Preparation Of Rigid Polyurethane Foams Research Articles

Rigid polyurethane foam with durable hydrophobicity and flame retardancy endowed by novel functional surfactants

Traditional rigid polyurethane foam (RPUF) with flame retardancy might be easily damaged in some moist condition due to its hydrophobicity, which would lead to unsafety. Therefore, novel surfactants with both hydrophobic fluorinated group and flame-retardant phosphorus group were synthesized. With lower surface tension and more hydrogen bonds formed in polyurethane, the mixed surfactants, which were used in the preparation of RPUF, have not only obviously improved the size uniformity and integrity of cells but also enhanced its hydrophobicity, compressive strength and thermal insulating performance. Besides, effective ‘protection’ could be constructed on the surface of RPUF by prepared surfactants, when ammonium polyphosphate (APP) and expandable graphite (EG) were introduced to provide good flame retardancy. As a result, with just 2.8 wt% content of those functional surfactants, hydrophobic and flame-retardant RPUF with water contact angle of 126 °, limiting oxygen index of 25 %, compressive strength of 1.3 MPa and thermal conductivity of 27 mW/mK, were finally obtained, which is ahead of other flame-retardant RPUF reported before. It’s worth noting that, this hydrophobic and flame-retardant RPUF exhibits more stable and durable properties when soaking in HCl solution (2 mol/L), NaOH solution (2 mol/L), NaCl saturated solution and various solvents (THF and EtOH), or under strong fiction for 100 times and high and low temperature cycling test for 20 times. This would provide a novel and effective strategy to endow RPUF with enhanced and durable flame retardancy, hydrophobicity, compressive strength and thermal insulating performance even under extreme conditions.

Microstructure and performances of rigid polyurethane foam prepared using double‐effect baking powder as a foaming agent

AbstractThe preparation of rigid polyurethane foam with uniform pore size is extremely challenging. In this work, double‐effect baking powder was used as foaming agent, and rigid polyurethane foam with regular morphology was successfully prepared through semi‐prepolymerization. The rigid polyurethane foam apertures with regular morphology were controlled by the secondary release of CO2 when the content of baking powder is 0.30 part. Combined with theoretical calculation and experimental test, it is found that the particle size distribution, wall thickness, and hole shape are uniform, regular, thin, polygonal, and few broken holes. The compression strength, contact angle, and surface energy of the rigid polyurethane foam are 33.36 kPa, 109.6°, and 21.8 mJ/m2 after adding 0.20 part of double‐effect baking powder, respectively. By adjusting the amount of double‐acting baking powder, the porosity, mechanical properties and foam rate of the polyurethane foams could be significantly improved. Due to the molecular solvation effect, rigid polyurethane foams will deform in the water and oil due phase, but it can remain stable for a long time at room temperature without solvent. It provides a new method for the preparation of rigid polyurethane foam, which is expected to be widely used in transportation and other fields.Highlights Baking powder was firstly used as a foaming modifier for rigid polyurethane. Baking powder releases CO2 twice to ensure uniform structure of polyurethane cell. Rigid polyurethane foam has long‐term stability and regular, uniform cell holes. The porosity and mechanical properties of foams could be significantly improved. Foaming mechanism of rigid polyurethane using baking powder was firstly revealed.

New bio-based polyurethane (PU) foams synthesized using crude glycerol-based biopolyol and humin-based byproducts from biomass hydrolysis

Exploring novel applications for solid waste in industrial production reduces the production cost of polyurethane (PU) foams, which is of great significance for sustainable development. In this study, crude glycerol was utilized to synthesize bio-based polyols via a one-pot method. Around 45 % of the glycerol components present in crude glycerol underwent esterification or transesterification reactions, resulting in the formation of polyhydroxy compounds. The synthesized polyol had a hydroxyl number of 406 mg KOH/g, a viscosity of 1092 mPa·s, and an acid number of 1.9 mg KOH/g, rendering it suitable for the preparation of rigid polyurethane foams. Humin-based residues (FRR, referring to residues from hydrolysis of furfural residue, and GR, referring to residues from hydrolysis of glucose) were further incorporated for the first time to reinforce bio-based PU foams. The effects of various fillers content (0, 1 %, 3 %, 5 %, 7 %, and 10 %) on the mechanical properties, morphology, thermal insulation properties, and thermal stability of PU foams were investigated. At an FRR level of 7 %, the maximum compressive strength reached 0.1536 MPa, representing an increase of 28.30 %. Similarly, when GR levels were set at 5 %, the maximum compressive strength was found to be 0.1581 MPa, reflecting an increase of 32.08 %. The addition of GR filler had a greater impact on enhancing compression strength, potentially due to its spherical and uniform particle shape, which could facilitate better dispersion within the polyols. The PU foam synthesized in this study showed comparable performance to those using cellulose-based fillers. Furthermore, the thermal conductivity of all foams containing fillers was lower than 0.0350 W/(m·K). The thermal gravimetric analysis demonstrated that the addition of humins as filler effectively enhanced the stability of the foam. As indicated from FT-IR and XPS analysis, urethane bonds were successfully formed, while the hydroxyl group on the surface of humins potentially enhanced the consumption of the –NCO group. The foams produced in this study exhibited highly favorable thermal insulation properties, while also offering superior economic and environmental benefits.

Combining hyperbranched polyol containing three flame retardant elements, P, N and Si, with expanded graphite to improve the flame retardancy of bio-based rigid polyurethane foam

The preparation of rigid polyurethane foam (RPUF) from vegetable oil and the improvement of its flame retardant properties are of great importance to broaden the application field of RPUF, which can satisfy the green environment and reduce the fire accidents caused by its flammability. In this paper, a reactive hyperbranched flame retardant polyol (DOPO-MASi) containing three flame retardant elements of P, N and Si was prepared by reacting 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a phosphorus-containing compound, with maleic anhydride, diethanolamine and Triethoxy(3-glycidyloxypropyl)silane (KH-561), respectively, and mixed with expandable graphite (EG) to obtain a vegetable oil-based flame retardant RPUF with the multi-flame retardant system. This foam has excellent flame retardant properties and smoke-suppressing effect, with a limiting oxygen index (LOI) of 30% and a “V-0″ level in the UL-94 vertical burning test, as well as its pHRR, THR, and TSP were reduced by 47.5%, 57.9% and 62.8%, respectively. More importantly, 5% EG/20% FR-RPUF also has good mechanical properties. The above properties provide a reference for the practical application of RPUF in environmental protection and flame retardant.

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.

Preparation of rigid polyurethane foam from lignopolyol obtained through mild oxypropylation.

Lignin, one of the main components of lignocellulose, can be used as an alternative to chemical polyols in the production of polyurethane because of its abundant phenolic and alcohol hydroxyls. Traditionally, lignin is directly applied in the preparation of polyurethane; however, modified lignin has been proved to be superior, especially that obtained by the oxypropylation reaction. Therefore, lignopolyol obtained by mild and efficient oxypropylation was utilized in the production of rigid polyurethane foam in this study. Specifically, the effects of the content of lignopolyol on the chemical structure, morphological structure, mechanical properties and thermal stability of the lignin-based rigid polyurethane foam were investigated. It was found that the compressive strength of the rigid polyurethane foam was significantly improved with the addition of lignopolyol compared with that of the pure polyurethane foam, which was attributed to the fact that oxypropylation made lignin into highly branched and functionalized polyols by transforming all phenolic hydroxyls into aliphatic hydroxyls. Moreover, when the molal weight of lignopolyol accounted for 40% of the added polyols, the generated foam showed optimal uniformity and regularity, and the compressive strength reached 0.18 MPa, meeting the requirements of industrial application, below which, the amount of undesired reactions is bound to increase. As a consequence, the added amount of lignopolyol was increased as much as possible on the basis of guaranteeing the desired properties, which was more conducive to realizing the green degradation and economic synthesis of rigid polyurethane foam.

Natural Oil-Based Rigid Polyurethane Foam Thermal Insulation Applicable at Cryogenic Temperatures.

This paper presents research into the preparation of rigid polyurethane foams with bio-polyols from rapeseed and tall oil. Rigid polyurethane foams were designed with a cryogenic insulation application for aerospace in mind. The polyurethane systems containing non-renewable diethylene glycol (DEG) were modified by replacing it with rapeseed oil-based low functional polyol (LF), obtained by a two-step reaction of epoxidation and oxirane ring opening with 1-hexanol. It was observed that as the proportion of the LF polyol in the polyurethane system increased, so too did the apparent density of the foam material. An increase in the value of the thermal conductivity coefficient was associated with an increase in the value of apparent density. Mechanical tests showed that the rigid polyurethane foam had higher compressive strength at cryogenic temperatures compared with the values obtained at room temperature. The adhesion test indicated that the foams subjected to cryo-shock obtained similar values of adhesion strength to the materials that were not subjected to this test. The results obtained were higher than 0.1 MPa, which is a favourable value for foam materials in low-temperature applications.

A novel catalytic two-step process for the preparation of rigid polyurethane foams: synthesis, mechanism and computational studies

Synthesis of polyurethane foams catalyzed by sodium chloride both in prepolymer preparation and elongation step. The reaction mechanism involves the role of a proton shuttle between two terminal OH groups of PEG 400.

Effect of the properties of polyether polyol on sorption behaviour and interfacial tension of polyol/CO2 solutions under high pressure condition

The interaction between CO2 and polyol plays crucial role in the preparation of rigid polyurethane foams using CO2 as blowing agent directly. The solubility and diffusivity of CO2 in polyether polyols with different molar mass and functionality were measured using magnetic suspension balance in pressure range of 2–6 MPa, and the interfacial tension of these polyol/CO2 systems were determined by pendant drop method. The solubility of CO2 in polyols became larger when their molar mass rose up to 1000 g·mol−1, and had the highest values when the functionality of polyether polyols was 3. The dual-mode sorption model can fit the solubility of CO2 in different polyols well. Both the diffusivity of CO2 in polyol and specific volume of polyol/CO2 solution increased with higher molar mass, but changed indistinctly with different functionality. The diffusivity of CO2 in polyols was (10−9–10−8) m2 s−1 order of magnitude, and the specific volume has a non-monotonic change with pressure. Higher solubility of CO2 in polyols resulted in lower interfacial tension of polyol/CO2 solutions, so that the interfacial tension of polyol/CO2 solution has lowest values for polyether polyol with molar mass of 1000 g·mol−1 and functionality of 3, which decreased with the increasing of pressure. All interfacial tension data of polyol/CO2 solutions can be correlated by a unified Macleod’s equation.

Rigid polyurethane foams from unrefined crude glycerol and technical lignins

The need for green materials has driven interest in the preparation of rigid polyurethane foam (PUF) from various biomass types. The present study aims at increasing bio-based content by utilizing by-products from both the pulp and paper and biodiesel industries. Bio-based polyols from respective liquefaction of kraft lignin, organosolv lignin and lignosulphonate in crude glycerol were employed to prepare rigid PUFs. The highest foam compressive strength was 345 kPa with density 79 kg m−3; thermal conductivity was 0.039 W m−1 K−1 and the corresponding material had 44 wt% renewable content. Thermal characteristics and biodegradability were also evaluated. Technical lignin type was found to determine product properties to a large extent. Based on the use of existing industrial scale by-products in this study, the findings can be beneficial for present and future biorefineries in the valorization of lower value by-product streams.

Preparation and characterization of water‐absorbing polyurethane foam composites with microsized sodium polyacrylate particles

ABSTRACTThis article introduces the preparation of rigid polyurethane foam (PUF) and studies the effect of various mass percentages of sodium polyacrylate (PAAS, microsized) on PUF hydrophilicity. The characterization of PUF (with 0–5.5 wt % PAAS) was conducted via scanning electron microscopy, contact angle analysis, differential scanning calorimetry, and pore size distribution. All modified foams showed an improvement in their water sorption and water maintenance capacities, and the PU foam content of 5.5 wt % PAAS showed a water absorption of 891%, and the water retention performance was 408% (96 h) compared to the pure PU foam. Through contact angle measurements, the relationship between the hydrophilicity of the modified foams and PAAS content was investigated. The compression strength of the samples was also tested. When the PAAS is 2.6 wt %, the compression strength of the composites decreased about 50% compared with the pure PU foam. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46702.

Aliphatic–Aromatic Polyols by Thiol–Ene Reactions

Aliphatic–aromatic polyols were synthesized by thiol–ene reactions (photochemical or thermal) using mercaptanized starting materials from bio-based compounds: limonene dimercaptan, thioglycerol, mercaptanized castor oil and isosorbide (3-mercaptopropyl) ether. Aromatic starting materials were phenols containing double bonds; ortho-allyl phenol (OAP, petrochemical-based) and eugenol (EUG, bio-based). The phenolic hydroxyl groups were blocked by alkoxylation with propylene oxide (PO) or glycidol (GLY) prior to use in thiol–ene reaction. The aromatic rings were attached to the mercaptans by reacting thiol groups with the double bonds of alkoxylated OAP (OAP–PO and OAP–GLY) and alkoxylated EUG (EUG–PO and EUG–GLY). These synthesized aliphatic–aromatic polyols were utilized for preparation of rigid polyurethane foams whose physical–mechanical properties were superior to those made only from bio-based aliphatic polyols. These rigid PU foams can be used in a wide range of applications; such as thermal insulation of freezers, buildings, pipes and storage tanks for food and chemical industries, as wood substitute, packaging materials and flotation materials.

Synthesis and Characterization of Functionalized Calix[4]arene Derivatives and Preparation of Rigid Polyurethane Foams by the Incorporation of Calixarene

SummaryCalix[4]arenes namely, 5,11,17,23 tetra tert butyl calix[4]arene and 5,11,17,23 tetra chlorosulfonyl calix[4]arene were synthesized to produce octakis (hydroxyl ethyl) sulfonamide calix[4]arene which was used in polyurethane‐calixarene rigid foam composite formulation. The effect of calixarene ratio on mechanical properties of synthesized composites was studied at three calixarene ratios including 1.5, 2, and 3 % (w/w). The obtained data indicate that the tensile strength and modulus are increased as the calixarene ratio increases while the fracture strain is decreased. Quantitatively, addition of 3% (w/w) of calixarene to the polyurethane resulted in 30.99% and 30.01% improvements in modulus and tensile strength, respectively. Contrarily, a decrease of about 13.1% was observed in fracture strain when compared to the properties of the pristine polyurethane rigid foam. The effect of Calixarene on thermal stability of Calixarene‐ polyurethane composite indicating that Calixarene component strictly enhances the thermal stability of composite.

New polyols with isocyanuric structure by thiol-ene “click” chemistry reactions

New polyols with isocyanuric structure were synthesized by thiol-ene “click” chemistry of triallyl isocyanurate with 1-thioglycerol and 2-mercaptoethanol. The synthesized polyols, prepared with high reaction rates and in very high yields, were chemically and structurally characterized. These polyols were used for the preparation of rigid polyurethane foams with excellent physical–mechanical properties and inherent flame retardancy. By alkoxylation of isocyanuric polyols with propylene oxide and/or ethylene oxide in a self-catalytic process, odorless polyols with lower hydroxyl numbers and lower viscosities were obtained, leading to PU foams with good properties, but without inherent flame retardancy. The synthesized polyols with isocyanuric structure are suitable for the preparation of all types of rigid polyurethane foams, including thermoinsulation of freezers, buildings, storage tanks and pipes for the food and chemical industry, for packaging, and as wood substitutes.

Preparation and characterization of biopolyol via liquefaction of rice straw

Biopolyols were prepared by the liquefaction of rice straw under the mild condition. The optimum liquefaction effect was obtained at 5 : 1 volume ratio of PEG400 to DEG, 4 : 1 liquid–solid ratio, H2SO4 3%, time 2.5 h, and reaction temperature120°C. Products were characterized by FTIR and gel permeation chromatograms (GPC) measurements. The hydroxyl value and weight-average molecular weight of the biopolyol produced based on the above optimal conditions were 260 mg KOH/g polyol and 420 g mol–1, respectively. Biopolyol obtained is suitable for the preparation of rigid polyurethane foam. This study has certain significance for the high added value use of rice straw and reducing the production cost and improvement biodegradability of polyurethane foams.

Preparation of rigid polyurethane foams using low-emission catalysts derived from metal acetates and ethanolamine

Abstract Two metal acetate-ethanolamine complexes, namely Cu(OAc)2(EA) and Zn(OAc)2(EA), were synthesized from metal acetates [M(OAc)2, where M=Cu and Zn] and ethanolamine (EA). These metal acetate-ethanolamine complexes can be used as catalysts in the preparation of rigid polyurethane (RPUR) foams. Both Cu(OAc)2(EA) and Zn(OAc)2(EA) were obtained as viscous liquids, which have very weak odor and could be easily dissolved in the starting materials of RPUR foam formulation. The results were compared with RPUR foam prepared from dimethylcyclohexylamine (DMCHA), which is a commercial catalyst with very strong amine odor. Considering the gel time and rise time, Cu(OAc)2(EA) had higher catalytic activity than Zn(OAc)2(EA) and both metal acetate-ethanolamine complexes had lower catalytic activity than DMCHA. Density and compressive strength of RPUR foam catalyzed by Cu(OAc)2(EA) were comparable to that prepared from DMCHA.

Metal acetylacetonate–amine and metal nitrate–amine complexes as low‐emission catalysts for rigid polyurethane foam preparation

ABSTRACTSix metal–amine complexes, Cu(acac)2(trien), Zn(acac)2(en), Zn(acac)2(trien), Cu(NO3)2(en)2, Cu(NO3)2(trien), and Cu(NO3)2(tetraen), are synthesized from metal acetylacetonates [M(acac)2, where M = Cu and Zn] or metal nitrate [M(NO3)2, where M = Cu] and aliphatic amines (en = ethylenediamine, trien = triethylenetetramine, and tetraen = tetraethylenepentamine). These metal–amine complexes can be used as catalysts in the preparation of rigid polyurethane (RPUR) foams. All metal–amine complexes emit very weak odor when compared with N,N‐dimethylcyclohexylamine (DMCHA), which is a commercial catalyst commonly used in the preparation of RPUR foams. DMCHA emits very strong amine odor that affects working environment in RPUR foam processing. Among all metal complexes, Cu(acac)2(trien) has the highest catalytic activity. In comparison with DMCHA, Cu(acac)2(trien) shows slightly higher catalytic activity in gelling reaction but lower catalytic activity in blowing reaction. RPUR foam prepared from Cu(acac)2(trien) has lower density and compressive strength than that prepared from DMCHA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42332.

Synthesis of a Novel Limonene Based Mannich Polyol for Rigid Polyurethane Foams

A novel bio based Mannich polyol using limonene was synthesized. Mannich polyols are a group of amino polyols with aromatic structure which provide fire resistance, good thermal and superior physico-mechanical properties. The synthesized Mannich polyol was structurally characterized using wet methods (hydroxyl number, acid value and viscosity), gel permeation chromatography, and FT-IR spectroscopy. The Mannich polyol was successfully used for preparation of rigid polyurethane foams. Thermal analysis of the rigid polyurethane foams indicated that they were thermally stable up to 250 °C. Studies based on dynamic mechanical analyses indicated that these rigid polyurethane foams have high glass transition temperature (~200 °C). These foams have also high compressive strength and very regular cell structure with uniform size distribution. The closed cell content of these foams was higher than 90 %. The synthesized Mannich polyol based on limonene was very reactive, indicating that it is very suitable for preparation of rigid polyurethane foams using “spray” process.

Novel Renewable Polyols Based on Limonene for Rigid Polyurethane Foams

Novel renewable polyols based on limonene were synthesized using thiol-ene “click” chemistry. These limonene based polyols were structurally characterized using wet methods (hydroxyl number, acid value and viscosity), gel permeation chromatography and spectroscopic methods. The results indicated that high yield of polyols from limonene based materials can be obtained using thiol-ene reaction. These limonene based polyols were used successfully for preparation of rigid polyurethane foams. These foams had regular shape cells and uniform cell size distribution. Thermal studies on these foams indicated that foams were thermally stable up to 250 °C. The glass transition temperature of the foams was higher than 200 °C. These rigid polyurethane foams had high compressive strength and the highest compressive strength of 195 kPa was observed. These foams have good physical–mechanical characteristics and could be suitable for all the applications of rigid polyurethane foams such as thermal insulation of freezers, storage tanks for the chemical and food industries, and packing materials for food industries.

Chemical Degradation of Polymers (Polyurethanes, Polycarbonate and Polyamide) by Esters of H-phosphonic and Phosphoric Acids

A review of the research efforts on the development of pathways for the degradation of polymer–wastes of polyurethanes, polycarbonates and polyamides by esters of H-phosphonic and phosphoric acids is presented. Our group has made it clear, thanks to a vast research program devoted to this subject, that alkyl esters of H-phosphonic and phosphoric acids can be used as very effective degrading agents for polymers. Products and mechanism of polyurethanes degradation by treatment with phosphonates are reviewed in this work. The interest of phosphorus-containing degradation products lies on the fire retardant properties that these phosphorous moieties introduce in the recovered molecules. Most of these phosphorilated molecules can be easily reapplied as reactive intermediates by treatment with propylene oxide and used for the preparation of rigid polyurethane foams. The interaction of poly[2,2-bis(4-hydroxyphenyl)-propanecarbonate] (PC) with H-phosphonic acid dialkyl esters [(RO)2P(O)H, where R = CH3 or CH2CH3], or with triethyl phosphate (CH3CH2O)3P(O) yielded interesting phosphorus-containing oligocarbonates. Polyamide-6 can be converted into functional reactive oligomers with new properties by treatment with diesters of the H-phosphonic acid.