivity of rigid polyurethane foam. The effect of different combinations and amounts of clay minerals on the test parameters of the foam was investigated. The surface morphology of the doped foams was investigated by scanning electron microscopy (SEM). Polyurethane foams were subjected to compressive-tensile strength and thermal conductivity tests. Improvement was observed in the thermal conductivity of polyurethane foams containing 1% bentonite and in the compressive and tensile strengths of polyurethane foams containing 2% dolomite. When clay minerals were added to polyurethane foam in combination, both thermal conductivity and compressive and tensile strengths were improved.

Developing polyols derived from natural sources and recycling materials attracts great interest for use in replacing petroleum-based polyols in polyurethane production. In this study, rigid polyurethane (PUR) foams with various isocyanate indices were obtained from polyols based on rapeseed oil and polyethylene terephthalate (RO/PET). The various properties of the prepared PUR foams were investigated, and the effect of the isocyanate index was evaluated. The closed-cell content and water absorption were not impacted by the change of the isocyanate index. The most significant effect of increasing the isocyanate index was on the dimensional stability of the resulting foams. This is due to the increased crosslink density, as evidenced by the increased formation of isocyanurate and increase of the glass transition temperature. Additionally, the influence on compression strength, modulus, and long-term thermal conductivity were evaluated and compared with reference PUR foams from commercially available polyols. Rigid PUR foams from RO/PET polyol were found to be competitive with reference materials and could be used as thermal insulation material.

Rigid polyurethane (PU) foams are widely used in modern life owing to excellent strength and weight carrying capacity. Most of the rigid PU foams in the market are based on polypropylene oxide (PPO) and methylene diphenyl diisocyanate. Amine catalysts, especially tertiary amines, are used to balance both the gelling and gas-foaming reactions, responsible for foam formation. The objective of present work is to prepare rigid PU foams from PPO based polyol and 4,4′- methylene diphenyl diisocyanate (MDI). The morphological and mechanical properties of polyurethane foam using tertiary amine and water blowing agent have been investigated. Moreover, acoustic and thermal insulation of polyurethane foam ordinary Portland cement mortar formulations were also examined. The results indicated that polyurethane ordinary Portland cement mortar formulations have good sound absorption and thermal insulation characteristics compared to blank formulations.

Rigid closed-cell polyurethane (PU) foam is well-known for its ability to withstand external force. On the other hand, due to the closed-cell nature, its ability to absorb sound is doubtful since hollowed materials are supposed be better in sound absorption. However, the composites fabrication with non-reactive fillers was thought to improve sound absorption ability since it might prohibit the formation of closed cell in the process. In this research, rigid polyurethane foam was prepared from polyether polyol and polymeric methylene di-isocyanate (p-MDI) formulated with water as a blowing agent. Natural rubber-wood sawdust was used as a filler. The percentages of rubber-wood sawdust in the polyurethane foam composites were varied by 0, 1, 3, 5 and 7%. The measurement of sound absorption coefficient has been done using impedance tube technique. The results showed that the rigid closed-cell polyurethane foam with 0% filler exhibits poor acoustic absorption. Additionally, sound absorption coefficient results showed that a sample with higher amount of rubber-wood sawdust allowed the sound wave to be absorbed at wider frequency range. This could be explained that the rubber-wood sawdust filler played an important role in sound absorption property.

A new kind of rigid polyurethane (PU) foam was synthesized from the oil phase of bio-oils from microwaveassisted pyrolysis of corn stover. The recipes for the PU foams consisted of polyol-rich bio-oils, water as blowing agent, polyethylene glycol (PEG) as both polyol donor and plasticizer, diphenylmethane-4,4’-diisocyanate (polymeric MDI) as cross-linking agent, silicon-based surfactant, and tin-based catalyst. The mechanical properties of rigid foams were measured with universal testing machine (Instron4206). The effects of individual ingredients on the physical and mechanical properties of the foams were studied. It was found that water content, bio-oil content, and isocyanate dosage were important variables in making PU foams in terms of mechanical strength, density, and cellular structure.Under optimal conditions, the compression strength of the prepared PU foams reached 1130 kPa with a density of 152.9 g/L. The results show that bio-oils are potential renewable polyol sources for making rigid PU foams. Key words: rigid polyurethane foam, PU, bio-oil, microwave pyrolysis, corn stover, physical properties DOI: 10.3965/j.issn.1934-6344.2009.01.040-050 Citation: Jianping Wu, Yuanhua Wang, Yiqin Wan, Hanwu Lei, Fei Yu, Yuhuan Liu, Paul Chen, Lirong Yang, Roger Ruan. Processing and properties of rigid polyurethane foams based on bio-oils from microwave-assisted pyrolysis of corn stover. Int J Agric & Biol Eng, 2009; 2(1): 40

Background: Polyurethane (PU) foams contained in construction and demolition wastes (CDW) represent a great environmental impact, since they usually end in landfill or incineration processes. The goal of this work is to develop a way to formulate PU foams, maintaining (or ever improving) their performance, by the re-use of those industrial wastes. This procedure will allow minimize both the volume of disposal to be treated by other ways and the amount of pristine raw material needed to produce new PU foams. Methods: In this work, new rigid and soft polyurethane (PU) foams have been formulated with addition of recycled PU foams coming from demolition of buildings. Density, Fourier transform infrared analysis, compression properties and thermal conductivity were measured to characterize the resulting foams. Results: The work showed that addition of filler coming from recycled PU foams should be limited to low percentages, in order to allow good foam evolution from the reactants. Thermal conductivity values of modified rigid foams are worse than those of pristine foam, which is undesirable for thermal insulation purposes; however, in the case of soft foams, this parameter improved to some extent with low levels of recycled PU foam addition. Conclusions: The studied procedure could contribute to reduce the thermal conductivity of pristine soft PU foam, which would be of interest for applications where thermal insulation matters.

Rigid polyurethane (PUR) and polyisocyanurate (PIR) foams are widely used as thermal insulation materials due to their excellent thermal conductivity and low density. However, fire resistance remains a critical property determining their safe application in construction, transportation, and energy systems. This study provides a comparative overview of the fire behavior of PUR and PIR foams, focusing on structural aspects, decomposition mechanisms, flame retardancy, and performance of emission of toxic gases during the combustion process. Despite extensive studies on PUR and PIR foams, systematic comparative investigations addressing the combined influence of recycled PET-based polyester polyols, isocyanurate content, and fire-related properties-including thermal degradation, heat release, and toxic gas emissions-remain limited. PIR foams, characterized by higher isocyanate indices and the presence of isocyanurate rings, show superior thermal stability, reduced heat release rates, and enhanced char formation compared with PUR foams. Experimental analysis of thermal degradation (TGA/DTG) and heat release (cone calorimetry) confirms that PIR foams demonstrate higher resistance to ignition and slower fire propagation. The results emphasize the critical role of molecular architecture and crosslink density in shaping the fire performance of rigid foams, highlighting PIR systems as advanced insulation solutions for applications requiring stringent fire safety standards. The PIR foam was prepared using a polyester polyol derived from recycled PET, which could help in achieving better fire properties during the combustion process. Compared with PUR foams, PIR foams exhibited an approximately 50% reduction in peak heat release rate, an increase in char yield from about 3 wt.% to over 22 wt.%, and a shift of the main thermal degradation peak by approximately 55 °C toward higher temperatures, indicating substantially enhanced fire resistance.