Stability Of Rigid Polyurethane Foams Research Articles

Flame Retardancy and Thermal Stability of Rigid Polyurethane Foams Filled with Walnut Shells and Mineral Fillers.

Recently, the influence of the concept of environmental sustainability has increased, which includes environmentally friendly measures related to reducing the consumption of petrochemical fuels and converting post-production feedstocks into raw materials for the synthesis of polymeric materials, the addition of which would improve the performance of the final product. In this regard, the development of bio-based polyurethane foams can be carried out by, among other things, modifying polyurethane foams with vegetable or waste fillers. This paper investigates the possibility of using walnut shells (WS) and the mineral fillers vermiculite (V) and perlite (P) as a flame retardant to increase fire safety and thermal stability at higher temperatures. The effects of the fillers in amounts of 10 wt.% on selected properties of the polyurethane composites, such as rheological properties (dynamic viscosity and processing times), mechanical properties (compressive strength, flexural strength, and hardness), insulating properties (thermal conductivity), and flame retardant properties (e.g., ignition time, limiting oxygen index, and peak heat release) were investigated. It has been shown that polyurethane foams containing fillers have better performance properties compared to unmodified polyurethane foams.

Effect of the silanization process on the fire resistance and thermal properties of closed-cell foams with sunflower husk ash

The topics covered in this paper are relevant to the further development of polyurethane materials and propose a new method for producing sustainable and innovative foams. In this study, the effect of filler silanization on the flammability and thermal stability of rigid polyurethane foam (RPUF) was investigated. The RPUF composites study was preceded by an analysis of sunflower husk ash (SHA). Thermal decomposition behaviour and particle size distribution were carried out for the SHA samples. More, the elemental composition and structure of the fillers were investigated. The use of silanization of the filler results in homogenization of its structure. Sunflower husk ash has higher characteristic melting points than most biomass ashes and good thermal stability. The foam flammability results were preceded by an analysis of density and cell morphology. The use of silanized filler in RPUFs results in a homogenized structure and a 14 % reduction in apparent density. A wide range of tests were carried out as part of the flammability tests, which included: limiting oxygen index (LOI), gross calorific value, cone calorimeter, and optical density test. Additionally, thermal analysis methods were used to investigate the thermal stability of the foams. Flammability tests carried out confirm the positive effect of filler salinization on flammability. Heat release during combustion is reduced by 10 % and the release of toxic gases is also reduced. On the other hand, the thermal stability results are similar for foam with unmodified filler and those with silanized ash. Based on the comprehensive flammability and smoke results, a trend towards improved flame-retardant properties of RPUFs was observed.

Study on flame retardancy and thermal stability of rigid polyurethane foams modified by amino trimethylphosphonate cobalt and expandable graphite

Abstract Amino trimethylphosphonate cobalt (Co2+-ATMP) flame retardant was prepared by ion exchange method, and rigid polyurethane foam (RPUF) modified by Co2+-ATMP and expandable graphite (EG) was prepared by one-pot and free-rise method. The flame retardancy, thermal stability and smoke toxicity of modified RPUF were studied by limiting oxygen index (LOI), cone calorimeter (Cone), thermogravimetric analysis (TG) and smoke toxicity characterization. The results showed that the flame retardancy, thermal stability and smoke toxicity of RPUF modified by Co2+-ATMP and EG are significantly improved. When the ratio of Co2+-ATMP to EG is 1:5, the LOI value is the highest, and the toxicity of flue gas was the lowest. The peak heat release rate (PHRR) and total heat release rate (THR) were both the lowest, 138 kW/m2 and 15.9 MJ/m2, respectively. Compared with RPUF-0, it decreased by 39.2% and 16.8% respectively. The research results can provide reference for the subsequent flame retardant modification of RPUF.

Studies of polyurethane foams prepared with hybrid silicon and hydroxymethylated lignin

AbstractToday's petrochemical resources are increasingly strained, and the search for renewable, green, and environmentally friendly clean biomass energy has become a necessity. In order to increase the total hydroxyl content of lignin, enhance its reactivity, and replace some polyols in the preparation of rigid polyurethane foam, alkali lignin was extracted and purified from papermaking black liquid, and the lignin was modified by a hydroxymethylation. Rigid polyurethane foam is extremely flammable, and it is very important for rigid polyurethane foam to reduce its flammability using low smoke, nontoxic, nonhalogenated flame retardants. The waste polyurethane foam was treated by a high‐temperature calcination process to create a halogen‐free flame‐retardant hybrid silicon. The flame‐retardant modified rigid polyurethane foam was synthesized by replacing some of polyols with hydroxymethylated lignin and using hybrid silicon as flame retardant. The process conditions used to prepare the hydroxymethylated lignin were optimized based on the response surface method. The optimal conditions used 33 g of formaldehyde, a reaction temperature of 86°C, a reaction time 2.2 h, and a total hydroxyl content of 14.862 mg KOH/g. Analysis of infrared (IR) spectra confirmed that lignin was successfully modified by the hydroxymethylation reaction. Raman spectra (RS) and IR measurements showed that the hybrid silicon foams contained Si3N4, SiC, and SiO2. The apparent densities of the modified polyurethane foams ranged from 39.5–49.6 kg/m3; the compressive strengths were between 0.184 and 0.241 MPa, and the thermal conductivities ranged from 0.019–0.025 W/(m‧K). The flame‐retardant polyurethane foams prepared from the hybrid silicon foams reached a maximum limiting oxygen index (LOI) of 28.5%. Thermogravimetric (TG) and derivative thermogravimetric (DTG) results showed that the hybrid silicon improved the thermal stability of rigid polyurethane foam and increased the amount of carbon residue remaining after decomposition of the foam. Scanning electron microscopy (SEM) results showed that the flame retardants were uniformly distributed in the hybrid foam and the cell size was uniform.

Synergistic effect of combining amino trimethylphosphonate calcium and expandable graphite on flame retardant and thermal stability of rigid polyurethane foam

Amino trimethylphosphonate calcium (Ca-ATMP) has been synthesized and applied to rigid polyurethane foam (RPUF). Synergistic effect of Ca-ATMP and expandable graphite (EG) on flame retardant and thermal stability of RPUFs has been investigated by using the limiting oxygen index (LOI) method, smoke toxicity analysis, Cone calorimeter analysis (CONE), and thermogravimetric analysis (TGA). The experimental results indicated that LOI of the RPUF was 26.3% when the ratio of Ca-ATMP and EG was 1:5. And the peak heat release rate (PHRR) of this proportion of RPUF decreased by 52.4% compared with that of RPUF without flame retardant. In addition, this modified RPUF possessed the maximum apparent activation energy (E) and produced the least toxic gas. On the basis the above data, it can be found that the synergistic effect of Ca-ATMP and EG on flame retardant and thermal stability of RPUFs has the most significant effect when the addition amount of Ca-ATMP and EG is 1:5, which is helpful for improving flame retardation of the RPUF.

Fly Ash as an Eco-Friendly Filler for Rigid Polyurethane Foams Modification.

There is currently a growing demand for more effective thermal insulation materials with the best performance properties. This research paper presents the investigation results on the influence of two types of filler on the structure and properties of rigid polyurethane foam composites. Fly ash as a product of coal combustion in power plants and microspheres of 5, 10, 15, and 20 wt.%, were used as rigid polyurethane foams modifiers. The results of thermal analysis, mechanical properties testing, and cellular structure investigation performed for polyurethane composites show that the addition of fly ash, up to 10 wt.%, significantly improved the majority of the tested parameters. The use of up to 20 wt.% of microspheres improves the mechanical and thermal properties and thermal stability of rigid polyurethane foams.

Mechanical, Thermal Properties and Stability of Rigid Polyurethane Foams Produced with Crude-Glycerol Derived Biomass Biopolyols

Rigid polyurethane foams of significant renewable content (up to 50%) were produced using biomass biopolyols obtained previously via crude-glycerol mediated solvothermal liquefaction of three industrial biomass residue feedstocks: digested sewage sludge, hemp stalk hurds and sugar beet pulp (DSS, HSH and SBP), and commercial diphenylmethane diisocyanate. The produced foams exhibited higher apparent densities 43–160 kg/m3 and compressive strengths 34–254 kPa compared to tested commercial analogues. Varying foam formulation isocyanate-to-hydroxyl group ratios and blending biomass biopolyols with blank crude glycerol biopolyols led to lighter and less strong products. Blank crude glycerol and DSS biopolyol foams exhibited slowest water absorption rates. Biopolyol foams exhibited higher thermal stability and the non-flame retarded foams showed lower potential for fire spread due to lower pyrolysis gas combustion heat release rates and total released amounts of heat. In terms of fire toxicity, biopolyol foams are suspected to be slightly less toxic than typical commercial PU rigid foams (CO and HCN yields of 172.2 and 6.19 mg/g, respectively), still generating significant amounts of irritant smoke in under-ventilated flaming fire scenarios. The products were stable dimensionally (below 1% elongation) and moderately biodegradable (specific rates of 0.25–0.53%/month). Overall, the foams produced show promise as sustainable alternatives in applications such as domestic construction filler foams, where low density is not crucial but fire safety is of utmost importance.

EFFECTS OF KAOLIN ADDITIONS ON THERMAL BEHAVIORS OF RIGID POLYURETHANE FOAMS

Thermal insulation is very important issue in many industrial applications and different materials are preferred to satisfy the thermal insulation depending on the applications. One of the most important properties of the thermal insulation materials is low thermal conductivity. In addition, the cost of the material is another important factor. Among the thermal insulation materials, rigid polyurethane foams are used in automotive, transportation and building sectors due to lower thermal conductivity. Although the thermal conductivity of the rigid polyurethane foam is lower than those of many other thermal insulation materials, other thermal insulation materials may be preferred in some applications due to their lower costs. Therefore, different natural inorganic minerals have been added as fillers into the foams, mainly to reduce raw materials costs. In this study, kaolin, which is a cheap natural inorganic mineral, was incorporated into rigid polyurethane foams in 5, 10 and 15 % in mass. Effects of kaolin addition on thermal decomposition and thermal conductivity of rigid polyurethane foams were investigated. The results revealed that the incorporations of kaolin into the foams slightly increased the thermal conductivities of the foams. However, it was found that kaolin addition enhanced the thermal stability of rigid polyurethane foams. 

Halogen‐free flame retarded rigid polyurethane foam: The influence of titanium dioxide modified expandable graphite and ammonium polyphosphate on flame retardancy and thermal stability

A titanium dioxide modified expendable graphite (EGT) was prepared and characterized. The synergistic effect between EGT and ammonium polyphosphate (APP) on the combustion characteristics and thermal stability of rigid polyurethane foam (RPUF) were investigated through limiting oxygen index (LOI), vertical‐combustion, microscale combustion calorimeter tests, and thermogravimetric/differential thermal gravimetric (TG/DTG) analysis. Results showed that EGT modified RPUF presented better thermal stability and flame retardancy than the normal expandable graphite (EG) modified RPUF. Addition of EGT improved the LOI value of 80RPUF/20EGT from 19.0% to 26.9%. Furthermore, the combination of EGT and APP caused the 80RPUF/10APP/10EGT to exhibit a LOI value of 27.8%, a vertical burning level of V‐0 and a total heat release of 16.5 kJ g−1. The research gave a body of evidence for synergistic performance between EGT and APP, and the effect of condensed phase mechanism was believed to be the main reason for such synergistic effect. POLYM. ENG. SCI., 58:2008–2018, 2018. © 2018 Society of Plastics Engineers

A systematic study substituting polyether polyol with palm kernel oil based polyester polyol in rigid polyurethane foam

The future depletion of petroleum resources is driving development of sustainable alternatives based on biomaterials. This study is aimed at developing rigid polyurethane foam using high bio-based polyester polyol content without sacrificing the mechanical or thermal insulation performance associated with traditional polyether polyol based rigid polyurethane foam. In this paper, we quantify the properties of a model rigid polyurethane foam formulation based on a commercially available polyether polyol and then systematically substitute the polyether polyol with a commercially available palm kernel oil based polyester polyol. The influence of the palm kernel oil based polyester polyol content on reaction kinetics, structure, morphology and mechanical properties of rigid polyurethane foam were evaluated by cup test, Fourier transform infra-red spectroscopy, optical microscopy, and compression testing. Reaction rate was increased by the substation of polyether polyol with palm kernel based polyester polyol. Rigid polyurethane foams were successfully prepared by blending up to 50% of palm kernel oil based polyol with polyether polyol. Mechanical and thermal properties, as well as dimensional stability of rigid polyurethane foam with up to 30% palm kernel oil based polyester polyol gave comparable or better properties to the 100% polyether polyol based foams. Improved compressive strength without compromising thermal insulation was achieved at around 20% palm kernel oil based polyester polyol. This can be due to the formation of hard block segments of rigid urethane linkages composed of palm-based-polyols, into the discrete domains. In terms of the thermal conductivity, the improved thermal insulation properties were achieved at a composition of around 10% palm kernel oil based polyester polyol. Upon substitution of palm based polyols, while the onset degradation temperature was slightly reduced, stability (50% weight loss) above 350°C was improved.

Thermal degradation behavior of rigid polyurethane foams prepared with different fire retardant concentrations and blowing agents

In order to understand the effect of flame retardant (FR) and blowing agents on the thermal stability of rigid polyurethane foams and their resultant chars, two series of polyurethane foams produced with different blowing agents (HCFC-141b and pentane) and various concentrations of a FR (0–50 wt%) were investigated using standard flammability test (ASTM, D-3014), solid-state 13C NMR, TGA and Py–GC/MS. The unique combination of these analytical techniques has proved to be a valuable method for understanding the thermal degradation of rigid polyurethane foams. The standard flammability tests indicate an optimum FR concentration of about 15 wt% for foams using HCFC-141b as the blowing agent, while no optimum condition was determined with pentane. The percent mass retained (PMR) values or char yields have a linear relationship with combustion flame temperature in both series of blowing agents. The solid-state 13C NMR studies clearly show that pentane is chemisorbed during the polymerization and is retained within the foam matrix. The chars have lower concentrations of methylene and oxygenated aliphatic carbons, but a subsequent increase in aromatics is observed. The FR investigated preserves the chemical structure of the polyurethane foam, and, therefore, results in a higher PMR or char yield. The TGA experimental data showed that the maximum combustion reactivities of the chars have a linear relationship with the FR concentration in the parent foams. Py–GC/MS results indicate that the aliphatic oxygenated functional groups are the first to evolve during the pyrolysis and combustion of the polymeric structure. Finally, this study has shown that the addition of FR to the foam formulation results in lower concentrations of small molecules being volatilized, and therefore, preserving the original chemical structure of the parent foam. However, the FR investigated does not seem to be as effective for the pentane series, and gives higher char aromaticities and PMR values than those reported for the HCFC-141b series.

The Effect of Blowing Agent Solubility on the Long Term Dimensional Stability of Rigid Polyurethane Foams

More environmentally acceptable blowing agents, such as hydrochlorofluoro-carbons (HCFCs), hydrofluorocarbons (HFCs), hydrocarbons, and carbon dioxide have now replaced chlorofluorocarbon (CFC) blowing agents in many rigid polyurethane (PUR) and polyisocyanurate-modified polyurethane (PIR) foam applications. However, these new blowing agents were not simply "drop-in" replacements for CFCs. In most cases, the structural matrix of the foam had to be adapted in order to accommodate the new blowing agent. Concerns about the long term performance of these new technologies have led to extensive programs of research, not only to address thermal performance, but also to understand the effects of these blowing agent changes on mechanical properties. While a great deal of progress has been made, the polyurethane industry is still in need of a means to fully assess long term mechanical and dimensional stability performance. One particular problem related to the long term dimensional stability of rigid polyurethane foams is the effect of blowing agent dissolution into the polymer matrix. Such dissolution may cause a softening of the matrix known as a "plasticization effect." In order to reduce the risk of mechanical failure, foam density may be increased, in order to strengthen the foam. However, this raises foam cost, and makes polyurethanes less competitive against other insulation materials. Clearly, the rigid polyurethane foam industry is in need of an accurate means of predicting lowest reasonable density which provides acceptable long term performance. This paper describes the results of a new test designed to quantify the plasticization effect, which provides a fast and accurate means of assessing long term dimensional stability. The new methodology was successfully applied to a number of PUR and PIR foams, expanded with several blowing agents. The degree of blowing agent uptake into the matrix was quantified, and its effects on mechanical properties of the foam was established. In addition, a few correlations were drawn between the new test and real life long term performance data. The results indicate that the methodology presented in this paper allows for effective prediction and quantification of possible plasticizing effects associated with any blowing agent in a PUR or PIR matrix.

The Influence of Temperature on Compressive Properties and Dimensional Stability of Rigid Polyurethane Foams Used in Construction

Rigid polyisocyanurate-modified polyurethane (PIR) foams remain the insulation materials of choice for many commercial and residential construction applications. PIR foam boards, produced by a continuous lamination process, provide an extremely cost-effective combination of thermal resistivity and structural integrity. Utilizing innovative chemistry and processing, the excellent performance of PIR boardstock has been sustained, while achieving compliance with recent environmental regulations concerning ozone depletion. Similarly, steel faced polyurethane (PUR) foam panels with fire retardant additives have also come to play an important role in the construction industry. In construction applications, PIR boards and PUR panels are exposed to widely disparate temperature extremes. However, the structural performance of these rigid foams is typically measured only at certain discrete temperatures. Compressive properties are normally measured at room temperature, and often only in one dimension. Dimensional stability is commonly assessed only under one cold (usually-20°F) and one hot/humid condition. The results of such testing are often taken to be representative of a foam's performance under all possible exposure conditions; clearly a bold assumption. This paper details a fundamental investigation into the influence of temperature on the compressive properties and dimensional stability of closed cell rigid foam. It is shown that these critical parameters are dependent on the physical and morphological properties of the polymeric cellular structure, as well as the thermodynamic properties of the gases used to expand the foam. The compressive properties of typical PIR and PUR foams were measured under a wide range of temperatures in three orthogonal directions. This data was fitted into a model based on fundamental material parameters, and the relationship between dimensional stability and compressive strength in an anisotropic foam was examined. Foams expanded with chlorofluorocarbons (CFC's), hydrofluorochlorocarbons (HCFC's), and several zero ozone depletion potential (ODP) blowing agents were evaluated, resulting in a methodology for predicting field performance under a wide variety of environmental exposure conditions. Foam cell morphology can have dramatic influence on foam structural performance. As the dimensional stability of rigid foams is controlled by the mechanical properties in the weakest direction, foams of similar matrix composition and density can exhibit tremendously different dimensional stability performances due to variations in cell orientation. The properties of the blowing agent also play a critical role in dimensional stability. While -20°F was an appropriate test temperature for CFC and HCFC blown foams, other temperatures may be more appropriate for the best possible assessment of zero ODP foam dimensional stability. The role of matrix composition is also significant. PUR foams plasticized by fire retardant additives appeared to exhibit stronger responses to temperature than highly crosslinked PIR foams. Ultimately, an effective combination of matrix strength (chemical composition and density), blowing agents, and processing (minimal cell orientation) for the application in question is the key to dimensionally stable rigid foam. The methodology presented validates the selection of a relatively weak matrix (PUR, low density), in conjunction with an HCFC blowing agent and excellent processing (isotropic cells), for metal faced panels. The methodology also supports the stronger matrix (PIR, higher density), necessary for permeably faced HCFC boardstock, due to the inherent cell orientation which results from the continuous lamination process.

Techniques to Assess the Various Factors Affecting the Long Term Dimensional Stability of Rigid Polyurethane Foam

CFC blowing agents have been eliminated from virtually all polyurethane foam applications and replaced, in many cases, with the more environmentally acceptable HCFCs, or in some cases in Europe, with hydrocarbons. At the same time, the search continues for zero ozone depletion potential blowing agents and some possible candidates are HFCs, hydrocarbons and water. The physical properties such as boiling point and solubility characteristics of the new blowing agents vary widely and formulations have had to be adapted to new types of blowing agents in order to achieve acceptable processing and resultant foam properties. One of the big limitations to adapting formulations has been the ability of the present test methods to predict performance of foam blown with the new blowing agents. Predictive tests for the dimensional stability of fully CFC-11 blown systems have proven their validity over the years. But such is not the case with foams blown with the new blowing agents. ICI developed a new, more stringent, test to predict the long term dimensional stability performance, and the results of some preliminary evaluations were presented at the last SPI meeting in Boston. This new test focuses on accelerating the normal diffusion processes that typically take place over a period of months or years. This latest paper is directed towards gaining an additional understanding of the matrix plasticization effects of various types of blowing agents and describes a method for quantifying such an effect. It also shows how these new evaluation techniques serve as useful development tools for foam based on third generation blowing agents. Both construction and appliance systems based on PIR and PUR technology are elucidated. Some results from the long term aging of boards and refrigerator/freezer cabinets and comparison of these results with the prediction of the new dimensional stability test method are also discussed. The results discussed here show that industry may be guided in selecting appropriate alternative blowing agents and in the development of current/future formulations and processing by more accurately comparing the long-term dimensional properties using the reliable and accurate test procedures developed in this fundamental study.

Influence of structure of hydroxyl‐terminated maleopimaric acid ester on thermal stability of rigid polyurethane foams

AbstractA series of hydroxyl‐terminated maleopimaric acid esters (HTMAEs) and rigid polyurethane (PU) foams based on these HTMAEs were synthesized using chemically modified natural gum rosin and its derivative maleopimaric acid as raw materials. Thermal stability of these polyols and their corresponding rigid PU foams was studied by a thermogravimetric method and a dimensional stability measurement. It was shown that the thermal stability of the final foams was strongly dependent on the structure of their corresponding polyols. The thermogravimetric analysis curves of these rosin‐based rigid PU foams displayed two distinct regions of weight loss. It has been shown that at the initial stage of weight loss the process was dominated by polyol component degradation; the second stage was governed by isocyanate component degradation. © 1995 John Wiley & Sons, Inc.

The thermal stability of rigid polyurethane foam in insulating pipes

AbstractThe rigid polyurethane, PUR, foam was prepared by reacting diphenylmethane diisocyanate, MDI, with aliphatic correactants of polyether type.The insulating pipe was made by moulding technic. The PUR pipe was subjected to isothermal aging by special equipment which was constructed for this purpose in order to study the structural changes in PUR foam under various temperatures and to define the maximal temperature at which it might be used as insulation in insulating pipes.The structural changes of PUR foam were studied by means of spectrophoto‐metric measurement and thermal analysis.The evidence of thermal degradation of PUR foam has been found. Its course and intensity depend upon the temperature and differ throught the verticale cross‐section of the insulating pipe.The correlation between chemical changes of PUR foam and its physical properties are also discussed.