Patent Application
20190194378
The present invention relates to a flexible or semi-flexible polyurethane foam comprising a polyester polyol which can be of bio-sourced origin.
Polyurethanes (PUs) are polyvalent polymers obtained by the reaction between a polyol and a polyisocyanate (Scheme 1, a). PUs are used in automobiles, furniture, construction, footwear, acoustic and thermal insulation. With global production of 18 Mt in 2016, PUs rank 6th in terms of annual global polymer production. Flexible foams represent the largest PU market with more than 1600 kt produced in Europe in 2011. Typically, PU foams are made from polyols, polyisocyanates, swelling agents, surfactants, and various catalysts to obtain a chemically crosslinked cellular material. Two types of swelling agents are used in the synthesis of PU foams: chemical swelling agents and physical swelling agents. Chemical swelling agents are compounds that react chemically in the foaming process to release gases. Water reacts with the isocyanate function to form urea and releases one mole of CO2 per mole of water (Scheme 1, b). Physical swelling agents are compounds having a low boiling point; isopentane derivatives, which evaporate during the exothermic foaming process may be mentioned as physical swelling agents.
In general, flexible and semi-flexible PU foams are obtained from polyols presenting a low hydroxyl content (OHV≤100 mg KOH/g) and high average molecular weight (Mn) value (3000 g/mol). ≤Mn≤6,000 g/mol), in order to increase the flexibility and reduce the crosslinking of the material. Semi-flexible foam boards are a very important part of PU foams. They are an interesting solution to the problems of our modern societies such as noise pollution, moreover, their open-cell structure is permeable to moisture. Permeable materials are in high demand in the insulation industry to prevent moisture build-up and mold growth. These materials generally have low bulk density, low thermal conductivity and, therefore, are inexpensive materials. This means that boards of semi-flexible foams are versatile insulation materials: acoustically and thermally.
The properties of flexible and semi-flexible PU foams come from the phase separation of rigid and flexible domains. Flexible domains are extensible chains, mainly provided by the polyols, which provide the elasticity of the material. Generally, the hard segments are described as a rigid structure that is physically cross-linked by polyol or by using an excess of polyisocyanate.
The excess of polyisocyanate leads to an increase in the biurea bond (Scheme 1, d), the allophanate bond (Scheme 1, c) or the isocyanurate bond (Scheme 1, e). The hard segment is also obtained from a chain extender and an isocyanate. Another way to improve the rigidity of the hard segments is to increase the low interchain forces in the rigid domain by introducing polar groups such as urea. The presence of urea leads to the increase of the amount of hydrogen bonds and the softening temperature.
The PU industry is highly dependent on petroleum-based polyols and polyisocyanates, which are toxic compounds derived from phosgene or diphosgene chemistry. The development of new polyols from high added value renewable synthons for the PU industry is now mandatory to reduce greenhouse gas emissions. The high diversity and functionality of the biomass synthons makes it possible to introduce new properties to PU materials. Sorbitol is one of those elements of interest that was cited as one of the top 12 value-added chemicals from biomass by the US Department of Energy in 2004 and more recently in a list updated by Bozell J J et al. in 2010 (J. J. Bozell, G. R. Petersen, Technology Development for the Production of Bio-sourced Products from Biorefinery Carbohydrates-US Department of Energy's “Top 10” revisited, Green Chem. 12 (2010) 539).
Sorbitol has a high functionality. It is a crystalline sugar alcohol bearing two primary hydroxyl groups and four secondary hydroxyl groups, which is convenient for chemical modification and its use in polyurethane chemistry. It is important to control the modification of sorbitol to polyol. The polyol functionality, the OH number and the viscosity of the polyol have a strong impact on the formation of the PU network, the density and the morphology of the PU foam. Beyond the open or closed nature of the PU foam cells, the size, shape and spatial distribution of these cells also have an effect on the physical properties of the foam. Thus, the thermal and mechanical properties of PU foams depend closely on the morphology of the foam.
Much research has focused on the development and physical characterization of bio-sourced polymer foams using different approaches. However, the mechanical and thermal properties of these materials have been less studied. For example, only a few studies deal with the studying and modeling of mechanical properties related to thermal properties. According to the classical model developed by Gibson and Ashby, the Young's modulus has a square dependence on the relative density, but without any dependence on the size of the cells. The effect of foam density is well established, but there have been few studies of (i) the influence of the size of cells having a constant density, and (ii) the effect of initial formulation foam.
Starting from a bio-sourced polyester polyol, the inventors have developed a novel bio-sourced polyurethane foam having good mechanical characteristics and in particular anisotropic mechanical characteristics according to the direction of solicitation of the foam, compared with the petrol-derived PU foam obtained from a classic petrol-sourced polyether polyol.
The inventors have established a comparative study and demonstrated correlations between the formulation of the foam, the characteristic foaming times (kinetics) and the mechanical properties of the bio-sourced PU foams.
The invention relates to a flexible or semi-flexible foam or a composition for obtaining a flexible or semi-flexible foam comprising a polyester polyol or a polymer comprising a polyester polyol, said polyester polyol being obtained by a first polycondensation (a) of a C3 to C8 sugar alcohol Z and two identical or different C4 to C36 diacids Y and Y′ and a second polycondensation (b) of the product obtained in (a) with two identical or different C2 to C12 X and X′ diols.
The invention also relates to a flexible or semi-flexible foam or a composition for obtaining a flexible or semi-flexible foam comprising a polyester polyol or a polymer comprising a polyester polyol, said polyester polyol is of general formula Rx-Ry-Z—Ry′-Rx′ in which
Typically, by the term “foam” as used, for example, in the terms “polyurethane foam” or “polyisocyanurate foam” is meant a compound of three-dimensional expanded type alveolar structure. Said foam may be rigid or flexible, with open or closed cells. The term “flexible or semi-flexible or semi-rigid foam” means a foam that returns to its initial shape (about 2-60 s) after a deformation in compression of 50%. Generally, such foams have a mixed structure composed of open and closed cells. Their properties are between those of flexible and rigid foams.
Non-rigid foams of polyurethane or polyisocyanurate are referred to as flexible or semi-flexible polyurethane or polyisocyanurate foams.
The term “closed cell foam” means a foam of which the alveolar structure comprises walls between each cell that form a set of attached and separate cells allowing for the imprisonment of an expansion gas. A foam is qualified as a closed cell foam when it has a maximum of 10% of open cells. Typically, closed cell foams are mostly rigid foams.
The term “open cell foams” means a foam whose alveolar structure is formed of a continuous cell matrix with an open wall between the cells which do not allow for the imprisonment of an expansion gas. Such a foam allows for the creation of percolation paths within the cell matrix thereof. Typically, open cell foams are mostly flexible foams.
The term “polyester polyol” refers to molecules that comprise hydroxyl groups (diols or sugar alcohols) bonded together by ester bonds. Thus, in the polyester polyol according to the invention, the molecules X, Y, Z, Y′ and X′ are bonded together by ester bonds. Typically, the diols X and X′ and the sugar alcohol Z are bonded to the two diacids Y and Y′ by ester bonds each formed between an acid function of Y or of Y′ and a primary hydroxyl function of Z, X or X′. Advantageously, the polyester polyol is of neutral pH, typically, when it is obtained by two successive polycondensations followed by a step of neutralisation (for example with potash or with sodium hydroxide).
The polyester polyol according to the invention advantageously has the general chemical formula CaHbOc having 22≤a≤42, 38≤b≤78, 14≤c≤22.
Typically, the polyester polyol according to the invention has a molecular weight of between 350 g/mol and 2000 g/mol, preferably between 420 g/mol and 1800 g/mol and more preferably between 450 and 1700 g/mol. According to the invention, the molar weight of the polyester polyol can be determined by various methods such as size exclusion chromatography. Advantageously, the polyester polyol has a hydroxyl number of 300 to 900 mg KOH/g. The hydroxyl number (IOH) can be calculated with the following formula:
IOH=functionality of polyester polyol×56109.37/Molar mass of polyester polyol.
The hydroxyl number corresponds to the number of mg of KOH necessary to deprotonate all the hydroxyl groups present in one gram of polyol. The hydroxyl number can be determined by reverse assay using potassium hydroxide, for example according to ASTM 4274-99 in which the colorimetric titration is replaced by a pH-metric titration.
The term “sugar alcohol” or “polyol” means a hydrogenated form of monosaccharide of which the carbonyl group (aldehyde or ketone) has been reduced to a primary or secondary hydroxyl. Typically, sugar alcohol is chosen from glycerol, sorbitol, erythritol, xylitol, araditol, ribitol, dulcitol, mannitol and volemitol.
The term “diacid” means a carbon chain comprising two acid groups. According to the invention, the polyester polyol comprises two molecules Y and Y′ of diacid. These molecules can be identical or different in C4 to C36, preferably C4 to C24. Typically, the two molecules of diacid are independently chosen from butanedioic acid (Succinic acid), pentanedioic acid (Glutaric acid), hexanedioic acid (Adipic acid), heptanedioic acid (Pimelic acid), octanedioic acid (Suberic acid), nonanedioic acid (Azelaic acid), decanedioic acid (Sebacic acid), undecanedioic acid, dodecanedioic acid, tridecanedioic acid (Brassylic acid), tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, fatty acid dimers having up to 36 carbons (C36) or mixture thereof. Typically, Y and Y′ are diacids in C5 to C16 or C6 to C12. Advantageously, the preferred molecules of diacid are independently chosen from adipic acid and succinic acid.
The term “diol” means a carbon chain comprising two alcohol functions. According to the invention, the polyester polyol comprises two molecules X and X′ of diols which are identical or different. Typically, the molecules of diol are independently chosen from 1,2 ethanediol, 1,3 propanediol, 1,4-butanediol, 1,6 hexanediol, 1,8 octanediol, 1,10 decanediol, 1,12 dodecanediol and mixtures thereof.
Advantageously, the polyester polyol according to the invention is chosen from bis(1,2 ethanediol)-sorbitol diadipate, bis(1,3 propanediol)-sorbitol diadipate, bis(1,4-butanediol)-sorbitol diadipate, bis(1,4-butanediol)-sorbitol diadipate modified with glycerol, bis(1,6 hexanediol)-sorbitol diadipate, bis(1,8 octanediol)-sorbitol diadipate, bis(1,10 decanediol)-sorbitol diadipate, bis(1,12 dodecanediol)-sorbitol diadipate, bis(1,4 butanediol)-sorbitol disuccinate and sorbitol-diadipate-sorbitol. Preferably, said polyester polyol is chosen from bis(1,8 octanediol)-sorbitol diadipate, bis(1,10 decanediol)-sorbitol diadipate and bis(1,4-butanediol)-sorbitol diadipate.
The invention also relates to a flexible or semi-flexible foam or a composition for obtaining a flexible or semi-flexible foam comprising a polyester polyol obtained by a process comprising the following steps:
a) a step of polycondensation at a temperature between 110 and 200° C., preferably, 120 to 180° C., more preferably, 130 and 170° C., typically 150° C., advantageously for 5 to 10 hours:
Advantageously, during the polycondensation step, the diols X and X′ and the sugar alcohol Z are at a molar ratio (X+X′)/Z of between 1 and 3, preferably between 1.5 and 2.5, more preferably between 1.8 and 2.2.
Typically, during the polycondensation step, the diacids Y and Y′ and the sugar alcohol are at a molar ratio (Y+Y′)/Z of between 1 and 3, preferably between 1.5 and 2.5, even more preferably between 1.8 and 2.2.
According to one embodiment, during the polycondensation step, the diols X and X′ and the diacids Y and Y′ are at a molar ratio (X+X′)/(Y+Y′) of between 0.5 and 2, preferably between 0.7 and 1.5, even more preferably between 0.8 and 1.2.
Advantageously, the polycondensation step comprises a first polycondensation (a) of the sugar alcohol Z and diacids Y and Y′ and a second polycondensation (b) of the product obtained in (a) with the diols X and X′. This polycondensation in two stages makes it possible to obtain the polyester polyol with this symmetric structure. Typically, the diacids Y and Y′ are identical and/or the diols X and X′ are identical.
According to one embodiment, the sugar alcohol Z is mixed with the diacid molecule(s) Y and Y′ and then incubated for more than one hour, more preferably between 2 and 5 hours, even more preferentially between 2.5 and 4 hours, typically for 3 hours. The diol molecule(s) X and X′ are added in a second step to the mixture and then incubated for more than 4 hours, preferably between 5 and 10 hours, typically between 5.5 and 7 hours. Preferably, the polycondensation step is carried out under vacuum.
Advantageously, during the polycondensation step, the diacid molecules Y and Y′ react with the primary alcohols of sugar alcohol molecules Z and diols X and X′. The water molecules resulting from the reaction are recovered in view of being eliminated.
The invention further relates to a flexible or semi-flexible foam comprising a polymer comprising the polyester polyol according to the invention, typically, said polymer is a polyurethane and/or a polyisocyanurate.
Typically, the polymer according to the invention has a molar mass greater than 1.7×106 g/mol. Typically, the polymer is a crosslinked polymer.
By “polyurethane” is meant a polymer comprising urethane functions, that is in other words, a urethane polymer. These polymers result essentially from the reaction of polyols, in particular the polyester polyols of the invention with polyisocyanates. These polymers are generally obtained from formulations having an index from 100 to 150, preferably from 105 to 130 corresponding to a NCO/OH ratio of between 1 and 1.5, preferably between 1.05 and 1.3.
By “polyisocyanurate” is meant the polymers resulting from the reaction of polyols, in particular the polyester polyol of the invention and polyisocyanates, which contain, in addition to urethane linkages, other types of functional groups, in particular rings. triisocyanuric compounds formed by the trimerization of polyisocyanates. These polymers, normally also called modified polyurethanes, are generally obtained from formulations having an index of 10 to 500, preferably between 115 and 460, even more preferably between 150-450, or an NCO/OH ratio of between 1.1 and 5.0 preferably between 1.15 and 4.6, preferably between 1.5 and 4.5.
According to the invention, said polymer is a mixture of polyurethane and polyisocyanurate. Such a mixture is observed for example when said polymer comprises major urethane functions and a minor portion of polyisocyanates trimerized to triisocyanuric rings. Typically, said polymer is a mixture of polyurethane and polyisocyanurate and has an index greater than 100 or less than or equal to 150, corresponding to an NCO/OH ratio greater than 1 or less than or equal to 1.5.
The term NCO/OH ratio means, in terms of this invention, the ratio between the number of NCO functions of the polyisocyanate and the number of OH functions of the sugar alcohol of the diol and of any other component comprising OH groups (water, solvents). The NCO/OH ratio is calculated with the following formula:
NCO/OH ratio=MexpPi×ME Pi/MexpSAI×ME SAI
where:
In the present invention, the term “urea bond” or “urea function” means a disubstituted urea linkage which is the product of the reaction between a primary amine function and an isocyanate function of a polyisocyanate. The amine functions are formed in situ by the reaction of a water molecule with an isocyanate function carried by a polyisocyanate. Typically, the foam according to the invention or the composition for obtaining such a foam comprising the polyester polyol according to the invention or the polymer according to the invention, further comprises, at least one reaction catalyst, at least one swelling agent, a stabilizer, at least one polyisocyanate having a functionality of at least 2, optionally at least one co-polyol and additives.
By “co-polyol” is meant a compound carrying two or more hydroxyl functions (diol type) (polyol) added to the composition comprising the polyester polyol in order to adjust the properties thereof such as the functionality or the viscosity, to create crosslinking nodes or chain extension. The co-polyols may be C2 to C8, preferably C2 to C7, advantageously C3 to C6. The copolyols may advantageously be chosen from ethylene glycol, glycerol, 1,4-butanediol, butane-1,3-diol, 1,3-propanediol and propane-1,2-diol. pentanediol, 1,6-hexanediol, 1,2-propylene glycol, 3-oxapentane-1,5-diol, 2-[2-(2-hydroxyethoxy) ethoxy] ethanol, benzene-1,2,4-triol, benzene 1,2,3-triol, benzene 1,3,5-triol sorbitol, erythritol, xylitol, araditol, ribitol, dulcitol, mannitol and volemitol. The preferred co-polyols are glycerol, 1,4-butanediol, 1,3 propanediol and sorbitol. Typically, the co-polyol(s) is/are added in a polyol polyester/co-polyol (s) ratio of 70/30 to 99/1, preferably 75/25 to 95/5, even more preferably between 80/20 a,d 92/8, typically between 82/8 and 90/10, for example 85/15.
According to the invention, the composition comprises two co-polyols, typically a co-polyol C2 and a co-polyol C3 or a co-polyol C2 and a co-polyol C4 or a co-polyol C2 and a co-polyol C5 or a co-polyol C2 and a co-polyol C6 or a co-polyol C3 and a co-polyol C4 or a co-polyol C3 and a co-polyol C5 or a co-polyol C3 and a co-polyol C6 or a co-polyol C4 and a co-polyol C5 or a co-polyol C4 and a co-polyol C6 or a C5 co-polyol and a co-polyol C6 or two co-polyols C3 or two co-polyols C4 or two co-polyols C5 or two co-polyols C6.
Advantageously, the composition comprises at least one C2 co-polyol, typically two co-polyols, typically ethylene glycol and glycerol, ethylene glycol and 1,4-butanediol, ethylene glycol and erythritol, ethylene glycol and xylitol, ethylene glycol and araditol, ethylene glycol and ribitol, ethylene glycol and dulcitol, ethylene glycol and mannitol or ethylene glycol and volemitol. According to the invention, the preferred mixture of co-polyols is glycerol and ethylene glycol. For example, the composition comprises two co-polyols, typically erythritol and sorbitol, xylitol and sorbitol, araditol and sorbitol, ribitol and sorbitol, dulcitol and sorbitol, mannitol and sorbitol or volemitol and sorbitol.
Advantageously, the composition comprises two co-polyols typically in a ratio between 95/05 to 50/50, preferably 90/10 to 55/45, preferentially 87/13 to 60/40, more preferably 85/15 to 62/38, still more preferably 80/20 to 65/35. Typically, a C3/C6 or C3/C5 or C4/C6 or C5/C6 ratio between 95/05 to 50/50, preferably 90/10 to 55/45, preferentially 87/13 to 60/40, more preferentially 85/15 to 62/38, even more preferably 80/20 to 65/35. According to the invention, the preferred ratio is 66/33, a particularly advantageous ratio in the context of the mixture of glycerol/sorbitol co-polyols, in particular for a final polyol polyester/glycerol/sorbitol 85/10/5 mixture.
The term “polyisocyanate” means any chemical compound comprising at least two separate isocyanate chemical functions (NCO), in other words, that have “a functionality at least equal to 2”. When the polyisocyanate has a functionality of 2, this is referred to as diisocyanate. The term functionality means, in terms of this invention, the total number of reactive isocyanate functions per molecule of isocyanate. The functionality of a product is evaluated via the titration of the NCO function by a method of return dosage of the excess dibultylamine by the chloridric acid. Typically, said polyisocyanate has a functionality between 2 and 5, preferably between 2.5 and 3.5 even more preferably between 2.7 and 3.3. Advantageously, said polyisocyanate is chosen from aromatic, aliphatic, cycloaliphatic polyisocyanates and mixtures thereof. Mention can be made for example of 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4- and 2,6-toluene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, cis/trans of cyclohexane diisocyanate hexamethylene diisocyanate, m- and p-tetramethylxylylene-diisocyanate, m-xylylene, p-xylylene diisocyanate, naphthalene-m, m-diisocyanate, 1,3,5-hexamethyl mesitylene triisocyanate, 1-methoxyphenyl-2,4-diisocyanate, 4,4′-diphenyl-methane diisocyanate, 4,4′-diisocyanabiphenylene 3,3′-dimethoxy-4,4′-diphenyl diisocyanate, 3,3′-dimethyl-4,4′-diphenyl diisocyanate, 4,4″,4″-triphenylmethane triisocyanate, toluene-2,4,6m-triisooyanate, 4,4′-dimethyl diphenyl methane-2,2′, 5,5′-tetraisocyanate, and aliphatic isocyanates, such as hydrogenated 4,4′-diphenylmethane diisocyanate, hydrogenated toluene diisocyanate (TDI) and hydrogenated meta- and paraxylene diisocyanate of tetramethylxylylene diisooyanate (TMXDI®isooyanate, product of American Cyanamid co, Wayne, N.J., USA.), 3:1 meta-tetramethylxylylene diisocyanate/trimethylolpropane (Cythane 3160® isocyanate, from the company American Cyanamid Co.), plurifunctional molecules such as poly-diisocyanate of diphenylmethylene (pMDI) and the analogues thereof.
Typically, the polyisocyanate is chosen from toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (or 4,4′-diisocyanate of diphenylmethylene or 4,4′-MDI), polymethylene polyphenylene polyisocyanate (polymeric MDI, pMDI) and mixtures thereof.
The term “reaction catalyst” means a compound that introduced in a small quantity accelerates the kinetics of the formation of the urethane bond (—NH—CO—O—) by reaction between the polyester polyol of the invention and a polyisocyanate or activates the reaction between a polyisocyanate and water or activate the trimerisation of the isocyanates. Typically the reaction catalysts are chosen from tertiary amines (such as dimethylcyclohexane), derivatives of tin (such as tin dibutyldilaurate), ammonium salts (such as methanaminium N,N,N-trimethyl of 2,2-dimethylpropanoate), carboxylates of alkali metals (such as potassium 2-ethylhexanoate or potassium octoate) amine ethers (such as bis(2-dimethylaminoethyle) ether), and triazines (such as 1,3,5-Tris(3-(dimethylamino)propyl))hexahydro-1,3,5-triazine).
Advantageously, a composition intended for obtaining a foam comprises said polyester polyol according to the invention or said polymer according to the invention, at least one reaction catalyst, at least one polyisocyanate having a functionality at least equal to 2, at least one swelling agent, a stabilizer and optionally a flame retardant or at least one co-polyol. Advantageously, when the composition is a foam or a composition making it possible to obtain a foam, the preferred polyester polyol is a neutral pH polyester polyol and/or comprises sorbitol as sugar-alcohol Z. Typically, the polyester polyol preferred is bis (1,2-ethanediol)-sorbitol-diadipate, bis (1,6-hexanediol) sorbitol-diadipate or bis (1,4-butanediol)-sorbitol-diadipate, more preferably, bis (1,4-butanediol)-sorbitol. diadipate, or bis (1,6 hexanediol)-sorbitol-diadipate.
According to the invention, a foam typically comprises, after polymerization, a polymer according to the invention, in particular a crosslinked polymer, at least one reaction catalyst, at least one swelling agent, at least one stabilizer, and optionally at least one co-polyol.
By “swelling agent” or “expansion agent” is meant a compound inducing by a chemical and/or physical action an expansion of a composition during a foaming step. Typically, the chemical swelling agent is chosen from water, formic acid, phthalic anhydride and acetic acid, the physical swelling agent is chosen from pentane and pentane isomers, hydrocarbons and hydrofluorocarbons, hydrochlorofluoroolefins, hydrofluoroolefins (HFOs), ethers and their mixtures thereof. Methylal may be mentioned as an example of an ether-type swelling agent. According to the invention, a preferred chemical and physical swelling agent mixture is for example a water/pentane isomers mixture or water/methylal or water/hydrofluoroolefins.
By “stabilizer” is meant, an agent allowing the formation of an emulsion between the polyol and the swelling agent, the formation nuclei sites of expansion of the swelling agent, as well as the physical stability of the polymer matrix during progress of the reactions. Typically, the stabilizers are chosen from any of the silicone glycol copolymers (for example Dabco DC198 or DC193 sold by Air Products), non-hydrolyzable silicone glycol copolymer (for example DC5000 from Air Products), polyalkylene siloxane copolymer (for example Niax L 6164 from Momentive), polyoxyalkylene methylsiloxane copolymer (for example Niax L-5348 from Momentive), polyetherpolysiloxane copolymer (for example Tegostab B8870 or Tegostab B1048 from Evonik), polydimethylsiloxane polyether copolymer (for example Tegostab B8526 from Evonik), polyethersiloxane (for example Tegostab B8951 from Evonik), a modified polyether-polysiloxane copolymer (for example Tegostab B8871 from Evonik), a block polyoxyalkylene polysiloxane copolymer (for example Tegostab BF 2370 from Evonik), derivatives thereof or mixtures thereof.
By “additives” is meant agents such as antioxidants (neutralisation agents of chain ends at the origin of the depolymerisation or co-monomer chains capable of stopping the propagation of depolymerisation), demoulding agents (talc, paraffin solution, silicone), anti-hydrolysis agents, biocides, anti-UV agents (titanium oxide, triazine, benzotriazole) and/or flame retardants (antimony, phosphorus, boron, nitrogen compounds).
The term “flame retardant” means a compound that has the property of reducing or preventing the combustion or the heating of the materials that it impregnates or covers, referred to as flame or fire retardant. Mention can be made for example to graphite, silicates, boron, halogenated or phosphorous derivatives such as Tris (1-chloro-2-propyl) phosphate (TCPP), triethyl phosphate (TEP), triaryl phosphate esters, ammonium polyphosphate, red phosphorous, trishalogenaryl, and mixtures thereof.
An example of a composition according to the invention for obtaining a flexible or semi-flexible or flexible open-cell foam is typically formulated with an index of 90 to 150, preferably 105 to 120, typically 115, or an NCO/OH ratio. from 0.90 to 1.5, preferably from 1.05 to 1, 20, typically 1.15.
Typically, such a composition comprises
A flexible or semi-flexible open-cell polyurethane foam comprises, for example, 100 parts of a polyester polyol, 160 parts of a polyisocyanate, 2 parts of an amine catalyst such as dimethylcyclohexyleamine, 2 parts of a swelling agent such as water and 13 parts of a swelling agent such as isopentane derivatives, 2.5 parts of a stabilizer such as a polyether-polysiloxane copolymer and 10 parts of a flame retardant.
A second example of open-cell flexible or semi-flexible polyurethane foam is a foam comprising 85 parts of a polyester polyol and 15 parts of a co-polyol, 330 parts of a polyisocyanate, 2 parts of amine catalyst such as dimethylcyclohexyleamine, 9 parts of a swelling agent such as water, 2.5 parts of a stabilizer such as a polyether-polysiloxane copolymer and 10 parts of a flame retardant.
The invention also relates to a panel or a block of flexible or semi-flexible foam comprising the flexible or semi-flexible foam of the invention, typically for thermal or acoustic insulation, namely thermal or acoustic insulation of buildings or cryogenic insulation of refrigerators, cold chamber, or for empty space filling or buoyancy help such as in buoyancy aids (belts or vests . . . ) or water sports, for the damping of shocks and vibrations (for example, shoes, carpets or mattresses, foams for packaging or padding hard structures in order to improve the comfort, typically roof lining, seating (seats, chairs . . . ), soles, areas for gripping for example the wheels of cars, . . . ), for filtration.
The term “panel” having approximately a rectangular parallelepiped shape having relatively smooth surfaces and the following dimensions from 0.3 to 50 m2 of surface for a thickness of 10 to 1000 mm, preferably from 0.5 to 20 m2 of surface for a thickness of 15 to 500 mm; even more preferably, from 0.8 to 15 m2 of surface for a thickness 17 to 400 mm typically, from 1 to 7 m2 of surface for a thickness of 20 to 250 mm Examples of dimensions are typically, a surface of 600*600 mm or 1200*600 mm for a thickness of 20 to 250 mm.
By block is meant a structure of any geometrical shape, cubic, parallelepiped, star-shaped or cylindrical, with or without recess(es), of a volume of between 1 cm3 and 100 m3, preferably 10 cm3 to 70 m3, even more preferentially 100 cm3 to 50 m3 typically 0.5 to 35 m3, typically 1 to 30 m3.
The invention also relates to a method for obtaining a panel or a block of flexible or semi-flexible foam block according to the invention, namely by molding.
The invention relates to a method for thermal, phonic or cryogenic insulation, namely for buildings, fluid transport pipes or a method of filling (cracks or free space), sealing (structures, cracks, etc.).), waterproofing or improving the floatation (typically buoyancy aids or water sports) or damping shock and vibration or filtration by depositing or introducing blocks or panels of flexible or semi-flexible foam according to the invention or by the projection of a flexible or semi-flexible foam or a composition for obtaining a flexible or semi-flexible foam according to the invention.
A composition for obtaining a flexible polyurethane foam typically has an index of 100 to 120 and comprises, for example,
A flexible polyurethane foam composition comprises, for example, 100 parts of the polyester polyol according to the invention; 5 parts of swelling agent such as water; 50 parts of polyisocyanate such as toluene diisocyanate; 1 part of stabilizer such as Tegostab BF 2370; 0.2 parts of catalyst such as tin dibutyldilaurate.
The invention also relates to an insulation panel such as a sound or acoustic insulation panel, a mattress, a seat, a seat, an armchair or a sofa such as a car seat or furniture comprising said flexible or semi-flexible foam of the invention.
The invention also relates to a process for obtaining a flexible or semi-flexible foam typically of polyurethane and/or polyisocyanurate comprising:
a step of obtaining a polyester polyol according to the invention or of a polymer according to the invention,
a step of adding at least one polyisocyanate, at least one reaction catalyst, at least one swelling agent and a stabilizer, and
a polymerization step.
The invention also relates to the use of a foam according to the invention in thermal and acoustic insulation or in the filling of space in the building or in the mechanical industry. Although having distinct meanings, the terms “comprising”, “containing”, “comprising” and “consisting of” have been used interchangeably in the description of the invention, and may be replaced by other.
The invention will be better understood on reading the following figures and examples given solely by way of example.
a. Reagents
Sorbitol was supplied by the company TEREOS (MERITOL®, 98%, water content <0.5%, reducing sugar content <0.1%). 1,4-Butanediol (BDO, 99%) was obtained from SIGMA ALDRICH. Adipic acid (AA) (99%) was obtained from ACROS ORGANICS. Polyol polyether is an oxypropylated polyol of the company Huntsman (Daltolac® R570), with an average functionality of 3.0 and an OH value of 570 mg KOH/g. The polyisocyanate is 4,4′-methylenebis (diphenyl isocyanate) (MDI) polymer BORSODCHEM (ONGRONAT 2500). Two typical catalysts for the polyurethane foam were used: N, N-dimethylcyclohexylamine (DMCHA) and the 15% by weight solution of potassium 2-ethylhexanoate (KB) from MOMENTIVE and BORSODCHEM, respectively. The flame retardant is SHEKOY Tris (1-chloro-2-propyl) (TCPP) phosphate, the surfactant was polydimethylsiloxane (B84501) obtained from EVONIK and glycerol (gly) (99.5%) was obtained from FISHER SCIENTIFIC. INVENTEC isopentane was used as a physical swelling agent.
All of these chemicals were used as received without further purification.
b. Synthesis of a Polyester Polyol Based on Sorbitol (BASAB)
The sorbitol-based polyester polyol was synthesized by a two-step bulk polycondensation from sorbitol, 1,4-butanediol and adipic acid. One molar equivalent of sorbitol and two molar equivalents of adipic acid were charged into a 600 ml Parr thermoregulated reactor (Model No. 4568) equipped with a heating mantle, a mechanical stirrer with a U-shaped blade, a thermocouple, a Dean Stark having an output at the top of the capacitor to be able to link a vacuum pump and a low output to recover the condensate, an inlet and an outlet of inert gas. The medium was heated at 150° C. for three hours and then 2 molar equivalents of 1,4-butanediol relative to sorbitol were added. The reaction was continued for another six hours. Finally, the reactor was cooled to 60° C. and the residual acidity of the unreacted adipic acid was neutralized by the addition of an appropriate amount of K2CO3.
A viscous yellow polyol (BASAB) was recovered from the reactor and the general properties of BASAB are summarized in Table 1 and compared to the petrol-sourced polyether polyol. Further details concerning this synthesis are given in the patent application FR 16/01253.
c. Synthesis of PU Foams
PU foams were prepared with an isocyanate/hydroxyl (NCO/OH) molar ratio of 1.15. In order to determine the isocyanate content, all the reactive hydroxyl groups are taken into account, that is to say the polyols, the water and the possible solvents associated with the different catalysts. On the basis of the two-component foaming process, a premix containing polyol(s), catalysts, surfactant (polydimethylsiloxane, B84501), flame retardant (TCPP) and the swelling agent (s) is prepared. The swelling agents were chosen between isopentane (physical swelling agent) and water (chemical swelling agent). The total ratio of swelling agent remains constant in all formulations. In each preparation, the number of TCPP and surfactant parts is constant and equal to 10 parts for TCPP and 2.5 parts of surfactants. The total amount of polyol never exceeds 100 parts. When crude crystalline polyols such as sorbitol are used, they are first dissolved in water to break the crystallinity and increase their reactivity.
The mixture is stirred mechanically until a fine white emulsion is obtained with total incorporation of the swelling agent. The temperature of the mixture is controlled and adjusted to 20° C. The temperature of the polyisocyanate is also controlled and an adequate amount thereof is added rapidly to the emulsion. The whole reaction mixture is vigorously stirred for 5 s and then foamed freely in a 250 ml disposable beaker at room temperature (controlled at 20° C.) to monitor the kinetics of the foam or in the FOAMAT device. For further analysis, the foam samples were stored for three days at room temperature for complete maturation of the foam.
d. Characterization of the Foams Obtained
Thermogravimetric (TGA) analyzes were performed using a TA Hi-Res TGA Q5000 instrument in reconstituted air (flow rate 25 mL/min). 1-3 mg samples were heated from room temperature to 700° C. (10° C./min). The main characteristic degradation temperatures are those at most of the derivative of the weight loss curve (DTG) (Tdeg, max).
Infrared spectroscopy was performed with a NICOLET 380 Fourier transform infrared spectrometer used in reflection mode equipped with an ATR diamond module (ATR-FTIR). An atmospheric background was collected before the analysis of the sample (64 scans, 4−1 cm resolution). All spectra were normalized to a stretch peak of the C—H bond at 2950 cm−1. Dynamic mechanical analysis (DMA) was performed on TRITEC 2000 (Triton) compressive devices. The samples were analyzed at a constant frequency of 1 Hz for a temperature range of 30 to 270° C. with a heating rate of 2° C./min and a constant static resistance of 0.5 N. Samples were 7.5×7.5×7.5 mm3.
The quasi-static compression tests were carried out with an INSTRON dynamometer (E1000, USA), equipped with a load sensor of 1 KN, at room temperature and at a constant strain rate of 2.5 mm/min. The cubic samples used for the compression tests have dimensions of 25*25*25 mm3. Samples were tested in the longitudinal direction (corresponding to foam expansion during the process) and in the transverse direction. Young's modulus was defined as the slope of the stress-strain curves in the elastic region and the elasticity rate as the first maximum of the stress curve.
Thermal conductivity was measured from the heat flux. Typically, the device consists of a heating element with two thermocouples to obtain the temperature on the front and rear surfaces. The device is also equipped with two sensors dedicated to the measurement of heating time and cycle time. The heating and cycle times are used to correct the maximum conduction heat flux, which is necessary for the calculation of the thermal conductivity coefficient, by the Fourier law, used in steady-state thermal conduction. Plates of different materials with dimensions of 300*400*3 mm3 were used for the determination of the thermal conductivity coefficient.
The temperature of the foams, the heights and the rate of expansion, the density and the pressure of the foam were recorded using a FOAMAT FPM 150 (Messtechnik GmbH) equipped with cylindrical containers of 180 mm height and 150 mm diameter, an ultrasonic probe LR 2-40 PFT recording the height of the foam, a NiCr/Ni type K thermocouple and a FPM 150 pressure sensor. The data was recorded and analyzed with specific software.
The open cell count is determined using a Quantachrome Instruments Ultrapyc 1200e based on the technique of gas expansion (Boyle's Law). Cubic samples of foams (approximately 2.5 cm×2.5 cm×2.5 cm) are cut for a first measurement. Then, the cubic sample was cut into eight equivalent pieces and the measurement was repeated. This second measure makes it possible to correct the level of the closed cells from the damaged cells because of the cutting of the sample. Measurements were made according to EN ISO4590 and ASTM 6226.
Measurements of the apparent density of the foams were carried out according to the standard method EN 1602.
Foam cell morphology was observed on a HITACHI TM-1000 Field Emission Scanning Electron Microscope (SEM). The cube-shaped foam samples were cut with a microtome slide and analyzed in two characteristic orientations, longitudinal and transverse from the direction of the rise of the foam.
Five foams have been formulated, the detailed formulations are presented in Table 2. A petrol-sourced foam (hereinafter REF) is used as a reference. Formulations B85-2, B85-4, B100-2 and B100-4 are bio-sourced foams to be evaluated. The characteristics of the formulations as well as the kinetics of the foams obtained are presented in Table 2. The reference foam (REF) has the fastest kinetics with a cream time of 10 s, while all bio-sourced foams are up to 15 s. A 15 s cream time is an acceptable time for the formulation of such foams especially for foam panels continuously produced for the insulation of buildings.
The tack-free time is a surface indication of the formation of the PU network, but is not indicative of the end of the foaming process. According to this parameter, the polymerization stage of REF ends at the surface in 66 s, the other bio-sourced foams have times greater than 100 s. The tack-free time offset indicates a lower end-of-foaming reactivity. Thus, in the case of bio-sourced formulations, the entire polyurethane network is reached at longer times than for petrol-sourced foams. This can be particularly advantageous in the case of production of foam blocks by molding.
The measurements made by FOAMAT indicate that the reference foam REF reaches its highest expansion speed of 5 mm/s (
Thus, for the bio-sourced foam B100-2, the expansion rate is five times lower than that of REF. At the same time, the attained foam temperature during the foaming step for B100-2 is lower than for REF. The decrease in these two measures is indicative of a lower reactivity of the polyester (BASAB bio-sourced) compared with that of the polyether (petrol-sourced). This lower reactivity is explained by the lower accessibility of the secondary hydroxyl groups and the lower reactivity of the terminal hydroxyl groups of the bio-sourced polyester compared to the reference polyether.
The temperature curve B100-2 (
An effect of the content of chemical swelling agent and in particular of water of the mixtures was also observed on the foaming parameters. Thus, the B100-4 foam was formulated with a higher water content than the B100-2 and REF mixtures. However, there is an improvement in the foaming parameters of B100-4 compared to B100-2 and REF. More particularly, B100-4 shows shorter string and tack-free times of 10 s and 5 s respectively compared to B100-2 (Table 2). Thus, the formulation B100-4 is advantageous in that it has foaming characteristics close to the petrol-sourced reference formulation (REF). Nevertheless, the formulation B100-2 remains of interest in that it allows a sufficiently long working time and suitable for production in molding for example of foam blocks.
The effect of water on foaming would be related to the high reactivity between isocyanate and water, namely a reactivity twice as high as that between isocyanate and alcohol. The exothermicity of the water-isocyanate reaction is clearly visible on the evolution of the temperature of the B100-4 foam from 30 to 140° C. at 47 s. Thus, there is an expansion rate for B100-4 which is respectively 1, 6 and 4 times greater than REF and B100-2, with an equivalent foam height.
In addition, if REF, B100-2 and B100-4 are compared, it is observed that the increase in the water content of the mixture compensates for the lower reactivity of BASAB and makes it possible to obtain a mixture having very good characteristics. temperature (
Consequently, compositions based on bio-sourced products having a good reactivity and therefore a foam kinetics completely comparable to that of petrol-based compositions in terms of temperature and rate of expansion can be obtained according to the invention.
In order to optimize the foaming kinetics, the impact of short, non-volatile and highly reactive polyols such as sorbitol and glycerol in the start of the foaming process has been studied (Table 2).
Compositions comprising only BASAB (B100-2 and B100-4) as a polyol or comprising a BASAB mixture, glycerol and sorbitol in a BASAB/glycerol/sorbitol ratio of 85/10/5 (B85-2 and B85-4) have been prepared.
The compositions B85-2 and B100-2 are distinguished from each other solely by the presence or absence of these small polyols. It is the same for the compositions B85-4 and B100-4. Thus, comparing the expansion rates of the B85-2 and B100-2 foams shown in
It has been previously shown that for formulations containing BASAB, the increase in the water content of the mixture (B100-2 versus B100-4) offers a significant increase in the reactivity of the foam.
In the case of formulations containing the BASAB, glycerol and sorbitol mixture, the increase in the water content of the mixture (B85-2 versus B85-4) has no noticeable effect on the foaming kinetics. Indeed, the observed foam heights and temperatures are similar (
If we compare this time the B85-4 and B100-4 formulations containing a high-water content and distinguished by the presence (B85-4) or not (B100-4) of short polyols, we observe a foaming profile faster for the formulation comprising BASAB alone. Indeed, the maximum foaming rate of the formula B100-4 is reached at a maximum value of 8 mm/s in 50 s, then decreases rapidly. While for formula B85-4, a maximum value of 3.5 mm/s in 100 s is observed. The main hypothesis explaining this phenomenon is the formation of channels inside the foam, obtained by deformation and coalescence of low mechanical resistance cells made of weakly crosslinked polymers. This phenomenon is promoted by the presence of short diols in the B85-4 formulation, which can act as a crosslinking agent. This hypothesis can be confirmed later with a study in SEM.
Compositions B85-2 and B85-4 both contain a BASAB mixture, glycerol and sorbitol, the B85-4 composition being distinguished by a high-water content. The resulting B85-2 and B85-4 foams reach a similar height with respect to the REF foam. Nevertheless, variations in expansion speed and temperature are observed.
Indeed, there is an increase in the temperature of the B85-2 foam after 60 s and a low foaming rate of 2 mm/s which is kept constant for 80 s. These variations can be attributed to the reaction of the short diols with the isocyanate functions carried by the polyisocyanates chosen for the formulation. When the temperature reaches 80° C., the BASAB polyol begins to react vigorously with free isocynate functions. There is then an increase in the foaming rate of B85-2 from 2 to 3 mm/s. A change in the slope is visible on the temperature curve shown in
As a result, the reactivity of the bio-sourced polyester polyol differs greatly depending on the foaming temperature and can be adapted using the combined or non-combined effects of swelling agent such as water and short diols such as glycerol and/or sorbitol.
Water is a chemical swelling agent and is the simplest way to increase the rate of expansion, but it also results in an increase in the urea bond content in the final foam. As these bonds induce a stiffness of the segments, the increase in their presence should affect the mechanical properties of the foam.
In view of the above results, it has been shown that the water content of the composition and thus the production of urea bonds can be limited by combining BASAB with short polyols such as glycerol and sorbitol. Indeed, they act as a reaction inducer and facilitate the physical expansion of the foam limiting the formation of urea.
The analysis of the chemical composition of the PU foams was carried out by infrared spectroscopy (FT-IR). Functional groups linked to PUs and polyisocyanurates (PIRs) were targeted (
The urea functions have already been described (A.M.B.M. MUSTAFE, FTIR studies on 2K polyurethane paint, 2005) as found in the form of a broad peak at 1647 cm−1. It has been assumed that their low urethane content induces a weaker signal at the origin of the offset from the baseline of the spectrum signal in the 1700-1600 cm−1 region. Then, the last important peak appearing on all the spectra at 1412 cm−1 is attributed to the isocyanurate absorption band. He indicates that even in the PU formulation with small isocyanate function excess, a small amount of isocyanurate is formed. The amount of isocyanurate bound to peak intensity (
In order to determine the temperature resistance of the foams, a thermogravimetric analysis (TGA) was performed on each of the foams and made it possible to obtain ATG and DTG thermograms (see
For example, the decomposition temperature of the urethane group is influenced by its surroundings. It has been reported that the urethane function surrounded by two alkyls has an initial decomposition at 250° C., while surrounded by two aryl groups, it would start at 120° C. (J. Simon, Chromatographia. 25 (1988) 99-106). This decomposition is mainly induced by the thermal reversibility of the urethane function, according to the main decomposition pathways, which are the reverse reaction, the dissociation, the formation of amines and the transcarbamoylation.
All bio-sourced foams have a lower thermal stability than the reference, with weight loss starting at 170° C. It should be noted that except in the case where a fire performance is required, the conditions of installation and use of the foams generally take place at temperatures well below 170° C. Therefore, the bio-sourced foams obtained represent an alternative of interest for many applications. The degradation of the foams as observed is complex because of the addition of the different chemical groups derived from the polyester polyol. In fact, the polyesters are subjected to two main impairments, which are the α and β hydrogen splits (H. Abe, Macromol. Biosci. 6 (2006) 469-486), resulting in competitive degradation with degradation of the urethane function. During this analysis, no particular effect related to the addition of the short polyols in the formulation was detected, since the DTG thermograms are similar for most bio-sourced foams.
Only the B85-4 sample with a BASAB, glycerol and sorbitol mixture and a high-water content shows different ATG and DTG thermograms. Its weight loss is slower than other bio-sourced foams. This is consistent with its formulation because its high-water content induces the formation of urea which is more thermally stable than the urethane function (D. K Chattopadhyay, J. Polym. Sci. Part B Polym. Phys. 44 (2006) 102-118). The latter foam therefore has better thermal stability than other bio-sourced foams and thus potentially has a better resistance to fire and high temperatures.
The analysis of the morphology of the foams was carried out by a SEM analysis and coupled to an evaluation of the anisotropic ratio (R) of the cells of the foam. The SEM images presented in
In the longitudinal direction, all cells have a polyhedral form with clear anisotropy (R) (Table 3) and ellipsoid forms (R=1.9 to 3.8). This phenomenon is increased by the partially free foaming process used with foam growth in the longitudinal direction. In contrast, cells are more spherical in the transverse direction (1.21≤R≤1.65) with the exception of B100-4 (BASAB and high water content) where the cells are ellipsoidal in both directions.
In addition to the shape of the cells, the SEM images provide the overall structure of the foams. When comparing foams obtained from a formulation comprising BASAB and a high-water content, B100-4 exhibits extensively elongated cells at the origin of small pipes in the material. While B100-2 corresponding to the formulation with BASAB and a lower water content, is closer to a conventional open cell structure. This difference can be easily explained by the high content of chemical swelling agent (water) in B100-4.
Water is very reactive, it induces a rapid release of carbon dioxide creating pipes oriented inside the foam and breaking the honeycomb structure. A physical swelling agent has a softer expansion control by evaporation in the air microbubbles incorporated during mechanical stirring of the polyol premix (N. S. Ramesh, et al., Polym. Eng. Sci. 34 (1994) 1685-1697), which gives a more spongy structure.
The foam samples from a formulation with a mixture of polyols (B85-2 and B85-4) show a cellular structure with an inferion coefficient R compared to B100-2 and B100-4. Their cellular structure is related to a higher crosslinking density during the formation of the PU network in the foaming process. The higher crosslinking density is induced by the addition of polyfunctional glycerol and sorbitol which limit gas expansion and increase the rigidity of the material.
Consequently, the variable reactivity of BASAB as a function of the content of expansion agent or of small polyols (C2 to C6) during the foaming process makes it possible to adapt the cellular structure of the foams obtained. The structure of the foam having an impact on its mechanical properties, the BASAB therefore allows the following formulation to obtain foams of various mechanical qualities.
BASAB also makes it possible to obtain foams having different structural characteristics from foams comprising products that are petroleum-based in alveolar form.
However, it is close to structures of other petrochemical foams not presented in this study. It will be noted that this difference in morphology gives these bio-sourced foams properties of semi-flexible structures with a formulation similar to that of the petrol-sourced reference presented.
A tomographic analysis was performed (not shown) and confirms the observations to the SEM. Indeed, the tomographic images show a very complex structure, with a non-homogeneous shape and size of the cells in agreement with the SEM images.
In order to better characterize mechanically and thermally the foams obtained, the thermal conductivity coefficients and the apparent density of all the foams studied (Table 4). The apparent densities of all foams are between 23 and 41 kg/m′ and the apparent density of the reference foam is measured at 30.7 kg/m3. Of the bio-sourced foams, B85-2 foam has an apparent density greater than 2 kg/m3 compared to B85-4 foam samples and the B100-2 density is 16 kg/m3 greater than density B100-4. This means that foams with a higher water content are more expanded, which is in good correlation with the previous observation.
Thus, all bio-sourced foams with a higher water content exhibit a higher rate of expansion and a higher temperature inducing an increase in gas expansion in these foams compared to the REF or their counterparts containing less water. water (B 100-2 VS B100-4 and B85-2 VS B 85-4). This phenomenon is particularly marked for samples B100-2 and B100-4 where the increase in the quantity of water causes a decrease of nearly 40% of the apparent density.
Furthermore, it is found that the REF foam shows the lowest thermal conductivity value of 25 mW/m. K because of its high content of closed cells. In fact, the level of closed cells is responsible for 60 to 65% of the thermal properties of low density foams (H. Fleurent, J. Cell. Plast. 31 (1995) 580-599). Surprisingly, even if bio-sourced PU foams have a thermal conductivity of between 35 and 51 mW/mK, they have a majority of open cells. Indeed, these values of thermal conductivity are equivalent to those observed for the air (40 mW/(m·K)) or glass wool (30 to 40 mW/(m·K)) which are very good thermal insulators.
The polyurethanes and the polyurethane-urea have a heat capacity (Cp) within a range of 0.422 to 0.665 cal. g−1·° C.−1 and 0.389 to 0.513 J·g−1·K, respectively (J. E. Mark, ed., Polymer data handbook, 2nd ed., Oxford University Press, Oxford, New York, 2009). In general, the low Cp values of the polymers constituting the foams are an explanation for the low thermal conductivity of the material compared with non-polymeric materials such as metal foams. The B85-4 and B85-2 or B100-4 and B100-2 foams show close thermal conductivity to each oter, probably because of their equivalent closed cell rate and similar cell sizes.
In this case, relative density does not seem to play a major role. However, the thermal conductivity of the B100-4 and B100-2 foam systems is lower than B85-4 and B85-2. Bio-sourced foams are generally open systems, so the main difference between B100-4 and B100-2 is their bulk density. The thermal conductivity coefficient of the B100-4 foam is lower due to its low bulk density compared to B100-2. B85-4 and B85-2 have the same bulk density and similar closed cell levels, roughly the same cell sizes; it therefore seems normal that the two foam systems have the same coefficient of thermal conductivity.
The prepared bio-sourced foams have characteristics of interest in terms of thermal conductivity and therefore insulating properties comparable to that of petrol-based foams. The best results are obtained for bio-sourced foams with a formulation with high water content and in the absence of co-polyol.
Surprisingly, the bio-sourced foams have a small percentage of closed cells, especially compared to the petrol-sourced foam used as a reference for the base of the formulations. Nevertheless, a large number of open-cell petrol-based foams are available on the market and do not necessarily have as good thermal conductivity as BASAB-based bio-sourced foams.
A Dynamic Mechanical Analysis (DMA) was performed to characterize the viscoelastic properties of the foams as a function of temperature, in particular to define the typical relaxation temperatures of the polyurethane network constituting the foam. The evolution of the conservation module, the loss module and the loss factor (Tan δ) as a function of the temperature for the reference (REF) is presented in
This confirms that in bio-sourced PU foams the mobility of the polymer chains is increased. This increase is mainly due to the presence of the residual OH groups, previously observed by FTIR in bio-sourced foams. The lowering of the relaxation temperatures and viscoelastic properties of bio-sourced foams makes it possible to deduce a decrease in their friability compared to the very rigid REF foam.
Thus, it is clear from the results reported in Table 5 that the conservation modules are similar for bio-sourced foams B100-2 and B10-4. On the other hand, the conservation module of the B85-4 bio-sourced foam is 1.65 times greater than the B85-2 foam conservation module. The slight increase in modulus of preservation and Tg for B85-4 foam compared to B85-2 foam is probably due to the presence of chemical swelling agent. As previously explained, this high level of chemical swelling agent leads to the formation of hard segments (due to the formation of urea linkages) in the material. All these variations in thermal and viscoelastic properties will be well explained in the section of mechanical properties.
The mechanical properties were evaluated by a 50% compression analysis of the foam samples. The various foams were analyzed on a plate compression bench in order to highlight the difference in compressive strength and resilience of the foams as a function of the orientation of the stress. These properties are evaluated by the measurement of the Young's moduli and conservation of different foam.
The difference observed between the mechanical properties of the foams depending on whether the stress exerted is longitudinal or transverse could be explained in the following manner After the elastic region, observed for all the foams, the structure of the cells oriented in the longitudinal direction breaks under the loading at the origin of the observed residual deformation. While in the transverse direction, the shape of the elongate cell is more likely to undergo greater deformation before breaking. These hypotheses are supported by the work of J. Anderson et al (J. Andersons, et al., Mater. Of. 92 (2016) 836-845), whose work has focused on the stiffness and strength of closed-cell polyisocyanurate foams and the anisotropy of foam stiffness between the longitudinal and transverse directions.
Compared to the reference, the B100-2 bio-sourced foam has different mechanical properties, with a Young's modulus and a lower plastic pour point shown in Table 5. In fact, the Young modulus and the plastic yield point in the longitudinal direction are respectively 8.5 and 0.31 MPa for the reference and 3 and 0.08 MPa for B100-2 (see Table 5). The same trends are measured in the cross direction for the B100-2 foam compared to the reference (Table 5). These drastic variations in properties come mainly from the morphology of the foams. In addition, the closed cell content of these foams decreased from 90 to 10% between the reference and B100-2, respectively (Table 4). Thus, under compression, the compression of the gas contained in the closed cells of the reference contributes to increasing its mechanical properties with respect to the B100-2 foam (J. D'Souza, et al J. Appl. Polym. Sci. 131 (2014)).
An analysis of the response to the deformation stresses of the foams was carried out on the bio-sourced foams in order to point out the variations of the mechanical properties among the bio-sourced foams. The stress-strain curves of all bio-sourced foams in the longitudinal direction are shown in
The B100-2 foam has a majority of open cells, small cells and a higher bulk density than other bio-sourced foams. In compression, the rapid densification and the good distribution of the load lead to improve the mechanical properties and more particularly the conservation modulus, Young's modulus and the plastic yield point.
Formulation B100-4 has water and isopentane as swelling agent. After the foaming process, the high open cell content and the lower density explain the weaker compression properties of the resulting B100-4 foam.
The slight improvement in the mechanical properties measured by the conservation modulus or the modulus in the transverse direction (Table 5) of B85-4 compared to the B85-2 sample is also due to the chemical structure of the two materials. Indeed, the B85-4 bio-sourced foam is produced with a higher water content than the B85-2 foam. In addition, it is also important to note that the presence of glycerol and sorbitol in the B85-4 and B85-2 formulations increases the crosslinking density. A similar phenomenon is observed if we compare the mechanical properties of B85-4 and B100-4 foams. Indeed, the B85-4 foam has better mechanical properties than the B100-4 foam. This confirms that the effect of water on polymerization is more moderate between B85-4 and B85-2 foams compared to B100-4 and B100-2 foams. As a result, the stress-strain curves of the B85-4 and B85-2 formulations are between those of the B100-4 and B100-2 formulations. These observations thus demonstrate the great influence of the swelling agent or crosslinking agent on the mechanical properties of the PU foam.
The transverse compression-stress curves of B85-4, B100-4, B85-2 and B100-2 are shown in
In conclusion, open cell PU foams have been successfully developed from sorbitol-based polyester polyol and have been studied. The swelling agent, polyol or mixture of polyols and co-polyol have been shown to be key parameters for the modulation of kinetics, foaming profile and properties of bio-sourced foams through the range of reactivity offered by BASAB. The use of water as a chemical swelling agent in the formulation of foams has effectively improved the characteristic times (kinetics), the expansion rate and the foaming temperature. It also significantly reduces the foam density from 41 to 25 kg/m3 with respect to the same foams inflated with a physical expansion agent (isopentane) when only the bio-sourced polyol is used. A range of PU foams with different mechanical properties was then obtained. The mechanical compression tests show that the mechanical properties are very different in the longitudinal and transverse direction.
Thus, the prepared foams exhibit a significant anisotropy of their mechanical properties. In addition, all of the foams exhibit significant changes in Young's modulus, plastic yield point, and stress at the beginning of the densification region. These results are fully consistent with the viscoelastic properties measured by DMA. The glass transition decreases when the bio-sourced polyol is used for the formulation, compared to the petro-sourced reference. In addition, for bio-sourced foams the use of chemical and physical swelling agents allows variations in bulk density, closed cell count and foam microstructure.
Bio-sourced PUR foams meet the requirements of a wide range of applications from furniture to acoustic and thermal insulation of buildings, as they have a low coefficient of thermal conductivity and a high rate of open cells. PU bio-sourced foams seem particularly suited to the new demand for thermal and acoustic insulation due to their high open cell content and their elastic behavior. The anisotropy of the mechanical properties of such foams can also be used for filling applications of all kinds in the building in particular. Indeed, foams also having a low thermal conductivity can be deformed in the longitudinal direction at the rise of the foam and then return to their original size to fill spaces present in a defective part of the initial insulation of a building.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16/01253 | Aug 2016 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/055116 | 8/24/2017 | WO | 00 |
